4. Hydroxychalcones: Synthetic Alternatives to Enhance Oxidative Stability of Biodiesel

In this chapter, the main aspects about biodiesel synthesis and established quality parameters are reviewed and discussed in the perspective of oxidative stability. First, the characteristics, which define biodiesel as a promising, renewable green fuel, are listed. On the other hand, the propensity of biodiesel to oxidation is explained as one of the limitations to its application. Along this line of thought, the majority of natural and synthetic antioxidants usually applied in the industry are discussed, in which it can be noted that phenolic compounds are very representative. Chalcones containing hydroxyl groups in its structure are phenolic compounds, and so, their origins, sources, and synthetic approaches to obtain these types of molecules are presented. Antioxidant effects of hydroxychalcones already reported in the literature are pointed, and then an experimental topic shows the influence of two synthetic hydroxychalcones, namely (E)-1-(2-hydroxyphenyl)-3-phenylprop-2-en-1-one and (E)-1-(2-hydroxyphenyl)-3-(3-hydroxyphenyl) prop-2-en-1-one, on the oxidative stability of biodiesel obtained from frying soybean oil. The effects assessed by calorimetric analysis revealed interesting effects on the enhancement of biodiesel oxidative stability.