In organic chemistry, the Fischer reaction is the conversion of an aryl sulfonic acid to an aryl chloride using chlorine:
The method was once used extensively in the preparation of chlorinated anthraquinones such as 1-chloroanthraquinone and 2-anthraquinones. forms from the . Illustrating some scope for this reaction, 1-chloroanthraquinone-2-carboxylic acid forms from the sulfonic-carboxylic acid.
Chlorine can be generated in situ from sodium chlorate and hydrochloric acid:
The acidity of this mixture means that sodium sulfonate salts can be used in situ, since they are readily protonated.