Ring opening and closing in heterocyclic compounds. Kinetic studies on solvent effects in the reaction between 6-nitrobenzothiazole and methoxide ion at 25 °C

Abstract

Kinetic studies on the ring opening reaction between 6-nitrobenzothiazole and methoxide ion in DMSO–MeOH at 25 °C are reported. The results demonstrate that dipolar aprotic solvents increase the equilibrium constant between reagents and the Meisenheimer-like adduct (2). The equilibrium constant between anion (2) and 2-methoxymethyleneamino-5-nitrobenzenethiolate (3) is lowered by this solvent mixture. The net effect of these counteracting influences is such that the DMSO favours the ring opening process.