Phosphorus oxychloride → 2,3-Dichloro-5-iodopyridine

A 100 ml 3-necked round bottom flask, fitted with a condenser topped with a N2 inlet, a mechanical stirrer and a thermometer, was charged with 17.2 g (0.0673 mole) of 3-chloro-2-hydroxy-5-iodopyridine, 14.85 g (0.0713 mole) of PCl5, and 1 ml (1.68 g; 0.0109 mole) of POCl3. The reaction mixture, containing solids, was slowly stirred and slowly heated to 130° C. The reaction mixture was stirred under N2 for 5 hours after which it was cooled to room temperature and allowed to stand overnight. The reaction mixture was cautiously poured into crushed ice and allowed to stand for 1 hour. Methylene chloride (200 ml) was added to the reaction mixture to dissolve the solids present in it. The layers was separated and the organic phase was washed with dilute base, water and saturated NaCl. After drying over anhydrous MgSO4 and filtration, the solvent was evaporated leaving 11.8 g of a yellow solid. The solid was recrystallized from methanol resulting in 6.60 g of solid that had spectral and physical properties identical to the product obtained in Example 1, STEP D.