JP2523753B2 - Method for producing 2,3-dichloropyridine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing 2,3-dichloropyridine useful as an agricultural / pharmaceutical intermediate.

[Conventional technology]

2,3-Dichloropyridine (hereinafter, 2,3-DCP) can be produced by liquid phase chlorination of pyridine or pyridine hydrochloride (JP-A-61-249965) or vapor phase chlorination of pyridine. According to the method described in JP-A-58-206564.
No.). Further, a method of manufacturing the chlorination of palladium chloride complexes pyridine (Synthesis, 5, 378 (198
0))

[Problems to be Solved by the Invention]

However, in the method using palladium chloride in the above method, although the yield is good, since expensive palladium chloride is used in an equivalent amount to the substrate, there is a practical problem. In another method, the desired product, 2,3-DCP, was obtained as a mixture with pyridine polychlorinated compound, and the reaction yield was 10-15.
There was a drawback that it was very low at%. For this reason, an operation such as distillation has to be used for further purification of the target product, which is complicated and further reduction of the yield cannot be avoided.

[Means for solving the problem]

The present inventor has found that 2,3,6-trichloropyridine (hereinafter referred to as TRCP
The present invention found that 2,3-dichloropyridine can be selectively obtained by reacting with hydrogen in the presence of a catalyst. Came to.

That is, the present invention provides a method for producing 2,3-DCP, which comprises reacting TRCP with hydrogen in the presence of a catalyst.

TRCP can be easily obtained, for example, by photochlorinating pyridine to give 2,3,6-trichloropyridine, and then chlorinating it in the presence of a ferric chloride catalyst.

As the catalyst, palladium, platinum, ruthenium,
Examples thereof include white metals such as rhodium, and Raney-based catalysts such as Raney nickel and Raney copper.

These catalysts may be supported on a carrier such as carbon or silica.

In addition, when the water content of the catalyst of the present invention is high, the hydrogenation further proceeds, and the tendency to change to monochloropyridine or pyridine increases. Therefore, the water content in the catalyst is preferably 10 wt% or less, more preferably 2-3 wt% or less.

The amount of catalyst is 0.01 to 20% by weight based on the metal, based on TRCP,
It is preferably 0.1 to 1% by weight.

Although it is not necessary to use a solvent to carry out the method of the present invention, hexane, hydrocarbons such as heptane, alcohols such as methanol, ethanol and isopropyl alcohol, formic acid, organic acids such as acetic acid, acetic acid. Esters such as ethyl may be used. The amount is sufficient to dissolve the pyridine chloride which undergoes hydrogenolysis, and is usually sufficient for the pyridine chloride which undergoes hydrogenolysis.
It is used 0.5 to 4 times by weight.

The reaction is promoted by adding a base such as sodium acetate, triethylamine, sodium carbonate.

The reaction temperature is at least the minimum temperature at which the reaction proceeds,
And, it is properly selected within a temperature range in which a certain degree of selectivity is maintained and which can be industrially easily carried out. It is usually carried out at 0 to 200 ° C, preferably at 30 to 150 ° C.

 The pressure can be either normal pressure or increased pressure.

The amount of hydrogen to be reacted and the reaction time may be appropriately selected depending on the shape, volume, structure of the reactor, the method of blowing hydrogen and the like.

As a post-treatment method after the reaction, the catalyst is removed by filtration or decantation (which is reused), the solvent is distilled off, the base substance is separated and removed by washing with water, and then purified by fractional distillation. The method is efficient.

〔The invention's effect〕

According to the method of the present invention, the reaction is carried out by a simple process,
Post-treatment can be carried out, and the target is extremely high.
2,3-dichloropyridine can be produced.

〔Example〕

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

Example 1 In a 500 ml four-necked flask equipped with a reflux tube, a hydrogen gas blowing tube, a thermometer and a stirrer, 2,3,6-trichloropyridine 86.7 g (0.48 mol), sodium acetate 39.4 g (0.48 mol), 2.0 g of a catalyst containing 5% by weight of palladium on carbon (water content of 1% or less) and 300.0 g of acetic acid were charged, and the mixture was heated to 50 ° C.
While maintaining 50 ℃, add 1 hydrogen gas from the gas blowing pipe.
Blow-off hydrocracking was continuously carried out at a rate of / H for 14 hours. The composition after the reaction is 2,3-dichloropyridine 33%, raw material 2,3,6-trichloropyridine 62%, other 5%
Met.

Claims (1)

(57) [Claims] 1. A process for producing 2,3-dichloropyridine, which comprises reacting 2,3,6-trichloropyridine with hydrogen in the presence of a catalyst.