Oxidation of adamantane with O 2 catalysed by VO(acac) 2 and reactivity of active species in acetic acid

Abstract

The oxidation of adamantane (470 mM) catalysed by VO(acac) 2 (0.5 mM) with 1 atm O 2 in acetic acid at 393 K was studied. The major product was 1-adamantanol, and minor ones were 2-adamantanol and 2-adamantanone. The selectivity for 1-adamantanol (3°-selectivity) was almost constant at 75% under all oxidation conditions. The VO(acac) 2 catalyst functioned efficiently in the oxidation with a turnover number (TON) of 440 over 600 min. The oxidation rate of adamantane was enhanced by 5.5 times by the addition of CF 3SO 3H (2.2 mM) to acetic acid. Reactivities of various alkanes in the presence of VO(acac) 2 catalyst and product selectivities indicated the contribution of electrophilic active species in the oxidation. The rate-determining step was dissociation of the C–H bond of alkane by electrophilic active V species. The activity of the VO(acac) 2 catalyst is significantly different from the autoxidation promoter, Co(acac) 3. A reaction scheme for the oxidation is proposed on the basis of the reactivities and UV–vis and ESR spectroscopic studies.