One-Pot Aerobic Cleavage of Monounsaturated Lipids Catalyzed by Mixed Oxides

The oxidative cleavage of nonedible monounsaturated lipids such as restaurant olive oil or oil extracted from high oleic sunflowers (HOSO) is a method to produce useful C9 mono- and dicarboxylic acids, namely, pelargonic and azelaic acids. In this study, we describe the synthesis and application of mixed oxides as cheap, recoverable, and reusable catalysts for the one-pot conversion of nonedible oils into products that may find application in several fields, from the cosmetic industry to the agrochemical sector (pelargonic acid) and to the biopolymer technologies (azelaic acid). The catalysts developed use oxygen as an oxidant and the alcohol selected for producing esters as a solvent or can operate in solventless conditions. The same catalyst is used for oxidation and transesterification/esterification. Oxidation is carried out under moderate PO₂ (0.6–0.8 MPa) and temperature (413–433 K) for 2–3 h. The conversion yield and selectivity toward 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) has been obtained, which represents the best cases so far available. The reaction pathway has been detected using a flow reactor that has allowed us to detect the species formed with time and measure their concentration using gas chromatography–mass spectrometry (GC–MS). This research has produced five key innovations: (i) a one-pot one- or two-step process for the conversion of monounsaturated oils into mono- and dicarboxylic acids; (ii) use of oxygen as an oxidant instead of ozone or hydrogen peroxide; (iii) elimination of sulfuric acid in the esterification/transesterification reaction; (iv) use of cheap, recoverable, and reusable mixed oxides as catalysts; and (v) use of a single catalyst for both the oxidation and esterification–transesterification reactions.