Toluene → Methylthioxanthone

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Dithiosalicylic acid [product of Wako Pure Chemical Industries, Ltd.] (10 parts) was dissolved in sulfuric acid (139 parts), and the solution was stirred at room temperature (about 25° C.) for one hour and then cooled in an ice bath. Toluene (25 parts) was added dropwise in small portions to the cooled solution, while the temperature of the cooled solution was controlled to 20° C. or lower. Thereafter, the temperature was recovered to room temperature (about 25° C.), and the solution was further stirred for two hours. The resulting reaction mixture was added in small portions to water (815 parts), and precipitated yellow solids were filtered. The yellow solids were dissolved in dichloromethane (260 parts). To the resulting solution, water (150 parts) was added, and then 24% KOH aqueous solution (6.7 parts) was added to alkalinize the aqueous phase. After stirring the resulting mixture for one hour, the aqueous phase was removed by a separation operation, and the organic phase was washed with water (130 parts) three times. Then, the organic phase was dried over anhydrous sodium sulfate, and the organic solvent was evaporated under reduced pressure. As a result, 8.7 parts of an intermediate (C122-2-1) was obtained (as yellow solids). The intermediate (C122-2-1) was a mixture of 2-methylthioxanthone and 3-methylthioxanthone.

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