Conversion of 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid to the corresponding hydroxy fatty acid by KOH: A kinetic study

Transformation of 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid (13S-HPOD) to 13(S)-hydroxy-9(Z),11(E)-octadecadienoic acid (13S-HOD) under alkaline conditions (0.05 to 5 M KOH) occurred first-order with respect to 13S-HPOD concentration. Overall yield was about 80%. The energy of activation at higher concentrations (3.75 to 5 M KOH) was determined to be in the range of 15.3 to 15.6 kcal. Compared to the 13S-HPOD conversion, 13(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid (13S-HPOT) was converted at a faster rate to the corresponding hydroxy fatty acid (13S-HOT), with the reaction also being first-order. Chiral phase high-performance liquid chromatography demonstrated that in the transformation the stereochemistry of both the 13S-HPOD and 13S-HPOT reactants was preserved. Manometric analyses of the KOH/13S-HPOD reaction showed an uptake of gas, which amounted to 11% of the mols of reactant 13S-HPOD on the assumption that the gas was O₂. As there is a theoretical loss of 1 oxygen atom in the reaction, the fate of this oxygen (possiblyvia active oxygen species) may involve reaction with 13S-HPOD/13SHOD to form the 20% by-products.