The mechanism of hydrolysis of 2-hydroxyethanesulfonyl chloride: the intermediacy of 1,2-oxathietane 2,2-dioxide (β-sultone)

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Abstract
The hydrolysis of 2-hydroxyethanesulfonyl chloride (1) has been investigated with the aid of kinetic and product analysis studies. The results are quantitatively consistent with the mechanism of hydrolysis shown in Scheme 1, the chief features of which are (a) formation of β-sultone (2) and its rapid further reaction (the major pathway), together with (b) a minor direct hydrolysis route. The kinetics of both the β β-sultone formation and the direct hydrolysis shows two terms, one first order in 1 alone, and the other first order in hydroxide as well; the rates of the first- and second-order reactions are lowered by added sodium chloride. It is suggested (a) that the unimolecular β-sultone formation involves 1 in a complex with water (as in 9) and that the water acts as a general base in the cyclization to 2, and (b) the hydroxide-promoted reaction proceeds by cyclization of the conjugate base of 1 (i.e., 10). The unimolecular direct hydrolysis is regarded as a conventional hydrolysis of a sulfonyl chloride with attack of the water with general base assistance from a second water molecule. The hydroxide-promoted direct reaction in D2O leads to no uptake of deuterium, showing that the reaction does not go by way of the sulfene, and a reaction by way of a six-membered cyclic transition state is tentatively proposed. Evidence is presented that the chloride ion rate suppression is not primarily due to reaction of β-sultone with Cl− to give back 1; the possible origins of the effect are discussed. Keywords: sulfonyl chlorides, 2-hydroxyethanesulfonyl chloride, β-sultone, kinetics of sulfonyl chloride hydrolysis, mechanisms of sulfonyl chloride hydrolysis.

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