[N+]([O-])([O-])=O.[Na+].N[C:7]1[CH:16]=[CH:15][CH:14]=[C:13]2[C:8]=1[C:9](=[O:22])[C:10]([O:20][CH3:21])=[C:11]([O:18][CH3:19])[C:12]2=[O:17].C(O)(=O)C.N([O-])=O.[Na+].[ClH:31]>O>[Cl:31][C:7]1[CH:16]=[CH:15][CH:14]=[C:13]2[C:8]=1[C:9](=[O:22])[C:10]([O:20][CH3:21])=[C:11]([O:18][CH3:19])[C:12]2=[O:17]A solution of sodium nitrate (0.69 g, 10 mmol) in water (5 ml) was added at 0°-5° C. to a solution of 5-amino-2,3-dimethoxy-1,4-naphthoquinone (1.17 g, 5 mmol) in 5:1 acetic acid:water (25 ml) containing concentrated hydrochloric acid (1.7 ml). A further quantity of sodium nitrite (0.69 g) was then added to the reaction mixture after cooling to -5° C., followed by a solution of cuprous chloride (0.6 g) in concentrated hydrochloric acid (5 ml). The mixture was allowed to warm to 22° C. and solid cuprous chloride was added portionwise until the mixture assumed a green color. Water was then added to the reaction mixture and the precipitated yellow solid filtered off, washed with water and recrystallized from methanol:water (2:1) giving 1.01 g of 5-chloro-2,3-dimethoxy-1,4-naphthoquinone, mp 120°-121° C.
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