Cl.[N:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[CH2:8][S:9][C:10]1[CH:19]=[N:18][C:17]2[C:12](=[CH:13][CH:14]=[CH:15][CH:16]=2)[N:11]=1.ClC1C=CC=C(C(OO)=[O:28])C=1.C([O-])(O)=O.[Na+]>C(Cl)(Cl)Cl.CO>[N:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[CH2:8][S:9]([C:10]1[CH:19]=[N:18][C:17]2[C:12](=[CH:13][CH:14]=[CH:15][CH:16]=2)[N:11]=1)=[O:28]In a mixture of 20 ml of chloroform and 5 ml of methanol was dissolved 2.51 g of 2-(2-pyridylmethylthio)-quinoxaline hydrochloride. To the chilled solution kept at a temperature of lower than 0° C. (temperature of solution) was portionwise added 1.95 g of m-chloroperbenzoic acid (purity: 70%). After the reaction was complete, chloroform and saturated aqueous NaHCO3 solution were added to the reaction mixture. The organic layer was separated and dried over sodium sulfate. The sodium sulfate was then removed by filtration, and the solvent was evaporated under reduced pressure from the filtrate. The residue was purified by silica gel column chromatography (acetone/hexane), and recrystallized from ethanol/ether to give 0.27 g of 2-(2-pyridylmethylsulfinyl)quinoxaline as a pale brown crystalline powder, m.p. 117°-122° C. (decompn.).
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