Flexible ligand synthesis, characterization and liquid phase hydroxylation of phenol by H2O2 with host (nanopores of zeolite-Y)/guest [VO([R]2–N2X2)]2+ (R = H, CH3; X = NH, O, S) nanocomposite materials

Abstract

Encapsulation of Oxovanadium(IV) complexes of 12-membered macrocyclic ligands having N2O2, N2S2 and N4 donor atoms in the nanocavity of zeolite-Y by the Flexible-Ligand Method (FLM) have been described. Oxovanadium(IV) complexes with macrocyclic ligands were entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of precursor ligand; 1,2-di(o-aminophenyl-, amino, oxo, thio)ethane, (N2X2); in the supercages of VO(IV)-Y; ([VO(N2X2)]2+-Y (X = NH, O, S); and (ii) in situ condensation of the oxovanadium(IV) precursor complex with glyoxal or biacetyl; [VO([R]2–N2X2)]2+-Y (R = H, CH3). The new Host–Guest Nanocomposite Materials (HGNM, [VO([R]2–N2X2)]2+-Y) have been characterized by FT-IR, DRS and UV–Vis spectroscopic techniques, XRD and elemental analysis, as well as nitrogen adsorption. Liquid-phase selective hydroxylation of phenol with H2O2 to a mixture of catechol and hydroquinone in CH3CN has been reported using [VO([R]2–N2X2)]2+-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, effect of time, volume of solvent and temperature. Under the optimized reaction conditions, [VO([H]2–N4)]2+-Y gave 50.1% conversion of phenol after 6 h. All these catalysts are more selective toward catechol formation.