The photolysis and pyrolysis of nitromethane and methyl nitrite

Abstract

The photolysis and pyrolysis of nitromethane and methyl nitrite have been studied using the techniques of flash photolysis and kinetic spectroscopy. The results show that photolysis of nitromethane yields methyl radicals and nitrogen dioxide, and that these fragments undergo recombination and disproportionation reactions to form methyl nitrite, methoxyl, and nitric oxide. In the presence of added nitric oxide, the methyl radicals react principally with nitric oxide to form nitrosomethane, which subsequently dimerizes and also reacts further with nitric oxide to yield nitrogen dioxide. The evidence also suggests that nitrosomethane is removed by a relatively efficient reaction with nitrogen dioxide at elevated temperatures to produce nitromethane and nitric oxide. In the case of methyl nitrite, light absorption results not only in photolysis, but also in the formation of an isomer of the nitrite which then reverts slowly to the stable form. The nature of this isomer is not known, but possibilities are suggested and discussed. It is concluded that the decomposition (photolytic or pyrolytic) of methyl nitrite occurs by the rupture of the O—N bond, and that the methoxyl radicals formed disproportionate to yield methanol and form aldehyde. Nitroxyl is also formed but only as a minor product, and the marked increase in intensity of its spectrum in the presence of added nitric oxide shows that it is not formed by a molecular elimination reaction, but probably by CH 3 O + NO → CH 2 O + HNO.