JPS6020385B2 - Purification method of 2-chloropyridine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and purifying 2-chloropyridine from a 2-chloropyridine-containing composition obtained by a photoreaction of pyridine and chlorine.

Many methods have been proposed for producing 2-chloro'lepyridine, and these methods can be broadly classified into gas phase methods and liquid phase methods.

When carrying out the gas phase method, various diluents, such as carbon tetrachloride, are used to prevent the formation of tar. vapor. nitrogen. Sulfur dioxide gas is used to allow the reaction to proceed while preventing combustion or explosion of pyridine within the system.
In the case of a liquid phase method, 2-chloropyridine is produced by using a halogenated hydrocarbon such as carbon tetrachloride as a diluent and bubbling chlorine gas under external radiation. However, it is known that the 2-chloropyridine produced in any of these cases is further chlorinated to become 2,6-dichloropyridine, and the amount thereof is about 0.2 to 10% of the yield of 2-chloropyridiso. It is being

In particular, when the gas phase method is applied and carbon tetrachloride is used as a diluent, hexachlorethane, which is thought to be a decomposition product of carbon tetrachloride, is produced, while when trichlene is used as a diluent, pentachlorethane is produced. However, in each case, the amount produced is about 0.1 to 40% based on the yield of 2-chloropyridine. It is difficult to separate high chloride products from these by-products or diluents from 2-chloropyridine, and even if they are purified by ordinary distillation methods, they may be mixed into the 2-chlorpyridine as an impurity, or they may be removed from the distillation column. This can cause undesirable phenomena such as blockage. The present invention provides 2-
The purpose is to provide a method for easily separating and purifying chlorpyridine with high purity, and its gist is that a mixture of pyridine and a diluent is a reaction composition containing 2-chloropyridine obtained by reacting chlorine under light irradiation. In this method, hydric acid is added to form a hydric acid salt of 2-chloropyridine, which is separated by water extraction, neutralized with an alkali, and then distilled to purify 2-chloropyridine.

In this case, the diluent is an organic solvent such as trichlene, carbon tetrachloride, etc. A mixture of these organic solvents and water may be used.

The mineral acid used in the present invention is an inorganic acid such as sulfuric acid or hydrochloric acid, which is passed through the reaction product containing 2-chloropyridine in the form of an aqueous solution, or when hydrochloric acid is used, it is passed in a gaseous state. The 2-chloropyridine in the mixed solution can be separated in the form of a salt by blowing into the solution.

The required amount of the acid at this time is sufficient as long as the produced 2-chloropyridine forms a salt, and is appropriately determined depending on the produced amount of 2-chloropyridine. The 2-chloropyridine mineral salt thus formed is extracted with water, separated from other water-retained components, taken to Alka River to neutralize the sharkic acid, and then distilled to obtain highly pure 2-chloropyridine. .
Accordingly, it is very difficult to separate 2-chloropyridine and other created compounds using conventional methods such as distillation after neutralization to obtain highly pure 2-chloropyridine. Then, by fixing 2-chloropyridine in the form of key salt, it can be easily separated.
Furthermore, 2-chloropyridine containing no impurities can be obtained.

Next, the present invention will be explained by examples. Example 1 67 keys of pyridine were placed in a glass reactor with a built-in light source lamp and having a diameter of 14 m and a length of 26 m. Torikuren 263 Toki,
And the temperature inside the reactor was raised to 200℃ through 60℃ of chlorine gas.
00 and allowed to react for 1 hour under irradiation with external rays, and when 310 g of hydrochloric acid gas was blown into the resulting reaction solution, white crystals were floating.

The crystals were then dissolved in water and separated from the organic layer. As a result of gas chromatography analysis, this organic layer contained 260 g of trichlene, 4 g of bentachloroethane, 6 g of 2-chloropyridine, and 2.3 g of 2.6-dichloropyridine. On the other hand, the aqueous layer previously separated from the organic layer was neutralized with a 20% aqueous sodium hydroxide solution until the pH value reached 11, and the liberated pyridine and 2-chloropyridine were extracted with trichlene, followed by distillation to remove pyridine. 515 g and 198 g of 2-chloropyridine were obtained.

The purity of the product 2-chloropyridine was greater than 99.8% and was substantially free of 2,6-dichloropyridine and pentachlorethane. Furthermore, when the refractive index of the product was measured, the value was n200=1.5324, which was a good result showing an approximate value of the theoretical value (n20=1.53). Example 2 13,881 g of carbon tetrachloride, 714 g of pyridine, 150 g of water, and 32 g of chlorine gas were blown into a glass 10Z reactor and reacted for 1 hour under external ray irradiation, and the resulting reaction solution had an organic layer of 136.1 g. Separated into two layers: water and water.

A 36% aqueous hydrochloric acid solution was added to this organic layer, and the liquid after the filtration was separated. By this operation, it was contained in the organic layer. 2
．． 6-diclopyridine could be substantially separated from pyridine and 2-chloropyridine hydrochloride.

Next, 9 spots of 39% sodium hydroxide aqueous solution were added to the hydrochloride aqueous solution of pyridine and 2-chloropyridine to obtain P.
The H value was neutralized to 11. On the other hand, 40% is added to the aqueous layer of the reaction solution.
Aqueous sodium hydroxide solution was added to a pH of 11 by adding 34 ml of aqueous solution, and the two were mixed. Next, this mixture was distilled, and pyridine and 2-chloropyridine were distilled out azeotropically with water until the boiling point reached 99.7%. To 1,771 g of this distillate was added 44 g of granular sodium hydroxide for dehydration to obtain a liquid of 71 ml, and further 45 g of pyridine and 24 g of 2-chloropyridine were obtained by milling. The purity of the product 2-chloropyridine was 99.7% or more as measured by gas chromatography, and it did not contain impurities such as 2,6-dichloropyridine or hexachlorethane. Moreover, the refractive index of the product was n-spot D=1.5327. As a reference example,
When the same reaction as in Example 2 was carried out and the product liquid was directly distilled, it contained about 2% of 2,6-dichloropyridine and about 0.3% of bentachlorethane, resulting in a highly pure 2. −
No chlorpyridine was obtained. Example 3 Aqueous layer 64, organic layer 1 obtained by the same operation as Example 2
98% sulfuric acid and 55 females were added to 361 females, and after sufficiently stirring, the liquid was separated.

Claims (1)

[Claims] 1. Photoreacting pyridine and chlorine in the presence of a diluent,
A mineral acid is added to the obtained mixed solution containing 2-chloropyridine to form a mineral acid salt of 2-chloropyridine, which is separated by water extraction, neutralized with alkali, and then distilled. A method for purifying 2-chloropyridine.