Transhalogenation

Transhalogenation is a substitution reaction in which the halide of a halide compound is exchanged for another halide.

Finkelstein reaction

A common method is halide metathesis. An example is the conversion of alkyl chloride into alkyl fluoride:
This kind of reaction is called Finkelstein reaction. However, it is also possible, for example, to produce phosphorus fluoride compounds by transhalogenating chlorine, bromine or iodine bound to phosphorus with a metal fluoride.

As a halogen source for transhalogenation, metal halides are often used, but also the use of onium halides is possible. Transhalogenation has been described as a gentle method for the synthesis of fluoroorganylboranes. It is also possible to produce aryliodides from the corresponding aryl chlorides or aryl bromides.
One investigation showed a possibility to perform transhalogenation by means of genetically modified enzymes.