Abstract: The present invention provides a process for producing 4,4?-dihydroxydiphenylsulfone of very high purity. In particular, the present invention provides a process for producing 4,4?-dihydroxydiphenylsulfone of high purity comprising the steps of subjecting phenol in combination with a sulfonating agent or phenolsulfonic acid to a dehydration reaction in the presence of an aromatic nonpolar solvent while suspending the resulting dihydroxydiphenylsulfone therein, mixing the reaction suspension with a polar solvent to at least partially dissolve the dihydroxydiphenylsulfone, and precipitating 4,4?-dihydroxydiphenylsulfone.

Abstract: The present invention provides a process for producing dihydroxydiphenylsulfone wherein trihydroxytriphenylsulfone and coloring impurities are effectively removed without altering the isomeric composition of dihydroxydiphenylsulfone. In particular, the present invention provides a process for producing dihydroxydiphenylsulfone comprising the steps of dissolveing or suspending in an aqueous solvent crude dihydroxydiphenylsulfone containing trihydroxytriphenylsulfone, adjusting the pH to 5–7, optionally cooling, and separating the crystalline dihydroxydiphenylsulfone thus precipitated.

Abstract: The present invention provides a process for producing 4,4?-dihydroxydiphenylsulfone of very high purity. In particular, the present invention provides a process for producing 4,4?-dihydroxydiphenylsulfone of high purity comprising the steps of subjecting phenol in combination with a sulfonating agent or phenolsulfonic acid to a dehydration reaction in the presence of an aromatic nonpolar solvent while suspending the resulting dihydroxydiphenylsulfone therein, mixing the reaction suspension with a polar solvent to at least partially dissolve the dihydroxydiphenylsulfone, and precipitating 4,4?-dihydroxydiphenylsulfone.

Abstract: A thermal recording material includes a thermosensitive coloring layer, which is made by applying a dispersion liquid, in which the developer and a coloring dye are dispersed, onto a supporting base, and then drying the base. The developer contains 4,4?-dihydroxydiphenyl sulfone as a major component; and 2,4?dihydroxydiphenyl sulfone, the 4,4?-dihydroxydiphenyl sulfone and the 2,4?-dihydroxydiphenyl sulfone being contained at a weight ratio greater than 90:10 and no more than 100:0, and the developer containing phenolsulfonic acid phenyl ester no more than 1.5% by weight with respect to a sum quantity of the 4,4?-dihydroxydiphenyl sulfone and the 2,4?-dihydroxydiphenyl sulfone. The present invention thus provides a thermal recording material causing less surface texture fogging and is superior in preservation ability, and also provides a developer suitably used as a component of the thermal recording material.

Abstract: The present invention provides a process for producing a mixture of dihydroxydiphenylsulfone isomers containing 2,4?-dihydroxydiphenylsulfone, the process comprising heating 4,4?-dihydroxydiphenylsulfone or a mixture of dihydroxydiphenylsulfone isomers containing at least 85 wt. % of 4,4?-dihydroxydiphenylsulfone in the presence of phenol and sulfuric or sulfonic acid.

Abstract: The present invention provides a process for producing dihydroxydiphenylsulfone wherein trihydroxytriphenylsulfone and coloring impurities are effectively removed without altering the isomeric composition of dihydroxydiphenylsulfone. In particular, the present invention provides a process for producing dihydroxydiphenylsulfone comprising the steps of dissolveing or suspending in an aqueous solvent crude dihydroxydiphenylsulfone containing trihydroxytriphenylsulfone, adjusting the pH to 5-7, optionally cooling, and separating the crystalline dihydroxydiphenylsulfone thus precipitated.

Abstract: The present invention provides a process for producing a mixture of 4,4?- and 2,4?-dihydroxydiphenylsulfones comprising heating trihydroxytriphenyldisulfone or a mixture of dihydroxydiphenylsulfone isomers containing trihydroxytriphenyldisulfone in the presence of phenol and an acid catalyst.

Abstract: The present invention provides a process for producing a mixture of dihydroxydiphenylsulfone isomers containing 2,4′-dihydroxydiphenylsulfone, the process comprising heating 4,4′-dihydroxydiphenylsulfone or a mixture of dihydroxydiphenylsulfone isomers containing at least 85 wt. % of 4,4′-dihydroxydiphenylsulfone in the presence of phenol and sulfuric or sulfonic acid.

Abstract: The present invention provides a process for producing a mixture of 4,4′- and 2,4′-dihydroxydiphenylsulfones comprising heating trihydroxytriphenyldisulfone or a mixture of dihydroxydiphenylsulfone isomers containing trihydroxytriphenyldisulfone in the presence of phenol and an acid catalyst.

Abstract: A sulfonating agent represented by the general formula ##STR1## wherein the groups R.sup.1 are the same or different and are each a lower alkyl group having 1 to 3 carbon atoms, n is an integer of 3, 4 or 5, m is an integer of 1 or 2, and n+m.ltoreq.6, and a process for sulfonating an aromatic compound with use of the sulfonating agent.