C([NH:5][S:6]([C:9]1[S:10][C:11]([CH3:17])=[CH:12][C:13]=1[C:14]([OH:16])=[O:15])(=[O:8])=[O:7])(C)(C)C.ClC1C=CC=CC=1Cl.[OH-].[Na+]>CCOCC>[CH3:17][C:11]1[S:10][C:9]([S:6](=[O:8])(=[O:7])[NH2:5])=[C:13]([C:14]([OH:16])=[O:15])[CH:12]=1A mixture of 5.0 gm (18 millimols) of 2-(N-tert. butyl)sulfamoyl-5-methyl-thiophene-3-carboxylic acid and 20 ml of o-dichloro-benzene was heated, while stirring, for 4 hours at 140° C. After cooling, the reaction mixture was taken up in a mixture of ether and the equivalent amount of dilute aqueous sodium hydroxide. After separation of the ether phase, the aqueous phase was acidified with hydrochloric acid, and the precipitated material was suction-filtered off. The filter cake was recrystallized from ethyl acetate/cyclohexane, yielding 3.3 gm (83% of theory) of 5-methyl-2-sulfamoylthiophene-3-carboxylic acid.
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