Hydrochloric Acid → 5-Methylisatin

An aqueous solution (222 ml) containing 16.7 g (0.10 mol) of chloral hydrate was mixed with 243 g of sodium sulfate, an aqueous solution (56.0 ml) containing 10.0 g (93.3 mmol) of p-toluidine and 9.56 ml of concentrated hydrochloric acid and an aqueous solution (242 ml) containing 20.5 g (0.29 mol) of hydroxylamine hydrochloride in that order and the resulting mixture was heated under reflux with stirring for 30 minutes. After cooling to room temperature, the mixture was filtered with suction to collect a yellowish-brown precipitate. The precipitate was dissolved in 500 ml of a 1.5N sodium hydroxide solution and neutralized with 2M hydrochloric acid. The resulting mixture was filtered and the filtrate was acidified with 2M hydrochloric acid. The thus precipitated isonitroso compound was collected by filtration and washed with iced water followed by drying. The dried product was added to 62 g of concentrated sulfuric acid which had been heated to 60° C. over 40 minutes and the mixture was heated further at 75° C. for 10 minutes. After cooling to room temperature, the resulting mixture was poured into 160 ml of iced water followed by filtration to obtain 10.0 g of 5-methylisatin. NMR (270 MHz, Acetone-d6):

1. temperaturethe resulting mixture was heated
2. temperatureunder reflux
3. filtrationthe mixture was filtered with suction
4. customto collect a yellowish-brown precipitate
5. dissolutionThe precipitate was dissolved in 500 ml of a 1.5N sodium hydroxide solution
6. filtrationThe resulting mixture was filtered
7. filtrationThe thus precipitated isonitroso compound was collected by filtration
8. washwashed with iced water
9. customby drying
10. additionThe dried product was added to 62 g of concentrated sulfuric acid which
11. temperaturehad been heated to 60° C. over 40 minutes
12. temperaturethe mixture was heated further at 75° C. for 10 minutes
13. temperatureAfter cooling to room temperature
14. additionthe resulting mixture was poured into 160 ml of iced water
15. filtrationfollowed by filtration

ORD record

ord-2f49c2fead844b5988cd1e467c75cb86

Source dataset

uspto-grants-1998_07

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US05780634