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The solubility of benzoic acid in (acetic acid + water) and (acetic acid + toluene) binary mixtures has been investigated by the gravimetric method. The study was carried out at different mass fractions of acetic acid ranging from 0.1 to 0.8 at 299.15 K. The results indicated that the solubility of benzoic acid in both binary mixtures exhibited an increasing trend with an increase in the mass fraction of acetic acid. The solubility of benzoic acid with respect to acetic acid in the (acetic acid + water) mixture was less than that in the (acetic acid + toluene) mixture. Furthermore, the refractive indices, n D , and densities, ρ, have been measured for (acetic acid + water) and (acetic acid + toluene) binary mixtures as well as mixtures saturated with benzoic acid salt at different temperatures over the entire composition range, and the same have been reported. The molar refractivity, R m , was estimated using refractive index, n D , and molar volume, V m , employing the Lorentz−Lorenz equation. The excess properties, namely deviations in molar refractivity, ΔR, and excess molar volumes, V m E , were calculated for both binary mixtures. The deviations in molar refractivity resulted in negative values for both binary mixtures, whereas the excess molar volumes V m E gave negative values for the (acetic acid + water) mixture and positive values for the (acetic acid + toluene) mixtures. The results obtained in the present study are discussed in terms of structural packing and interactions present among the mixing components and are fitted to the Redlich−Kister third order polynomial equation. Different mixing rules were also employed to predict the refractive index and compared with experimental values.

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Kinetic studies have been carried out on the esterification of free fatty acids (FFAs) in jatropha oil with methanol in the presence of sulphuric acid catalyst at 5 and 10 wt% concentrations relative to free fatty acids (0.4–0.8 wt% relative to oil) and methanol–FFA mole ratios ranging from 20:1 to 80:1. It has been found that a 60:1 methanol–FFA mole ratio and 5 wt% catalyst at 60°C and 500 rpm or above provided a final acid value lower than 1 mg KOH/g oil within 60 min. A kinetic model has been proposed with second‐order kinetics for both the forward and backward reactions. The effect of temperature on the reaction rate constants and equilibrium constant has been determined using Arrhenius and von't Hoff equations, respectively. The heat of reaction was found to be −11.102 kJ/mol.

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