THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 14, No. 6
Studies on the Nitrotoluenes' VIII-Binary
Systems of m-Nitrotoluene with Another Mononitrotoluene By James M. Bell2 and Joseph L. McEwen UNIVERSITY
OF
NORTH C A R O L I N A , CHAPEL HILL, NORTH CAllOLINA
HIS paper contains the data and the curves for the binary systems of mnitrotoluene with o-nitrotoluene and with p-nitrotoluene. The data and curve for the binary system of o-nitrotoluene with p-nitrotoluene have already been given in the fifth paper of this series, by Bell, Cordon, Spry and White.s The effect of other components on the freezing point of m-nitrotoluene has been studied by J ~ n a , ~ w iat hrange never over 6 per cent of the second component. Menschutkins has made a complete study of binary systems of m-nitrotoluene with a halide of antimony and found a compound (1 : 1)in two cases. In a recent Paper, Gibson, Ihckman and Fairbairn' have given data for the system m- and p-. A brief comparison of their results with the present results is given below. In the first stage in the nitration of toluene, all the three isomers, m-, and p-9 are formed. Such mixtures, Of course, be by direct methods' it becomes necessary to resort to some indirect means. This Can easaJ' be accomplished, for emmple, by preparing a dlart of the freezing points of different mixtures of the compounds. Then, in order to analyze a sample mixture, it is necessary only to determine the freezing point of the sample in question, and refer directly to the chart. The value and use of such curves and charts are, therefore, quite obvious.
T
Received March 13, 1922. Professor of Physical Chemistry, University of North Carolina. 8 THIS JOURNAL, I S (1921), 59. 4 Gael;. chim. i l d . , S9, I1 (1909), 289. 6 J . Russ. Phys. Chem. SOC., 44 (1912), 1939,from C. A . , 7 (1913), 1176. a J. Chcm SOC.,181 (19221, 270. 1 p
/OO%
100% FIG.A-BINARY S Y S T ~OB M MNT-PNT
PURIFICATION OF COMPOUNDS Crude p-nitrotoluene was recrystallized several times from solutions in hot alcohol and benzene. It was filtered by suction and allowed to dry in a warm place. A constant melting point of 51.3" (cor.) accorded well with the earlier work. m-Nitrotoluene was obtained in a pure form from the Eastman Kodak Company of Rochester, N. Y. The melting point of this compound was found to be constant at 15.53" (cor,). o-Nitrotoluene was purified by partly freezing the liquid, decanting off the remaining liquid, allowing the crystals to. melt, and again partly freezing. By this process of fractional the impurities were left in the unfrozen liquid and were thus removed. This was done repeatedly until a constant melting point of - 10.370 (cor.) was obtained for the metastable form. The meliing point of the stable form was found to be -4.310 (cor,). These agree very well with the work done before. EXPERIMENTAL PROCEDURE AND RESULTS The weighed material whose melting point was to be determined was placed in an %in. test tube and provided with a looped-glass stirrer and a thermometer, graduated in 0.1". This test tube was placed in a larger tube, in order to provide an air bath, and the whole was immersed in a bath which was approximately 10" below the freezing point of the mixture. Readings of the temperature were taken at regular
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1922
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intervals and the points were plotted. For temperatures above -15", ice and salt were used, but for the lower temperatures, necessary in the binary system of m-nitrotoluene with o-nitrotoluene, solid carbon dioxide was used. In the binary system of m-nitrotoluene with p-nitrotoluene, the eutectic temperature was found, by experiment, to be -2.8", corresponding, from the chart, to about 37 per cent of p-nitrotoluene. In the case of the*binary system of m-nitrotoluene with o-nitrotoluene, the eutectic temperature was found by experiment to be -31.65', corresponding, from the chart, to about 48 per cent of m-nitrotoluene.
TABLE I-BINARY
SYSTEM:
100.00 96.005 92.242 86.02 66.8 60.25 50.16 42.11 34.12 21.44 10.76 0.00
0.00 3.995 7.758 13.98 33.2 39.75 49.84 57.89 65;88 78.66 89.24 100.00
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@-NITROTOLUENE
Freezing Point C. (Cor.)
15.53 13.74 11.96 +8.97 -0.61 +2.8 16.48 24.25 30.2 39.42 46.24 51.3
Supercooling was encountered regularly in these systems. Some investigators, in working upon the freezing points of binary mixtures, have taken the point at which crystals first appeared as the true freezing point. Others have chosen the maximum point of crystallizationtas the correct point. Rut, as has been shown in the third paper of this series, by Bell and Herty,' both of these methods are erroneous. The true freezing point of such a mixture can be obtained only by THISJOURNAL, 11 (1919),1124.
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EXPLANATION AND DISCUSSION
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TABLE 11-BINARY
S Y S T E M : m - N I T R O T O L U E N E W I T H 0-NITROTOLUENE Freezing Point Per cent by Weight Meta Ortho O.C. (Cor.) Metastable Form -10.37 0.00 100.00
5.29 9.52 16.83 8.86 19.90 25.74 38.65 50.09 55.02 63.65 73.89 84.59 100.00
94.71 90.48 53.17 Stable Form 91.14 80.10 74.26 61.35 49.91 44.98 36.35 26.11 15.41 0.00
-12.66 -14.76 -19.3 -8.42 -14.11 -17.3 -24.57 -22.88 -13.41 - 6.1 1.8 8.43 15.53
+
extrapolating that portion of the curve representing freezing liquid, back to the portion representing cooling liquid. This is the method that is here used in obtaining the true freezing points. An examination of Fig. 1will serve t o make this more clear. A is the point at which crystallization began; B the maximum temperature of crystallization; and C the correct freezing point obtained by extrapolation. All of the points that have
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been used in plotting the curves for these binary mixtures were obtained in this way. For the sake of simplicity only a few of the readings taken have been indicated. Fig. 1 corresponds to point No. 1, Fig. 2 to point No. 2, etc., of Fig. A. Similarly, Fig. la corresponds to point No. 1 of Fig. B, etc. I n the binary system of m-nitrotoluene with p-nitrotoluene there are very simple conditions, two curves meeting in a eutectic point. The diagram given by Gibson, Duckham and Fairbairn6 indicates three curves, the third curve being very short and flat, and corresponding to the eutectic temperature which we have found. It seems probable that the freezing points as obtained by Gibson, Duckham and Fairbairn are too low, an error which would throw both the main curves too low. Furthermore, it is extremely unlikely that two components, as similar in structure as these, would form a binary compound.
In the binary system of m-nitrotoluene with o-nitrotoluene, it will be noticed that there are two curves on the o-nitrotoluene side. These represent the stable and metastable forms. The solid lines represent conditions which were attained. The broken lines have been sketched in and represent conditions which were not attained experimentally. The curve for the metastable form begins a t - 10.37O and descends roughly parallel to that of the stable form. It can be seen from the projected lines that if it were possible to reach the lower eutectic, it would probably be found to be about -39", corresponding to about 46 per cent of m-nitrotoluene.
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