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 (13 S ‐HPOD) to 13( S )‐hydroxy‐9( Z ),11( E )‐octadecadienoic acid (13 S ‐HOD) under alkaline conditions (0.05 to 5 M KOH) occurred first‐order with respect to 13 S ‐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 13 S ‐HPOD conversion, 13( S )‐hydroperoxy‐9( Z ),11( E ),15( Z )‐octadecatrienoic acid (13 S ‐HPOT) was converted at a faster rate to the corresponding hydroxy fatty acid (13 S ‐HOT), with the reaction also being first‐order. Chiral phase high‐performance liquid chromatography demonstrated that in the transformation the stereochemistry of both the 13 S ‐HPOD and 13 S ‐HPOT reactants was preserved. Manometric analyses of the KOH/13 S ‐HPOD reaction showed an uptake of gas, which amounted to 11% of the mols of reactant 13 S ‐HPOD on the assumption that the gas was O 2 . As there is a theoretical loss of 1 oxygen atom in the reaction, the fate of this oxygen (possibly via active oxygen species) may involve reaction with 13 S ‐HPOD/13 S HOD to form the 20% by‐products.