Quaternization reaction of aromatic heterocyclic imines in methanol - A case of strong anti-reactivity selectivity principle with isoselective temperature

Abstract

Accurate second-order rate constants were measured at 5 degreesC intervals in the temperature range 20-60 degreesC for the Menshutkin reaction of 1-methylbenzimidazole, 2-amino-1-methylbenzimidazole and N,N-dimethylaniline with iodomethane and iodoethane in methanol. In every case a good linearity in the Eyring plots was observed. Values for the activation enthalpy and entropy are reported. Analysis in terms of Exner's redefinition of the reactivity-selectivity principle (RSP) identified the present reaction series as a case of strong anti-RSP for selectivity towards the substrate. This case is shown to represent an isoselective relationship with the isoselective temperature lower than the experimental temperatures (beta (is) = -52 degreesC). The isokinetic relationship does not hold in the reaction series with a fixed substrate. These findings suggest an early transition state in the Menshutkin reaction of polyfunctional aromatic imines.