KINETIC-STUDY OF THE EPOXIDATION OF ALKENES BY IODOSYLBENZENE CATALYZED BY IRON(III) TETRA(4-N-METHYLPYRIDYL)PORPHYRIN IN METHANOL

A kinetic analysis of the epoxidation of alkenes by iodosylbenzene cat alysed by iron(III) tetra(4-N-methylpyridyl)porphyrin dagger (Fe(III)T 4MPyP) in methanol solution is presented. Using the initial rate metho d, the rates of epoxidation are found to be first-order in Fe(III)T4MP yP and to show saturation kinetics in both the oxidant and the substra te. Interestingly, for the two most reactive styrenes, 4 -methoxy- and 4-methylstyrene, the rate of epoxidation is first-order in the substr ate: saturation kinetics in substrate are not observed. A Michaelis-Me nten-like rate equation is derived for the system, under conditions wh ere the catalyst is saturated in oxidant, and is used to compare the r ates of epoxidation of a selection of aliphatic alkenes and styrenes. The reactivity of an alkene is found to be determined by the influence of the substituent on the formation of a complex with the active oxid ant and on the subsequent breakdown of this intermediate to give produ cts. The results from the less reactive styrenes are analysed using th e Hammett equation and the mechanism of the epoxidation is discussed.