JP2523760B2 - Method for producing chloro-2-pyridinol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to chloro-2-pyridinol represented by 3,5,6-trichloro-2-pyridinol useful as an intermediate for insecticides such as chloropyrifos. Regarding the manufacturing method of.

[Conventional technology]

Conventionally, various methods are known as a method for producing chloro-2-pyridinol represented by 3,5,6-trichloro-2-pyridinol. Among these, if the production method of 3,5,6-trichloro-2-pyridinol is taken as an example, 2,3,5,
A method is known in which an aqueous alkaline solution is added to 6-tetrachloropyridine for hydrolysis, and then an acid is added to precipitate and filter 3,5,6-trichloro-2-pyridinol.

[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. The crude tetrachloropyridine obtained could not be used directly.

This is because in unpurified tetrachloropyridine, a catalyst for metal salts such as ferric chloride necessary for chlorination of pyridine and
Impurities such as tar-like substances generated under high temperature reaction of 150 to 500 ℃ are included, 2,3,5,
This is because when 6-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 hydroxides and tar-like substances from 3,5,6-trichloro-2-pyridinol.

In order to solve such a problem, there is a method of hot filtration as disclosed in JP-A-62-39570. According to this method, the metal oxide as an impurity is surely removed. However, 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. Further, this method has a drawback that the reaction takes a long time.

On the other hand, Japanese Patent Publication No. 59-53259 discloses a method of adding a phase transfer catalyst, focusing on the fact that the hydrolysis reaction is carried out in a two-phase mixed state in order to improve the promotion of the above reaction. However, in this method, since an alkaline aqueous solution having a high temperature of 140 ° C. and a high concentration is used, there is a problem that the apparatus such as the reaction vessel needs heat resistance and alkali resistance.

Further, as shown in the examples of JP-A-62-39570 and Japanese Patent Application No. 62-225336, even when a large amount of potassium hydroxide is used and the reaction is carried out at 95 to 100 ° C., it is usually 20
It is clear that it takes ~ 30 hours or longer depending on the stirring condition. For example, a reaction time of at least 20 hours was required even if the stirring speed was increased to 600 rpm on a two-scale scale.

From the above-mentioned circumstances, there has been a demand for a method for producing chloro-2-pyridinol which directly obtains high-purity chloro-2-pyridinol using crude chloropyridine as a starting material and does not require a long time for the reaction.

Therefore, an object of the present invention is to shorten the reaction time, and to use an unpurified chloropyridine synthesized from pyridine or the like as a starting material, which has an extremely low content of impurities such as tar-like substances and metal salts. It is to provide a novel method for producing chloro-2-pyridinol.

[Means for solving the problem]

The present inventors have conducted extensive studies and research to solve the above problems, and at the time of hydrolysis, the tar content contained in the unpurified product of 2,3,5,6-tetrachloropyridine was also hydrolyzed at the same time. Paying attention to the fact that the degree of decomposition is significantly affected by stirring conditions and the amount of alkali used, during the hydrolysis, the reaction solution is circulated through the outside of the reaction vessel and mixed by stirring, whereby the reaction time and product We have succeeded in simultaneously solving problems related to purity.

That is, the present invention has the general formula A method for producing chloro-2-pyridinol by heating a chloropyridine represented by the formula in an aqueous alkaline solution to hydrolyze it, and producing a chloro-2-pyridinol, wherein the reaction solution in the reaction tank at the time of hydrolysis. The present invention provides a process for producing chloro-2-pyridinol, characterized in that, after being stirred, it is introduced from the bottom of the reaction tank to the outside and then re-introduced into the reaction tank to circulate and mix.

In the present invention, the starting material chloropyridine is
2,3,5,6-Tetrachloropyridine represented by the above general formula, 2,3,4-trichloropyridine, 2,3,5-trichloropyridine, 2,5,6-trichloropyridine, 2 , 3,4,5
-Tetrachloropyridine, pentachloropyridine, etc. may be used, or a mixture thereof may be used. Especially 2, 3, 5,
Using 6-tetrachloropyridine, 3,5,6-trichloro-, which is useful as an intermediate for insecticides such as chloropyrifos
2-Pyridinol is obtained in high purity. Hereinafter, the production method of the present invention will be described in the case of producing 3,5,6-trichloro-2-pyridinol using 2,3,5,6-tetrachloropyridine as a starting material.

In the present invention, in particular, unpurified 2,3,5,6-tetrachloropyridine obtained by tetrachlorinating a chlorinated product of pyridine or picoline is targeted, and the effect of the present invention on such unpurified substance is extremely remarkable. Become.

In the present invention, the aqueous alkali solution used for hydrolysis may be an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. The amount of such alkali metal used for chloropyridine is 2,3,5,6.
-2.2-3.5 mol is preferable and 2.5-3.0 mol is particularly preferable for 1 mol of tetrachloropyridine. If the amount is less than 2.2 mol per mol of 2,3,5,6-tetrachloropyridine, the reaction takes a long time, the tar-like substance is difficult to decompose, and the purity of the purified product is lowered, which is not preferable. Further, when it exceeds 3.5 mol, the product 3,5,6-trichloro-2-
It is not preferable because the alkali metal salt crystals of pyridinol are likely to precipitate by salting out.

The concentration of the above-mentioned alkaline aqueous solution depends on the chloro-
It is necessary to appropriately select the solubility of the alkali metal salt of 2-pyridinol in an aqueous solution, but the amount of water used here is 8.3 times the weight of chloropyridine when sodium hydroxide is used in the alkaline aqueous solution. When potassium hydroxide is used, the amount is preferably 3.5 times or more the weight of chloropyridine. If the amount of the alkali metal to be used with respect to chloropyridine exceeds the above range, the solubility of the alkali metal salt of 3,5,6-trichloro-2-pyridinol in water decreases due to the salting-out phenomenon, so that it is necessary to further increase the amount of water. There is.

According to the present invention, during the hydrolysis, it is necessary to introduce the reaction solution from the bottom of the reaction tank to the outside with stirring and then reflow it to, for example, the upper part of the reaction tank to circulate and mix it. Therefore, for example, a reaction solution discharge port is provided in the lower part of the reaction tank, a reaction solution introduction port is provided in the upper part of the reaction tank, the discharge port and the introduction port are connected by a pipe, and a liquid feed pump is provided in the middle of the pipe. It is preferable that a device for interposing the above is constituted, and the solution in the reaction tank is fed from the lower part to the upper part through the external pipe by the pump to circulate and mix the solution in the reaction tank. Furthermore, it is advantageous to install a line mixer in the pipe.

According to the present invention, the solution obtained by the hydrolysis by the above-mentioned external circulation mixing is treated with an acid, but impurities may be removed as a previous step by, for example, hot filtration. As the acid solution used for the acid treatment, sulfuric acid or hydrochloric acid can be used, and the pH of the acid solution is adjusted to 2 to 6 to precipitate 3,5,6-trichloro-2-pyridinol, which is cooled and then separated by filtration. To do. At this time, the tar hydrolyzed by the above external circulation mixing dissolves in the aqueous solution and is separated and removed from the product as a filtrate.

As above, the production method of the present invention has been mainly described for the case where 2,3,5,6-tetrachloropyridine is used as a starting material,
Even if the starting materials are various chloropyridines represented by the above general formula, chloro-2-pyridinol corresponding to each chloropyridine can be obtained in a highly pure and short-time reaction.

[Work]

The present invention makes it possible to terminate the hydrolysis reaction in an extremely short time by performing a mixing operation by external circulation during hydrolysis, and further, the tar content in the product is remarkably reduced, and the coloring is high and the purity is low. It has become possible to produce chloro-2-pyridinol. This is because by performing external circulation mixing, the two-phase unreacted liquid having an interface is dispersed and mixed into fine droplets through collision with the casing or piping of the circulation pump, resulting in hydrolysis of the reactants. It is considered that the reaction is accelerated. Further, the reason why the purity of the product is improved is that, as the hydrolysis reaction of the reaction substance is promoted, the tar component contained as an impurity is also hydrolyzed at the same time to become water-soluble and can be separated from the product. It is believed that there is.

On the other hand, according to the experiments conducted by the present inventors, it has been confirmed that the above remarkable effects cannot be obtained by ordinary stirring and mixing no matter how the stirring conditions are changed.

〔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 2.0%, pentachloropyridine 1.5%)
434 g (2.00 mol), water 1736 g (4 times the weight of crude tetrachloropyridine), and potassium hydroxide 294 g (5.265 mol)
The mixture consisting of was introduced into a reaction tank equipped with an external circulation pipe and a water pump, and heated at 95 to 100 ° C., and at the same time, the reaction solution was externally circulated and mixed at a rate of 10 / hr. For stirring in the reaction tank, a flat blade was used and the rotation speed was 100 rpm.

11 hours after the reaction started, the reaction solution was analyzed and the conversion rate was 99%.
The reaction was stopped because the temperature exceeded 80 ° C., and the solution was filtered while hot while keeping the liquid temperature at 85 ° C. or higher to remove iron and insoluble matters. Then, while maintaining the temperature at 85 ° C and stirring, 97% sulfuric acid was added to the filtrate at pH 3.5.
Until it becomes Then, it was cooled to about 50 ° C, separated by filtration, washed with warm water, and dried to give 362.3 g of 3,5,6-trichloro-2-pyridinol, which was close to white (GC internal standard method, purity 98.8%). Got The yield based on crude tetrachloropyridine was 91.3%.

Comparative Example 1 The same process as in Example 1 was carried out except that the stirring rotation speed was 300 rpm and no external circulation mixing was performed. As a result, 23 hours after the start of the reaction, the conversion rate exceeded 93% in analysis. The obtained crystals are grayish brown (GC internal standard method, purity 97.8
%), And the yield based on crude tetrachloropyridine was 89.1%.

〔The invention's effect〕

As described above, according to the method of the present invention, highly pure chloro-2-pyridinol having a very low tar content is obtained from crude chloropyridine by an extremely simple operation of externally mixing the reaction solution. It becomes possible to manufacture. Furthermore, the production method of the present invention is capable of significantly shortening the reaction time as compared with the conventional method, and thus is a very effective method for improving productivity.

Claims (2)

(57) [Claims] 1. A general formula A method for producing chloro-2-pyridinol by heating a chloropyridine represented by the formula in an aqueous alkaline solution to hydrolyze it, and producing a chloro-2-pyridinol, wherein the reaction solution in the reaction tank at the time of hydrolysis. Is introduced from the bottom of the reaction tank to the outside under stirring, and then again flows into the reaction tank to circulate and mix, thereby producing chloro-2-pyridinol. 2. The process for producing chloro-2-pyridinol according to claim 1, wherein potassium hydroxide is used in an amount of 2.5 to 3.0 mol per mol of chloropyridine as the alkali.