Radical anions of esters of carboxylic acids. Effects of structure and solvent on unimolecular fragmentations

Article abstract of DOI:10.1021/ja00207a014

Pulse radiolysis of alkyl benzoates produces the ester radical anions, which have optical absorptions near 310 nm (~35000 M^-1 cm^-1) and 450 nm (~9500 M^-1 cm^-1). The radical anions undergo fragmentation to form alkyl radicals and carboxylate anions with rates that depend upon the presence of radical stabilizing groups on the alkyl fragment, the nature of the ester group, and the solvent. This cleavage occurs competitively with other processes, such as acyl carbon-oxygen (Bouveault-Blanc) cleavage and electron transfer. The decay rates in ethanol solvent correlate empirically with the bond dissociation energies BDE(R-H) of the alkyl fragments. Cleavage to form methyl, primary, or secondary alkyl radicals occurs sufficiently slowly that the other mechanisms of decay are found to predominate.