NOTES
Oct., 1957 many ionic systems,46$7 where it is generally found that an increase in pressure stabilize8 the state with the greater number of ionic charges. One can obtain a quantitative measure of this stabilizing effect from the approximate relation
aaQ/aP = -nFdE+/hP
1445
120 110 100
where AG is the free energy change of the reaction. Using the experimental values of El/,, we find bAG/ bP = 0.53 cal. mole-l atm.-I. Although the work described has been only of an exploratory nature, sufficient results have been obtained to show that voltammetry using a stationary Pt-microelectrode is feasible at high pressures and can yield useful information under these conditions. ( 6 ) 9. D. Hamann and W. Strauss, Trans. Faraday SOC.,61, 1684 (1955). ( 7 ) A. H. Ewald and 8. D. Hamann, Aust. J . Cham., 9, 54 (1956). (8) T. Pavlopoulos and J. D. Striokland, J . Electrochem. SOC.,104, 116 (1957).
THE SYSTEM 1,3$-TRINITROBENZENE2,4-DINITROTOLUENE BY LOHRA. BURKARDT Chemistry Division, U. S. Naval Ordnance Test Station, China Lake, California Received M a y 17, 1867
The system 1,3,5-trinitrobenzene-2,4-dinitrotoluene does not appear to have been previously investigated. This study of the system was made with an apparatus' which permitted a stepwise heating approach to the liquidus point. Solidliquid equilibrium a t each thermal step was assured by demonstrating constancy of the light transmission of the sample a t each thermal step. The 1,3,5-trinitrobenzene was recrystalliied from ethyl alcohol, washed with ethyl alcohol and air-dried. Before use, it was fused and allowed to crystallize under a vacuum twice. The melting point was then 123.6'. The 2 , 4 dinitrotoluene was recrystallized from hot ethylene dichloride after which it was fused and allowed to crystallize under a vacuum twice. It then melted at 80.2'. Six-gram samples of the required compositions were melted and stirred thoroughly. The temperature of the sample was allowed to fall until a small amount of solid was formed. The temperature was then raised step-wise. At each step the temperature was held constant until the light transmission of the sample became constant indicating equilibrium between the solid and liquid. In this manner the temperature was raised to a point at which a few crystals were in equilibrium with the liquid. The temperature was
90
5 j 80 70 60 50
0
10
20 30 40 50 60 70 80 1,3,5,-Trinitrobenzene, mole %. Fig. 1.
90 100
then raised in very small increments until by visual observation the last crystals disappeared. The temperature at this p o h t was taken as the liquidus temperature. The melting point of the eutectic was obtained by heating the completely solid sample through the eutectic melting point with a tem erature gradient of less than a tenth of a degree between t i e bath and Sam le. With such a small temperature gradient, a flat is ottained at the eutectic melting point, This system forms a eutectic mixture at 34 mole % of 1,3,5-trinitrobenzene. The eutectic melts at 51.3'. Data for this system is presented in Table I and shown graphically in Fig. 1.
ELECTRIC MOMENTS FROM EXTRAPOLATED MIXED SOLVENT DATA. 11. MOLECULAR ASSOCIATION1 BY GEORGEK. ESTOK AND S. P. SOOD Dept. of Chemistry and Chemical Enginesl.ing, Texas Technolooical Colleoe, Lubbock, Tezas Received May 2.8, lBb7
In a previous paper,2 which may be considered as Part I of this series, some preliminary results were reported on a method for obtaining electric moments of substances which cannot be studied directlv in benzene solution because of association or insufficient solubility. The moment in hypothetical benzene solution mag be calculated from data obtained by extrapolating the experimental values TABLE I MELTINQP O I N T DATAFOR THE SYSTEM 1,3,5-TRINITRO- obtained in mixed benzene-dioxane solvent, of varying composition, to pure benzene as solvent. BEN.EENE-2,4DlNITROTOLUJGNE It has been found necessary to modify the Eutectio 1,3,5-Trinitrobenzene. Me P mole % OC." m.p., OC. method previously reported, as will be indicated 0 70.2 later. Results are reported here on three compounds of decreasing association and benzene solu10 65.0 bility, respectively : benzoic acid, benzamide and 20 60.5 51.2 30 54.3 51.2 benzenesulfonamide. 40 50 60 70 80 90 100
60.0 73.9 86.7 97.4 106.3 114.5 123.6
(1) L. A. Burkardt, W. 9. McEwan and Inst., 2T, 693 (1956).
51.3 51.4
H. W. Pitman, Rev. Sci:
Experimental Preparation and Purification of Compounds.-Benzene (thiophene free) was refluxed overnight or longer with phosphorus entoxide, and then any low boiling material removed gy fractionation through a four foot, glass helix packed column. Constant boiling benzene was collected (1) This work was supported by a Frederiok Gardner Cottrell grant from Research Corporation, New York. N. Y. (2) G. K. Estok and C. H. Stembddge, J. Am. Chsm. Xoc., 76,4316
(1954).
1446
Vol. 61
NOTES TABLE I ELECTRIC MOMENTS AND RELATED DATA(25'") (benzene, VI = 1.145; dioxane, y1 = 0.973) Solute
MRD
Benzoic Acid
34. Id
UP
Solvent
Pam
am
P
Illit.
0.8535
Benzene' 2.86 60.9 1.72 1.6430' Dioxane 3.20 96.2 1.72 1. 71,d 1.783; Benzamide 34.2/ 0 . 863h Benzene 13.00 327.3 3.77 3.6536 Dioxane 15.78 345.3 3.88 3.8480: 3.7780' Benzene39. Oi 0.702' Benzene' 16.60 523.6 4.84 4.736 sulfonamide Dioxane 21.13 579.5 5.12 5 . Ogiei a Unless indicated a t 30'. * Hypothetical benzene solution. E H. A. Pohl, M. E. Hobbs and P. M. Gross, Ann. N . Y . Acad. Bci., 40, 389 (1940). C. J. Wilson and H. H. Wenzke, J . Am. Chem. Soc., 57, 1265 (1935). e C. S. Brooks and M. E. Hobbs, ibid., 62, 2851 (1940). W. W. Bates and M. E. Hobbs, ibid., 73, 2151 (1951). 0 R. Davis, H. S. Bridge and W. J. Svirbely, ibid., 65, 857 (1943). W. E. S. Turner and E. W. Merry, J . Chem. Soc., 97, 2069 (1910). E. N. Gur'yanova, J . Phys. Chem., USSR, 21, 633 (1947). 2 W. D. Kumler and I. F. Halverstadt, J . Am. Chem. Soc., 63, 2182 (1941). Solvent composition (mole dioxane). 20 40 60 80
0
Solvent composition (mole yo dioxane). 20 40 60 80
0
100 22
.
I
'
-
1
'
1
'
0
I
'
I
.
8
.
0
18
0
,n
.,
0
100
'
"
3 .O
6 2.5
8
.'
,
BENZENESULFONAMIDE 2 5 % DlOX
BENZOIC ACID
2.0
1.5
5 8
0
2 4 6 10 Wt. % benzoic acid (WZ X 100). Fig. 1.-Family showing change of a ; L e . , AE/WZ,versus solute concentration for benzoic acid in different benzenedioxane solvent environments. Dashed line is plot of family ordinate intercepts versus solvent composition.
and stored in contact with sodium ribbon. Dioxane was refluxed about 24 hours with metallic sodium, and then handled as already indicated for benzene. Benzoic acid, an Eastman Kodak white label product, was recrystallized; m.p. 122-123'. Benzamide,. also Eastman Kodak white label product, was recrystallized twice from benzene. After drying in an oven a t 105-110' the compound melted 127-128'. Benzenesulfonamide was prepared by a standard procedure from benzenesulfonyl chloride and ammonium hydroxide. The product was recrystallized twice from a 5 : l water-alcohol mixture; m.p. 153-154'. Measurements and Calculations.-Measurements were made with a heterodyne beat apparatus tuned with a carefully calibrated General Radio type 722-N precision condenser, and operating at a frequency of 1 megacycle. For benzoic acid solutions a dielectric cell of about 96 mmf. was used. For the very dilute solutions of benzamide and benzenesulfonamide a special cell, consisting of three concentric stainless steel cylinders held in place by Teflon spacers, was constructed. It had a capacitance of about 354 mmf The usual subscripts are used: i.e., 1, solvent; 2, solute; and 12, solution. Where no subscript is used, solution values are understood. The method of operation previously reported2 was modified as follows: solutions were made up on a weight basis by weighing out the proper amount of solute, dioxane and benzene in such a way as to keep the mixed solvent composition constant for a number of solutions of varying weight fraction solute, w2. The dielectric constant of the appropriate mixed solvent was also determined just prior to a set of solution measurements. Values of Ae/w2; %.e.,(eI2 - el)/w2, hereinafter called a,were
.
BENZAMIDE
0.0 Fig. 2.-Plots
0.2 0.4 0.6 0.8 1 .o Wt. % solute ( w , X 100). (analogous to Fig. 1) for benzamide and benzenesulfonamide.
determined for each solution, and plotted versus wt. % solute ( w , X 100) along a line of constant mixed solvent composition. The line was then extrapolated to infinite dilution to obtain a value of a m for the solute in that particular mixed solvent environment. Values of a m were obtained a t a number of different solvent compositions, and these were plotted versus mixed solvent composition expressed in mole % dioxane. Extrapolation of the resulting straight line to 0% dioxane (100% benzene) as solvent yielded a value of a m from which an electric moment) (corresponding to benzene solution) was calculated. These operations may be inferred from Figs. 1 and 2. Electric moments were calculated at 25" from the equation: fi = 0.2208 (P2m- 1.05MR~)'/n. The total molar polarization at infinite dilution, PZm, was obtained from the relation
where Y: is the specific volume of the solvent, and vt the partial specific volume of solute. No solution densities were measured, a value of v2 being estimated by methods indicated in another paper.8 Sources of values of Y Z and MRa are given in footnotes to Table I. (3) G . K. Estok, Tnis JOURNAL, 60, 1336 (1950).
i
