1,10-Phenanthroline catalysis of the chromium(VI) oxidation of alcohols: a kinetic and mechanistic study

Abstract

Several primary, secondary and tertiary alcohols are oxidised in acidic solutions using CrVIas an oxygen donor and 1,10-phenanthroline (Phen) as catalyst. A large primary kinetic isotope effect, kie(kH/kD∼ 10) suggests a linear transition state in the noncatalytic system, whereas a moderate kinetic isotope effect observedin the catalytic pathway can be associated with a cyclic transition state. The kD2O/kH2Oratio does not seem to indicate any significant solvent isotope effect. CrIII inhibition, reflected in the firstorder plots, can be explained by exchange reactions. PhCH2OH reacts ca. 7 times faster than MeOH. Moderately negative ρ* values indicate ahydride abstraction mechanism. Imperfect correlation is observed in the LFER between catalytic and noncatalytic reaction systems.Enhanced reactivity has been observed in the presence of 2,2′-bipyridyl, whereas the catalytic activity is insignificant with picolinicacid, imidazole and oxalic acid. Consideration of the kinetic behaviour of catalytic and noncatalytic reaction pathways provides valuable mechanistic insight into the systems studied.