Kinetic and mechanistic studies of the reactions between 2-nitrothiazole, 2-nitrobenzothiazole and some nucleophiles

Abstract

Kinetic data for the reactions between some 2-nitrothiazoles and nucleophiles (alkoxide and piperidine) are reported. The kinetic behaviour of the nitro group parallels that of the more usual leaving groups and a two-step mechanism involving nucleophilic aromatic substitution may be suggested to be in operation. A change of counter ion (Li⁺, Na⁺, K⁺) of the anionic nucleophile indicates that the presence of the ion pairs partially favours reactivity, probably by interaction with the nitro group. The autocatalytic behaviour of the reactions between 2-nitrothiazole and piperidine is explained by the presence of an interaction between the substrate and the nucleophile in an equilibrium preceding the substitution process. Comparison of the nucleofugicity of nitro and chloro groups (as leaving groups) indicates that the presence of hydrogen bonds between the leaving group and the solvent (or the nucleophile) produces considerable variations in the observed reactivities.