Novel Schiff base complexes as catalysts in aerobic selective oxidation of β-isophorone

Abstract

A series of novel metal–Schiff base complexes with the general formula ML n X m (where M = Cu, Ce, Nd, etc., L = disalicylaldehyde–arginine (DSALA) and the derivatives, n = 1, 2, X = Cl, m = 1, 2, 3) have been synthesized and applied in aerobic oxidation for the first time, especially, the oxidation of β-isophorone to keto-isophorone was explored. The ML n X m complexes were synthesized from arginine, salicylaldehyde with the derivatives and metal chloride. They were characterized by physicochemical methods such as elemental analysis, IR, 1H NMR and 13C NMR spectra, etc. A new practical method was studied for β-isophorone oxidation with Cu–DSALA and the derivatives. Compared with the general ones, the catalysts described herein are much more efficient with the β-isophorone conversion up to nearly 100% and the keto-isophorone yield exceeding 95%. Moreover, the catalysts in use were much less than that of salen catalysts, while the reaction time was relatively shorter. Additionally, the mechanism of β-isophorone oxidation with influence factors such as temperature, catalyst, solvent, assistant solvent, etc. were also studied in detail.