Brønsted Acidic Ionic Liquids‐Promoted Halogenations of 2‐Methylquinoline With Potassium Halide Under Metal‐Free and Ambient Conditions

A metal‐free, operationally straightforward and environmentally benign halogenation of substituted 2‐methylquinolines has been accomplished with inexpensive potassium halides as halogen sources under ambient conditions. This protocol bypasses conventional metal catalysis and proceeds efficiently at room temperature with broad substrate compatibility. The synthetic utility is demonstrated by gram‐scale preparation, facile product derivatization, and good reusability of the Brønsted acidic ionic liquid (BAIL) promoter, which remains highly active for at least four cycles. Mechanistic studies support a free‐radical pathway initiated by in situ generated halogen radicals. This work offers a practical, mild, and sustainable route to 2‐halomethylquinolines—versatile building blocks for pharmaceuticals and functional materials.