Catalytic activity of chromium(III), iron(III) and bismuth(III) complexes of 1,2-bis(2-hydroxybenzamido)ethane (H2hybe) encapsulated in zeolite-Y for liquid phase hydroxylation of phenol

Abstract

Iron(III), chromium(III) and bismuth(III) complexes of amidate ligand 1,2-bis(2-hydroxybenzamido)ethane (H2hybe) encapsulated in the super cages of zeolite-Y have been isolated and characterized by various physico-chemical measurements. 3D model structure generated for [Fe(hybe)·2H2O]+ suggests that zeolite-Y can accommodate these complexes in its super cages without any strain. These encapsulated complexes catalyze hydroxylation of phenol using H2O2 as oxidant to give catechol as a major and hydroquinone as a minor product. A suitable reaction condition has been optimized for [Fe(hybe)·2H2O]Cl–Y by considering the effect of various parameters such as concentration of substrate, amount of oxidant and catalysts, reaction time, temperature, and volume of solvent for the maximum hydroxylation of phenol. The results obtained over these new encapsulated catalysts showed that selectivity of the catechol formation is ca. 85%, though transformation of phenol varied in the order [Fe(hybe)·2H2O]Cl–Y (43.5%)>[Cr(hybe)·2H2O]Cl–Y (32.8%)>[Bi(hybe)·2H2O]Cl–Y (30.6%). Catalytic performance of these catalysts has been compared with different metal complexes encapsulated in zeolite-Y.