Sulfuric Acid → 4,6-Difluoro-1H-indole-2,3-dione

Participants

Reaction Conditions

Reaction Steps

A solution of 3,5-difluoroaniline (10.8 g) in a mixture of 12N aqueous hydrochloric acid solution (7.5 ml) and water (90 ml) was added to a stirred mixture of chloral hydrate (9.2 ml), sodium sulphate decahydrate (240 g) and water (210 ml). A solution of hydroxylamine hydrochloride (18.6 g) in water (90 ml) was then added and the mixture was heated to 120° C. for 45 minutes. The mixture was cooled to ambient temperature and the precipitate was isolated and dried under vacuum. The material so obtained was added to concentrated sulphuric acid (60 ml) and the mixture was stirred and heated to 80–90° C. for 10 minutes. The mixture was cooled to ambient temperature and poured onto a 1:1 mixture of ice and water (600 ml). The precipitate was isolated, washed with water and dried under vacuum at 50° C. to give 4,6-difluoro-2,3-dioxoindoline (14 g); NMR Spectrum: (DMSOd6) 6.61 (m, 1H), 6.9 (m, 1H).

Provenance & Evidence