Direct hydroxylation of 1,4‐Dichlorobenzene to 2,5‐Dichlorophenol over Activated Carbon Catalysts

Abstract

The direct hydroxylation of 1,4‐dichlorobenzene (1,4‐DCB) to 2,5‐dichlorophenol (2,5‐DCP) with green oxidant, to replace the conventional multi‐step processes attracted much attention. In this work, activated carbons were prepared by modification firstly using nitric acid, and then the resultant samples were treated with hydrogen peroxide or thermally under nitrogen flow. The prepared samples were applied as heterogeneous catalysts in the one‐step hydroxylation of 1,4‐DCB, and were characterized by XRD, BET, XPS, and Boehm titration. Acetonitrile, isopropanol, glacial acetic acid, and the mixture of them were used as the reaction solvents and EPR was carried to characterize the reaction systems in these solvents. The reaction parameters, such as the feeding speed of H2O2, moles of 1,4‐DCB used, molar ratio of H2O2 to 1,4‐DCB, mass ratio of catalyst to 1,4‐DCB, reaction temperature, and reaction time were optimized. It was found that the direct hydroxylation of 1,4‐DCB could be efficiently catalyzed by activated carbon with acetonitrile as a suitable solvent. Under the optimized conditions, the highest 2,5‐DCP yield of 14.4 % with selectivity of 86.4 % was obtained. The amount of oxygen functional groups on the activated carbon samples resulted in differences in adsorption capacity of 1,4‐DCB and decomposition rate of H2O2, the integrated effect of which might be responsible for the activity.