Reactions with Acids and their Derivatives

Carboxylic acid esters by heating with an equimolar mixture of phthaloyl chloride and chlorosulfonic acid at 70-250 C gave good yields of the corresponding acid chlorides. Thus, ethyl chlorofluoroacetate, by heating with the mixture at 180 °C, afforded chlorofluoroacetyl chloride (88% yield), but when the ester was heated with chlorosulfonic acid alone the yield of the acid chloride was reduced to 50%. The procedure provides a valuable synthetic route for the direct conversion of carboxylic acid esters into the corresponding acid chlorides (see Chapter 5, p 167).  

The latter reaction gave a substantially increased jdeld of methanedisulfonyl chloride (39, 61%), although chlorosulfonic acid under these conditions did not yield pure methanedisulfonyl chloride 39, which was instead obtained by warming methanedisulfonic acid 36 with phosphorus pentachloride. However, it is possible that the disulfonyl chloride 39 could have been prepared as the sole product by 

Alkanedisulfonic acid diphenyl esters 40 react with chlorosulfonic acid under nitrogen to give the corresponding diphenyl ester disulfonic acid 41 (Equation Ih). The sulfonation of 40 to 41 was improved by using chlorosulfonic acid instead of oleum or other sulfonating agents. 

---