Process of producing high purity bis(4-hydroxyphenyl)sulfides and heat-sensitive recording materials containing the same

In a method of producing high purity bis(4-hydroxy-phenyl)sulfides which comprises reacting phenols which have the general formula of ##STR3## wherein R.sup.1 and R.sup.2 independently represent a hydrogen or an alkyl of 1-4 carbons, with sulfur dichloride in an organic solvent, to provide bis(4-hydroxyphenyl)sulfides having the general formula of ##STR4## wherein R.sup.1 and R.sup.2 are the same as before;

• the improvement comprising:
• (a) reacting the phenols with sulfur dichloride in a nonpolar organic solvent, which is selected from the group consisting of an aliphatic hydrocarbon, an alicyclic hydrocarbon, and carbon tetrachloride, at temperatures ranging from -10.degree. C. to 30.degree. C.;
• (b) removing partly or wholly the nonpolar organic solvent by distillation from the resultant reaction mixture after the reaction;
• (c) adding a polar organic solvent, which is selected from the group consisting of a halogenated aromatic hydrocarbon and a halogenated aliphatic hydrocarbon, to the reaction mixture to dissolve the reaction mixture therein at temperatures ranging from 70.degree.-100.degree. C.;
• (d) filtering the resulting mixture to remove solid materials at temperatures ranging from 70.degree.-90.degree. C.;
• (e) washing the resultant filtrate with an aqueous alkaline solution at temperatures ranging from 70.degree.-100.degree. C.;
• (f) separating an organic layer from the filtrate at temperatures ranging from 60.degree.-90.degree. C.;
• and
• (g) cooling the organic layer to crystallize out the bis(4-hydroxyphenyl)sulfides and separating the sulfides.