Perchlorate esters. Part 8. Kinetics and mechanism of the methanolysis of methyl perchlorate in benzene

Abstract

Methyl perchlorate reacts with 0.07–0.4M-methanol in benzene with a kinetic order of ca. 2.3 in methanol. The reaction is accelerated by addition of nitromethane but, in contrast to the corresponding methanolysis of triphenylmethyl chloride, decelerated by added phenol. Small concentrations of tetra-n-butylammonium perchlorate cause very large increases in the methanolysis rate. The mechanism is essentially S_N2 in character but subject to general-base catalysis, either by additional methanol molecules or by perchlorate ion. With phenol present, deactivation of methanol molecules by hydrogen bonding outweighs any electrophilic assistance rendered to perchlorate-ion departure. An alternative mechanism for the previously studied methanolysis of triphenylmethyl chloride in benzene is presented; unlike previous proposals, this mechanism is compatible with the retardation of the methanolysis by moderate concentrations of tetra-n-butylammonium chloride.