Decomposition of diacyl peroxides. Part VIII. Mechanism of thermal decomposition of cyclopropaneacetyl peroxide

Abstract

The thermal decomposition of cyclopropaneacetyl peroxide in CCl₄ has been studied in detail. Major products of the decomposition at 55° were cyclopropylmethyl cyclopropaneacetate, cyclopropylmethyl cyclopropaneacetyl carbonate, 1,1,1,3,5-pentachloropentane, and carbon dioxide. A tracer study with [¹⁸O]carbonyl labelled peroxide indicated that there was no oxygen scrambling in the original peroxide while there was oxygen scrambling both in the resulting carbonate formed via carboxy-inversion and in the ester. The carbonate did not give the ester under the conditions employed for the decomposition of the peroxide. On the basis of the ¹⁸O and other studies, radical cage recombination is suggested for the formation of the ester and a cyclic mechanism is ruled out. The distribution of ¹⁸O in the carbonate is explained by the assumption of transient formation of a common intermediate prior to both the radical and carboxy-inversion processes. Thermal decomposition of the carbonate to give the ester was also studied and this proceeds by acyl–oxygen bond fission.