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In Friedel-Crafts sulfone synthesis; in other sulfonylation reactions.

Benzenesulfonic anhydride is prepared on a large scale by heating benzenesulfonic acid with excess phosphorus pentoxide mixed with an inert support. An inert support of 1:1 Supercel kieselguhr and Gooch asbestos  was mixed with phosphorus pentoxide and slowly added to benzenesulfonic acid, first at rt then heating to 100 °C. The resultant mixture was heated at 100 °C for 5 h, 1,2-dichloroethane was added, and the solution  was refluxed for 10 min. After cooling and successive filtrations, benzenesulfonic anhydride was recovered in 70% yield.

The reagent can be stored at rt for extended periods under anhydrous conditions. Liquefication occurs upon exposure to air for 2.5 h. Explosive when mixed with 90-95% H2O2.

Crystallise the anhydride from Et2O (m 88.5-91.5o), CHCl3 or chlorobenzene (m 90-92o). Store it dry. [Field J Am Chem Soc 74 394 1952, Beilstein 11 H 3, 11 I 11, 11 II 23, 11 III 50, 11 IV 50.]