[N+]([O-])(O)=[O:2].C([O:7][C:8]1[CH:17]=[C:16]2[C:11]([C:12]([OH:19])=[CH:13][C:14](=[O:18])[O:15]2)=[CH:10][CH:9]=1)C>C(Cl)(Cl)Cl>[OH2:2].[OH:19][C:12]1[C:11]2[C:16](=[CH:17][C:8]([OH:7])=[CH:9][CH:10]=2)[O:15][C:14](=[O:18])[CH:13]=1Fuming nitric acid (25 ml) was added to a stirred suspension of 7-ethoxy-4-hydroxycoumarin (m.p. 267°-8°; 5.0g) in chloroform (500 ml) at room temperature over 1.5 hours. After a further two hours, the solvent was removed in vacuo and 6N hydrochloric acid (100 ml) added to the residue. Filtration and recrystallisation from ethanol gave the product, m.p. 153°-4°(d); (C11H9NO6 requires C, 52.59; H, 3.61; N, 5.58. Found: C, 52.48; H, 3.36; N, 5.29).
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