Studies on the Kinetics and Mechanism of Decomposition of Di- and Tri -Substituted Triazenes

Abstract

The kinetics of decomposition of various di- and tri-substituted triazenes in aqueous buffer were investigated. Determination of the rates of decomposition of 1,3-di-n-butyl-3-methyltriazene strongly support the conclusion that the reaction is specific acid catalyzed. This implies that the reaction involves a fast, reversible protonation of the triazene followed by the rate-determining heterolysis of the protonated species to the n-butyldiazonium ion and n-butylmethylamine. The kinetic analysis of the decomposition of 1,3-dimethyltraizene in nitrogen-acid buffers, such as CAPS, also supports a mechanism which involves specific acid catalysis. However, the decomposition of 1,3- dimethyltraizene in oxygen-acid buffers, such as phosphate, indicates a specific acid/general base catalyzed mechanism. These data imply that the decomposition of 1,3-dimethyltriazene in oxygen-acids involves a fast, reversible protonation of the triazene followed by a rate determining step in which a proton, different from the one involved in the first step, is transferred from the protonated triazene to the conjugate base of the general acid. The resulting products from this decomposition were postulated to be diazomethane and methylamine. The possibility of a methyldiazonium ion-diazomethane equilibrium was also examined. The results indicate that at pH 7.4 the methyldiazonium ion equilibrates it's hydrogens with a deuterated buffer and that the dynamic equilibrium involves the formation of diazomethane. Previously it has been assumed that the methyldiazonium ion remained intact at physiological pH. The data may have an important impact on the understanding of the interactions of methyldiazonium ions with biological systems.