Trichloroacetic acid

Trichloroacetic acid (also known as trichloroethanoic acid) is an analogue of acetic acid in which the three hydrogen atoms of the methyl group have all been replaced by chlorine atoms. It is a strong acid, comparable to sulfuric acid.

It is prepared by the reaction of chlorine with acetic acid in the presence of a suitable catalyst.
 * CH3COOH + 3Cl2 → CCl3COOH + 3HCl

It is widely used in biochemistry for the precipitation of macromolecules such as proteins, DNA and RNA. Its sodium salt is used as a weedkiller. Solutions containing trichloroacetic acid as an ingredient are used for tattoo removal and the treatment of warts, including genital warts. It is considered safe for use for this purpose during pregnancy.

Salts of trichloroacetic acid are called trichloroacetates. Reduction of trichloroacetic acid results in dichloroacetic acid, a pharmacologically active compound that shows promise for the treatment of cancer.

History
The discovery of trichloroacetic acid by Jean-Baptiste Dumas in 1840 delivered a striking example to the slowly evolving theory of organic radicals and valences. The theory was contrary to the beliefs of Jöns Jakob Berzelius, starting a long dispute between Dumas and Berzelius.