Some nucleophilic displacement reactions on organic sulphites

Abstract

The acid catalysed hydrolysis of several Organic sulphites has been investigated. The rate of hydrolysis is found to be directly proportional to the acid concentra-tion below 0.5 molar acid. Above this, deviations from linearity occur. These are attributed to an ionic strength effect. The effect of added salts on the acid catalysis has also been investigated. In this case also added salts, the anion of which are nucleophilic reagents, show a specific catalysing action. This is attributed to bi-raolecular attack of the anion of the salts or acid on the sulphur atom of the protonated ester, a reaction which proceeds concurrently with, and competes with, the normal hydrolysis which involves attack by a water molecule on the same species.Evidence is produced that the first step in the acid-catalysed hydrolysis is a fast non-rate-determining proton transfer and that the rate-determining step involves a water molecule. The effect of added salt is found to be a linear function of the salt concentration.From the proceeding survey of the Chemistry of Organic sulphites it may be seen that it might be possible to change the point of bond fission from sulphur-oxygen which is the preferred mode of fission in hydrolysis to carbon-oxygen for reactions in non-aqueous solvents with sodium alkoxides.A detailed study has therefore been made of the reaction of a number of cyclic and open-chain sulphites with sodium methoxide and sodium ethoxide. The rates of reaction have been measured and the stoicheiometry of the process have been determined. The structural effects have been interpreted in terms of a normal steric effect.