Industrial process for the production of diphenyl sulfone compounds

A process for producing 4-isopropoxy-4′-hydroxydiphenyl sulfone useful as the developer for leuco dyes to be used in thermosensible papers, which is excellent in productivity, economical efficiency and safety and permits the production of the compounds from constantly available raw materials. This process is improved in productivity and economical efficiency as compared with those of the prior art both by shortening the production time by the use of an isopropyl iodide, which is more reactive than isopropyl bromide which have been used in the prior art.