Selective Oxidation of Phenol in the Presence of Transition-Metal Substituted Polyoxometalates

Abstract

Tetrabutylammonium salts of lacunary Keggin anions with supported Co and Mn cations soluble in organic solvents were prepared and characterized by thermogravimetric analysis, FTIR spectroscopy and X-ray diffraction. These salts were applied as catalysts for phenol oxidation in acetonitrile solution with iodosobenzene diacetate as single oxygen donor. Deposition of cobalt ions in the lacunary Keggin anions strongly increases the catalytic activity. The conversion of phenol is proportional to concentrations of catalyst and single oxygen donor. The dependence of the conversion of phenol on time indicates that the reaction is 1st order with respect to phenol. The catalyst retains its activity after recycling. On the basis of catalytic results reaction mechanism was elucidated.

Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

“…A review of the literature shows greater attention given to systems where the cobalt cation (Co 2+ ) occupies the position of the addenda atom . Modified systems, usually synthesized as various salts, as well as the comparison with systems modified by other transition metals, were tested in oxidation reactions in the presence of hydrogen peroxide [17][18][19][20][21][22], molecular oxygen [23][24][25][26][27][28], air [29][30][31][32][33], iodosylarenes [35,36], or t-butyl hydroperoxide [37,38]. Cobalt-modified Keggin heteropolyanin exhibits high catalytic activity and selectivity in processes such as oxidation of cyclohexane [26,27,35,37,38,40], esterification of n-butanol [25,39], epoxidation of olefins (cyclohexane, 1-hexene, norbornene, cyclooctene) [25], phenol oxidation [23], oxidation of methyl isobutyrate [24], oxidation of alpha-pinene [40], oxidation of alcohols 2-propanol [19] and hexanol [20], and lactonization of diols [22].…”