1120-95-2

3-Chloropyridazine (cas# 1120-95-2) is a useful reagent for the preparation of benzopyran and imidazole derivatives.

Step A: 3-(2H)-pyridazinone (5.0 g, 52.0 mmol) was mixed with phosphorus trichloride (17 mL, 179 mmol) and reacted at 85 °C for 4.5 hours. Upon completion of the reaction, the mixture was slowly poured into 400 g of ice-water mixture and the pH was adjusted to >10 with 50% NaOH solution, followed by extraction with ethyl acetate (4×). The organic phases were combined, washed with saturated brine, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The resulting crude product was purified by silica gel column chromatography (Hak-Pak, eluent ratio 1:1 hexane/ethyl acetate) to afford 3-chloropyridazine (2.8 g, 46% yield).

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