NOTES
382
Vol. 58
T H E THERMAL DECOMPOSITION OF CYCLOTRIMETHYLENETRINITROSAMINE BY JOHN P. FOWLER AND MARVIN C. TOBIN' ArLhur D. Litfle, Inc.,Cambridge, Mass. Received Januaru 14, io64
As part of a program of study of the decomposition of nitrogen-oxygen compounds2 the authors had occasion to examine cyclotrimethylenetrinitrosamine, (CH2)3(NN0)3,in the melt and in the solid state. It is hoped that this program will shed light on the little-investigated fields of the deconiposition of solids and pure liquids. Experimental The sample of cyclotrimcthylenetrinitrosamine (CTT) was prepared by the method of B a ~ h m a n n . ~It was purified by twice recrystallizing from isopropyl alcohol, m.p. 105-106'. The purified material was powdered and dried under vacuum for one hour. The samples for the studies on the solid were taken from the same batch of powder, so as to standardize the particle size.
L
1
30
E lli
0
0
200
400
600 800 1000 1200 1400 1600 Time, hours. Fig. 1.-Weight loss us. time for solid CTT, ( A ) 0 , 80°, sample wt. 0.4060 g.; (B) 0, go", sample wt. 0.4135 g. The decomposition of the solid and melt were in general followed by the weight loss method. The solid was heated in a n oven in open sample tubes. The tubes were removed at intervals, cooled, weighed and returned. The times reported were corrected for time lost in wei hing. No fusion was observed a t any time in these sampfes. The data at 80 and 90' are shown in Fig. 1. Weight loss for the melt was followed by suspending the sample into an oven from 10 h
C
I
D
10 30 50 10 30 2 4 6 8 Time, hours. Fig. 2.--log (w 30)/(280 - w)us. time for C T T melt above 10% decomposition: A, 114", sample wt. 0.5010 g.; B, 117", sample wt. 0.5028 g.; C, 125",sampIewt.0.4997g.; D , 136O, sample wt. 0.5015 g. 0
40
80
+
(1) This work was done under Contract DAI-19-020-501-ORD (P) 33 with the Office of the Chief of Ordnance and has been released by the War Department for publication. (2) For the first paper of this series, see M. C. Tobin, J. P. Fowler, H. A . Hoffman and C. W. Sauer, J . Am. Chem. Soc., in press. (3) U'. Bachmann and N. Deno, (bid.. 73, 2777 (1951).
e
200 300 400 Time, hours. Fig. 3.-Cc. gas a t S.T.P. evolved for C T T solid at 90". ( A ) 0,sample wt. 0.5390 g.; (B) 0 , sample wt. 0.1150 g. 0
100
a Roller-Smith torsion balancc on which weight loss could be measured as a function of time. Measurements were made at 114, 117, 125, 136 and.146' (see Fig. 2). Other experiments on the solid were made by heating thc solid at 90" in a n evacuated sample tube leading to a mercury manometer. The tube was removed from the oven a t frequent intervals, cooled to room temperature and the volume change read. Data were recorded in terms of cc. of gas evolved a t S.T.P. versus time. The data are shown in Fig. 3. All temperatures were followed on a Brown multi-channel recording thermocouple, and are estimated accurate to a t least &lo. The weighing on the solid is estimated to be accurate to =kO.OOOl g., that on the melt to 0.002 g. The volumes recorded for gas evolution are estimated to be accurate to f O . l cc.
Results for Melt It was found that the melt of CTT, originally a pale yellow, darkened to blood red on heating. Decomposition was complete a t 114, 117, 125 and 136" a t some 55% weight loss, leaving a red, glassy residue. Cursory examination of this residue showed it to consist of a t least two fractions, one water-soluble. At 146O, the sample fumed off a t 2 hours, leaving a dark porous mass a t the top of the sample tube. This is ascribed to self-heating. The plots of weight loss us. time are of the sigmoid type, with one possible odd feature, a suggestion of a plateau observable a t the beginning of the decomposition. The curves are reminiscent of the decomposition of nitroglycerin, which also shows this initial p l a t e a ~ . ~ It was found possible to fit the experimental curves above 10% decomposition to the equation a t all four temperatures. Here w is the weight loss in mg. to time t (hours), 280 is the mean final weight loss in mg. (all samples were very nearly the same weight), k and c are constants, "k having the dimensions of a rate constant." A plot of log k us. 1/T gives a straight line, leading to an activation energy of 36.2 kcal./mole. The values for IC and c a t each temperature are given in Table I. Equation l does not match the experimental curves below 10% decomposition, in particular predicting ( 8 ) N. Seinenoff, "Chemical Kinetics and Chain Reactions," Oxford University Press, N e w York. N . Y . , 1935, p. 426.
NOTES
April, 1954 a small weight loss a t zero time. However, in view of the peculiar nature of the initial stages of the decomposition, it was not thought worthwhile to try to match the early stages of the curves.
c
tion. These data are not sufficient to make possible a classification of frequencies, but it does seem reasonable to assign 1345 em.-' to the nitroso N-0 stretching frequency.6 (5) E. Lieber, D. Levering a n d L. Patterson, Anal. Chem., 2 8 , 1504
TABLE I T ,'C. k , hr.-1
383
114
117
125
130
0.0094 -0,920
0.0172 -0.772
0.0360 -0.800
0.128 -0.923
Discussion The results of the weight loss measurements on the solid show no unusual characteristics. They show the qualitative features indicated by Tobin, Fowler, Hoffman and Sauer,2 and these are ascribed t o the same general phenomena. The gas evolution curves are quite interesting. The decomposition evidently remains in an induction period for an extended period, the induction period ending suddenly in a very sharp increase in reaction rate. This indicates violent autocatalysis of solid CTT by its gaseous reaction products, since no such phenomenon appears in the weight loss experiments, where the gaseous products are allowed to escape. It is not clear why the rate of gas evolution is the same for the 0.1150-g. sample as for the 0.5390-g. sample during the induction period or why the induction period for the smaller sample is only twice that for the larger sample. The larger sample showed no sign of fusion a t any time, but the smaller sample started to fuse during the sharp rise in pressure. The experiments were stopped when the pressure in the tube reached one atmosphere. When the sample tubes were opened to the atmosphere, brown fumes formed, showing that one of the gaseous products is nitric oxide. Sigmoid curves of the type obtained here for the melt may arise as the result of an equilibrium reaction, a sequence of consecutive reactions, or an autocatalytic reaction. The first possibility may be disregarded, due to the continuous removal of reaction product from the system. Other than this, little may be said about the mechanism. It is of interest to note that equation 1 has the same algebraic form as the equation representing the loss of reactant or evolution of non-catalytic product for seperal types of autocatalytic reactions. There is no doubt that the reaction is a complex one, so that the activation energy calculated from IC in equation 1 must be regarded as a composite quantity. The Infrared Spectrum of Cyclotrimethylenetrinitrosamine.-In the course of this work, occasion arose to obtain the infrared spectrum of cycIotrimethylenetrinitrosamine. The spectrum was obtained in Nujol mull on a Perkin-Elmer automatic recording spectrophotometer a t Arthur D. Little, Inc. The region 650-1400 cm.-l was covered with a NaCl prism, the region 1400-3500 em.-' with a CaFzprism. The observed bands, in cm.-l are 3050 (m), 2960 (s), 2890 (E)*, 1485 (9, v. br.) 1442 (br)*, 1370 ( I x ) * , 1345 (8, br), 1300 (s), 1255 (s) 1150 (m), 1075 (5, br), 995 (m), 952 (s, br), 875 (s), 800 (m, shoulder to 875), 840 (m);765 (s), 700 ( 9 )
The asterisks represent regions of Nujol absorp-
(1951).
THE LIQUIDUS CURVE O F T H E BINARY SYSTEM CADMIUM ACETATEPOTASSIUM ACETBTE BY ALEXANDER LEHRMAN AND DONALD SCHWEITZER Department of Chemistru, The City Colleue of New York, New York $ 1 , N . Y. Received December $9, 1963
The binary system cadmium acetate-potassium acetate was explored as part of a program' of investigating the double salts of acetates. Experimental Materials.-Analytical Reagent potassium acetate was dried in an oven a t 140" for one week before weighing. Cadmium acetate of C.r. grade to which 5-10 drops of glacial acetic acid had been added to prevent decomposition of the cadmium acetate was dried in an oven at 140' before weighing. Apparatus.-The initial crystallization temperatures were measured with a copper-constantan thermocouple of No. 24 wire in conjunction with a potentiomet,er (16-millivolt range), the cold junction being cracked ice. The e.m.f. could be read to 3Z0.02 niv. The couple was encased in a narrow guard tube that, was made by drawing out Pyrex tubing and sealing one end. I t was standardized by determining the e.m.f.'s a t the boiling point>sof water and of benzophenone, the melting points of U. S. Bureau of Standards tin and of purified potassium nitrate, and then plotting the deviations from the standard table of Adams.z A molten salt-bath was used to heat t,he mixtures. It consisted of a eutectic mixture of lithium, potassium and calcium nitrates3 contained in a tall Pyrex beaker. Method.-Definite mixtures of the salts (total weight between 25 and 35 g.) were made by weighing the components to the nearest centigram, and in some cases to 3Z3 milligrams. The mixed salts were finely ground together and placed in 2.5 X 20 cm. Pyrex test-tubes. In order to prevent decomposition of cadmium acetatme on heating, 5 drops of glacial acetic acid were added to each tube before immersing it in the hot salt-bath. The acetic acid distilled out of the mixtures during melting since the temperatures were raised to about 200". However, the mixtures rich in cadmium acetate began to decompose a t the temperatures needed for fusion, and determinat,ions on mixtures above 0.7 mole fraction of cadmium acetate could not be made. The tube containing the mixture of acetates and the couple in its guard tube was suspended in the molten nitratebath until the mixture was liquefied, and then the tube was allowed to cool slowly while stirring constantly. A beam of light was passed through the mixture, and the init,ial crystallization temperature was observed. Crossed Polaroid filters, one on each side of the tube, made the detection of the initial crystal easier. Supercooling was prevented by repeated insertions and withdrawals of a capillary glass rod into the mixture when the initial crystallization temperature was approached. When the capillary was withdrawn from the mixture the few drops clinging to it immediately solidified, and the insertion served to inoculate the melt. At least three determinations of the initial crystallization temperature of each mixture were made, or until agreement to within l owas achieved. To make sure that no breaks in the curve were overlooked, and to fix t8heeutectic temperatures, simultaneous cooling and differential cooling curves of mixtures over the range (1) For IxeviouR work see A . Lehrtnan and E. Leifet, J . A n . Chem. Soc., 60, 142 (1938); A. Lelirinan and P. Skell, ibid., 61, 3340 (1939). (2) Pyrometric Practice, U. 5. Bureau of Standards Technological Paper No. 170, p . 309. (3) A . Lelirinan. e / al.. J . Am. Chem. S o c . , 59. 170 (1037).
