Reactions of allylic radicals. Part 1.—Disproportionation between allyl and ethyl radicals

Abstract

Allyl radicals may be generated in the presence of a large excess of ethyl radicals by the illumination of a gaseous mixture of diethyl ketone and diallyl with 3130 Å light between 134 and 175°C. Generation proceeds by the sequence of reactions: C₂H^˙₅+C₆H₁₀→ C₈H^˙₁₅→C₅H₁₀+C₃H^˙₅ having activation energies of 6.6±0.4 and 16±4 kcal/mole respectively. Conditions may be controlled so that the allyl radicals are removed exclusively by combination and disproportionation with ethyl radicals, and the allene and propene found among the products are formed solely by the two possible modes of this cross-disproportionation. Product analysis reveals the pattern of combination and disproportionation between allyl and ethyl radicals : [graphic omitted] The experimental results agree moderately well with the corresponding values calculated from the equation of Holroyd and Klein, and which are given above in square brackets. These results are discussed in relation to the patterns of disproportionation and combination found for the allyl radical in other systems.