Study On The Synthesis Of Phytosteryl Esters Using Ionic Liquids And The Separation Process

Phytosterols, which have a structure that is very similar to that of cholesterol, are widely known for their effect in lowering serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) absorption. Over the last decade, acidic ionic liquids (ILs) had been extensively investigated for many chemical and biochemical transformations because they have high catalytic capacity, easy separation and recovery properties. The esterification of phytoserol and fatty acids would be studied in the presence of ionic liquids for the first time.Six common ionic liquids, including [Bmim]BF4, [Bmim]CF₃SO₃, ChCl·2SnCl₂, ChCl·2ZnCl₂, ChCl·2.5SnCl₂ and ChCl·2FeCl₃, were evaluated to determine the satisfactory catalyst for the esterification, and the results showed that ChCl·2SnCl₂ was the most suitable catalyst in this study. The ionic liquid could be reused for many times and the structure of the spent IL remained intact. Moreover, it was found that the catalytic activity of ionic liquids for the esterification enhanced with the increase of their Lewis acidity, which was determined by pyridine as IR spectroscopic probe.The effect of dose of ChCl·2SnCl2, molar ratio of lauric acid to phytosterol, reaction temperature and time on the esterification of phytosterol and laurate acid were researched. Response surface methodology (RSM) based on a three-level, four-variable Box-Behnken design (BBD) was used to evaluate the interactive effects of these variables. The optimum conditions derived via RSM were: substrate molar ratio 2.9:1, dose of IL 6.6, 148 oC, and 4.3 h, and the esterification rate could reached a greatly high level of 92.30%. With the comparison of esterification rate and peroxide value, the reaction conditions were further surveyed in the synthesis of phytosterol and linoleic acid and the experimental esterification rate reached a greatly high level of 90.12% using ChCl·2SnCl2 as catalyst with the molar ratio 2:1 (linoleic acid : physterols) at 160 oC for 4 h.The reaction kinetics of phytosterol with linoleic acid and laurate acid using ionic liquid ChCl·2SnCl2 as catalyst were studied. It confirmed that the esterification could be considered as a second-order irreversible reaction. Morover, the reaction activitation energy of the synthesis of phytosteryl linoleate was about 81.08 kJ/mol and reaction rate equation could be expressed as r = 4.07×10¹⁰exp[81.08/(RT)]cAcB. The reaction activitation energy and reaction rate equation of the synthesis of phytosteryl laurate was about 58.55 kJ/mol and r = 1.27×10⁷exp[58.55/(RT)]cAcB.TLC, HPLC, FT-IR, and NMR analyses were adopted to evaluate the phytosterol and synthesized phytosteryl esters. The solubility properties of phytosterol and phytosteryl esters in different organic solvent were investigated which showed that n-hexane and ethanol could be considered as the extraction solvents. Moreover, the separation and purification processes for phytosteryl laurate were researched with the comparison of purification and recovery rate. The composition of n-hexane, ethanol and NaHCO3 were selected as extraction solvents and the separation process conditions were also explored.