JPH01308256A - Gas-phase chlorination of pyridine - Google Patents

Abstract

PURPOSE:To obtain a compound useful as a synthetic intermediate for drugs and agricultural chemicals at a promoted reaction rate and in high yield without causing polymerization of pyridine, etc., by blending pyridine with a chlorine gas in a diluent in a gaseous state and reacting in a gas phase. CONSTITUTION:Pyridine is premixed with a chlorine gas in the presence of a diluent such as water, carbon tetrachloride or nitrogen gas, fed to a reactor, chlorinated in a gas phase at >=120 deg.C and neutralized to give 2-chloropyridine and/or 2,6-dichloropyridine. The diluent is added to prevent contamination of ultraviolet lamp and to suppress conversion of pyridine into tar and the amount of the diluent used is 10-30 mols based on pyridine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention produces 2-chloropyridine and/or 2-chloropyridine, which is useful as an intermediate for pharmaceuticals and agricultural chemicals, from pyridine and chlorine through a gas phase reaction.
, 6-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. By the way, long-term stable operation is a major factor in industrialization, but the following unique phenomenon poses a problem in this reaction.

If only pyridine and chlorine are used, it may be difficult to continue the reaction stably, as the lamp may become dirty or the reactant outflow piping may become clogged due to the generation of cool substances originating from the pyridine-chlorine complex.

To avoid this, there is an example of using carbon tetrachloride as a diluent (US Pat. No. 3,297,556).

However, this method has the disadvantage that by-product pyridine hydrochloride adheres to the lamp, reducing lamp efficiency. In addition, there are improvements in which at least 1 mole of water vapor or halogenated hydrocarbon-steam is added to pyridine (Japanese Patent Publication No. 52-3935, Japanese Patent Publication No. 52-39).
No. 36, Special Publication No. 55-4742).

However, these methods also have the drawback that the yield of 2-chloropyridine is only about 30% due to the low conversion rate of pyridine. In addition, when operating with an increased molar ratio of chlorine to pyridine in order to obtain 2,6-dichloropyridine as the main product, for example, if 2 moles of chlorine is charged, half of it becomes unreacted chlorine in the exhaust gas. contained within. As a result, the conversion rate of pyridine was still as low as 50%.

As mentioned above, a large amount of unreacted pyridine remains,
When there is a large amount of unreacted chlorine gas, many problems arise in the process.

First, unreacted pyridine condenses in the exhaust gas line, where it reacts with hydrochloric acid gas to form pyridine hydrochloride, which begins to precipitate, causing blockage.

Furthermore, if the amount of exhaust gas is large, unreacted pyridine will also accompany it, and its loss cannot be ignored. The recovery rate of pyridine is also not that good due to the complexity of the post-process, so increasing the conversion rate of pyridine and the reaction rate of chlorine gas are considered to be important points for stable operation of the process. I'm crazy.

If the amount of diluent such as water or carbon tetrachloride is reduced in order to speed up the reaction, side reactions such as pyridine polymerization will proceed during the reaction. On the other hand, the reaction temperature is usually 2.
It is difficult to operate above 00°C, and it was thought that measures to essentially accelerate the reaction were required.

[Means to solve the problem]

As a result of intensive studies to improve the above-mentioned problems, the inventors of the present invention found that even if pyridine and chlorine gas were mixed in advance in the presence of a diluent and supplied to the reactor, pyridine polymerization, etc. They discovered that the reaction rate was significantly improved without causing any problems, and came up with the present invention.

That is, the present invention is a gas phase method of pyridine, which is characterized in that, when reacting pyridine and chlorine in a gas phase, pyridine and chlorine gas are mixed in a gaseous state in the presence of a diluent and then supplied to a reactor. This is a chlorination reaction method.

It is known that blowing chlorine gas in the liquid phase into pyridine alone or in the presence of a diluent causes severe tarring, but if pyridine is mixed with pyridine in the presence of a diluent without the presence of light, for example at 120°C, When chlorine gas is mixed in the gas phase, the liquid obtained after cooling is jet black, indicating that pyridine is unstable in the gas phase and under conditions where the reaction does not proceed (in the absence of light or below 250°C). It was thought that polymerization occurs via chlorine salts.

This phenomenon is generally accepted as a well-known fact, and in the examples of Japanese Patent Publication Nos. 3935-1982, 3936-1982, and 4742-1987, chlorine is directly blown into the reactor. The same is true for gas phase thermal bulk plating reactions.
In Japanese Patent Publication No. 35-2930, Japanese Patent Publication No. 52-952, Japanese Patent Publication No. 54-22983, Japanese Patent Publication No. 43-9224, and U.S. Patent No. 3.251.848, chlorine gas is supplied to the reactor alone. Introduced in the Tokko Sho 4] = 20946
No., JP-A-60-166664, JP-A-61-831
In No. 62, a mixture of chlorine gas and diluent is injected. Among them, Japanese Patent Publication No. 43-9224 recommends that chlorine and pyridine be separately preheated and supplied.

The present inventors first found that the above-mentioned tar formation does not occur in the gas phase in the presence of a diluent, but occurs only in the liquid phase upon condensation. Therefore, the problem of tarring can be solved by preventing the mixed gas supplied to the reaction tank from condensing. Furthermore, as the reaction progresses in the reaction tank, all unreacted pyridine will exist in the condensate as hydrochloride, so the lamp, which is present in the gas phase, will not be contaminated and tar will not occur. It was.

It has been found that when the gas mixture thus obtained is supplied to a reactor and a gas phase photochlorination reaction is performed, the reaction rate is significantly accelerated compared to when pyridine and chlorine are introduced separately into the reactor. . That is, when such a mixed gas is supplied to a reactor, the conversion rate of pyridine can usually be increased to 80% or more, although it depends on the type of reactor.

In addition, when using the method of attaching a stirrer to the reactor (Japanese Patent Application No. 1982-256104, which is an earlier application of the present inventor),
The reaction results become even more favorable.

In this case, the raw material gases are sufficiently mixed, so compared to the case where pyridine and chlorine gas are supplied from separate ports,
The advantage is that the size and rotational speed of the stirrer can be quite small.

Any type of blade can be used, such as a turbine type, a Faudler type, or a propeller type. Although the rotation speed varies depending on the size and shape of the reaction tank, the rotation speed is 50 to 300 rpm.

When carrying out the reaction according to the method of the invention, the residence time is 10
~30 seconds is sufficient, but even if the residence time is longer than this, the reaction results will not be affected, so the amount charged can be changed arbitrarily. The molar ratio of pyridine and chlorine, which are reaction raw materials, is arbitrarily selected depending on whether 2-chloropyridine or 2,6-dichloropyridine is used as the main product.

The reaction temperature is 120°C or higher, preferably 140°C or higher. The higher the reaction temperature, the higher the reaction rate, but as mentioned above, due to problems with the reactor material, the temperature is usually 200°C.
Temperatures exceeding 100% are difficult.

The diluent is added to prevent staining of the ultraviolet lamp and to suppress cooling of the pyridine, and any of water, carbon tetrachloride, nitrogen gas, etc. can be used. In the conventional method, the dilution rate could not be increased very much because the reaction was slow, but according to the present reaction method, no problem occurs even if the dilution rate is 20 times or more by mole. Usually, a diluent of 10 to 30 moles (to pyridine) is used.

The reaction mixture is passed through a condenser using hot water as a coolant.
Condense and lead to a vessel with an exhaust line.

The obtained reaction solution is neutralized with sodium hydroxide, extracted with carbon tetrachloride, and then subjected to simple fractional distillation to obtain the desired product.

〔Effect of the invention〕

By the method of the present invention, 2-chloropyridine or 2,
6-dichloropyridine can be obtained in a yield several times higher than that of conventional methods. Furthermore, it has become possible to operate stably for a long period of time without problems such as blockages.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples.

Example 1 As a photoreaction can, the lamp is installed at the mouth, the stirrer is installed at the mouth,
A 51 Pyrex can with a jacket that has a thermometer port, gas inlet, gas outlet, etc., and 1 as a light source.
A 00W, high pressure mercury lamp was used.

The lamp was installed approximately in the center of the reactor, and a Teflon propeller-type stirring blade with a blade diameter of 5 cm was attached to the top of the reactor.

The stirring rotation speed was 200 rl1m.

Pyridine 90.0 g/H1 Water 512 g/H is evaporated in an evaporator, and chlorine gas is added to the mixed gas at 121 g/H.
The raw material gas was mixed through a line mixer with an internal volume of 200 ml. These mixed gases were then supplied to a reaction vessel preheated to 130°C. At this time, heat the line mixer etc. to prevent the mixed gas from condensing.

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

On the other hand, the reaction gas was condensed in a hot water condenser and then stored in a 1β receiver with hot water circulating through the jacket, and was extracted intermittently. As a result, 719 g/H of the reaction solution was obtained, of which 8.2 g/H, 2-chloropyridine 71.7 g/H, 2,6-dichloropyridine 56.4 g/H, unreacted pyridine.
It was found that g/H was contained. From the above, the conversion rate of pyridine is 91%, the selectivity of 2-chloropyridine is 61.0%, and the selectivity of 2,6-dichloropyridine is 3.
It was 6.8%. Further, the reaction rate of the blown chlorine gas was 83.0%.

Example 2 The same procedure as in Example 1 was carried out except that the stirrer in the reaction tank was stopped. As a result, a reaction solution of 712 g/H was obtained, which contained 15.4 g of unreacted pyridine/66.3 g of H12-chloropyridine/39.2 g/I-(of H12,6-dichloropyridine). From the above, the conversion rate of pyridine was 83%, the selectivity of 2-chloropyridine was 70.3%, and the selectivity of 2,6-dichloropyridine was 28.0%. The reaction rate was 72%.

Comparative Example 1 In the operation of Example 2, except that chlorine gas was directly blown into the reactor through a separate supply port provided in the reaction tank.
Treated in the same way. As a result, 52.4 g of unreacted pyridine/H12-chloropyridine 3 was found in the reaction solution and exhaust gas.
7.8g/H,2,6-dichloropyridine 19.7g
/H was contained.

The conversion rate of pyridine was 41.8%, and the absorption rate of chlorine gas was only 35%.

Claims (1)

[Claims] 1. In reacting pyridine and chlorine in the gas phase,
A gas phase chlorination reaction method for pyridine, which comprises mixing pyridine and chlorine gas in gaseous form in the presence of a diluent and then supplying the mixture to a reactor. 2. The method for gas phase chlorination of pyridine according to claim 1, characterized in that the gas in the reactor is stirred and mixed.