[S:1]([O-:4])([O-])=[O:2].[Na+].[Na+].[C:7](=O)(O)[O-].[Na+].[N+](C1C=C(S(Cl)(=O)=O)C=CC=1C(Cl)=O)([O-])=O.[Na].ClCC(O)=O.[N+:34]([C:37]1[CH2:45][C:44](=S=O)[CH:43]=[CH:42][C:38]=1[C:39]([OH:41])=[O:40])([O-:36])=[O:35]>O>[N+:34]([C:37]1[CH:45]=[C:44]([S:1]([CH3:7])(=[O:4])=[O:2])[CH:43]=[CH:42][C:38]=1[C:39]([OH:41])=[O:40])([O-:36])=[O:35]A 100 mL round bottom flask equipped with a reflux condenser, thermometer and magnetic stirrer was charged with 1.9 g (15 mmol) of sodium sulfite, 5.1 g (60 mmol) of sodium bicarbonate and 20 mL of water. The resulting slurry was cooled to 15° C. and 4.0 g (14 mmol) of 2-nitro-4-(chlorosulfonyl)benzoyl chloride was added over 5 minutes. The reaction mixture was stirred at 15° C. for three hours and then at ambient temperature overnight. After warming to 40° C., 3.1 g (27 mmol) of the sodium salt of chloroacetic acid was added to the aqueous solution of 2-nitro-4-sulfinylbenzoic acid and the reaction mixture heated to reflux. After heating for 7 hours, the reaction mixture was allowed to cool to ambient temperature, diluted with 30 mL of water and washed with 50 mL of ethyl acetate. The aqueous layer was acidified with concentrated HCl and extracted with 75 mL of ethyl acetate. The organic solution was concentrated to afford 3.0 g (87% yield) of 2-nitro-4-(methylsulfonyl)benzoic acid as a pale yellow solid.
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