Kinetics of the direct borane reduction of pinacolone in THF

Abstract

The kinetics of the borane reduction of the ketone pinacolone in THF depend strongly on the borane reagent. NaBH₄, which is present in commercial BH₃–THF as stabilizer, strongly catalyzes the reaction. The use of commercial BH₃–THF results in the borane reaction order of 1.6. In contrast, freshly prepared, pure BH₃–THF yields kinetics for which the main reaction, the reduction of the ketone by BH₃–THF forming the monoalkoxyborane, are first order in both reactants. Two further subsequent reactions have to be included in the reaction scheme in order to fit the kinetics by numerical integration. Results of semiempirical calculations are compared with experimental findings to eludicate the possible reaction mechanism of the main reaction.