4-Bromophthalic anhydride (purity 99.5%) 22.7g (0.10 mol), sodium sulfide 9 hydrate 13. 2g (0.055 mol) and γ-butyrolactone 200 g were allowed to react for 8 hours under reflux 200 ~ 205°C while stirring. 5ml of water was added to the reaction mixture 0.5g, boiled for 1 hour, this solution was analyzed by HPLC. The reaction rate of 4-Bromophthalic anhydride was 99.9%, yield of 4,4'-thiodiphthalic anhydride was 93%. γ-Butyrolactone from the reaction mixture was distilled off under reduced pressure, acetic acid 200g was added to the obtained residual substance solid, and the heating dissolution was carried out. This solution was cooled to room temperature, the precipitated crystals were filtered off and then under reduced pressure, and dried for 1 hour at 100°C. Purified 4,4'-Thiodiphthalic anhydride 23.5g (isolated yield 72%) was obtained. The purity was 99.6% from the analysis by HPLC.
Then, the resulting 4,4'-Thiodiphthalic anhydride 20.0g (0.061 mol), 12-tungstophosphoric acid (H3PW12O40 · 30H2O) 1.0g and acetic acid 250g were charged to four-necked flask made of glass equipped with reflux condenser, thermometer, dropping funnel and stirrer, dissolved by heating to 110°C. Cooled to 80°C, under stirring, the reaction temperature was maintained at 80°C and 9% peracetic acid· acetic acid solution 77.5g (0.091 mol) was added dropwise and takes 4 hours, further reacted for 2 hours. The reaction mixture was cooled to 15°C, the obtained crystals were then filtered, under reduced pressure, and dried for 3 hours at 100°C. 4,4'-Sulfonyldiphthalic anhydride 19.9g (isolation yield 91%) was obtained. This thing was analyzed by HPLC as hydrolysis, as a result purity was 98.9%.