Kinetic and mechanistic studies for the molybdenum- catalyzed oxidation of organic sulfides and olefins by t- DuO2H (1982)

This research was focussed on the effects of light, solvent and&#13;\nsubstituents in the molybdenum-catalyzed oxidation of phenylmethyl sulfides&#13;\nwith t-Bu02H and on the effect of light in the molybdenum-catalyzed&#13;\nepoxidation of l-octene with t-Bu02H.&#13;\nIt was shown that the Mo(CO)6-catalyzed oxidation of phenylmethyl&#13;\nsulfide with t-Bu02H~ at 35°C, proceeds 278 times faster underUV light than&#13;\nunder laboratory lighting, whereas the Mo02(acac)2-catalyzed oxidation&#13;\nproceeds only 1.7 times faster under UV light than under normal laboratory&#13;\nlighting. The difference between the activities of both catalysts was&#13;\nexplained by the formation of the catalytically active species, Mo(VI).&#13;\nThe formation of the Mo(VI) species, from Mo(CO)6 was observed from&#13;\nthe IR spectrum of Mo(CO)6 in the carbonyl region.&#13;\nThe Mo(CO)6-catalyzed epoxidation of l-octene with t-Bu02H showed that&#13;\nthe reaction proceeded 4.6 times faster under UV light than in the dark or&#13;\nunder normal laboratory lighting; the rates of epoxidations were found to&#13;\nbe the same in the dark and under normal laboratory lighting.&#13;\nThe kinetics of the epoxidations of l-octene with t-Bu02H, catalyzed&#13;\nby Mo02(acac)2 were found to be complicated; after fast initial rates, the&#13;\nepoxidation rates decreased with time.&#13;\nThe effect of phenylmethyl sulfide on the Mo(CO)6-catalyzed epoxidation&#13;\nof l-octene waS studied. It was shown that instead of phenylmethyl sulfide,&#13;\nphenylmethyl sulfone, which formed rapidly at 85°C, lowered the reaction rate. The epoxidation of l-octene was found to be 2.5 times faster in&#13;\nbenzene than in ethanol.&#13;\nThe substituent effect on the Mo02(acac)2-catalyzed oxidations of p-OH,&#13;\np-CHgO, P-CH3' p-H, p-Cl, p-Br, p-CHgCO, p-HCO and P-N02 substituted&#13;\nphenylmethyl sulfides were studied. The oxidations followed second order&#13;\nkinetics for each case; first order dependency on catalyst concentration was&#13;\nalso observed in the oxidation of p-CHgOPhSMeand PhSMe.&#13;\nIt was found that electron-donating groups on the para position of&#13;\nphenylmethyl sulfide increased the rate of reaction, while electronwithdrawing&#13;\ngroups caused the reaction rate to decrease. The reaction&#13;\nconstants 0 were determined by using 0, 0- and 0* constants. The rate&#13;\neffects were paralleled by the activation energies for oxidation.&#13;\nThe decomposition of t-Bu02H in the presence of M.o (CO)6, Mo02 (acac)2&#13;\nand VO(acac)2 was studied. The rates of decomposition were found to be very&#13;\nsmall compared to the oxidation rates at high concentration of catalysis.&#13;\nThe relative rates of the Mo02(acac)2-catalyzed oxidation of&#13;\np-N02PhSMe by t-Bu02H in the presence of either p-CH30PhSMe or PhSMe clearly&#13;\nshow that PhSMe and p-CHgOPhSMe act as co-catalysts in the oxidation of&#13;\np-N02PhSMe.&#13;\nBenzene, mesity1ene and cyclohexane were used to determine the effect&#13;\nof solvent in the Mo02 (acac)2 and Mo(CO)6-catalyzed oxidation of phenylmethyl&#13;\nsulfide. The results showed that in the absence of hydroxylic solvent, a&#13;\nsecond molecule of t-Bu02H was involved in the transition state. The&#13;\ncomplexation of the solvent with the catalyst could not be explained.The oxidations of diphenyl sulfoxide catalyzed by VO(acac)2,&#13;\nMo(CO)6 and Mo02(acac)2 showed that VO(acac)2 catalyzed the oxidation&#13;\nfaster than Mo(CO)6 and Mo02 (acac)2_ Moreover, the Mo(CO)6-catalyzed&#13;\noxidation of diphenyl sulfoxide proceeded under UV light at 35°C.