Reaction of hydroperoxy t-butyl radicals and t-butyl peroxyt-butyl radicals in relation to chain propagation in combustion

Abstract

Hydroperoxyl t -butyl radicals (I) or t -butyl peroxy t -butyl radicals (II) were generated in an oxygen-free system. This allowed an unequivocal measure of the ratio of olefin to epoxide formation to be made. For hydroperoxy alkyl radicals, the two paths are competitive over the temperature range 413–473 K with olefin production becoming more dominant as the temperature is raised. Some controversy surrounds the primary mechanism for the oxidation of alkyl radicals at temperatures up to 900 K. Strong arguments have been put forward for both exclusive olefin and exclusive epoxide formation. By comparing our results with this work, we conclude that the primary path is indeed exclusive olefin formation. The controversy may be reconciled by proposing that epoxide formation arises as the result of secondary reactions involving the addition of HO 2 or RO 2 to the primary olefin product. Pressure-dependent processes complicate the issue. However, it is difficult to see how any collisional stabilisation process would lead to increased epoxide formation in view of the present evidence available. This work shows that the addition of RO 2 to olefins results in the almost exclusive production of epoxide, at least at lower temperatures. For t -butyl peroxy t -butyl radicals over the temperature range 363–403 K, the path involving the production of epoxide is ≥98%. Further evidence is required on the reaction of hydroperoxy and alkylperoxy alkyl radicals.