Cl.[Cl:2][C:3]1[CH:9]=[CH:8][C:7]([Cl:10])=[CH:6][C:4]=1[NH2:5].[N:11]([O-])=[O:12].[Na+].[O:15]=[C:16]1[O:22][C@H]([C@H](CO)O)C(O)=[C:17]1[OH:18]>O>[C:17]([OH:12])(=[O:18])[C:16]([OH:22])=[O:15].[Cl:2][C:3]1[CH:9]=[CH:8][C:7]([Cl:10])=[CH:6][C:4]=1[NH:5][NH2:11]
To a 500 ml flask under a nitrogen atmosphere, concentrated HCl (180 ml, 32%, 10.17 M, 1.83 moles) was charged and cooled down to −2 to 0° C. 2,5-Dichloroaniline (30 g, 185 mmoles) was added in one portion as a solid. The acidic suspension was re-cooled to −2 to 0° C. and sodium nitrite (15.3 g, 222 mmoles) dissolved in water (30 ml) was added dropwise to the acidic mixture through an addition funnel over a period of 1 hour at −2 to 0° C. The resulting mixture was kept with stirring for 1 hour at −2 to 0° C. Next, L-ascorbic acid (34.2 g, 194 mmoles) was added portionwise as a solid at −2 to 0° C. The reaction mixture was allowed to come to room temperature (18-20° C.). A thick orange suspension was formed. The reaction mixture was diluted with concentrated HCl (50 ml, 32%, 0.51 moles, 2.7 eq) and water (150 ml) and then filtered. The wet solid was triturated in water (650 ml) at 20-25° C. for 16 hours, filtered, washed with water and dried to constant weight to afford 34 g of crude oxalic acid derivative as a red crystalline solid.
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