[F:1][C:2]1[CH:8]=[CH:7][C:6]([CH2:9][CH2:10][CH3:11])=[CH:5][C:3]=1N.N([O-])=O.[Na+].C(O)(=[O:18])C.[S:20](=[O:22])=[O:21]>S(=O)(=O)(O)O.O.[Cu](Cl)Cl>[F:1][C:2]1[CH:8]=[CH:7][C:6]([CH2:9][CH2:10][CH3:11])=[CH:5][C:3]=1[S:20]([OH:18])(=[O:22])=[O:21]A solution of 12.53 g of 2-fluoro-5-n-propylaniline dissolved in a mixed solution of 73 ml of conc. sulfuric acid and 120 ml of water was cooled to -10° C. and an aqueous sodium nitrite solution containing 6.15 g of sodium nitrite dissolved in 15 ml of water was added dropwise thereinto at a temperature of -5° C. or lower, followed by stirring at this temperature for 25 minutes to prepare a diazonium salt solution. The diazonium salt solution was added dropwise into a mixed solution of 120 ml of acetic acid saturated with sulfur dioxide and 2.92 ml of copper chloride dissolved in 20 ml of water at a temperature of -20° C., and after stirred at -10° C. for 30 minutes and further at 0° C. for one hour, the oily substance separated was extracted with ethyl acetate. Ethyl acetate was evaporated under reduced pressure from the extract, and to the residue were added 90 ml of 2 N sodium hydroxide solution and 200 ml of dioxane. After the mixture was heated at 100° C. for 5 minutes, it was neutralized with acetic acid and the reaction product was purified by silica gel chromatography (eluant:chloroform:methanol:acetic acid =500:50:6) to give 7.13 g (yield: 39.9%) of the above title compound as a paste.
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