The Keggin-type anions [Mn-III(H2O)BW11O39](6-) and [BW12O40](5-) were used for the first time as catalysts in studies of oxidation of monoterpenes by hydrogen peroxide. The oxidation of geraniol 1, nerol 2, (+)-3-carene 3, thymol 4 and carvacrol 5 was examined. The reactions were carried out in acetonitrile, at room temperature (for 1 and 2) or at reflux (for 3, 4 and 5). Compounds 1 and 2 were preferentially epoxidised at the C-2-C-3 double bond, whereas 3, under controlled reaction conditions, could afford only the alpha-epoxide. The oxidation of 4 and 5 yielded a mixture of benzoquinones. For tetrabutylammonium salts, the Mn-III substituted anion was found to be a more efficient catalyst than [BW12O40](5-). The infrared spectra of the recovered solids at the end of reaction showed that the Keggin anions were still present, but the electronic spectra of the manganese residues indicate that oxidation of Mn-III had taken place. (C) 2002 Elsevier Science B.V. All rights reserved.