A particularly common α-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their α positions by reaction Cl, Br or I in acidic solution. Bromine in acetic acid solvent is often used.
Remarkably, ketone halogenation also occurs in biological systems, particularly in marine alga, where , bromoacetone, , and other related compounds have been found.
The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate.