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General procedure for the synthesis of 4,6-dichloro-2-hydroxypyridine from 2-amino-4,6-dichloropyridine: A solution of sodium nitrite (64 mg, 0.93 mmol) dissolved in water (0.6 mL) was added dropwise to a stirred solution of 2-amino-4,6-dichloropyridine (126 mg, 0.77 mmol) in a 5% aqueous sulfuric acid solution (5 mL) at 0 °C. in aqueous 5% sulfuric acid (5 mL), and the time of dropwise addition was controlled within 5 min. The reaction mixture was continued to be stirred at 0 °C for 1 hour. Subsequently, the reaction solution was diluted with deionized water (20 mL) and extracted with dichloromethane (3 x 20 mL). The organic phases were combined, washed with saturated saline (20 mL), dried over anhydrous magnesium sulfate and concentrated under reduced pressure to afford the target product 2,4-dichloro-6-hydroxypyridine (116 mg, 0.71 mmol, 92% yield). Mass spectrum (ESI) m/z: 164,166 [M+H]+.

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