6-Chloro-2-benzothiazolamine → 2-Amino-5-chlorobenzenethiol

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Reaction Steps

Potassium thiocyanate (38.8 g, 0.40 mole) and 4-chloroaniline (50.9 g, 0.40 mole) are dissolved in 300 mL of glacial acetic acid. The solution is cooled below 10° C. in an ice bath and while stirring, bromine (10 mL, 0.40 mole) in glacial acetic acid (50 mL) is added dropwise over one hour with the temperature maintained below 10° C. with external cooling. Stirring is continued for an additional 30 minutes. The reaction mixture is stirred at room temperature for 16 hours. The hydrobromide salt of 2-amino-6-chlorobenzothiazole 5 (X=Cl) is washed with hexane (2×25 mL). The salt is dissolved in warm water (300 mL) and the product precipitated by addition of dilute (10%) sodium hydroxide. The crude product is filtered and recrystallized from ethanol (mp 198-200° C., yield 16.47 g, 63.3%). A mixture of 2-amino-6-chlorobenzothiazole 5 (15 g, 0.08 mole), potassium hydroxide (75 g, 1.34 mole), and water (150 mL) is heated with stirring under reflux over nitrogen for 8 hours. The vigorous reaction subsides slowly. The mixture is then diluted with water (20 mL) and filtered. To the filtrate is added 5 N acetic acid with vigorous stirring and cooling until it is just acid to pH paper. The yellow crystals are filtered, washed with cold water and recrystallized from absolute ethanol and decolorized with neutral Norit. Yield of 5-chloro-2-aminobenenethiol (6, X=Cl); 40%; mp 108-110° C. (lit 110° C.).

Provenance & Evidence