Method for producing sulfonamides

A process for preparing a sulfonamide of formula I

• wherein:
• R1, R2, R3 and R4 are each hydrogen, halogen, cyano, nitro, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy or C1-C6-haloalkoxy;
• R5 and R6 are each C1-C6-alkyl;
• by reacting a m-nitrobenzoyl chloride of formula II
• wherein the variables R1, R2, R3 and R4 are each as defined above:
• with an amino sulfone of formula III
• H2N—SO2NR5R6 III,
• wherein the variables R5 and R6 are each as defined above;
• under the influence of B equivalents of alkali metal or alkaline earth metal hydroxide as base, wherein, in a first step, the amino sulfone of formula III is reacted with B1 equivalents of alkali metal or alkaline earth metal hydroxide, and, in a second step, the reaction mixture resulting from the first step is reacted with m-nitrobenzoyl chloride of formula II and B2 equivalents of alkali metal or alkaline earth metal hydroxide;
• wherein
• B is 1.5-3 equivalents of alkali metal or alkaline earth metal hydroxide with respect to the amino sulfone of formula III;
• B1 is a subportion of B and is in the range from 0.1-1.3 equivalents of alkali metal or alkaline earth metal hydroxide with respect to the amino sulfone of formula III;
• and
• B2 is a subportion of B and is the difference between B and B1.