Enthalpies of Solutions of Four Triacylglycerols in Trichloromethane and Benzene at Infinite Dilution at 298.15K

Abstract

Enthalpies of solution of four triacylglycerols (triglycerides) in trichloromethane and in benzene were measured calorimetrically at infinite dilution at 298.15K. All compounds dissolve in both solvents endothermally. In order to compare their enthalpy-of-solution values with those of methyl alkanoates, the observed values were transformed into those at the hypothetical liquid state at 298.15K, by the use of molar enthalpies of fusion and molar heat capacities reported by Charbonnet and Singleton. In the course of evaluation of the enthalpies of fusion at 298.15K, although large uncertainites may be introduced into them, the results show that triglycerides dissolve in trichloromethane with evolution of heat, while they dissolve in benzene with absorption of heat. Comparing the enthalpies of solution of the liquid triglycerides with those of methyl alkanoates and with those of soybean oil, it can be concluded that in trichloromethane solutions trilaurin, trimyristin, and tripalmitin molecules take an asteroid conformation, while tristearin molecule has a conformation in which only end groups of three acyl groups apart one another and their roots are in a bundled state. In benzene solutions, on the contrary, three acyl groups of each triglyceride molecule are all bundled, and only outer surface of the bundled acyl groups can contact with the solvent molecules.