The catalytic activity of the molybdenum catalysts, molybdenum naphthenate, Mo(CO)(6), H-2[Mo2O4(ox)(2)(H2O)(2)].4H(2)O.Me-2-CO, MO(O)(2)(acac)(2), and [MO(O)(2)(SAP)(EtOH)], was investigated in the reaction of oleic acid epoxidation by organic hydroperoxides.A new highly efficient and selective system for the epoxidation of unsaturated aliphatic acids was developed with tert-butyl hydroperoxide (t-BuOOH) and the [Mo(O)(2)(SAP)(EtOH)] complex. The epoxidation reaction of oleic acid shows 86.8% selectivity to 9,10-epoxystearic acid at 67% conversion of t-BuOOH. Routine kinetic measurements were performed to determine the reaction orders with respect to t-BuOOH and the catalyst. They are 1.00 +/- 0.05 and 0.51 +/- 0.05, respectively. The activation energy and enthalpy, E-a = 99 +/- 4 kJ mol(-1) and DeltaH = 96 +/- 4 kJ mol(-1), were calculated from the temperature dependences.The results allowed us to propose a reaction mechanism whose outline is consistent with the generally accepted mechanism of the catalytic epoxidation of olefins by organic hydroperoxides. (C) 2003 Elsevier Science B.V. All rights reserved.