1976
Vol. 63
NOTES TABLE I HEATEVOLVED BY MERCURIC BROMIDE IN COOLING FROM INITIAL TEMPERATURE TO 300°K.
Temp. rise calorimeter
Total
2.11 1141.81 2.00 1082.28 1.48 800.80 1.99 1076.87 1.00 541.14 1.04 562.79 1.00 541.14 0.93 503.26 2.03 1098.51 2.16 1168.86 a 40.2528 g. HgBrz.
Heat evolved (cal.) Capsule Sam le” alone onPy
124.59 116.86 111.11 112.83 106.24 108.92 102.43 98.13 120.82 129.27
1017.22 965.42 689.71 964.04 434.90 453.87 438.71 405.13 977.61 1039.57
HgBrr (1 mole)
9106.71 8642.97 6174.66 8630.62 3893.46 4063.29 3927.57 3626.95 8752.82 9306.80
Brodersen4 reported values of 5010, 4617, and 5010 cal./mole, respectively, for the heat of fusion derived cryoscopically. KelleySa derived a value of 4020 cal./mole from the available phase diagram data in the literature. A second value, from an analysis of the available vapor pressure data, 3960 cal./mole, was recommended by Kelley6b as the best value for the heat of fusion. One value for mercuric bromide obtained calorimetrically,6 4614 cal./mole, differs from the above best value but insufficient information is given in this early study to account for the discrepancy. The present note reports a redetermination of the heat of fusion by the method of drop calorimetry. Experimental Heat of Fusion Apparatus and Accessories.-The calorimetric assembly designed to yield results with an accuracy of 2 ~ 2 %for heats of fusion in the range 2-4 kcal./mole, and the recording differential potentiometer for the temperature-time measurements were the same as described elsewhere in detail.’,* For salts for which the vapor pressure is appreciable at the fusion temperature, e.g., HgBrz, 105 mm., some modification of the platinum capsule design is necessary so that the sample can be hermetically sealed in the capsule without loss due to volatilization. It was found that a small latinum tube, 5 cm. long X 3 mm. diameter, welded to tge lid of the crucible to serve as a filling tube, proved adequate. With the modified lid soldered to the empty crucible, the sample was loaded conveniently through the platinum chimney tube, after which the upper end of the “chimney” was crimped shut and welded to give the sealed system required for the calorimetric measurements. Sample evaporation in the latter operation was prevented by cooling the “chimney” with wet cotton wool. Mercuric Bromide.-The mercuric bromide (reagent grade) was purified by vacuum drying and resublimations as described elsewhere.9 The reproducibility and sharpness of the melting point, 238.1 f 0.lo, were taken as criteria of purity.
Results The procedure for calibration of the calorimeter and measurement of the heat of fusion have been adequately described elsewhere.’,* The data and results for a series of 10 determinations over the temperature range 210-360’ to establish the en(4) G. Jander and K. Brodersen, 2. anorg. allgem. Cham., 264, 57 (1951). (5) (a) K.K. Kelley, U. 8. Bur. Mines Bull. 393, Washington, 1936; (b) ibid., 383, Washington, 1935. ( 6 ) M. Guinchant, Comp. rend., 149, 479 (1909). (7) J. Goodkin, C. Solomons and G. J. Janz, Rev. Sci. Inatr., 29, 105 (1958). (8) C. Solomons and G. J. Janz, Anal. Cham., 80, 623 (1959). (9) G. J. Janz and J. D. E. McIntyre, Proc. N. Y.Acad, Sci., Conference on Molten Salts (1959).
E n t h a l ~ ychange, (caKlmole) Cor. to 300’K. HT - Ham
Final temp.
~
(OK.)
298.8 301.5 303.9 303.4 301.5 302.6 302.4 301.5 298.6 300.3
-23.41 29.27 76.09 64.38 29.27 50.73 46.82 29.27 -23.41 5.85
9083.30 8672.24 6250.75 8695.00 3922.97 4114.02 3974.39 3656.22 8729.41 9312.65
Initial
“CY< 533.4 522.3 513.9 516.6 502.5 507.4 496.3 487.4 526.8 544.1
thalpy change for HgBrz above and below the melting point are summarized in Table I. The analysis of the data followed the calculations described elsewhere for the LiC1-KC1 eutectic. lo From a graph of the enthalpy change versus temperature, the heat of fusion of HgBrz at its melting point (238.1’) is found to be 4280 f 80 cal./mole from these data. Discussion From the heat of fusion found in the present study, 4280 f 80 cal./mole, the values 8.4 e.u. and 32.8 deg. mole-1 1000 g.-l are found for the entropy of fusion and cryoscopic constant for HgBrz. Insufficient details are given in the early calorimetric work of Guinchants to resolve the sources of error leading to the higher value 4.7 kcal./mole for the heat of fusion. The values based on earlier cryoscopic s t ~ d i e s z - are ~ indirectly derived. Organic solutes were used in the cryoscopic measurements so that some of the scatter in the values may possibly be attributed to impurities formed by thermal decompositions which may be initiated by prolonged heating of organic compounds in this temperature range. The U. S. National Bureau of Standards best value,ll 3.96 kcal./mole, is based on Kelley’s analysis6 of vapor pressure data. It would appear from the present work that the latter value, also based on an indirect method, is approximately 15% too low. The present value, 4280 f 80 cal./mole, is recommended for adoption as the most reliable value for this parameter, being derived from direct calorimetric experiments. Acknowledgment.-Active participation in the early phases of this work and continued interest by Cyril Solomons is gratefully acknowledged. (10) C. Solomona, J. Goodkin, H. J. Gardner and G. J. Janz, THIS JOURNAL,62, 248 (1958). (11) U. 8.National Bureau of Standards, Circular 500, Washington,
1952.
CHEMICAL REACTIONS OF ACTIVE NITROGEN BY HAROLD A. DEWHURST Research Laboratory, General Electric: Company, Scheneclady. New York Received April 30, 1869
The chemical reactions of active nitrogen with hydrocarbons have been studied extensively by
a
< b
Nov., 1959
1977
NOTES
Winkler and co-workers.' In general it was found that hydrogen cyanide was the major product of the active nitrogen reaction and the only one that contained nitrogen. Because of this they postulated that nitrogen atoms do not attack hydrocarbons by hydrogen atom abstraction but rather by a direct approach to the carbon atom. We have recently studied the reactions of active nitrogen with silanes and hydrocarbons and have found that significant quantities of ammonia are formed.
ucts from the benzene reaction, a dark brown unidentified material was deposited,
Experimental The active nitrogen was produced by a condensed discharge using the apparatus described by Winkler and COworkers.2 The discharge tube and reaction vessel were not oisoned. Prepurified Linde nitrogen was passed through a fquid nitrogen trap and then directly to the discharge tube. The nitrogen flow rate was maintained constant a t 1.2 X 10-6 mole/sec. which corresponded to a pressure of 1.2 mm. The reactant flow rate was determined by pressure decrease in a calibrated volume. The following hydrocarbond were used: purified %-hexane,* Phillips research grade cyclohexane and benzene, and Phillips pure grade neopentane. The methylamine and ethylamine were Matheson C.P. and the tetramethylsilane was Dow Corning purified grade. The amount of hydrogen cyanide formed was determined by gas liquid partition chromatography using a calibrated 2-meter didecyl phthalate column. Ammonia was identified by its characteristic infrared spectrum and determined quantitatively by its absorption at 968 cm.-l. Acetylene and ethylene were determined b infrared absorption a t 725 and 946 cm.-l, respectively. &,her products were studied by gas-liquid chromatography using a tetraisobutylene column.
*C4H14 C-CaHla CsHs CHiNHa CzRsNHn
TABLE I
ACTIVENITROGEN REACTIONS Flow
m.t,n. _ -__,
Reactant (CHI)& (CHa)rSi
x
10'
moles/ Temp., HCN NHI CZHI 880. OC. ------moles/sec. 28 1 . 6 0.32 0.17 40 250 25 4.5 .BO 0.30 28 0.7 .35 11 250 10 3.2 1.2 250 4.9 1.0 1.0 10.2 14.2 250 5.8 0.7 0 . 6 14 250 4.9 0.9 1.2 250 15.5 5.3 4.7 0 250 2 . 0 1.3 0.35 3.3
.. ..
CnHi
Cs
CI
.. ..
.. .. .. ,.
..
X 107-
..
.. 1.4 1.5 0 0 0.11
.. .. ..
0.5 0.3 0.5 0.3 0 (2.3) 0 0
..
..
The reaction with methylamine produced approximately equal amounts of hydrogen cyanide and ammonia. The amount of hydrogen cyanide formed was equal to the amount of methylamine reacted. Freeman and Winkler6 have reported that the ammonia formed is about 25% of the hydrogen cyanide formed. The reason for this discrepancy is not apparent. I n the ethylamine reaction the ratio of ammonia formed to hydrogen cyanide formed was almost one-half. Small amounts of acetylene and ethylene were also formed. The formation of significant amounts of ammonia in the reaction between active nitrogen and hydrocarbons has not been reported heretofore. It appears unlikely that ammonia is formed by a series Results and Discussion of hydrogen atom abstraction reactions since, in The details of the active nitrogen reactions are the first step, imine radicals are formed which very given in Table I. In all cases it was found that likely disproportionate to hydrogen and nitrogen. ammonia was a significant reaction product. With It is also known that for hydrocarbons the first step neopentane and tetramethylsilane the ratio of is appreciably endothermic.' The combination of ammonia to hydrogen cyanide was approximately nitrogen atoms with hydrogen atoms is known to 20 and 40%, respectively. The neopentane results, produce ammonia,6and it is conceivable that such with the exception of the ammonia formation, are a mechanism could account for the ammonia obin good agreement with the results of Onyszchuk served in the active nitrogen reactions. The uniand Winkler.4 The reaction of active nitrogen with fied mechanism proposed by Winkler and cotetramethylsilane produced a solid deposit on the workers can be adapted to account for the ammonia walls of the reaction vessel. Infrared examination formation by postulating that a given fraction of of the deposit indicated the presence of Si-N and the nitrogen atom-reactant complexes decompose Si-C bonds. It is of interest that the ratio of either to an amine radical or directly to ammonia. The author is indebted to R. S. McDonald for hydrogen cyanide from neopentane and tetramethylsilane is approximately the ratio of the considerable assistance with the infrared assignments. carbon atoms in each molecule. The reactions with hexane, cyclohexane and ben(5) G. R. Freeman and C. A . Winkler, ibid,, 69, 780 (1955). zene a t high temperature and high flow rates pro(6) B. Lewis. J . Am. Chem. Soc., 50,27 (1928). duced approximately the same yield of hydrogen cyanide and ammonia. In addition appreciable FLUID PHASES I N MUTUAL CONTACT: quantities of Cz, CSand C4 products were obtained FURTHER EXPERIMENTAL with hexane and cyclohexane whereas with benzene apparently only Cz and C4 products were CONSIDERATIONS formed. The Cq product results for benzene shown BYWILLIAMFox1 in Table I were obtained by gas chromatography 667 Oakland Avenue, Staten Island, N . Y . with a didecyl phthalate column. The hydrocarR6ceived February B6, 1868 bon product identifications were based entirely on retention time data and therefore can only be Presented in this communication are some fundaconsidered as tentative identifications. After mental physical facts regarding fluid phases in muwarm-up of the liquid nitrogen condensable prod- tual contact and a description of experimental approaches which will be extended to yield a new (1) H. G. V. Evans, G . R. Freeman and C. A. Winkler, Can. J . Chem., 84, 1271 (1956). method for the determination of absolute values of (2) P. A. Gartaganis and C. A. Winkler, i b i d . , 34, 1457 (1956). (3) H. A . Dewhurst, THIEJOURNAL,68, 15 (1858). (4) M.Onysrchuk and C. A. Winkler, ibid., 69, 868 (1956).
(1) Faculty of Police Science, Baruch School, City College of New York, New York, N. Y. Police Department, City of New York.
