Kinetics and mechanism of a one-step alternative to the Grignard reaction

Abstract

The kinetics of the ‘one-step alternative to the Grignard reaction’ between bromobenzene, benzaldehyde, and lithium have been studied with tetrahydrofuran as solvent. The rate of formation of the product, diphenylmethanol, is first-order in bromobenzene and in lithium surface area, and zero-order in benzaldehyde. The activation energy is 3.42 ± 0.59 kJ mol^–1. These data are consistent with a rate-determining step involving intermediate formation of phenyl-lithium by reaction of bromobenzene with lithium. The one-step process has also been employed with organic bromides to synthesise ketones from nitriles and alkylarylhydroxylamines from 2-methyl-2-nitrosopropane. In the former the yields were poorer than from conventional reactions but in the latter yields compared very favourably with those from the Grignard reaction.