Nucleophilic replacement by catalytic methanolysis: Interaction of benzimidazole-2-thione with 2,3-dicholo-5,6-dicyano-1,4-benzoquinone involving substitution reaction via initial charge transfer complexation

Interaction of benzimidazole-2-thione (MBI) with a typical π-type charge transfer acceptor, 2,3-dicholo-5,6-dicyano-1,4-benzoquinone (DDQ) has been studied by using several spectral techniques, viz. UV/Visible, FT-IR, 1H and 13C NMR and Mass spectra. Electronic absorption spectra of the system MBI-DDQ in methanol, a protic solvent, have indicated initial formation of an outer-sphere charge transfer (CT) complex (MBI.DDQ). Formation constant (KCT), molar absorption coefficient (εCT) and the thermodynamic properties, ΔH, ΔS, and ΔG, of this CT complex have been determined and discussed. The first formed CT complex (MBI.DDQ) has led to a substitution reaction involving a nucleophilic replacement catalyzed by methanol.