At 0° a diazonium salt solution prepared from 2.5 g of 2-fluoroaniline, 1.58 g of sodium nitrite, and 10 ml of 6N hydrochloric acid is added dropwise to a solution of 6.25 g of 4,5-bis(4-methoxyphenyl)-2-mercaptoimidazole in a mixture of 240 ml of dimethylformamide, 10 ml of 2N sodium hydroxide solution, and 1.45 g of powdered copper. The solution develops a reddish brown color under nitrogen evolution. The mixture is further stirred for 3 hours, concentrated under vacuum, and the residue is distributed between water and ethyl acetate. The organic solution is dried over sodium sulfate and concentrated to dryness under vacuum. The residue is subjected to column chromatography on 500 g of silica gel. Elution with acetone/hexane 2:3 yields 2.71 g of 4,5-bis(4-methoxyphenyl)-2-(2-fluorophenylthio)imidazole having a melting point of 195° after recrystallization from hot diisopropyl ether.
