Aromatic substitution in ball mills: formation of aryl chlorides and bromides using potassium peroxomonosulfate and NaX

Abstract

Aryl chlorides and bromides are formed from arenes in a ball mill using KHSO₅ and NaX (X = Cl, Br) as oxidant and halogen source, respectively. Investigation of the reaction parameters identified operating frequency, milling time, and the number of milling balls as the main influencing variables, as these determine the amount of energy provided to the reaction system. Assessment of liquid-assisted grinding conditions revealed, that the addition of solvents has no advantageous effect in this special case. Preferably activated arenes are halogenated, whereby bromination afforded higher product yields than chlorination. Most often reactions are regio- and chemoselective, since p-substitution was preferred and concurring side-chain oxidation of alkylated arenes by KHSO₅ was not observed.