Kinetics and mechanism of decomposition of N-chloro-α-amino acids

Abstract

The kinetics of decomposition of N-chloro derivatives of the following amino acids have been studied in phosphate buffer solution in the pH range 6–13: glycine, alanine, 2-aminoisobutyric acid, N-methylglycine, N-methylalanine, 2-(methylamino)isobutyric acid, proline, N-methylvaline, valine, isoleucine, and L-tert-leucine. The rates of decomposition of N-chloro-α-amino acids were found to be independent of the initial concentrations, ionic strengths, buffer concentrations and pH in the studied range. The first-order rate constants were found to increase as the relative permittivity decreased. The decomposition of N-chloroamino acids was followed by either a spectrophotometric method or an iodometric method, and in some cases the reaction was monitored by determining the rate of CO₂ evolution. The three methods gave results that were in good agreement. The effects of both α-carbon substitution and N-substitution on the rate of decomposition were investigated. All the kinetic data obtained appear to be consistent with a concerted mechanism in which dechlorination and decarboxylation take place concomitantly, resulting in the formation of an imine intermediate via an imine-like transition state. The imine may then be hydrolysed to the corresponding aldehyde or ketone, and amine. The kinetic data suggest that factors which influence the stability of the imine-like transition state affect the rate of decomposition of the N-chloro amino acid. The data from the decomposition of N-chloro amino acids may be useful in designing chemically stable, biodegradable germicidal agents.