Bayer Aktiengesellschaft

Horst-Dieter Kramer

Dietmar Mayer

Werner Mentzel

Eike Gabel

Wilfried Kohler

Ruthard Potthast

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.

Process for the preparation of alkali metal diphenylates and free

A process for the preparation of an alkali metal salt of 3-hydroxybenzoic acid and the preparation of 3-hydroxybenzoic acid therefrom is disclosed wherein sulphophthalic acid or a salt thereof is reacted with an alkali metal hydroxide at a temperature in the range of 200.degree. to 300.degree. C. at a pressure of 10 to 30 bars.

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Leverkusen, Germany

Horst-Dieter Kramer