CS261311B1 - Process for preparing 2-naphthylamino-6,8-disuic acid - Google Patents

Abstract

A method for producing 2-naphthylamine-6,8-disulfonic acid by the Bucherer reaction, in which the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid is subjected to a reaction in the presence of sulfite or disulfite anions at a temperature of 140 °C to 190 °C, wherein the molar ratio of the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid and ammonia is 1:3 to 9, preferably 1:5.

Description

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 ammonium potassium salt of 2-naphthol-6,8-disulfonic acid with ammonia in the presence of sulfite or disulfite ions.

The production of some amino derivatives in the naphthalene series is often carried out by the so-called Bucherer ration consisting in the reaction of the corresponding naphthol with ammonia in the presence of sulfite or disulfite anions. The reactions are carried out mostly at 150-180 ° 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, potassium or ammonium 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, the starting material is either the dipotassium salt of 2-naphthol-6,8-disulfoic acid or the dipotassium salt. In the case of the dipotassium salt, the Bucherer reaction proceeds at 185 ° C and a pressure of 2.5 MPa for 30 hours, when the desired conversion of 96.5% is achieved.

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, particularly sulfuric acid, present in the dipotassium salt of 2-naphthol-6,8-disulfonic acid. '· ’

In the case of the 2-naphthol-6,8-disulfoic acid, the ammonium salt, the Bucherer reaction is carried out at 185 ° C and a pressure of 2.5 MPa for 10 hours with a conversion of 96.5%. The disadvantage of this process is the possibility of producing 2-naphthylamine-6,8-disulfonic acid contaminated with unwanted 2-naphthylamine-6-sulfonic acid (Brenner acid), resulting from 2-naphthol-6-sulfonic acid, often contained in amounts of 0.2 to 0.5% in 2-naphthol-6,8-disulfoacid paste.

Research has shown that the disadvantages of both processes can be overcome by using the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid as the starting material for the Bucherer reaction. The process according to the invention consists in reacting the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid at 140-195 ° C and at a pressure of 1-4 MPa with ammonia in the presence of sulfite or disulfite ions, the molar ratio of the ammonium potassium salt 2-naphthol-6,8-disulfonic acid and ammonia are 1: 3 to 9, preferably 1: 5. Indeed, it has been found that the reaction time required to obtain a conversion of 96.5% is the same for ammonium potassium ammonolysis as for the ammonolysis of a barium ammonium salt, i. 10 hours. The product obtained does not contain a higher amount of unwanted 2-naphthylamine-6-sulfonic acid as compared to the dipotassium salt-based product, since the starting dipotassium and ammonium potassium salts of 2-naphthol-6,8-disulfonic acid contain undesirable 2-naphthol-6-sulfonic acid. 0,1 I.

Due to the higher purity of the ammonium potassium salt over the dipotassium salt, the resulting ammonium potassium salt of 2-naphthylamine-6,8-disulfonic acid contains a lower amount of undesirable inorganic impurities.

The produced ammonium potassium salt of 2-naphthyl-6,8-disulfoacid can be used directly or after conversion to the sodium potassium salt for the preparation of important dyeing intermediates, e.g. for the production of 2-naphthylamine-3,6,8-trisulfoacid or 2-amino-8- hydroxy-6-naphthalenesulfonic acid.

The process of the invention can be illustrated by these examples.

He did

1 940 ml of 25% ammonia water was introduced into the autoclave and 68% 2-naphthol-6,8-disulfonic acid ammonium salt paste containing 2,400 g of active ingredient was introduced with stirring. After the addition of 151 g of 92% sodium metabisulfite, the autoclave was closed and heating was started. After 1 hour a temperature of 160 ° C was reached, after which the contents were heated at a heating rate of 5 ° C per hour to 185 ° C, at which temperature the contents were allowed to react for 4 hours at a pressure of 2.3 MPa. . After this time a conversion of 96.7% was achieved.

Example 2

A dried ammonium potassium salt of 2-naphthol-6,8-disulfoic acid containing 355 g of active ingredient was charged into the autoclave. After addition of 20.3 g of 92% sodium metabisulfite, 425 g of water was added and the autoclave was closed. 100 g of liquid ammonia was then added from the cylinder. The autoclave was heated as in Example 1, at a pressure of 2.4 MPa at 185 ° C. After 5 hours of reaction at 185 ° C, a conversion of 96.9% was achieved.

Claims (1)

SUBJECT OF THE INVENTION A process for producing 2-haphtylamine-6,8-disulfonic acid by a Bucherer reaction, characterized in that the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid is reacted in the presence of sulfite or disulfite anions at a temperature of 140 to 190 ° C, wherein the molar ratio the ammonium potassium salt of 2-naphthol-6,8-disulfonic acid and ammonia is 1: 3 to 9, preferably 1: 5.