Catalytic activity of a dinuclear manganese complex (MnMeTACN) on the oxidation of ethyl linoleate

Abstract

Catalytic activity of a dinuclear manganese-based complex [Mn 2 IV (μ-O) 3 L 2 ](PF 6 ) 2 (MnMeTACN) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), and its combination with a polyamine, 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), was investigated on the oxidation of ethyl linoleate (EL). When MnMeTACN was molecularly mixed with EL in a co-solvent (methanol), MnMeTACN alone was found to be a very active catalyst for the oxidation of unpurifed EL (containing a small amount of hydroperoxides), similar to the catalytic activity of a Co-based catalyst. For purified EL (free of hydroperoxides), the addition of tert -butyl hydroperoxide was necessary to rapidly initiate the EL oxidation. A tentative catalytic cycle for MnMeTACN was proposed on the basis of electrospray ionization mass spectrometry (ESI-MS) investigation. The existence of HMTETA significantly accelerated the decomposition of the formed hydroperoxides into alkoxy free radicals, which in turn led to a high level of volatile aldehyde byproducts due to β-scission reactions. The catalytic activity of a dinuclear manganese-based complex, [Mn IV 2 (μ-O) 3 L 2 ](PF 6 ) 2 (MnMeTACN) on the oxidation of ethyl linoleate (EL) was found to be similar to that of a Co-based catalyst. The presence of hydroperoxide was necessary to rapidly initiate the EL oxidation. A tentative catalytic cycle for MnMeTACN was proposed on the basis of ESI-MS investigation.