Micellar catalyzed hydroxylation of 1,2,3-trichloro-4,6-dinitrobenzene: Role of cationic head group-π interaction

The micellar catalysis of the hydroxylation of 1,2,3-trichloro-4,6-dinitrobenzene (DNTCB) with aqueous NaOH, to synthesize 2-chloro-4,6-dinitroresorcinol (CDNR), was studied using cationic, anionic and non-ionic surfactants at different concentrations to promote the reaction kinetics. The micellar catalysis using cationic surfactants at optimum concentrations was effective giving highest conversion of DNTCB (92-100%), which was ascribed to high solubilization capacity of the micellar solutions for DNTCB, surface positive charges of micelles increasing OH- ions concentration near micellar surface, and the cation-rr interaction of surfactant molecules (through cationic head group) with DNTCB molecules. The cation-rr interaction plays important role in solubilization process, substrate activation and catalysis of the reaction. The higher surfactant concentrations retard the reaction owing to strong solubilization of DNTCB in micelles and reduced OH- ions concentration around the micelles. The cationic micellar solutions at optimum surfactant concentrations can be effective catalytic system for the aromatic nucleophilic substitution reactions. (C) 2020 Elsevier B.V. All rights reserved.