[OH-].[Na+].[CH3:3][C:4]1[CH:13]=[CH:12][C:7]([C:8]([O:10]C)=[O:9])=[C:6]([N:14](S(C)(=O)=O)[S:15]([CH3:18])(=[O:17])=[O:16])[CH:5]=1.CC1C=CC(C(OC)=O)=C(NS(C)(=O)=O)C=1>CO>[CH3:3][C:4]1[CH:13]=[CH:12][C:7]([C:8]([OH:10])=[O:9])=[C:6]([NH:14][S:15]([CH3:18])(=[O:17])=[O:16])[CH:5]=1An aqueous solution of sodium hydroxide (11.0 g) was added to a solution of a mixture of methyl 4-methyl-2-[N,N-bis(methylsulphonyl)amino]benzoate and methyl 4-methyl-2-(N-methylsulphonylamino)benzoate (2326 g) in methanol and the resulting suspension was heated at reflux for 1 hour. It was cooled and the methanol was removed by evaporation. The aqueous solution was acidified and the resultant solid was filtered off to give 4-methyl-2-(N-methylsulphonylamino)benzoic acid (16.42 g) as a cream solid, m.p. 202-205° C.
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