New Environmentally Friendly Oxidative Scission of Oleic Acid into Azelaic Acid and Pelargonic Acid

Oleic acid (OA) is a renewable monounsaturated fatty acid obtained from high oleic sunflower oil. This work was focused on the oxidative scission of OA, which yields a mono-acid (pelargonic acid, PA) and a di-acid (azelaic acid, AA) through an emulsifying system. The conventional method for producing AA and PA consists of the ozonolysis of oleic acid, a process which presents numerous drawbacks. Therefore, we proposed to study a new alternative process using a green oxidant and a solvent-free system. OA was oxidized in a batch reactor with a biphasic organic-aqueous system consisting of hydrogen peroxide (H₂O₂, 30 %) as an oxidant and a peroxo–tungsten complex Q₃{PO₄[WO(O₂)₂]₄} as a phase-transfer catalyst/co-oxidant. Several phase-transfer catalysts were prepared in situ from tungstophosphoric acid, H₂O₂ and different quaternary ammonium salts (Q⁺, Cl–). The catalyst [C₅H₅N(n-C₁₆H₃₃)]₃{PO₄[WO(O₂)₂]₄} was found to give the best results and was chosen for the optimization of the other parameters of the process. This optimization led to a complete conversion of OA into AA and PA with high yields (>80 %) using the system OA/H₂O₂/[C₅H₅N(n-C₁₆H₃₃)]₃{PO₄[WO(O₂)₂]₄} (1/5/0.02 molar ratio) at 85 °C for 5 h. In addition, a new treatment was developed in order to recover the catalyst.