Issue 11, 2002

Kinetics and mechanism of hydrolysis of phenylureas

Abstract

The hydrolysis of phenylureas has been found to be affected by temperature, pH and buffer concentration. Kinetic evidence suggests that the formation of phenylisocyanate, the initial product in the title reaction, occurs via an intermediate zwitterion. Depending on pH and buffer concentrations, the zwitterion can be produced through three parallel routes: at low pH, specific acid–general base catalysis, followed by slow deprotonation of a nitrogen atom by a general base; at high pH, specific basic–general acid catalysis, followed by slow protonation of a N atom by a general acid; at intermediate pH the reaction proceeds through a proton switch promoted by buffers. Bifunctional acid–base buffers such as HCO3/CO32−, H2PO4/HPO42− and CH3COOH/CH3COO are very efficient catalysts. At high buffer concentration, as well as at pH < 3 or > 12, the breakdown of the zwitterion is rate-determining. The results are discussed in relation to recently published papers reporting different pathways.

Graphical abstract: Kinetics and mechanism of hydrolysis of phenylureas

Article information

Article type
Paper
Submitted
25 Jun 2002
Accepted
06 Sep 2002
First published
11 Oct 2002

J. Chem. Soc., Perkin Trans. 2, 2002, 1889-1893

Kinetics and mechanism of hydrolysis of phenylureas

S. Salvestrini, P. Di Cerbo and S. Capasso, J. Chem. Soc., Perkin Trans. 2, 2002, 1889 DOI: 10.1039/B205850B

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