Mechanisms of reactions of sulfonyl compounds with nucleophiles in protic media
The mechanism ofthe reaction of ethylene sulfone (thiirane 1,l-dioxide) with hydroxide in water and methoxide in methanol, been examined. Evidence has been obtained for two distinct pathways (respectively first order and second order in hydroxide), which are believed to proceed has via attack of hydroxide on the sulfone to give a trigonal-bipyramidal monoanion which reacts either with water or with another hydroxide ion to form ethanesulfonate anion or ethylene plus sulfite anion in quite different proportions. Study of the mechanisms of hydrolysis of alkanesulfonyl chlorides has been extended to (a) cyclopropanesulfonyl, (b) trimethylsilylmethanesulfonyl, (c) tris- (trimethylsily1)-methanesulfonyl, (d) 2,2,2-trifluoroethanesulfonyl, and (e) 2-methyl-2- propanesulfonyl chlorides. The last hydrolyzes by initial t-butyl cation formation, while the others go by more or less precedented routes, usually by way of a sulfene. Reactions of arenesulfonyl chlorides with a number of primary and secondary amines show pH-yield profiles indicating third-order processes to the sulfonamide at high pH. The propensity for third-order reactivity increases with increasing hydrophobic character of the alkyl group(s). A practical result is that a number of amines are efficiently converted into their benzenesulfonamides using only a slight (5%) excess of benzenesulfonyl chloride in 1 M NaOH. For a number of years we have been interested in the study of the mechanisms of reactions of the sulfonyl group, particularly those processes which lead to overall nucleophilic substitution. This paper presents three related topics each of which deals with the reactions of nucleophiles with a sulfonyl group in water. The specific topics, involve 1) ethylene sulfone and the final stage of the Ramberg-Blcklund reaction, 2) the hydrolysis of alkanesulfonyl chlorides, and 3) new mechanisms of reaction of arenesulfonyl chlorides with nucleophiles. 1. The Ramberg-Backlund reaction and the reactions of ethylene sulfone with nucleophiles The general course of the well-known Ramberg-Backlund reaction is shown below.