JPS603385B2 - 2. Separation method of 6-dichloropyridine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides 2.
The present invention relates to a method for efficiently separating 2,6-dichloropyridine from a mixed solution containing 6-dichloropyridine.

More specifically, the present invention relates to a method of adding water and sulfur dioxide in the step of separating a mixed solution containing 2,6-dichloropyridine. Several methods have been proposed for producing 2,6-dichloropyridine using pyridine or 2-chloropyridine as a raw material, and these methods can be broadly divided into thermal reactions and photoreactions.

As the former method, for example, there is a method described in U.S. Pat. Manufactures pyridine.Also,
An example of the latter is the method described in US Pat. No. 3,557,124, in which 2-chloropyridine is reacted with chlorine and a halogenated hydrocarbon in the liquid phase at temperatures between 90 and 180°C.

In order to separate and obtain 2.6-dichloropyridine from the mixed solution obtained by these reactions, the reaction chlorine is usually neutralized with an alkali, the halogenated hydrocarbon is removed by distillation, and then the 2.6-dichloropyridine is -Dichloropyridine may be obtained, but since 2-chloropyridine and other chlorinated substances are present in the mixed solution, it is necessary to sequentially separate products other than 2,6-dichloropyridine. An example of a method for separating and purifying 2-chloropyridine from the mixed solution obtained by the above reaction is to add mineral acid to the reaction product solution to make 2-chloropyridine potate, and then extracting with water.
There is a method of separation and distillation (Japanese Unexamined Patent Publication No. 1987-197).

When this purification method is applied to separate 2,6-dichloropyridine, for example, concentrated hydrochloric acid is added to the solution produced by the reaction, and 2-chloropyridine is extracted and separated in the form of a hydrochloride.

An aqueous alkali solution is added to the residual solution and mixed, the unreacted chlorine elements dissolved in the reaction solution are removed as hypochlorite, and then the halogenated hydrocarbons are removed by distillation.
- This is the process of obtaining dichloropyridine. In this way, the separation method in which the purification method for 2-chloropyridine is applied to 2.6-dichloropyridine has the advantage that the impurity in this case, 2-chloropyridine, can be extracted from the liquid in the form of a salt. However, in this reaction, in order to increase the yield of 2,6-dichloropyridine, the reaction is usually carried out with excess chlorine, so a relatively large amount of alkali is required to treat unreacted chlorine, and as a result, Since the resulting aqueous chlorine solution after bleaching contains a small amount of organic matter, a method for detoxifying the solution must also be considered.

The present inventors have obtained 2.6-dichloropyridine from a mixture containing 2.6-dichloropyridine obtained by reacting pyridine or 2-chloropyridine with chlorine in the presence of a halogenated hydrocarbon.
- As a result of extensive research into a method for efficiently separating dichloropyridine, we found that if the mixed solution is reduced by directly adding water and sulfur dioxide gas, the reduction reaction of unreacted chlorine will be completed in an extremely short time. The generated acid is 2 in the reaction solution.
- We arrived at the present invention after learning that the effect of fixing clonolepyridine as a salt can also be achieved.

That is, the present invention involves adding sulfur dioxide in the presence of water to a mixture containing 2,6-dichloropyridine obtained by reacting pyridine or 2-chloropyridine with chlorine in a halogenated hydrocarbon solvent. , while reducing unreacted dissolved chlorine, extracting 2-chloropyridine in the form of salt with water,
This method of separating 2,6-dichloropyridine is characterized in that carbon tetrachloride is then removed by distillation to obtain a product.

In the method of the present invention, the reaction occurs by adding sulfur dioxide to a mixed solution containing 2,6-dichloropyridine in the presence of water. At the same time, dissolved chlorine in the solution is reduced and removed, and sulfuric acid and hydrochloric acid are produced at this time, so that the effect of fixing 2-chloropyridine in the form of a salt can also be achieved by this acid.

The sulfur dioxide used in the present invention can be used as it is by filling it in a high-pressure reactor and taking it out as is. (a few percent) can also be used in castles. In this case, since it is an exhaust gas, it is advantageous because it can be treated at low cost. In the present invention, the amount of water added to the mixed solution may be an amount commensurate with the remaining chlorine, and as shown in the reaction formula, 2 moles or more is required per 1 mole of chlorine.

Of course, if water is present in the mixed solution after the reaction and the amount is sufficient for the residual chlorine, it is sufficient to add only sulfur dioxide immediately after the reaction without adding water for reduction. When the residual amount of chlorine in the mixed solution is more than 2 to 3%, it is often convenient for subsequent operations to add a slightly larger amount of water.
In reality, sulfur dioxide is often aerated after adding about 2 to 30% of water to the mixed solution. The time required for reduction treatment by adding sulfur dioxide varies depending on the amount of liquid to be treated and the amount of dissolved chlorine, but is in the range of 5 minutes to 1 hour, and usually 1 minute to 30 minutes is sufficient. .

In addition, the temperature during reduction is 50 to 70, usually 2yo to 39.
Perform at a temperature of 0. Methods for detecting the equivalence point of sulfur dioxide required to reduce chlorine include methods to determine by the color of the treatment solution, methods to confirm using detection paper, and methods that are particularly useful when treating the reaction solution in a continuous manner. It is convenient to measure the equivalence point using a potentiometer. After the reduction treatment, the mixed solution is separated into two layers: a halogenated hydrocarbon layer and an aqueous layer, so as in the conventional method, the halogenated hydrocarbon layer containing 2,6-diclopyridine is washed with a small amount of alkali. ,
After removing the halogenated hydrocarbons, further distillation produces 2.6
- Diclopyridine can be separated. The present invention will be explained below with reference to Examples.

Example 1 A thermometer, a sulfur dioxide blowing nozzle, and a sulfur dioxide blowing nozzle were attached to a 300-inch upper four-necked flask, and one neck was connected to a cooling tube and a washing bottle containing a 10% NaOH aqueous solution.

Put 180% of chlorination reaction solution (containing 1.8% chlorine) and 180% of water into a flask, and while cooling to around 25% in a water bath, add 100% to 100% of sulfur dioxide using the above-mentioned blowing nozzle.
Aeration was performed for 10 minutes at a rate of 120'/min.

Sulfur dioxide was blown into a cylinder to near the theoretical amount while being measured, and untreated free chlorine was detected using KI-starch paper to confirm the equivalence point. The composition of the carbon tetrachloride solution before treatment was 1.84% by weight of 2-chloropyridine, 2.6-
While the diclopyridine content was 3.8% by weight, after the treatment the concentrations were 0.02% by weight for 2-chloropyridine and 4.01% by weight for 2.6-diclopyridine. Further, although a slight amount of chlorine was detected in the NaOH absorption liquid, sulfur dioxide and sulfur sulfate were not detected.

Example 2 A chlorination reaction solution (containing 1.8% chlorine) was continuously sent to the treatment tank using a metering pump with a residence time of 13.7 min, and at the same time, water was pumped into the treatment tank with a retention time of 13.7 min. 7th evening/
sulfur dioxide was blown in at a rate of 0.8 m/min for reduction treatment.

A potentiometer was used to detect the equivalence point, and the aqueous layer of the treated solution was continuously measured. The equivalence point was 700 wv. As a result of analyzing the composition of the carbon tetrachloride layer after treatment, it was found that before treatment, 2
-Chlorpyridine2. 2.6-diclopyridine was 2.94% by weight, but no 2-chloropyridine was contained at all, and 2.6-diclopyridine was 3.94% by weight.
It was 1 box weight%.

Claims (1)

[Claims] 1. Sulfur dioxide is added in the presence of water to a mixed solution containing 2,6-dichloropyridine obtained by reacting pyridine or 2-chloropyridine with chlorine in a halogenated hydrocarbon solvent.2 .6-Dichloropyridine separation method.