Determination Of Enthalpies Of Formation Of Fatty Acids And Esters By Density Functional Theory Calculations With An Empirical Correction

Abstract

Scarcity of reliable thermochemical data of biodiesel molecules motivated the use of computational calculations to accurately predict standard enthalpies of formation of fatty acids and esters by combining B3LYP/6-311+G(d,p) calculations with an empirical correction. This correction is based on information on the molecular structure and is optimized by using the least-squares method to minimize the deviation between theoretical and experimental enthalpies for some fatty acids and esters. The mean absolute deviation between calculated and experimental enthalpies decreased from 122.3 to 5.3 kJ mol(-1) when the parametric correction equation was applied to the B3LYP/6-311+G(d,p) results for fatty acid molecules. The calculated data were used to estimate thermochemical properties of the esterification reactions of oleic and linoleic acids with methanol. Results confirmed the endothermic and the nonspontaneous characteristics of these reactions. Thus, the proposed correction is a suitable alternative to calculate thermodynamic properties of fatty acids and esters, with remarkable accuracy and low computational cost.