THEORETICAL-STUDIES ON THE SUBSTITUTION-REACTIONS OF SULFONYL COMPOUNDS .2. HYDROLYSIS AND METHANOLYSIS OF METHANESULFONYL CHLORIDE

Ab initio molecular orbital calculations have been performed to study the gas-phase hydrolysis and methanolysis of methanesulfonyl chloride. The overall reaction occurs via a concerted S(N)2 mechanism with a tr igonalbipyramidal transition state, and the transition structure is lo oser when the reaction is catalyzed by additional solvent molecules. T he reactivity in a mixed solvent agrees well with the gas-phase proton affinity of the hydrogen-bonded solvent complex, and the methanol-cat alyzed methanolysis reaction in the gas phase is the fastest among the reactions discussed. The catalytic role of such solvent molecules app ears to be bifunctional as in the hydration of a carbonyl group, but g eneral-base catalysis is more important than general-acid catalysis. T he MP2/6-31G activation energy is reduced considerably by two catalyt ic water molecules.