Decomposition of pyridinyltriazenes in aqueous buffer: Kinetic and mechanistic comparison with other aryltriazenes

1-(X-pyridinyl)-3-alkyltriazenes where X = 2, 3 or 4 were prepared as prototypes of new chemotherapeutic agents. The products of their decomposition in aqueous buffer were the corresponding aminopyridines and alkyl alcohols. pH-rate profiles (pH 3.5-12.00) gave sigmoid curves with slopes asymptotically approaching 0 at the extremes. Near neutral pH, the half-life of the 2 and 4-isomers is $\sim$100x shorter than that of the 3-isomer. This difference can be explained by protonation of the pyridinyl N, which leads to direct dissociation only for the 2- and 4-isomers. The reactions were specific acid catalyzed (A1), for 2-PBT and specific acid followed by general base catalysis (A2) for 3-PBT and 4-PBT. The solvent isotope effect was $<$1.0 and there was no dependence upon buffer concentration.