N-bromobutanimide → 5-Bromo-2-oxindole

Participants

Reaction Conditions

Reaction Steps

2-Oxindole (53.3 g) was suspended in 640 mL acetonitrile and the mixture cooled to 7° C. in an ice bath with mechanical stirring. Solid N-bromosuccinimide (74.8 g) was added in portions over 20 minutes. After about one-third of the N-bromosuccinimide had been added (over 5 minutes), the temperature had increased to 12° C. The addition was halted until the temperature of the mixture had dropped to 10° C. The addition was resumed keeping the temperature below 12° C. After the addition was complete, the mixture was stirred for 1 hour at 10° C. and then for 1 additional hour during which the mixture was allowed to warm to ambient temperature. The precipitate was collected by vacuum filtration, washed with 80 mL of ethanol and sucked dry for 20 minutes in the filtration funnel to give product containing 6.4% of 2-oxindole by HPLC. The solid was suspended in 1440 mL of denatured ethanol and slurry-washed by stirring and refluxing for 5 minutes at which time most of the solid had dissolved. The mixture was cooled in an ice bath to 13° C. The solid product was collected by vacuum filtration, washed with 80 mL of ethanol and dried under vacuum to give 57.7 g (68.0%) of 5-bromo-2-oxindole containing 1.13% 2-oxindole by HPLC. Slurry-washing with 30% less ethanol gave a better yield (88%) but contained more 2-oxindole (1.76%).

Provenance & Evidence