tags
iodideiodinephosphorushypophosphorusammonium persulfatehydriodicDCMmandelicphenylacetic
video tutorial Phenylacetic acid from mandelic acid via HI reduction
- Aim: reduce mandelic acid to phenylacetic acid using hypophosphorous acid and iodine; hydriodic acid generated in situ as the active reducing species.
- Substrate preparation: mandelic acid (10 g) dissolved to a slurry with a small amount of water (≈10 mL) in a 250 mL flask.
- Reagent addition and conditions: 15 mL of ≈70% hypophosphorous acid added in large excess; mixture cooled to ≈10°C; 20 g solid iodine added gradually with stirring; iodine reduced to hydriodic acid in situ; the mixture heated to reflux and refluxed for 3 hours.
- Workup and products: after cooling, crystals formed and were filtered and washed with ice-cold water to yield 5.3 g of phenylacetic acid (first batch).
- Purification of remaining product: filtrate extracted with 25 mL dichloromethane, separated, and the organic phase evaporated to yield a second batch of 1.5 g phenylacetic acid; total yield 6.8 g from mandelic acid (76%).
- Notes on purity: second batch less pure (less well-formed and slightly discolored).
- Iodine recovery: the aqueous phase from the DCM extraction is treated with an equal molar amount of ammonium persulfate to oxidize iodide back to iodine, which can be filtered off; see linked video for details.
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