August, 1962
SOLID-LIQUID PHASEEQUILIBRIA
elect,rolyte mixtures. Concentrated hydrochloric acid solutions would appear t o be poor media, for
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such investigations because of the possible complication arising from bichloride ion formation.
SOLID-LIQUID PHASE EQUILIBRIA AND SOLID COMPOUSD FORMATION PN RTTXTURES OF ARO5fPATIC COMPOUNDS WITH CARBON TETRACHLORIDE BY J. BEVAX OTT,J. REXGOATES, AND ALLEN €I. BUDGE Department of Chemistry, Brigham Young University, PTOVO, Utah Received December I I , 2962
Solid-liquid phase diagrams have been obtained from time-temperature cooling curves for the four binary systems containing carbon tetrachloride with benzene, toluene, pseudocumene, and anisole. Solid compounds with the following empirical formulas were found: CC14-C6H6,( CC14)2CsHa,CC14CBH&H3,cc14*1,2,4c6H,( CH&, and (CC&Cf,H,OC&. A number of other systems composed of carbon tetrachloride and aromatic compounds were screened for possible compound formation,, No compounds were observed in the mole fraction range of approximately 0.25 to 0.75 for systems composed of carbon tetrachloride with o-xylene, m-xylene, chlorobenzene, bromobenzene, or a,a,a-trifluorotoluene. A number of other chemicals were used in only a few exploratory measurements to check on the presence or absence of compound formation. These were either reagent or research grade chemicals that were used without further purification. Measurements and Accuracy .-Both time-temperature cooling and warming curves were obtained with a platinum resistance thermometer in an apparatus that has been described previously.6 The solutions generally supercooled, and their freezing points were obtained by extrapolation of the. time-temperature curve back across the supercooled region. Supercooling was especially pronounced in the anisole and the toluene systems, sometimes being as much aB 30". Most of this supercooling could be eliminated, however, by melting the solid and then freezing a second time. If the sample was not allowed to warm more than about 2" above the freezing point during the melting process, the supercooling during the second freezing generally was reduced to a few tenths of a degree. The accuracy of the freezing points of the pure substanc;s is estimated to be f0.05', and that of the solutions, f 0 . 1 . The meritectic and eutectic values where stirring was possible Calibration of the also are considered accurate to 3zO.l'. resistance thermometer has been described previously.6 was rechecked periodically during these Chemicals.-Reagent grade benzene, toluene, anisole, The calibration a t the mercury freezing point (234.29"K.), ice pseudocumene, and carbon tetrachloride were further puri- measurements oint (273.150' K.), and the sodium sulfate transition point fied by distillation. The purified reagents contained the 305.534"K.). S o measurable changes in the resistance of following amounts of liquid soluble-solid insoluble im uri- the thermometer were found. ties: CeHs, 0.04 mole %; C6Hjc&, 0.24 mole %; &H&OCHa, 0.01 mole %; .and CClr, 0.02 mole %. Results Because of difficultlep in obtaining equilibrium during the Solid-liquid phase equilibria data were obtained freezing of pseudocumene, we were unable to obtain a satisfactory freeaing curve from which the per cent impurities in for the four binary systems of carbon tetrachloride thiei substance could be calculated. The starting material with benzene, toluene, pseudocumene, and anisole. for the preparation of the sample was Phillips' "pure" grade The freezing point data for the CC14-C6% system pseudocumene, which is listed as better than 99% pure. are summarized in Table I. This material was vacuum distilled in a vacuum jacketed, Figure 1 is the phase diagram of the cCl4-c&6 170-cm. column packed with glass helices and operated at a reflux ratio of 1OO:l. The center third cut was used. Its system over the composition range 0.0 to approxiindex of refraction itgreed to the fourth decimal place with mately 0.8 mole fraction CCL. I n all of the phase the A.P.I.* value. Gas chromatograms of the purified chemical showed no impurities detectable by this method. diagrams of this paper, circles are used for freezing Further evidence of high purity is that the eutectic tempera- points, triangles for either eutectic or meritectic ture of the mixtures containing pseudocumene did not, vary values, and squares for solid phase transition data. appreciably with amount of material frozen. The significant features of Fig. 1 are the meritectic
I n a previous paper, we reported evidence from heats of mixing and freezing point measurements for the existence of a 1:1 solid compound in the sy.sitem cC14-CaH6.1 More recently, Rastogi and Nigam2 Found not only a 1:I, but also a 2: 1 compound. I n an earlier study, Kapustinskii3 had reported a 3 :1 as well as a 1:1 and 2 : 1 compound in this system. I n addition to the problem of the number of compounds, there appears to be some question as to the exact composition of the compound described as 1:l. For these reasons it appeared desirable to obtain in detail the solid-liquid phase diagram of the CC14-C6Hs system in the composition range where compound formation is likely. This paper reports the results of such a study, together with the solid-liquid equilibrium properties of solutions of CC14 with several other aromatic hydrocarbons. Experimental
P
(1) J. R. Goates, R. J. Sullivan, and J. B. Ott, J. Phys. Chem., 63, 589 (1959). (2) R. P. Rastogi and R. K. Nigam, Trans. Faraday Soc., 66, 2005 (1959). (3) A. F. Kapustinskii, Bull. Aead. Sci. USSR, 435 (1947).
(4) F. D. Rossini, K. S. Pitzer, W. J. Taylor, J. P. Ebert, J. E. Kilpatriok, (2. W. Beckett, M. G. Williams, and H. G. Werner, "Selected Values of Properties of Hydrocarbons," American Petroleum Institute Research Project 44, Natl. Bur. Std. Circ. 461, U. S. Govt. Printing Office, Washington, D. C.,1947.
lines a t 239.12 and 232.130K1., indicating the presence of t w o compounds with incongruent melting points. Graphs of the length of meritectic halt us. mole fraction of carbon tetrachloride show maximum values a t mole fractions of 0.500 and 0.667, which correspond to compounds with the ( 5 ) J. R . Goates, J. B. Ott, and A. N. Budge'. J . Phvs. Chem., 66, 2162 (1961).
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J. BEVAN Om, J. REX GOATES, AND ALLENII. BUDGE
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Vol. 66
TABLE T FREEZING POIXTS CARBON T E T i ~ A C I I L O R I D E - B E N z E ~ ~
$
270
RIole frnction CClr
260
0 0000 .1179 2030 .3155 3557 4255
w ' K 250
K W
L
I W
+
240
230
0
0.2
04
0.6
0.8
MOLE F R A C T I O N CCI4. Fig. 1.-Phase diagram of carbon tctrachloride-benzene.
250
230
y' 0
wi [L
2
210
a. a w a I w I-
190
170
0
0 2
04
I'rerzing poiiit,
I
