Isolation of 4,4'-ditholylsulphone (I) from a mixt. (II) of isomeric ditolylsulphones is achieved by dissolving (II) in aliphatic carboxylic acid(s) (III), opt. mixed with inert solvent(s) (IV), with heating, and sepg. pure (I) crystallising on cooling the soln. (I) is the starting material for the prodn. of 4,4'-disulphonyl-dibenzoic acid, which can give interesting polyesters, polyamides, polybenzoxazoles, polybenzimidazoles and polyurethanes. Effective sepn. can be attained in a single stage. (III) pref. is HOAc and (IV) H2O and their wt. ratio is 1-0.01-1, pref. 1:0.1-0.5. (I) is isolated at a temp. 20-150, pref. 50-100 degrees C below the temp. at which (II) dissolves completely in the solvent concerned. E.g. 99.9% pure (I) was recovered in ca. 71% yield from (II) contg. 63.3% (I).
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