US 4,393,234 A · Process for the preparation of 3-hydroxybenzoic acid

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.degree. C. to +40.degree. C.

Claims28

Dependent claims

In a process for the preparation of 3-hydroxybenzoic acid by contacting 3-sulphobenzoic acid with an alkali metal hydroxide at an elevated temperature, the improvement which comprises:

(A) employing a technical 3-sulphobenzoic acid mixture containing sulphuric acid and/or sulphur trioxide, which technical mixture 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;
(B) the technical mixture is contacted with mixing at an elevated temperature with sufficient 50 to 100% strength by weight alkali metal hydroxide, the remaining 50 to 0% by weight consisting essentially of water, such that 2.5 to 8 mols of alkali metal hydroxide are present per mol of 3-sulphobenzoic acid, after neutralization of the sulphuric acid and all of the sulpho and carboxyl groups;
(C) the resultant alkaline reaction mixture is reacted at a temperature in the range of 220.degree. to 450.degree. C. under a pressure of 1 to 120 bars;
and
(D) the alkaline reaction mixture so obtained is acidified with a mineral acid to a pH value less than 4 and 3-hydroxy benzoic acid is recovered at a temperature in the range of -5.degree. to +40.degree. C.

2 more elements

A process for the preparation of 3-hydroxybenzoic acid which comprises:

(A) contacting benzoic acid with 0.01 to 0.5 mol of sulphuric acid per mol of benzoic acid and sulphonating the reaction mixture at an elevated temperature with 1 to 1.2 mols of SO.sub.3 per mol of benzoic acid, the SO.sub.3 being in the gaseous and/or liquid form and containing 0 to 35% by weight of sulphuric acid, relative to the H.sub.2 SO.sub.4 --SO.sub.3 mixture, whereby to obtain a reaction mixture containing 3-sulphobenzoic acid;
(B) the reaction mixture so obtained containing 3-sulphobenzoic acid is thereafter contacted with sufficient 50 to 100% strength by weight alkali metal hydroxide, the remaining 50 to 0% by weight consisting essentially of water, such that 2.5 to 8 mols of alkali metal hydroxide are present per mol of 3-sulphobenzoic acid, after neutralization of the sulfuric acid and all the sulpho and carboxyl groups;
(C) the reaction mixture is reacted at a temperature in the range from 220.degree. to 450.degree. C. under a pressure of 1 to 120 bars;
and
(D) the reaction mixture so-obtained following the reaction of step C is acidified with a mineral acid to a pH less than 4 and 3-hydroxybenzoic acid is recovered at a temperature in a range from -5.degree. to +40.degree. C.

2 more elements

Dependencies are inferred from the claim text.

Process for the preparation of 3-hydroxybenzoic acid

Life of this patent

Process for the preparation of 3-hydroxybenzoic acid

Life of this patent

Abstract

Claims28