D. BEGGS,C. BLOCK, AND D. WILSON
1494
The Thermal Decomposition of Nitryl Chloride in Solution'
by David Beggs, Catherine Block, and David J. Wilson Department of Chemistry, University of Rochester, Rochester, N e w Y o r k
(Received J a n u a r y 13, 1964)
The decomposition of nitryl chloride (SOzC1) dissolved in trifluorochloroethylene polymer oil was studied in the temperature range 127-141". The rate constant is satisfactorily represented by k = 1012.0exp(-28,500/RT) set.-'. The results are in disagreement with calculations made by Slater. This may be due to solvent cage effects.
Introduction The gas phase pyrolysis of nitryl chloride, first studied by Schumacher and Sprenger, was intensively reinvestigated by Johnston and his co-workers. These lnvestigators showed that the rate-controllingstep in the reaction is unimolecular, and that the mechanism of the reaction is almost certainly that given in eq. 1. s02c1-+~02 KOzC1
+ C1 -+
+c1 KO2
k , (slow)
+ Clz
(1)
k z (fast)
Photochemical evidence for the second step has also been found.4 The reaction has also been studied a t high temperatures by shock tube techniques.5 Cordes and Casaletto3 agree that the high-pressure limiting value of the activation energy is about 29.0 kcal./ mole; however, none of the gas phase measurements was at a pressure high enough for the rate constant to have approached its high-pressure limit. (This result is expected, since the pressures a t which the high-pressure limit is approached increase rapidly with decreasing molecular complexity.) Slater has published6 a calculation of the rate of deconiposition of nitryl chloride ; he finds a frequency factor at the high-pressure liniit of about 1.5-1.6 X 1013 sec.-l and concludes that one should be within 25y0 of the high-pressure limit at pressures of the order of 50 atm. We desired to check his high-pressure factor and to check the extrapolated value of the activation energy. However, we were not enthusiastic about the experimental difficulties of studying this reaction at pressures of several hundred atmospheres of nitrogen. Since the relevant parameter in reaching the highpressure limit is the frequency with which a reactant molecule suffers collisions, the possibility of studying the T h e Journal of Physical Chemistry
reaction at ordinary pressures in solution suggested itself. There follows a report of such an investigation. Experimental Sitryl chloride was prepared and purified by the method of Wise and Volpe, as described by Volpe and J o h n ~ t o n . ~The solvent used was Fluorolube HO-125 trifluorochloroethylene polymer oil, obtained from the Hooker Chemical Corp. This material was pretreated with nitryl chloride for several hours a t 127" ; this was necessary to eliminate impurities which react with nitrogen dioxide.' All stopcocks were lubricated with Kel-F No. 90 grease (obtained from the 3 nl1 Company). The apparatus is diagrammed in Fig. 1. A tungsten lamp (GE1188) was used as a light source (1); the beam was collimated (2), filtered (3) through Corning filters 3389 and 5113 (nitrogen dioxide absorbs strongly in the region 400-475 mp passed by the filters, while nitryl chloride does not), chopped (3) so as to pass alternately through the reaction cell (4) or an empty tube (5), and focused (2) onto an R.C.A. 1P21 photomultiplier tube (6), the output of which was monitored by a Varian G 11A recorder. The experimental set-up (1) This work was supported by the National Science Foundation. (2) H . J. Schumacher and G. Sprenger, 2. Elektrochem., 35, 653 (1929); Naturwiss., 17, 997 (1929); 2. physik. Chem., B12, 115 (1931). (3) H . F. Cordes and H . S. Johnfiton, J . Am. Chem. Soc., 76,4264 (1954); M. Volpe and H . S. Johnston, ibid., 78, 3903 (1956); M . Volpe and H . S. Johnston, ibid., 78,3910 (1956); G . Casaletto, Ph.D. Thesis, Stanford University, 1956; D. J. Wilson, Ph.D. Thesis, California Institute of Technology, 1957. (4) A. S. Dohner and D. J. Wilson, J . Chem. P h y s . , 35, 1510 (1961) (5) H. Hiraoka and R. Hardwick, ibid., 36, 2164 (1962). (6) N . B. Slater, "Theory of Uniniolecular Reactions," Cornel1 University Press, Ithaca, S . Y., 1959, pp. 175-180. (7) We are indebted to Prof. Gilbert Mains for helpful words of caution and advice in connection with the preparation of the solvent.
THERMAL DECOMPOSITION OF NITRYLCHLORIDE IN SOLUTION
1495
PUMP
I
I
I
0
11
Figure 1. The apparatuii: 1, light source; 2, collimating lens; 3, light chopper and iilters; 4, sample cell; 5, empty tube; 6, photomultiplier tube; 7, 100-ml. bulb, magnetic stirrer; 8, heat transfer coil; 9, 250-ml. bulb; 10, Ca804 drying tube; 11, nitryl chloride storage and purification traps; 12, Bourdon gage assembly; 13, solvent port; 14, nitryl chloride port.
was similar to those used by Johnston and his coworkems The thermostat was filled with inhibited mineral oil, stirred, and heated electrically. The temperature was controllled to k0.1". The presence of small thicknesses (about 1 mm.) of oil in the optical path a t either end of the 10-cm. Pyrex cell caused no difficulties. Solvent was introduced into bulb 9 from port 13; it was then degassed by boiling under vacuum. Runs were made as follows. A suitable pressure (about 10-20 mm.) of nitryl chloride was introduced into bulb 7 from the purification and storage traps (11). Then dry air was used to drive solvent from bulb 9 to bulb 7 , and the gaseous react,ant readily dissolved (with magnetic stirring) in the solvent. Next, dry air was used to drive this solution through the heating coil 8 into the reaction cell 4. The stopcocks between bulb 7 and the cell were left open to prevent thermal expansion of the solution from bursting the cell or causing leaks; the nitryl chloride solution in the cell was under a pressure of slightly over 1 atm., and showed no signs of degassing nitryl chloride. After the reaction had gone to completion (as indicated by the phototube output), the solution was driven by dry air into bulb 9, where it was degassed by boiling under vacuum before the solvent was used again.
Results The reaction was firfit order, as indicated by the plot in Fig, 2; and the rate constants were independent of initial nitryl chloride concentration. The time required to heat the solution to the temperature of the t]hermostat is appreciable, which prevents one from
I20 240 360 480 600 720 840 960 1080 1200 1320 TIME (SECONDS)
Figure 2. First-order rate plot.
Figure 3. Activation energy plot.
Table I T
K X 104, 8ec.-1
134.8 134.8 135,O 135.6 135.8 140.8 140.9 141.2 141.2 141,2 141.2 127.4 127.7 127.8
5,608 5.366 5.442 5.928 5.607 9.375 9,520 8,957 8.943 8,691 8,305 2,909 2.850 3.048
making measurements a t temperatures much above 140"; below 127" the reaction is too slow for convenient measurement. Table I lists the rate constants (calculated on an IBM 1620 by the method of least squares) and temperatures; the standard deviations of the rate Volume 68, hlumber 6
June, 196.4
GEORGEBLYHOLDER AND NORA FORD
1496
constants were about 1-2% as large as the rate constants themselves. A plot of log k us. 1000/RT is shown in Fig. 3; the Arrhenius parameters calculated from this graph are given by =
1012.01 0 . 3 exp (-28,500
f
500/RT) sec.-l
This value for the activation energy is in satisfactory
agreement with the extrapolations of Cordes and Casaletto,a especially in view of the narrow temperature range to which we were limited. Our value for the pre-exponential factor is lower than that calculated by Slater by a factor of 15-16; this could either be due to inadequacies in his theory or to the recombination of solvent-caged nitrogen dioxide and chlorine atoms, since this is a dissociation reaction.
Far-Infrared Spectra of Some Mono- and Polynuclear Aqua-Substituted Cobalt-Ammine Complexes
by George Blyholder and Nora Ford Department of Chemistry, C'niaersity of Arkansas, Fayetteville, Arkansas (Received J a n u a r y 16, l S 6 4 )
The infrared spectra in the CsBr region of C~~-[C~(NH~)~(HZO)Z]Z(SO~)~~ 3H20, cis-[Co(XH3)4(H20)(OH) ]SO4 .HzO, and cis- [Co(NH3)4(HzO)(Cl) ]SO4 have been obtained. Frequencies for skeletal vibrations of the first complex ion are found at 521, 494, 461, 449, 428, and about 330 cm.-'. The spectra of the latter two compounds are similar. These bands are assigned as skeletal vibrations by treating these molecules as perturbations of [ c o ( N & ) ~ ] + ~The . correlation treatment lends further support to the assignment of a weak band at 502 cm.-' as a fundamental vibration of [CO(NHB)B]+~. The infrared spectra
1
in the CsBr region of several polynuclear complexes, of which [Co {
