Sulfuric Acid → Indazole-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

Isatin (10 g, 0.067 mol) was added to a solution of NaOH (2.8 g, 0.07 mol) in H2O (44 mL) at 50° C. The stirred clear solution was cooled to 0° C. and a solution of sodium nitrite (4.69 g, 0.067 mol) in H2O (17 mL) was added and stirring continued. A solution of concentrated H2SO4 (12.9 g) in H2O (136 mL) was cooled to 0° C. and added dropwise to the reaction mixture in such a way that the dropper was below the level of the reaction mixture. Stirring was continued for 15 min and a cooled solution of tin(II) chloride dihydrate (36.7 g, 0.16 mol) in concentrated HCl (58 mL) was added over 20 min. The reaction mixture was stirred for 1 h and the orange solid was filtered then heated in H2O at 100° C. The insoluble solids were removed by filtration and the product crystallised from the solution affording the title compound as a yellow solid (3.4 g, 31%). Mp 261-263° C. d, lit 260-261° C. v.Auwers, Dereser Chem. Ber. 1919, 52, 1343. 1H NMR (300 MHz, DMSO-d6) ppm 7.26-7.31 (m, 1H), 7.40-7.46 (m, 1H), 7.63-7.66 (m, 1H), 8.08-8.10 (m, 1H), 12.95 (s, 1H), 13.80 (s, 1H). MS(EI) m/z 162 [M+].

Provenance & Evidence