Benzothiazole, or more specifically 1,3-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. Firefly luciferin can be considered a derivative of benzothiazole. It has a sulfurous odor and meaty flavor.
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. For example, acid chlorides are effective:T. E. Gilchrist "Heterocyclic Chemistry" 3rd Edition, Longman, 1992. 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.
Naturally occurring benzothiazoles are proposed to arise by condensation of cysteine with quinones.
Uses Dyes The dye thioflavin is a benzothiazole derivative.
Food additives Benzothiazole occurs naturally in some foods but is also used as a food additive. It has a sulfurous odor and meaty flavor. The European Food Safety Authority assessment had "no safety concern at estimated levels of intake as a flavouring substance".
Rubber additive Accelerators for the sulfur vulcanization of rubber are based on 2-mercaptobenzothiazoles.
Pharmacology
Benzothiazoles have been widely investigated for their bioactivity. 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 1-alkylpiperidines that act on dopamine D4 receptor
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.
References
External links MSDS