Metal catalysts for transesterification of vegetable oils can cause autoxidation side reactions which reduces the fuel quality of the biodiesel. On the other side, oxidation of highly unsaturated oils can open opportunities for the synthesis of other important renewable chemical products. This study reports catalytic oxidation of fatty acids of Jatropha curcas oil (JCO) by Li-CaO/Fe2(SO4)3 catalyst during transesterification at mild reaction conditions. The catalytic oxidation of the triglycerides was shown to be enhanced by the presence of lithium incorporated in the otherwise active catalyst combination of CaO/Fe2(SO4)3 used for high conversion into FAME. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to assess the reaction products. 1. Introduction Biodiesel is a renewable fuel which has similar energy density and physical properties with conventional diesel fuel. Transesterification is the most applied chemical method for biodiesel production from vegetable and nonedible oils. This chemical process proceeds in the presence of either homogeneous or heterogeneous catalysts. Biodiesel can replace the conventional fossil diesel fuel when its specifications on oxidative stability fulfill the European Standard EN 14214 or the American Standard ASTM D6751 [1, 2]. However, there are chemical processes which affect the quality of biodiesel during transesterification process or storage. One of the main causes of loss of quality is autoxidation. Due to the high unsaturated composition of vegetable oils and their derivatives, oxidation is a common phenomenon. Autoxidation of unsaturated oil and fatty acid methyl esters is a chemical reaction which can be initiated by thermolysis at elevated temperature, by the presence of metal catalysts or impurities, by hydrolysis in the presence of humid medium, or photolysis due to exposure to light [3–5]. Autoxidation proceeds by radical mechanism in the presence of molecular oxygen as oxidant. Although autoxidation usually has an induction time and is dependent on the structure of the saturated or unsaturated fatty acid of the feedstock and final product, the initial oxidation step is believed to proceed through hydroperoxide formation resulting in the creation of compounds such as acids and aldehydes or further reaction with another group of fatty acids to form dimers [2, 6–8]. Catalytic autoxidation has been used in many organic reactions and transition metal catalysts are frequently mentioned as the type of heterogeneous catalysts in the process [9, 10].
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