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Synthesis and Tribological Investigation of Lipoyl Glycerides

Girma Biresaw, Joseph A. Laszlo, Kervin O. Evans, David L. Compton, Grigor B. Bantchev
Journal of agricultural and food chemistry 2014 v.62 no.10 pp. 2233-2243
free fatty acids, high performance liquid chromatography, mass spectrometry, enzymatic interesterification, density, alcohols, sunflower oil, viscosity, differential scanning calorimetry, oxidation, food chemistry, triacylglycerols, oxidative stability, solubility, lipoic acid, cold, pressure, surface tension, mixing, transesterification, solvents
Lipoyl glycerides were synthesized by enzymatic transesterification of lipoic acid with high-oleic sunflower oil in 2-methyl-2-butanol solvent. The synthesis gave a crude product mixture comprising unreacted lipoic acid, free fatty acids, and several lipoyl glyceride structures of varying lipoic acid substitution. A more purified product mixture, devoid of unreacted lipoic acid and free fatty acids, was obtained in 61% yield. The crude and purified product mixtures were thoroughly characterized and their components positively identified. The tribological properties of the product mixtures were further investigated using a variety of methods. The product mixtures displayed significantly improved oxidation stability, cold-flow, and extreme pressure properties over those of the parent high-oleic sunflower oil. The extreme pressure results for the neat products showed a higher weld point for the crude than for the purified mixture. This was attributed to differences in the chemical properties of the components in the two product mixtures.