Step I. Synthesis of 2,3-dioxoindoline-7-carbonitrile
To a 100 ml three-necked flask equipped with a stirrer, a thermometer and a reflux condenser tube was added 2,3-dioxoindoline-7-carbaldehyde, hydroxylamine hydrochloride, sodium acetate, 30 mL of glacial acetic acid and 1 mL of acetic anhydride, and refluxed to react. After cooling, it was poured into ice water to precipitate a solid, filtered, washed with water and dried, and recrystallized to obtain 2,3-dioxoindoline-7-carbonitrile.
Step II, Synthesis of 2,3-dioxoindoline-7-carboxylic acid
To a 100 ml three-necked flask equipped with a stirrer, a thermometer and a reflux condenser tube was added 2,3-dioxoindoline-7-carbonitrile, NaOH, water, and refluxed to react. After cooling and filtration, the filtrate was acidified with dilute hydrochloric acid to pH<3, a solid was precipitated, filtered and dried to obtain the compound 2,3-dioxoindoline-7-carboxylic acid.
