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Abstract
Our previous isolation of branched-chain fatty acid (BCFA) methyl esters from lanolin was improved and scaled up. Also, oleate esters of isopropanol, oleyl alcohol and normal alcohols of 1-12 carbons chain lengths were prepared. Esters were made by interesterification with sodium alcoholates and by esterification with Candida antactica lipase. It proved easier to obtain pure esters by the enzymatic synthesis. Melting points and viscosities over the range of 0-70 °C were determined in order to better identify potential lubricant targets that might be produced by genetically modified oilseed crops. Isopropyl and butyl oleate have melting points of -33 and -32 °C, respectively and viscosities that range from ~17 cp (0 °C) to ~2.5 cp (70 °C). They should have suitable stability for lubricants. BCFA esters had viscosities similar to their straight chain analogs. Viscosities increased with alcohol chain length and decreased with temperature. The dependence of viscosity on temperature was fit with an equation based on Erying's rate equation. Some esters with branched acid or branched alcohol moieties, and some oleate esters might be utilized as biolubricants or biofuels on the basis of their melting points and viscosities.
Keywords Branched chain fatty esters * Melting point * Oleate esters * Viscosity
Introduction
Lipids used as lubricants should have suitable viscosities, low melting points and good stability to oxidation. For maximum economic advantage they should require only extraction and limited refining to be ready for use. Low melting-lipids with good oxidative stability can be achieved by using esters of monounsaturated fatty acids. An alternate solution is to use branched-chain fatty acids (BCFAs) and alcohols. By expressing surface coat genes that control wax synthesis in oil seed tissue the biosynthesis of such esters might be achieved. Physical property data for such esters is limited, which prevents rational target selection. Previously, we reported the melting points of methyl and isopropyl esters of BCFAs with chain lengths of 13-18 [1]. Their attractive melting points encouraged us to measure the viscosity of these molecules, so we scaled up and refined our previous methods to produce larger quantities of some branched esters from lanolin. Methyl oleate melts at -20 °C and has fairly good oxidative stability [2], which suggests that oleate esters might be suitable candidates for biolubricants.
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