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.
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