The Herz reaction, named after the chemist Richard Herz, is the chemical conversion of an aniline to the benzodithiazolium salt by its reaction with disulfur dichloride. The salt is called a Herz salt. Hydrolysis of this Herz salt give the corresponding sodium thiolate, which can be further converted to the 2-aminothiophenol. The 2-aminothiophenols are suitable for diazotization, giving benzothiadiazoles. Instead the sodium 2-aminothiophenolate can be converted to a 1,3-benzothiazole.

Dyes

Aniline 5 is converted to compound 6, in three steps; The compound, (thioindoxyl, 7) is an important intermediate in the organic synthesis of some dyes. Condensation with acenaphthoquinone gives 8, a dye of the so-called Ciba-Scarlet type, while condensation of 7 with isatin results in the thio-Indigo dye 9.