Synthesis of δ‐stearolactone from oleic acid

Abstract

Abstractδ‐Stearolactone was prepared from oleic acid using concentrated sulfuric acid under various conditions in the presence of polar, nonparticipating solvents. δ‐Stearolactone was formed in as high as 15∶1 ratios over the thermodynamic product, ψ‐lactone, in the presence of methylene chloride, 100% wt/vol, at room temperature with two equivalents of sulfuric acid for 24 h. This procedure is applicable to other olefinic fatty acids such as estolides and fatty acid methyl esters. Temperature plays a role in the regioselectivity of the cyclization for δ‐lactone, as lower temperatures (20°C) gave higher σ/ψ ratios. At higher temperatures (50°C) in the presence of sulfuric acid and methylene chloride the yield of lactone was 75% but with a σ/ψ ratio of only 0.3∶1. Cyclization of oleic acid to lactone also occurred with other acids. Oleic acid underwent reaction with perchloric acid, one equivalent, in the absence of solvent at 50°C, which yielded σ‐lactone in a modest yield with a 3.1 σ/ψ ratio. The same temperature effect was observed with perchloric acid that was observed in the case of sulfiric acid. Because σ‐stearolactone is much more reactive than the corresponding fatty acid, fatty acid ester, or ψ‐lactone, we believe that it will be a useful synthon for many new industrial products including new biodegradable detergents.