A stirred solution of (3-aminophenyl)propionic acid (4.91 g, 29.7 mmol) in water (50 mL) and concentrated H2SO4 (4 mL) was stirred at -7 C. A solution of NaNO2 (2.4 g, 34.7 mmol) in a minimum amount of water was added to the (ice-salt bath), draining the nitrite solution below the surface of the solution and maintaining the temperature below 0C. After 10 min, the mixture was checked for the presence of excess NO2- using starch-KI indicator paper to ensure that diazotization was complete. Ether (50 mL) was added, followed by a slow addition of a solution of KI (15 g, 90 mmol) in a minimum amount of water to control the dramatic release of N2. After addition, the reactants were stirred and warmed to ambient temperature within 3 hours. The layers were separated and the aqueous layer was extracted with additional ether (2 x 50 mL). The combined ether layers were back-extracted with 5% (w/v) NaHSO3 (aqueous), brine (1 x 25 mL), dried over MgSO4, filtered and concentrated to give (3-iodo)phenylacetic acid in 8.0 g yield.
