Supported sulfonic acids: Metal-free catalysts for the oxidation of hydroquinones to benzoquinones with hydrogen peroxide

Some silica- and polystyrene-supported sulfonic acids, prepared by tethering or sol-gel techniques, were employed as metal-free heterogeneous catalysts in the oxidation of hydroquinones to the corresponding 1,4-benzoquinones, carried out with 30% aqueous hydrogen peroxide. The activity of these catalysts was tested in the model oxidation of methylhydroquinone under batch conditions: high yield and selectivity at room temperature and under environmentally friendly conditions can be achieved in the presence of SiO2-(CH2)(3)-SO3H. The heterogeneous catalyst, that can be easily recovered by simply filtration, can be used for at least three cycles affording the same good results (similar to 80% yield, similar to 91% selectivity). (C) 2011 Elsevier B.V. All rights reserved.