Separation of Palmitic and Palmitoleic Acid Using Transition Metal Salts: Experimental vs Theoritical Analyses

Fatty acids (FAs) play a major role in many physiological functions and offer various health benefits. Separation and isolation of fatty acids thus, is of great interest. A set of experiments were conducted to evaluate the effectiveness of select transition metal salts in separating a saturated FA from mixture of C16:0 and C16:1 FAs. In an initial study, ZnSO4, CuSO4 and AgCl were able to cause significant precipitation of C16:0 FA from a mixture of C16:0 and C16:1 FAs in methanol. A follow-up study was conducted to ascertain the effect of ZnSO4 concentration on the ability to separate individual FAs from a mixture of saturated and unsaturated FAs in methanol. Results indicated that a 30 mg/ml ZnSO4 solution could remove 58% of C16:0 FA from a mixture containing both the saturated and the unsaturated FA forms. IR spectra suggest formation of a complex between zinc ion and the carboxylate group of the C16:0 FA, which in turn may cause precipitation. Computational chemistry calculations indicate that specific complex formation with the saturated FA might be due to more favorable thermodynamics between zinc ion - C16:0 FA complexation (with more negative value of Gibbs free energy of the reaction) than that between the metal ion and the unsaturated FA.