Novel Triazenes and Triazolines from the Base-Catalyzed Hydrolysis of 1,3-Dialky1-3-acyltriazenes

The products and mechanism of hydrolytic decomposition of a series of 1,3-dialkyl-3-acyltriazenes were studied in alkaline buffers. In general the mechanism of decomposition involves deacylation leading to the formation of the parent 1,3-dialkyltriazene. The solvent deuterium isotope effect (k_H2O/k_D2O) is less than 1.0, indicating specific base catalysis. A plausible mechanistic explanation is rapid reversible attack by hydroxide ion, followed by rate-limiting heterolysis of the N(1)-acyl bond. The resultant, 1,3-dialkyltriazene is somewhat unstable under the reaction conditions and undergoes subsequent hydrolysis, a reaction previously shown to be specific acidcatalyzed. When the N(1) alkyl group is 2-chloroethyl, unusual products are obtained. For the 3-acetyl and 3-carbethoxy derivatives, the initial deacylation product, 1-(2-chloroethyl)-3-methyltriazene, efficiently cyclizes to form 1-methyltriazoline. The 3-(methylcarbamoyl) derivative does not deacylate, but instead undergoes dehydrohalogenation to 1-vinyl-3-methyl-3-(methylcarbamoyl)triazene.