A moderate and efficient method for oxidation of ethylbenzene with hydrogen peroxide catalyzed by 8-quinolinolato manganese(III) complexes

Hexadentate 8-quinolinolato manganese(III) complexes (Q 3 Mn III ), with ammonium acetate and acetic acid as additives, were found to be active and selective for the side chain oxidation of ethylbenzene with aqueous hydrogen peroxide in environmentally benign acetone–water media, affording acetophenone as a major product. Based on the UV–vis spectra, a free radical mechanism for the Q 3 Mn III catalytic system was also proposed. ▶ Changeable hexadentate 8-quinolinolato mangese(III) complexes. ▶ Novel oxidation catalysts with a feature of pH-regulated molecular switches. ▶ A moderate and efficient method for selective oxidation of ethylbenzene with hydrogen peroxide. The oxidation of ethylbenzene with 30% aqueous hydrogen peroxide (H 2 O 2 ) in an acetone–water medium at 30 °C was investigated using hexadentate 8-quinolinolato manganese(III) complexes (Q 3 Mn III ) as catalysts. The results indicated that the Q 3 Mn III complexes, with ammonium acetate and acetic acid as additives, selectively catalyzed the side chain oxidation of ethylbenzene at secondary carbon atoms, affording acetophenone as a major product. Among the Q 3 Mn III complexes examined, the 5,7-dibrominated Q 3 Mn III catalyst was the most active, and provided the ethylbenzene conversion of 26.1% and the oxidation yield of 65% under the optimum conditions. The influence of various parameters on the reaction was checked in detail. Based on the UV–vis spectra, a free radical mechanism for the Q 3 Mn III catalytic system was also proposed.