CS211093B1 - Method of isolation of pure o-toluensulphonamide - Google Patents

Abstract

The purpose of the invention was to find an optimal one conditions for the isolation of pure o-toluenesulfonamide from a mixture of its isomers. This the target is achieved by mixing the isomer mixture with dissolved in a mixed solution of ethanol-water, at a temperature of 73 to 80 ° C, 1 to 1 ° C is added 5 wt. vaccine crystals of pure o- -toluenesulfonamide and the mixture was cooled constant speed of 2 to 12 ° C / h. Excluding o-toluenesulfonamide crystals of purity at least 99.5% are further used in production of saccharin

Description

The invention relates to a process for the isolation of pure o-toluenesulfonamide from a mixture of its isomers.

In the Pahlberg process for the production of saccharin, one of the intermediates is o-toluenesulfonamide. This is produced from technical o-toluenesulfon chloride by reaction with dilute ammonia and subsequent washing of the reaction mixture with water. This gives a so-called crude amide containing about 70 to 75 wt. % o-toluenesulfonamide, 5 wt. % m-toluenesulfonamide, 20 wt. p-toluenesulfonamide and minor amounts of p, p'-ditholysulfones. The o-toluenesulfonamide is obtained from the crude amide by crystallization from a mixed solvent of ethanol-water.

The crystallization has so far been carried out by pouring the calculated amount of crude amide into the crystallizer, adding the necessary amount of alcohol and water to produce a solvent containing 55% by volume of ethyl alcohol, and stirring the mixture thus prepared at a temperature above 80 ° C. After dissolution of the crude amide, the solution is cooled uncontrolled to about 35 ° C and the precipitated crystals are separated on a centrifuge and washed with water. The crystallization product is 95% pure o-toluenesulfonamide containing up to 5% by weight of the product. water. The average crystallization yield is 81%. The remaining 19% of o-toluenesulfonamide, together with the other constituents in the mother liquors, leaves the crystallization and is exported to landfill after distilling off the alcohol.

A major drawback of the present crystallization process is that the process does not allow the desired o-isomer to be completely separated from the others, with the result that the product contains up to 5% by weight. especially the undesired β-isomer.

The process of isolating pure o-toluenesulfonamide by cooling crystallization of a mixture of isomers dissolved in the ethyl alcohol-water solution according to the present invention is characterized in that from 1 to 5 wt. . of pure o-toluenesulfonamide seed crystals, then cooled at a constant rate of 2 to 12 ° C per hour to a temperature below 40 ° C while precipitating pure o-toluenesulfonamide crystals.

By controlling the crystallization by the process according to the invention, a significantly better purification effect of the crystallization is achieved. The purity of o-toluenesulfonamide is increased to at least 99.5%.

In carrying out the process of the present invention under optimal conditions, the solution containing the crude amide is cooled from a temperature above 80 ° C to a temperature slightly below the saturation temperature of the solution, which is usually 75 to 78 ° C. At this temperature, about wt. (calculated on the weight of the whole solution) of the seed crystals of solid o-toluenesulfonamide from the previous batch. After seeding, the solution is cooled with constant stirring, preferably at 5 ° C / h, to a temperature of about 35 ° C. Then, the crystalline product is centrifuged, washed with cold water and further processed to saccharin.

Exemplary embodiment

728 kg of the crude amide containing 19% water and 71.8% o-component in dry matter were charged to a crystallizer with a volume of 1.5 ml, to which 557 1 81% ethyl alcohol and 125 1 water were added. The mixture was heated to 80 ° C and maintained at this temperature with stirring for

h. Then the solution was cooled to 78 ° C and 30 kg of the toluene sulfonamide from the previous crystallization were introduced into the crystallizer as seed crystals. The solution was further cooled at a constant rate of 5 ° C / h for 8.5 h to 35 ° C. The resulting suspension was centrifuged and the crystals on the centrifuge were washed with a stream of cold water. Crystallization was obtained

306.5 kg of pure o-toluenesulfonamide with a water content of 3% by weight.

Claims (1)

SUBJECT OF THE INVENTION A process for the isolation of pure o-toluenesulfonamide by cooling crystallization of a mixture of isomers dissolved in a mixed solution of ethanol-water, characterized in that 1 to 5 wt. of pure o-toluene sulfonamide seed crystals, then cooled at a constant rate of 2 to 12 ° C / h to a temperature below 40 ° C while precipitating pure o-toluenesulfonamide crystals.