Kinetics and mechanism of the epoxidation of unsaturated fatty acids

A study was made of the epoxidation of octadecenoic acids with peroxybenzoic acid in benzene. Activation energies, frequency factors, enthalpies of activation, entropies of activation, and free energies of activation were obtained for the following fatty acids: cis‐9‐octadecenoic acid (oleic), trans‐9‐octadecenoic acid (elaidic), 12‐hydroxy‐cis‐9‐octadecenoic acid (ricinoleic), 12‐hydroxy‐trans‐9‐octadecenoic acid (ricinelaidic), cis‐11‐octadecenoic acid (vaccenic), and cis‐6‐octadecenoic acid (petroselinic). It was observed that the reaction rate was adversely affected by the proximity of the carboxyl group, that is, the closer the carboxyl to the reaction site the lower the rate. A shift from a trans to a cis configuration results in an approximate 50% increase in reaction rate with a corresponding decrease in free energy of activation of 260 cal/mol. The effects of isomerism and the replacement of substituent groups on the reaction rate were generally additive. A mechanism for the peroxydation of octadecenoic acids is proposed.