In organic synthesis the Bechamp reaction, first reported in 1863 by Antoine Béchamp, is used for producing arsonic acids from activated aromatic rings; for example the synthesis of arsanilic acid from aniline.

The reaction is an electrophilic aromatic substitution, using arsenic acid as the electrophile. Important products of this reaction include roxarsone; which exhibits an anticoccidial action and promotes growth in animals.