Nucleophilic substitution at a trigonal carbon. Part 6.1 Substituent and bromide/chloride leaving group effects in the reactions of aromatic acyl chlorides with methanol in acetonitrile

Abstract

For the methanolyses in acetonitrile at 25.0 °C of benzoyl chloride and eleven para- or meta-substituted derivatives, the kinetics of methyl ester formation have contributions both first-order and second-order in methanol. The Hammett plots for the overall second- and third-order processes are curved and both plots can be analyzed in terms of the simultaneous operation of two reaction channels. An addition–elimination process is favored by electron-withdrawing substituents and a loose S_N2 process by electron-supplying substituents. Comparisons of widely varying halogen leaving-group effects suggest that the addition–elimination processes for solvolyses of haloformate esters and acyl halides have an identical addition step but they then differ in the sequence of the two elimination steps.