The alkyl nitrites: chemiluminescence in decomposition and related processes

Abstract

Chemiluminescence has been observed in the decomposition of methyl and ethyl nitrites. Their decomposition has been investigated in the temperature range 290 to 400° C and the critical pressure limit measured above which the luminescence accompanies decomposition. The properties of this luminescent mode have been established. It is affected by the nature of the surface; it is facilitated by increasing the temperature, by adding inert gases and by decreasing the surface/volume ratio of the reaction vessel. In the presence of oxygen or nitrogen dioxide luminescence occurs readily and explosive ignition is possible as well. Critical pressure limits for the two processes have been measured in mixtures with oxygen and with nitrogen dioxide. Nitrogen dioxide is more effective than oxygen in bringing about both luminescence and explosion. The existence of the luminescence has been used to elucidate the decomposition of the alkyl nitrates and nitrites. Experiments on stoicheiometrically similar mixtures—of methyl nitrite with nitrogen dioxide and methyl nitrate with nitric oxide—have confirmed the correctness of the initial steps R O—NO → R O + NO, R O—NO 2 → R O + NO 2 , R = CH 3 , C 2 H 5 , etc., in the thermal decomposition of both nitrites and nitrates, and the luminescent mode shown by both families has been ascribed to the presence of the alkoxy radical R O. Values for the heats of formation ∆ H° f of the radicals CH 3 O and C 2 H 5 O have been obtained. They are —0·5 and —9·0 kcalmole -1 respectively. These values are used to derive previously unknown bond dissociation energies (kcalmole -1 ) in compounds containing the alkoxy group. These include the oxygen-carbon bond in the alkoxy radical itself, D ( R — O) = 92, the oxygen-carbon bond in the ethers, D ( R —O R ) = 77, and the oxygen-hydrogen bond in the alcohols, D ( R O—H) = 99·5.