CS238944B1 - Processing of highly pure sulphobezoic acid imide - Google Patents

Abstract

Process for the production of the o-sulfo acid imide - benzoic / saccharin / high purity oxidation o-toluenesulfonamide and the following fractional precipitation of the sodium potassium resulting solution o-sulfamoylbenzoic acid salts by acidification with hydrochloric acid, characterized by with the fact that the second fraction precipitates hot at 85 ° C to 95 ° C.

Description

Process for producing high purity o-sulfobenzoic acid / saccharin / imide.

SUMMARY OF THE INVENTION The present invention provides a process for the preparation of high purity o-sulfobenzoic acid imide (saccharin) by oxidation of o-toluenesulfonamide and subsequent fractional precipitation of a solution of the resulting sodium-o-sulfoamoylbenzoic acid sodium salt by acidification with hydrochloric acid.

The technology currently used is based on the oxidation of o-toluenesulfonamide with potassium permanganate in an alkaline environment. The resulting mixture of sodium-potassium salts of o-sulfamoylbenzoic acid and unreacted sodium salt of o-toluenesulfonamide was separated by fractional precipitation with hydrochloric acid.

In the first fraction, non-oxidized o-toluenesulfonamide precipitates out of the reaction mixture by addition of hydrochloric acid to pH 3. After filtration, the second fraction is precipitated from the remaining solution of the sodium-o-sulfaraoylbenzoic acid sodium salts as the second fraction at normal operating temperature of 15-25 ° C. hydrochloric imide of o-sulfobenzoic acid / saccharin which is centrifuged and dried.

The imide thus produced contains impurities such as o-toluenesulfonamide, p-toluenesulfonamide and p-sulfamoylbenzoic acid in a total amount of up to 5% by weight. This amount of impurities in the product is substantially reduced by using the process of the present invention which utilizes the increasing solubility of the impurities in proportion to the temperature and consists in precipitating the second fraction from a dilute o-sulfamoylbenzoic acid sodium salt solution with a slight excess of hydrochloric acid at high solution temperature. in the range of + 85 to + 95 ° C until the imide is completely precipitated from solution.

COOK

SOjNHNa

The advantage of the invention lies mainly in the simplicity of implementation and thus in economic advantage over the prior art methods which use either extraction of the impurities from the produced imide or converting the water-insoluble imide into a soluble sodium salt to purify impurities. precipitate the imide by acidification.

Both methods require separate technological equipment with special handling and the use of them increases product losses, which worsens economic parameters. The invention makes it possible to use essentially existing technological equipment and does not require the extension of the operator.

The imide produced complies with world-class pharmacopoeias for its quality.

Example

A solution of the sodium-potassium salts of o-sulfamoylbenzoic acid in water, obtained from the oxidation of o-toluenesulfonamide after precipitation of the first fraction and filtration of the precipitate, is diluted to about 10% by weight. It is then heated to a temperature of min. 85 ° C and precipitated slowly with stirring by the addition of 15% w / w. % of hydrochloric acid as long as other o-sulfobenzoic acid (saccharin) imide crystals are dropped, i.e., a virtually slight excess of acid.

After the precipitation was complete, the liquid over the precipitated imide crystals was immediately aspirated and the crystals were decanted with warm (60 ° C) water. The imide is then filtered (centrifuged) and dried. The product obtained contains 99.6 to 99.9% o-sulfobenzoic acid imide, melting point 227 ° C to 228 ° C.

Claims (1)

SUBJECT OF THE INVENTION A process for the production of high purity o-sulfobenzoic imide by oxidation of o-toluenesulfonamide and fractional precipitation of the resulting solution of sodium-potassium salts of o-sulfamoylbenzoic acid with a slight excess of hydrochloric acid, characterized in that it precipitates at a solution temperature of 85-95 ° C. until the imide precipitates completely, which is then isolated after decantation, if necessary, with 60 ° C water.