Iron-substituted polyoxotungstates as catalysts in the oxidation of indane and tetralin with hydrogen peroxide

The homogeneous liquid phase oxidation of indane and tetralin with hydrogen peroxide catalysed by tetrabutylammonium salts of iron(III)-substituted polyoxotungstates of general formula [XW11Fe(H2O)O-39](n-), X=P, Si or B is described. The system presented here gives rise to benzylic monooxygenation and dioxygenation products. Indane oxidation reactions produce also dehydrogenation and hydroperoxidation products. As a result, 1H-indene and indane hydroperoxide are formed. Interestingly, tetralin gives rise to the cleavage of carbon-carbon bond, producing 4-(2-hydroxyphenyl)butanal. In the present conditions, this aldehyde is probably arising from tetralin hydroperoxide. Depending on the reaction conditions, moderate selectivities for the corresponding ketones are obtained, affording conversions as high as 59% and 34% for indane and tetralin, respectively. In order to understand the reactions pathway, the oxidation of 1-indanol, 1-indanone, 1H-indene, 1-tetralol and 1-tetralone is also carried out with an iron(Ill)-substituted polyoxotungstate as catalyst and H2O2 as oxidant. The results show that 1-indanol and 1-tetralol give an important contribution for the formation of the corresponding ketones. As far as we know, the use of iron-substituted polyoxotungstates in the oxidation of these arenes is presented for the first time. (C) 2009 Elsevier B.V. All rights reserved.