Aerobic oxidation of 2,3,6-trimethyl-phenol to trimethyl-1,4-benzoquinone with 2.5 mol% copper(II) chloride as catalyst in ionic liquid 1-n-butyl-3-methyl-imidazolium chloride, [BMIm]CI, with n-butanol as co-solvent affording 86% yield provides a new alternative to the copper(II) chloride catalysed aerobic oxidation. The advantage of this catalytic system is that only a catalytic amount of copper(II) chloride is necessary. This catalytic system is also applicable for oxidation of 2-methyl-1-naphthol to 2-methyl-1,4-naphthoquinone. This catalytic reaction was systematically investigated under different conditions. (c) 2005 Elsevier B.V. All rights reserved.