Nitromethane pyrolysis

Early kinetic experiments on the thermal decomposition of nitro compounds established that for the simplest derivative, nitromethane, the process was first order, but that the reaction was chemically complex owing to further reactions between the products and nitromethane. Cottrell et re-examined the nitromethane pyrolysis and reported values of = 53.2 kcal.mole" and log A = 13 for the Arrhenius parameters of the homogeneous decomposition a radical mechanism was proposed, initiated by C-N cleavage... 

A number of groups of workers have sought to clarify the situation presented by these conflicting interpretations In particular, Gray et performed pyrolyses at temperatures between 240 and 800° C, and using a flow system carefully analyzed and estimated the products quantitatively. Paneth mirrors were removed in the case of nitromethane pyrolysis and the free radical mechanism (a) was confirmed. The decomposition of nitroethane at around 480 °C corresponds to the stoichiometric equation... 

The products of the thermolysis of 3-phenyl-5-(arylamino)-l,2,4-oxadiazoles and thiazoles have been accounted for by a radical mechanism.266 Flash vacuum pyrolysis of 1,3-dithiolane-1-oxides has led to thiocarbonyl compounds, but the transformation is not general.267 hi an ongoing study of silacyclobutane pyrolysis, CASSF(4,4), MR-CI and CASSCF(4,4)+MP2 calculations using the 3-21G and 6-31G basis sets have modelled the reaction between silenes and ethylene, suggesting a cyclic transition state from which silacyclobutane or a trcins-biradical are formed.268 An AMI study of the thermolysis of 1,3,3-trinitroazacyclobutane and its derivatives has identified gem-dinitro C—N bond homolysis as the initial reaction.269 Similar AMI analysis has determined the activation energy of die formation of NCh from methyl nitrate.270 Thermal decomposition of nitromethane in a shock tube (1050-1400 K, 0.2-40 atm) was studied spectrophotometrically, allowing determination of rate constants.271... 

The use of the direct thermal decomposition method has been fairly widespread, and the values obtained by it will be discussed in the appropriate sections of this book. The O - N bond in alkyl nitrates and nitrites, and the G N bond in nitromethane are among those whose dissociation energy has been measured by this method, but in view of the possible kinetic complexities which may be encountered, such as those already mentioned in connection with the pyrolysis of organic iodides (see Section 4.2.4) the values obtained are often at best only tentative. 

Crawforih and Waddington (72) examined pyrolysis of nitromethane between 305 and 440 C. They found the reaction tobe pressure dependent. Above 150 mm it is approximately of the first order... 

Considerable work has been reported on the possible chemical reaction pathways for both pyrolysis and detonation processes in nitromethane [30-34]. Most of these proposed mechanisms are based upon a unimolecular process. As far as we can determine, only this work and one other (see reference 26) show experimentally that the reaction under pressure results from a bimolecular process, although the results reported in reference 26 were derived from the effect of pressure on time-to-explosion measurements. Based on theoretical electronic orbital calculations a bimolecular process has been proposed [32] as follows ... 

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