DE2550716A1 - (2)-Alkyl piperidine prepn. from (2)-alkyl pyridines - by hydrogenation at low press. using supported ruthenium catalyst and no solvent - Google Patents

Abstract

2-Alkyl piperidines are prepd. by hydrogenation of 2-alkyl pyridines, at 50 (5-10) atmos. over-press. and 250 (160-180) degrees C. A supported Ru catalyst is used. Alkyl gp. may contain 1-5 (1-3) C. Quantitative conversions are achieved. No solvent is used. Highly pure 2-alkyl piperidines are obtd. Catalyst can be re-used, without loss in activity. In an example, 97% pure alpha-Me piperidine was prepd. by hydrogenating alpha-picoline at 10 atmos. over-press., 170 degrees C, using 5% Ru on C as catalyst.

Description

"Process for the preparation of 2-alkylpiperidines."

The invention relates to a process for the preparation of 2-alkylpiperidines by hydrogenation of 2-alkylpyridines.

It is known from French patent 1,315,260, a-picoline in the presence of ruthenium dioxide at pressures of 117 atm to convert to 2-methylpiperidine.

In the known hydrogenation processes with ruthenium catalysts high pressures had to be applied to make the reaction successful and at high levels To be able to perform yields.

The aim of the invention is a process for the hydrogenation of 2-alkylpyridines at lower pressures.

According to the method of the invention, this has been achieved in that the reaction at pressures up to 50 atü and temperatures below 2500C in the presence a catalyst made of ruthenium is carried out on a carrier.

In a preferred implementation form, the implementation is when pressing from 8 to 10 atü and temperatures from 1600 to 1800C.

The inventive reaction is carried out without a solvent, because at the reaction pressures used, low-boiling solvents, for example Ethanol, cannot be used. higher boiling solvents, for example n-Butanol-1 or n-pentanol-1 can form mixtures that are difficult to separate by distillation lead, for example in the conversion of a-picoline to a-methylpiperidine.

For example, water and a-picoline form azeotropes with a-methylpiperidine Mixtures. Therefore it makes sense to work according to a method that is quantitative Conversions of 2-alkylpyridines made possible.

The catalyst used in the process according to the invention contains 0.1 to 10% by weight of ruthenium or ruthenium oxide on a support. As a carrier you can Activated carbon, A1203 or other substances known per se can be used.

The reaction can be carried out in a known manner in an autoclave equipped with equipped with a stirrer, or carried out in a fixed bed reactor will.

For example, 99% strength 2-alkylpyridines can be used as starting products and after the practically quantitative implementation with hydrogen, the corresponding 2-alkylpiperidines by filtering off the catalyst in high purity be won.

The alkyl group of the 2-alkylpyridines can have 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms.

Examples of such compounds are a-picoline, 2-ethylpyridine and 2-isopropylpyridine or 2-propyl pyridine.

The catalyst can be reused without any loss of activity.

Example 1 200 g of a-picoline (99.2%) and 2.0 g of ruthenium catalyst (58 Ruthenium on activated carbon) were in an autoclave, dz with a stirrer and a Was equipped pressure measuring device, introduced. The one present in the reaction vessel Air is replaced with nitrogen and the autoclave with 99.98 in hydrogen up to applied to a pressure of 6 atü. The mixture was heated at a low stirring speed to 1600C and increased the stirring speed several times at this temperature. The reaction started immediately. Throughout the reaction that roughly Lasted 5 hours, the pressure and temperature were as accurate as possible at 10 atm and held at 1700C. After no more hydrogen consumption could be determined, the hydrogen was replaced by nitrogen and after opening the reactor the reaction mixture could be filtered. Gas chromatographic analysis of the product showed an α-methylpiperidine content of 97% with practically quantitative conversion. The catalyst was used for further approaches, after no decrease in activity could be determined after the fourth use.

Example 2 Instead of α-picoline, 200 g of 2-ethylpyridine (99.5%) weighed in. The reaction conditions were kept exactly the same as in the example 1 described.

After a reaction time of 5 hours, the conversion was practically quantitative and the reaction product had a content of 97.9% 2-ethylpiperidine.

Example 3 Instead of α-picoline, 200 g of 2-isopropylpyridine were used (99.0%) weighed out. The reaction conditions corresponded exactly to those of Example 1. After a reaction time of 170 minutes, the conversion was quantitative and the reaction product contained 97.4% 2-isopropylpiperidine.

Claims (2)

P a t e n II t ä n s p r ü c h e 1. Safekeeping for the production of α-alkylpiperidines by hydrogenation of α-alkylpyridines, characterized in that the reaction at pressures up to 50 atü and temperatures below 250 0C in the presence of a catalyst made of ruthenium is carried out on a carrier. 2. The method according to claim 1, characterized in that the reaction at pressures of 5 to 10 atmospheres and temperatures of 160 ° C to 180 ° C.