Novel change in rate-determining step within an E1cB mechanism during aminolysis of a sulfamate ester in acetonitrile

Abstract

The observation of biphasic Bronsted plots (β1ca. 0.7 and β2ca. 0) in the aminolysis (alicyclic amines, pyridines) of 4-nitrophenyl N-benzylsulfamate 1a in MeCN is interpreted as being due to a mechanistic change from (ElcB)irrev to (ElcB)rev; the change in rate-determining step occurs at approximately the pKa of 1a and other more basic substrates give straight line plots; an entropy study supports the change from a bimolecular to a unimolecular mechanism.