Mechanisms of hydrolysis of phenyl- and benzyl 4-nitrophenyl-sulfamate esters?

Organic & Biomolecular Chemistry Pub Date: 2010-10-25 DOI: 10.1039/C0OB00362J

Abstract

The kinetics of hydrolysis at medium acid strength (pH interval 2–5) of a series of phenylsulfamate esters 1 have been studied and they have been found to react by an associative SN2(S) mechanism with water acting as a nucleophile attacking at sulfur, cleaving the S–O bond with simultaneous formation of a new S–O bond to the oxygen of a water molecule leading to sulfamic acid and phenol as products. In neutral to moderate alkaline solution (pH ≥ ～ 6–9) a dissociative (E1cB) route is followed that involves i) ionization of the amino group followed by ii) unimolecular expulsion of the leaving group from the ionized ester to give N-sulfonylamine [HN[double bond, length as m-dash]SO2] as an intermediate. In more alkaline solution further ionization of the conjugate base of the ester occurs to give a dianionic species which expels the aryloxide leaving group to yield the novel N-sulfonylamine anion [?N[double bond, length as m-dash]SO2]; in a final step, rapid attack of hydroxide ion or a water molecule on it leads again to sulfamic acid. A series of substituted benzyl 4-nitrophenylsulfamate esters 4 were hydrolysed in the pH range 6.4–14, giving rise to a Hammett relationship whose reaction constant is shown to be consistent with the E1cB mechanism.

Graphical abstract: Mechanisms of hydrolysis of phenyl- and benzyl 4-nitrophenyl-sulfamate esters
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