[F:1][C:2]1[CH:3]=[C:4]([CH:11]=[C:12]([F:18])[C:13]=1[O:14][CH2:15][C:16]#[CH:17])[C:5]([O:7]CC#C)=[O:6].[OH-].[Na+]>C(O)C>[F:1][C:2]1[CH:3]=[C:4]([CH:11]=[C:12]([F:18])[C:13]=1[O:14][CH2:15][C:16]#[CH:17])[C:5]([OH:7])=[O:6]To 10 ml of ethanol were added 2.2 g of 2-propynyl 3,5-difluoro-4-(2-propynyloxy)benzoate and 6 ml of a 15% aqueous sodium hydroxide solution, and the resulting mixture was stirred at 50° C. for 1 hour. Thereafter, the reaction mixture which had been allowed to cool to near room temperature was concentrated under reduced pressure, and hydrochloric acid was added to the residue to make the mixture acidic. The precipitated crystals were collected by filtration, and dried, and 1.8 g of 3,5-difluoro-4-(2-propynyloxy)benzoic acid was obtained.
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