THOMAS J. HOUSER AND BETTY M. H. LEE
3422
Pyrolysis Kinetics of Ethyl Nitrate
by Thomas J. Houser and Betty M. H. Lee1 Department of Chemistry, Western Michigan Universzty, Kalamazoo, Michigan
(Receiued February $7, 1967)
The pyrolysis rate and mechanism of ethyl nitrate have been studied in the temperature range of 242-260’. The reaction kinetics were found to be one-half order with respect to the reactant; a major portion of the organic product was a polyether, probably formed from formaldehyde. The activation energy and frequency factor were determined to be 46.8 kcal/mole and 1019*2 (mmole/l.) ’’’ sec-’, respectively. These data are consistent with a radical chain mechanism in which termination occurs through the interaction of two of the monomolecularly decomposing chain-carrying species, which is the ethoxide radical in the proposed mechanism.
Interest in the pyrolysis kinetics and mechanisms of ethyl nitrate was revived because of the ability of this compound to detonate when subjected to mechanical shock. There is evidence that the presence of gas or vapor bubbles is helpful, and in some cases necessary, in promoting detonation. In addition, the presence of oxygen in the gas bubbles greatly increases the sensitivity of compounds such as ethyl nitrate, nitroglycerine, etc.2 Thus it is reasonable to conclude that detonation is initiated in the gas phase and involves the pyrolysis rates and mechanisms of the particular compound being detonated. Although mechanisms for shock-induced detonations have been d i s c u ~ s e d ,the ~,~ role of reactant pyrolysis in the process has not been clarified. The pyrolysis rate and mechanism of ethyl nitrate has been extensively studied at temperatures up to about 200” using static systems, principally manometric technique^.^-^ In addition, a few higher temperature kinetic studies have been made, generally with the ethyl nitrate flame.10-12 Considering the very short time for detonation, the pyrolysis mechanisms of interest are those for reactions at higher temperatures. It is apparent, from the radical chain nature of explosive reactions, that the low-temperature pyrolysis mechanism, postulated to have the rate-controlling step a unimolecular type of decomposition, is considerably different from that controlling the detonation process for ethyl nitrate. In addition, the observation that oxygen inhibits the pyrolysis,* contrary to its effect on detonation of ethyl nitrate, is further evidence for this T h e Journal of Physical Chemistry
difference. Therefore, the current higher temperature study was initiated using a flow system with a stirredflow reactor in order to obtain differential rate datal3 under relatively well-controlled conditions. Experimental Section
A p p a r a t u s and Procedure. The experiments were carried out in a conventional flow system utilizing a stirred-flow reactor, the design of which had been tested for stirring efficiency.I4 The reactor was an 80-ml ~
(1) This research is in partial fulfillment of requirements for a Master’s degree. (2) F. P. Bowden, M. F. R. Xulcahy, 1%.G. Vines, and B . Yoffe, Proc. R o y . SOC.(London), A188, 291 (1947). (3) A. MaEek, Chem. Rea., 62, 41 (1962). (4) T. A. Erikson and E. L. Grove, A R F 3197-15, “Fundamentals of Liquid Propellant Sensitivity,” 1962. The authors have proposed that the vaporization rate is the limiting step; however, in drop weight testing the pressures necessary t o validate their mechanisms are not attained without reaction occurring first. (5) G. K. Adams and C. E. H. Bawn. Trans. Faraday Soc., 45, 494 (1949). (6) L. Phillips, n’ature, 165, 564 (1950). (7) J. B. Levy, J . Am. C h a . SOC.,76, 3254 (1954). (8) J. B. Levy, {bid., 76,3790 (1954). (9) F. H. Pollard, H. S. B. Marshall, and A . E. Pedler, T r a n s . Farad a y SOC.,52, 59 (1956). (10) €1. Theile, Angew. Chem., A60, 65 (1948). (11) G. D. Adams and J. Scrivener, S y m p . Combust., 5th, Pittsburgh, 1954, 656 (1955). (12) J. A. Hicks, S y m p . Combust., 8th, Pasadena, Calif., 1960, 487 (1962). (13) A. A. Frost and R. G. Pearson, “Kinetics and JIechanism,” 2nd ed, John Wiley and Sons, Inc.. New York, N . Y., 1961, p 265.
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