vol. 19 july 1975 no

UK ISSN 0032-1400

PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of developments in their applications in industry

V O L . 1 9 J U L Y 1 9 7 5

Contents

The Manufacture of Continuous Glass Fibres

Mixed Metal Catalysts for the Synthesis of Azelaic Acid

Selective Rhodium Plating for Electrical Contacts

New Technology for Industrial Hydroformylation

Intercrystalline Rupture of Platinum Alloys

Effects of Vacancies on the Physical Properties of Platinum

Stabilised Carbonium Ions in the Organic Chemistry of Platinum

Fire-resistant Silicone Rubber

Centenary of the Convention of the Metre

Abstracts

New Patents

NO. 3

82

88

92

93

95

96

100

109

1 1 0

1 I 4

120

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey & Co Limited, Hatton Garden, London ECl P 1 A E

The Manufacture of Continuous Glass Fibres PRESENT TRENDS IN THE USE OF PLATINUM ALLOYS by K. L. Loewenstein Fibertech Consultants Limited, Fleet, Hampshire

One of the most exacting applications of platinum is in the production of glass fibre. This involves the rapid $ow of molten glass at temperatures around 1300°C through a series of small orifices which must retain their siae and alignment. Current trends in the design ofplatinum alloy bushings are towards a greater output of fibre per unit weight of platinum employed.

Almost all continuous glass fibres are manufactured by the attenuation of molten drops of glass exuding from nozzles located in the base of a special fibre drawing furnace called a bushing. Nearly all bushings are constructed from platinum alloy despite the high investment cost involved; one basic reason is that, when expressed in cost per kilogram of fibre produced, the use of platinum alloys is cheaper than the use of other metals, e.g., nimonic alloys. A second reason is that, at the operating temperatures required, metals other than platinum alloys do not have adequate mechanical strength. The main platinum alloys used are 10 and 20 per cent rhodium-platinum. The current trend of bushings design development aims at greater output of fibre per unit weight of platinum alloy employed.

Bushings are basically of two types : (i) Remelt or marble bushings operating

from cold glass marbles as the feedstock and fulfilling the dual functions of melting the glass and conditioning it to the correct temperature for fibre drawing (see Fig. 2).

(ii) Direct melt bushings, which are supplied with liquid glass near the operating temperature for fibre drawing and are attached to a feeder channel of a furnace into which the raw materials for glassmaking are fed (see Fig. 3).

Because of their dual function, remelt bushings are larger and weigh about twice that of direct melt bushings for the same output of fibre. For economic reasons, the majority of continuous glass fibres are now made from direct melt bushings and design development of remelt bushings, except for the production of special fibre products, has ceased. This article concentrates on direct melt bushings, although much of their development can be applied to remelt bushings also.

Bushing Design Bushing design is always in a state of

development. With an average operating life of one year it is rare that an old bushing is replaced by one of identical design; the nozzle sizes may have been increased to achieve an increase in output, or some structural weakness may have been eliminated. But of all the changes over recent years the most important is related to the size, spacing, and the manufacturing technique of nozzles. This has led to much closer spacing of nozzles and also to a reduction in the use of platinum alloy per unit weight of fibre produced.

Originally, nozzles were made by taking the base plate, pressing small indentations in it where the nozzles were due to be located, and then building up solid nozzles by melting platinum alloy wire and placing it drop by

Platinum Metals Rev., 1975, 19, (3), 82-87 82

drop on the apex of each indentation. Periodically, during this build-up, each nozzle would be inserted in a small press- tool and the outside smoothed. When the nozzle build-up was completed the holes were drilled individually, including a counterbore if required. It can be readily appreciated that the manufacture of base plates for bushings by this technique was extremely laborious. Technically it placed a limit on the minimum distance between nozzles since access was required not only for the welder but also for simple tools needed for shaping the outside of the nozzle as well as for centering tools required for ensuring that the holes drilled in the nozzles were central to the nozzle itself.

The consistency of nozzle shape and loca- tion was improved by pre-manufacturing solid nozzles and inserting them into holes in a base plate followed by welding around each joint. But this method also called for access around each nozzle on both sides of the base plate and did nothing to enable more nozzles to be placed in a base plate of given area.

The objective of placing more nozzles in a given area of bushing base plates was brought about by the coming together of two separate developments. These were the demonstration that a nozzle counterbore was not necessary in order to achieve efficient production rates, and a new method of nozzle manufacture.

Nozzle Manufacture As referred to above, most nozzles were

originally made with a counterbore (see Fig. 4 (a)) : This stemmed from the early period when bushings were made from pure platinum; due to the low glass/platinum surface tension the nozzles were frequently wetted by glass which travelled up the outside of the nozzle and across to adjacent nozzles, thus covering the underside of the base plate with glass. This seriously interfered with fibre drawing operations. By providing a counterbore, that is by thinning down the

Fig. 1 Glass-JibreJilaments are formed by drawing molten glass through hundreds of small ori$ces in a bushing constructed in a rhodium-platinum alloy. Great attention is given to the design of the bushing and to the method of manufacture of the nozzles to achieve maximum productivity. At the very high temperatures at which the process is operated only platinum alloys possess the necessary strength, while their use is most economical in terms of the amount of jibre produced.

Photograph by courtesy of Owens-Corning Fiberglas

Platinum Metals Rev., 1975, 19, (3), 83

wall of a nozzle at the exit, this problem was reduced. Although the subsequent introduction of rhodium-platinum alloys increased the glass/metal surface tension, the nozzle counterbores remained until the underlying reason for meniscus stability at the base of the nozzle was more clearly understood. It is now sufficient to say that, for rhodium-platinum alloys, provided the wall thickness at the base of a nozzle is 0.2 mm, then the glass will not normally wet the outside of the nozzle. Nozzle counterbores are therefore no longer needed. The fact that nozzles could now be drilled in one operation and that a counterbore

was no longer necessary meant that the overall wall thickness of nozzles could be reduced.

The next development was a new method of nozzle manufacture based on coining and deep-drawing (see Fig. 5). The starting material was a base plate of such a thickness that it contained slightly more than all the metal required for the base plate of final thickness plus the metal needed for the drilled-out nozzles. By a process of coining, the metal in excess of that required for the final thickness of the base plate is concen- trated in those positions where nozzles will be located; these are then deep-drawn in


stages, with annealing between the stages when necessary to prevent fracture. This gives nozzles which have very accurate outside and inside dimensions as well as a very smooth bore; however, they are still closed at the outlet end. The outlets are opened by punching foIIowed by smoothing the ends of the nozzles by surface grinding. A typical bushing of this type is shown in Fig. 6 before mounting in refractory brick and its metal frame.

Rate of Flow of Glass This development clearly involves con-

siderable work on special tooling and an understanding of the behaviour of platinum alloys when subjected to deep-drawing. The process itself could clearly be made simpler if the nozzles could be reduced in length. Having demonstrated that, for the stability of the fibre drawing process, the counterbore was no longer necessary and that metal could be saved by thinning down the nozzle walls, then the next stage was to aim to make shorter nozzles, which would, however, maintain a given rate of glass flow.

The rate of flow of a liquid through a pipe is given by Poiseuille's equation:

r4h F'X-

F is the rate of flow, r is the radius of nozzle bore in its narrowest cylindrical section, 1 is the length of the cylindrical section, h is the height of the liquid above the nozzle and q is the viscosity of the glass.

It is clear that if dimension 1 is reduced, then, in order to maintain the flow rate, dimension r must be reduced; if it is assumed that the clearance between adjacent nozzles is at a minimum for bushing manufacture then the distance between nozzles can also be reduced. Since several hundred nozzles are located in a bushing, even a small change in distance between adjacent nozzles can lead to a significant change in the number of nozzles that can be accommodated in a given base plate. For example, the base plate originally holding 400 of the longer nozzles, could readily be changed to accommodate about 600 of the shorter ones.


“uddering”. This is entirely due to creep at the operating temperature under the small load imposed by the load of glass above the base plate. There are several techniques for minimising this defect. The first is to use an alloy of low creep; for this reason 20 per cent rhodium-platinum is now preferred to the 10 per cent rhodium-platinum alloy. (The costs per unit volume of the two alloys are practically identical.) Alternatively, the use of zirconia-stabilised platinum will reduce creep. A second or additional method is to place internal stiffeners on the bushing base plate to prevent the sagging commonly experienced (one may be seen in Fig. 3). In some cases, indeed, the base plate has been provided with an inverted V in the longitudinal direction to provide stiffening. However, this method has a drawback since the base plate requires more platinum. As in most cases, a compromise has to be struck between bushing life and operating efficiency, But, even so, bushings

With improvements in the operating efficiency of fibre drawing processes it became clearly desirable to increase still further the number of nozzles in the base plate of a given bushing since this leads to savings in the use of platinum alloy as well as to other production cost savings. However, even after placing nozzles as closely as possible together on the base plate, this inevitably leads to an increase in the size of the base plate and the bushing overall. Since platinum alloys, at the operating temperatures of bushings are liable to creep, larger bushings lead to increasing danger of distortion of the bushing during operation.

Distortion of the bushing is most serious on the base plate, since this can affect the efficiency of fibre drawing. The most serious danger is what is colloquially referred to as


Fig. 6 A completed 400 nozzle bushing, fabricated in 20 per cent rhodium- platinum alloy, before mounting i n its support frame. The two pairs of coiled wires are the thermocouples

with over 1000 nozzles are now widely employed for many fibre products.

A further use of a platinum metal in association with fibre drawing is the use of nozzle shields. It was found some years ago that the stability of fibre drawing could be improved by placing radiation-absorbing shields between adjacent rows of nozzles. It was also found that the placing of these shields between alternate rows of nozzles was almost equally effective. Originally these fins were made of silver and attached to a


water-cooled manifold acting as a heat sink. In some cases coolers made of flattened metal tubing were preferred, especially for use with bigger bushings, and have come into wide use. A suitable metal for these flattened tubes is rhodium-platinum alloy; a cheaper and equally effective metal is palladium.

Acknowledgement The author wishes to thank Elsevier Scientific Publishing Company for permission to reproduce the diagrams from his book The Manufacturing Technology of Continuous Glass Fibres.

Mixed Metal Catalvsts for the J

Svnthesis of Azelaic Acid J

ACTIVITY OF A PALLADIUM-IRON COMPLEX

By D. T. Thompson I.C.I. Limited, Corporate Laboratory, Runcorn, Cheshire

Azelaic acid is an important intermediate in the production of a speciality Nylon, and it is shown that a palladium-iron system may be used very selectively in its preparation. This work was described at the recent Chemical Congress at York by the author, who is now Manager of the Catalyst Department in the Johnson Matthey Research Laboratories.

There are numerous examples reported in the literature showing clear evidence that mixtures of metal oxides, or indeed of the metals themselves, produce increased catalytic activity by comparison with the individual metal oxides or metals respectively.

Bond and Webster (I), using mixed metal catalysts derived from mixed oxides using a modification of the Adams method, demonstrated that a mixed ruthenium-platinum catalyst is more effective in the reduction of organic nitrocompounds than either of the pure metals. (See Figure.) The mixed oxides are reduced by hydrogen under ambient conditions to yield what are thought to be finely divided alloys of the two metals. It was shown by Rylander (2) that catalysts made by fusing platinum and palladium, rhodium, iridium, or ruthenium salts with sodium nitrate varied widely in hydrogenation activity and showed marked synergistic effects. Platinum- rhodium catalysts were especially active for reduction of nitrobenzene, nitropropane, cyclohexanone oxime and xylenes, whereas platinum-palladium catalysts were most active for hydrogenation of butynediol.

On the industrial manufacturing scene there are examples of both heterogeneous and homogeneous mixed metal systems. A mixture of bismuth and molybdenum oxides is used as a catalyst for the partial oxidation

Hydrogenation of aromatic nitro-compounds in the presence of ruthenium-platinum catalysts. 0 o-Nitrophenal in methanol A a-Nitrophenal in 96% ethanol-results of Sokol'skii and associates multiplied by 10 8 2, 4-Dinittotoluene in acetonelisapro- panol


of propylene to acrolein. The best results are obtained when the Bi:Mo ratio is I:I.

In the Haber ammonia synthesis the most widely used catalyst is a-iron containing an oxide such as molybdenum for widening the lattice and enlarging the active interface of the catalyst with the substrates. In biological systems both molybdenum and iron are necessary in the nitrogen fixation process.

Perhaps the most spectacular use of two metals in a heterogeneous catalyst is in the Ziegler-Natta titanium-aluminium systems for polymerising a-olefins. The important species involved is thought to be either a chlorobridged dinuclear molecule or a species having direct Ti-A1 bonds. Some soluble Zieglers have been reported to be stereospecific under certain conditions. Stereo- specific polymerisation is helped by the catalyst surface in the heterogeneous variety but the orientation of the monomer can also be controlled during the critical propagation step in the homogeneous systems provided that the monomer has at least two sites capable of co-ordinating to the catalyst (e.g. CH,=CHCN or CH,CH=CH, at low temperatures). Butadiene has also been polymerised stereospecifically in homogeneous media. Wilke has shown that certain n-allylic nickel compounds such as n-ally1 nickel chloride are active homogeneous

species is probably a halogen bridged nickel- aluminium compound.

Another homogeneous reaction carried out successfully in industry using two metals simultaneously is the Hoeschst-Wacker oxidation of ethylene to acetaldehyde in the presence of Pd(I1). The Pd(0) thus produced can be reoxidised to Pd(1I) using CuCl,, and the Cu(1) thus produced reoxidised in turn with oxygen. The presence of both palladium and copper simultaneously makes the reaction catalytic with respect to metal and it is quite possible that a discrete copper-palladium species is present in solution. A similar situation may be present in the catalyst system necessary to convert ethylene to vinyl acetate.

There is therefore considerable evidence that both in heterogeneous and in homogeneous systems and both in the laboratory and on the industrial scale mixed metal effects can be useful. We therefore investigated ways of synthesising mixed metal complexes.

Synthesis and Activity of a Palladium-Iron Catalyst

One of the most interesting compounds synthesised was a palladium-iron tetranuclear complex formed by reaction between x-allyl- palladium chloride and diphenylphosphine- irontetracarbonyl in toluene (3) :

This palladium-iron compound is a good catalysts for dimerising olefins, and it has seIective hydrogenation catalyst (I~S"C/IOO now been shown that the rate of dimerisation atm/I h) for the hydrogenation of hex-I-yne can be greatly accelerated if aluminium alkyl in the presence of hex-I-ene. Under test is added to the nickel catalyst. The active conditions (10 p.p,m. moles metal/mole


substrate), 93 per cent of a sample of hex-I-yne in benzene was reduced to hexene and only 3 per cent to hexane. This is unexpected since palladium is normally an excellent catalyst for the hydrogenation of olefins. The effect probably results from easier formation of a palladium-acetylene coordinate bond than a palladium-olefin bond. The rate of hydrogenation of the olefin on its own is in fact faster than the acetylene on its own. The effect is analogous to those found with

hydrocarbons to carboxylic acids and esters under “mild” conditions (e.g. 60”C, 300-700 atm for 1,5-cyclooctadiene) using PdCl, (PPh,), as catalyst. The use of the PPh, ligands had considerably increased the yield of ester per mole of palladium compared with the use of non-liganded PdC1, (7).

The carbonylation of oct-I-ene was studied under mild conditions using both the palladium-iron complex and PdC1,(PPh,)z and the results of the two series of experiments compared:

co _ _ / CH3(CH,),CH=CH, P CH~(CH~)SCH, + CH3(CH&C02Et

4% HCl, EtOH Catalyst

supported palladium catalysts (5 per cent Pd-BaSO,) and described as molecular queueing (4).

This Pd-Fe complex is also a selective isomerisation catalyst and in its presence oct-I-ene is isomerised to oct-a-ene but not to the 3- and 4-isomers. Most palladium complexes promote the isomerisation of A1-octene to a mixture of Al, A2, A3, and A4 octenes ( 5 ) and the reason for the selectivity in this case may be steric in that Al-octene may be more accessible to the palladium than the A2-octene.

‘C02Et

At 75”C, 50 atm, the total yield of esters was ten times greater for the mixed metal catalyst than for PdC1,{PPh3),. The thres- hold temperature for the reaction was ca. 30°C lower in the palladium-iron case than in the palladium. The isomer distribution of products is, however, ca. I :I in both cases, with a tendency for the is0 to predominate.

Carbonylation of 1, 5-Cyclo- octadiene

Since the 50:50 a:im ratio obtained with linear olefins had comparatively little industrial interest we next turned our attention to ~,-j-cyclooctadiene (1,5-COD) :

C02Et - dieters

If the reaction could be stopped selectively at the first stage (I), it was known that this ester could be converted into azelaic acid in c 80 per cent overall yield by means of two straightforward hydrolysis steps :

Extension of this work into the field of carbonylation was prompted by the appear- ance of a review article by Bittler et al. (6), who described carbonylation of unsaturated


H2 OH-, 32oOC (3) 1 H02C(CH&C02H

Azelaic acid is of interest since it is an intermediate needed in the manufacture of the commercially important nylon-6,g. For the carbonylation step, a series of experiments using PdCl,(PPh,), and p-toluene sulphonic acid showed that the optimum temperature for producing the monoester (I) was ca. 110°C (8). At this temperature no diester is formed (not detectable by g.1.c. at high sensitivity). Lower temperatures gave lower rates according to the normal rate laws. Higher temperatures also gave lower rates, presumably due to catalyst decomposition. The optimum pressure seems to be ca. IOO atm. Higher pressures give little change in rate. Lower pressures reduce the rate and increase the amount of isomerisation of unchanged 1,s- COD to 1,3-COD. The pressure and temperatures are, however, interrelated as far as ideal conditions are concerned.

Optimisation of the reaction at IIO"C/IOO atm showed that yields of up to 7000 moles ester/g.atom Pd could be obtained using anhydrous ethanol (rather than MeOH), PPh, ligand (rather than PBu,) and a Lewis acid such as FeCl,, TiC1, or NbC1,. Highest yields were obtained when the catalyst was preformed rather than prepared in situ from PdCl, and PPh, and when a common chloride ion was used. Under these conditions, no I ,~-COD isomerised to 1,3-COD- unchanged starting material could therefore be recycled. The Pd-Fe complex was also an effective catalyst but not as good as PdCl,(PPh,),/FeCl,, which could be giving [PdCl(PPh,),]+[FeCl,]-.

Hydrolysis of

ene-1-carboxylate The atmospheric pres-

sure, aqueous hydrolysis of the cyclic ester carbonylation product obtained from 1,5-COD and ethanol to give cyclic acid (step z), was found to be complete

after 0.5-1.0 h in refluxing solution. The mixture had become homogeneous after this time and isolation of the product gave yields of ca. 96 per cent. With the ethyl

Ethyl~y~loo~t-4-

ester, as the temperature is raised to 90 to 95°C a strongly exothermic reaction sets in and the mixture becomes homogeneous during a few minutes.

It is acceptable to use "crude" ester product from step (I) in this stage of the reaction and then remove the ethanol and I ,~-COD at the end of this stage. The removal of the ethanol before stage (3) is essential. Most of the palladium is then precipitated during this stage (a very small quantity of palladium is also found on the walls of the glass liner in the carbonylation stage) and is removed by filtration. The black solid obtained dissolves readily in nitric acid, and would presumably dissolve in aqua regia to give H,PdCI,. Evaporation of the aqua regia would give PdCl, which could be readily converted to the catalyst with PPh, (via Na,PdCI,).

Conversion of Cyclooct-4-ene-l- carboxylic acid to Azelaic Acid

The caustic cleavage step was performed in closed Inconel autoclaves under a self-generated pressure of up to 1000

p.s.i.g. water, and approximately z-jo p.s.i.g. hydrogen. The use of ca. 32oOC (internal temperature) for I hour was found to give higher yields of purer product than 300°C for 10 hours. Since the reaction is complete after I hour it is preferable to discontinue


heating at this point to prevent discolorisa- tion and condensation of the product. The shorter heating period may therefore account for the greater purity of this “crude” azelaic acid compared with samples obtained after longer heating periods. Two comparative g.1.c. traces for the esterified products from our work and the currently available acid derived from the ozonolysis of castor oil showed a single product in our case, whereas the commercial product contained 8 per cent of impurities. We therefore have an excellent, potentially commercial route to azelaic acid from ~,~-cyclooctadiene, the three stages of which proceed in almost theoretical organic yield to give a pure “crude” product.

Most of the practical work was performed by Mr. R. Jackson and I would like to express my thanks to him, and to Dr. D. E. H. Jones for discussions on aluminium chemistry.

References I G. C. Bond and D. E. Webster, Platinum

Metals Rev. 1969, 13, (z), 57 z P. N. Rylander et al., Engelhard Znd. Tech.

Bull., 1967, 8,25 3 B. C. Benson, R. Jackson, K. K. Joshi and

D.T. Thompson, Chem. Commun., 1968, 1506 4 L. Crombie and P. A. Jenkins, Chem. Commun.,

5 J. F. Harrod and A. J. Chalk, J. Am. Chem.

6 K . Bittler et al., Angew. Chem. Znternat. Ed.

7 J. Tsuji et al., Bull. Chem. SOC. Japan., 1966,

8 R. Jackson and D. T. Thompson, British

’g69J 394

SOC., 1964, 86, 1776

En., 1968, 7, 329

399 141

Patent 1,340,873, 1973

Selective Rhodium Plating for Electrical Contacts The use of rhodium for light duty contact

purposes is well established, as are the techniques for restricting this expensive metal to those areas required for contact only. The problems of cracking, microcracking and exfoliation have been well documented and these factors are covered extensively in a paper presented by Afsar A. Khan of G.T.E. Automatic Electric Laboratories Inc., North Lake, Illinois to the meeting of the American Electroplaters’ Society in New York during March 1975.

The paper discusses controlled depth selective electrodeposition of rhodium on iron-base alloys for dry reed contact applications. Selective plating of reed blades is a necessary design requirement rather than a cost reduction approach since rhodium deposits, while needed on the contact area, are detrimental to glass-to-metal sealing. Nominal plating thickness should be held to within &13 per cent. The plating area is mainly controlled by maintaining a smooth laminar flow of the recirculating plating solution in the tank through a series of baffles and also by maintaining a uniform depth of immersion of the contact reeds to &O.OIO in. Tem- perature is 40 to 50°C to minimise solution evaporation and to provide even plating thickness on the rack.

In this case the substrate is unusual in that the iron-base alloy for reed switches is easily attacked by the rhodium sulphate electrolyte.

All rhodium plating solutions yield highly stressed deposits but as phosphate solutions are prone to higher levels of stress and cracking than sulphate solutions, the latter are the natural choice for plating crack-free rhodium in thicknesses up to zoo pin. To minimise the problem of attack by these solutions the author states that a gold undercoat is used to protect the iron-base alloy but he does not specify the thickness of this undercoat.

Experience elsewhere has shown that a low stress gold deposit beneath rhodium can give rise to marked changes in the stress cracking of the rhodium deposit. Unless the quality of the undercoat is very carefully controlled this can have a significance greater than the methods outlined in this paper. The recommended careful attention to cleanliness, frequent carbon treatment together with the attendant filtration, and careful exclusion of organic contamination are all, of course, useful contributions to good rhodium plating practice.

The sections devoted to the correction of faults in deposits are interesting, particularly those parts concerned with defects associated with the evolution of hydrogen at the work face, No explanation is attempted for why a momentary “dwell” in the electrolyte before plating commences leads to elimination of this problem.

H. R. J. W.


New Technology for Industrial Hydroformylation RHODIUM-BASED CATALYST SYSTEM FOR OX0 PROCESS PLANTS

By F. J. Smith Johnson Matthey Chemicals Limited, London

New technology for the hydroformylation of olefins has been developed jointly b.y Union Carbide Corporation, navy Powergas Limited and Johnson Matthey & Co. Limited. The process employs a novel rhodium-based homogeneous catalyst system at signijicantly lower pressures and temperatures than conventional cobalt-using processes, resulting in major savings in capital investment and operating costs. Another most important feature of the new process is that it provides much higher ratios of norma1:iso aldehydes produced when propylene and other olefins are used as feedstocks than is possible with Conventional processes. Several plants utilising the new system are now under construction.

The use of carbon monoxide in industrial organic chemistry is of fast growing importance. Much of the work on which this growth has been based was carried out within the last forty years. The crucial discovery of the hydroformylation or 0x0 reaction was made by Roelen of Ruhrchemie A.G. in 1938 and it is from his studies that the technology of hydroformylation has developed.

Hydroformylation is defined as the reaction of an unsaturated olefinic compound with hydrogen and carbon monoxide to yield an aldehyde. The original 0x0 reaction of Roelen showed that propionaldehyde was formed from ethylene :


and that diethylketone was also formed. However, ketone formation occurred to a large extent only with ethylene and consequently Adlrins’ term “hydroformylation” for this reaction is a better general description than “0x0”. The reaction is exothermic- with propylene 30 kcal/mole is evolved. The heat evolved with other olefins varies between 28 and 35 kcal/mole depending on their structure and molecular weight.

In addition to olefins (alkenes) it would be possible to use as feedstocks for hydroformylation alkyl alkenoates, alkenyl alkanoates, alkenyl alkyl ethers, and alkanols. Polymers, i.e. polyolefins, might also be reacted similarly.

One of the principal reasons for employing this technique of hydroformylation is that a second stage process using hydrogen can convert aldehydes from the standard hydroformylation process into the so-called 0x0 alcohols, which are of great industrial significance. 0x0 products and their deriva- tives include such diverse chemicals as plasticisers, solvents, paint resins, and- more recently-bio-degradable detergent intermediates and lube oil additives.

Suitable Catalysts The essential key to the hydroformylation

reaction is the use of a suitable catalyst. Roelen originally employed the solid Fischer -Tropsch catalyst based on cobalt but it was subsequently discovered that the catalytic mechanism is homogeneous in nature. The process was therefore developed using homo-

geneous cobalt catalysts such as cobalt hydrocarbonyl HCo(CO),. A number of mechanisms for the action of this catalyst were proposed and the influence of catalyst concentration on the variation in reaction products was established. In due course, however, it was found that modification of HCo(CO), by replacing one or more of the carbonyl ligands by other ligands was beneficial.

From theoretical considerations it became apparent that catalysts based on Group VIII metals other than cobalt might have application in the hydroformylation reaction. Rhodium and ruthenium both seemed to be promising candidates for study and work was undertaken on these platinum group metals. Of particular importance was the work carried out by Professor Geoffrey Wilkinson, F.R.s., at Imperial College, Lon- don, and also certain associated investigations carried out by staff at the Johnson Matthey Research Laboratories at Wembley and by Davy Powergas Limited at Stockton, Teesside.

Willrinson introduced the concept of triphenylphosphine ligands substituted into rhodium hydrocarbonyl (analogous to cobalt hydrocarbonyl). His RhH(CO)(PPh,), homogeneous catalyst is well known. It has been claimed that this makes it possible to under- take reactions at temperatures as low as 25°C and at pressures as low as one atmosphere, while giving the very desirable ratio of normal to iso-aldehydes of about 20, a figure very much greater than in conventional processes based on the use of cobalt catalysts.

The superior thermal stability of modified hydrocarbonyls is explained by the fact of trivalent phosphorus ligands being better o-donors than CO but poorer x-acceptors. Thus the remaining CO ligands are more strongly bonded, because the transition metal atom has the tendency to transfer the increased negative charge obtained from the phosphorus to the CO ligands through x-back donation.

Phosphine-modified catalysts possess greater stereoselectivity than unmodified hydrocarbonyl catalysts. Various arguments

have been put forward to account for this behaviour. However, isomerisation of the feedstock materials is almost completely suppressed when working with rhodium carbonyls and excess trialkylphosphines, giving virtually complete conversion to aldehydes.

An essential stage in any catalytic process is the separation and recovery of the catalyst. The ease and completeness of this operation is of great economic importance to 0x0 plant operators. In the case of homogeneous reactions where the feedstock, the catalyst and the reaction products all exist in the same medium it is particularly important to carry out the separation efficiently to arrive at both purity of reaction product and availability of the catalyst material for recycling.

New Technology So far we have considered the principles of

hydroformylation and have indicated some of the problems that have to be solved in developing a successful commercial operation of the process. The aim has been to eliminate the need to operate at very high operating pressures, and to increase the selectivity to obtain more of the desired normal-chain isomer products.

New technology that meets this aim has now been developed jointly by Union Carbide Corporation, Davy Powergas Limited and Johnson Matthey after work extending over more than seven years. The essence of this work lies in the development of a satisfactory rhodium-based catalyst, which permits olefins such as propylene or ethylene to be converted economically on a large production scale into n-butyraldehyde and propionaldehyde, respectively, in high yield and with great selectivity. The selectivity is stated to be IO:I for n:iso butyraldehydes from propylene, for example. This means a saving of 20 per cent of propylene compared with what would be required in the production of n-butyraldehyde by conventional cobalt-using processes, where in general the rz:iso ratio is only 3:1. It is possible that a


saving of $6,000,000 per year on propylene plus synthesis gas (C0-tH.J feedstock may be achieved on a large commercial plant. Previously it has been necessary to recycle the unwanted isa-butyraldehyde, for example as fuel, and pressures of around 300 atmos- pheres have had to be used with the cobalt catalysts.

The new process technology possesses other advantages. The relatively low pressures in the reaction enable synthesis gas to be introduced directly into the 0x0 plant and obviates the necessity to use high pressure compression equipment. This in turn reduces both capital costs and operating costs, as might be expected from the relative sim- plicity of the techniques employed. The catalyst is much easier to handle during operation.

The first three plants using the new technology are being built for Union Carbide Corporation itself. A 130,000 ton/year

plant for the production of n-butyraldehyde from propylene is under construction at the Ponce complex in Puerto Rico. Two units with a capacity of 45,000 ton/year for the production of propionaldehyde from ethylene are under construction at Texas City. These new plants will come into operation during 1975.

The first external licensee of the new process is in Sweden. Berol Kemi of Stenungsund is to build an 0x0 plant based on the propylene-to-n-butyraldehyde conversion to go on stream by early 1978. This plant is to have a capacity of IOO,OOO ton/year of n- butyraldehyde. Other products to be manufactured in this plant include butanol, octanol and octanoic acid.

Davy Powergas Limited, a member of the Davy International Company, will participate in the construction of all these plants, and the rhodium-containing catalyst will be supplied by Johnson Matthey Chemicals Limited.

Int ercryst dine Rupture of Platinum Allovs J

GRAIN BOUNDARY MIGRATION AND INTERCRYSTALLINE SLIP NEAR WELDS

The fabrication of articles from platinum alloys generally requires the use of welding techniques but the difficulty sometimes arises that intercrystalline cracking occurs in the vicinity of the welded seam. The exact conditions under which this problem arises have yet to be fully defined. However, progress in this direction has been made by a team of workers at the Ural Polytechnic Institute named for S. M. Kirov (V. V. Stepanov, T. A. Chernyshova and V. V. Shevelev, Fiz. Metal. Metalloved., 1975, 39, (I), 183-188).

The alloys studied were 7 per cent rhodium- platinum, 10 per cent rhodium-platinum and 5 per cent rhodium-15 per cent palladium- platinum. Results were obtained for the effect of chemical composition on the tendency to crack formation and for the process of grain growth during repeated welding cycles.

A large number of welds and their surrounding zones were observed in all three alloys. These indicated that twice as much cracking occurred in the ternary alloy as in 7 per cent rhodium-platinum but that the least amount of cracking occurred in 10 per

cent rhodium-platinum. Small additions of magnesium, iron, calcium, aluminium, and silicon and of their combinations were made to the alloys. I t was found that more cracking resulted, particularly induced by additions of silicon, aluminium and calcium.

Fractographic analysis was undertaken to establish the mechanism of cracking before attempting to eliminate it. Two features became apparent. First, lines of intercrystalline slippage develop and, secondly, secondary phases in the form of fine dark deposits occur on the facets and boundaries of the crystals. The latter incorporate the deleterious additions.

A suggested mechanism for crack formation is that voids form between crystals because of slip. The links between crystals are thus broken and cracking is initiated. To verify this mechanism grain growth was observed closely in the weld and in the surrounding area. The thermal effects of welding induce grain growth in the alloys and this in turn may cause the intercrystalline slip which leads to voids and rupture at certain temperatures of welding, especially for impure alloys.


Effects of Vacancies on the Physical Properties of Platinum By A. H. Seville Department of Physics, The City University, London

Most of those who work with metals at high temperature think of vacancies (vacant lattice sites) as important only in the context of diffusion. It is usually left to the solid- state physicist to study the effects of vacancies on such physical properties as thermal expansion, enthalpy and electrical resistivity, and even he may be interested largely in what he can learn about the vacancies themselves. Of course, whereas diffusion is a process controlled by vacancies, vacancies merely influence these other properties to a limited extent. Nevertheless, the influence can be sufficient to be of direct concern to those who use platinum as a high-temperature reference material.

The Size of Vacancy Effects As is well known, the equilibrium mono-

vacancy concentration C(T) in a metal is an

exponential function of the absolute temperature T:

C(Tj =exp(S’/k)exp( -EF/kT)

where C is the atomic fraction of vacancies, SF is the monovacancy formation entropy, E” is the monovacancy formation “energy” (enthalpy), and k is Boltzmann’s constant.

Because of this, at temperatures approach- ing the melting point T, the variation of C with temperature is so rapid that, although the effect of vacancies on, say, the electrical resistivity may be quite small (c I per cent), the effect on the corresponding dzfferential property-the temperature coefficient of resistivity-is an order of magnitude larger at least.

To make precise estimates of vacancy effects in platinum is not altogether easy. The “traditional” experiment (I) of accurately

I i The Effect of Vacancies on Some Physical Properties of Pure Platinum.

Creation of Vacancies as the Temperature Rises Makes the Indicated Percentage Contributions to the Properties Shown

Temperature K

1450

1550

1650

1750

1850

1950

Temperature Coefficient of Electrical Resistance

2%

3%

46%

8%

13%

23%

Coefficient of Linear Thermal Expansion

1%

2%

3$%

6%


Specific Heat

comparing specimen length and X-ray parameter to give vacancy concentration is difficult a t the high temperatures involved. Diffusion studies are complicated by the tendency of monovacancies at high concentration to aggregate into divacancies, and quenching studies are difficult to relate to the high-temperature near-equilibrium situation. A combination of techniques is necessary to arrive at a set of self-consistent vacancy parameters (2). SF/k=1.3 and EF= I .49 eV are accepted values, giving C(T,) =

8 x IO-*. Using these with other data, we can estimate the effect of vacancies on some physical properties to be as shown in the Table; the large effect on the temperature coefficient of electrical resistance is evident.

Until quite recently, controversy existed (3, 4) as to whether these estimates were correct, as a different procedure was in use which gave the vacancy concentration to be an order of magnitude higher. In this procedure the values measured for a physical property below about 1400K were extrapolated to higher temperatures and taken to define the “background” values appropriate to an ideal vacancy-free metal. Subtraction from the observed high-temperature values then gave an estimate of the vacancy effect. Thus for platinum the observed sharp rise of the specific heat vs. temperature curve was used (5) to estimate C(T,) to be as high as I per cent. This estimate is now known to be too large (2, 6). Much of the difference between the extrapolated and experimental curves is now attributed to anharmonic inter- atomic forces, so that the true background cannot be found by simple extrapolation (7) (Fig. I); an additional complication in determining the background is the temperature variation of the electronic specific heat.

Transient Effects of Vacancies Vacancy effects, then, are only part of the

reason why values of physical properties measured above 2/3 T, differ from those measured below that temperature. But

Platinum Metals Rev., 1975, 19, (3),

vacancy effects are different from the rest in that they alone can give rise to time delays in the measured properties at high temperatures; this is because the vacancy concentration takes a measurable time to adjust to a change of temperature. Vacancies have to be created at definite sources or des- troyed at definite sinks, so that diffusion of vacancies must take place before the vacancy concentration everywhere relaxes to the value appropriate to the new temperature.

97

All vacancy-affected physical properties will similarly take this time to reach their final values.

Instead of concentrating on time-delay behaviour, we may regard these properties as frequency-dependent (8) (just as simple dielectric relaxation may be expressed as a Debye spectrum). The detailed frequency dependence is determined by the vacancy diffusion coefficient, the source /sink geometry, and the source/sink efficiency. We must therefore expect the frequency dependence to be influenced by temperature (via the vacancy diffusion coefficient, D, at least).

The sources and sinks for vacancies above 2/3 T, cannot be identified certainly; it is not safe to assume, say, that sinks identified in an annealing experiment below 1/3 T, will operate at the higher temperature. However, Heigl and Sizmann (9) have studied the generation of vacancies in platinum wires pulse-heated to temperatures up to ZIZOOK for times ranging from W I ms. From a detailed study of the kinetics, they concluded that the vacancy sources were quasi-planar, with a spacing put at " 5 pm; the sources were thus presumed to be dislocations in low-angle sub-grain boundaries.

Assuming this geometry, and that these sources function with ideal efficiency as source/sinks (so that at the boundaries the vacancy concentration is always at the equilibrium value appropriate to the in- stantaneous temperature), we can calculate (10) the frequency dependence of, say, the temperature coefficient of resistance for small temperature changes about a given mean temperature. This is shown in Fig. za. Although the curves look superficially like Debye relaxation curves, they cannot strictly be described by a single relaxation time, even for a given mean temperature: at high frequencies, the variation depends on wi (and not the Debye w-'). This is because only the region of the sub-grain within a distance (D/o)* of the boundary can participate in the changes in vacancy concentration.

The time scale for vacancy relaxation effects calculated in this way is very much a lower limit: if, for any reason, the internal source/sinks should function with less than ideal efficiency, then the time scale will be longer. As an upper limit, we may take the surface of the specimen to be the only source/ sink, and, for example, calculate that for wires of 50 pm diameter the time scale is


increased by a factor of IOO (Fig. zb) compared with that for internal source/sinks.

The Practical Importance of Vacancy Effects

The most important factor in determining the efficiency of the internal source/sinks is the vacancy subsaturation (or super- saturation), which provides the forces causing the dislocation to climb, with emission (or absorption) of vacancies (12). In pure platinum, temperature changes of only a few kelvin should be sufficient to cause the internal source/sinks to operate. The time scale of vacancy relaxation effects will then approximate to Fig. za, too short to be of interest in conventional potentiometry. How- ever, for temperature transients in electrically heated wires and foils, the time scale can become significant.

Temperature modulation experiments com- bine the short time scale with the accuracy needed to observe these effects. A.C. heating is used to cause in a hot wire specimen a near-sinusoidal temperature variation of, say, +IK at 30Hz. For platinum the temperature variation may conveniently be measured by using the variation in light emitted. The measured variation in electrical resistance then gives the temperature coefficient of resistivity appropriate to the modulation frequency. At 1850K and 3oH2, this coefficient is found to be some 5 to 10 per cent below the quasi-static value, con- firming a vacancy relaxation effect (6). The accuracy of the measurements is not sufficient to determine exact vacancy kinetics and source/sinl< efficiency though the efficiency is clearly less than ideal. But already it is clear that to neglect the frequency dependence of the temperature coefficient of resistance will cause significant systematic error in experiments in which resistance changes during thermal transients are used to measure the temperature changes involved. Systematic errors of this kind inflate specific heat values (5) and thermal expansion coefficient values

(13) reported from modulation experiments in which quasi-static values of temperature coefficient of resistance were (erroneously) used throughout.

The situation in impure platinum is less clear. Impurities may be expected to decrease the efficiency of the internal source/sinks, and effects of this have been reported in other metals (rq), where the time scale of events became the time needed for vacancies to diffuse from the surface into the bulk. Similar effects in impure platinum, or platinum alloys, could possibly influence conventional potentiometric measurements. However, the impurities in platinum are often of the platinum group of elements, and these might have little effect on the internal source/sinks.

Further work on this problem undertaken at the City University cooperation of Johnson Matthey Limited.

is to be with the and Co

References I R. 0. Simmons and R. W. Balluffi, Phys. Rev.,

1960, 119, 600 2 D. Schumacher, A. Seeger and 0. Harlin,

Phys. Stat. Solidi, 1968, 25, 359 3 Ya. A. Kraftmakher and P. G. Strelkov,

“Vacancies and Interstitials in Metals”, North Holland, 1970, p. 59

4 M. Hoch, Ibid., p . 81 5 Ya. A. Kraftmakher and E. €3. Lanina, Fiz.

6 A. H. Seville, Phys. Stat. Solidi A, Appl. Res.,

7 A. H. Seville, J. Chem. Thermodynamics, 1975 7,383

8 J. Van den Sype, Phys. Stat. Solidi, 1970, 391 659

9 F. Heigl and R. Sizmann, Crystal Lattice Defects, 1972, 3, 13

10 A. H. Seville, Ph.D. Thesis, University of Edinburgh, 1972, p. 30

11 V. E. Zinoviev, I. G. Korshunov and P. V. Geld, Fiz. Tverd. Tela, 1971, 13, 3459

12 V. M. Lomer, “Vacancies and Other Point Defects in Metals and Alloys”, Institute of Physics Monograph and Report Series No. 23, 1958, P- 94

13 Ya. A. Kraftmakher and I. M. Cheremisina, Zh. Prikl. Mekh. Tekh. Fiz., 1965, 2, 114

14 B. S. Bokshtein, S. Z. Bokshtein, A. A. Zhukovitskii, S. I. Kishkin, L. G. Kornelyuk and Yu. S . Nechaev, Dokl. Akad. Nauk S.S.S.R., 1968, 183, 1280

Tverd. Tela, 1965, 7 , 123

1974, 21, 649


Stabilised Carbonium Ions in the Organic Chemistry of Platinum THE EVIDENCE FOR THEIR EXISTENCE

By Professor M. H. Chisholm Frick Inorganic Chemical Laboratories, Princeton University, New Jersey

This account of research on the organometallic chemistry of platinum summarises work which indicates that platinum may induce carbonium ion reactivity i n 1.c-bonded hydrocarbon ligands and stabilise carbonium ions in the reactions of a-bonded unsaturated hydrocarbons. It is based on a lecture at the Chemical Society annual meeting held at York in April.

Historically, platinum has played a prom- inent role in organometallic chemistry. The compounds KPtCI,(C,H,)H,O (I), PtMe, (X) (2) and Chugaev's salt [PtC,H,,N,],Clx (3, 4) present some of the fist examples of stable metal-olefin, metal-alkyl and metal- carbene complexes, although ironically the nature of the bonding in these compounds was not immediately recognised. In the study of organometallic reaction mechanisms platinum has also been in the forefront, for example, in studies of the decomposition pathways of metal-alkyls (5, 6); oxidative- addition reactions (7-9); C-C and C-H reductive-elimination reactions (10-14); and M-H and M-C insertion reactions (15-22).

Certain aspects of the organometallic chemistry of platinum are well suited for the study of organic reactions occurring at metal centres (23) :

(i) There exists a diverse organometallic chemistry for platinum in its well-defined valence states 0, 2+ and 4f.

(ii) For a given valence state platinum shows a well-defined coordinated chemistry. Pt(o) compounds are either three or four coordinate. Pt(2+) compounds show a remark- able preference for a four coordinate square planar geometry; five coordination is comparatively rare. Compounds of Pt(4-k) are almost invariably six coordinate.

(iii) Platinum-carbon bonds are stable to oxygen, water and thermolysis. This stability results from a combination of thermodynamic and kinetic factors.

(iv) Platinum compounds are well suited to a wide variety of spectroscopic techniques. In particular the presence of 19TtJ I=:&, 34 per cent natural abundance, provides a useful mechanistic probe in n.m.r. studies of organoplatinum compounds.

This account summarises work in our laboratories which indicates that platinum may induce carbonium ion reactivity in ~ i -

bonded hydrocarbon ligands and may stabilise carbonium ions in the reactions of o-bonded unsaturated hydrocarbons.

Organoplatinum Cations By taking advantage of the high truns-

influence (24) of the methyl ligand we set out to synthesise a series of cationic methylplatinum compounds trans- [PtCH,(un)L 2] +

PF,-, I, where un=an unsaturated hydrocarbon and L ==a tertiary phosphine or arsine, according to reaction A below.

solvent A rrans-PtCH,(CI)L, -1-unf-AgPF, ~

trans-[PtCH,(un)L,l'PF, +AgCl

Compounds I were considered ideal for detailed studies of the bonding and reactivity


of the unsaturated ligand un. However, the products derived from A were found to be dependent on the nature of the unsaturated hydrocarbon, the ligands on platinum, the solvent, and the reaction conditions. Reactions involving dialkyl or diary1 acetylenes, un RCzCR, in acetone solvent did lead to the isolation of cationic methylplatinum(2 -) acetylenic compounds as white air stable crystalline salts (25, 26). From a comparison

the methylplatinum group in I, where un= RCzCR, with related values observed for methylplatinum(2 -) cations trans-[PtCH, (L')Lz]-, where L'=a neutral donor ligand, the following trans-influence series may be formulated : (27)

Of v&?t-c), y19OP~-H and y196Pt 13C for

platinum(2 ->) cation. In contrast, coordination to zerovalent platinum as in (P(CBH5)3)BPt(CH3C-CCH3) causes a much greater reduction in this stretching frequency, Indeed the value of vstr(C-C) is lowered to a value comparable to that observed for cis-2-butene. Similarly the 13C shieldings of the acetylenic carbons (see the Table) reveal (28) the very different nature of the metal- acetylene bond in trans-[PtCH,(CH,C= C- CH,) L,]- and (P(C,H,),),Pt(CH,C~CCH,). A single crystal X-ray determination on

2]lPFs - revealed (29) a CGC bond length of 1.22& c.f. (30)~ 1.21 a for free 2-butyne, and an average C=C-C angle of 168".

tr~m-[PtCH,( CH3C =CCH,)(P( CH3) ZC oHJ-

:C' > PR, > CO = CNR = As(CH,), > py '> R C S R > RCN > acetone

'R,

This series shows that the acetylenic triple bond exerts a relatively weak trans-influence, somewhere between the nitrogen donor ligands pyridine and alkylnitriles.

Further insight into the nature of the platinum-acetylene bond in I can be obtained from a consideration of the data shown in the Table. This pertains specifically to I , un= CH,C=CCH,. vstr(C-C) which occurs at - 2200 cm-l in free 2-butyne is reduced only 100 cm on coordination to the methyl-

In summary all available spectroscopic data suggests that, based on the original Dewar (31)-Chatt-Duncanson (32) pictorial descrip- tions of metal-acetylene bonding below,

R

PtL,(CH,C S C H , )

[PtCH,(CH&=CCH,)L,]-

cis-CH,CH -CHCH,

Isp or sp2-carbon; p.p.m. downfield from TMS; data from ref. 28


Compound vstr(C =C)cm-'

-2200

1750

2100

-1 650

73.9

122.8

69.5

124.3

CH,C_rCCH,

h

Y

co

platinum or acetylene x* bonding is of minor importance in I. This is in marked contrast to the bonding in zero valent platinum acetylene compounds which may be considered to show a sizeable degree of cyclopropenoid character. The primary mode of bonding in I , un=RCrCR, appears to be a cr-interaction involving donation from filled x-acetylenic orbitals to vacant platinum hybrid orbitals.

Although dialkyl and diary1 acetylenes did yield I according to A, the reaction of

terminal acetylenes, RCECH, in methanol solvent gave cationic methylplatinum meth- oxy-carbene complexes according to B (25,33 ). Analogous reactions in ethanol gave the appropriate ethoxy-carbene complexes. This formation of the alkoxy-carbene ligand in B was unexpected and requires specific comment.

Initially we proposed (25, 33) a mechanism in which a cationic acetylenic complex I reacts with the solvent to produce a cationic

- I -

MeOH 1 r ) L, I * PFG- - 1 - AgCl B trms-PtCH,(CI)L, 1 RC-CH - 1 - AgPF, - trans- PtCH, C

L' MePt+ t L'

Scheme 1

I R' (111)

H-or 1 R- shift

Pt +

CHZCI,

-H' Me I

R2 H, \ Pt+-C- C-R

1

c (VIII)

Pt'-CECR -! CH,

+RC=CH

-;RC=CH polymers and

ethers

,,CHR MePt-C , (VII) CH'CR Or

\ Some reactions of trans-[ PtMe(H1C_CR2)Lz]+Z-(L= PMezl'h or AsMe,; Z= PF6 or Cl ) ( I ) [ Z = P F , , R=allcyI or aryl], (111) (L=PMe,Ph, R1=R2zC02Me, C02H, CH,OH, or Me), ( V ) [ Z = P F , , R = H or alkyl], ( V I ) ( Z = C l , L=PMe,Ph, R = H or M e ) , (F'III)(Z=PF,, L=AsMe,, K=Ph), ( I X ) ( Z = P F , , L=PMe,Ph, L'==PR,, AsR,, CO, RCN, olejns, allene, acetone), ( X I ) and ( X I I I ) (Z=PFs , L=YMe,Ph). The ligands L have been omitted in the scheme for brevity.


x-vinyl ether complex, which then by hydride shift yields the alkoxy- carbene ligand. However, we were subsequently able to isolate cationic methylplatinum x-vinyl ether complexes (21). These were stable below +80°C and did not rearrange to give alkoxy-carbene derivates. This observation together with many other reactions of cationic acetylenic platinum complexes, summarised in Scheme I, led us to propose a general carbonium ion model for the activation of unsaturated ligands in organoplatinum cations trans-[PtR ( u a 2 1 + (21, 34).

The Carbonium Ion Model We proposed (21, 34) that activa-

tion occurs by delocalisation of the positive charge from platinum to the unsaturated moiety un; this

Scheme 2 RZ

I CH,-Pt-C=C-Y

I i" R1

/SY Ri

C I

R2=H C&-h+l/l ___) CH,-Pt-C E C R ~

C

R2 I

CH&l, \ PtL-C= YH3 C-RZ

I R1

has the effect of inducing carbonium ion insertion into a group already bound to reactivity. Specifically for acetylenes co- platinum leading to cis-vinylic products. ordinated to platinum(z+) cations this can Aside from these three types of reactions be pictured by the resonance shown below. (Scheme 2) many other aspects of organo-

platinum chemistry illustrate the generality of this platinum induced carbonium ion model. For example,

1 " electron withdrawing trifluoro- methyl group increases the electro-

R L

bound to platinum in I by the more CH3-Pt+-11/1 +----+ substitution of the methyl group

\

R'

I

I L R' L

The carbonium ion reactivity of the coordinated acetylene is thus dependent on the nature of the substituents of the acetylene, R and R'; the ligands on platinum, X and L, since these determine the electrophilicity of the platinum cation; the solvent; and the nature and availability of a nucleophile.

Thus most of the reactions shown in Scheme I may be reduced to three fundamental types of reactions shown in Scheme 2. These are (i) nucleophilic attack on the coordinated acetylene leading to trans-vinylic products, (ii) proton elimination or abstraction by the solvent when R=H (this is favoured in polar aprotic solvents), and (iii)


philicity of the organoplatinum cation and hence increases the carbonium ion reactivity of the acetylene in trans-[PtCF,(RC=CR')L,] relative to I. Although we have been unable to isolate such simple dialkylacetylene cations, they are the reactive intermediates in the polymerisation of acetylenes, a process which occurs much faster than for I in the absence of a polar protic solvent. A terminating step in the polymerisation of dimethylacetylene is the formation of the cationic tetra-methyl- cyclobutadiene complex [PtCF,(C,(CH,),)

Another reaction in organoplatinum chemistry which is consistent with the platinum

(P(CH3)2 C6H5)21fPF6- (35, 36)*

103

CH,OH Pt-C=C Pt+cC

OCH, \ H \

-H+ 11 +H+

R

Pt-C=CR +HI

Scheme 3

induced carbonium ion model is the formation of an alkoxy-carbene ligand from a platinum (4 +) cationic acetylenic intermediate (35).

Mechanism of Formation of the Carbene Ligand

The mechanism for the formation of the alkoxy-carbene ligand from the elements of RCECH and R'OH deserves specific comment. The proposed mechanism, based on the carbonium ion model, is shown in Scheme 3. The essential feature of this mechanism involves the intermediacy of a platinum vinyl carbonium ion which, once formed, reacts with the alcohol solvent to yield the alkoxy- carbene ligand. A platinum vinyl carbonium ion may be formed by one of two routes; (i) an intramolecular mechanism involving an H- shift or (ii) an intermolecular mechanism involving deprotonation (abstraction of H~t by solvent) to give a platinum acetylide followed by protonation of the triple bond. Reactions carried out in CH,OD showed (21) that the acetylenic hydrogen was not lost to the solvent but rather was incorporated on the u-carbene carbon. This demonstrates that the intramolecular mechanism is operative and furthermore shows that the reaction of the vinyl carbonium ion with alcohol solvent is fast (at least relative to deprotona-


tion) and irreversible. The exact role of platinum in facilitating this hydride shift is not clear and the intermediacy of a platinum- hydride cannot be excluded. However, in the reaction of cationic acetylenic intermediates of Pt(4+), which also yield the carbene ligand (35), formation of a platinum-hydride intermediate seems most unlikely since this would be formally a hydride of Pt(6f). Finally, it should be recognised that an alkyl shift rather than a hydride shift could be operative. Based on the relative migratory aptitudes of H- and R-, and the fact that acetylene, HCECH, gives the alkoxy (methyl) carbene ligand we prefer to believe in the H- shift mechanism. Of course, a 13C labelling experiment involving the specific labelling of one of the acetylenic sp-carbons could distinguish between these two possibilities. However, the salient feature of the proposed mechanism involves the intermediacy of a vinyl carbonium ion and is thus independent of which group migrates.

The concept of a platinum stabilised vinyl carbonium ion is an interesting one since simple vinyl carbonium ions are rather reactive species (37), indeed it is only recently that they have become respectable intermediates in the carbonium ion community (38). However metal vinyl carbonium ions

(iii) with HPF, in methanol to give quantitative formation of the methoxycarbene complex

7 L,M -C-C

/ H

\ R \x L,M-C -C

could be stabilised by a metalloallene resonance form as shown above.

o-Routes to Platinum Stabilised Carbonium Ions

If organoplatinum cations can induce carbonium ion reactivity in a ;c-bonded unsaturated hydrocarbon ligand and at the same time show evidence of stabilising the carbonium ion so formed, it is reasonable to expect that this carbonium ion stabilisation should be reflected in the reactions of o-bonded unsaturated hydrocarbons.

We have now examined some reactions of divalent platinum acetylides of the type trans-Pt(C =CR) 2L, and trans-PtCl(C ECR) L, where R -H, CH,, CF, and C,H,, and L =

P(CHJ2C,H,). These reactions are also of interest since they allow a direct comparison with the chemistry of organo-platinum compounds PtR,L, and PtCl(R)L, where R: alkyl or phenyl, and the presence of a four coordinate ds metal and a coordinated alkynyl ligand provides the opportunity to compare the reactivity of inorganic and organic sites of unsaturation. Our initial findings show (39, 40) that these compounds exhibit a very intricate chemistry based on reaction at either the metal or the triple bond.

The reactions involving protic acids are particularly pertinent to the carbonium ion model outlined previously. For example trans-PtCl(C E CR)(P(CH,),C,H;), reacts:

(i) with anhydrous HC1 to give almost quantitative formation of the vinylic product

(addition of HCl to the triple bond gives a mixture of cis- and trans-vinylic isomers but is specific in giving only the x-chlorovinylic isomer PtCCl =C(H)R);

(ii) with anhydrous HC1 in methanol to give trans-PtC1 (COCH,R) (P (CH 3 ) , C,H,) , and methylchloride;

trans-PtCl(CC1- C(H)R)(P(CH,),C,H,), j

where R-H, CH, and C,H,. Addition of a one molar equivalent of LiCl to an acetone solution of

leads to quantitative formation of trans-PtC1 (COC,H,)(P(CH,),C,H,), with the formation of methyl chloride. Consequently we consider that propionyl formation in the reaction involving anhydrous HCI in methanol proceeds via initial formation of

which readily eliminates CH,CL irreversibly. These reactions provide further evidence

for the intermediacy of platinum vinyl carbonium ions. However, the initial or prefer- ential site of protonation is uncertain and again we must recognise the possible intermediacy of hydridoplatinurn(4 +) cations. Scheme 4 overleaf shows possible equilibria which may, either directly or indirectly, lead to platinum vinyl carbonium ions. Our work thus far has clearly demonstrated the existence of certain of these pathways. For example, cationic acetylenic intermediates yield alkoxy-carbene and acetylide complexes in alcohols and T H F respectively. However, the intermediacy of hydrido-alkynylplatinum species remains a possibility. This potential route to metal vinyl carbonium ions leads us to predict a new synthetic route to alkoxy- carbene ligands according to C.


PF6- + AgCl CH,OH / OCHs

C L,M(H)(CI)[C =CR) -1 - AgPF, LnMI-C

Complexes suited to this type of reductive rearrangement could well involve Co, Rh and Ir.

Finally we note that the reaction of HPF, in methanol with trans-PtX(C =CEI)L,, in which either the Y or p acctylenic carbon is specifically labelled, could form the basis for ascertaining the intermediacy of a cationic x-acetylenic complex in this route to alkoxy- carbene complexes.

As a further test of our hypothesis that low valent metals can stabilise vinyl carbonium ions we predict a direct solvolytic routc to alkoxy-carbene ligands as in D where L,M provides an electron-rich metal site.

Scheme 4

H I

L,(X)Pt'-C I ECR

D LnMCC1-- CHR + AgPF, v L n M ' - C /OCH3 PF,- - AgCl CH,OH

CH,R \

'This type of solvolysis reaction is unpre- cedented in the reactions of simple organic vinyl halides but should be possible when the metal can assist in stabilising the vinyl car-

(ii) Reaction of PtUr(CC1 z-C(H)R)L, with AgPF, in MeOH gives only the chloro- platinum complex

bonium ion as a metalloallene cation described

previously. While reactions C and D are hypothetical we have recently shown (41) that alkoxy- carbene ligands can be generated quantita- tively according to E

zrans- [ PtCl [ r , ) L { C PF,-

CH,R

(Analysis showed<o.I per cent Rr).

where R=H, CH, and C,H, and L=P(CH,), C,H,.

Several observations indicate that reaction E proceeds via the mechanism shown in Scheme 5 (opposite page):

(i) Alcoholysis reactions of PtX(CC1 C (H)R)L, only occur when the Pt-X bond is labile towards Pt LX- solvolytie heterolysis e.g. X --Cl, Br and I.

(iii) Reaction in MeOD shows that the vinylie hydrogen is lost to the solvent.

(iv) trans-PtCl(CC1 -C(H)Nle)I,, dissolves in MeOH saturated with anhydrous NH, to give tram-PtCl(C _CMe)L, and NH,CI.

(v) trans-PtCl(CC1- C(II)IMC)L, does not react with anhydrous NH, in benzene; cf. (iv) above.

Platinum Metals Rev., 1975, 19, (3) 106

previously.

PF6- + AgCl CH,OH / OCHs

C L,M(H)(CI)[C =CR) -1 - AgPF, LnMI-C

Complexes suited to this type of reductive rearrangement could well involve Co, Rh and Ir.

Finally we note that the reaction of HPF, in methanol with trans-PtX(C =CEI)L,, in which either the Y or p acctylenic carbon is specifically labelled, could form the basis for ascertaining the intermediacy of a cationic x-acetylenic complex in this route to alkoxy- carbene complexes.

As a further test of our hypothesis that low valent metals can stabilise vinyl carbonium ions we predict a direct solvolytic routc to alkoxy-carbene ligands as in D where L,M provides an electron-rich metal site.

Scheme 4

H I

L,(X)Pt'-C I ECR

D LnMCC1-- CHR + AgPF, v L n M ' - C /OCH3 PF,- - AgCl CH,OH

CH,R \

'This type of solvolysis reaction is unpre- cedented in the reactions of simple organic vinyl halides but should be possible when the metal can assist in stabilising the vinyl car-

(ii) Reaction of PtUr(CC1 z-C(H)R)L, with AgPF, in MeOH gives only the chloro- platinum complex

bonium ion as a metalloallene cation described

previously. While reactions C and D are hypothetical we have recently shown (41) that alkoxy- carbene ligands can be generated quantita- tively according to TT

zrans- [ PtCl [ r , ) L { C PF,-

CH,R

(Analysis showed<o.I per cent Rr).

where R=H, CH, and C,H, and L=P(CH,), C,H,.

Several observations indicate that reaction E proceeds via the mechanism shown in Scheme 5 (opposite page):

(i) Alcoholysis reactions of PtX(CC1 C (H)R)L, only occur when the Pt-X bond is labile towards Pt LX- solvolytie heterolysis e.g. X --Cl, Br and I.

(iii) Reaction in MeOD shows that the vinylie hydrogen is lost to the solvent.

(iv) trans-PtCl(CC1 -C(H)Nle)I,, dissolves in MeOH saturated with anhydrous NH, to give tram-PtCl(C _CMe)L, and NH,CI.

(v) trans-PtCl(CC1- C(II)IMC)L, does not react with anhydrous NH, in benzene; cf. (iv) above.

Platinum Metals Rev., 1975, 19, (3) 106

previously.

The observations (i)-(v) above demonstrate the importance of Pt-CI heterolysis and that H+ is abstracted by the solvent. We cannot distinguish between a concerted or a stepwise elimination of the elements of HC1.

/H

‘R

HA Elimination from pt-c+=c

Subtle changes in the ligands bound to a metal often provide the basis for important modifica- tions of catalytic processes. In this regard it is interesting to note that the reactivity of

/H

R \

trans-PtX( L,)C+= c

Scheme 5

H

L I

L Hh:O-Me +I <I I

Cl-Pt-C 7 C-R CI-l‘t-C zC-R I kl L c1 I

L +HCl

MeOH

1; /OM= c1- - c1-Pt+-C ‘i //O

L I \CH,R L

el-rt-c

CH,R I \

+MeCl

is sensitive to the nature of the trans-ligand X. This is indicated by the following (42): (I) trans-PtCH,(Cl)L, reacts with AgPF, and H C r C H in MeOD to give

irans- [tCH3 1 /OMe ,cHz)] PF,-

in which both acetylenic hydrogens are incorporated in the a-carbene methyl group. (2) trans-Pt(C=CH),L, reacts with DPF, in MeOD to give

in which the acetylenic H/D ratio is - 2:1

and the methyl H/D ratio is less than 1:6. (3) The reaction of DPF, in MeOD with tram-PtCl(C~CH)L, and the reaction of trans-PtCl(CCl=CH,)L, with AgPF, in MeOD both yield

The above reactions indicate that the relative rates of H ~ I elimination versus carbene formation from

is sensitive to the nature of X. H i- elimination is favoured X=CI>C=CH>CH,.

H’ Catalysed Isomerisations of Vinylic Ligands

In a study of halovinyl complexes of platinum(I1) Lewis and co-workers (43) noted that the reaction between trichloroethylene and PtL,, L =PMePh,, was stereospecific in giving

However, upon treatment with anhydrous HC1 the apparent thermodynamic equilibrium


distribution of vinylic isomers was obtained as indicated below.

L H L c1 C1-Pt-C- C-CI Cl-I't-C -C-H

I I HC1 I 1

I 1 L c1

I I L c1

30:; 70" 0

Two plausible mechanisms were suggested (43) to account for this isomerisation-an addition-elimination sequence or a carbonium ion mechanism. Addition of HC1 could occur to give either I I or III .

f. 77 L H H I I I

Cl-Pt-C-c-c1 I I I L C1 c1

Cl-Pt-C-C-H

L c1 CI I I I

11 IIl

Based on our concepts of platinum-stabiliscd carbonium ions we felt that the kinetically controlled mode of addition should lead to I I I . Consistent with this expectation was our observation (42) that the DCl catalyscd isomerisation was accompanied by imme- diate vinyl-H/D scrambling as evidenced by the dirninuation of the vinylic proton nmr signals. This observation does not rule out that addition of HC1 may occur to give I1 but indicates that it is not the kinetically favoured mode of addition.

We have also found (42) that this vinylic isomerisation can be catalysed by the addition of each of the following acids: CF,COOH, HPF, and HSO,F/SbF, to CD,Cl, solutions of

sphere of a metal it has often been implicitly assumed and sometimes explicitly stated (44) that the ability of a metal to act either as a source or a sink of electrons makes the common organic reactive intermediates carbonium ions and carbanions unfavourable. Contrary to this view there is now, in our opinion, a good deal of evidence to support the view that platinum may either induce or stabilise carbonium ion intermediates within its coordination sphere, Consequently we believe that the concept of metal-induced stabilised carbonium ions should be valuable both in interpreting and designing many organometallic reactions. Of course, there exists a certain fundamental problem in terminology. The reactivity of a metal- stabilised carbonium ion may be far removed from its simple organic analogue. In the extreme this may be compared to the dramatic difference in reactivity often observed for a carbene bonded to a metal (45-47) relative to its free organic existence (48). However, in regard to the reactions of organoplatinum complexes described above the carbonium ion terminology seems quite appropriate.

Acknowledgements The author is indebted to Professor H. C. Clark of the University of Western Ontario, Canada, with whom this work was initiated, to Dr. D. A. Couch andMr. R. A. Bell, for their continuing work in this area; to Matthey Bishop, Inc. for their generous loan of platinum and to the Petroleum Research Fund and National Science Foundation for their current support of this work through grants PRF 7722-AC3 and NFS GP-426gX.

These observations lead us to believe that a simple protonation-deprotonation sequence involving the platinum-stabilised carbonium ion trans-PtCl(&Cl-CH,Cl)L, provides the basis for vinyl isomerisation.

Conclusions In attempting to describe the organic

reactions that occur within the coordination


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Fire-resistant Silicone Rubber A continuing and increasing interest in the

use of platinum or platinum-containing compounds for the production of fire-resistant silicone rubbers is shown by the patents being filed on this subject.

Specialised rubbers used where fire resistance is particularly desirable may have their fire retardant properties improved by the addition of very small amounts of platinum in a variety of forms, probably together with other materials such as silica fillers, sulphur- free carbon black or Group I1 metal oxides.

Suggested applications for such rubbers include the insulation of electrical conductors,

transformer encapsulants, heater ducts, and window gaskets. With the performance and safety of ships and aircraft depending largely on the correct functioning of electrical de- vices and wiring i t is clearly advantageous for the insulation employed to be flame resistant.

Patents include those held by Dow Corning (Bvitish Patents I, I 6 1,052; 1,3 3 5,6 I 9; 1,262,845 ; U.S. Patent 3,635,874); General Electric (U .S . Patents 3,539,530; 3,514,424; 3,7I 1,520; French Patent 2,016,946; British Patent 1,380,323); Shinetsu Chemical (British Patent 1,389,393), and Toshiba Silicone (Japan Kokai74 67,933; 7467,934; 74 67,935).


Centenarv of the J

of the Metre INTERNATIONAL STANDARDS IN IRIDIUM-PLATINUM

Convention

MANUFACTURED

By Basil Swindells National Physical Laboratory, Teddington

The inexorable progress of the metric system of weights and measures has resulted in a steady erosion of the traditional standards of measurement. The system, which had originated during the turmoil of the French revolution, received increasing international recognition, which became formalised one hundred years ago, and has been the basis for continuing cooperation. The first international standards, fabricated in iridium-platinum alloy, were largely produced by George Matthey.

In France, before the start of the Revolu- tion in 1789, there had been no uniformity of weights and measures. Trading had been difficult and fraud had been easy, so in 1790 the French National Assembly called for uniform new measures to put a stop to the abuses taking place. Charles Maurice Talleyrand, Bishop of Autun, presented to the Assembly a scheme based upon “natural” measures which he proudly stated would be “for all people, for all time”. This was modified by the Academy of Science, which also strongly favoured the new measures forming a decimal system as follows. The unit of length, the metre, was to be equal to the ten-millionth part of the arc of meridian between the North Pole and the equator and passing through Paris. The gram was to be the “absolute weight” of a volume of pure water, equal to the cube of the hundredth part of the metre and at the temperature of melting ice.

The length of the quarter meridian was calculated from measurements made between Dunkirk and Barcelona. The survey was by two astronomers, Jean-Baptiste Delambre and Pierre Mechain who, because of the troubled state of the country, narrowly

missed losing their heads on a number of occasions after being arrested as spies. Long before this work was completed the measurement of length, area and volume based on the metre and mass (weight) based on the gram had been made obligatory by a law of 1793, with an approximate value for the metre.

After the geodetic survey and calculations for the metre and hydrostatic weighing for the gram had been completed, four bars and four cylinders of platinum were produced to form more convenient reference standards for the units than the “natural” standards. The bars, which were end standards, and the cylinders (to represent 1000 grams because this was of a more practical size) had been manufactured from native platinum by Marc Etienne Janety about 1795, possibly using the arsenic method of refining. A law of 10 December 1799 specified that one particular bar was to be the definitive standard of length throughout the Republic of France, and one cylinder the definitive standard of weight; these later became known as the Kilo- gramme des Archives and the Metre des Archives. The French did not take happily to the introduction of the metric weights and measures so in 1812 Emperor Napoleon


A contemporary engraving showing the melting of some of 236 kg of iridium-platinum for the standard metre at the Conseruatoire des Ar t s et Mktiers in Paris. The operation icas conducted hy Henri Tresca and George Matthey with Sainte-Claire Deville and Dehray as technical advisers

allowed again the use of old names of measures but now with fixed new values in terms of the metre or kilogram (1000 grams). A further law of 1837 made the use of metric measures obligatory again from I

January 1840. Elsewhere in Europe, The Netherlands had been truly metric from 1820 and Greece from 1836.

World-wide interest in the use of metric measures grew with the increase of world trade and the rapid advances of science during the first half of the nineteenth century. Prince Albert’s Great Exhibition in Hyde Park in 1851 and the Paris International Exhibition in 1867 each pointed to the need for world- wide uniformity. At the Paris Exhibition a committee of delegates from many countries strongly recommended the universal adoption of metric weights and measures. This recommendation, together with similar re- commendations of the Academy of Science of St. Petersburg and the International As-

sociation of Geodesy, led in 1869 to the French Government sponsoring an Inter- national Metric Commission. The objective of the Commission was to establish a purely scientific organisation for the ‘cconstruction and verification with the best appliances of modern science, of new international standards of the metre and the kilogram”. The Franco-Prussian war delayed the work of the Commission at the start but in 1872 the first full meeting took place with 29 states represented. Three British scientists gave valuable service throughout the life of the Commission; they were Sir George Biddel Airy, the Astronomer Royal; Henry Williams Chisholm, First Warden of the Standards, London; William Hallowes Miller, Pro- fessor of Mineralogy, Cambridge.

After two years of committee work a detailed policy had been formulated for the construction of international prototypes for the metre and kilogram, for an international


The kilograms were to be solid cylinders with height closely equal to diameter. It was also decided that in order to ensure uniformity, especially of the cocfficients of expansion, between all of the standards likely to be required, all should be made from one ingot of alloy. The French Govern- ment agreed to sponsor the manufacture of the standards on behalf of the French Section of the International Metric Commission. The work was undertaken with great caution since at that time really pure platinum and iridium had never been obtained and the largest casting of platinum yet produced was one of IOO kg made by George Matthey in 1862; a 250 kg casting was now required.

Henri Sainte-Claire Deville and J. Henri Debray, who had previous experience in the refining and melting of platinum, undertook to supervise the relining of the metals and the casting of the alloy, the necessary metals of Russian origin being supplied by George Matthey. The alloying was effected in three castings of 80 kg, 85 kg and go kg each; the ingots were then cut into pieces of about 2 kg each. On 13 May 1874 at the Conservatoire des Arts et Metiers, the whole was remelted into a single ingot under the direction of Henri Tresca, his son Gustav Tresca, and George Matthey, with Deville and Debray in technical control. After cleaning, the ingot weighed 236 kg. Later the ingot was forged and cut into bars and these were then cold-drawn to produce the X cross-section; however, there had been some cracking, resulting in considerable scrap and only 27 metre bars weighing about 90 kg were obtained from the original ingot. (Subsequently many of these bars were found to contain cracks and fissures.) The International Committee at this stage was satisfied with the results but Deville later found that the density was barely 21.1 g/cma whereas it should have been at least 21.385 g/cmS; analysis showed that iron and ruthenium were present in appreciable quantities.

In September 1877 the International Committee of Weights and Measures estab-

The X section originally designed by Henri Tresca for the standard metrp in iridium-platinum on the grounds of its maximum rigidify. This tuns later abandoned on the recommendation of George Matthey i t ho advised that it IL‘UJ impossible to draic the section without contamination from the dies

bureau and for establishing the means of permanent liaison between states. The French Government then convened a Diplo- matic Conference of the Metre early in 1875 and on 20 Msy 1875 the Convention du Metre was signed in Paris by the diplomatic representatives of 17 states. Great Britain did not join the Convention until 1884.

The International Metric Commission had decided in 1872 that the future international standards should reproduce as nearly as possible the units defined by the Archive standards, and that no attempt would be made to remeasure and recalculate the quarter meridian of the earth. I t was also agreed that the material of the standards should be an alloy of 90 per cent platinum and 10 per cent iridium and that the metre should be defined by a “line” standard and not an “end” standard as the French had used. The bars were to have an X cross- section which had been designed by Henri Tresca to provide the greatest rigidity of bar for the quantity of material used. This cross- section also allowed the defining lines to be placed on the neutral plane of the bar with adequate protection against damage.


lished under the Convention of the Metre decided, after considerable discussion, to reject the bars made in 1874. On the advice of Matthey it was decided provisionally to abandon the X-form since he considered that the iron in the alloy might have been picked up during extensive cold drawing of the bars.

In 1878 George Matthey was invited to make two rectangular metre bars. Applying his continually advancing knowledge of the preparation and metallurgy of iridium- platinum, he made these in London from one small casting. The bars were planed, drawing being applied only to obtain the final shape, and on analysis they were found to contain only 0.23 per cent of foreign metals as compared with 2.9 per cent in those of the 1874 alloy; the density of the metal was 21.52 g/cm8. This improvement was sufficient to encourage the Committee to have a bar of the X cross-section made in the same way. It required 448 hours of labour to plane the bar from a square to the X cross-section! The bar was delivered by Matthey in 1879; in this same year he also made three cylinders for kilogram standards.

During the years 1876 to 1878, George Matthey made other metre bars and a standard 4 metres long for the Association GCodCsique Internationale. Also during this period there were differences of opinion between the members of the original French Section of the International Commission and the In- ternational Committee, which was in reality an enlargement of the original French Section. These differences of opinion were about what to do with the metal and the bars of the 1874 alloy. George Matthey was invited to produce three more bars of X cross-section by forging, rolling and then planing to final size; these also were delivered in 1879. Following extensive tests, the International Committee decided that the new International Standard was to be made from pure metals but the bars of the 1874 alloy could be used for National Standards since no significant difference between the various bars was found. In the event,

practically every state requested a metre bar made from pure metals.

In August 1882 the French Government, acting again as sponsor, placed an order with Johnson Matthey for the production of 30 bars for metre standards and 40 cylinders for kilogram standards. George Matthey was left free to employ whatever methods he thought best. The density of the metal had to be 21.5 g/cm3 at least and the composition of the alloy: platinum 90.25 to 89.75 per cent, iridium 9.75 to 10.25 per cent; other con- stituents were not to exceed ruthenium 0.1 per cent, iron 0.1 per cent, rhodium and/or palladium 0.15 per cent, copper, silver, gold or other metals 0.02 per cent. The cylinders were delivered by 1884 and the bars by 1887. The International Committee was responsible for the graduation of the bars and the adjust- ment of the cylinders. At the First General Conference of Weights and Measures in 1889, one of these metre bars was designated the International Prototype Metre and a kilogram of George Matthey's 1879 manufacture was designated the International Prototype Kilogram.

Between 1892 and 1940 nine determinations of the metre in terms of the wavelength of light were made at the International Bureau of Weights and Measures and at other national standards laboratories. These showed that the metre as defined by the International Prototype had been stable to within 3 parts in 10 millions-the mean of the nine results became the basis of the new definition of the metre in terms of the krypton-86 wavelength which was passed by the Eleventh General Conference in 1960. At the same conference the International Prototype Metre was deposed. Nevertheless, the International Prototype Kilogram remains as the ultimate standard for the world. It can thus be said that the choice of iridium-platinum for the standards was directly responsible for providing the incentive for substantial progress to be made in the refining and melting of the metals, while the standards produced in the last century have served the world impeccably.


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES A Comparison of Palladium-Silver and Palladium-Yttrium Alloys as Hydrogen Separation Membranes D. FORT, J. 1’. G. FARR and I. R. HARRIS, 7. Less- common Metals, 1975, 39, (z), 293-308 Y-Pd alloys developed as H, diffusion membranes show significantly higher permeabilities than commercial Ag-Pd membranes and are also stronger. Oxidation of the membrane surface was also investigated.

The Vacancy Formation Energy in Platinum J. S. ZETTS and J. BASS, Phil. Mag., 1975, 31, (z), 419-440 The resistivities of quenched Pt wires of diameters 16, 10 and 4 mil were measured as a function of quench temperature for a variety of quench speeds and the data were analysed in terms of the (FBL) theory of vacancy-annealing to fixed sinks during a quench. For fast quenches from below 950°C~ where few if any vacancies should be lost during the quench, the data for the different wire diameters yield effective formation energies, ranging from 1.16 to 1.35 eV.

Reaction of Alkanes on Platinum-Tin and Platinum-Rhodium Alloy Films z. KARPINSKI and J. K. A. CLARKE,~ . Chem. Soc., Furaduy Tram. I., 1975, 71, (4), 893-902 Studies of the reactions of n-hexane and n- pentane in excess H on Sn-Pt and Rh-Pt films showed that increase of Rh content in Rh-Pt alloys caused a regular increase in hydrogenolysis selectivity. Hydrogenolysis selectivities with both hydrocarbons on Sn-Pt alloys decreased with increase of Sn content. 1,s-Cyclisation selectivity patterns are explained in terms of the change in active site (Pt) number and the possibly modified bonding capability of carbided surfaces for hydrocarbon intermediate.

Residual Resistivity of the Pd-Ag-H System G. BAMBAKIDIS, R. J. SMITH and s. A. OTTERSON, Phys. Status Solidi A, Appl. Res., 1974, 26, (I), 53-60 Electrical resistivity studies of Pd,- yAgy alloys (o(ys0.5) with H up to H/Pd atom ratio of 0.8 at 4.2 K using the Mott two-band model showed the decrease in sp-d scattering caused by filling of the 4d band by H. The results indicate that HjPd atom ratio is more important than H/Metal, which shows that Pd-H interaction ratio, is stronger than that between Ag and H.

The Temperature Programmed Desorption of Hydrogen from Platinum and Platinum- Gold Films J. J. STEPHAN, V. PONEC and w. M. H. SACHTLER, Surface Sci., 1975, 47, (I), 403-412 Spectrometric measurements of the thermal desorption of H from Pt and Au-Pt films showed that H is more loosely bound on the alloys than on pure Pt. About 50:/0 of the absorbate is desorbed by pumping at 78 K from the alloys while only a very small amount is desorbed from Pt. After maximum coverage of Pt films by H adsorption three desorption peaks have been observed: y ( n o K), ZOO K) and p2(330 K).

Investigation of Valence Band Structures in Cu-Pd Alloys V. V. NEMOSHKALENKO, M. G. CHUDINOV, V. G. ALESHIN, w. N. KUCHERENKO and L. M. SHELUDCHENKO, Solid State Commun., 1975, 16,

X-ray photoelectron spectra of valence bands were obtained for Cu-Pd alloys and the density of electron states was calculated by the coherent potential method. The results show that d- resonance states of Pd are present in alloys with high percentage of Cu but there are no apparent d-resonance states of Cu in the alloys containing a high percentage of Pd.

Adsorption of Hydrogen by Palladium- Copper Alloys. Part 1. Experimental Meas- urements. Part 2. Theoretical Analysis R. BURCH and R. G. BUSS,y. Chem. soc., Faraday Trans. I., 1975, 71, (41, 913-921, 922-929 Electrical resistance, and pressure against composition isotherms, studies of the adsorption of H by 5, I O , I ~ and 207; Cu-Pd alloys at 303-373 K showed that for each alloy, the relative resistance increased continually with H content. The solubility of H is smaller in Pd-Cu alloys than in electronically equivalent Pd-Ag alloys. The results are discussed in terms of the lattice parameters of the alloys.

Optical and Magneto-optical Properties of Nickel-Palladium Alloys N. M. VOLOSHINSKAYA, I. I. SASOVSKAYA and M. M. NOSKOV, F k . Metal. Metalloved., 1974, 38, (6) ,

Optical constants and magneto-optical effects in 2 and 20 at.:: Pd-Ni alloys at 0.42-16 pm were measured and showed that they can be explained by an interband adsorption mechanism, rather as optical data and Hall effect data are explained.

(61, 755757

1134-1138

PZutinumMetuZsRev., 1975, 19, (3),114-119 114

Auger Spectroscopy Analysis of Palladium Silicide Films s. THOMAS and L. E. TERRY, AppL Phys. Lett., 1975Y26, ( 8 ) Y 433-435 The formation of PdzSi in Pd films sputter deposited on Si substrates and heated up to 400°C was studied spectroscopically by measuring the depth profile and Arf ion sputtering. The depth profile showed that the silicide phase is formed at the PdjSi surface even in the un- annealed films.

Effect of Long-range Order and Hydrogen Content on the Low-temperature Heat Capacity of Pd,Fe P . MERKER, G. WOLF and B. BARANOWSKI, Phys. Status Solidi A, Appl. Res., 1974,26, (I), 167-173 Measurements of the heat capacity of Pd,Fe in the ordered and disordered states at 2-8 K showed a great decrease of the y-coefficient of electronic heat capacity with increased long-range order parameter. Charging of the ordered sample with H does not influence the magnitude of y. As the reason for the observed change of y a strong change of the d-band shape in ordering is assumed.

The Microstructure and Properties of Sin- tered Tic-Ruthenium Alloys R. WARREN and M. B. WALDRON, Powder Metall. Internat., 1975~7, (I), 18-21 Sintering behaviour, microstructure, hardness and resistance to cracking studies of Tic-Ru alloys show alloys of full density can be produced by sintering at <1840"C. The alloys are harder than cemented carbides with corresponding fractions of more conventional binder materials such as Ni, but Ru is less effective than Co or Ni in improving the resistance to cracking of T i c .

Thermodynamic Investigations in the Thorium-Rhodium System

common Metals, 1975, 39, (2), 235-246 The Gibbs free energy of formation of the intermetallic phases existing in the Th-Rh system were determined between 990 and 1170 K by e.m.f. measurements using solid galvanic cells with a CaF, electrolyte. Thermodynamic data for the intermetallic actinide-Group VIII metal phases are given.

M. MURABAYASHI and H. KLEYKAMP, 3. Less-

A Diffuse Reflectance Study of the Oxidation of Palladium M. TARDY and F. BOZON-VERDURAZ, compt. Rend., Sbr. C, 1975, 280, (6), 317-320 A study of the oxidation of Pd by oxygen made by diffuse reflectance spectroscopy in the temperature range 20-9oocC detected only PdO. The three absorption bands observed at 435,335 and 260 nm were ascribed to d-d transitions.

Electrical Resistivity and Antiferromag- netism of Chromium-Platinum Alloys S. ARAJS, K. V. RAO and E. E. ANDERSON, solid State Commun., 1975, 16, (31, 331-333 Electrical resistivity (p) was measured as a function of temperature (T) in 0.47~0.93 and 1.63 at.*/, Pt-Cr alloys. The onset of antiferro- magnetism causes anomalies in the p vs T curves which incrcase with increasing Pt concentrations.

Some Physical and Mechanical Properties of Uranium- (0.05-6 at.%) Ruthenium Alloys F. H. HAMMAD and A. A. AROU-ZAHRA, J . Less- common Metals, 1975, 40, (I), 79-90 The thermal expansion, crystalline lattice parameters, density and microhardness of U-Ru alloys with 0.05 to 6 at.yA Ru have been studied in the as-cast state and as oil quenched from 720 and 900°C. The results are reported.

Field Dependent Susceptibility and Localised Spin Fluctuations in PdRhNi Alloys R. w. COCHRANE, F. T. HEDGCOCK, J. P. TIDMAN and

145-150 Low temperature magnetisation measurements have been made on a series of Ni-Rh-Pd alloys containing 1-7 at.:$ Rh and up to I at.?: Ni in magnetic fields up to 55 kOe. The results indicate a critical concentration of Ni for ferro- magnetism close to 2

Superconductivity in Metastable Pd- Alloys Produced by Ion Implantation at Low Temperatures B. STRITZKER and J. BECKER, Phys. Lett., 1g75,51A, (311 147-148 Superconductivity has been observed in Pd after implantation of H at liquid He temperatures with a maximum transition temperature Tc of 9 K. Replacing H by D gave a maximum Tc of about 11 K. Pd also became superconducting after the implantation of B and C.

M. J. ZUCKERMANN, Can. J. Phys., 1975, 53, (2),

CHEMICAL COMPOUNDS Complexes of Rh(III), Ir(III), Pd(II), Pt(I1) with Dimethyl(1-naphthy1)arsine L. SINDELLARI, L. VOLPONI and B. ZARLI, Irrorg. hrucl, Chem. Lett., 1975, 11, (5 ) , 319-322 Studies were made of the reaction products of the analogous dimethyl( I-naphthy1)arsine (L) with Rh(III), Ir(III), Pd(II), Pt(I1) to investigate the ability of this ligand to form internally metallated compounds. Rh and I r gave octahedral complexes of formula MX,L, (M-Rh and Ir; X=Cl or Br) but no metallated compounds were prepared. After refluxing in a-ethoxyethanol, Ir complexes gave mixtures of inseparable metallated and unmetallated products. Pt complexes gave metallated compounds PtX(As-C)L where As-C= CloH,AsMe,; X-CI, Br or I.


Thermal Expansion of the One-dimensional Conductor K,Pt(CN),Br,. ,.xH,O and K,Pt (CN),.xH,O W. STURM,S. DROSDZIOK and H. HAW, Solid State Commun., 1975, 16, (9,485-487 Measurements of the thermal expansion coefficient of K,Pt(CN),Bro.,.xH,O and K2Pt(CN),.xH20 show a large anisotropy of the a- and c-directions. Their temperature dependence is described by a simple Griineisen theory, In the range 80-330 K no anomaly is found.

Reactions of Metal Complexes. Rearrange- ment Reactions of Bromotrifluoroethylene- his( substituted Phosphine) -Platinum( 11) V. A. MUKHEDKAR, B. J. KAVATHEKAR and A. J. MUKHEDKAR, 3. h r g . Nucl. chm., 1975,37, (2), 483-48 5 Studies of the vinyl rearrangement of (Ph,PMe), Pt(C,F,Br) and (Ph,P),Pt(C,F,Br) show that the rearrangement takes place through an addition intermediate, probably with a trigonal bipyramidal configuration. This reaction is used in the synthesis of a new series of complexes with the formula (Ph,MeP),Pt(CF=CF,)X and (PhsP), Pt(CF=CF,)X with X =SCN-, NO; and NO;.

Synthetic Methods in Transition Metal Nitrosyl Chemistry K. G. CAULTON, Coordination Chern. Rev., 197514,

A comprehensive review is given of all methods available for introducing the nitrosyl func- tionality into Pt metal group and other coordination complexes. (253 refs.)

Coordination Polymers M(II)[Pt(CN)J, I. Preparation, Crystal Lattice and Absorption Spectra H. SIEBERT and M. WEISE, z. Nuturf, 1975, 30B,

Hexacyanoplatinates (IV) M(II)[Pt(C"),].xH,O (M(II)=Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd; 0 5 x 2 2 ) have been prepared and a new simple method to prepare K,IJ't(CN),] developed. X-ray studies show the structure of the compounds to be cubic except for the Cr and Cu salts which are tetragonal. Absorption spectra data for the compounds have been obtained.

The Free Energy of Formation of Iridium Oxide by Solid Electrolyte Galvanic Cell E. S. RAMAKRISHNAN, 0. M. SREEDHAFUN and M. S. CHANDRASEKHARAIAH, y. Electrochem. sot., 1975, I Z Z I (31, 328-331 The value of AGof of IrO,(s) was determined between 875 and 1175 K by the solid oxide electrolyte galvanic cell method, using calcia- stabilised zirconia as the electrolyte. The results enable estimates of Ir loss from Ir-Pt alloys at high temperatures to be made and allowed for.

317-355

33-39

ELECTROCHEMISTRY Adsorption of Hydrogen on Skeleton Rho- dium-Zirconium Electrode Catalysts M. v. AVRAMENKO, v. M. TSINTSEVICH and G. P. KHOMCHENKO, Zh. F ~ z . Khim., 1975,49, (z), 457- 461 Charging curves of H, adsorption in 0.1 N H,SO, on 0-100 wt.o/, Zr-Rh electrodes showed that adsorption decreases with increased Zr content. The amount of H, adsorption on 5 and 40 wt.% Zr-Rh electrodes decreased with increased temperature, on pure Zr at 20-6ooC there is little change, and at 80°C on pure Zr the length of the Hz region of the charging curve increases.

On the Reduction of Oxygen at Platinum- Oxygen Alloy Diaphragm Electrodes J. P. HOARE, Electrochim. Acta, 1975, 20, (4), 267- 272 The kinetics of the reduction of O e on the front side of a Pt foil diaphragm has been studied both before and after the back side had been anodised. Strong anodisation converts the Pt to a P t -0 alloy and the results show how the presence or absence of 0, in Pt can affect the processes.

The Adsorption, Desorption, and Exchange Reactions of Oxygen, Hydrogen, and Water on Platinum Surfaces. 11. Hydrogen Ad- sorption, Exchange and Equilibration Y. K. PENG and P. T. DAwSON, Can. J. Chem., 1975,

The adsorption, desorption, exchange and equilibration reactions of H, and D, on a Pt filament have been studied by thermal desorption mass spectrometry. The results show that for polycrystalline Pt surfaces heterogeneity is important for the exchange and equilibration reactions of H2.

Contribution to the Study of the Oxygen Electrode on Platinum in Alkaline Solution M. APPEL and J. APPLEBY, Compt. Rend., s&.c, 19753 28% (91, 551-554 A study has been made of the 0, reduction on Pt in alkaline solution using the rotating ring-disc electrode method. The p H dependence of the process has enabled the rate-determining steps for the formation of H,O and H,Oz to be identified.

The Reaction of Hydrogen Atoms with Palladium and its Alloys w. A. OATES and T. B. FLANAGAN, Can. J. Chm.,

It has been found that when H atoms generated in the gas phase are allowed to interact with Pd quite high concentration of interstitial H, can be introduced, even in the absence of poisons. The kinetics of the uptake and subsequent loss of H, from the Pd are considered.

53, (21,298-306

1975, 53, (51, 694-701

Platinum Metals Rev., 1975, 19, (31, 116

ELECTRODEPOSITION AND SURFACE COATING A Practical Approach to the Plating of Platinum Group Metals A. J. FOSTER, Electroplating Metal Finish., 1975, 28, (I), 8-13; (2), 15-17 The plating of Pt group metals is described and typical solutions for their deposition given. Trends in Pt plating and its applications in the electrical and electronics industries are discussed.

LABORATORY APPARATUS AND TECHNIQUE The Detection and Estimation of Airborne Sulphur-containing Compounds by Means of a Novel, Dry, Ultra-rapid, and Extremely Sensitive Method

A new instrument system is described which utilises the reversible and sensitive surface ‘poisoning’ of H permeable Pd metal membranes or foils by S compounds to measure total S in air or other sources.

Automatic Dew Point Mirror for Air Con- ditioning R. GASSER, sulzer Tech. Rev., 1974, 56, (4), 214- 220

An automatic dew point mirror hygrometer incorporating Pt resistance thermometers developed to meet the most exacting demands of air conditioning is described.

A Four Point-probe Cell for Resistivity Measurement at High Temperature

E : Sci. Instrum., 1975, 8, (I), 13-15 A four point probe cell for measuring electrical resistivity of semiconducting compounds at high temperature was fabricated using 40Oi: Rh-Pt pins on a Zr block as the probe assembly. Re- sistivities from 0.1-106 f2 can be measured against temperature with an accuracy of 3-0.5u4.

R. W. PIERCE, 1.S.A. TrUnX., 1974,131 (4), 291-29s

A. M. GEORGE and I. K. GOPALAKRISHNAN,J. Phys.

HETEROGENEOUS CATALYSIS Estimation of Platinum Catalyst Require- ment for Ammonia Oxidation D. ROBERTS and G. R. GILLESPIE, Adv. Chem. Ser.

Mass transfer coefficients for stacked metal screens are used to estimate the amount of Pt catalyst required for satisfactory operation of a commercial NH3 burner, despite the temperature gradients present in the Pt catalyst pad and the usual surface rearrangement of the Pt. Calcula- tions indicate that operation at a higher mass velocity or with closer mesh screens woven from finer wire would reduce catalyst requirement.

1.33, I974,600-611

The Effect of Additions of Rhenium on the Activity and Thermal Stability of Platinum/ Alumina Catalysts in the Dehydrogenation of Cyclohexane N. s. KOZLOV, E. A. SKRIGAN, M. v. ZARETSKII and G. A. ZHIZHEKKO, Neftekhimiya, 1975, 15, (I), 69-73 Studies of the dehydrogenation of cyclohexane over Pt/AI,O, showed that, for o.sy& Pt/AI,O,, Re additions have little effect on catalyst activity but increase the thermal stability, whereas for o.oI-~.I% Pt/Al,O, the addition of Re increases catalytic activity. Re causes the dispersion of Pt particles to increase and retards their aggregation during heating.

Hydrodealkylation of Toluene on Platinum Group Metals

WLYANSKII and L. P. ERDYAKOVA, Neftekhimiya, 1975, 15, (1),95-100 Studies of the hydrodealkylation of toluene over Pt group metals on y-Al,O, at 350-560°C, atm. pressure, showed that at 490°C the order of activity is Rh>Ir>Os>Pd>Ru>Pt. The selectivity of dealkylation depends on the nature of the metal and for toluene conversions up to so?(, varies from 99 to 80 mo1.06 over the series. Determinations of the activation energies for each metal indicated an inverse relationship between activation energy and heat of sublimation.

V. N. MOZHAIKO, G. L. RABINOVICH, G. N.

Characterisation of Some Supported Metal Catalysts by Alkene Titration G. c. BOND and P. A. SERMON, React.Kinet. Card.

The method of characterisation of Pt on supports by alkene titration is based on the reaction of an alkene with H absorbed on certain pre-reduced supported metal catalysts; the reaction occurs on the metal particles. The technique is applied successfully to the characterisation of Pt/SiO, and Pt/a-Al,O, catalysts at IOOOC, but its application to Pt/y-Al,O, is complicated by retention and cracking of I-pentene.

Lett., 1974, 1% (11, 3-6


Effect of the Nature of the Hydrogenation Catalysts on the Selectivity of Hydrogenation of Mixtures of Olefins N. B. DOBROSERDOVA, A. I. LEONOVA and I. V. GOSTIJNSKAYA, Neftekhimiya, 1975, 15, (I), 57-61 Studies of the hydrogenation of binary mixtures of olefms with 2- and 3- substituted double bonds over Pt and Pd blacks showed that with Pt, which has low activity for double bond transfer, the selectivity of hydrogenation is related only to the structure of the olefins in the initial mixture. With Pd, which has high activity for isomerisation, the selectivity is related to the structure of the olefins formed by isomerisation of the initial hydrocarbons and to the amount of isomerisation.

Role of Olefins in the Hydrogenolysis of Butanes on a Platinum Catalyst A. SARKANY, L. GUCZI and P. - I ~ ~ N Y I , React. Kinet. CatuZ. Lett., 1974, I, (2), 169-173 Studies of the reaction of 2-methylpropane in presence of He and H, over Pt black catalyst at 370°C showed a decrease in the activity of Pt catalyst in He. The effect of the decreasing catalytic activity was overcome by using an oxidation-reduction cycle between the runs. The formation of olefins is strongly obstructed even by the presence of a small amount of H, and thus the subsequent rate of hydrogenolysis increases.

The Influence of Ionising Radiation from a Nuclear Reactor on the Activity of Palladium Catalyst on a Support D. v. SOKOL’SKII, B. T. NADYKTO, E. I. GIL’DEBRAND, M. M. NOVIKOVA and E. A. BOGDANOVA, Kinet. Kutaliz., 1975, 16, (I), 156-161 Studies of 0.5% Pd on spectrally pure y-Al,O, modified by HF and LiOH after irradiation by neutrons and y-rays from a nuclear reactor showed that exposure to a beam of I O ~ ‘ neutrons/ cm2 or more causes increased catalytic activity of 0.5% Pd/Al,03 in the liquid phase hydrogenation of dimethylethynylcarbinol. Exposure of the modified y-Al,Os reduces catalytic activity. The possible mechanism of radiation modification of catalyst supports is considered.

Investigation of the Efficiency of Pd/Zeolite Catalysts in the Hydrogenation of Dimethyl- ethynylcarbinol. I. Activity of Pd/Zeolite Catalysts Produced by the Method of Impregnation

SOKOL’SKII, Zh. Fiz. Khim., 1975~49, (2), 337-339 Studies at room temperature and atmospheric pressure of the efficiency of Pd-impregnated CaA and CaX zeolites in catalysing liquid-phase hydrogenation of dimethylethynylcarbinol showed that, whereas the zeolites themselves do not possess hydrogenating properties, the efficiency of the Pd catalyst reaches maxima at 0.3-3.4‘7; and at somewhat higher metal concentrations. The maxima are caused by single Pd atoms, like those of Pt, in the first case and, perhaps, the onset of Pd crystallisation at 0.8-0.g% Pd.

N. A. GOGOL’, N. L. SHLIOMENZON and D. V.

11. Efficiency of Pd/Zeolite Catalysts Pro- duced by the Cation Exchange Method N. A. GOGOL’, D. v. SOKOL’SKII and L. D. ZHUBANOVA, Ibid., 3 4 - 3 4 The activity and efficiency of Pd/NaY zeolite was studied under mild conditions. Pd was supported on the outside and was introduced into the zeolite by cation exchange. Catalyst activity for hydrogenation of dimethylethynylcarbinol depends on the amount of Pd. Single atoms of Pd appear active up to 0.6% Pd content.

Noble Metal Catalysts for Non-selective Oxidation and Pollution Control E. 1. SERCOMBE, Chem. &’ Ind., 1975, (4), 157-161 A comprehensive review is given of the uses of noble metal catalysts, supported and non- supported, in non-selective oxidation and pollution control. The reactions of interest were classified according to whether the material oxidised is inorganic, H, itself, or organic. The use of “Honeycat” Pt catalyst in a wire enamelling plant is described.

Hydrocracking of n-Butylbenzene, sec-Butyl- benzene and Benzene with Palladium on Silica-Alumina Catalysts

Studies of 0.3% Pd/SiO,-Al,O, catalysts during the hydrocracking of n-butylbenzene, sec-butylbenzene at 82 atm. and 10 moles H,/hydrocarbon show that some of these catalysts lose activity for complete hydrogenation in about 4oh, and in Iooh in the case of benzene. In contrast to n- butylbenzene, the level of deakylation of sec- butylbenzene remains high at 95% because the Pd is still effective in preventing poisoning of the acid sites. The results suggest that intermediate species generated on the acid sites of Si02-A1203 migrate to Pd sites and cause deactivation.

Reduction of Nitric Oxide by Monolithic- supported Palladium-Nickel and Palladium- Ruthenium C. H. BARTHOLOMEW, Ind. Engng. Chem., Product

Laboratory reactor studies of the performance of monolithic-supported Pd-Ni and Pd-Ru alloys in reducing NOx showed promising results although long term stability is a problem. Performance is influenced by temperature, poisons, reactant concentrations and changes in space velocity.

C. J. EGAN,J. CUtU&XiS, 1975, 36, (3), 313-319

Res. Dev., 1975, 14, (11, 29-33

Electrocatalysis on Binary Alloys. I. Oxida- tion of Molecular Hydrogen on Supported Pt-Rh Alloys P. N. ROSS, K. KINOSHITA, A. J. SCARFELLIN0 and P. STONEHART, J . Electroanul. Chem. Interfac. EZectrochem., 1975, 59, (2), 177-189 Investigation of Rh-Pt alloys supported on graphitised C used as electrocatalysts for the electrochemical oxidation of H, in CO/H, gas mixtures showed a maximum catalytic activity at 24at.x Rh. This corresponds to minimum activation energy and maximum paramagnetic susceptibility. Poisoning of the alloy surfaces by CO varied only slightly with alloy composition.

Catalyst Screens C. HAMA”, Wire, 1g75,25, (Mar.-Apr.), 52-53 Pt and Rh-Pt catalyst gauzes can now be produced up to 5000 mm wide on weaving machines specially developed for the purpose.


Platinum Adsorption Catalysts in Vapour- phase and Liquid-phase Hydrogenation of Cy clohexene N. I. KOBOZEV, ZH. v. STREL'NIKOVA and L. E.

Khim., 1975, 16, (I), 23-25 Pt jSi0, catalysts possessed considerably higher activity in the vapour-phase hydrogenation of cyclohexene than in the liquid-phase hydrogenation. Lower activity in the latter case is connected with solvent effects.

MARTYSHKINA, vest. Moskov. univ., Ser. IIJ

HOMOGENEOUS CATALYSIS Differences between Homogeneous and Heterogenous Metal Catalysts. Isotope Orientation in the Platinum-catalysed Ex- change of the Polyphenyls, Particularly 0- Terphenyl K. I?. DAVIS and J. L. GARNETT, J . Chem. Soc., Chem. Commun., 1975, (3), 79-80 Studies of the isotope orientation in Pt-catalysed exchange of the polyphenyls, other than o- terphenyl, showed the deactivation of all ar& positions to meta and para isotope incorporation species during initial deuteriation. By contrast, a-terphenyl shows the expected mtho deactivation with homogeneous PtCl,?- and on heterogencous Pt, all mtho protons of the centre ring exchange readily during the initial stages of the reaction. The difference in deuterium orientation of o-terphenyl is attributed to particular conforma- tion of o-terphenyl in the adsorbed state.

Liquid Phase Oxidation of Benzaldehyde Catalysed by Low-valent Transition Metal Complexes J.-I. HOJO, S. YUASA, N. YAMAZOE, I. MOCHIDA and T. SEIYAMA,J. CUtU&s& 1975, 36, (I), 93-98 Catalytic studies of d8 and d10 noble metal complexes during the oxidation of benzaldehyde to benzoic acid and perbenzoic acid showed that the catalytic activity of the complex catalysts was in the order of RhCI(CO)(PPha),>PdO,(PPh,), -Pd(PPh,), > RhCl(PPh,)s > [RhCl(PPh,),], > IrO,Cl(CO)(PPh,), 2: PtO,(PPhJ,. From the kinetic studies using PdO,(PPh,),, the initial rate of 0 consumption was described.

On the Selectivity in the Catalytic Hydro- genation of Methylacetylene on Group VIII Metals N. YOSHIDA and K. HIROTA, Bull. chem. soc. Japan, 1975~48, (I), 184-190 The reaction of methylacetylene with H,, and with D,, was studied over Pd, Pt, Rh, Ir and Ru at 25°C and Pd was found to be the most selective for C,H, formation. With Ru the isomerisation of methylacetylene to allene occurred simultaneously with the hydrogenation. Only three H atoms were deuterated in the C,H, produced over Pd and Pt.

CHEMICAL TECHNOLOGY Corrosion Behaviour of Platinum-Titanium Contacts in Aggressive Medium S. S. MARKOV, G. A. SERYSHEV, V. G. FOMICHEV, A. F. KOPYLOVA, and s. v. oTTAs, Zashchita Metal., 1975, 11, (I), 5-52 Studies of the corrosion behaviour of Pt-Ti alloys made in HCIOI and HC1 solutions, at 18-23°C and electric potential of 1.05-1.2 V showed the lowest corrosion resistance for 69-78". Pt-Ti alloy in 5oog/1 HCIOI and Iog/l HCI and electric potential of 1.05-1.1 V. This low corrosion resistance for Pt-Ti alloys is explained.

Corrosion Resistance of Titanium-Ruthen- ium Alloys

The corrosion resistance of various Ti-Ru alloys (0.07-0.55 wt.O/, Ru) were evaluated and compare with published data on Ti-Pd alloys. The results showed that the corrosion resistance of Ti-Ru alloys were equivalent to that of Ti-Pd alloys in boiling o-100;b H,SO, solutions, and only slightly inferior in boiling O-IO"$ HCI solutions. The Ti-Ru aIloys, however, picked up less H during corrosion than Ti-0.2';; Ru alloy. I t is proposed that in H,S04 solutions, the passivating mechanism involves dissolution and re-precipitation of Ru.

A. J. SEDRIKS, Corrosion, 1975, 31, (2), 60-65

ELECTRICAL AND ELECTRONIC ENGINEERING Yew Tri-metal Process Brings Hermeticity to Plastic-packaged ICs Electronics, 1975, 48, (9), 29-30 RCA states that a new process utilising thin layers of Pt, Au and T i has been developed to prevent corrosion caused by moisture in plastic- packaged integrated circuits. Initial tests over 14,000 hours at 27'C and a relative humidity of 9c-98:& produced no failures.

TEMPERATURE MEASUREMENT Application of High Temperature Film Thermocouples in Investigations of Temper- ature Fields of Components of Gas Turbine Engines L. S. GRIGOR'EV and D. P. SIMBIRSKII, Tepl. Nupyazh. Elem.Konstr., 1974,14, 137-139 Thermoelectric and stability studies were made of the Pt-refractory materials annealed at 20-1000°~, and the thermo-c.m.f. of thermocouples built from these materials were compared with the thermo-e.m.f. of Pt :Rh-Pt thermocouples. The thermo-e.m.f. stability was characterised by S dispersion and for almost all alloys 8 was -0.5%. The influence of microstructure changes on thermo-e.m.f. is also evaluated.


NEW PATENTS CHEMICAL COMPOUNDS Platinum Complexes Containing Sulphur DOW CORNING LTD. British Patent 1,385,041 New complexes for use in preparative organo- silicon chemistry have the formula PtX,(SR’R”), where X is C1, Br or I, R’ is the R,SiQ-group, R is I - I ~ C alkyl, aryl, aralkyl or alkaryl or Me&, Q is a I-r6C organic group and R” is I-18C alkyl, aryl, aralkyl or alkaryl and‘or R SiQ-. For example [(Me,SiCH,),S],PtCl,.

Olefin Metallorganic Complexes of Saline

SNAM PROGETTJ S.P.A. U.S. Patent 3,857,867 Complexes have the formula [Rh(L)n(CH3CN)a]X, where L is ethylene or cyclooctene and X is an anion BF,-, PF,-, C10,- and NO,-, provided that when L is ethylene and n is 2 or 3, a is 2 and when L is cyclooctene and n is I, a is 3 and when n is 2, a is 2 or 3. A typical complex of this salt type is [Rh( C,HJ ,(MeCN),] BF,.

ELECTROCHEMISTRY Electrolytic Electrodes DIAMOND SHAMROCK CORP. British Patent 1,384,836 A new cell uses a number of substantially parallel anodes and cathodes placed face-to-face without diaphragms. The anodes may be constructed from valve metals faced with Pt, Pt alloys and/or solid solutions of noble metal oxides.

Electrochemical Cells

British Patent 1,385,201 An electrochemical cell for monitoring purposes, has active working electrodes of Ptjl’d or Ru-Pt.

Electrolysis Electrode ASAHI KASEI K. K. British Patent 1,386,090 An electrolysis electrode consists of a T i base coated with a mixture of (a) crystalline Ru having a lattice constant which is at least 0.1”; greater than the normal lattice constant when Ru is used alone, and (b) at least 3O: of crystalline Pt or Rh which has a lattice constant at least 0.1~4 smaller than normal.

Type

NATIONAL RESEARCH DEVELOPMENT CORP.

ELECTRODEPOSITION AND SURFACE COATING§ Rhodium-Platinum Plating Bath O.M.F. CALIFORNIA INC. British Patent 1,383,850 Rh sulphate, Pt “P” salt and sulphamic acid arc used to give a brighter alloy electroplated deposit. In an example, the bath contains 2gjI Rh.

Process for Coating Refractory Oxides

U.S. Patent 3,840,389 A refractory oxide having a surface area of about 10-500 mz/g is coated with Ru andlor Rh alone or in combination with at least one of Pt, Pd, OS, or Ir by impregnating the oxide with a solution of a salt of at least one of the metals while maintaining the pH between about 0.7-2.2 and contacting with H,S at a temperature of about 1595°C to precipitate the metals as sulphides before drying.

Electrolytic Deposition of Platinum, Iridium and Their Alloys RHONE-PROGIL U.S. Patent 3,841,980 Baths which are aqueous, acidic and substantially bromide-ion free for Pt and /or Ir electroplating are formed from compounds of Pt andlor Ir giving, in aqueous solution, primarily the bromoiridic and bromoplatinic anions, and at least one acid selected from NHO,, €€,SO,, HC10, and HBrO,. The Pt andjor Ir concentrations are 0.140 gil and the acid is present in an amount of between about 0.05-1 equiv.11.

Valve Metal Electrode ELECTRONOR CORP. U.S. Patent 3,846,273 A valve metal Ti or Ta base is coated with a mixture in liquid form which on heating forms an oxide layer on the base consisting of 39.2-78”, TiO,, 6.4-47.5‘)0 of a Pt group metal oxide and I-17.7~~) V, La andlor Co doping metal. Typi- cally Ru and Ir are used as the Pt group metals.

Process Employing Catalyst-coated Yam Processing Rolls

GULF HESEARCH & DEVELOPMENT CO.

E. I. DU FONT DE NEMOURS & CO. INC. U.S. Patent 3,849,177

In the hot processing of textile materials, the lubricating films are removed chemically, rather than physically, by the use of heated rolls coated with irregular, rounded surface nodules whose interstices contain finely divided Pt, Pd, etc.

Palladium Electroplating Bath FA. DR. TH. WIELAND German Offen. 2,328,243 Better hardness, gloss and corrosion resistance are obtained with Pd films deposited from a bath containing Ni as well as Pd; preferably there are ten parts Pd to each part Ni.

Brazing of Titanium, etc.

German Offen. 2,329,613 Group IV-VII metals and alloys, especially Ti, Zr and their alloys, are brazed using molten salt baths to deposit electrolytically a Pt group metal which assists in bonding. The metal is especially Ir, Rh and/or Ru.

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT


LABORATORY APPARATUS AND TECHNIQUE Air Fuel Ratio Sensor GENERAL MOTORS CORP. U S . Patent 3,84419zo 0, in an exhaust gas stream is sensed by a sensor having a hollow ZrO, body with Pt elements.

Method of Oxygen Detection and Removal

U.S. Patent 3,849,539 A gas with an 0, content of less than I 7" is dried over a zeolite or Mg perchlorate before passage through a Pd tube coil surrounded by a pure H, atmosphere. The 0, combines with H, diffusing through the tube and the water that forms is detected. The tubing is Ag-Pd alloy.

U S . ATOMIC ENERGY COMMISSION

HETEROGENEOUS CATALYSIS Noble/Base Metal on Torvex Catalyst

British Patent 1,39o,1Sz A catalyst for oxidation, reduction, steam reforming, etc., consists of an inert material coated or impregnated with a metallic mixture or alloy of Pt, Rh and one or more base metals selected from Al, Mg, Cr, Mo, W, Mn, Fe, Co, Ni, Ti, V, Th, U, Cu, Ag, Zn, Cd, Hg, In, T1, Bi, Sn, Pb, Sb, the lanthanides and actinides; 1-50"/0 Rh and 0.01-25:.;, base metal are present, supported on a porous refractory monolith. In an example, an I.C.E. exhaust gas catalyst consists of 2076 Ni, 6% Rh and 74'3, Pt deposited on "Torvex".

JOHNSON MATTHEY & CO. LTD.

Oil Production from Garbage

British Patent 1,390,356 Agricultural, domestic or industrial waste containing cellulose material is reacted with one or more reducing gases at elevated temperature and pressure in the presence of a Cu, Ru, Rh, Pd, Ir, 0 s and/or Pt catalyst to give an organic oil suitable for use as a fuel oil.


Hydrocarbon Conversion Catalyst

British Patent 1,390,625 A long life catalyst for conversion reactions consists of an A1,0, support carrying 0.005-1% Pt, 0.005-1 % Ir and o.oo5-5% of one or more of the lanthanide metals. A typical catalyst contains 0.27; Pt, o.o50/b Ir and 0.574 La.

High Purity Hydrogen Production

British Patent 1,391,004 A process is described for the recovery of H, in high purity from a liquid petroleum reforming process using Pt/AI,O, catalyst.

STE. FRANCAISE DES PRODUITS POUR CATALYSE

UNIVERSAL OIL PRODUCTS CO.


NO, Removal from Exhaust Gases

The amount of NO, in I.C.E. exhaust gases is reduced by operating the .engine to give gases which have chemically reducing properties and passing the gases over finely divided Ru or 0 s catalysts, preferably Ru on a cordierite support.

Nitroso-modified Polymers SNAM PROGETTI S.P.A. Britisk Patent 1,391,846 Modified polymers are obtained by reacting a diene polymer or another unsaturated polymer with gaseous NO in the presence of a catalyst which may be a Pt group metal complex, e.g., RhCI(PPh3)

Hydrocarbon Conversion

U.S. Patent 3,839,192 A gasoline fraction is reformed by contacting it and Hz with a Pt-free catalytic composite containing 0.01-20/6 Pd, o.o~-za/, Ir and 0.1-3.59; halogen, the Pd and I r components being present in an atomic ratio of 0.5:1 to I , ~ : I .

Hydrocarbon Conversion with a Trimetallic Catalytic Composite

U.S. Patent 3,839,193 A hydrocarbon is converted by contacting it with a porous carrier material containing o.o~--zo/; Pt or Pd, 0.01-2% Ir, O.OI-S% Ge and 0.1-3.5",a halogen; the Pt or Pd, Ir and Ge are uniformly dispersed throughout the porous carrier material and substantially all the Pt, Pd and I r are present in the metallic state and the Ge is present in an oxidation state above that of the elemental metal.

High Severity Reforming Process with a Platinum-Iridium Catalyst

U.S. Patent 3,839,194 In a naphtha reforming process a naphtha feed stock and H, are contacted with a catalyst containing A1,0, in association with 0.15-0.759& Pt, 0.15-0.45q:O Ir and 0.3-2.07./0 C1, each based on total anhydrous catalyst. The surface area of the Pt and Ir/Al,03 is at least about zoo mz/g Pt and Ir.

FORD MOTOR CO. LTD. British Patent 1,391,509



ESSO RESEARCH & ENGINEERING CO.

Gasoline Reforming with a Platinum-Lead Catalyst

U.S. Patent 3,839,195 A gasoline fraction is contacted with a catalyst containing a porous carrier material containing o.o~-zoj, Pt group metal, 0.1-3.5x halogen and Pb in an amount sufficient to result in an atomic ratio of Pb to Pt group metal of 0.05:1 to 0.9:r. The Pt group metal, preferably Pt itself, is uniformly dispersed throughout the porous carrier material as metal.


Catalyst Comprising an Intermediate Coating of an Oxide of Scandium Yttrium or the Lanthanides and a Platinum Rhodium Top Coating

U.S. Patent 3,839,225 A catalyst consists essentially of an inert material, an intermediate coating containing at least one of the Sc, Y or La oxides and a catalytically active surface coating of an alloy selected from: (I) I -~o% Rh-Pt alloys; (2) 1-507$ Rh-Pt-base metal, the base metal from 0.01-25o/u.

Platinum-Rhodium-Base Metal Catalyst

U.S. Patent 3,840,471 A catalyst consists essentially of an inert material impregnated or coated with an alloy of Pt, Rh and a base metal, the base metal being Ni, Co,Fe, Cu, Nd, In, Sn, Zn, Ag and/or Cr.

Bimetallic Catalyst Preparation MOBIL OIL CORP. U.S. Patent 3,840,475 A supported bimetallic catalyst containing a Pt group metal, which is active in hydroprocessing reactions, is produced by intimately associating a porous A1,0, with a compound capable of furnishing a complex ion containing both the Pt group metal and Sn, for instance (PtC1,SnClJ cations.

Isomerisation Catalyst Activation Process SHELL OIL CO. U.S. Patent 3,842,114 A process for activating a catalyst containing one or more Pt group metals supported on H- mordenite, for isomerising aliphatic saturated 4-6C hydrocarbons at temperatures between 200-30o0C, e.g. Pt/H-mordenite, consists of dehydration at a specified rate.

Multicomponent Dehydrogenation Catalyst

U.S. Patent 3,843,560 A catalytic composite is a combination of Pt metal, Ir metal, an alkali or alkaline earth metal oxide and 0.05-0.5:& S with a porous carrier material. The Pt and I r are uniformly dispersed in the carrier material, in amounts giving an atomic ratio of I r to Pt of about O.S:I to about 1.5:1.

Platinum-Magnesium Reforming Catalyst EXXON RESEARCH & ENGINEERING CO. U.S. Patent 3,846,281 The octane quality of naphthas is improved by contacting the naphtha in reforming conditions with a porous inorganic oxide support carrying 0.3-374 halogen and 0.01-5(% of a hydrogenation- dehydrogenation component which contains a Group VIII noble metal and 0.1-50/b of a Group IIA metal halide.




Trimetallic Catalytic Composite

US. Patent 3,846,282 A gasoline fraction is reformed by contacting the gasoline fraction, at a temperature of 800-1 IOO'F, a pressure of 0-1000 p.s.i.g., a liquid hourly space velocity of o.I-Io/hr, and a mole ratio of H, to hydrocarbon of I:I-20:1, with a catalytic composite of 0.1-3.574 halogen, 0.01-2:4 Pt or Pd, 0.01-2% I r and 0.01-50ib Ni.

Hydrocracking Process for the Production of L.P.G.

U.S. Patent 3,847,796 A Group VIII metal, especially Pt or Pd, is deposited on a combined support of A1,0, and mordenite to act as a hydrocracking catalyst.

Sulphur-free Reforming with a Platinum- Tin Catalyst

U.S. Patent 3,847,794 A process for catalytically reforming a substantially S-free gasoline fraction contacts a gasoline fraction and a H, stream in reforming conditions with a substantially S-free catalyst combination of o.or-z% Pt group metal, e.g. Pt or Pd, 0.01-5% Sn and 0.1-3.5 "/, halogen. Sn component is uniformly dispersed throughout the porous carrier material in a particle size which is less than IOO A in maximum dimension.

Hydroformylation Process and Catalyst PHILLIPS PETROLEUM CO. US. Patent 3,847,997 In a hydroformylation process in which an olefin is reacted with CO and H,, the catalyst is produced by contacting a solid P-containing polymer of at least one vinyl phosphine with at least one Co, Rh, Ru, Pt, and/or Pd carbonyl, the metal being present in an amount of 0.2-20 m o l e s of metal per gg of polymer support.

Hydrocracking Process UNION OIL CO. US. Patent 3,849,293 A feedstock is hydrocracked to produce lower boiling hydrocarbons using a Pt group metal catalyst deposited on a siliceous zeolite carrier. When the catalyst is spent it is regenerated using hydrothermal treatment with a 0.1-307" aqueous NH, solution. A typical catalyst consists of 0.47 % Pd/Y molecular sieve support of the cracking catalyst type.

Hydrogenation of Aromatic Hydrocarbons TEXACO INC. U.S. Patent 3,851,001 In a process for the production of cyclohexane having a purity of at least gg.50j0, a mixture consisting essentially of benzene and cyclohexane is passed in the presence of added He into contact with a supported Pt catalyst promoted with 0.01- 5% T1. The catalysts of two examples contain o.7so/0 Pt and 0.57" Tl/Al,O,.

UNIVERSAL OIL PRODUCTS GO.




Dehydrogenation Method and Multicom- ponent Catalytic Composite

U.S. Patent 3,851,003 A catalyst for dehydrogenating a 2-3oC normal paraffin hydrocarbon, alkylaromatic hydrocarbons and naphthenes is a composite consisting of an Sn component and a Pt component on a carrier material which is prepared by impregnating a high surface area, porous carrier material with a solution of a complex chlorostannate(I1)-chloroplati- nate anionic species. Typically A1,03 is impregnated with 0.6% Pt, o.5yo Sn, 1.5% K and less than 0.2% chloride.

Reforming with Platinum on a New Alumina Support

A naphtha feedstock is reformed in contact with a catalyst containing 0.01-50/’0 Pt/Al,O, which is obtained by removing water from A1 hydroxide produced as a by-product from a Ziegler higher alcohol synthesis reaction and calcined at 1150- 1350°F to have a surface area of 165-215 m2/g.

Reforming Process Catalyst PHILLIPS PETROLEUM GO. U.S. Patent 3,856,660 A process for the catalytic reforming of hydrocarbons consists of contacting at reforming conditions naphtha and H, with a catalyst having increased activity and selectivity which is a refractory support promoted with o.01-59/, of Pt, I r and Ga respectively.

Dehydrogenation with a Nonacidic Multi- metallic Catalyst

US. Patent 3,856,870 A method for dehydrogenating a hydrocarbon consists of contacting it with a nonacidic catalytic composite containing a porous carrier material, 0.01-2% Pt or Pd, 0.01-27& Ir, 0.01-5% Ge and 0.01-50/0 of an alkali or alkaline earth metal, where the Pt or Pd, Ir, Ge and alkali or alkaline earth metal components are uniformly dispersed throughout the porous carrier material.

Catalyst Cartridge

Catalyst particles are embedded in thin green ceramic or metal foil sheets which are bent into an arcuate shape and fixed between a heat sink and/or an outer shell. The catalyst particles may consist of Pt group metals, Au and Ag (among others).

Exhaust Purification KALI-CHEMIE A.G. French Appl. 2,216,438 The gas is contacted with a catalyst consisting of a calcined support containing at most 0.5% Pt in combination with 0.5% Ru, Rh or Re.

UNIVERSAL OIL PRODUCTS GO.

CHEVRON RESEARCH GO. U.S. Patent 3,852,190


S.A.E.S. GETTERS S.P.A. U.S. Patent 3,857,680

Dicyanogen Production ROHM G.m.b.H. German Offen. 2,341,370 Dicyanogen is produced by the oxidation of HCN using a metallic Pt catalyst in which up to 5oo, of the Pt may be replaced by Re. Rh may also be present, e.g. a 9o’;Pt - 8O;Rh - z”i,Re alloy in the form of a gauze.

Exhaust Gas Treatment Catalyst

German Offen. 2,431,768 A high stability catalyst for I.C.E. exhaust treatment consists of Ru or a Ru alloy and a metal oxide, especially a Group IIA oxide, able to form a stable mixed oxide or ‘ruthenite’ with RuO,. Typically, Ba ruthenite for catalytic purposes is formed from Ba peroxide and Ru sponge.


HOMOGENEOUS CATALYSIS Oxidising Epoxides to Acids

In the production of carboxylic acids an cpoxide of an a-olefin is contacted with a percarboxylic acid oxidising agent in the presence of a Ru containing catalyst selected from Ru metal, inorganic Ru salt and organic Ru salts and an inert paraffinic or halogenated hydrocarbon solvent at the reflux temperature of the solvent. Suitable catalysts are Ru(CO),, Na,[Ru(C,O,),] and Ru tris(ethy1ene- diamine).

Preparation of Carbonyl Compounds

Alcohols and ketones are prepared by reacting ethylene, propylene and/or butylene under effectively anhydrous conditions at 50-15o”C with PdCI, and t-butyl alcohol to form alkanols, alkanones and isobutylenc.

Hydroformylation Catalyst MONSANTO GO. U.S. Patent 3,855,307 The hydroformylation of 2-6C unsaturated hydrocarbons in the presence of CO and H, is catalysed by a multiphase catalyst based on a porous, solid carrier having dispersed in it a liquid catalytic component including a solvent having a vapour pressure at 100°C of from 10-l~ to 10 mm, and an aryl phosphine complex of Rh.

ATLANTIC RICHFIELD CO. U.S. Patent 3,839,376

ATLANTIC RICHFIELD GO. u. s. Patent 3,847,996

FUEL CELLS Fuel Cell Electrode

U S . Patent 3,844,839 A hydrazine-air electrochemical cell in which the amount of NH3 generated is reduced when the cell is operating has an approximate 60% porous Fe plaque anode impregnated with about 3 mg/sq2 of Pd black, an air cathode and a solution of 2 molar hydrazine in 5 molar K hydroxide as electrolyte.

U.S. SECRETARY OF THE ARMY


CATHODIC PROTECTION Anode Containing Pin-type Inserts

U.S. Patent 3,844,921 An anode for a cathodic protection system or similar electrolytic process has a lead metal anode body and pins extending into the body from the outer surface made from Ta, Ti, Nb, Zr, V and/or their alloys coated with a Pt group metal.

ESSO PRODUCTION RESEARCH CO.

CHEMICAL TECHNOLOGY Organopolysiloxane Compositions DOW CORNING cow. British Patent 1,384,008 A few p.p.m. of Pt are used to cure non-hazing siloxane resins for optical use.

Impregnation of Graphite with Ruthenium

U.S. Patent 3,850,668 A method of treating a porous body of C or graphite with Ru consists of removing gaseous fluid from the body, contacting the body with a solution of Ru acetylacetonate, evaporating the solvent and heating to cause the Ru acetylacetonate within the pores of the body to decompose. Even impregnation is obtained as the acetylacetonate sublimes causing an atmosphere of Ru throughout the pores of the body, prior to decomposition.


Palladium (Alloy) Diaphragm URALSKY ORDENA TRUDOVOGO KRASNOGO ZNAMENI POLITEKHNICHESKY INSTITUT IMENI S.M. KIROVA French Appl. 2,217,267 Extremely pure H, is prepared by passing industrial Hz or H, separated from a mixture of gases through a Pd (alloy) diaphragm at I atm and at 2 o w ° C . Steam is introduced into the gaseous stream before passing through the diaphragm until the partial pressure is 5mm Hg.

ELECTRICAL AND ELECTRONIC ENGINEERING Electrical Switch Contact FUJITSU LTD. British Patent 1,386,157 In an electrical switch contact, the contact material is an alloy consisting of 45 to 85 at.'); of Pd and 55 to 15 at.?!, of Al, e.g. PdzA1 or PdAl.

Thick Film Circuit Ink JOSEPH LUCAS (INDUSTRIES) LTD. British Patent 1,387,267 The problems of soldering noble metal printed circuits are overcome by diluting the Pd used in an ink with Pb in a 3:I to 3:2 ratio. The ink also contains a glass frit and a liquid vehicle.

Metal Silicide-Silicon Schottky Barrier R.C.A. CORP. U.S. Patent 3,841,904 A silicon body is cleaned with HF and contacted with a HF/HCl solution of an Os, Ir and/or Pt salt to form a metal silicide layer.

Process for Treating Thermopiles NUCLEAR BATTERY cow. US. Patent 3,842,489 Terminal wires made from Pd, Au, Ni, Au plated Ni or 92 4'" Au-8% Pd alloy are applied to telluride and/or selenide elements under pressure and a capacitance discharge pulse applied to heal defects and irregularities in the elements.

Glass Ceramic Capacitors

U.S. Patent 3,845,365 Ternary electrodes consist of a metal film of noble metal powder dispersed in an inert vehicle, the powder consisting of 20-9oo.b Au, 2-3oo; Pd and 3-70:b Ag.

Electroconductive Paste Composition OWNS ILLINOIS INC. U.S. Patent 3,846,345 An electroconductive body of material has a plurality of particulate bodies of less than about 10 pm in diameter embedded within a fused glassy matrix of dielectric material. The particulate bodies have a core of dielectric material selected from glass, A1,0,, Be or ceramic material and surrounded by material selected from Pd, Rh and,'or their oxides and alloys.

Reed Switches with Oxidised Rhodium Con- tacts

US. Patent 3,857,175 A method of manufacturing a reed switch consists of forming Rh contacts on leads, oxidising the Rh contacts and sealing the leads with the oxidised Rh contacts in a sealed envelope.

Printed Circuit Board Material Incorporating Binary Alloys THE MICA CORP. U.S. Patent 3,857,683 A printed circuit made has an insulating base coated with at least one electrical resistance layer and a highly conductive circuit. A number of binary alloys are suggested for the resistance layer, including alloys of Co with 16-9496 Ru and of Pd with 9-40~~ Mo.

Conductive Ink Composition Containing Palladium and Lead Metal Powders

U.S. Patent 3,857,798 An ink for use in the manufacture of a thick film circuit contains Pd powder, Pb powder (the ratio of the weight of the Pd powder to the weight of the Pb powder being in the range of 3:1 to 3:2), an inorganic bonding material and a binder liquid.

E. I. DU PONT DE NEMOURS & GO.

O.K.I. ELECTRIC INDUSTRY GO. LTD.

JOSEPH LUCAS (INDUSTRIES) LTD.


vol. 19 july 1975 no

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