High purity 2,4'-dihydroxydiphenylsulfones useful as developers for thermal recording paper can be produced efficiently and with high selectivity by reacting one or more phenols and sulfuric acid in the presence as of at least one of phosphonic acid, phosphinic acid and salts thereof, in the absence of a solvent or in the presence of an aromatic hydrocarbon solvent having a boiling point at atmospheric pressure of 130.degree. to 200.degree. C., and then purifying the thus-produced crude 2,4'-dihydroxydiphenylsulfones using a mixed solvent containing (1) 5 to 20 weight % of at least one lower aliphatic alcohol and 95 to 80 weight % of at least one aromatic hydrocarbon which does not contain halogen, (2) 10 to 40 weight % of at least one ketone and 90 to 60 weight % of at least one aromatic hydrocarbon which does not contain halogen or (3) 10 to 40 weight % of at least one ester of acetic acid and 90 to 60 weight % of at least one aromatic hydrocarbon which does not contain halogen.
高纯度的2,4'-二羟基
二苯砜可作为热记录纸的显影剂,通过在至少一种
膦酸、
膦酸和其盐的存在下,无溶剂或在具有130至200摄氏度大气压下沸点的
芳香烃溶剂的存在下,通过将一个或多个
酚和
硫酸反应,可以高效且高选择性地生产,然后使用含有(1)至少一种低级
脂肪醇的5至20重量%和至少一种不含卤素的
芳香烃的95至80重量%的混合溶剂,(2)至少一种酮的10至40重量%和至少一种不含卤素的
芳香烃的90至60重量%,或(3)至少一种
乙酸酯的10至40重量%和至少一种不含卤素的
芳香烃的90至60重量%来纯化因此产生的粗2,4'-二羟基
二苯砜。