CS256840B1 - Process for preparing 2-naphthylamino-6,8-disulfonic acid - Google Patents

Abstract

A method for producing 2-naphthylamine-6,8-disulfonic acid by the Bucherer reaction, in which the diammonium salt of 2-naphthol-6,8-disulfonic acid is subjected to a reaction with ammonia in the presence of sulfite or disulfite anions at a temperature of 140 to 195 °C and a pressure of 1 to 4 MPa, with the molar ratio of the diammonium salt of 2-naphthol-6,8-disulfonic acid and ammonia being 1:3 to 9, and preferably 1:5. 2-naphthylamine-6,8-disulfonic acid is used as a dye intermediate.

Description

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The present invention relates to a process for the preparation of 2-naphthylamine-6,8-disulfonic acid. It is based on the reaction of the diamine salt of 2-naphthol-6,8-disulfonic acid with ammonia in the presence of sulfite or disulfite anions.

The so-called Juchereltf reaction is often used in the production of some amino derivatives in the naphthalene series, consisting of the reaction of the corresponding naphthol with ammonia in the presence of sulfite or disulfite anions. The reactions are generally carried out at a temperature of 150 to 180 ° C under increased pressure in an autoclave.

In the case of the production of amino derivatives of aromatic sulfo acids, the Bucherer reaction does not start from the free sulfo acids but from the sodium or potassium salts resulting from the isolation of the corresponding naphtholsulfo acids from the sulfonation products of 1- or 2-naphthol. In the preparation of 2-naphthylamine-6,8-disulfonic acid, starting from the dipotassium salt of 2-naphthol-6,8-disulfoic acid, the latter is isolated from the sulfonation product of 2-naphthol after neutralization with potassium hydroxide as a slightly soluble dipotassium salt. . The Bucherer reaction is generally carried out at a pressure of 2 to 3 MPa and a temperature of 170 to 190 ° C, under which conditions the desired conversion of the -OH group to the -H ₂ group of 95 to 96% is achieved after a reaction time of 30 hours. This long reaction time is highly disadvantageous since it requires the supply of a considerable amount of energy, reduces the capacity of the production equipment and increases the wear of the apparatus per unit of production. A further disadvantage of using the dipotassium salt is that. the resulting product contains a certain amount of inorganic impurities formed from inorganic substances, in particular sulfuric acid, present in the dipotassium salt of 2-naphthol-6,8-disulfonic acid, since this paste contains from 2% to 3% of inorganic substances due to poor filterability , predominantly sulfuric acid

It has been found that these drawbacks can be overcome by the use of barium ammonium salts, prepared for example according to AO 246 653, as starting material for the production of 2-naphthyl-6,8-disulfonic acid instead of the dipotassium salt of 2-naphthalene.

The process according to the invention is characterized in that the bivalent ammonium salt of 2-naphthol-6,8-disulfonic acid is subjected to a Bucherer reaction at a temperature of 150 to 195 ° C and a pressure of 1 to 4 MPa in the presence of ammonia and sulphate of tin or sulphate anions. The ratio of diammonium salt of 2-naphthol-6,8-disulfoic acid to ammonia is 1: 3 to 9, preferably 1: 5. times to 1/4, in addition the 2-naphthylamine-6,8-disulfo acidification thus prepared contains less undesirable inorganic substances ·

The 2-naphthylamine-6,8-disulfoic acid produced (E) can be used either directly or after conversion to the disodium salt to prepare important dyeing intermediates, e.g., to produce 2-naphthylamine-3, 6,8-trisulfoacid or 2-amino- 8-hydroxy-6-naphthalenesulfonic acid (gamma acid).

The process according to the invention can be illustrated by the following examples:

Example 1

582 g of 85.8 $ 2-naphthol-6,8-disulfonic acid as a bivalent ammonium salt, 27 g of sodium metabisulfite, 472 ml of 26% ammonia water and 155 g of water were charged into a laboratory stainless steel stirred autoclave with a useful volume of 1.2 liters. . The contents of the autoclave were heated to 160 ° C over 1 hour, then the temperature was raised to 185 ° C over five hours. After 1 hour reaction at 185 ° C, 96.1% conversion of 2-naphthol-6,8-disulfoic acid to 2-naphthylamine-6,8-disulfoic acid was achieved.

Example 2

The autoclave described in Example 1 was charged with 6.10 g

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85.8% of 2-naphthol-6,8-disulfonic acid as the ammonium salt, 28 g of sodium metabisulfite, 560 ml of 26% ammonia water and 160 ml of water. The reaction mixture was heated to 160 ° C over 1 hour, then the temperature was raised to 180 ° C over 4 hours. During the reaction at 180 ° C, the pressure in the autoclave reached 2.0 MPa.

After a reaction time of 2 hours at this temperature, the conversion of 2-naphthol-8-disulfoic acid to 2-naphthylamine-6,8-disulfoic acid was 96.5% ·

Example 3

The autoclave described in Example 1 was charged with 508 g of 75% 2-naphthol-6,8-disulfoacid in the form of a bivalent ammonium salt,

150 ml 36% aqueous ammonium sulfite solution, 571 g 16% ammonia water, 90 g liquid ammonia and 195 g water. After 6 hours of reaction at 190 ° C the conversion of 2-naphthol-6,8-disulfoic acid to 2-naphthylamine-6,8-disulfoic acid was 96.6%.

Claims (1)

BEFORE THE INVENTION Process for the preparation of 2-naphthylamine-6,8-disulfonic acid by a Bucherer reaction, characterized in that the bivalent ammonium salt of 2-naphthol-6 is reacted with ammonia in the presence of sulfite or disulfite anions at a temperature of 140 to 195 ° C and a pressure of 1 to 4 MPa. 8-disulfonic acid, wherein the molar ratio of the bivalent ammonium salt of 2-naphtol-6,8-disulfonic acid to ammonia is 13 to 9, preferably 15.