The addition of alcohols to vinyl sulphones and sulphonamides

Abstract

A number of mono- and di-vinyl sulphones and sulphonamides have been prepared and the kinetics of their reaction with alcohols in the presence of a basic catalyst have been studied. In a series of pure alcohols, the reaction is of the first order with respect to both vinyl compound and catalyst; its rate at first increases and then becomes practically constant on ascending the homologous series from methanol to n-decanol. The rate of the reaction with ethanol is increased by the addition of dioxan. These results accord with the view that the mechanism of the reaction consists in the addition of the nucleophilic alkoxide ion to the vinyl compound followed by rapid protonation of the intermediate carbanion so formed.

In dimethyl sulphoxide the reaction between equivalent amounts of vinyl compound and alcohol does not go to completion because the intermediate carbanion is stabilised sufficiently to be present in appreciable concentration.

The addition of 2-hydroxyethanethiol to N-methyl-N-phenylvinylsulphonamide was studied in the course of devising an analytical method for the determination of activated vinyl groups. It proved to be of the first order in vinyl compound and catalyst and of zero order in thiol. This independence of thiol concentration of the reaction rate is ascribed to the relatively high acidity of this compound.