Herz reaction
The Herz-reaction, named after the chemist Richard Herz
Richard Herz
Richard Herz was a German chemist.He discovered the Herz reaction.-References:...

, is the chemical conversion of an aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...

-derivative (1) to a so-called Herz-salt (2) with disulfur dichloride
Disulfur dichloride
Disulfur dichloride is the chemical compound with the formula S2Cl2 . Some alternative names for this compound are sulfur monochloride , disulphur dichloride and sulphur monochloride...

, followed by hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of this Herz-salt (2) to the corresponding sodium thiolate
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...



The sodium thiolate 3 can be converted to an intermediate zinc mercaptide with Zinc sulfate
Zinc sulfate
Zinc sulfate is the inorganic compound with the formula ZnSO4 as well as any of three hydrates. It was historically known as "white vitriol". It is a colorless solid that is a common source of soluble zinc ions.-Production and reactivity:...

, followed by reaction of the mercaptide with for instance benzoyl chloride
Benzoyl chloride
Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula C6H5COCl. It is a colourless, fuming liquid with an irritating odour...

, forming a 1,3-benzothiazole
Benzothiazole is an aromatic heterocyclic compound with the chemical formula . It is colorless, slightly viscous liquid. Although the parent compound, benzothiazole is not widely used, many of its derivatives are found in commercial products or in nature...



Aniline 5 is converted 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
    Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

     function to a nitrile
    A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...

     via the Sandmeyer reaction
    Sandmeyer reaction
    The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. It is named after the Swiss chemist Traugott Sandmeyer....

  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
    Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...


The compound, (thioindoxyl, 7) is an important intermediate in the organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 of some dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

s. Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 with acenaphthoquinone
Acenaphthoquinone is a quinone derived from acenaphthene. It is insoluble in water, but soluble in alcohol. It is used as an intermediate for the manufacturing of dyes, pharmaceuticals and pesticides. It is also used in chemical research as a drug and therapeutic agent.The substance is classified...

 gives 8, a dye of the so-called Ciba-Scarlet type, while condensation of 7 with isatine results in the thio-Indigo dye
Indigo dye
Indigo dye is an organic compound with a distinctive blue color . Historically, indigo was a natural dye extracted from plants, and this process was important economically because blue dyes were once rare. Nearly all indigo dye produced today — several thousand tons each year — is synthetic...

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