OBSERVATION OF A LARGE ISOTOPE EFFECT IN MANGANESE DIOXIDE OXIDATION OF BENZYL ALCOHOL

An intramolecular isotope effect for the manganese dioxide oxidation of α-deuteriobenzyl alcohol in benzene solution is determined to be 14.2 ± 0.9, indicating that the rate-determining step for this heterogeneous reaction involves C-H bond cleavage. When equal amounts of benzyl alcohol and α,α-dideuteriobenzyl alcohol are allowed to compete for a limited amount of activated manganese dioxide, an isotope effect of 18.2 is observed, presumably resulting from the combined primary and secondary kinetic isotope effects, and indicating that the assumed adsorption step is reversible. A primary adsorptive isotope effect is postulated as a possible explanation for the magnitude of the isotope effect observed in this work. These findings are considered in terms of current concepts about the mechanism of oxidations with activated manganese dioxide. © 1969, American Chemical Society. All rights reserved.