Hydrochloric Acid → 5-Hydroxy-2-pyridinecarboxaldehyde
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[OH:1][C:2]1[CH:3]=[CH:4][C:5]([CH3:8])=[N:6][CH:7]=1.OO.Cl.C(=O)([O-])[O-:13].[Na+].[Na+]>C(O)(=O)C.N1C=CC=CC=1>[CH:8]([C:5]1[CH:4]=[CH:3][C:2]([OH:1])=[CH:7][N:6]=1)=[O:13][OH:1][C:2]1[CH:3]=[CH:4][C:5]([CH3:8])=[N:6][CH:7]=1.OO.Cl.C(=O)([O-])[O-:13].[Na+].[Na+]>C(O)(=O)C.N1C=CC=CC=1>[CH:8]([C:5]1[CH:4]=[CH:3][C:2]([OH:1])=[CH:7][N:6]=1)=[O:13]
To a stirred solution of 21.8 g of 5-hydroxy-2-picoline (0.2 mol) in 200 mL of glacial acetic acid was added 18 mL of 30% hydrogen peroxide (0.159 mol) in one portion. The mixture was heated in an oil bath at 80°-85° C. with stirring for 3 h. Then another 18 mL of hydrogen peroxide was added and the mixture was stirred for 3 h at the same temperature. Excess solvent was removed in vacuo followed by the addition of acetone, which caused the pyridine N-oxide to crystallize. Without further purification, 200 mL of acetic anhydride was added to the solid and the mixture was heated at 120° C. with stirring in an oil bath for 2 h. After cooling to room temperature, excess acetic anhydride was removed by high vacuum distillation. The oily material was again oxidized with 30% hydrogen peroxide twice and rearranged with acetic anhydride following the same procedure and amounts depicted above. The black oily material obtained was hydrolyzed with 200 mL of 1N HCl (0.2 mol) at room temperature for 3 weeks (hydrolysis at higher temperature may be harmful to the pyridine nucleus). The mixture was neutralized with anhydrous sodium carbonate, indicated by litmus paper and then extracted three times with 300 mL of diethylether. The combined ether extracts were dried (MgSO4), filtered and evaporated to leave a solid material in a small mount of oil. The pure product (7.8 g, 32%) was obtained by filtering the solid, followed by washing it with a small amount of ether. It is yellow in color and shows a sharp melting point at 186°-187° C. 1H NMR (d6 -DMSO) d: 11.i0 (br. s, 1H, OH); 9.87 (s, 1H, CHO); 8.35 (d, J=2Hz, 1H); 7.58 (d, J=9 Hz, 1H); 7.35 (d of d, J=2Hz, 9Hz, 1H).
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