C([O:3][C:4](=[O:20])[CH2:5][O:6][C:7]1[C:17]([Cl:18])=[C:16]([Cl:19])[C:10]2[S:11][C:12]([CH2:14][OH:15])=[CH:13][C:9]=2[CH:8]=1)C>C(O)C.Cl.O>[Cl:18][C:17]1[C:7]([O:6][CH2:5][C:4]([OH:20])=[O:3])=[CH:8][C:9]2[CH:13]=[C:12]([CH2:14][OH:15])[S:11][C:10]=2[C:16]=1[Cl:19]A suspension of 6.05 g of ethyl[(6,7-dichloro-2-hydroxymethylbenzo[b]thien-5-yl)oxy]acetate in 40 ml of 95% ethanol and 56 ml of 3N hydrochloric acid is stirred under a reflux for 1 hr. The cooled mixture is diluted with 200 ml of water and made acidic with concentrated hydrochloric acid until pH=2. The precipitate is extracted into ethyl acetate (3×200 ml) and the combined organic extracts are washed with brine, dried over anhydrous magnesium sulfate, filtered and concentrated. Recrystallization of the residue from acetone-hexane gives 0.5 g of [(6,7-dichloro-2-hydroxymethylbenzo[b]thien-5-yl)oxy]acetic acid, mp 187.5°-188.5°.
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