CS255665B1 - Method of crystallization of tartrazines - Google Patents

Abstract

A method of crystallization of tartrazine from an aqueous sodium chloride solution, the amount of which added to the reaction mixture before crystallization is adjusted depending on the concentration of the dye.

Description

The invention relates to the crystallization of tartrazine from aqueous sodium chloride solution to form a well filterable suspension.

Conventionally manufactured tartrazine, i. the dye formed by the azocopulation reaction of diazotized sulfanilic acid with 1- (4'-solfophenyl) -5-pyrazolone-3-carboxylic acid, is isolated from the reaction mixture by crystallization with optional addition of an inorganic salt, most often sodium chloride. The precipitated product is usually filtered and dried without further treatment. After adjusting the selected concentration, it is then used for dyeing textile fibers, leather, wood, etc. For this purpose, the tartrazine conventionally produced is suitable. However, if it is intended, for example, for coloring foodstuffs or pharmaceuticals, the requirements for its concentration and purity are much higher. By using technically more sophisticated filtering devices it is possible to obtain a dye cake with a relatively higher dry matter content and thus somewhat cleaner than, for example, using a conventional filter press. washing with a saturated solution of the same dye according to the author's certificate 253803.

It has now been found that tartrazine of relatively high concentration and purity can be obtained by separating a suitable crystalline form of the dye prepared by the tartrazine crystallization process from the aqueous sodium chloride solution of the present invention, which comprises the amount of sodium chloride added to the reaction mixture. prior to crystallization, it is adjusted depending on the dye concentration in the mixture. In the concentration range of 0.23 to 0.13 mol.l · the amount of sodium chloride is adjusted to a final concentration of 14 to 22% by weight, while reducing the dye concentration by 0.01 mol.l below 0.23 mol.l *. increases the final concentration of sodium chloride by 0.5 to 0.8 wt.

If the prescribed ratio of sodium chloride to dye is maintained within the specified concentration range, tartrazine is obtained in a well filterable form and the dye cake formed after filtration or. centrifugation has a high dry matter content and is easy to swell. Indeed, at the said salt / dye ratio, tartrazine begins to precipitate out of solution in the temperature range of 40 to 50 ° C, which results in the formation of a suitable crystalline form of the product.

The invention is illustrated by the following examples, which are not intended to limit or limit the invention in any way. The examples below also represent only some basic variants suitable for carrying out the proposed method. The relationship between parts by volume and weight corresponds to the liter-kilogram relationship.

Example 1 wt. d. sulfanilic acid is dissolved by adding 56 vol. d of sodium hydroxide solution (Cp ^{= 1} mol ^{= 1} in 470 vol. water). To this solution is added 149 vol. of hydrochloric acid ⁼ 9 mol.l with cooling. sodium nitrite solution ( ^c NaNO ~ 5 mol.l) at a temperature of 112 DEG C. The resulting diazo compound suspension is impregnated to a solution prepared from 162 wt.% 1- (4-sulfophenyl) -5-pyrazolone-3-carboxylic acid. Of sodium hydroxide of the above concentration and 350 vol. Of water During the azocopulation, the pH of the reaction mixture is maintained at 6 to 7 by successively admitting about 40 vol. Of sodium hydroxide solution. Dilute to 1,500 vol d of water, i.e. to a final dye concentration of 0.19 mol.l The resulting mixture is heated to 80 ° C and 550 wt. d of sodium chloride is added, the total amount of sodium chloride in the reaction mixture. then corresponds to 17% by weight mixture to 20-30 ° C, the dye out of solution in the form of filtering well.

Example 2

The coupling mixture prepared as in Example 1 was diluted with 2,000 vol. d. sodium chloride and 10 wt. d. diatomaceous earth, filtered at 80 ° C. The filtrate is further diluted with 850 vol. D of water used to wash the filter device. The dye solution obtained having a concentration of about 0.13 mol.l ³ 'containing 20% by weight of dye. sodium chloride, cooled to 20-30 ° C. Tetrazine precipitates from the solution in a well filterable form

Claims (1)

SUBJECT OF THE INVENTION Process for crystallizing tartrazine from aqueous sodium chloride solution, characterized in that the amount of sodium chloride added to the reaction mixture prior to crystallization is adjusted, depending on the dye concentration in the mixture, so that in the dye concentration range 0.23 to 0.13 mol.l the amount of sodium chloride is adjusted to a final concentration of 14 to -1 By reducing the dye concentration by 0.01 mol.l below 0.23 mol.l, the resulting sodium chloride concentration is increased by 0.5 to 0.8% by weight.