Sulfuric Acid → 5-fluoro-1H-indazole-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

A solution of 5-fluoroisatin (2 g) and sodium hydroxide (0.509 g) in water (20 ml) was heated to 50° C. for 30 minutes, then cooled and then treated with sodium nitrite (0.836 g). This mixture was added over 10 minutes to a solution of concentrated sulfuric acid (2.26 g) in water (200 ml), at 0° C., whilst maintaining the temperature below 5° C. After a further 15 minutes a solution of tin (II) chloride (5.51 g) in concentrated hydrochloric acid (10.5 ml) was added and the resulting mixture maintained at 5° C. for a further 30 minutes. The mixture was then stirred for a further 1 hour whilst warming to ambient temperature then filtered. The light brown paste was dissolved in ethyl acetate and the solution was dried over magnesium sulfate and then evaporated to yield 5-fluoro-1H-indazole-3-carboxylic acid (0.863 g) as a light brown solid which was used without further purification.

Provenance & Evidence