Process for making 4,4'-dihydroxydiphenyl sulfone

A process is described to make a dihydroxydiphenol sulfone product with a 4,4'-dihydroxydiphenol sulfone purity in excess of 90 wt. % by reaction of phenol and concentrated sulfuric acid in a solvent mixture containing a lower-boiling and a higher-boiling hydrocarbon, removal by azeotropic distillation of water, hydrocarbon, and phenol, phase separation of the distillate, and return of at least the phenol to the reaction at a rate which maintains a phenol to sulfuric acid mol ratio in the reaction of at least 2 to 1.