DD160111A1 - PROCESS FOR PREPARING PURE 2,6-DICHLOR-4-NITROANILINE - Google Patents

Abstract

The invention relates to a process for the preparation of 2,6-dichloro-4-nitroaniline, which must satisfy high purity requirements as an intermediate for dyes. The aim of the invention is to avoid the disadvantages occurring in known processes (high technical complexity, low space-time yields, impurities of the final product by interfering by-products, additionally necessary cleaning operations with high material losses, safety risks). It has been found that a 2,6-dichloro-4-nitroaniline is obtained which satisfies all requirements in the preparation of azo dyes when 4-nitroaniline is reacted with gaseous chlorine at temperatures above 20 ° C. in the presence of catalytic amounts of hydroquinone or in the reaction mixture chloroform converted conversion products of hydroquinone in a solvent mixture of 5 to 40 parts, preferably 15 to 25 parts of acetic acid and 60 to 95 parts, preferably 75 to 85 parts of concentrated hydrochloric acid and the reaction mixture then at temperatures not above 40 degrees C with an alkali metal salt of sulfuric acid treated.

Description

VEB CHEMIEKOMBIHAT BITTEEFELD Bitterfeld, 19.2.1980

2057

Process for the preparation of pure 2,6-dichloro-4-nitroaniline

Field of application of the invention

The invention relates to a process for the preparation of pure 2,6-dichloro-4-nitroaniline, which is widely used, above all, as a Zwisohenproduct for the production of azo dyes.

Characteristic of the known technical solutions

For the preparation of 2,6-dichloro-4-nitroaniline, various processes are known which are based on the direct chlorination of 4-nitroaniline in suitable solvents. The preferred reaction medium used is a mixture of 3 parts of concentrated hydrochloric acid and 1 part of glacial acetic acid the chlorination takes place at 0 ^° C. (J · formerly Soo. <£ 1774 »Berschitsch · Ges. 51, 784) ·

Uachteilig in this process is that the maintenance of such a low temperature in the exothermic Eeaktionsgemisch the use of a technically complex and costly

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Cooling system requires and that the Eeaktionsführung at 0 ⁰ C has long reaction times and thus low tree-time yields to PoIge. In addition, it is known (PL PS 51540) that even a slight increase in temperature above 0 ⁰ C to form tarry weaving products and relatively unstable !! - Chlorverbindungen of 2,6-dichloro-4-nitroaniline, especially of N,] i, 2 , 6-tetrachloro-4-nitroaniline, which catalyzes a further resinification of the final product »Already a small amount of impurities in the 2,6-dichloro-4-nitroaniline, however, substantially complicates its further processing into azo dyes.

It is also known (Houben-Weyl, Bd, V / 3, p. 796) that in the production and processing of! - Chlorine compounds for reasons not yet clarified repeated explosions have occurred.

The resulting by-products which accumulate in the separation of the 2,6-dichloro-4-nitroaniline partly as oily substances in the filtrate and thus prevent its reuse, but partly adhere to the pest product as tarry resins, therefore not only lead to a significant reduction in quality of Pinalproduktes, but represent an additional safety Eisiko especially when drying.

Object of the invention

The aim of the invention is to avoid the disadvantages of the previous process in the preparation of 2,6-dichloro-4-nitroaniline.

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Explanation of the essence of the invention

The invention was therefore based on the object to develop a process for the preparation of 2,6-dichloro-4-nitroaniline, which allows a reaction with significantly shorter reaction times and without high technical complexity of refrigeration units, the formation and the negative influence of unstable N- Chloride compounds of 2,6-dichloro-4-nitroaniline and other tarry byproducts largely excludes the re-use of the filtrate permitted avoids safety risks and guarantees optimum quality of the final product.

According to the invention, this object is achieved by reacting 4-nitroaniline with gaseous chlorine at temperatures above 20 ⁰ C in the presence of catalytic amounts of hydroquinone or formed in the reaction mixture conversion products of hydroquinone in a Lbsungsmittelgemisch of 5 to 40 parts, preferably 15 to 25 parts Chlorinated acetic acid and 60 to 95 parts, preferably 75 to 85 parts of concentrated hydrochloric acid and the reaction mixture is then treated at temperatures not above 40 ⁰ C with an alkali metal salt of sulfurous acid ·

The amount of the hydroquinone added to the starting mixture or of the hydroquinone conversion products formed in the reaction mixture is from 0.01 to 0.5, preferably from 0.05 to 0.3, percent by weight, based on 4-nitroaniline used. The alkali metal salts of the sulfurous acid are or potassium sulfites or -hydrogensulfite, but preferably sodium sulfite or sodium hydrogen sulfite, in the form of aqueous solutions or as a solid added to the reaction mixture, the amount of which is one-hundredth to one-tenth of the amount by weight of the 4-nitroaniline used.

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This gives a 2,6-dioxor-4-nitroaniline which is free from interfering impurities and satisfies all requirements in the preparation of azo dyes with a degree of purity of at least 99 % .

The solution according to the invention was not foreseen and must be surprising insofar as in the prior art in the chlorination of 4-Nltroaniline in glacial acetic acid / hydrochloric acid as solvent already at temperatures slightly above 0 ⁰ C and substantially increased above 20 ⁰ C with a substantial resinification of Final product had to be expected by unwanted lifting reactions.

The advantages of the method according to the invention over previously known production processes are the particularly high purity of the product, the unlimited reuse of the filtrate, the avoidance of safety risks during processing and drying, a high Eaum-time yield with minimal energy consumption and the associated cost-effectiveness.

embodiment

670 l of concentrated hydrochloric acid and 170 l of acetic acid are placed in a 2 m stirring crucible1 and 69 kg of 4-nitroaniline and 200 g of hydroquinone are introduced with stirring. For finer distribution of the 4-mt ro aniline, the suspension is stirred for one hour at room temperature. Then 75 kg of gaseous chlorine are introduced at 20 to 25 ⁰ C under water cooling so that an reaction temperature of 30 ⁰ C is not exceeded. Subsequently, the reaction mixture with 3.9 kg of 38 #igen Hatriumhydrogensulfitlösung and one hour at 30 ⁰ C. stirred.

219153

- 5 - 2057

The crystallized 2,6-dichloro-4-nitroaniline is separated by filtration. The resulting filtrate is made up to the initial volume by adding hydrochloric acid and acetic acid and is immediately reused for the following batch. The filter cake is approximately 2% pure Sodium hydroxide solution and water washed acid-free and dried at 80 ⁰ C in a vacuum.

This gives 99 kg (96 % of theory ) of 2,6-dichloro-4-nitroaniline in the form of yellow crystals.

Melting point; 192 ⁰ C with a purity of 99.6 $ ·

Claims (4)

219153 -6- Claim for Existence 1. A process for the preparation of pure 2,6-dichloro-4-nitroaniline by chlorination of 4-hitroaniline, characterized in that 4-hltroaniline with gaseous chlorine at temperatures above 20 ⁰ C in the presence of catalytic amounts of hydroquinone or in the reaction mixture chloroform converted conversion products of hydroquinone in a solvent mixture of 5 to 40 parts, preferably 15 to 25 parts of acetic acid and 60 to 95 parts, preferably 75 to 85 parts of concentrated hydrochloric acid and the reaction mixture then at temperatures not above 40 ⁰ C with an alkali metal salt of sulfurous acid treated. Method according to item 1, characterized in that the amount of hydroquinone or of the hydroquinone conversion products formed in the reaction mixture is from 0.01 to 0.5% by weight, preferably from 0.05 to 0.3% by weight, based on the amount of 4-liters of aniline, amount 3. The method according to the items 1 and 2, characterized in that the amount of alkali metal sulfite or alkali metal bisulfite used one hundredth to one tenth of the amount by weight of the used 4-ITitroanilins.