Sulfuric Acid → 4,5-Dichloro-7-nitroisatin

Reaction equation

[Cl:1][C:2]1[C:10]([Cl:11])=[CH:9][CH:8]=[C:7]2[C:3]=1[C:4](=[O:13])[C:5](=[O:12])[NH:6]2.OS(O)(=O)=O.[N+:19]([O-])([O-:21])=[O:20].[K+]>C1C=CC=CC=1>[Cl:1][C:2]1[C:10]([Cl:11])=[CH:9][C:8]([N+:19]([O-:21])=[O:20])=[C:7]2[C:3]=1[C:4](=[O:13])[C:5](=[O:12])[NH:6]2

Participants

Procedure

To a solution of 4,5-dichloroisatin (13f, 430 mg, 2.0 mmol) in cone H2SO4 (5 mL) was added powdered KNO3 (300 mg, 2.5 mmol) at 0° C. in portions with stirring. The mixture was stirred at 22° C. for 16 h, poured into ice-H2O (50 mL). The precipitate was filtered, washed with H2O (5×10 mL) and dried to give 295 mg (54%) of 13 h as a yellow powder. The analytical sample was obtained by crystallization from benzene, mp 204°-5° C. IR 1776, 1768, 1749, 1614, 1473, 1340, 1227 cm-1 ; 1H NMR δ 11.932 (s, 1H), 8.535 (s, 1H). HRMS Calcd for C8H2Cl2N2O4 : 259.9391; Found: 259.9389.