Dual Reactivity of Methoxymethyl Benzenesulfonate in Nucleophilic Substitution

Article abstract of DOI:10.1246/bcsj.65.2672

Hydrolysis of methoxymethyl benzenesulfenate is catalyzed by both acid and base.Acid-catalyzed hydrolysis is further accelerated by various nucleophiles like halide ions, thiocyanate, dialkyl sulfide, and the substrate itself.The catalytic constants coincide with those for ethyl benzenesulfenate within 2-fold in magnitude.The nucleophilic reactivity strongly suggests the reaction at the sulfenyl sulfur, but examination of the products from the 18O-labeled substrate showed that the bond cleavage occurs mostly between the oxygen and the proformyl carbon except for the acid-catalyzed water reaction which undergoes the S-O cleavage.A mechanism for a nucleophilic reaction at the sulfur to form a sulfurane intermediate which breaks down with the C-O cleavage is presented.The hydrolysis rate is also strongly dependent on the second order of buffer concentrations in carboxylate and tertiary amine buffer solutions.The third-order term involves both the general acid and the conjugate base of the buffer, and the latter reacts at the sulfur as a nucleophile in the rate-determining step but leads to the C-O cleavage in the same way as the other catalytic nucleophiles.