Butanesulfonyl chloride

Chlorobutane gives 1- and 4-chloro-2-butanesulfonyl chloride and 4-chloro-l-butanesulfonyl chloride,204 hydrolysis of which affords the corresponding sulfonic acids 4-chloro-2- and -1-butanesulfonic acid lose hydrogen chloride when heated, passing into sultones205 (internal anhydrides of hydroxy sulfonic acids). 

When a sulfonic acid such as butanesulfonic acid (111 see Chapter 16, Section 16.9) is treated with thionyl chloride or phosphorus trichloride, the product is a sulfonyl chloride. In this case. 111 is converted to what is known as butanesulfonyl chloride, 112. When 112 reacts with an alcohol, a sulfonate ester is produced. Treatment of 112 with ethanol leads to 113 (ethyl butanesul-fonate) and treatment with methanol leads to 114 (methyl butanesulfonate). A variety of sulfonate esters can be prepared in this manner. It is also possible to react a sulfonic acid with an alcohol under acid catalysis conditions to give sulfonate esters, but that reaction is not discussed until Chapter 20. 

Esters are prepared from carboxylic acids by the reaction between an acid chloride and an alcohol or between a carboxylic acid and an alcohol under acidic conditions. Both sulfonic acids and sulfonyl chlorides react with alcohols to form sulfonate esters. When butanesulfonyl chloride (177) reacts with propanol, usually in the presence of a base such as triethylamine, propyl butanesulfonate (180) is formed. A wide range of sulfonyl esters can be formed this way from an alcohol and a sulfonic acid. 

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