?-Acceptor Induced Reactions: Radicals vs. Ions in Thermally Induced Ether Cleavage Reactions

Article abstract of DOI:10.1016/S0040-4020(01)81576-3

The reactions of benzyl ether (1a) and 4,4'-dicyanobenzyl ether (1b) with a wide range of ?-acceptors in acetonitrile at 190 deg C have been studied.The ?-acceptors were chosen in order to systematically vary the ΔG⁰ for hydride or electron transfer from the ethers to the ?-acceptors.The products of thermal activation of the bond cleavage reaction are the aldehyde and the alcohol derived from the starting ethers.A linear free energy correlation of the two relative thermal reaction rates of 1a and 1b with the reduction potentials of the quinones was obtained.This relationship indicates that the rate of radical pair separation becomes increasingly important relative to the rate of the second electron transfer and subsequent product formation through the hydride transfer intermediate as the electron affinity of the quinone decreases.