Investigation of [Ni{Me4Bzo2[14]aneN4}]Cl2 catalyzed selective hydroxylation of phenol to catechol by H2O2 in the homogeneous medium

Chemical and electrochemical conversion of phenol to 1,2-dihydroxy benzene using H2O2 as oxidant was studied in presence of[Ni{Me(4)Bzo(2)[14]aneN(4)}]Cl-2 as homogeneous catalyst. The reaction products were analyzed using gas chromatograph. The phenoxide salt of the complex, [Ni{Me(4)Bzo(2)[14]aneN(4)}](C6H5O)(2) exhibits a new irreversible oxidation wave at E-p.c 0.45 V versus Ag/AgCl, which is unlike that observed in its dichloride salt with E-p.c 0.25 V, and arises due to catalyzed electro-oxidation of the phenoxide counter ions. The chemical oxidation by H2O2 was investigated in presence of different solvents and a predominant formation of catechol was observed over hydroquinone (with molar ratio 9:1). The reaction conditions were optimized, in terms of the effect of reaction temperature, amount of catalyst, H2O2 concentration, phenol concentration, nature and volume of solvent used, reaction time and pH, for the maximum transformation of phenol as well as for better selectivity towards the formation of catechol. (C) 2004 Elsevier B.V All rights reserved.