JPH0610195B2 - Method for producing 3,5,6-trichloro-2-pyridinol - Google Patents

Description

TECHNICAL FIELD The present invention relates to the production of 3,5,6-trichloro-2-pyridinol useful as an intermediate for pesticides such as chloropyrifos.

(Prior Art and Problems) Conventionally, various methods have been known for producing 3,5,6-trichloro-2-pyridinol. For example, JP-B-59-53259 discloses 2,3,5,6. -A method for producing 3,5,6-trichloro-2-pyridinol by adding an aqueous alkaline solution to tetrachloropyridine for hydrolysis and then adding an acid is described. In addition, a method for isolating a desired product after adding the acid to precipitate the desired product is also known.
However, in this method, when a desired pyridinol is produced using purified 2,3,5,6-tetrachloropyridine, a highly pure product can be obtained. If unpurified tetrachloropyridine produced by tetrachlorination is used, a highly pure product cannot be obtained. That is,
Such unpurified tetrachloropyridine may be produced by a catalyst such as a metal salt such as ferric chloride which is usually used in the production, or a small amount of tar generated for reaction at a high temperature of 150 to 500 ° C. Are contained as impurities,
When this is used as it is as a raw material for the production of pyridinol, these impurities react further during hydrolysis with alkaline water to form insoluble metal oxides and tar-like substances, which are acidified to precipitate crystals. It is believed that these are incorporated into the crystals and reduce the purity of 3,5,6-trichloro-2-pyridinol.

The object of the present invention is to solve such a problem, and even when 2,3,5,6-tetrachloropyridine containing impurities such as metal salts is used as a raw material, a highly pure 3,5,6 -Trichloro-2
To obtain pyridinol.

(Means for Solving Problems) As a result of earnest research, such as extraction method, crystallization method, etc., in order to increase the purity of the product, the present inventors have found that in order to remove these impurities, alkaline hydrolysis is completed. After that, they found out that they need to pass the heat, and reached the present invention.

That is, the present invention, 2,3,5,6-tetrachloropyridine containing a metal salt is heated in an alkaline aqueous solution, after hydrolysis, by adding an acid, 3,5,6-trichloro-2 In the method for producing pyridinol, the method is a method for producing 3,5,6-trichloro-2-pyridinol, which is characterized in that after the hydrolysis, before heating, the acid is added.

In the present invention, the metal salt-containing 2,3,5,6-tetrachloropyridine is, as described above, containing a catalyst such as a metal salt such as ferric chloride usually used in the production, 2. 3,5,6
-Tetrachloropyridine, for example US Pat.
It is manufactured according to 8,100.

Alkali which can be used in the present invention includes potassium hydroxide, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like.

The reaction formula of hydrolysis in the present invention is considered to be as follows.

That is, 3,5,6-trichloro-2 produced by hydrolysis
-Pyridinol is a weak acid and consumes metal hydroxide immediately, so theoretically 2 equivalents of metal hydroxide are required. In practice, a slight excess of alkali is used to shorten the reaction time.

In the present invention, the term “heat-aging” is performed at 75 ° C. or higher under normal pressure, preferably at 85 ° C. or higher. During this heat pass, it is necessary that the generated 3,5,6-trichloro-2-pyridinol alkali salt is in a dissolved state, and therefore, depending on the alkali used, The amount of water required is chosen accordingly. 3,5,6-trichloro-2
-The solubility of pyridinol alkali metal salt in water is very small, and when sodium hydroxide is used, the amount of water that can be heated is 8.3% by weight with respect to tetrachloropyridine at 95 ° C. More than double.

When potassium hydroxide is used, the solubility of 3,5,6-trichloropyridinol potassium salt in water is higher than that of sodium salt, and the amount of water that can be heated is 95%.
It may be 3.5 times or more the weight of tetrachloropyridine at ℃. That is, when using a reaction can of the same volume, when potassium hydroxide is used, it has twice or more the capacity as when sodium hydroxide is used, and potassium hydroxide is preferably used as the alkali. On the other hand, even in the case of sodium hydroxide, from reaction to heat
Although water can be reduced by operating under pressure so that the temperature becomes 0 ° C. or higher, chlorinated compounds such as sodium chloride exist under pressure at high temperature, so there is a risk of corrosion in the SUS system, such as tantalum. Special materials are required.

The present invention is implemented as follows, for example. That is, water in an amount capable of dissolving metal-containing unpurified crude tetrachloropyridine and trichloropyridinol alkali salt (at 95 ° C., when the alkali is sodium hydroxide, 8.3 times or more that of tetrachloropyridine, potassium hydroxide). In this case, a mixture of 3.5 times or more) and 2.2 mole times or more of alkali hydroxide is usually heated and stirred at a temperature of 95 to 100 ° C. At the initial stage of the reaction, it is a two-layer system consisting of an organic layer and an aqueous layer, but as the reaction proceeds, it becomes a homogeneous phase and some other insoluble matter remains. After confirming that tetrachloropyridine has disappeared by gas chromatography, the temperature of the liquid is preferably maintained at 85 ° C. or higher, and a thermal pass is performed. While maintaining the temperature, add sulfuric acid or hydrochloric acid to the solution to adjust the pH to 3-4 and cool it to 3,5,6
-Precipitate trichloro-2-pyridinol and overseparate. After washing with warm water and drying, 3,5,6-trichloro-2
-Pyridinol is obtained.

This method is not limited to 2,3,5,6-tetrachloropyridine,
Unpurified 2,3,4-trichloropyridine, 2,3,5-trichloropyridine, 2,5,6-trichloropyridine, 2,3,4,5-tetrachloropyridine, pentachloropyridine, etc. It can also be applied to hydrolysis.

(Effect of the invention) In the present invention, by carrying out heat passing, even when unpurified 2,3,5,6-tetrachloropyridine containing a metal salt such as ferric chloride is used as a raw material, Highly pure 3,5,6
-Trichloro-2-pyridinol can be obtained.

(Examples) The present invention will be described below with reference to Examples and Comparative Examples.

Example 1 Crude 2,3,5,6-tetrachloropyridine synthesized according to US Pat. No. 3,538,100 (GC purity, 36.0% ferric chloride, tetrachloropyridine 96.0%, 2,3,6-trichloropyridine) 2.0%, pentachloropyridine 1.5%) 217 g
(1.00 mol), 868 g of water (4 times the weight of crude tetrachloropyridine), and 128 g of potassium hydroxide (2.29).
Mol) was heated and stirred at 95 to 100 ° C. The starting material tetrachloropyridine disappeared in 18 hours.
After insoluble matter was removed by heating while keeping the liquid temperature at 85 ° C. or higher, 97% sulfuric acid was added until the pH of the liquid reached 3.5 (while consuming 69 g) while stirring at 85 ° C. About 5
After cooling to 0 ° C., superseparation, washing with warm water, and drying, 178.0 g of off-white 3,5,6-trichloro-2-pyridinol (GC internal standard method, purity 97.5%,
mp171 ° C.) was obtained. The yield based on crude tetrachloropyridine was 89.7%.

Comparative Example 1 Crude tetrachloropyridine 21 same as that used in Example
95-100 parts of a mixture consisting of 7 g (1.00 mol), water 868 g, and potassium hydroxide 128 g (2.29 mol).
The mixture was heated and stirred at ℃. The starting material tetrachloropyridine disappeared in 18 hours. The liquid temperature was maintained at 85 ° C. or higher, and 97% sulfuric acid was added without stirring until the pH of the liquid became 3.5 (70 g was consumed). After cooling to about 50 ° C., washing with warm water, and drying, 180.3 g of brown-gray crystals (GC internal standard method, purity 93.3%, mp
165 ° C.) was obtained.

Claims (1)

[Claims] 1. 2,3,5,6-Tetrachloropyridine containing a metal salt is heated in an alkaline aqueous solution to hydrolyze, and then an acid is added to 3,5,6-trichloro-2-. In the method for producing pyridinol, the method for producing 3,5,6-trichloro-2-pyridinol is characterized in that after the hydrolysis, before heating, the acid is added.