The chlorination of N-methyl amino acids with hypochlorous acid: kinetics and mechanisms

Simon, Fruzsina and Kiss, Eszter and Szabó, Mária and Fábián, István (2020) The chlorination of N-methyl amino acids with hypochlorous acid: kinetics and mechanisms. CHEMICAL RESEARCH IN TOXICOLOGY. pp. 1-27. ISSN 0893-228X (print); 1520-5010 (online)

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Abstract

The formation and decomposition kinetics of N-chloro-N-methyl amino acids were studied to predict the fate and impact of these compounds in water treatment technologies and biological systems. These compounds form in fast second order reactions between N-methyl amino acids and hypochlorous acid. The comparison of the activation parameters for the reactions of Nmethyl substituted and non-substituted branched chain amino acids reveals the transition state features less organized structure and stronger bonds between the reactants in the reactions with the N-methyl derivatives. This is due to a combined positive inductive effect of the N-methyl group and the alkyl sidechain, as well as to the steric effects of the substituents. N-methyl-Nchloro amino acids decompose much faster than the non-substituted compounds. The reaction rates do not depend on the pH and the same final product is formed in the entire pH range. N-chlorosarcosine is an exception, it decomposes via competing paths, kdobs = kd+ kdOH[OH−], yielding different final products. This feature is most likely due to the lack of an alkyl substituent on the α-carbon atom. Under physiological pH, aldehydes and methylamine form in these reactions which are not particularly toxic.

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