CH632739A5 - METHOD FOR PRODUCING NITRO-Armstrong acid-MAGNESIUM SALT. - Google Patents

Description

632739

PATENT CLAIMS

1. A process for the crystallization of 3-nitronaphthalene-1,5-disulfonic acid dimagnesium salt (NAS-Mg salt), characterized in that 3-nitronaphthalene-1,5-disulfonic acid (NAS) from the acidic reaction mixture of the nitration crystallized from 1,5-naphthalene disulfonic acid (Armstrong acid) by means of an aqueous magnesium salt solution at a temperature between 90 and 120 ° C.

2. The method according to claim 1, characterized in that crystallized out at a temperature between 95 and 100 ° C.

3. The method according to claim 1, characterized in that magnesium sulfate solution (Epsom salt solution) is used as the magnesium salt solution.

4. The method according to claim 1, characterized in that one carries out the precipitation in 40 to 60% sulfuric acid as the reaction medium.

5. The method according to claim 1, characterized in that one uses the magnesium salt in amounts of 110 to 130 mol%, based on the content of nitro-Armstrong acid.

6. The 3-nitronaphthalene-l, 5-disulfonic acid dimagnesium salt prepared by the process according to claim 1.

The magnesium salt of nitro-armstrong acid (3-Ni-tronaphthalene-l, 5-disulfonic acid magnesium salt) - hereinafter referred to as NAS-Mg salt - represents an intermediate stage for the preparation of the corresponding 3-aminonaphthalene-l, 5-disulfonic acid of the so-called C. Acid.

C-acid is used as a diazotization component for cotton dyes and as an intermediate for the production of 2-naphthol-4,8-disulfonic acid. It is produced on an industrial scale by a process described in Ullmann's Encyclopedia of Industrial Chemistry, 8th edition, volume 9, page 629, by nitrating naphthalene to naphthalene-1,5-disulfonic acid and then reducing it. After the nitration step, crystallization of the nitration product is required to remove undesired isomeric by-products. The largest proportion of undesirable by-product is 2-nitronaphthalene-4,7-disulfonic acid. Like nitro-armstrongic acid (3-nitronaphthalene-1,5-disulfonic acid), this compound forms a poorly soluble magnesium salt.

However, the solubility of the 2-nitronaphthalene-4,7-disulfonic acid dimagnesium salt in water increases with increasing temperature more steeply than that of the nitro-armstrong acid di-magnesium salt. Therefore, by precipitation and filtration of the nitration mixture in the form of the magnesium salts at 60 ° C, the by-products including the 2-Ni-tronaphthalene-4,7-disulfonic acid can be kept largely in solution and separated with the mother liquor and practically pure nitro-Armstrong acid remains as a filter residue -re-dimagnesium salt back.

There was now the prejudice that when using magnesium salt amounts of more than 122 mol%, in particular more than 130 mol%, based on the content of nitro-armstrongic acid, the 2-nitronaphthalene-4,7-disulfonic acid was only present at significantly higher levels Temperatures, with loss of product yield and partial decomposition of the nitro compounds can be selectively separated.

On the other hand, the NAS Mg salt is obtained in the form of very fine, difficult to filter crystals. The NAS-Mg salt crystallizes in 45 to 50% sulfuric acid as hexahydrate:

S03MSl / 2

The solubility in the mother liquor at 60 ° C is about 0.1 to 0.2 percent by weight. It was believed that the low solubility in combination with the rapid ionic formation reaction for the NAS Mg salt apparently resulted in the formation of extremely fine crystals with X50o / o values of 3 to 7 µm grain diameter (5 to 10% of the crystals have caused grain diameters of less than 1 | im), and 20 were of the opinion that the fine crystallinity is even more pronounced at elevated temperature with a simultaneous increased formation reaction.

The filtration of these fine crystals represents a real engineering problem and an ecological problem at the same time, since 25 large quantities of dilute sulfuric acid and washing water are required for washing.

Surprisingly, it has now been found that, contrary to these prejudices, the NAS Mg salt is used at higher temperatures

"3o a) is obtained in the form of large, easily filterable crystal grain distributions and b) the yield of pure NAS-Mg salt is increased still further.

The new process for the crystallization of 3-nitronaph-35 thalin-l, 5-disulfonic acid dimagnesium salt (NAS-Mg salt) is characterized in that 3-nitronaphthalene-1,5-disulfonic acid (NAS) is obtained from the acidic reaction mixture of Nitration of 1,5-naphthalenedisulfonic acid (Armstrong acid) crystallized using an aqueous magnesium salt solution 40 at a temperature between 90 to 120 ° C.

The reaction mixture from the nitration of 1,5-naphthalene disulfonic acid contains sulfuric acid from the mixed acid nitration. This is diluted and serves as the reaction medium during crystallization.

45 Due to the water required for the filtration and washing of the NAS Mg salt and the necessary recycling of the washing water, a minimum dilution of the sulfuric acid to 50% is advantageous for the precipitation.

However, the sulfuric acid concentration can vary between 40 and 60%.

Magnesium salts and mineral magnesium oxides are suitable as magnesium-containing precipitants. However, magnesium sulfate in the form of epsom salt (magnesium sulfate heptahydrate) is preferred.

55 The magnesium salt (Epsom salt solution) is used in amounts of 110 to 130 mol%, based on the content of nitro-armstrong acid. 120 to 122 mol% are optimal.

The most advantageous precipitation temperature is between 95 60 and 100 ° C.

In detail, the method can be carried out, for example, as follows:

The water required to dilute the sulfuric acid is placed in an agitator tank. The Ni-65 tration solution of 1,5-naphthalenedisulfonic acid is then introduced at such a rate that the solution remains at about 100 ° C. with only gentle cooling. Then the crystallization of the NAS-Mg salt takes place by means of bitters

saline solution. The concentration of the Epsom salt solution is chosen so that the total amount can be added within approx. 60 minutes. It is usually approx. 20 to 25% MgS04. After the precipitation, stirring is continued for about 60 minutes at about 90 to 100 ° C. for the purpose of crystal growth, and the mixture is cooled to about 60 ° C. for about 60 minutes and filtered. The filter cake is washed with water. The filter cake obtained in this way can be further processed directly in the reduction stage.

The NAS-Mg salt obtained according to the new crystallization process has a particle size distribution between 30 and 100 µm. The salt is easy to filter and wash, resulting in very little washing liquid. The purity of the product increases considerably. The contaminating isomeric by-products could be reduced to below 2%.

A continuous crystallization variant can e.g. can also be designed in such a way that the two solutions of the NAS reaction mixture and Epsom salt solution are continuously sprayed into one another, the synchronous metering which has taken place with this - if appropriate in the presence of inoculation germs - producing an optimal precipitation result.

The following example illustrates the new process.

3 632739

example

1123 g of water are introduced into the corrosion-resistant reactor with a double jacket, and 1604.3 g of the nitrating solution of 1,5-nitronaphthalenedisulfonic acid 5 are added over the course of 30 minutes with vigorous stirring. The temperature is kept at 100 ° C. by slight cooling. The reaction mixture goes completely into solution. After the feed has ended, the NAS Mg salt is selectively precipitated by metering in 654 g of an aqueous Epsom salt solution (MgSO 4 content 158.0 g) over 60 minutes.

Then 390 g of wash liquor from a previous precipitation are added over 5 minutes. The suspension is then slowly stirred at 95 ° C. for a further 60 minutes, cooled to 60 ° C. and stirred for a further 60 minutes. Now the coarse crystalline suspension is filtered. The filter cake is then pressed on and the mother liquor is suctioned off well. The filter cake is then washed with 300 g of cold water and sucked dry, the washing liquor being collected separately. The following are obtained: 2o 604 g of filter cake, which corresponds to 336.6 g of dry substance of 3-nitronaphthalene-1,5-disulfonic acid dimethyl salt. The proportion of isomeric by-products in the product is less than 1.5%.

This produces 3077.3 g of waste sulfuric acid and 390 g of 25 wash liquor, which is recycled.

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