JP2011063551A - Process for producing 2-chloropyridine and 2,6-dichloropyridine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and inexpensively produce 2-chloropyridine and 2,6-dichloropyridine while inhibiting secondary formation of tar, for example, in a distillation and purification step in a process for producing 2-chloropyridine and 2,6-dichloropyridine, for example, by subjecting chlorine and pyridine to gas phase reaction. <P>SOLUTION: The process for producing 2-chloropyridine and 2,6-dichloropyridine comprises reacting chlorine with pyridine and thereafter furthermore reacting the resulting reaction mixture with a reducing agent. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing 2-chloropyridine and 2,6-dichloropyridine by reacting chlorine with pyridine in a gas phase.

  As a method of chlorinating pyridine to obtain 2-chloropyridine or 2,6-dichloropyridine, chlorine and pyridine are reacted in a gas phase at about 300 to 420 ° C. in the presence of carbon tetrachloride gas, and 2-chloropyridine is obtained. A method of obtaining pyridine (Patent Document 1), a method of obtaining a chlorinated pyridine by reacting chlorine and pyridine in a gas phase at 200 to 300 ° C. in the presence of a specific radical initiator (Patent Document 2), and A method is known in which chlorine is reacted in the gas phase at 180 to 300 ° C. under irradiation with ultraviolet light using water as a diluent to obtain 2-chloropyridine and 2,6-dichloropyridine (Patent Document 3). .

US Pat. No. 3,153,044 JP-A-2-59558 JP-A-6-199794

  However, according to the method for producing 2-chloropyridine and 2,6-dichloropyridine described in Patent Documents 1 to 3, for example, a relatively large amount of a tar-like substance is by-produced in the distillation, purification process, etc. If it decreases, or a tar-like substance accumulate | stores, it will cause various malfunctions, such as obstructing piping, such as a manufacturing apparatus.

  The present invention provides a method for producing 2-chloropyridine and 2,6-dichloropyridine, which suppresses by-product formation of a tar-like substance, and yields 2-chloropyridine and 2,6-dichloropyridine in a high yield in a simple and inexpensive manner. It aims at providing the method of manufacturing by.

  As a reaction mechanism for generating the tar-like substance, for example, as shown in the following formula, when unreacted chlorine is ring-opened by forming a complex with chlorinated pyridine and water is present, a dialdehyde compound is used. And these are considered to condense.

  Further, even in the absence of water, it is considered that unreacted chlorine easily forms a ring by forming a complex with chlorinated pyridine, and a tar-like substance is easily generated.

  According to the experiments of the present inventors, when chlorine is blown into pyridine or 2-chloropyridine, taration proceeds with time at a heat treatment temperature of about 70 ° C. or more, and pyridine or 2-chloropyridine remains after 1 hour. A phenomenon was observed in which the rate dropped to 90-97%.

  The present invention relates to a process for producing 2-chloropyridine and 2,6-dichloropyridine in which chlorine is reacted with pyridine and then further reacted with a reducing agent.

  The method for reacting pyridine and chlorine is not particularly limited. For example, in the liquid phase or gas phase, pyridine is thermally chlorinated with chlorine at 350 to 420 ° C., or chlorinated using a radical initiator. And a method of chlorination under ultraviolet irradiation.

  In the method of chlorination using a radical initiator and the method of chlorination under ultraviolet irradiation, the reaction temperature is preferably, for example, 160 to 300 ° C, more preferably 180 to 220 ° C.

  In this invention, it is preferable that it is 0.1-3 mol with respect to 1 mol of pyridines, and, as for the usage-amount of chlorine, it is more preferable that it is 0.3-2 mol.

  In the present invention, examples of the reducing agent include sulfur dioxide, sulfites such as sodium sulfite and potassium sulfite, and borohydride salts such as sodium borohydride and potassium borohydride. Among these, sulfur dioxide and sodium sulfite are preferably used from the viewpoint of economy.

  The ratio of the reducing agent used is preferably 0.1 to 10 mol, and more preferably 0.3 to 2 mol, per 1 mol of unreacted chlorine. When the use ratio of the reducing agent is less than 0.1 mol, there is a risk that the suppression of tar-like product generation may be insufficient, and when the use ratio of the reducing agent exceeds 10 mol, an effect commensurate with the use amount is obtained. It is hard to be done and it is not economical.

  Examples of a method for setting the use ratio of the reducing agent include a method in which the amount of unreacted chlorine is measured in advance and added as a ratio to the amount of unreacted chlorine.

  As temperature at the time of adding the said reducing agent, it is preferable that it is 0-100 degreeC, and it is more preferable that it is 30-80 degreeC.

  Among the methods of reacting pyridine and chlorine, a method of reacting pyridine and chlorine in a gas phase under ultraviolet irradiation is preferable from the viewpoint of increasing the efficiency of the chlorination reaction.

  Examples of the ultraviolet light source include a high pressure mercury lamp, an ultra high pressure mercury lamp, a low pressure mercury lamp, and an ultraviolet LED.

  In the gas phase reaction between pyridine and chlorine, water is preferably used as a diluent in order to suppress a rapid increase in reaction temperature.

  In the gas phase reaction between pyridine and chlorine, when water is used, the ratio of water used is preferably, for example, 1 to 30 mol with respect to 1 mol of pyridine.

  When water is not used in the gas phase reaction between pyridine and chlorine, the reaction solution after the reduction reaction is a mixed solution of unreacted pyridine, 2-chloropyridine and 2,6-dichloropyridine.

  However, when water is used, the reaction solution after the reduction reaction is mainly composed of an upper layer composed of unreacted pyridine, water and 2-chloropyridine and a lower layer composed of 2-chloropyridine and 2,6-dichloropyridine. Separate into two layers.

  The 2-chloropyridine and 2,6-dichloropyridine thus obtained can be isolated by subjecting the reaction solution to a treatment such as distillation.

  According to the method of the present invention, 2-chloropyridine and 2,6-dichloropyridine can be produced in a high yield simply and inexpensively while suppressing the by-product of the tar-like substance.

Example 1
A 3 L capacity gas phase reaction section with a 100 watt high pressure mercury lamp at the upper center and two blowing pipes at the upper end, and a 2 L capacity 3 with a condenser, blowing pipe and branch pipe connected to the lower part of the reaction section. A photochlorination reaction was carried out by the following procedure using a reactor composed of a three-necked flask.

  A 42% by weight pyridine aqueous solution that had been completely vaporized by heating to 110 ° C. or higher in advance was introduced into the reactor at a rate of 20 g / min and chlorine at a rate of 3.7 g / min, respectively, from the blowing tube at the upper end. And reacted at 190 ° C. The reaction product was condensed in a lower condenser and received in the flask as a reaction solution.

  When the reaction liquid started to flow into the flask, sulfur dioxide was introduced into the reaction liquid at a rate of 0.8 g / min using the lower blowing tube.

  That is, the reaction was performed at a molar ratio of pyridine: chlorine: water: sulfur dioxide = 1: 0.47: 6.1: 0.12. In addition, the amount of unreacted chlorine before blowing in sulfur dioxide was 0.11 mol with respect to 1 mol of pyridine.

  After 80 minutes from the introduction of the sulfur dioxide, 2760 g of a reaction solution was obtained.

  The reaction solution was separated, and 470 g of 25% aqueous sodium hydroxide solution was added to the upper layer (2330 g) to adjust the pH to 11 or more, followed by rectification at 105 to 150 ° C. for 2 hours at normal pressure. 745.3 g of aqueous solution (pyridine concentration 55.0%, pure pyridine recovery amount 409.9 g) and 107.0 g of 2-chloropyridine were obtained.

  Further, the lower layer (430 g) of the reaction solution was subjected to rectification at 20.0 to 6.7 kPa at 100 to 150 ° C. for 7 hours to obtain 288.1 g of 2-chloropyridine and 25.2,6-dichloropyridine. 1 g and 1.7 g of tar-like material were obtained.

  Regarding the total yield and yield, 409.9 g of pyridine (recovery 61.0%), 335.1 g of 2-chloropyridine (34.7% of pyridine yield), 25.1 g of 2,6-dichloropyridine ( Yield of pyridine with respect to 2.0%) and 1.7 g of a tar-like substance.

Example 2
In Example 1, instead of using sulfur dioxide, a photochlorination reaction was carried out in the same manner as in Example 1 except that 630 g (1.0 mol) of a 20 wt% sodium sulfite aqueous solution charged in advance in the flask was used. went.

  The pyridine aqueous solution and chlorine were introduced into the reactor for 80 minutes to obtain 3326 g of a reaction solution in the flask.

  Separation and rectification were carried out in the same manner as in Example 1, and the total yield and yield were 410.1 g of pyridine (recovery 61.0%) and 335.5 g of 2-chloropyridine (vs. pyridine yield). 34.7%), 25.1 g of 2,6-dichloropyridine (2.0% yield of pyridine) and 1.5 g of a tar-like substance.

Comparative Example 1
In Example 1, a photochlorination reaction was performed in the same manner as in Example 1 except that sulfur dioxide as a reducing agent was not used.

  The aqueous pyridine solution and chlorine were introduced into the reactor for 80 minutes to obtain 2696 g of a reaction solution in the flask.

  Separation and rectification were performed in the same manner as in Example 1, and the total yield and yield were 397.6 g of pyridine (recovery 59.2%) and 311.6 g of 2-chloropyridine (vs. pyridine yield). 32.3%), 22.1-g of 2,6-dichloropyridine (1.8% yield of pyridine) and 20.4 g of a tar-like substance were obtained.

Claims (4)

  A method for producing 2-chloropyridine and 2,6-dichloropyridine, in which chlorine is reacted with pyridine and then further reacted with a reducing agent.   The method for producing 2-chloropyridine and 2,6-dichloropyridine according to claim 1, wherein chlorine is reacted with pyridine in the presence of water.   The method for producing 2-chloropyridine and 2,6-dichloropyridine according to claim 1 or 2, wherein chlorine is reacted with pyridine under ultraviolet irradiation.   The method for producing 2-chloropyridine and 2,6-dichloropyridine according to any one of claims 1 to 3, wherein the reducing agent is sulfur dioxide or sodium sulfite.