Abstract
In the reaction of N-methylbenzenesulfenamide (1) with thioanisole (4) in the presence of trifluoroacetic acid (TFA), the initial rate υ0 of total appearance of 2- and 4-(methylthio)phenyl phenyl sulfides (5) is first and zero order with respect to the initial concentrations of 1 and 4, respectively: υ0=kobs[1]0. The pseudo-first order rate constant kobs is evaluated as 5.2×10-4 sec-1 with varying concentrations of 4 (0.72 to 5.0 M) in a mixture of 4 and CH2Cl2 in the presence of TFA at 10 °C. This data supports the notion that a phenylsulfenium ion intermediate 3 interacting with both the counter ion and the unshared electron-pair of amine is generated by heterolytic N-S scission of the protonated sulfenamide 2, leading to the observed formation of 5.
Highlights
Many researchers have made proposals concerning the generation of sulfenium ion intermediates [1]; this intermediate can only be isolated in the case of coordination with two nitrogen atoms [2], yet several studies [3] have failed to find evidence supporting its existence, as it has too short a lifetime to Molecules 2003, 8 exist as the free ion, being converted to sulfonium [4] or thiiranium ions [5] by reaction with sulfides or alkenes, respectively
We have proposed that a sulfenium ion with a very short lifetime can exist by interacting with both a counter ion and the unshared electron pair of an amine, considering the effects of the counter ion, the amine, solvent nucleophilicity, etc. on the reactions of N-alkylarenesulfenamides or azides with alkyl aryl sulfides in the presence of trifluoroacetic acid [6]
We have already proposed that mechanistically the reactions of N-alkylbenzenesulfenamides with 4 in the presence of trifluoroacetic acid (TFA) give 2and 4-(alkylthio)phenyl phenyl sulfides by phenylthiolation of a phenylsulfenium ion intermediate [6]
Summary
Received: 23 January 2003; in revised form: 25 March 2003 / Accepted: 27 March 2003 / Published 30 April 2003
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