ELECTROCHEMICAL OXIDATION OF LIMONENE

Abstract

The electrooxidation of R(+)-limonene was carried out in acetic acid using p-Et4NOTs as supporting electrolyte on platinum electrode at constant current (2.5, 5 and 10 mA) up to 2 F.mol-1 of charge. The influence of the additives LiCl and NaOAc was investigated. Depending on the reaction conditions, the following products were obtained: cis-carvyl acetate, trans-carvyl acetate, p-mentha-1,8-dien-3-ol acetate, perillyl acetate, p-menta-1,8-dien-2-ol acetate, ï?¡-terpinyl acetate, carvone, perilladehyde, cis-dihydrocarvone, trans-dihydrocarvone, cis-carveol, trans-carveol and p-cimenene. The products distribution changed in function of the current and additives. However, acetates were the predominant products. trans-Carvyl acetate is preferentially obtained in the presence of LiCl. The presence of NaOAc increased the overall faradaic yield. The solvation power of limonene by NaOAc could be responsible for this effect. However, in all the conditions investigated the overall faradaic yield was very low even in the NaOAc presence. This phenomenon can be related to the poor solubility of limonene in the reaction medium. The reaction products were identified based on their mass spectra and retention indexes. Keywords: electrochemical oxidation, limonene, catalysis, retention index.