Benzothiazole

Benzothiazole, or more specifically 1,3-benzothiazole, is an aromatic heterocyclic compound with the chemical formula C
₇H
₅NS. 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. Firefly luciferin can be considered a derivative of benzothiazole.^[1] It has a sulfurous odor and meaty flavor.^[2]

Benzothiazole

Space filling model of benzothiazole Ball-and-stick model of benzothiazole
Names
Preferred IUPAC name 1,3-Benzothiazole
Identifiers
CAS Number	95-16-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:45993 Y
ChEMBL	ChEMBL510309 Y
ChemSpider	6952 Y
ECHA InfoCard	100.002.179
PubChem CID	7222
UNII	G5BW2593EP Y
CompTox Dashboard (EPA)	DTXSID7024586
InChI InChI=1S/C7H5NS/c1-2-4-7-6(3-1)8-5-9-7/h1-5H Y Key: IOJUPLGTWVMSFF-UHFFFAOYSA-N Y InChI=1/C7H5NS/c1-2-4-7-6(3-1)8-5-9-7/h1-5H Key: IOJUPLGTWVMSFF-UHFFFAOYAC
SMILES n1c2ccccc2sc1
Properties
Chemical formula	C7H5NS
Molar mass	135.1863 g/mol
Appearance	colorless liquid
Density	1.238 g/mL
Melting point	2 °C (36 °F; 275 K)
Boiling point	227 to 228 °C (441 to 442 °F; 500 to 501 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The three structural isomers of benzothizaole are 1,3-benzothiazole, 1,2-benzothiazole and 2,1-benzothiazole.

Structure and reactivity

Benzothiazoles consist of a 5-membered 1,3-thiazole ring fused to a benzene ring. The nine atoms of the bicycle and the attached substituents are coplanar. The heterocyclic core of the molecule is readily substituted at the methyne (CH) centre in the thiazole ring. Thiazole is electron-withdrawing.

Synthesis and biosynthesis

Benzothiazoles are typically prepared by treatment of 2-mercaptoaniline.^[3] For example, acid chlorides are effective:^[4]

C₆H₄(NH₂)SH + RC(O)Cl → C₆H₄(N)SCR + HCl + H₂O

Many other precursors have been used, commonly aldehydes in the presence of oxidants. In some cases, benzothiazoles are prepared directly from anilines, a process that entails ortho functionalization.^[5]

Naturally occurring benzothiazoles are proposed to arise by condensation of cysteine with quinones.^[1]

Uses

Dyes

The dye thioflavin is a benzothiazole derivative.^[6]

Food additives

Benzothiazole occurs naturally in some foods but is also used as a food additive.^[1] It has a sulfurous odor and meaty flavor.^[7] The European Food Safety Authority assessment had "no safety concern at estimated levels of intake as a flavouring substance".^[8]

Rubber additive

Accelerators for the sulfur vulcanization of rubber are based on 2-mercaptobenzothiazoles.^[9]

Pharmacology

Ziprasidone is used to treat schizophrenia and bipolar disorder.

Benzothiazoles have been widely investigated for their bioactivity.^[10][11] The benzothiazole moiety is, for example, seen in certain dopamine-acting drugs, e.g. riluzole and pramipexole. Moreover, benzothiazole derivatives act as monoamine oxidase inhibitors or dopamine antagonists:

• 6-oxoethers and derivatives of thiadiazole, thiazolyhydrazine that act selectively on either MAO-A or MAO-B depending on the O-sidechain^[12][13][14]
• 1-alkylpiperidines that act on dopamine D₄ receptor^[15][16]

See also

• thiazoles, which lack the fused benzene ring.
• Benzoxazoles, which substitute an oxygen for the sulfur atom.
• 2-Aminobenzothiazoles, well-studied derivatives of benzothiazole

Safety and environmental considerations

Benzothiazoles are widely used in the vulcanization of rubber, so their possible role in the environment has attracted attention. Evidence suggests that they biodegrade readily.^[17]