The gaseous oxidation of 2-methyl-but-2-ene II. Carbon-14 tracer studies

Abstract

An investigation is described of the slow combustion of [2-$^{14}$C] and [4-$^{14}$C] 2-methylbut-2-enes. The reaction products have been separated and the position occupied by the carbon-14 in the labelled products has been determined by degradation. The results strongly suggest that acetone and acetaldehyde, the principal early non-peroxidic products, arise by the simple breakdown of a cyclic peroxide formed by addition of oxygen to the olefin at the double bond, and that rearrangements of a biradical also produced during such addition yield the minor products (methyl ethyl ketone, propionaldehyde, isopropyl alcohol and tert-butyl alcohol). The formation of methyl isopropyl ketone involves hydroperoxylation of the olefin, and methyl alcohol arises from the further oxidation of acetaldehyde. It is likely that two modes of initial attack of the olefin by oxygen, addition at the double bond and hydrogen abstraction leading to hydroperoxylation, both occur concurrently. With 2-methyl-but-2-ene, which has no $\alpha$-methylene group, the former reaction is the more important.