In chemistry, the Halex process is used to convert aromatic chlorides to the corresponding aromatic fluorides. The process entails Halide exchange, hence the name.[1] The reaction conditions call for hot (150-250 °C) solution of the aryl chloride and anhydrous potassium fluoride. Typical solvents are dimethylsulfoxide, dimethylformamide, and sulfolane. Potassium chloride is generated in the process. The reaction is mainly applied to nitro-substituted aryl chlorides. Sometimes more soluble fluorides, such as caesium fluoride and TBAF are used.[2]
The following reactions are practiced commercially in this manner:[3]
The nitro groups in the above compounds can be reduced to give the corresponding aniline. For example, selective hydrogenation of 4-fluoronitrobenzene gives 4-fluoroaniline. Thus, the Halex method provides access to a host of fluoroanilines.
For producing aryl fluorides, the Halex process is complementary to the Balz-Schiemann reaction and its variants.