JP2563432B2 - Method for producing chloro-2-pyridinol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention uses chloro-2-, typified by 3,5,6-trichloro-2-pyridinol, which is useful as an intermediate for insecticides such as chloropyrifos. The present invention relates to a method for producing pyridinol.

[Conventional technology]

Heretofore, various methods have been known as a method for producing trichloro-2-pyridinol represented by 3,5,6-trichloro-2-pyridinol. Of these, taking the method for producing 3,5,6-trichloro-2-pyridinol as an example,
An aqueous alkaline solution is added to 2,3,5,6-tetrachloropyridine for hydrolysis, and then an acid is added to add 3,5,6-trichloro-
A method of precipitating and filtering 2-pyridinol is known.

[Problems to be Solved by the Invention]

In the above method, high purity 3,5, which is preferable as a product,
In order to obtain 6-trichloro-2-pyridinol, it is essential to use purified 2,3,5,6-tetrachloropyridine as a starting material. Obtained crude 2,3,
It was not possible to use 5,6-tetrachloropyridine directly.

This is because in unpurified tetrachloropyridine, a catalyst for metal salts such as ferric chloride necessary for chlorination of pyridine and
It contains impurities such as tar-like substances generated under high temperature reaction of 150-500 ℃. 2,3,5,6
This is because when tetrachloropyridine is used as a starting material, impurities react to form insoluble metal hydroxides or tar-like substances in the 3,5,6-trichloro-2-pyridinol during the above hydrolysis. It was extremely difficult to separate such metal hydroxide and tar from the product 3,5,6-trichloro-2-pyridinol. Furthermore, in such crude tetrachloropyridine, 2,
In addition to 3,5,6-tetrachloropyridine, 2,3,6, -trichloropyridine and pentachloropyridine are contained, and hydrolysates of these, especially pentachloropyridine hydrolyzate are also products3. It needs to be separated from 5,6-trichloro-2-pyridinol.

In order to solve such a problem, there is a method of hot filtration as disclosed in JP-A-62-39570, but this method surely removes the metal oxide as an impurity. There is a drawback that the tar-like substance cannot be effectively removed. As a result, the 3,5,6-trichloro-2-pyridinol crystals obtained were off-white or off-brown.

Therefore, an object of the present invention is to produce chloro-2-pyridinol, which has high purity and little coloring even when unpurified chloropyridine is used as a starting material.
To obtain 2-pyridinol.

[Means for solving the problem]

As a result of earnestly studying and researching the above problems, the present inventors have
After hydrolysis of chloropyridine, add acid to add chloro-2-
In the step of crystallizing pyridinol, it was found that the content of the tar-like substance in the product and the hydrolysis product of pentachloropyridine as an impurity in the product is significantly reduced depending on the pH value at the end point, and the present invention is completed. Came to.

That is, the present invention has the general formula In the method for producing chloro-2-pyridinol, in which chloropyridine represented by is heated and hydrolyzed in an alkaline aqueous solution, and then acid is added to precipitate and separate chloro-2-pyridinol, the above acid is added to chloropyridine. Chloro-2-pyridinol characterized by precipitating chloro-2-pyridinol by adjusting the pH of the end point for precipitating 2-pyridinol to be higher than the pH at the equivalence point with respect to the alkali metal salt of chloro-2-pyridinol The present invention provides a method for manufacturing the same.

In the present invention, the starting material chloropyridine is
Not only 2,3,5,6-tetrachloropyridine represented by the above general formula, 2,3,4-trichloropyridine, 2,3,5-trichloropyridine, 2,3,6-trichloropyridine, 2 , 3,4,5
Any of tetrachloropyridine, pentachloropyridine and the like may be used. In particular, when 2,3,5,6-tetrachloropyridine is used, 3,5,6-trichloro-2-pyridinol useful as an insecticide intermediate such as chloropyrifos can be obtained in high purity. Hereinafter, using 2,3,5,6-tetrachloropyridine as a starting material, the production method of the present invention will be described by taking the case of producing 3,5,6-trichloro-2-pyridinol as an example. .

The present invention is particularly directed to unpurified 3,5,6-trichloro-2-pyridinol obtained by tetrachlorinating a chlorinated product of pyridine or picoline, and the effect of the present invention on such unpurified product is obtained. Very noticeable. Such unpurified products include tar-like substances, metal salts, and 2,3,5,6 such as 2,3,6-tetrachloropyridine and pentachloropyridine.
-Contains said chloropyridines other than tetrachloropyridine.

According to the present invention, 2,3,5,6-chloropyridine, which is the above-mentioned starting material, is hydrolyzed by heating in an alkaline aqueous solution, and then acid-treated to give 3,5,6-trichloro-2-pyridinol. To precipitate the alkali metal salt of. In such an acid treatment step, it is necessary to maintain the end point pH higher than the pH at the equivalent point of the alkali metal salt. Where the equivalence point is
Since the pH is said to be in the range of 2-3, it is particularly preferable that the pH at the end point is 4.5-6. When the pH at the end point is equal to or lower than the pH at the equivalence point, the content of the tar and the hydrolyzate of pentachloropyridine contained in chloro-2-pyridinol that precipitates is significantly increased, which is not preferable.

Examples of the acid used in such an acid treatment step include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and the like, which can be appropriately selected from these depending on the material and cost of the apparatus. The acidification step is preferably carried out at a temperature at which the alkali metal salt is dissolved or higher, and usually 80 to 90 ° C. After completion of such an acid treatment step, it is cooled, separated by filtration, washed with warm water, and dried to obtain 3,5,6-trichloro-2-pyridinol.

In the present invention, examples of the alkaline aqueous solution used for the hydrolysis which is the previous step of the acid treatment include aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of such an alkali metal to be used with respect to 2,3,5,6-tetrachloropyridine is theoretically required to be 2 times or more moles, and the same applies even if another chloropyridine is used as a starting material. Further, the amount of water, which is a solvent of such an alkaline solution, is appropriately selected depending on the type of alkali used and the amount thereof. For example, when sodium hydroxide is used in the alkaline aqueous solution, it is preferably 8.3 times by weight that of chloropyridine, and when potassium hydroxide is used, it is preferably 3.5 times or more by weight of chloropyridine. The reaction liquid hydrolyzed in this way is subjected to an acidification step after removing impurities such as iron by filtration while hot.

In the present invention, in the acid treatment step as described above, in order to adjust the pH higher than the pH at the equivalence point, the product is an alkali of chloro-2-pyridinol such as 3,5,6-trichloro-2-pyridinol. The metal salt will remain in the filtrate and the yield of chloro-2-pyridinol will be somewhat reduced. Therefore, in the present invention,
The product chloro-2-pyridinol was precipitated and the filtrate separated by filtration was acidified to precipitate chloro-2-pyridinol remaining in the filtrate as crystals, and then the crystals were subjected to the hydrolysis step again. It is preferable to put it back. The recovered crystals have a black hue and are 3,5,6-trichloro-2.
In addition to -pyridinol, it contains a large amount of 3,4,5,6-tetrachloro-2-pyridinol as impurities. By recycling this to the above hydrolysis process, impurities 3,4,5,
6-Tetrachloro-2-pyridinol is hydrolyzed to be a diol, and the tar contained at the same time is also hydrolyzed to be water-soluble, and is contained in the filtrate and separated in the acid treatment step.

By repeating such a recycling process,
The yield of chloro-2-pyridinol is recovered, and even if the pH is made higher than the pH at the equivalence point as described above, the recovery of the purified product is not lowered. Further, no impurities are accumulated in the system.

As above, the case where 2,3,5,6-tetrachloropyridine is used as the starting material has been mainly described, but using the above-mentioned chloropyridines other than 2,3,5,6-tetrachloropyridine, respectively. The chloro-2-pyridinol corresponding to chloropyridine can be obtained in high purity and without coloring.

[Work]

In the present invention, the pH of the end point is higher than the pH at the equivalent point in the acid treatment step as described above, and more preferably the pH is 4.5 to.
It is to adjust so that it becomes 6. In the conventional acid treatment step, the equivalent point of chloro-2-pyridinol to the alkali metal salt is said to be in the pH range of 2-3, so the pH at the end point was adjusted to approximately this range.

However, according to a study conducted by the present inventors, 2,3,6-trichloropyridine contained as an impurity in the raw material by hydrolyzing an unpurified 2,3,5,6-tetrachloropyridine is, Alkali metal salt of 3,6-dichloro-2-pyridinol, pentachloropyridine is 3,4,5,6
-Change to an alkali metal salt of tetrachloro-2-pyridinol or an alkali metal salt of 2,3,5,6-tetrachloro-4-pyridinol. Further, it was revealed that the tar component was also chlorinated and subjected to a hydrolysis reaction in the tetrachloropyridine production process.

Of these impurities, most of the hydrolysates of 3,6-dichloro-2-pyridinol, 2,3,5,6-tetrachloro-4-pyridinol and tar components have high water solubility,
Contamination into the crystals during the acidification process is not a problem, but some tar and 3,4,5,6-tetrachloro-
2-pyridinol is a cause of reducing the purity of the product.

Then, the present inventors have conducted a detailed investigation on the relationship between the end point pH of the acidification step and the content of impurities of a specific chloro-2-pyridinol which is a product, based on such findings, and as shown in Table 1, It has been found that the content of 3,4,5,6-tetrachloro-2-pyridinol in the product increases significantly as the end point pH decreases to 6.0-3.0.

The reason why such effects were obtained is 3,4,5,6-
Tetrachloro-2-pyridinol and tar-like substances are 3,5,6
It is considered that this is because the acidity is higher than that of trichloro-2-pyridinol. On the other hand, even if the pH is increased, 6.0
Up to the above, the residual amount of the desired alkali metal salt of 3,5,6-trichloro-2-pyridinol in the filtrate is not so large as shown in the first indication, and the yield thereof is not so much decreased.

Therefore, it is desired that the pH be selected between 4.5 and 6.0. If it is 6.0 or more, the residual rate in the filtrate becomes high.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these.

Example 1 Crude 2,3,5,6-tetrachloropyridine synthesized according to US Pat. No. 3,538,100 (2% ferric chloride, 2% tar)
Including, GC purity Tetrachloropyridine 96.0%, 2,3,6-
Trichloropyridine 1.0%, Pentachloropyridine 3.0
%) 217 g (1.00 mol), water 868 g (4 times the weight of crude tetrachloropyridine), and potassium hydroxide 128 g (2.29 mol)
The mixture consisting of was heated and stirred at 95 to 100 ° C. The raw material tetrachloropyridine disappeared in 22 hours.

The reaction liquid was filtered while hot while keeping the liquid temperature at 85 ° C or higher to remove iron and insoluble matters. Then, 97% sulfuric acid was added to the filtrate at pH 4.5 with stirring at 85 ° C. After cooling to about 50 ° C, separating by filtration, washing with warm water, and then drying, 175.9 g of 3,5,6-trichloro-2-pyridinol 3,5,6-trichloro-2-pyridin (gray internal standard method, purity 98.2
%, 3,6-dichloro-2-pyridinol 0.3%, 3,4,5,6
-Tetrachloro-2-pyridinol 0.65% content) was obtained. The residual amount of 3,5,6-trichloro-2-pyridinol in the filtrate was 1.9 g, which corresponded to 1.1% of the total valuables contained in the product and the filtrate.

Example 2 Hydrolysis and acid treatment were performed in the same manner as in Example 1 except that the end point pH of acidification was 5.5. As a result, the hue of the obtained 3,5,6-trichloro-2-pyridinol was white, and the purity was 99.0% by GC internal standard method, 3,6-dichloro-2-pyridinol 0.3%, 3,4, 5,6-Tetrachloro-
It contained 0.35% of 2-pyridinol. The amount of the obtained product was 172.6 g, and the amount remaining in the filtrate was 5.2 g.

Example 3 In the procedure of Example 2, the filtrate is again adjusted to pH 3.0 at 50 ° C.
Acidified until and then filtered off. While adding the wet crystals to the next reaction mixture, the same hydrolysis reaction and drying as in Example 1 were repeated. As a result, as shown in Table 2, stable quality 3,5,6-trichloro-2-pyridinol was obtained after each operation. The yields based on crude tetrachloropyridine are averaged
It was 89.4%.

Comparative Example 1 The operations of hydrolysis and acid treatment were performed in the same manner as in Example 1 except that the acidification end point pH was 3.5. As a result, 3,5,6
176.8 g of trichloro-2-pyridinol (GC internal standard method, purity 97.5%) was obtained, but the hue of the product was gray.

〔The invention's effect〕

As described above, the present invention, in the acid treatment step after the alkaline hydrolysis step of the unpurified chloropyridine, by a very simple treatment means of making the end point of the acidification pH higher than the pH at the equivalence point, The product chloro-2-
It has become possible to significantly reduce the coloration of pyridinol and significantly improve the purity. Further, according to the present invention, there is an advantage that the yield of the product can be maintained high by re-acidifying the valuable substance contained in the separated filtrate, separating and recovering it, and recycling it to the hydrolysis step.

Claims (3)

(57) [Claims] 1. A general formula In the method for producing chloro-2-pyridinol in which chloropyridine represented by is hydrolyzed by heating in an alkaline aqueous solution, an acid is added to precipitate and separate chloro-2-pyridinol, Chloro-2-pyridinol characterized by precipitating chloro-2-pyridinol by adjusting the pH of the end point for precipitating 2-pyridinol to be higher than the pH at the equivalence point with respect to the alkali metal salt of chloro-2-pyridinol Manufacturing method. 2. Chloro-2- according to claim 1, wherein 2,3,5,6-tetrachloropyridine is used as chloropyridine and the pH at the end point is adjusted to the range of 4.5 to 6.0. Process for producing pyridinol. 3. Precipitating chloro-2-pyridinol and acidifying the filtrate separated by filtration to precipitate crystals containing chloro-2-pyridinol, and then subjecting the crystals to a hydrolysis step again to give chloro-2. -The method for producing chloro-2-pyridinol according to claim 1 or 2, which comprises an operation of recovering pyridinol.