Synthesis of estolides from oleic and saturated fatty acids

Abstract

Oleic acid and various saturated fatty acids, butyric through stearic, were treated with 0.4 equivalents of perchloric acid at either 45 or 55°C to produce complex estolides. Yields varied between 45 and 65% after Kugelrohr distillation. The estolide number (EN), i.e., the average number of fatty acid units added to a base fatty acid, varied as a function of temperature and saturated fatty acid. The shorter-chain saturated fatty acids, i.e., butyric and hexanoic, provided material with higher degrees of oligomerization (EN = 3.31) than stearic acid (EN = 1.36). The individual, saturated fatty acid estolides each have very different characteristics, such as color and type of by-products. The higher-temperature reactions occurred at faster rates at the expense of yield, and lactones were the predominant side products. At 55°C, lactone yields increased, but the δ-γ-lactone ratio decreased; this led to lower estolide yields. The opposite trend was observed for the 45°C reaction. The saturate-capped, oleic estolides were then esterified with 2-ethylhexyl alcohol, and the chemical composition of these new estolides remained consistent throughout the course of the reaction.Paper no. J9799 in JAOCS 78, 557-565 (June 2001).Estolides are a class of esters, based on vegetable oils (1-4), that form when the carboxylic acid functionality of one fatty acid reacts at the site of unsaturation of another fatty acid to form an ester linkage. These linkages are used to help characterize the structure of the estolide since the estolide number (EN) is defined as the average number of fatty acids added to a base fatty acid (Scheme 1, EN = n + 1). The secondary ester linkages of the estolide are more resistant to hydrolysis than those of triglycerides, and the unique structure of the estolide results in materials that have far superior physical properties for certain applications than vegetable and mineral oils (5). Estolides have been found in nature (6,7) and have been synthesized (1-4,8) in the laboratory. Isbell and Kleiman (9) synthesized estolides from oleic fatty acids and found them to have interesting chemical behavior. The double bond in oleic acid is located at the 9 position which, under the correct conditions of acid concentration, reaction time, and temperature, undergoes estolide formation with minimal migration. The proposed mechanism involves formation of a carbocation that can undergo nucleophilic addition with or without carbocation migration along the length of the chain. If the migration continues to the C4 and C5 position, the fatty acid will cyclize to form lactones, the major side product to estolide formation (Scheme 2) (10-15).Lactones are formed from an intramolecular cyclization of a fatty acid carboxyl group with a carbocation located at the 4-or 5-position on a fatty acid backbone. Under the correct conditions, Showell et al. (13) and Cermak and Isbell (14,15) were able to produce γ-and δ-lactones, respectively. A major side product in the estolide synthesis, lactones are an interesting class of compounds...

Oleins as a source of estolides for biolubricant applications

“…On the contrary, estolide viscosities significantly decrease after 12h reaction time, a fact related to a lower molecular weight. This result confirms that estolide viscosity is controlled by the oligomerization degree (Cermak et al, 2001). The viscosity index for the estolides synthesized in this work was 178 Ϯ 5, regardless of reaction time, slightly lower (7%) than that obtained for olein.…”

“…Estolides are a class of ester resulting from the reaction between a carboxylic group in a fatty acid molecule and an unsaturation in another fatty acid molecule to form an ester linkage (Isbell et al, 1994, Isbell et al, 2000, Cermak et al, 2001. The number of these linkages determines the structure and properties of estolides.…”

Chemical, thermal and viscous characterization of high-oleic sunflower and olive pomace acid oils and derived estolides

“…Typically, estolides are a class of ester resulting from the reaction between a carboxylic group in a fatty acid molecule and an unsaturation in another fatty acid molecule to form an ester linkage , Isbell et al, 2000, Cermak et al, 2001. The number of these linkages determines the structure and properties of estolides.…”

Chemistry and physical properties of estolides

“…The capping fatty acid of the estolide was evaluated for the impact of chain length on pour points (Cermak and Isbell 2001;Cermak and Isbell 2002;Cermak and Isbell 2009). Table 8 provides a summary of the work by Cermak and Isbell (2002) which demonstrated that a decanoyl capping group for the estolide provided the lowest pour points within this series.…”