Kinetics and mechanism of the alkaline release of phenyl(mercapto)tetrazoles from α-oximes

Abstract

Compounds such as α-phenyl(mercapto)tetrazole (PMT) oxime (9) undergo rapid elimination of the PMT anion in base via a nitrosoene intermediate. Solution kinetics and HPLC analysis of reaction products are consistent with the mechanism shown in Scheme 2. For open chain oximes such as 4, substitution α to the oxime increases the rate of release of PMT and is attributed to the relief of strain when a crowded reactant is converted to a less-crowded product. For cyclic oximes, the six-membered ring compounds are more reactive than the corresponding five-membered compounds. A linear isokinetic relationship between the entropy and enthalpy of activation was found with β= 346 ± 51 K. Entropies of activation were found to range from –7 to +24 c.u. (1 c.u. = 4.184 J mol^–1 K^–1) and support the proposed mechanism.