JPH0791270B2 - Method for producing 2,3,5-trichloropyridine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing 2,3,5-trichloropyridine, which is useful as an agricultural / pharmaceutical intermediate.

(Prior Art) Several methods for producing 2,3,5-trichloropyridine are known. However, there are few cases where the yield is good and the process is efficient, and there are many cases where industrialization is actually considered difficult. As a relatively efficient example, 2-pyridone or 2-aminopyridine is chlorinated at the 3-position and 5-position, and then 2
There is a method of chlorinating the hydroxyl group (carbonyl group) at the position and the amino group. (British Patent 1,215,387, JP-A-53-68783, JP-A-54-59283, US Pat. No. 4,287,347) Also, there is a method of reducing the α-position of 2,3,5,6-tetrachloropyridine. As a reducing agent, zinc (J. Hetero-cycl Chem 17 .493. US Patent
4259495, 4258194, 4111938), electrolytic method (Eur.Pat.1806
9), lithium aluminum hydride (JCSD (20) 121
1) etc. are used.

(Problems to be Solved by the Invention) The above-mentioned chlorination method for 2-pyridone and 2-aminopyridine is disadvantageous in cost because the raw materials are expensive and the reaction process is long. Although 2,3,5,6-tetrachloropyridine is relatively inexpensively available, the reduction methods known so far require the use of a large amount of solvent and the so-called space-time yield is poor. Also, when using zinc as a reducing agent, an equivalent amount is required, and because the toxicity of zinc salts produced in large amounts pollutes rivers by wastewater, it is necessary to recover zinc when industrially implemented. Become.

(Means for Solving the Problem) The inventors have used 2,3,5,6-tetrachloropyridine to
The present invention has been achieved as a result of extensive studies on a method for producing 2,3,5-trichloropyridine that is highly efficient and does not cause pollution problems such as drainage. That is, the method is characterized in that 2,3,5,6-tetrachloropyridine is contacted with hydrogen in the presence of a white metal such as palladium or platinum, or a catalyst such as Raney nickel. There is no conventional example for the hydrogen catalytic reduction method of 2,3,5,6-tetrachloropyridine, and the present invention is the first example.

As the catalyst, as mentioned above, palladium, platinum,
A white metal such as ruthenium or rhodium, or a Raney catalyst such as Raney nickel or Raney copper is used.

As the solvent, hydrocarbons such as hexane and heptane, alcohols such as methanol, ethanol and isopropyl alcohol, organic acids such as formic acid and acetic acid, and esters such as ethyl acetate can be used. The amount is
The amount is sufficient to dissolve 2,3,5,6-tetrachloropyridine, and it is usually used in an amount of 0.5 to 3 times by weight that of 2,3,5,6-tetrachloropyridine. The reaction is further promoted by the addition of a base such as sodium acetate, triethylamine or sodium carbonate. The reaction temperature is generally at least the minimum temperature at which the reaction proceeds, and is a temperature range that maintains a certain degree of selectivity and can be easily carried out industrially, and is usually 0 ° C. to 150 ° C. Pressure is normal pressure,
It can be carried out under either pressure. In a long reaction,
Since the target 2,3,5-trichloropyridine may be further reduced, the progress should be checked by GC chromatography or the like to stop the reaction at the most economical composition. Usually, 2,6-dichloropyridine, 2,3,6-trichloropyridine, etc. are by-produced slightly, but these can be separated from the target 2,3,5-trichloropyridine by distillation, and chlorine is further applied. Therefore, the starting material is 2,3,5,
It can be recovered as 6-tetrachloropyridine.

As a post-treatment method after the reaction, the catalyst is removed by filtration or decantation (which can be reused), the solvent is distilled off, and the basic substance is removed by washing with water, followed by fractional distillation or re-dosing. The method of purifying by crystals is efficient.

(Effects of the Invention) According to the method of the present invention, the reaction using the inexpensive raw material 2,3,5,6-tetrachloropyridine, the post-treatment is simple, and the by-product can be recovered as the raw material. 2,3,5-trichloropyridine can be made by an efficient process that can be done. In addition, there is no problem of pollution such as drainage as in the case of using zinc.

EXAMPLES Next, the present invention will be described in more detail based on examples. The reaction was carried out using a 300 ml SUS autoclave, containing 2,3,5,6-tetrachloropyridine (purity 96.8%, other impurities including 2,3,6-trichloropyridine 1.5%, pentachloropyridine 1.7%). 26.2g (1.2mol), solvent is 3 times the weight of tetrachloropyridine, 5% wet as catalyst
1.3 g of Pd / C (water content 50%) was charged. The addition amount of each base was equimolar to tetrachloropyridine. The hydrogen pressure was room temperature, the initial pressure was 15 kg / cm ² , the temperature was raised to 50 ° C., and the reaction was continued until the pressure became 0 or the pressure drop stopped. The results are summarized in the table below.

Claims (1)

[Claims] 1. A method comprising reacting 2,3,5,6-tetrachloropyridine with hydrogen in the presence of a catalyst.
-Method for producing trichloropyridine