p-sulfonic anhydride  (CAS NO.: ) could be produced through the following synthetic routes.

A mixture of 213 g. (1.5 moles) of phosphorus pentoxide and 14 g. of kieselguhr is prepared by shaking in a dry, stoppered 1-l. Erlenmeyer flask. About one-half of the mixture is then added to a mixture of 7 g. of asbestos and 190 g. (1.0 mole) of p-toluenesulfonic acid monohydrate in a 1-l. round-bottomed flask with one standard-taper neck protected from atmospheric moisture with a drying tube containing calcium chloride. The mixture, which soon becomes quite hot, is allowed to stand for 1 hour with occasional swirling. It is then heated in an oil bath held at about 125° for 9 hours, the remainder of the phosphorus pentoxide mixture being added in four portions during the first 3 hours. During this total 9-hour period the mass is mixed as well as possible with a metal spatula from time to time.

The drying tube is replaced by a condenser, and 400 ml. of ethylene chloride is added. The mixture is heated under reflux for several minutes. The flask is closed with a glass stopper and shaken well. A thin pad of glass wool is then inserted into the lower part of the flask neck, and the extract is decanted. This extraction and decantation process is repeated with three 100-ml. portions of ethylene chloride. The extracts are combined in a 1-l. round-bottomed flask, the solvent is removed by distillation under reduced pressure, and the molten solid is swirled briefly at 3 mm. pressure until cessation of bubbling indicates complete removal of solvent. The dark oily solid, which is formed on cooling, amounts to 138–143 g. and melts in the range 80–124° (sealed tube). This material is purified by dissolving it in the minimum amount (about 200 ml.) of boiling anhydrous benzene and, after cooling to about 50°, adding 300 ml. of anhydrous ether. After crystallization is well advanced, the mixture is stored at -5° overnight. The solvent is removed by forcing it under nitrogen pressure either through a 6-mm. glass tube packed with glass wool up to a constriction about 1 in. from the bottom or through a sintered-glass filter stick. Residual solvent is removed at 3-mm. pressure through a stopcock which is then closed to permit storage of the anhydride at low pressure. The yield is 77–114 g. (47–70%) of light brown or gray prisms. The product, which softens at about 90° and melts at 110–127° (sealed tube), is sufficiently pure for most purposes.