The cool-flame oxidation of 3-ethylpentane

Abstract

Detailed studies have been carried out of the combustion of 3-ethylpentane with special reference to the chemical changes taking place in the cool-flame region, where at least 74 individual products are formed. At ca. 300 °C, the first products to appear are 3-ethylpent-1-ene and 3-ethylpent-2-ene, C₇ O-heterocycles and alkenes of carbon number less than seven; the rates of consumption of 3-ethylpentane and of formation of all products increase dramatically just before propagation of the first cool-flame but do not vary appreciably when subsequent cool-flames pass. As the temperature is raised to ca. 400 °C, the quantities of 3-ethylpentane consumed and of lower molecular mass products formed increase markedly while the amounts of most C₇ products decrease. Consideration of the analytical results indicates that alkylperoxy radical isomerization plays an important part in the primary chain-propagation cycle both in and out of the cool-flame region and at temperatures as high as 400 °C. It appears that the initial reaction of alkyl radicals with oxygen takes place, largely, if not exclusively, by direct addition to form alkylperoxy radicals. Different modes of isomerization of these radicals leads to the wide variety of products found and decomposition of the a-hydroperoxyalkyl radicals by direct loss of HO₂ is probably the sole source of the conjugate alkenes. The results also provide the first recorded evidence of ethyl group migration during alkylperoxy radical isomerization.