Stearyl oleate is an unsaturated long-chain wax ester formed by esterification of oleic acid (C18:1 cis-Δ9) with stearyl alcohol (C18:0). It bridges saturated wax esters such as stearyl palmitate and symmetric oleyl oleate through its chain symmetry while introducing a monounsaturated acyl kink. This lipid imparts a soft, creamy texture in semi-solid emulsions, as the cis-double bond lowers the melting point and enhances plasticity compared with fully saturated C18/C18 homologs.
Chemical Structure
Stearyl oleate has the molecular formula C36H70O2 and a molecular weight of 534.94 g/mol. Its structure—CH3(CH2)17OOC(CH2)7CH=CH(CH2)7CH3 (cis)—includes 33 rotatable bonds and one cis-unsaturation. It has a TPSA of 26.3 Ų, an estimated XLogP3 of ~17–18, and no hydrogen-bond donors. The oleoyl kink disrupts tight molecular packing, promoting more fluid crystalline phases.
Physical Properties
Stearyl oleate is described as a white to pale yellow waxy solid with a melting point around 28.5°C. It is insoluble in water but soluble in lipids, chloroform, and hot ethanol. It is typically stored at -20°C and exhibits low volatility. Its low HLB value (~2–4) makes it suitable for lipophilic emulsion systems and it has a mild, odorless profile.
Synthesis and Production
Stearyl oleate can be synthesized through acid-catalyzed esterification (e.g., using NaHSO4 at 130°C) or via enzymatic condensation of oleic acid (from tall oil or olive sources) with stearyl alcohol (from palm-derived feedstocks or industrial byproducts). High-purity yields (96%+) may be achieved through distillation, while greener lipase-based methods allow catalyst recycling and improved sustainability.
