HPDROXYMETHYLPHOSPHINIC ACID AND SOME HOMOLOQUES. 423

LI1.-Hydroxymethyl-phosphinic Acid and Some Homo log ues.

By HAROLD JAMES PAGE.

FOSSEK (Monutsh., 1884, 6, 121, 627; 1886, 7, 20) found that the admixture of phosphorus trichloride (1 mol.) and an aldehyde (3 mols.) resulted in the formation of a viscid oil, with the libera- tion of a considerable quantity of heat. When the oil was treated with water, twethirds of the initial quantity of aldehyde were regenerated, together with hydrogen chloride; and an acid of the type R = C H ( O H ) * P 0 8 ~ was formed according to the following equations :

3RsCHO + PC18 = [SR*@HO,PC18] [3R*CHO,P@l,] + 3H%O =2R*CHO + 3HClf R*CH(OH)*PO8Hp Fossek (Zoc. ci t . ) could gain no information as to the constitution

of the intermediate oil, which is accordingly provisionally designated by the formula [3R*CH0,PC13]. He prepared the acids in which R represents methyl, ethyl, isopropyl, kobutyl, hexyl, and phenyl by the interaction of phosphorus trichloride and met-, propion-,

F F 2

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424 PAGE : HYDROXYMETHYLPHOBPHINfC ACID

kobutyr-, isovaler-, hepb, and benz-aldehydes respectively ; more- over, he advanced conclusive evidence that their structure is as represented above.

The present communication deals with a repetition and extension of Fossek's investigations, and was undertaken for two reasons: first, on account of the exceedingly interesting nature of the reaction whereby the hydroxyphosphinic acids are produced ; and secondly, because the first member of the series, hydroxymethyl- phosphinic acid, O H * C q * P O , q , was not prepared by Fossek.

Fmek's results have been confirmed, but certain minor modifica- tions in his methods have been of advantage; these are mentioned in the experimental part of this communication.

The intermediate oil is of an extremely unstable nature; an attempt to distil i t in a vacuum resulted in its decomposition into aldehyde, hydrogen chloride, etc. There is, however, no doubt that it contains 3 molecules of aldehyde to 1 of phosphorus trichloride in chemical union, for if these two are mixed in any other propor- tions, the whole of the exceea of one or the other above these proportions can be rapidly removed in a vacuum at the ordinary temperature. The regeneration of two of the three initial molecules of aldehyde by the action of water has also been amply confirmed. Any attempt a t explaining the mechanism of the reaction and the constitution of the intermediate oil must take account of these facts; it must also explain the fact that, whereae at the commencement of the reaction the phosphorus is in the tervalent condition, in the final product, the hydroxyphosphinic acid, the phosphorus is quinquevalent. The above considerations have led the author tentatively to advance the following explanation of the mechanism of the reaction:

The phosphorus trichloride and aldehyde first combine to form an additive compound, in which the phosphorus is linked to each of the carbon atoms of the original aldehyde groups by the oxygen atoms of these groups, In view of the well-known tendency of phosphorus to pass from the tervalent t o the quinquevalent condi- tion wherever possible, the molecule of this compound undergoes a rearrangement to produce a compound of formula (I), in which the phcephorus has assumed the quinquevalent condition, and a t the same time has become directly united to a carbon atom. The compound (I) when acted on by water is decomposed in such a way

c1 0GH.R c1 0

P-C1 -I- 0 C E . H -+ P-CH*R

01 0CH.R O*CHCI.R O H

I /? CH(OH)*R I \OCIICl.R

?$ f& i

(1.) (11.1

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AND SOME HOYOLOOUeS. 425

that the P.0-C linking8 are hydrolysed, whereas the P-C linkhg is unchanged, and the hydroxyphosphinic acid (11) is formed. This explanation is in harmony with all the known facts of the reaction; and the instability of the intermediate oil, although it renders experimental proof well-nigh impossible, supports the constitu- tion (I).

The obvious method of preparing hydroxymethylphosphinic acid would appear to be by the interaction of dry formaldehyde with phosphorus trichloride. Fossek (Zoe. cit.), however, had already found that in the case of acetaldehyde the reaction was so violent that his usual method had to be modified considerably. It was hence to be anticipated that the reaction with formaldehyde would be still more violent; and, moreover, the experimental difficulties are increased by the excessive tendency of dry formaldehyde to polymerise. A satisfadory method waa finally found in the inter- action of phosphorus trichloride with paraformaldehyde or trioxy- methylene, the termolecular polymeride of formaldehyde. By this means hydroxymethylphosphinic acid, OH*C-PO,H,, was obtained in 93 per cent. yield. A t the same time, i t was deemed advisable to attempt the preparation of this compound, for purposes of comparison, from formaldehyde and phosphorus trichloride ; ulti- mately a method was devised whereby a small quantity of the desired product was obtained, not sufficiently pure for analysis, but its identity with the product from trioxymethylene was established.

Hydroxymethylphosphinic acid was found to be in most respects analogous to the other members of the series; being, however, the typical member, i t was t o be expected to show certain anomalous properties, and such was, in fact, found to be the case. Especially interesting is the property which it possesses of inhibiting the precipitation of phosphates by ammonium molybdate. It is also extraordinarily hygroscopic and deliquescent ; moreover, i t reduces ammoniacal silver nitrate readily at looo. These properties are not found in the other members of the senea. Some explanation is possibly to be found in the fact that i t contains a primary alcoholic group, whereas the other members contain secondary alcoholic groups.

EXPERIMENTAL. Preparation of a-Hydroxy benrylphosphinic Acid, OH.C,H,*PO,&.

This compound was prepared by Fosaek's (Zoc. &t.) original method. One hundred And fourteen grams of benzaldehyde were cautiously mixed with 37 grams of phosphorus trichloride, and set aside for twenty-four bu r s . A faintly red, fluorescent, viscid oil

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426 PAGE : HYDROXYMETHYLPHOSPHINIC ACID

resulted, which waa poured into 3 litres of cold water with constant stirring. The lower layer of benzaldehyde waa separated, and shaken with successive quantities of water, which were added to the main aqueous portion. This was filtered through a wet filter paper to remove globules of benzaldehyde, and evaporated on the water-bath to a syrup, which was redissolved in water and reevaporated several times in order to remove all traces of hydrochloric acid. Contrary to Fossek’s statement, i t waa found that the syrup did not cryatallise; on treatment with ether, however, it became beautifully crystalline without previously passing entirely into solution. These crystals were collected, and recrystallised from a mixture of two parts of benzene and one part of glacial acetic acid. The yield waa 42 grams, that is, 84 per cent. of the theoretical. (Found, C=44*3*; H = 4 * 9 ; P-16.5.t Calc., U=44*68; H=4*79; P=16*5 per cent.)

The a-hydroxybenzylphosphinic acid melted sharply a t 2110 (uncorr.). Fossek (Zoc. c i t . ) found 173O.

The calcium salt waa prepared by adding calcium chloride to a neutral solution of the ammonium salt of the acid, and boiling; this precipitates the calcium salt, which is much less soluble a t looo than i t is at the ordinary temperature. It was collected at looo, and dried at llOo:

Found : P = 13’3. U,H,O,PCa requires P = 13’7 per cent.

Investigation of the Oily Intermediate Compound.

Thirty-one grams (1 mol.) of phoephorus trichloride were mixed as before with 95’5 grams (4 mols.) of benzaldehyde. The mixture waa set aside for twenty-four hours, and then kept in a vacuum until its weight was constant. It was then found to weigh 103 grams, which corresponds with the loss of 23’5 grams (1 mol.) of benzaldehyde. Fifty grams of this oil were poured into 1000 C.C.

of water. The benzaldehyde liberated, together with that dissolved in the water, amounted to 48 grams, that is, twethirds of the benzaldehyde in the intermediate oil had been regenerated. The remainder of the oil was fractionally distilled in a vacuum. Three

In these combustions, the substance wan mixed with lead chromate in the boat j otherwise a residue of phosphoric acid containing unburnt carbon was left.

t This, and all subsequent determinations of phosphorus, are carried out by Neumann’s method, as modified by Plimmer an8 Bayliss (J. PhySioZ., 1906, 38, 439). The substance is oxidisod with a mixture of nitric and sulphuric acids, diluted with water, and the phosphoric acid precipitatad with ammonium molybdate under standard conditions. The precipitate is collected, washed, and d i o l v e d in excess of standard sodium hydroxide ; tho exce~s of alkali ia titrated with acid after boiling off all ammonia.

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AND SOME HOMOLOGIUES. 427

main fractions were obtained, which were further divided into eight sub-fractions. These were all colourless and mobile, and had an odour resembling that of a mixture of benzaldehyde and hydrogen chloride. On keeping in air they were all completely converted into benzoic acid. They contained no phosphorus, and amounte of chlorine which increased from 3.6 per cent. in the first fraction to 27.64 per cent. in the eighth. These fracfions were clearly either solutions of hydrogen chloride in benzaldehyde, or they contained some extremely unstable compound which readily gave these two substances.

Preparation of a - H y d r o ~ i s o a m y l ~ h o s ~ h ~ n i c Acid, OH~C,H,,*PO,H,.

This compound waa prepared by Fossek’s (loc. cit.) original method. Twenty-seven grams (4 mols.) of isovaleraldehyde were cautiously mixed with 11 grams (1 mol.) of phosphorus trichloride, and the mixture set aside for twenty-four hours. It was then poured into 750 C.C. of water, and thoroughly stirred. The upper layer of isovaleraldehyde was separated, and amounted to 18 grams. The aqueous layer waa filtered through moist filter paper, and evaporated to a syrup on the water-bath, when on cooling it crystallised com- pletely. It was recrystdlised from a mixture of alcohol and ethyl acetate, and dried a t llOo. When it waa analysed, even after mixing intimately with lead chromate, i t was found that it gave values for carbon which varied between 1 and 2 per cent. below the true value. (Found, Ci=33*6, 33.2, 34.0. Calc., @=35*7 per cent.)

Messinger’s method, as modified by Fritsch ( A n d e n , 1897, 294, 79), in which the carbon is estimated by oxidation with sulphuric acid and potamium dichromate, gave results even lower than this, namely, C=21*3 per cent.

Since Fossek (Zoc. cit.) obtained theoretical results for carbon, it is obvious that he must have used some modification of the ordinary method, which he does not mention. It is noticeable that the diffi- culty was not encountered with a-hydroxybenzylphosphinic acid. The resulh for hydrogen and phosphorus are, however, well in agreement with theory, and serve to make the identity of the compound assured. Calc., H = 7.7 ; P = 18.5 per cent.) The a-hydroxyisoamylphosphinic acid melted at 188O (uncorr.) ; Fossek’s preparation melted a t 184-185O.

(Found, H = 7.7 ; P = 18.6.

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428 PAGE : HYDROXYMETHYLPHOSPHINIC ACID

Eydroxymethylphosphinic Acid, OH.CH2.P08H,.

Seventy-eight grams of trioxymethylene were added in successive small portions to 118 grams of phosphorus trichloride. Each addition of trioxymethylene caused the evolution of much heat, and the mixture was cooled thoroughly after each addition. A viscid mass, in appearance resembling starch paste, was produced. When this was heated on the water-bath for a few minutes it gradudly became clear, and after an hour it waa a fairly viscous oil. This was set aside for twenty-four hours, and then poured into 4000 C.C. of water. The oil first sank to the bottom, but gradually dissolved, wibh the evolution of a considerable quantity of form- aldehyde. After the oil had completely disappeared, the aqueous liquid was filtered, and evaporated on the water-bath until of constant bulk. When s e t aside for twenty-four hours out of contact with air, the whole mass crystrtlliaed in long, flat prisms radiating from the point of contact of a glass rod with the basin. The mass was broken up, and separated so far as possible from the small quantity of viscid, oily liquid which it contained. When placed in a vacuum over concentrated sulphuric acid i t was not observed to become any drier; indeed, it waa found to be more hygroscopic than sulphuric acid. It could, however, be dried over phosphoric oxide. A second crop wm obtained in a similar way from the mother liquor, the total yield being 90 grams, or 93 per cent. of the theoretical (for 1 mol. PCI, : 1 mol. CH,O). The only effective method of recrystallisation was to dissolve in absolute alcohol, and add ethyl acetate until a permanent cloudiness ww obtained. After some hours a mass of crystals (slender, rectangular prisms) was obtained. These were separated, and dried in a vacuum over phosphoric oxide, when they melted a t 8 5 O (uncorr.). The same difficulty with regard to combustions was met with as in the case of a-hydroxyisoamylphosphinic acid, even when the substance was intimately mixed with dry lead chromate (in absence of air, since the acid is very hygroscopic).

Found: C=9*3, 9.6.

Here, again, the Fritsch-Messinger wet method gave even more discordant results. (Found, C=5*56, 5.67.)

The reasons for the non-applicability of any of the known methods of combustion to these compounds axe not known, and the matter is being further investigated. The values for hydrogen and phos- phorus, together with the analyses of various salts, were, however, sufficient proof of the identity of the substance with hydroxymethyl- phosphinic acid.

CH,O,P requires C=10*7 per cent,

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AND SOME EOMOLWUES. 429

Found: H=4.2, 4.1; P=27*9,27*5. 0.2290 gram lowered the freezing point of 23.31 grams of glacial

acetic acid by 0'324O. M.W.=118. CH,O,P requires H.=4.5; P=27*7 per cent. M.W.=112.

This shows that the substance has the simple formula CH,O,P, and is hence a derivative of formaldehyde, not of trioxymethylene, which latter is hence depolymerised during its reaction with phosphorus tridhloride.

H y d r o ~ y m e t h y l p ~ o s p h ~ ~ c acid is a white solid, crystallising in rectangular platelets. It is exceedingly hygroscopic and deliquescent. It is a dibasic acid, as shown by the following titrations:

A solution of the acid was titrated with NlZ-sodium hydroxide, using, first, phenolphthalein, and, secondly, alizarin-red as indicators.

Volume of Volume of Jndicator. acid solution. iVI2-NaOH.

Alizarin-red ... .. . .. . . . . .. 8-95 C.C. Phenolphthalein ...... 25 8 l 13.90 l l

It is not decomposed by boiling with dilute acid or dkd i . When treated with potassium permanganate in acid solution it is entirely oxidised, the whole of the phosphorus being converted into phos- phoric acid. It reduces ammoniacal silver nitrate solution rapidly on heating, but does not produce a mirror. It haa no action on Fehling's solution. When heated alone it first melts, then evolves formaldehyde, leaving a residue of phosphorous wid, which on further heating evolves phwphine, leaving a residue of phosphoric acid.

The inhibitory action of hydroxymethylphosphinic acid on the precipitation of ammonium phosphomolybdate, although it itself forms no insoluble compound with the latter, is shown by the following experiment. Saturated sodium phosphate solution was added drop by drop to the contents of each of two test-tubes, the first of which contained 10 per cent. of ammonium molybdate in 2N-nitric acid, and the second contained 10 per cent. of ammonium molybdate and N I 2-hydroxxymethylphosphink acid in 2N-nitric acid. mereas the first arop of sodium phosphate produced a copious, yellow precipitate of ammonium phosphomolybdate in the first tube, no precipitate was produced in the second, even after the addition of fifteen drops, and i t was only after several C.C. of sodium phosphate had been added that any phosphomolybdate was precipi- tated, and then only after some time. The nature of this inhibitory a t i o n is not yet understood.

25 C.C.

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430 HYDROXYMETHYLPHOSPHINIC ACID AND SOME HOMOLOQUES.

Sdts of Hydroxymethylphosphinic Acid.

The barium and barium hydrogen salts were prepared by the addition of the calculated quantity of barium hydroxide to a solution of the acid. The barium hydrogen salt is precipitated by alcohol, but not in a filterable form. When its solution is evaporated, crystals of the neutral salt separate, and free acid remains in the mother liquor.

Barium ~drozymethyl~hos2lh~.inate may be prepared as above, or by boiling its solution in water, when i t is precipitated in pearly plates. It is leas soluble in hot water than in cold.

Found : P = 12.6.

Silver hydroxymetAylph.osphinate is a white, amorphous sub-

Found : P = 9'3.

Pyradiniunt hydroxymethylphosphinate,

CH,O,PBa requires P = 12.5 per cent.

stance. When heated to looo it rapidly becomes black.

CHs04PAg2 requires P = 9.6 per cent.

OHG~PO,H,,C,H,N, is obtained in glistening, white needlea by the addition of pyridine to a solution of hydroxymethylphoephiic acid in absolute alcohol. It melts at 1 0 5 O (uncorr.). I n similar concentrations, u-hydroxy. benzyl- and or-hydroxyisoamyl-phosphinic acids do not form insoluble pyridinium salts. The salt readily loses pyridine.

Found : P = 16.7. CH,O,P,C,H,N requires P = 16.3.

Calcium hydroxymethylphosphinate is a white, amorphous substance, much more soluble in cold water than in hot. The calcium hydrogen Balt is an uncrystallisable syrup. The following salts are amorphous : the lead and zinc salts (colourless), the c u p k salt (pale blue), and the ferric salt (pale yellow).

The mercwric and magnesium salts are soluble in water.

Action of Formaldehyde on. PhosphQrus Trichloride.

Dry formaldehyde generated by the action of heat on trioxy- methylene was passed into thoroughly cooled phoephmus trichloride. A considerable quantity of heat wag liberated. Long before the theoretical amount of formaldehyde had been passed in, the whole of the tubes were blocked by the polymerisation of the formaldehyde to trioxymethylene. The intereating point, however, was that the greater part of the formaldehyde coming into contact with the phosphorus trichloride had polymerid and produced a starch-

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DUNNINGHAM : THREE COMPONENT SYSTEM, ETC. 431

paste-like mass similar to that produced in the preparation of hydroxymethylphosphinic acid. This mass was shown to contain trioxymethylene; i t is hence evident that the action of phosphorus trichloride on formaldehyde is preceded by, or a t any rate accom- panied by, polymerisation of the formaldehyde. When the starch- paste-like mass was heated, i t became clear, and although hydroxy- methylphosphinic acid could not be isolated in the pure state from the liquid produced by treating with water, on account of the large amount of phosphorous and phosphoric acids present, a product was obtained which possessed all the properties of hydroxymethylphos- phinic acid, including that of inhibiting the precipitation of phosphomolybdate.

The author wishes to express his thanks to Dr. R. H. Aders Plimmer for valuable advice, and to the Government Grant Com- mittee of the Royal Society for a grant, which has partly defrayed the expenses of this investigation.

LUDWIG MOND RESEARCH LABORATORIES FOR BIOLOGICAL CHEMISTI~Y, INSTITUTE OB PHYSIOLOGY,

UNIVERSITY COLLEGE, LONDON.

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