JPH01308254A - Production of chlorinated pyridine - Google Patents

Abstract

PURPOSE:To obtain a compound useful as a synthetic intermediate for drugs and agricultural chemicals, by a simple operation while preventing formation of colored substance and insoluble substance in a neutralization process, by chlorinating pyridine in a gas phase, heating the reaction solution for <=a fixed time, degassing contained chlorine and then neutralizing. CONSTITUTION:Pyridine is chlorinated by using a diluent such as water or N2 in a gas phase and cooled to give a reaction solution. The reaction solution is heated at a boiling point or a temperature close to the temperature within one hour to degas contained chlorine. Then the resulting substance is neutralized with an alkali such as NaOH to give 2-chloropyridine and/or 2,6- dichloropyridine. In the degassing process, a condensed solution is heated by a receiver of the reaction solution, the reaction solution is most suitably heated at the boiling point or the temperature close to the boiling point within one hour, retention time as a solution containing a chlorine gas is a time corresponding to a piping between a condenser-a receiver and the amount of the solution changed is negligible.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention produces 2-chloropyridine and/or 2,6-chlorinated pyridine, which is a pyridine chloride useful as an intermediate for pharmaceuticals and agricultural chemicals, from pyridine and chlorine through a gas phase reaction. This invention relates to improvements in the method for producing dichloropyridine.

[Problems to be solved by conventional techniques and inventions] Below,
The present invention will be described in detail by taking photoreaction as an example of gas phase chlorination of pyridine.

Pyridine and chlorine are reacted in the gas phase under ultraviolet irradiation,
Several methods for synthesizing 2-chloropyridine and/or 2,6-dichloropyridine are already known.

For example, carbon tetrachloride is used as a diluent to prevent lamp dirt and generation of cool substances (U.S. Patent No. 3).
．． 297.556) or at least 1 for pyridine.
Method of adding mol or more of water vapor or halogenated hydrocarbon-steam (Japanese Patent Publication No. 52-3935, Japanese Patent Publication No. 52-3
No. 936, Special Publication No. 55-4742).

However, in these examples, the halogenated hydrocarbon reacts slightly during the photoreaction, producing a product that is difficult to separate from 2-chloropyridine by distillation. Therefore, the reaction solution is treated with an acid to remove byproducts derived from the halogenated hydrocarbon. After that, complicated post-processing of neutralization and fractional distillation is required (Japanese Patent Application Laid-Open No. 1977-1979)
No. 53, Japanese Unexamined Patent Publication No. 56-90058).

As an improved method of this, a method using nitrogen as a diluent instead of halogenated hydrocarbon (Japanese Patent Application Laid-open No. 60'-78967
There are two methods: dilution with a large excess of water, etc., using a reactor equipped with a stirrer (Japanese Patent Application No. 62-256104), and these methods eliminate by-products derived from halogenated hydrocarbons. It has the advantage of requiring a relatively simple purification process since it does not contain living organisms.

The present inventors investigated the yield and post-processes of these methods in detail, and found that significant coloring occurred during the process of neutralizing the reaction solution, extracting and separating the liquid, and that intermediates formed at the interface, especially during the liquid separation process. We discovered the problem of the existence of layers. Perhaps because of this, the amount of valuable materials obtained after neutralization and liquid separation was not necessarily high, and the amount of valuable materials that would turn into colored or insoluble materials was thought to be far from negligible. .

[Means to Solve the Problem] As a result of intensive studies to improve the above points, the present inventors have found that unreacted chlorine contained in the reaction liquid obtained by cooling and condensing the reaction gas is It was found that this is because it reacts with valuables and produces undesirable by-products.

When water is used as a diluent, the reaction solution exists in two liquid phases, and a considerable amount of chlorine gas is dissolved in the organic layer in addition to 2,6-dichloropyridine and 2-chloropyridine. In addition to pyridine hydrochloride and 2-chloropyridine hydrochloride, a small amount of 2,6-dichloropyridine and chlorine gas are dissolved in the water layer.

The present inventors have discovered that the amount of dissolved chlorine gas decreases over time and becomes extremely small after several hours. They discovered that the reduction in chlorine gas content is closely related to the amount of coloring and insoluble matter in the subsequent process.

That is, the photochlorination reaction liquid is pale yellow, and its hue does not change even if it is left for a long time. However, while left standing, the valuables react with the chlorine content, producing undesirable by-products. It has now become clear that the by-products begin to polymerize when alkaline conditions are reached during the neutralization process, producing colored substances and insoluble substances. Initially, it was thought that such colored substances and insoluble substances were generated during the gas-phase photochlorination reaction, but it was a completely unexpected result that they were generated while the condensed reaction liquid was left standing. Ta.

The inventors of the present invention focused on such reactions that change over time, and as a result of intensive studies on ways to prevent them, the inventors discovered a very simple method of keeping the generated reaction liquid at or near the boiling point within one hour. The present invention was achieved based on the discovery that it is possible to completely prevent the formation of colored substances and insoluble substances during the neutralization process by operation.

Therefore, the present invention provides a method for chlorinating pyridine in a gas phase, cooling it to obtain a reaction solution, and neutralizing this to obtain a chlorinated pyridine, within one hour after obtaining the reaction solution. , relates to a method for producing a pyridine chloride, which is characterized by heating a reaction solution to a boiling point or a temperature close to this to degas the chlorine content.

This time-dependent reaction can be prevented by degassing the chlorine content at a temperature close to the boiling point, but the time from the reaction to the degassing process is a problem. Become. It is necessary to carry out the degassing step within one hour at the latest after the reaction solution is generated. The best method for this is to heat the condensate in a reaction liquid receiver to a temperature at or near the boiling point. According to this method, the residence time of the liquid containing chlorine gas is only the length of the piping between the condenser and the receiver, and the amount of change over time can be almost ignored. Further, if possible depending on the equipment used, the inside of the receiving tank can be depressurized and degassed.

The reaction solution thus obtained is colorless and transparent, exhibits almost no coloring even when neutralized with an alkali, and does not generate any insoluble matter. The neutralized liquid is separated and the organic layer is distilled to easily separate and recover the solvent, pyridine, 2-chloropyridine, and 2,6-dichloropyridine.

The heating temperature of the reaction solution is preferably normal pressure or the boiling point under reduced pressure to achieve a reflux state. If the temperature is 20°C lower than the boiling point, the effect will be diminished, so it is desirable to keep the temperature higher than this.

As the reaction diluent, water is most preferred, but the present invention is also applicable when N2, carbon tetrachloride, etc. are used. If water is not used as a diluent, it is desirable to fill the receiver tank with water. When an organic solvent is not used as a reaction diluent, it is preferable to add an organic solvent to the condensed gas.

As the alkali, a strong base such as sodium hydroxide or potassium hydroxide is usually used.

The vapor phase photochlorination reaction of pyridine has been described in detail above, but this article will discuss other methods for vapor phase chlorination of pyridine, such as a hot vapor phase chlorination reaction carried out at 200°C to 500°C, and a reaction in which the pyridine is passed through a catalyst packed bed. Of course, this method can also be applied.

〔Effect of the invention〕

We discovered the mechanism behind the change over time in the gas-phase chlorination reaction solution of pyridine, and as a preventive measure, we developed a very simple method of holding the reaction solution at or near its boiling point and degassing the chlorine. , coloring during the neutralization process,
It was possible to prevent the generation of insoluble matter and improve the yield.

〔Example〕

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 As a photoreaction can, a 51 Pyrex can with a jacket was used, which had a port for installing a lamp, a port for installing a stirrer, a thermometer port, a gas inlet, a gas outlet, etc., and a 10 Pyrex can as a light source.
A 0W, high pressure mercury lamp was used.

A solvent addition port and a cooler are attached to the gas outlet, and ■
A spear stirrer and a jacketed receiver are installed.

In addition, a Dimroth type cooler is attached to the receiver as an exhaust gas cooler, and the exhaust gas exiting from this can be used to absorb unreacted chlorine, etc. in an alkali absorption tower.

Hot oil at 100°C is introduced into the jacket of the receiver, allowing it to be heated.

The temperature inside the reactor was preheated to 130℃, pyridine was charged at 90.0 g/H, and water was added at 410 g.
/H1 Chlorine gas was charged at 121 g/H.

The reaction was continued while adjusting the temperature of the heat medium in the jacket so that the reactor temperature was maintained at 160°C.

Charge carbon tetrachloride at 200 g/H to the reaction gas outlet,
After cooling the mixed gas to nearly 80° C. using hot water, the condensate was led to a receiving tank.

The receiving tank was heated with a jacket and was in a reflux state, and the temperature was 83°C.

When the reaction liquid was taken out through a cooler, the reaction rate was 80% per hour.
0 g of reaction solution was obtained. P the reaction solution with aqueous caustic soda solution.
When neutralized to H8, the pure caustic soda content was 55g/H.
(1,38 mol/H) was consumed.

The reaction solution thus obtained contains 8.0% unreacted pyridine.
0g/H3P-chloropyridine 78.6g/H
It contained 48.3 g/H of 12,6-dichloropyridine.

The conversion rate of pyridine was 91.1%, the yield of 2-chloropyridine was 60.8%, and the yield of 2,6-dichloropyridine was 28.7%. The balance loss of valuables was estimated to be 1.6% of the pyridine used.

The neutralized solution turned dark yellow after being left for one day, but no insoluble matter was present at the interface.

Example 2 The same process as in Example 1 was carried out except that the amount of water charged was 200 g/H. 590 g of reaction solution was obtained per hour. When the reaction solution was neutralized to pH 8 with aqueous caustic soda solution,
Caustic soda pure content: 56 g/H (1,40 mol/H)
H) Consumed. This reaction solution contained 7 unreacted pyridine.
．． 5g/H12-chloropyridine is 57.6g/H,2
, 6-dichloropyridine in an amount of 74.6 g/H.

The conversion rate of pyridine was 91.2%, the yield of 2-chloropyridine was 44.6%, and the yield of 2,6-dichloropyridine was 44.3%. The balance loss of valuables was estimated to be 2.3% of the pyridine used.

The neutralized solution showed a yellow color after being left for one day, but no insoluble matter was present in the interfacial layer.

Comparative Example 1 Tap water was passed through the receiving tank jacket and gas outlet cooler,
The same operation as in Example 1 was performed except that the temperature of the receiving tank was maintained at 50°C. After 5 hours had elapsed, the resulting reaction solution was adjusted to ρ[18] with an aqueous solution of caustic soda, and 62 g/H (1.55 mol/H) of pure caustic soda was consumed. When the reaction solution was analyzed, unreacted pyridine was found to be 5.7
g/H1 now 2-chloropyridine 73
．． 9g/H, 2,6-dichloropyridine 49.9g/H
It was found that it was included.

Pyridine conversion rate is 937%, 2-chloropyridine yield is 57.2%, 2,6-dichloropyridine yield is 29.6
%, and the balance loss of valuables was found to be 6.9% relative to the charged pyridine.

When neutralized, the reaction solution turned brown, and a black tar-like intermediate was present at the interface after one day.

Comparative Example 2 Tap water is passed through the receiver tank (jaken) and the gas outlet cooler,
The same operation as in Example 2 was performed except that the temperature of the receiving tank was maintained at 50°C. After 5 hours had passed, the resulting reaction solution was adjusted to p[18 with a caustic soda aqueous solution, and 68 g/H (1.70 mol/H) of pure caustic soda was consumed. When the reaction solution was analyzed, unreacted pyridine was found to be 5.6
g/H3P-chloropyridine is 48.9 g/H
It contained 70.9 g/H of 3P,6-dichloropyridine.

The conversion rate of pyridine was 93.8%, the yield of 2-chloropyridine was 37.8%, and the yield of 2,6-dichloropyridine was 4%.
The loss of valuables was estimated to be 13.9% with respect to the charged pyridine.

The neutralized solution showed a blackish brown color after being left for one day, and a large amount of tar-like intermediates were present at the interface.

Claims (1)

[Claims] 1. Chlorinate pyridine in a gas phase and cool it to obtain a reaction solution,
In the method of neutralizing this to obtain pyridine chloride,
A method for producing a pyridine chloride, which comprises heating the reaction solution to a boiling point or a temperature close to this within one hour after obtaining the reaction solution to degas the chlorine content. 2. The method for producing a pyridine chloride according to claim 1, wherein the reaction gas is cooled and the chlorine content is degassed by maintaining the condensed reaction liquid at a temperature at or near its boiling point in a receiving tank.