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43.5 G. (0.18 mol) of the obtained 3-chlorosulfonylthiophene-2-carboxylic acid methyl ester are dissolved in 450 ml. of absolute chloroform and dry methylamine is led through the solution at 10° C. until a moistened pH paper shows an alkaline reaction with the solution. The mixture is then allowed to react at room temperature for a further 2 hours, the solution always remaining alkaline. The solution is then shaken out with 500 ml. of water and 500 ml. of a 5% sodium bicarbonate solution [the aqueous phases are back-extracted in each case once with chloroform]. The combined organic phases are dried over sodium sulfate and then evaporated. The crystalline residue is digested with ether for purification. There is obtained 3-methylsulfamoylthiophene-2-carboxylic acid methyl ester of melting point 115°-122° C.

1. customis led through the solution at 10° C. until a moistened pH paper
2. customan alkaline reaction with the solution
3. customto react at room temperature for a further 2 hours
4. extractionof a 5% sodium bicarbonate solution [the aqueous phases are back-extracted in each case once with chloroform]
5. dry with materialThe combined organic phases are dried over sodium sulfate
6. customevaporated
7. customThe crystalline residue is digested with ether for purification