Iodine → (2-Chloro-4-mercapto-phenoxy)-acetic acid

To a refluxing solution of PH3 (17 g, 500 mmol) and I2 (2.4 g, 9.4 mmol) in glacial acetic acid (100 ml) was added slowly a solution of (4-chlorosulfonyl-2-chloro-phenoxy)-acetic acid ethyl ester (47.5 g, 151 mmol) in glacial acetic acid (1000 ml). The reaction mixture was refluxed for 24 h. Water (20 ml) was added carefully and the mixture was refluxed for further 1 h. After cooling, the reaction mixture was filtered and the filtrate diluted with water (500 ml). The mixture was extracted with dichloromethane (3×100 ml), and the organic phases were washed with water. After drying the dichloromethane phase was evaporated to give crude (2-chloro-4-mercapto-phenoxy)-acetic acid in 17 g yield.