Herz reaction

The Herz-reaction, named after the chemist Richard Herz, is the chemical conversion of an aniline-derivative (1) to a so-called Herz-salt (2) with disulfur dichloride, followed by hydrolysis of this Herz-salt (2) to the corresponding sodium thiolate (3) :



Benzothiazoles
The sodium thiolate 3 can be converted to an intermediate zinc mercaptide with Zinc sulfate, followed by reaction of the mercaptide with for instance benzoyl chloride, forming a 1,3-benzothiazole 4.



Dyes
Aniline 5 is converted in three steps to compound 6, in three steps;
 * 1) conversion to an ortho-aminothiol through the Herz-reaction (aniline 5 and disulfur dichloride), followed by
 * 2) conversion to an ortho-aminoarylthioglycolacid and
 * 3) conversion of the aromatic amine function to a nitrile via the Sandmeyer reaction.
 * 4) In a last step the nitrile is hydrolysed resulting in  6. This compound is converted to 7 via a ring-closing reaction and decarboxylation.

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 isatine results in the thio-Indigo dye 9.