Lipase‐catalyzed synthesis and properties of estolides and their esters

Abstract

Abstract 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 α,ω‐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.