JPS5926619B2 - Separation method of 2,6-naphthalenedisulfonic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating 2,6-naphthalenedisulfonic acid.

Specifically, the purpose is to separate 2,6-naphthalenedisulfonic acid with high purity and high yield from a sulfuric acid solution of a mixture of naphthalenedisulfonic acid isomers, and by adding aniline to the sulfuric acid solution, - This invention relates to a method for separating 2,6-naphthalenedisulfonic acid, which comprises precipitating only 6-naphthalenedisulfonic acid as anilinium salt crystals. A conventional method for separating 2,6-naphthalenedisulfonic acid from a sulfuric acid solution of a naphthalenedisulfonic acid isomer mixture is to add an excess of an inorganic alkali salt to a sulfuric acid solution of a naphthalenedisulfonic acid isomer mixture obtained by a high-temperature sulfonation reaction of naphthalene. 2.
Crystals of 6-naphthalenedisulfonic acid alkali salt are precipitated and analyzed.

Thereafter, the filtered crystals are washed with an aqueous solution of an inorganic alkali metal salt such as NaCl, 2S04, etc., and the desired 2
- A method of obtaining an alkali salt of 6-naphthalenedisulfonic acid has been adopted. However, in this separation method using inorganic alkali salts, the difference in solubility between 2, 6-naphthalenedisulfonic acid and other alkali disulfonic acid salts is not noticeable at room temperature, so filtration at high temperatures is required to improve the separation effect. However, there are problems with the material of the filtration device, workability, etc.

In addition, 2,6-naphthalenedisulfonic acid alkali salts generally have a high solubility in water and cannot be washed with water, making it extremely difficult to prevent inorganic salts from entering the crystals. In order to obtain it, further purification steps such as recrystallization are required.

For this reason, it was not possible to extract a large amount of 2,6-naphthalenedisulfonic acid in a good yield.On the other hand, 2,6-naphthalenedisulfonic acid is an industrial raw material for dye intermediates such as Shufer's acid and Brenner's acid, and brighteners for plating. It is also an important raw material, and in the field of fine chemicals, extremely high purity is required to fully demonstrate its performance.
In view of the current situation, the present inventors conducted various studies with the aim of industrially obtaining 2,6-naphthalenedisulfonic acid with high purity and high yield, and as a result, they found that an inorganic alkali salt was used. Aromatic organic amine is a method to obtain only 2,6=naphthalenedisulfonic acid in high purity and high yield from a sulfuric acid solution of a mixture of naphthalenedisulfonic acid isomers with simple operations, which has not been achieved in the past. It has been found that this can be easily achieved by using aniline.

That is, when aniline is used within a certain range for 2,6-naphthalenedisulfonic acid in a sulfuric acid solution of a naphthalenedisulfonic acid isomer mixture, and the isomer mixture is formed into an anilinium salt, something surprising occurs. In this book, we found that not only the anilinium salt of 2,6-naphthalenedisulfonic acid precipitated as crystals, but also that the amount of crystals corresponded to almost the entire amount of 2,6-naphthalenedisulfonic acid in the isomer mixture solution. It is a completed invention.

The present invention will be explained in more detail below. An appropriate amount of aniline is added to a sulfuric acid solution of a mixture of naphthalenedisulfonic acid isomers, and the mixture is stirred at 50 to 70°C for several hours.

Thereafter, it was cooled to room temperature and the precipitated crystals of anilinium salt of 2,6-naphthalenedisulfonic acid were separated. By washing the crystals with water or a saturated aqueous solution of aniline and removing the adhering mother liquor, 2,6-naphthalenedisulfonic acid anilinium salt with a purity of 99% or more and a high yield can be obtained. In this case, the amount of aniline used is equimolar to the isomer mixture excluding 2,6-naphthalenedisulfonic acid, and 0.2 to 4.0 aniline is used relative to the content of 2,6-naphthalenedisulfonic acid. twice the mole, preferably 0
．． It is preferable to use 5 to 2.0 times the molar amount of aniline.

If it is less than this range, the yield will decrease, and if it is more than this range, the purity 2 of the target 2,6-naphthalenedisulfonic acid anilinium salt will decrease. The anilinium salt of 2,6-naphthalenedisulfonic acid obtained by the method of the present invention can be easily converted into an alkali salt by adding an alkali to the aqueous solution, and the aniline liberated at this time can be easily recovered and used. Naturally, it is reused for inventions.

The naphthalene disulfonic acid isomer mixtures described in this invention are generally obtained by high temperature sulfonation reactions of naphthalene.

It means an isomer mixture whose main components are 2.6-1 and 2.7-naphthalenedisulfonic acids.

The present invention will be explained in more detail below using Examples, but the present invention is not limited to these Examples in any way.

Example 1 98% sulfuric acid 4007 was placed in a four-bottle flask, and naphthalene 1287 was added with stirring, followed by reaction at 160 to 175°C for 7 hours.

The composition obtained in this case was 0.24 m of 2,6-naphthalenedisulfonic acid, 0.53 m of 2,7 naphthalenedisulfonic acid, and 0.53 m of 2,6-naphthalenedisulfonic acid.
It was 08m011 and other 0.15m01. Water 12007 is added to this naphthalenedisulfonic acid isomer mixture, and aniline 1487 is added at 60°C. After stirring at the same temperature for 2 hours, the mixture was cooled to 40°C, and the precipitated crystals of anilinium 2,6-naphthalenedisulfonic acid salt were separated by filtration and washed with water. An equivalent amount of aqueous caustic soda solution is added to the crystals to convert the anilinium salt of 2,6-naphthalenedisulfonic acid into the sodium salt, and the aniline liberated at this time is recovered together with water. The above results are shown in Table 1. Example 2 98% sulfuric acid at 250V was placed in a four-bottle flask, and naphthalene 1287 was added with stirring, followed by a sulfonation reaction at 160 to 175°C for 25 hours.

The composition obtained in this case was 0.30 m of 2,6-naphthalenedisulfonic acid, 0.55 m of 2,7 naphthalenedisulfonic acid, and 0.55 m of 0.111.6-naphthalenedisulfonic acid.
06m01, others 0.09m01. Water 6007 is added to this naphthalenedisulfonic acid isomer mixture, and aniline 121y is added at 70'C.

Claims (1)

[Claims] 1. Separation of 2,6-naphthalenedisulfonic acid, characterized by adding aniline to a sulfuric acid solution of a mixture of naphthalenedisulfonic acid isomers, and precipitating only 2,6-naphthalenedisulfonic acid as anilinium salt crystals from the sulfuric acid solution. Method.