JPH0442374B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to hydrolyzing 3,4,5,6-tetrafluorophthalonitrile in an aqueous sulfuric acid solution to produce 3,4,5,6-tetrafluorophthalonitrile. This invention relates to a method for industrially producing phthalic acid.

3,4,5,6-tetrafluorophthalic acid is
It is useful as a polymer material or an intermediate for medicines and agricultural chemicals.

(Prior art) 3,4,5,6-tetrafluorophthalonitrile is hydrolyzed in an aqueous sulfuric acid solution to produce 3,4,5,
The method for producing 6-tetrafluorophthalic acid is
Ishikawa et al., Journal of Industrial Chemistry, Vol. 73, p. 447 (1970
year). According to this method, 3,
4,5,6-tetrafluorophthalonitrile 80g
was boiled in 500 ml of 60% sulfuric acid aqueous solution for 5 hours, allowed to cool, filtered the precipitated crystals, washed with 18% hydrochloric acid, and dried to obtain 3,4,5,6-tetrafluorophthal. Acid is obtained (yield 88.5%).

(Problems to be solved by the invention) However, in this method, the production efficiency of 3,4,5,6-tetrafluorophthalic acid must be low because the raw material concentration is too low, and the production efficiency of 3,4,5,6-tetrafluorophthalic acid is low, and the There are various problems that need to be improved before it can be applied to large-scale production. In other words, crude 3, 4,
Although 5,6-tetrafluorophthalic acid is purified by washing and recrystallization using an aqueous hydrochloric acid solution, it is difficult to apply it to actual equipment because hydrochloric acid is highly corrosive to the equipment. There is still room for improvement in the reaction yield of 3,4,5,6-tetrafluorophthalic acid. Technical problems such as those mentioned above can be pointed out.

Therefore, the object of the present invention is to hydrolyze 3,4,5,6-tetrafluorophthalonitrile in a sulfuric acid aqueous solution in a highly concentrated state to produce an industrially advantageous 3,4,5,6-tetrafluorophthalonitrile.
The objective is to produce 4,5,6-tetrafluorophthalic acid.

(Means for Solving the Problems) The present inventors have discovered that 3,4,5,6-tetrafluorophthalic acid is produced by hydrolyzing 3,4,5,6-tetrafluorophthalonitrile in an aqueous sulfuric acid solution. Regarding the manufacturing method, various studies have been conducted on hydrolysis reactions using highly concentrated raw materials. As a result, the solubility of both ammonium sulfate, a by-product of hydrolysis, and 3,4,5,6-tetrafluorophthalic acid, the target product, in an aqueous sulfuric acid solution varies greatly within a specific range of the sulfuric acid concentration. Has an inflection point, does not precipitate ammonium sulfate at all, 3.
The present invention was completed by discovering that only 4,5,6-tetrafluorophthalic acid can be selectively precipitated.

That is, the present invention provides a method for producing 3,4,5,6-tetrafluorophthalic acid by hydrolyzing 3,4,5,6-tetrafluorophthalonitrile in an aqueous sulfuric acid solution. While adjusting the sulfuric acid concentration of the reaction solution to about 57% by weight or less and keeping the temperature of the reaction solution in the range of 0 to 40°C, 3, 4,
This is a method for producing 3,4,5,6-tetrafluorophthalic acid, characterized by selectively precipitating 5,6-tetrafluorophthalic acid.

The present invention will be specifically explained below with reference to FIG. 1, which shows the solubility of 3,4,5,6-tetrafluorophthalic acid and ammonium sulfate in an aqueous sulfuric acid solution.

Figure 1 shows the solubility of the above two substances at liquid temperatures of 10°C and 35°C.As can be understood from this figure, the solubility of ammonium sulfate is has changed significantly,
At a sulfuric acid concentration of 60% by weight or more, its solubility decreases considerably, but at a concentration of 50% by weight or less, its solubility maintains an almost constant high value. and,
The inflection point in the solubility curve of ammonium sulfate is the temperature of 57% by weight sulfuric acid.

On the other hand, the solubility of 3,4,5,6-tetrafluorophthalic acid is unaffected by the sulfuric acid concentration and liquid temperature and remains low when the sulfuric acid concentration is approximately 20% by weight or more. is lower than 20% by weight, its solubility shows a low value at a low temperature of about 10°C, but as the liquid temperature rises to 35°C, its solubility increases rapidly.

The present invention has been completed based on the above findings.

In other words, 3,4,5,6-tetrafluorophthalic acid and ammonium sulfate, which are produced by hydrolyzing 3,4,5,6-tetrafluorophthalonitrile in an aqueous sulfuric acid solution, each have different inflection points in their solubility relative to the sulfuric acid concentration. Therefore, the sulfuric acid concentration of the reaction solution after hydrolysis is adjusted to 57% by weight or less, and the temperature of the reaction solution is adjusted to 0 to 40℃.
If maintained within this range, 3,4,5,6-tetrafluorophthalic acid precipitates in a high yield because of its extremely low solubility, whereas ammonium sulfate has a high solubility and does not precipitate at all. Even when high-concentration raw materials are used (that is, the concentration of by-produced ammonium sulfate becomes high), by adjusting the reaction solution after hydrolysis to the conditions specified by the present invention, 3, 4, Only 5,6-tetrafluorophthalic acid can be selectively precipitated.

Hereinafter, production examples according to the present invention will be further explained, but the present invention is not limited thereto.

3,4,5,6-tetrafluorophthalonitrile used in the present invention can be synthesized, for example, by supplying phthalonitrile together with chlorine onto activated carbon at a temperature range of 270 to 350°C, followed by halogen exchange.

If you want to increase productivity, 3, 4, 5,
It is desirable to charge 100 to 700 parts of the sulfuric acid aqueous solution to 100 parts of 6-tetrafluorophthalonitrile.

The concentration of sulfuric acid in the aqueous medium is preferably in the range of 20 to 80% by weight, preferably 35 to 57% by weight. When the concentration of sulfuric acid is high, rapid reactions tend to occur and are dangerous due to exothermic reactions. When the sulfuric acid concentration is low, the reaction rate decreases and productivity decreases, which is not preferable. Therefore, it is necessary to select an appropriate sulfuric acid concentration.

The reaction temperature for hydrolysis is preferably selected in the range of 100 to 170°C, particularly preferably in the range of 120 to 150°C.

If the reaction temperature is high, a rapid reaction occurs and is dangerous due to exothermic reaction. If the reaction temperature is low, the reaction rate decreases and productivity decreases, which is not preferable.

When the reaction temperature is carried out under reflux, it is particularly controlled by the sulfuric acid concentration, but it is preferable to carry out the reaction under reflux. However, the process may be carried out under pressure using an autoclave so that the temperature is not controlled by the sulfuric acid concentration, and even if the process is carried out at normal pressure, it is not necessarily necessary to carry out the process under reflux, and it may be carried out by controlling the temperature to an even lower temperature. good.

The reaction time is not particularly limited, but it is preferably carried out within a range of 5 to 40 hours.

After the reaction is completed, dilute with water so that the sulfuric acid concentration in the aqueous medium is approximately 57% by weight or less, preferably 20 to 57% by weight. Water may be added to cause the reaction.

After the reaction is completed, maintain the sulfuric acid concentration above, and
By adjusting the liquid temperature to 40°C, preferably 10 to 35°C, a precipitate of 3,4,5,6-tetrafluorophthalic acid can be obtained. They can be removed from the aqueous medium by, for example, conventional methods.

The crystals of 3,4,5,6-tetrafluorophthalic acid thus obtained contain water,
Therefore, a small amount of sulfuric acid and ammonium sulfate remain. One method for purifying them is to remove sulfuric acid and ammonium sulfate by washing with a saturated or nearly saturated aqueous solution of 3,4,5,6-tetrafluorophthalic acid. Alternatively, washing may be performed using water at a temperature of 15° C. or lower, at which the solubility of 3,4,5,6-tetrafluorophthalic acid in water rapidly decreases. In this case, a part of the washed aqueous solution can be used as the aqueous medium for the reaction and also as the dilution water referred to in the present invention.
4,5,6-tetrafluorophthalic acid is effectively recovered again.

Yet another method is to extract 3,4,5,6-tetrafluorophthalic acid from an aqueous medium using a solvent such as ethers or ketones. After extraction, the solvent was removed by evaporation to dryness, and 3,4,5,6
- Tetrafluorophthalic acid can be extracted.

In the present invention, any method may be used for purification. In some cases, it can be used as is as a raw material for the next reaction without purification.

Hereinafter, the present invention will be specifically explained using Examples, but the present invention is not limited thereto.

Example 1 In three lo flasks of 1, 3, 4, 5, 6
- Tetrafluorophthalonitrile 200.1g (1.00
mol) and 600.0 g of a 60% by weight aqueous sulfuric acid solution were charged, and the mixture was reacted for 16 hours with stirring under reflux (approximately 135 to 140°C).

To reduce the sulfuric acid concentration to approximately 47% by weight after the reaction is complete.
127g of water was added dropwise for dilution.

Next, after cooling (liquid temperature 20°C), the precipitate was filtered and separated from the aqueous medium. Wash with a saturated aqueous solution of 3,4,5,6-tetrafluorophthalic acid and then dry to remove 3,4,5,6-tetrafluorophthalic acid.
229.0 g (yield 96.2 mol% of 3,4,5,6-tetrafluorophthalonitrile, purity 99.5%) could be obtained.

Example 2 A reaction was carried out in the same manner as in Example 1, except that 700.0 g of a 54% by weight aqueous sulfuric acid solution was charged and the reaction was carried out under reflux (approximately 129 to 131°C) for 17 hours. After the reaction was completed, the mixture was allowed to cool and the precipitate was filtered, and then the same procedure as in Example 1 was carried out to obtain 231.7 g of 3,4,5,6-tetrafluorophthalic acid (3,4,5,6-tetrafluorophthalic acid). −
Tetrafluorophthalonitrile yield 97.3 mol%)
I was able to get

Example 3 133.4 g (0.67 mol) of 3,4,5,6-tetrafluorophthalonitrile and 543.3 g of a 51.5% by weight sulfuric acid aqueous solution were charged and heated under reflux (approximately 124 to 127°C).
The reaction was allowed to proceed for 25 hours, and after the reaction was completed, the solution was diluted with 182 g of water so that the sulfuric acid concentration was approximately 35% by weight. After cooling, the precipitate was filtered at a liquid temperature of 20°C and separated from the aqueous medium. Wash with 10℃ water and then dry.3.4.
146.9 g of 5,6-tetrafluorophthalonic acid (yield 92.1% based on 3,4,5,6-tetrafluorophthalonitrile) could be obtained.

[Brief explanation of drawings]

FIG. 1 is a graph showing the solubility of 3,4,5,6-tetrafluorophthalic acid and ammonium sulfate in an aqueous sulfuric acid solution. 1... Solubility curve of ammonium sulfate at 35°C, 2... Solubility curve of ammonium sulfate at 10°C, 3... 3,4,5,6- at 35°C
Solubility curve of tetrafluorophthalic acid, 4...10
Solubility curve of 3,4,5,6-tetrafluorophthalic acid at °C.

Claims (1)

[Claims] 1 Hydrolyze 3,4,5,6-tetrafluorophthalonitrile in an aqueous sulfuric acid solution to produce 3,4,5,
When producing 6-tetrafluorophthalic acid, the sulfuric acid concentration of the reaction solution after hydrolysis is adjusted to about 57% by weight or less, and the temperature of the reaction solution is adjusted to 0 to 40°C.
A method for producing 3,4,5,6-tetrafluorophthalic acid, which comprises selectively precipitating 3,4,5,6-tetrafluorophthalic acid while maintaining the above range.