The Role of the Supporting Electrolyte in the Electrochemical Methoxylation of 4-Methylanisole

Abstract

The subject of this paper is the mechanism and kinetics of 4-methylanisole methoxylation in NaClO4 -methanol and KF-methanol solutions. The electrochemical behavior of 4-methylanisole, 4-methoxy-benzyl-methyl-ether, and 4-methoxybenzaldehyde-dimethylacetale was studied by voltammetry on both stationary and a rotating disk electrode. While NaClO4 classically behaves as an indifferent supporting electrolyte, in methanol solutions KF is electrochemically active in the potential region identical to that of the organic compounds studied. The mechanism of this interaction remains unclear. Methoxylation kinetics of the individual compounds was described in terms of Tafel kinetics. A generalized form of the Tafel equation was utilized to determine the rate-determining step of the methoxylation process in the presence of NaClO4. Batch experiments revealed that the selectivity of methoxylation in NaClO4 electrolytes is low, mainly due to the oligomerization of the methoxylation intermediates and the fast 4-methoxybenzaldehyde dimethylacetale overoxidation. The process proceeded with high selectivity to the 4-methoxybenzaldehyde-dimethylacetale in the presence of KF as the supporting electrolyte. ? 2009 The Electrochemical Society.