CS277137B6 - Process for preparing an orange dye - Google Patents

Abstract

The method of preparing a mixed orange dye resulting from the azo coupling of diazotized sulfanilic acid with a mixture of azo components consisting of 50 to 99% 1-naphthol and 50 to 1% 2-naphthol consists in that the azo coupling is carried out in three stages. In the first stage, the mixture of azo components is treated with diazotized sulfanilic acid at pH 0 to 2 for a period of 0.5 to 10 min, in the second stage at pH 2 to 4 for a period of 2 to 10 min and in the third stage at pH 4 to 9 for a period of 0.1 to 4 min. The dye in sufficient purity can be obtained by direct drying of the reaction mixture.

Description

The invention relates to a process for the preparation of an orange dye formed by azocoupling diazotized sulfanilic acid with a mixture of azo components consisting of 1-naphthol and 2-naphthol.

The product of the azocoupling of diazotized sulfanilic acid with 1-naphthol belongs to the classical azo dyes and is known as orange I. It is not very suitable for dyeing textile fibers and is not produced in larger quantities for other applications. For dyeing paper, wood, etc. however, a mixed dye containing, in addition to the above-mentioned orange I, orange II, which is the product of the azocoupling of diazotized sulfanilic acid with 2-naphthol, has been used successfully. This dye is obtained from 1-naphthol heavily contaminated with 2-naphthol, which falls off during the production of 1-naphthol of a quality suitable for normal processing. .

According to the known synthetic methods, the azocoupling takes place either for a relatively long time at low pH, with a clear decomposition of the unstable diazo substance, or is carried out at a pH higher than 4 and is therefore accompanied by undesired subsequent reactions. The coupling mixture thus always contains a considerable amount of by-products, in particular the respective disazo dye and colorants, resulting from its further spontaneous transformations. A practical dye can be isolated from the reaction mixture after the addition of sodium chloride by filtration, with most of the color impurities which reduce the quality of the product being removed together with the mother liquors. The actual yield of the mixed dye, i.e. orange I and orange II, is far from the theoretical yield.

It has now been found that a very pure orange dye formed by azocoupling of diazo-forming sulphanilic acid with a mixture of azo components consisting of 50 to 99% 1-naphthol and 50 to 1% 2-naphthol can be obtained according to the invention by carrying out the azocoupling in three stages, in the first stage the mixture of azo components is treated with diazotized sulfanilic acid at pH 0 to 2 for 0.5 to 10 min, in the second stage at pH 2 to 4 for 2 to 10 min and in the third stage at pH 4 to 9 for 0.1 to 4 min. The azocoupling is preferably carried out at a temperature of 20 to 50 ° C and the dry dye can be obtained in sufficient purity by direct drying of the reaction mixture.

Using the process of the present invention, at pH 0 to 2, most of the 1-naphthol reacts substantially uniformly to the desired monoazo dye. The initially very dense reaction mixture gradually dilutes due to the subsequent change in the crystalline form of the precipitated product, which allows easy adjustment of the pH to 2 to 4, without local alkalization during the addition of alkali and thus the formation of more undesired disazo dye. Further rapid alkalization creates the conditions for 2-naphthol to react. In addition, the process according to the invention allows a considerable increase in the concentration of the reaction mixture, which in turn makes it possible to obtain the dye by drying it directly under economically advantageous conditions.

The synthesis procedure is illustrated by the following example:

75.0 vol. Vol. Of sodium sulphanilate solution (c = 1.0 mol.l ^-1 ) are acidified by adding 20.0 vol.

9.0 mol m ^"1) and after cooling the resulting suspension to 10 ° C, the amine in the usual manner by addition of 15.0 vol zdiazotuje. D. A solution of sodium nitrite (c = 5.0 mol.l" ^1). 46.3 vol. Of a solution of sodium naphthalate (c = 1.7 mol. ^-1 ), prepared in the usual manner from 1-naphthol containing about 20% of 2-naphthol, are impregnated with the resulting diazo compound suspension with stirring. After stirring the suspension for pH 4 minutes for 4 minutes, the pH is adjusted to 2.5 ^{with sodium hydroxide solution (c = 10.0 mol.l 1).} While maintaining a constant pH, the reaction mixture is stirred for 5 minutes, and after this time the pH of the reaction mixture is raised to 8.0 ^{by further addition of sodium hydroxide solution (c = 10.0 mol.l -1).} After 10 s, the reaction was stopped and the coupling mixture was dried in a spray dryer.

Claims (2)

PATENT CLAIMS A process for the preparation of an orange dye formed by azocoupling of diazotized sulfanilic acid with a mixture of azo components consisting of 50 to 99% of 1-naphthol and 50 to 1% of 2-naphthol, characterized in that the azocoupling is carried out in three stages. acts with diazotized sulfanilic acid at pH 0 to 2 for 0.5 to 10 min, in the second step at pH 2 to 4 for 2 to 10 min. and in a third step at pH 4 to 9 for 0.1 to 4 min. Process according to Claim 1, characterized in that the azocoupling is carried out at a temperature of 20 to 50 ° C. and the dry dye is preferably obtained by direct drying of the reaction mixture. End of document