[F:1][C:2]1[CH:12]=[CH:11][C:5]([CH:6]=[CH:7][C:8]([OH:10])=[O:9])=[CH:4][CH:3]=1.[CH3:13]O.S(=O)(=O)(O)O.O>C(OCC)C>[CH3:13][O:9][C:8](=[O:10])[CH:7]=[CH:6][C:5]1[CH:4]=[CH:3][C:2]([F:1])=[CH:12][CH:11]=1A one liter round bottom flask was charged with 50 grams (0.30 moles) of 4-fluorocinnamic acid, 500 milliliters of methanol, and 5.0 grams of concentrated sulfuric acid. This mixture was brought to reflux and kept there for 18 hours. After cooling, one half of the methanol was stripped under vacuum, and the remaining solution was poured into 600 milliliters of water. The precipitated solid was taken into 500 milliliters of diethyl ether and the aqueous phase was discarded. The ether solution was washed three times with 10% aqueous sodium hydroxide and once with water. After drying over magnesium sulfate, the mixture was filtered and stripped under vacuum to give methyl-4-fluorocinnamate as a white crystalline powder. Yield was 40 grams.
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