5-Amino-8-quinolinol dihydrochloride

• 5-acetamido-8-hydroxyquinoline hydrochloride
• 5-(p-tolylsulfonylimino)quinolin-8-one
• 5,8-quinolinesemiquinone via ferric chloride oxidation

A solution of NaNO2 (30 g) in water (100 ml) was added to a mixture of 8-hydroxyquinoline (58 g, 0.4 mol) in distilled water, concentrated hydrochloric acid (75 ml) and ice (200 g) at 0-4C. The reaction mixture was kept at 0C overnight. Within 1 hr C. The reaction mixture was kept at 0 C. overnight and then filtered by washing with cold water to give 5-nitroso-8-hydroxyquinoline hydrochloride (95%).

Step 2: Preparation of 5-amino-8-hydroxyquinoline dihydrochloride

5-Nitroso-8-hydroxyquinoline chloride (40 g) was added to a mixture of water (160 ml) and 5N-NaOH (260 ml) and heated to 40C. Na2S2O4 (95 g) was added to the reaction mixture and the temperature was raised to 75-80C. The reaction mixture was cooled to 50C and 12N-HCl (250 ml) was added. The reaction mixture was then cooled to 0 C and filtered to give 5-amino-8-hydroxyquinoline dihydrochloride (34 g, 69%).