Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/1996
Publication Date: N/A
Interpretive Summary: Certain fatty acids have important industrial uses and they are naturally available from few sources such as the castor bean. These fatty acids, called hydroxy fatty acids, can be produced by enzyme processes followed by alkali treatment from other more readily available fatty acids. The alkali treatment improves the yield of hydroxy fatty acids by up to 75%. We report herein our exploration of the mechanism of the alkali reaction in an effort to understand how improvements in the yield of hydroxy fatty acids might be obtained.
Technical Abstract: Alkali converts linoleic and linolenic acid hydroperoxides to the corresponding hydroxy fatty acids without loss of regio- or stereo-configuration in about 75% yield. This communication elucidates the mechanism of this transformation. Reaction of 18O2-hydroperoxide-labeled (13S,9Z,11E)-13-hydroperoxy-9,11- octadecadienoic acid ([hydroperoxide-18O2]13S-HPODE) with 5 M KOH showed that one 18O was retained in the (13S,9Z,11E)-13-hydroxy- 9,11-octadecadienoic acid (13S-HODE) product, but the other oxygen was transferred to other products. Of these, (9Z,11R,S,12S,R)- 13-oxo-11,12-epoxy-9-octadecenoic acid (EPK), serves as the principal intermediate for a number of other fatty acids by Favorskii Rearrangement. Double labeling experiments showed that product 13S-HODE was stable in KOH, and EPK was formed from an earlier intermediate, 13-oxo-9,11-octadecadienoic acid, by an intermolecular epoxidation by peroxyl anion. As expected, a hydroperoxide without unsaturation, like methyl 12-hydroperoxyoctadecanoate, was more resistant to the presence of alkali. A mechanism is indicated that peroxyl anion attacks alpha,beta-unsaturated ketones to form epoxides with accompanying conversion of peroxyl anion into the hydroxyl anion.