BINARY SYSTEMS OF CERTAIN NITROTOLUENES W I T H BENZOIC ACID
n. D. CROCKFORD
ASD A. E. HUGHES
The temperature-composition diagrams for the binary systems: 2-4-6trinitrotoluene, 2-4-dinitrotoluene, and p-nitrotoluene with salicylic acid have been determined by Crockford and Zurburg.' I n this paper are given the data for the temperature-composition diagrams for the above-mentioned nitrotoluenes and o-nitrotoluene with benzoic acid. The work is a continuation of a series of investigations on the nitrotoluenes which have been carried out in the Department of Chemistry of the Cniversity of Korth Carolina. Purification of Materials The z-4-6-trinitrotoluene, ~-4-dinitrotoluene,and the p-nitrotoluene were purified by two crystallizations from hot benzene, two from carbon tetrachloride, and one from absolute ethyl alcohol. The o-nitrotoluene was purified by four crystallizations from the liquid material. The benzoic acid was purified by three crystallizations from distilled water followed by sublimation. Xlelting points (corrected) were obtained as follows: z-4-6-trinitrotoluene, 80.8"; ~-4-dinitrotoluenc, 69.75'; p-nitrotoluene, 51.5'; o-nitrotoluene, - 10.4'; and benzoic acid, 1 2 1 . 7 j"C.
Experimental Procedure Cooling curves for the various mixtures were obtained by means of a n apparatus somewhat similar to that used by John Johnston2 and his coworkers for similar work. h sketch of the essential features of the apparatus is given. The evacuated Dewar flask (D) had a n inside diameter of 3" and a height of 4-112". A constant temperature was maintained in the bath (C) by means of a mercury regulator. The bath served as the constant junction for the thermocouple (B) in part of the determinations. The sample was placed in a thin-walled tube which in turn was placed in a glass vessel within the Dewar flask. A heating unit in the Dewar flask (leads shown at A) enabled the temperature to be raised as desired and two tubes leading into the glass vessel permitted the addition of hot or cold air. An opening was provided for placing a thermometer (F) in the glass vessel but the thermometer was removed during the course of a determination. The thermocouple (B) used was made from Yo. 40 copper and S o . 35 constantan wire. The leads were connected to a sensitive wall galvanometer and the temperature changes were followed by the changing galvanometer deflection. H. D. Crockford, H. and F. W. Zurburg: J. Phye. Chern., 34, 214 (1930). D.H.Andrews, G. T. Kohrnan and John Johnston: J. Phys. Chern., 29,914(1925).
H. D. CROCKFORD .4SD 4.E . HUGHES
2118
The calibration curves for the thermocouple and galvanometer were obtained from the melting points of the pure constituents and by comparison with a calibrated thermometer. The magnitude of the galvanometer deflection &'as regulated by means of resistances in the galvanometer circuit. Supercooling to any marked extent was avoided by dipping a fine nichrome wire in the melt, drawing it out, and suspending it above the molten material. As the freezing point was approached crystals were jarred into the melt. Preliminary runs were made to determine the approximate freezing point.
TABLE I p-nitrotoluene-benzoic acid freezing point
eutectic
. 00
51 . s o
__
5.95
jO.2j
44.1
mol percenl acid
16.19
48 4 46.3
2 ; .;1
51.2
31.99 37.96
58.1
11.11
j ,
, >!
>, ,,
6 j .o
mol percent acid
freezing point
eutectic
42.8; 47.99 5 3 ,I8 5i.69 62.j o 9; .60
i o .3 i i .3
44.1
83.I 88.2 94.0 "9.3
100.00
12I.jj
,f
,, ,,
,, ,, f,
2-4-6-trinitrotoluene-benzoic acid
. 00 20.0
80.8" 75.5 70 3
38.9
i7.5
j0 . O
88.6
13. 8
__
64.5
>, >f 1,
69.0 77.6 8j.6 96.4 100.0
103.9 109.4 113,s
119.9 121,;s
2-~-dinitrotoluene-benzoic acid . 00
69.I
14.3
69.i~ 65.3
__
26.;
59.8
59.4
39.0
3 83.I 91.6
j0,o
60 . o
,f
72
f
j j . 8
85.i 93 ' 1 100.0
99 7 106.9 113.3 118.2 I21 . ; 5
1,
o-nitrotoluene-benzoic acid .oo j.6
-Io.4a -10.1
__ ~
j3 , ? 62.j
84.3 94 3 1 0 2 ,;4
-14.1 - I 4 .o
3 2 .o
16. o 39.9 56.6
-13.8
91 . o
109.9 116.8
42.9
71.1
-14.0
100 .oo
1 2 1 . jj
11.1
22
.4
i3.2 81.5
,, ), >I
B I S A R P SYSTEMS O F SITROTOLUENES .4PiD B E S Z O I C ACID
2119
I n making a determination the temperature of the sample, the weight of which varied from 0.5 to 1.j grams, was brought above its melting point by means of the heating unit. The molten mass was then allowed to cool to the constant temperature of the bath. Galvanometer readings were recorded and the cooling curves established from the galvanometer reading-temperature calibration curves. I n the case of the 2-4-6-trinitrotohene, 2-4-dinitrotoluene, and the p-nitrotoluene the cooling was to 30OC. I n the case of the o-nitrotoluene the cooling was to - 18OC. This last temperature was secured by means of an ice-sodium chloride solutions mixture in the bath.
Results and Conclusions The freezing points of the various mixtures are given in Table I together with the eutectic temperatures found with the various melts. The data are accurate to O . I T except in the case of the o-nitrotoluene eutectics where the - - - - - - - - - - - - - - - - - - - -agreement is not so good. FIG.I I t was not thought necessary to draw Apparatus for Determination the temperature-composition diagrams of Cooling Curves as the systems all prove to be simple ones with no sign of compound formation The eutectics all lie well on the nitrotoluene side of the diagrams, being found a t the following temperatures and compositions: Xitrotoluene
z-4-6-trinitrotohene 2-4-dinitrotoluene o-ni trotoluene p-nitrotoluene
Mol Fraction Benzoic Acid ij.00
74.7
94 7 77,33
Eutectic
6 4 . j"C
59.4 -i4.0 44.1
If the values of log,,x (x = mol fraction of solvent) be plotted against the reciprocal of the absolute freezing point of the mixtures it is found that in the case of the 2-4-6-trinitrotoluene and the 2-4-dinitrotoluene systems on the acid side of the diagram the points fall on the same straight line thus proving that van't Hoff's equation holds for this part of the systems. However, in the case of the p-nitrotoluene and the o-nitrotoluene the points fall on the same smooth curve but it departs appreciably from the straight, line established by the other two systems at the higher corlcentrations. On the nitrotoluene side of the diagrams the points fall on smooth curves and not straight lines thus indicating non-ideality in this part of the systems. However the number of points established are hardly sufficient in number to draw reliable conclusions.
2120
H. D. CROCKFORD AXD A. E. HUGHES
summary The temperature-composition data have been determined for the systems: benzoic acid with 2-4-6-trinitrotoluene, 2-4-dinitrotoluene, p-nitrotoluene, and o-nitrotoluene. The data show that these pairs form simple systems with no compound formation. The eutectics lie well over on the nitrotoluene side of the diagrams. The plotting of log,,x against I/Tgives a straight line for the acid side of the 2-4-6-trinitrotoluene and 2-4-dinitrotoluene diagrams. These data for all other parts of the systems fall on curves departing from straight lines thus indicating non-ideality. Department of Chemistry, Universaty of North Carolina.
