Decomposition of diacyl peroxide—VII : Oxygen scrambling in 1-apocamphoryl peroxide and related diacyl peroxides-general remarks on the relationship between the stability of acyloxy radical and amounts of cage recombinations and ester formation in the decomposition of diacyl peroxide |
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Authors: | K Fujimori S Oae |
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Institution: | Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Sumiyoshi-ku, Osaka, Japan |
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Abstract: | Thermal decomposition of 1-apocamphoryl peroxide has been investigated in CCl4 using the 18O-labelled peroxide. 1-Apocamphoryl peroxide is the first example which undergoes radical decomposition, carboxy-inversion and oxygen scrambling reaction between carbonyl and peroxidic O atoms in the peroxide in comparable rates. The major product of the decomposition was the inversion product, 1-apocamphoryl 1-apocamphyl carbonate (52·5%), and only a minute amount of 1-apocamphyl 1-apocamphorate (2·2%) was formed. The rates of oxygen scrambling were found to be 2·70±0·21 × 10?6 (55°), 1·85±0·12 × 10?1 sec?1 (70°) and 9·33±0·18 × 10?5 sec?1 (84·3°) (Ea, 27·5 Kcal/mol, ΔS3, ?2·3 e.u.). The cage recombination mechanism was suggested for the oxygen scrambling and the amounts of cage recombination of 1-apocamphoryloxy radical pair were calculated as 65% (55°), 60% (70°) and 52% (84·3°). The yield of the ester and the amount of cage recombination of geminate acyloxy radical pair were rationalized in terms of the stability of acyloxy radicals formed in the cage. |
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