REACTIONS OF AZOLIUM CATIONS .1. KINETICS AND MECHANISM OF ALKYLATIONOF 5-PHENYLTETRAZOLE WITH ISOPROPYL-ALCOHOL IN AQUEOUS SULFURIC-ACID MEDIA

Alkylation of 5-phenyltetrazole with isopropyl alcohol in 84-99% sulfu ric acid medium occurs regioselectively at N2 position of the heterocy cle to produce 2-isopropyl-5-phenyltetrazole. The regioselectivity is conditioned by 1H, 4H-5-phenyltetrazolium cation being the alkylation substratum. The reaction mechanism is proved to be two-stage one. Its first and rate-limiting stage is an interaction between the azolium ca tion and isopropyl cation generated from protonated isopropyl alcohol. The reaction rate constant was estimated as 0.47 L mol-1 s-1 at 25-de grees-C. Water activity scale was used for quantitative description of equilibrium of isopropyl cation formation from the protonated alcohol , and the equilibrium constant pK(R+) = -5.3 was evaluated from the da ta of the alkylation kinetics. (C) 1993 John Wiley & Sons, Inc.