MECHANISM OF RUO4-MEDIATED OXIDATIONS OF SATURATED-HYDROCARBONS, ISOTOPE EFFECTS, SOLVENT EFFECTS AND SUBSTITUENT EFFECTS

Adamantane and 1,3,5,7-tetradeuterioadamantane were oxidized by RuO4 i n two solvent systems, CCl4-CH3CN-H2O and acetone-water, yielding two kinetic deuterium isotope effects (KIEs), 4.8+/-0.2 and 7.8+/-0.1, res pectively, very similar to those obtained in analogous reactions with cis-decalin and perdeuterio-cis-decalin, 4.8 and 6.8. These results we re interpreted as primary KIEs and small or negligible secondary KIEs. From this, sp(2)-hybridized intermediates were not involved in the re action path, The kinetic effect of the solvent was investigated by per forming the reaction in aqueous acetone and acetonitrile. The rates we re correlated with Grunwald-Winstein Y values and with Reichardt E(T)( 30) values, Both correlations showed the reaction to be only moderatel y dependent on the solvent polarity. I-Substituted adamantanes were ox idized in CCl4-CH3CN giving a Taft rho value of -2.5+/-0.1. These res ults were regarded as support for a reaction consisting of a pre-equil ibrium with formation of a substrate-RuO4 complex followed by a rate-d etermining concerted reaction, [GRAPHICS] The results did not support a reaction mechanism with a carbocation or radical intermediate, or a scheme with two competing reactions, one with a carbocation intermedia te and the other with a concerted mechanism.