Sulfonic acids salts, reaction with thionyl chloride

Sulfonyl chlorides (51) may also be obtained by heating the sulfonic acid or its sodium salt with thionyl chloride or phosphorus pentachloride (Scheme 31). The reaction with thionyl chloride is catalysed by the addition of a few drops of DMF. The chlorosulfonation of organic compounds may also be achieved by reaction with sulfur dioxide and chlorine this is an important industrial process (the Reed reaction) (Scheme 32). 

When pyridine is treated with thionyl chloride, a synthetically useful dichloride salt is formed, which can, for example, be transformed into pyridine-4-sulfonic acid. The reaction is believed to involve initial attack by sulfur at nitrogen, followed by nucleophilic addition of a second pyridine at C-4 (cf. 8.12.2). ... 

Chlorobenzene reacts with an equimolar amount of chlorosulfonic acid to give mainly the p-sulfonic acid together with a little of the sulfonyl chloride and the sulfone. With an excess of the reagent good yields of p-chlorobenzenesulfonyl chloride are obtained. The kinetics of the sulfonation of chlorobenzene with chlorosulfonic acid have been studied, and the reaction has been reported in several patents. These involved various modifications such as the use of excess reagent in hydrocarbon solvents containing alkali metal or ammonium salts, or a mixture of the reagent with thionyl chloride in the presence of sulfamic acid, sodium sulfate or dimethylformamide. In the reaction, the yield of 4,4 -dichlorodiphenyl sulfone can be increased under a variety of conditions the... 

Sulfonyl and Sulfinyl Chlorides from Sulfonic and Sulfinic Acids. Alkyl or arylsulfonyl chlorides are prepared by heating the acid with thionyl chloride DMF catalyzes this reaction. (+)-Camphorsulfonyl chloride is produced in 99% yield without a catalyst. Use of the salts of sulfinic acids minimizes their oxidation p-toluenesulfinyl chloride is produced in about 70% yield from sodium p-toluenesulfinate dihydrate with excess thionyl chloride. Phosphorus(V) Chloride is more commonly used for this transformation. 

Chlorosulfonation of 2-ethoxybenzoic acid was found to be very regioselective a mole of thionyl chloride needs to be added to ensure the intermediate sulfonic acid is converted to the sulfonyl chloride (see Scheme 16.3). The sulfonyl chloride was converted to sulfonamide 9 by reaction with A-methylpiperazine. Initially triethylamine was used as a base, and compound 9 could only be isolated as its hydrochloride-triethylamine double salt, which was very insoluble and difficult to use in subsequent steps. A key breakthrough was obtained when it was discovered that sulfonamide 9 also could be isolated as its highly crystalline zwitterion. 

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