Azo–hydrazo conversion. Kinetics of isomerization of 1-tosylazocyclohexene to cyclohex-2-enone tosylhydrazone

Abstract

The spontaneous and base-catalysed isomerization of 1-tosylazocyclohexene to yield cyclohex-2-enone tosylhydrazone has been studied in benzene, dioxan, chlorobenzene, and anisole. In benzene solution, the effectiveness of tertiary amines in catalysing the reaction is roughly proportional to their pK_a measured in water, and related to a consistent decrease in the activation energy. The catalytic activity of triethylamine is solvent-dependent and increases in the order: benzene < dioxan < chlorobenzene < anisole. The uncatalysed reaction is, however, only slightly sensitive to solvent changes. For the base-catalysed reaction, a mechanism is suggested, involving the release of one allylic proton from the cyclohexene ring in a slow step.