The preparation of arylsulphonyl chlorides

Arylsulphonic acids, either free or in the form of their sodium salts, are converted into the acid chloride by reaction with phosphorus pentachloride (or phosphorus oxychloride). 

The arylsulphonyl chlorides may be obtained more conveniently from the aromatic hydrocarbon by reaction with an excess of chlorosulphonic acid (chlorosulphonation) 

The latter general procedure is illustrated by the chlorosulphonation of toluene which yields a mixture of toluene-o- and p-sulphonyl chlorides which may be separated by cooling to — 10 to — 20 °C when most of the para isomer, which is a solid, m.p. 69 °C, separates out (Expt 6.41). 

In a 750-ml three-necked flask equipped as in Fig. 6.2 place 400 g (228 ml, 3.44 mol) of chlorosulphonic acid (CAUTION see Section 4.2.16, p. 424) and cool to 0°C in a freezing mixture of ice and salt. Introduce 100 g (115 ml, 1.09 mol) of pure dry toluene from the dropping funnel dropwise at such a rate that the temperature of the well-stirred mixture does not rise above 5 °C. When all the toluene has been added (about 3 hours), stir the reaction mixture for 4 hours, and then allow to stand overnight in a refrigerator. Pour 

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The preparation of arylsulphonamides from arylsulphonyl chlorides (Expts 6.42 to 6.45). 

The preparation of arylsulphonate esters from arylsulphonyl chlorides (Expt 6.46). 

Arylsulphonyl chlorides may be readily converted into the corresponding arylsulphonamides (e.g. by treatment with solid ammonium carbonate or with concentrated ammonia solution) or into a substituted arylsulphonamide (by reaction with the appropriate amino compound). Arylsulphonylhydrazides (for use in the preparation of aliphatic nitriles, Section 5.13.2, p. 712) may be prepared by a similar reaction using anhydrous hydrazine.20... 

These are prepared by the interaction of the arylsulphonyl chloride and an alcohol or phenol in the presence of sodium hydroxide solution or of pyridine (Expt 6.46). 

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