DE3544510A1 - METHOD FOR PRODUCING ALIPHATIC TERTIA AMINES - Google Patents

Description

The invention relates to a method for manufacturing tertiary amines by reacting primary or secondary Amines with formaldehyde and subsequent hydrogenation of the intermediate N-methylolamines in the presence of palladium catalysts at elevated pressure and elevated temperature.

Tertiary amines are used in many different ways. you are e.g. B. valuable intermediates in the synthesis of Pharmaceuticals, catalysts for the production of polyurethanes, Bactericides and color enhancing and delaying agents.

For the production of tertiary amines by catalytic Hydrogenation of the corresponding N-methylol compounds are known various processes. They are different essentially by the type of hydrogenation catalysts used and the reaction conditions to be observed. Nickel or cobalt catalysts are used in the implementation especially in the form of Raney metals or mixed catalysts made of nickel, cobalt and additions of manganese or Molybdenum use. They require temperatures of 40 up to 200 ° C and pressures from 0.35 to 20 MPa. A disadvantage of these catalysts is their high hydrogenation activity. they leads to the fact that the alkyl groups contained in the amine from  Nitrogen atom of the amine are split off. On this Pathways form secondary and primary amines as well as amines, which have a different composition due to transalkylation than desired.

Other processes use copper catalysts, e.g. B. copper chromite, a. These generally less active hydrogenation catalysts require the use of higher pressures and temperatures and thus an increased energy and apparatus expenditure.

Moreover, all of these catalysts often need to be larger Concentration can be applied, causing problems with the Separation of the reaction product and catalyst occur.

It is also known to use noble metal catalysts Hydrogenation of aromatically bound N-methylol groups and to use for the production of dimethyl amino acids (see Houben-Weyl, Methods of Organic Chemistry, Volume 11/1, Pages 641 and 642).

The task now was to create a process Providing tertiary amines that is technically simple is to be carried out, ensures high yields and a easy separation of reaction product and catalyst enables.

This object is achieved by a manufacturing process aliphatic tertiary amines by reaction of primary or secondary amines with formaldehyde and subsequent Catalytic hydrogenation of the resulting N-methylolamines  at elevated temperature and pressure. It is because of it characterized in that hydrogenation catalysts are used, which contain palladium.

The inventive method has the advantage that the Methylol compounds largely in the corresponding Methyl compounds are transferred without degradation to primary or secondary amines.

Primary or secondary, aliphatic or cycloaliphatic amines, furthermore aliphatic or cycloaliphatic diamines, hydroxyamines and etheramines used. The amines mentioned contain up to 20 carbon atoms and especially up to 12 carbon atoms. The secondary amino groups can also be part of a be hydrocyclic ring system, especially one those that have 5 to 7 ring links. Suitable amines are z. B. ethylamine, propylamine, butylamine, 2-ethylhexylamine, Cyclohexylamine, dibutylamine, 2-ethylhexylamine, Dimethylaminopropylamine, dicyclohexylamine, morpholine, Piperidine and piperazine.

It has proven useful to use formaldehyde as a concentrated aqueous Solution, e.g. B. as a 25 to 44% solution. Besides but it can also in its polymeric forms, eg. B. as Paraformaldehyde, find application.

Amines and formaldehyde are in a stoichiometric ratio implemented, d. H. per methyl group to be introduced 1 mol of formaldehyde applied. A formaldehyde excess from about 5 to 10% is advantageous.  

Amine and formaldehyde can first be reacted will. The reaction takes place without pressure at temperatures between 0 and 100 °, in particular 40 to 90 °. in a second stage the N-methylol compound obtained at temperatures from 50 to 200 °, in particular 80 to 150 ° and pressures of 0.1 to 10 MPa, preferred 1 to 5 MPa, hydrogenated.

According to a preferred one-stage embodiment of the The inventive method are amine and catalyst submitted and aqueous formaldehyde solution continuously fed.

According to a further preferred one-stage embodiment put amine, paraformaldehyde and catalyst and introduces hydrogen into the reaction mixture. In in both cases one works under hydrogenation conditions, i. H. at temperatures between 50 and 200 ° C, especially 80 up to 150 ° C and pressures from 0.1 to 10 MPa, in particular 1 to 5 MPa.

The methylation of amines using the new method takes place in the presence of palladium catalysts. The palladium can be used as a metal in finely divided form be used. However, it is particularly cheap Metal on a support, e.g. B. activated carbon. The supported catalysts advantageously contain 0.2 to 20% by weight, in particular 1 to 10% by weight, of palladium on the catalyst mass. In addition, you can also Activators are present. The production of the catalysts is done by impregnating the carrier with hydrochloric acid Palladium solution.  

The catalysts are very active. You can therefore in extremely low concentrations can be used. Based to primary or secondary amine as a starting material preferably 0.01 to 0.05% by weight of Pd is used as finely divided Metal or fixed on a support.

The low catalyst use has the advantage that for the separation from the reaction product is not complex Filtration is required. The catalyst can recover almost completely and can be discontinuous Batches can be recirculated more than 20 times without that a decrease in activity in the methylation reaction is recorded.

The tertiary amines are obtained from the reaction mixture by fractional distillation. Advantageously removed the water present in the reaction mixture azeotropic distillation or by dehydration with sodium hydroxide solution.

In the following examples, the invention Procedure explained in more detail.

example 1

2040 g (20 mol) of dimethylaminopropylamine are placed in a 10 l stirred autoclave and 10 g of a Pd / activated carbon Catalyst (Pd content: 5% by weight, corresponding to 0.025 % By weight, based on the amine used), and heated to 100 ° C with a hydrogen pressure of 2 MPa. Then over a period of 3 hours 3570 g of a solution of formaldehyde in water (37% by weight Formaldehyde, based on the solution, corresponding to 44 mol Formaldehyde) added. At the beginning of the addition, a  constant gas absorption (about 0.4 MPa / 15 minutes) observed, so that an ongoing addition of hydrogen 2.0 MPa becomes necessary. An hour after the completion of the Adding formaldehyde, the reactor is cooled, the reaction product removed and examined by gas chromatography. Dimethylaminopropylamine is fully implemented. After dewatering and distillation you get 2342 g of N, N, N ', N'-tetramethyl-1,3-diaminopropane, which corresponds a yield of 90.1% of theory.

Example 2

3600 g of dicyclohexylamine are placed in a 10 l stirred autoclave (20 mol), 960 g (32 mol) paraformaldehyde and 18 g des catalyst used in Example 1 (corresponding 0.025 wt .-% Pd, based on the amine used) submitted. The mixture is 8 hours at 130 ° C and 2.0 MPa pressure stirred, taking hydrogen to the extent of its consumption is added. After cooling, the product is gas chromatographed examined. The amine used can only can still be detected in traces. After distillation 3779 g of N-methyl-dicyclohexylamine are obtained, correspondingly a yield of 97.4% of theory.

Example 3

In a 10 l stirred autoclave, 1720 g of piperazine (20 mol) dissolved in 860 g of methanol. After adding 17.2 g of the catalyst used in the previous examples (corresponding to 0.05% by weight of Pd, based on Amine used) the solution is heated to 100 ° C and a hydrogen pressure of 2.0 MPa was set. over a period of 3 hours will then be continuous  2992 g 44 mol of a solution of formaldehyde in water (44% by weight of formaldehyde, based on the solution, accordingly 44 mol of formaldehyde), the hydrogen pressure is kept constant via a control valve. After cooling, dewatering and distillation, 2175 g 1,4-dimethylpiperazine, that is 95.4% of theory.

Claims (5)

1.) Process for the preparation of aliphatic tertiary amines by reacting primary or secondary amines with formaldehyde and subsequent catalytic hydrogenation of the resulting N-methylolamines at elevated temperature and pressure, characterized in that hydrogenation catalysts which consist of finely divided palladium or contain palladium are used. 2.) Method according to claim 1, characterized in that the hydrogenation at 50 to 200 ° C, especially 80 to 150 ° C and pressures from 0.1 to 10 MPa, in particular 1 to 5 MPa. 3.) Method according to claim 1 and 2, characterized in that the catalyst 0.2 to 20 wt .-%, in particular 1 to 10% by weight of palladium, based on the catalyst mass, contains. 4.) Method according to claim 1 to 3, characterized in that 0.01 to 0.05 wt .-% palladium, based on primary or secondary amine as finely divided metal or fixed on a carrier. 5.) Method according to claim 1 to 4, characterized in that submitted amine and catalyst and formaldehyde is added continuously as an aqueous solution.