Chemical modifications of Sterculia foetida L. oil to branched ester derivatives

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Abstract

An experimental study to modify Sterculia foetida L. oil (STO) or the corresponding methyl esters (STO FAME) to branched ester derivatives is reported. The transformations involve conversion of the cyclopropene rings in the fatty acid chains of STO through various catalytic as well as stoichiometric reactions. Full conversion of the cyclopropene rings was obtained using Diels–Alder chemistry involving cyclopentadiene in water at 40°C without the need for a catalyst. Olefin metathesis reactions were performed using a Grubbs 2nd generation catalyst and cyclopropene ring conversion was ≥99 and 54 mol% with 2,3-dimethyl-2-butene and 1-octene, respectively. Oxidation reactions were performed using established epoxidation (Sharpless) and dihydroxylation (Prilezhaev) protocols using aqueous hydrogen peroxide as the oxidant. For both reactions, full conversion of the cyclopropene rings was obtained at RT to yield the corresponding α,β-unsaturated ketone in good selectivities. Rearrangement reactions of the cyclopropene rings to the corresponding conjugated diene were successfully performed using homogeneous and heterogeneous palladium catalysts. Excellent conversions (≥99%) were obtained using homogeneous palladium catalyst in a biphasic cyclohexane–water mixture (1:1) at 90°C. Relevant cold flow properties of all products were determined and compared to crude STO and STO FAME. Best results were obtained for the metathesis products of STO with 1-octene, with a cloud point (CP) and pour point (PP) of −12°C.

Practical applications: The S. foetida L. tree produces a tropical oil with high potential to be converted to various oleochemical products. The oil contains cyclopropene rings in the fatty acid chains which are known to be very reactive and as such excellent starting materials for various chemical modification reactions. We here report an experimental study on the modifications of STO into novel branched ester derivatives which are prospective products for a range of applications. Examples are the use as cold-flow improvers for biodiesel or biolubricants (ester derivatives with long, aliphatic branches), as reactive building block material for resin, coatings and/or packaging application (derivatives containing unsaturated (cyclic) structures in the fatty acid chains).

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