Chemically catalyzed oxidative cleavage of unsaturated fatty acids and their derivatives into valuable products for industrial applications: a review and perspective

Oils and fats of vegetable and animal origin have recently attracted growing interest as renewable raw materials in oleochemical industries. This attention arises from not only environmental reasons, but also economic ones. Unsaturated fatty acids (UFAs), as the constituent of lipids, can be oxidized to produce mono-and dicarboxylic acids which are valuable materials in different industries. This oxidation process is called oxidative cleavage, since during the reaction carbon-carbon double bond(s) get cleaved. Although the oxidative cleavage of UFAs has now been developed using ozonolysis, hazardous problems associated with the use of ozone still represent controversial challenges. Replacing ozone with a more benign oxidant requires the use of an active catalyst. Several different combinations of transition metals like Os, Co, Mo, Cr, Au, Mn, Fe, Ru, and W have been investigated for this purpose, with a great deal of emphasis on the latter two, particularly tungsten. In this paper, we have tried to review all of the recent works regarding the use of different catalyst/oxidant systems in the oxidative cleavage of UFAs and their derivatives. Herein, we divided the reported catalytic systems into three classes: homogenous, heterogeneous, and semi-heterogeneous (nanoparticle (NP)-based) catalysts. Important features such as catalytic activity and recoverability, with specific respect to the viewpoint of commercialization, are discussed in a critical fashion for each class to be able to reasonably plan future works. The unique and interesting properties of NPs lead them to be proposed as the frontier of homogeneous and heterogeneous catalysts that can exploit the best features of both simultaneously. These properties, along with recent breakthroughs which would interestingly increase the performance of NP-based catalysts in the biphasic oxidative cleavage reaction of UFAs, are also reviewed.