[Cl:1][C:2]1[C:7]([Cl:8])=[C:6]([C:9](=[O:13])[CH2:10][CH2:11][CH3:12])[CH:5]=[CH:4][C:3]=1[OH:14].C(=O)([O-])[O-].[K+].[K+].Br[CH2:22][CH2:23][CH2:24][C:25]([O:27]CC)=[O:26].[OH-].[Na+].Cl>CN(C)C=O.O>[Cl:1][C:2]1[C:7]([Cl:8])=[C:6]([C:9](=[O:13])[CH2:10][CH2:11][CH3:12])[CH:5]=[CH:4][C:3]=1[O:14][CH2:22][CH2:23][CH2:24][C:25]([OH:27])=[O:26]A mixture of 2,3-dichloro-4-butyrylphenol (69.9 g, 0.30 mole), potassium carbonate (75 g, 0.54 mole) and ethyl 4-bromobutyrate (87.8 g, 0.45 mole) in N,N-dimethylformamide (900 ml of sieve-dried material) were stirred and heated at 55°-60° C. for 16.5 hours. The mixture was then treated with 10 normal sodium hydroxide solution (120 ml) and water (600 ml) and stirring and heating at 100° C. maintained for 2 hours. The solution was cooled and poured into ice water (4 liters) containing concentrated hydrochloric acid (250 ml). The solid that separated was removed by filtration, washed with water and dried. The product (88 g) was recrystallized from butyl chloride (500 ml) to give 78.6 g of 4-(2,3-dichloro-4-butyrylphenoxy)butyric acid, m.p. 111°-113° C.
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