Process for the preparation of alkali metal diphenylates and free hydroxydiphenyls

Abstract

Hydroxydiphenyls can be prepared by reacting diphenylsulphonic acids or their alkali metal salts with an alkali metal hydroxide at elevated temperature and elevated pressure, in the presence of water. For this purpose, the diphenylsulphonic acids or their alkali metal salts are reacted, at a temperature between 280.degree. and 330.degree. C. and a pressure of up to 120 bar, with an amount of aqueous alkali metal hydroxide having a concentration of at least 50% by weight, such that, after all acidic groups have been neutralized, 3 to 25 mols of alkali metal hydroxide per equivalent of sulphonate group are present in the reaction mixture. Mineral acids are added to the alkaline reaction mixture, after it has been cooled and diluted with water, until the pH value is less than 8, and the precipitated hydroxydiphenyl is isolated at a temperature from -5.degree. C. to +100.degree. C.

Dependencies are inferred from the claim text.