Mechanistic investigation of the anodic oxidation of p-methoxytoluene in dry and wet acetonitrile

Alkyl aryl ethers are oxidized in acetonitrile in two very closely spaced w aves. A detailed investigation has been carried out in the case of p-methox ytoluene, using both voltammetry and preparative electrolysis. The kinetics of the first anodic peak correspond to a second order rate law, both in an hydrous medium, and in the presence of water. On the preparative scale, the controlled potential electrolysis at a potential located on the first wave gives different products depending on the operating conditions. When small amounts of water were present, two new compounds were obtained as the majo r products: a 2,5-cyclohexadienone substituted in the 4 position by the sta rting compound, and the phenol resulting from an acid catalyzed rearrangeme nt of this cyclohexadienone. A mechanism accounting for the nature of the r eaction products in wet acetonitrile is proposed on the basis of the voltam metric and coulometric data as well as of the result of the electrolysis pe rformed in the presence of O-18 labeled water. (C) 1999 Elsevier Science S. A. All rights reserved.