Electrocatalytic synthesis of α,α-gem-dihalide ketones from α-mono-halide ketones and unexpected dimer condensation

Abstract

A novel, environmentally friendly electrocatalytic process has been developed to prepare α,α-gem-dihalide (F, Cl, and Br) ketones from α-mono-halide ketones in an aqueous solution containing alkali halide salts. The gem-dihalides could have the same or different halogens on the same carbon, depending on the reactant and inorganic halide salt used. An electron-withdrawing group, such as carbonyl, located at the α-site of mono-halogenated carbon, was essential to the reaction. The electrosyntheses were performed under ambient conditions without inert gas protection and displayed yields of about 80%. This method avoided the classical haloform elimination reaction. However, when the aqueous solution contained NaOH, two α-mono-halide ketone molecules had a special dimer condensation. The reaction mechanisms were explored by conducting GC-MS, EPR, and CV with DFT calculations. These revealed that in situ generation of a halogen radical initiated electrocatalytic halogenation, while the dimer condensation involved a hydroxyl radical-mediated C1 fragment elimination.