NotesZone Melting Studies of Organic Eutectic

Mixtures: Naphthalene-Catechol &Naph thalene-p-Chloroni trobenzene

Systems

R. P. RASTOGI, N. R. SINGH & NARSINGH BAHlI.DUR SINGH

Department of Chemistry, University of Gorakhpur

Received 30 [unc 1976; accepted 24 February 1977

The effective distribution coefficient, direction ofsolute transference and the separation efficiency havebeen determined for the naphthalene-catechol andnaphthalene-p-chloronitrobenzene eutectic systemsusing zone melting technique.

ZONE melting was originally developed by Pfannl

as a refining process taking the advantage ofdifference in solubilities in the solid and liquidstates. Yue2,3 has determined the effective distri-bution coefficient and the effect of various factors,like the number of pa"se", temperature and theconcentration on the effective distribution coefficientfor various alloys by means of zone melting tech-nique. Such studies for organic eut ectics arelimited although many other studies have beenmade". 'vVe report ill this note the results of ourstudies on the naphthalene-catechol and naphthalene--b-chloronitrobcnzene eutectic systems. Parameterssuch as direction of solute transference, separationefficiencv and the effective distribution coefficienthave be~~n determined.

Naphthalene and catechol were purified byrepeated distillations and finally by zone meltingprocess. p-Chloronitrobenzene was purified byfractional crvstallization and finally by zone meltingtechnique. The purity was checked by determiningthe melting points. The observed melting pointswere in good agreement with the literature values",

The phase diagrams were studied using thaw-melt method" and the zone melting studies weremade using a horizontal single heating zone-meltingunit. In this unit the heater is fixed and the tubecontaining samples moves. A nichrome wire (length= 15 em, diameter =, 0·1 cm) in the form of acircular coil was used as the heater. The diameterand the breadth of the heating coil were 1 and 2·4ern respectively. A pyrex glass tube filled withthe sample (diameter = 0·7 ern, length = 30 ern)rested at V-shaped aluminium grooves (well polishedto minimise friction) fitted on a wooden base.Sample tube was moved by a geared motor witha speed of 4 em/hr. Temperature was controlledby an autotransformer. The zone length waskept 4 and 3 ern for one and four passes respectively.

Naphthalene-catechol system - The phase diagramof this system is shown in Fig. 1. The zone melting

experiment was carried out for naphthalene-catecholmixture containing 10 wt % catechol. Determi-nation of the concentration of catechol at differentdistances showed that catechol moves towards thedirection of zone travel. Concentration ratio CICowas determined for various values of xll. Theresults were compared with the empirical .Eq. (1)for the region C!Co<l,

CjCo= a exp eX) ...(1)

where C is the concentration at the length x, Cois the initial concentration, l is the zone length,a and b are constants. k , the effective distributioncoefficient, is defined as CICo= k at xl! = O. Thiswas determined by plotting log CjCo against xll(Fig. 2) and noting the value of a at x/I == O. Thevalues of the constants a and bin Eq. (1) are foundto he 0·48 and 0·045 respectively and hence thevalue of the effective distribution coefficient comesout to be 0·48.

Naphthalene - p - chioronitrobenzene system _. Thephase diagram for this system is due to Rastogict al». The zone melting experiment was carriedout using a mixture of 20% (by wt) of p-chloro-nitrobenzene as an impurity. The results indicatedthat jl-chloronitrohellzene travels towards thedirection of zone travel. The effective distributioncoefficient determined using Eq. (J) is found tobe 0·42. The values of constants a and b, as cal-culated from Fig. 2, are 0·42 and 0·034 respectively.

Equations have been theoretically deduced forzone melting of eutectic systems" for the case of(i) complete mixing and (ii) non-mixing. Eq, (2)is followed in the case of complete mixing:

... (2)

Here x is the length of the purified material, l isthe zone length, Ce is the eutectic composition,Co is the original composition and PI and P. arethe liquid and solid densities respectively.

-,+~10tffi 90n,:l:~8Clz570UJ:t: 60

50L-~0~'--~0'~2~O~3~0~'4--0~'5~70~6~0~'7--~~~~O~9~'OWEIGHT FRACTION OF CATECHOL

Fig. 1 - Phase diagram of the naphthalene-catechol system[0 melting points; • thaw points]

819

INDIAN J. CHEM., VOL. ISA, SEPTEMBER 1977

High Temperature X-Ray Diffraction Study of.Barium Pyrophosphate

+0'2

oU

U

01o

o 3X It

6

Fig. 2 --- l'lcts of lug CIC., against xlll.x naphthalene-catecholsystem; 0 Ilapl;thaklle-p-chlordllltn,bellzenc system]

For the case of non-mixing, Eq. (3) is followed:

C = Co[1+ (~~ -1) exp (-;Vp:s)]where D is the diffusion coefficient and v is thevelocity of zone movement. . .

From Eq. (2) it follows that for complete rruxingthere should not be any change in the concentrationwith change in the value of x. This is. ~ot v=in the present case. Hence, complete mixmg uoesnot take place in the zone melting of the samplesstudied in the present case. In order to test Eg.(3), log (1- CICu) was plotted agai~lst x. Straightlines were not obtained. Hence It follows thatthe equation for non-mixing is also not applicable.Since the rate of zone movement is large and Eqs.(2) and (3) do not fit the da ta, it app.ears that partialmixing occurs in the prcse.nt e~tec.tJc ~ystems. .

Since the value of effective distribution coefficientis less than unity in both the systems, the impuritiesare preferentially rejected by the solid and pile upin the liquid close to the interface. Further, greaterthe deviation from unity in the value of It, ~hegreater is the separation efficiency. The. separationefficiency in the naphthalene-p-chlorol1ltrobenzenesystem is greater than in the naphthalene-catecholsystem.

The financial assistance from COSIP scheme isgratefully acknowledged.

... (3)

References

1. l'FA~:\", \V. G., Trans. met.all. Sac, AfME,I<J4 (1952). 794.2. VUE, ,\. S., Trans. metall. Soc., AIME, 248 (1970), 19.3. VUE, A. S., Trans. met all . Soc., AIAIE, 212 (1958). 88.4. "VILCOX, \V. R & HERINGTON, Zone ",dling (1 organic

com-pounds (John Wilcv, New York). 1963.S. TI;\lMER~lA:-<S, T, Physicochemical crmslu nls of pllre

organic compounds (Elsevier, Houston, Texas), 1950.6. RASTOGI, R. P. & RAM VERMA, K. T.,]. (/"!III. Soc. (1 (56),7. NIPPON J\'OJDIA, H., Kagaku Zasshi, 91 (1970),810.8. R~STOGI, R. P., SINGH. N. B. & SINGH, l'\ARSIC<"GHBHADUR,

j. Cryst. Growth, 37 (1977), 3299. WILCOX, W. R, SEGUNDO, EL., FRIEDENBERG, R &

BACK, NATHAN, Chern. Reo., 64 (1964), 187.

820

SAFJA IVfEHDI, M. RAZA HUSSAIN & B. RAMA RAO

Regional Research Laboratory, Hyderabad 500009

Received 10 May 1976; revised and accepted 6 May 1977

Hi~h temperature X-ray diffraction study of bariumhydrogen phosphate has been undertaken in order tofind out whether any phase changes take place in it.It has been observed that this compound ~ets com-pletely converted into barium pyrophosphate at 550°,On heating the latter to further higher temperaturesthere is no change in phase but the d-values decreaseafter 850°. This behaviour is similar to that of UP201'X-ray powder pattern of barium pyrophosphate hasbeen indexed. The system is orthorhombic with thefollowing crystal data: a=9·200 A, b=14·120 A, c=5·420A, %=4, D",=4·45 ~ crrr" and space group symmetry isPmmm or Pmm2 or P222-

THE effect o~ heat ,on barium hydrogen phosphatehas been investigated by X-ray methods and

the results are described in this paper.X-ray diffraction patterns were taken o~ a P~ilips

PW 1010 X-ray diffractometer employing nickelfiltered CuK radiation, The samples were heatedby means of a high temperature attachment to thediffractometer. Pure barium hydrogen phosphatewas heated up to 1000° starting from room tempe-rature, and X-ray patterns were taken at intervalsof 100°. The accuracy of temperature measurementann uniformity of temperature have been checkedby known lattice spacing-temperature relation ofsilver. Calibration at room temperature was donefrom the positions of high angle peaks by extra-polation methods. ..

It is observed that the conversion of bariumhydrogen phosphate into barium pyroph~sphatebegins at 270° and is complete at about 550, TheX-ray pattern of this pyrophosphate is s~mil~r tothe pattern of a-pyrophosphate reported in litera-ture! (except for the presence of a few extra weakreflections, which could be located by us becausethe patterns were taken on a diffractometer andnot on a camera), But the temperature of for-mation of a-barium pyrophosphate observed hereis much less than that reported. The low tem-perature or a-phase has not been observed at all.The pattern obtained at 550° is completely that ofa-pyrophosphate. It is stable at room temperatureand is unaffected by further heating even up. to1400°. Also, there is no indication of the formationof another phase. However an interesting pheno-menon has been observed. The values of theinterplanar spacings increase when the temperaturereaches about 850° and then start decreasing onheating to higher temperatures. This ~an. be, seenfrom the plots in Fig. 1, ",'here the var iation 111 d-spacings with temperature is shown for four str?ngreflections, This unusual behaviour of banumpyrophosphate is similar to that of uranium pyro-phosphate- which expands up to about 400° andthen contracts till 1200°, Since the structure of