One-Pot aerobic cleavage of mono-unsaturated lipids catalyzed by mixed-oxides

The oxidative cleavage of non-eatable monounsaturated lipids such as restaurant olive oil or oil extracted from high oleic sunflowers-HOSO is the way to produce useful C9 mono- and di-carboxylic acids, namely pelargonic and azelaic acid, respectively. In this paper we describe the synthesis and application of mixed oxides as cheap, recoverable and reusable catalysts for the one-pot conversion of non-eatable oils into products that may find application in several fields, from the cosmetic industry, to the agrochemical sector (pelargonic acid) and to the bio-polymer technologies (azelaic acid). The catalysts developed use oxygen as oxidant and the alcohol selected for producing the esters as solvent or can operate in solventless conditions. The same catalyst is used for oxidation and transesterification/ esterification. The oxidation is carried out under moderate PO2 (0.6-0.8 MPa) and temperature (413-433 K) in 2-3 h. The conversion yield and selectivity towards the target products depend on both the catalyst composition and the reaction conditions. In best cases, 63-72% of a mixture of C7-C9 acids with 40-56% of C9 (% yield of C9 with respect to the starting oil) have been obtained that represent the best cases so far available. The reaction pathway has been revealed by using a flow-reactor that has allowed to detect along time the species formed and measure their concentration by GC-MS. This research has produced five key innovations, namely: i. One-pot one- or two-step process for the conversion of mono-unsaturated oils into mono- and di-carboxylic acids; ii. Use of oxygen as oxidant instead of ozone or hydrogen peroxide; iii. Elimination of sulphuric acid in the esterification/transesterification step; iv. Use of cheap-, recoverable-and reusable-mixed oxides as catalysts; v. Use of a single catalyst for both the oxidation and esterification-transesterification steps.