Process for the preparation of 3-hydroxybenzoic acid

US4393234A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Heinz U. Blank · Odenthal, DE
• Eike Gabel · Bensberg, DE
• Ernst Goldschmitt · Dormagen, DE
• Werner Mentzel · Cologne, DE

Key dates

• Filing date: May 17, 1982
• Grant date: Jul 12, 1983
• Expiry date: May 17, 2002

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C07C51/367
• WIPO field: Organic fine chemistry
• WIPO sector: Chemistry

Abstract

3-Hydroxybenzoic acid is obtained by reaction with an alkali metal hydroxide at a temperature of 220.degree. to 450.degree. C. and under a pressure of 1 to 120 bars, from a technical 3-sulphobenzoic acid mixture which contains sulphuric acid and/or sulphur trioxide and which contains at least 75% by weight of 3-sulphobenzoic acid, relative to the total organic constituents present, and not more than 35% by weight of sulphuric acid and/or SO.sub.3, relative to the total mass. For this purpose, this technical 3-sulphobenzoic acid mixture, if desired after dilution with an equal volume of water, is mixed with sufficient 50 to 100% strength by weight alkali metal hydroxide wherein the remaining 50 to 0% by weight consists essentially of water, for 2.5 to 8 mols of alkali metal hydroxide to be present per mol of 3-sulphobenzoic acid, after neutralization of the sulphuric acid and all the sulpho and carboxyl groups. In general, 10 to 45% by weight of water are present in the batch. The reaction mixture is acidified with a mineral acid to a pH value of less than 4, if appropriate after dilution with water, and the 3-hydroxybenzoic acid is isolated at temperatures within the range from -5.…