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