[NH2:1][C:2]1[CH:3]=[C:4]([S:8]([OH:11])(=[O:10])=[O:9])[CH:5]=[CH:6][CH:7]=1.C(=O)(O)[O-].[Na+].[C:17](OC(=O)C)(=[O:19])[CH3:18]>O1CCCC1.O>[C:17]([NH:1][C:2]1[CH:3]=[C:4]([S:8]([OH:11])(=[O:9])=[O:10])[CH:5]=[CH:6][CH:7]=1)(=[O:19])[CH3:18]A solution of 1.48 g of 3-aminobenzene sulfonic acid in 1:1 tetrahydrofuran/water was treated at 0° C. with 1.43 g of sodium bicarbonate. After 5 min, 1.30 g of acetic anhydride was added dropwise and the reaction allowed to warm to ambient temperature under an atmosphere of nitrogen over 14 h. The reaction mixture was passed through a column of Amberlyst 15 ion exchange resin, eluted with water, and concentrated in vacuo to yield an oil which upon treatment with benzene and azeotropic removal of water in vacuo yielded 1.8 g of the title product as a white crystalline solid. (1H)-NMR (CDCl3) consistent with structure.
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