Kinetic studies of the reactions of some phenyl aryl sulfides with aliphatic amines in dimethyl sulfoxide; the mechanism of base catalysis

Abstract

The reactions of n-butylamine, pyrrolidine and piperidine with 4′-R-phenyl 2,4,6-trinitrophenyl sulfides (R = H, Me, Br, NO₂), 4a–d, result in the rapid formation of σ-adducts by attack at the unsubstituted 3-position; rate and equilibrium data are reported and substituent effects examined. Attack by amine at the 1 -position of 4a–d, phenyl 2,4-dinitronaphthyl sulfide 9, and phenyl 2,6-dinitro-4-trifluoromethyl sulfide 11, results in displacement of the phenylthio group. The substitutions by butylamine show a first order dependence on the amine concentration indicating that nucleophilic attack is rate determining. However the substitutions by pyrrolidine are subject to general base catalysis and it is argued that here the rate limiting step is deprotonation of the initially formed zwitterionic intermediate.