JPH01193246A - Production of 2,3-dichloropyridine - Google Patents

Abstract

PURPOSE:To obtain the above compound useful as an intermediate for pharmaceuticals, in high selectivity at a low cost with a simple process, by using 2,3,6-trichloropyridine as a raw material and reacting the material with hydrogen in the presence of a catalyst. CONSTITUTION:The objective compound can be produced by reacting 2,3,6- trichloropyridine with hydrogen in the presence of a catalyst at 0-200 deg.C, preferably 30-150 deg.C. The catalyst is a palladium-group metal such as palladium, platinum, ruthenium, etc., or a Raney catalyst such as Raney-nickel, Raney- copper, etc., and its amount is 0.01-20wt.%, preferably 0.1-1wt.% based on the 2,3,6-trichloropyridine used as a raw material. The water-content of the catalyst is preferably <=10wt.%, especially 2-3wt.% or less. The reaction can be accelerated by the addition of a base such as sodium acetate, triethylamine, sodium carbonate, etc.

Description

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

[Conventional technology]

2.3-dichloropyridine (hereinafter referred to as 2.3-DCP) can be produced by liquid phase chlorination of pyridine or pyridine hydrochloride (Japanese Unexamined Patent Publication No. 61-249965).
(No.) and a method of producing by gas phase chlorination of pyridine (Japanese Patent Application Laid-open No. 206564/1983). In addition, a method for producing by chlorination of palladium chloride complex of pyridine (S
Synthesis, 5, 378 (1980)).

[Problem to be solved by the invention]

However, the method using palladium chloride in the above method has a good yield, but has a practical problem because an equivalent amount of expensive palladium chloride is used relative to the substrate. In other methods, the target product 2,,3-DCP is obtained as a mixture with polychlorinated pyridine, and the reaction yield is also very low at 10 to 15%. For this reason, operations such as distillation have to be used for further purification of the target product, which becomes complicated and further decreases in yield are unavoidable.

[Means to solve the problem]

The present inventor has discovered that 2,3,6-)dichloropyridine (hereinafter T
As a result of intensive investigation into a method for producing 2.3-DCP with good yield using RCP, we discovered that 2,3-dichloropyridine can be selectively obtained by reacting with hydrogen in the presence of a catalyst. This led to the invention.

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

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

Examples of the catalyst include platinum metals such as palladium, platinum, ruthenium, and rhodium, and Raney catalysts such as Raney nickel and Raney copper.

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

Furthermore, if the water content of the catalyst of the present invention is high, there is a high tendency for hydrogenation to proceed further and change to monochloropyridine or pyridine. Therefore, the water content in the catalyst is 19wt%
The content is preferably 2 to 3 wt% or less.

The amount of catalyst is 0.01 to 20% of TRCP on a metal basis.
% by weight, preferably from 0.1 to 1% by weight, is suitable.

Although the use of solvents is not necessary in carrying out the process of the invention, hydrocarbons such as hexane, heptane, alcohols such as methanol, ethanol, nopeisopropyl alcohol, formic acid, acetic acid, etc. Organic acids, esters such as ethyl acetate, etc. may also be used. The amount thereof may be sufficient to dissolve the pyridine chloride to be hydrogenolyzed, and is usually used in an amount of 0.5 to 4 times the weight of the pyridine chloride to be hydrogenolyzed.

Note that the reaction is accelerated by the addition of a base such as sodium acetate, triethylamine, or sodium carbonate.

The reaction temperature is appropriately selected within a temperature range that is higher than the minimum temperature at which the reaction substantially proceeds, and that maintains a certain degree of selectivity and can be easily carried out industrially. It is usually carried out at a temperature of 0 to 200°C, preferably 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, hydrogen blowing method, etc. of the reactor.

After the reaction, the post-treatment method is to remove the catalyst by filtration or decantation (this will be reused), distill off the solvent, separate and remove the base by washing with water, and then purify by fractional distillation. The method is efficient.

〔Effect of the invention〕

According to the method of the present invention, the reaction and post-treatment can be carried out through a simple process, and the desired 2
, 3-dichloropyridine can be produced.

〔Example〕

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

Example 1 86.7 g (0.48 mol) of 2.3.6-dolichloropyridine and 39.4 g of sodium acetate ( 0.48 mol), 2.0 g of a catalyst containing 5% by weight of palladium on carbon (less than 1% moisture).

and 300.0 g of acetic acid were charged and heated to 50°C.

Inject 1 liter of hydrogen gas from the gas blowing pipe while maintaining the temperature at 50°C.
Hydrogenolysis was carried out by blowing continuously for 14 hours at a rate of 1/H. The composition after the reaction is 2,3-dichloropyridine 3
3%, raw material 2,3.6-)dichloropyridine 62
%, and others 5%.

Claims (1)

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