CS253803B1 - A process for preparing low impurity dyes - Google Patents

Abstract

A method for preparing dyes with a low impurity content by washing the dye separated from the reaction mixture or crystallization mixture with an aqueous, preferably saturated solution of the same dye, preferably obtained by diluting a portion of the unfiltered reaction or crystallization mixture with the optional addition of sodium chloride or sulfate, and part or the entire amount of the solution used is optionally returned to the production process and added to subsequent batches of the dye being produced.

Description

253803 2

BACKGROUND OF THE INVENTION The present invention relates to a process for preparing low impurity dyes by removing most of the inorganic and organic impurities by washing the crude dye with a solution of the same dye. Most synthetic dyes are isolated from the reaction mixture by crystallization with optional addition of an inorganic salt, most often sodium chloride. The deposited product is usually filtered and dried without further purification operations. After adjusting the selected concentration, it is then used for dyeing textile fibers, leather, paper, wood, etc. For these purposes, it is fully satisfactory. However, if certain dyes are intended for special purposes, for example, for dyeing medicaments, their purity requirements are very high. high.

By using technically more demanding filtering devices, it is possible to obtain a dye cake having a relatively high dry matter content and thus somewhat cleaner than, for example, using a conventional dyeing machine, but the effect is usually not as required. However, this is the only technically or economically viable process which, so far, in addition to recrystallization, for many reasons, has made it possible to at least partially increase the quality of some dyes. The prior art methods for washing the filter cake have not been considered, as many dyes are too soluble in water and in dilute solutions of inorganic salts. When using concentrated salt solutions, the amount of salt contained in the final product would be high.

It has now been found that dyes of superior quality can be prepared by the process of the present invention such that the dye separated from the reaction or crystallization mixture is washed with an aqueous, preferably saturated, solution of the same dye, preferably obtained by diluting a portion of the non-filtered reaction or crystallization mixture in the presence of an addition sodium chloride or sodium sulfate, and a portion of the amount of solution used is optionally returned to the production process and added to the further batches of the dye produced preferably at the synthesis or isolation stage.

In this way it is possible to obtain a very pure dye, virtually lossless, i.e. in an amount corresponding to the yield of the crude dye. The smaller the inorganic salts contain the washing solution, the higher the concentration of the substance in the final product after drying. If a saturated, almost saturated aqueous solution of the colorless salt-free dye is used for washing, and the washing is efficiently effected, the product is obtained with a content close to 100% of the actual substance in the dry matter.

The invention is further illustrated by the following non-limiting examples. The examples below also represent only some basic variants suitable for carrying out the proposed method. The relationship between volumetric and weight parts corresponds to a liter-kilogram relationship.

EXAMPLE I Sulxanilic acid diol is dissolved by adding 56 parts by volume of a hydroxidusccinate solution = 10 mol.l in 430 parts by volume of water. To the thus prepared solution, 149 v / v of sodium chloride (c = r = 9 mol.l with simultaneous cooling at 20 [deg.] C. of parts of sodium nitrite solution (cNaNc > 2 ~) are added. The diaphragms are impregnated with a solution prepared from 162 µl of 1 - [(4 S) -phenyl] -5-pyrazolone-3-carboxylic acid, 97 vol. water in the azocopulation range, the pH of the reaction mixture is maintained at 6 and 7 by gradually exiting the sodium hydroxide solution. Upon completion of the coupling operation of 1000 vol. D. Of water, the dye is eliminated from the equilibrium by adding koni horse Ό nm. d> sodium hydroxide, 95% νηηκια is subjected to filtration, xe. the remaining cm 5 1. ij i i iL otj .. o se-prumvva: iorlr. ; Ø 390 mm Ord. d. Water, Thus. ími !; The solution of Ocr-yvu, which contains ool ioloxide, was added. to, is washed with a filtering agent which, after drying, provides a bed product of about 93-95%. Unwashed nur in x, i-jjyioil i s. p. - c! 3 - '' own. substances.

Claims (1)

EXAMPLE 2 All of the dye suspension prepared as described in Example 1 is filtered and the filter cake obtained is washed with a liquid prepared by dissolving about 150 wt. d. a wet product from a previous batch in 500 vol. d of cold water. The optimum cleaning effect is achieved when the solution is saturated. The washing liquid used is collected and the following batch is added to the reaction mixture after the azocopulation has ended. In this case, a product containing about 98-99% of the substance by weight in the dry matter is obtained and the entire purification operation is practically free of losses. EXAMPLE 3 All of the dye suspension prepared by the process described in Example 1 is filtered and the obtained filter cake is washed with a liquid prepared by dissolving about 30 wt. d. a previously produced moist product in 500 vol. d. sodium sulfate solution. A very pure product is obtained, containing about 93-95% of the substance by weight, about 5-7% of inorganic salts and only a very small amount of organic impurities. Example 4 38.1 wt. d. sulfanilic acid is dissolved by adding 22 vol. d of sodium hydroxide solution (c = 10 mol / l) in 230 vol. To the thus prepared solution is added 59 µl, N aoh d of hydrochloric acid (cHCl - 9 ml. With simultaneous cooling at 20 ° C) of a solution of sodium nitrite (5 mol / l). The resulting suspension of diazolate is impregnated to a solution prepared from 50 wt.% Of 2-naphthol-6-sulfonic acid, 25 vol. D, sodium hydroxide of the above concentration and 500 vol. The reaction mixture is maintained at 5-6 by gradually adding about 6 vol. d of sodium hydroxide solution, and after completion of the reaction, the dye formed precipitates out of solution by addition of 190 wt. However, a clear solution is prepared by dissolving about 3 wt.% of a wet dye obtained by spraying the suspension prepared by the process described in this example at 250 vol. The washing liquid used is preferred to obtain and add subsequent blends after the end of azocopulation, thereby obtaining a product containing, according to the efficacy of the selected process, the% of the substance in the soil. · • ·. in the form of a foam. r: low-impurity sy: u.-rviv grade, characterized in that the dye ο-ρ- · ar?-vn. 30% by weight, preferably saturated solution, of the reaction crystals of the ophthalmic lens. or a portion of the entire bypass. r: .cesia;. It is advantageous for further batches to be produced by burv