LIPASE-CATALYZED SYNTHESIS AND PROPERTIES OF ESTOLIDES AND THEIR ESTERS

Eight lipases were screened for their ability to synthesize estolides from a mixture that contained lesquerolic (14-hydroxy-11-eicosenoic) acid and octadecenoic acid. With the exception of Aspergillus niger lipase, all 1,3-specific enzymes (from Rhizopus arrhizus and Rhizomucor miehei lipases) were unable to synthesize estolides. Candida rugosa and Geotrichum lipases catalyzed estolide formation at >40% yield, with >80% of the estolide formed being monoestolide from one lesquerolic and one octadecenoic acyl group. Pseudomonas sp. lipase synthesized estolides at 62% yield, but the product mixture contained significant amounts of monoestolide with two lesquerolic acyl groups as well as diestolide. Immobilized R. miehei lipase was chosen to catalyze the esterification of mono- and polyestolide, derived synthetically from oleic acid, with fatty alcohols or alpha,omega-diols. Yields were >95% for fatty alcohol reactions and >60% for diol reactions. In addition, the estolide linkage remained intact through the course of the esterification process. Esterification of estolides improved the estolide's properties-for example, lower viscosity and higher viscosity index-but slightly raised the melting point. Estolides and, particularly, estolide esters may be suitable as lubricants or lubricant additives.