N([O-])=O.[Na+].[CH3:5][O:6][C:7]1[CH:8]=[N:9][C:10]2[C:15]([CH:16]=1)=[CH:14][C:13](N)=[CH:12][CH:11]=2.Cl.S(=O)(=O)(O)[OH:20].C(=O)([O-])[O-].[Na+].[Na+]>O>[CH3:5][O:6][C:7]1[CH:8]=[N:9][C:10]2[C:15]([CH:16]=1)=[CH:14][C:13]([OH:20])=[CH:12][CH:11]=2
A solution of sodium nitrite (3.49 g, 50.5 mmol, 1.1 eq) in water (20 mL) is added dropwise at 0° C. to a stirred solution of 3-methoxy-quinolin-6-ylamine (8.0 g, 45.9 mmol, 1.0 eq) in hydrochloric acid (160 mL, 321.3 mmol, 7.0 eq). The mixture is stirred at 0° C. for 2 hours before its addition to a vigorously stirred solution of 10% sulfuric acid (600 mL) at 85-90° C. within 20 minutes. The resulting solution is stirred at 90° C. for 1 hour, cooled down to room temperature, neutralized with sodium carbonate and extracted with ethyl acetate (3×250 mL). The combined organic layers are dried over sodium sulfate, filtered and concentrated to give a crude product that is purified by column chromatography (silica gel, eluent: petroleum ether:ethyl acetate:triethylamine, 3:1:0.1, v/v/v) to afford 3-methoxy-quinolin-6-ol as a red solid (2.9 g, 34% yield).
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