Preparation of secondary amines from nitriles

Details Preparation of secondary amines from nitriles Preparation of secondary amines from nitriles

2001-12-27

2003-02-25

Davis, Brian (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C564S415000, C564S448000, C564S493000

Reexamination Certificate

active

06525223

ABSTRACT:

This application claims priority from GER. 10/00319-5 filed Jan. 5, 2001.
The present invention relates to a process for preparing secondary amines from nitriles over a rhodium catalyst.
Processes for preparing amines from nitriles over particular rhodium catalysts are known.
U.S. Pat. No. 3,117,162 relates to the hydrogenation of nitriles, in which coupling reactions are said to be minimized. Rhodium-containing catalysts can be used, and the hydrogenation is carried out at pressures in the range from 1 to 50 atmospheres. For example, 5% of rhodium on carbon is used as catalyst. In addition to primary amines, secondary amines are also obtained, cf. Table V. The reaction is carried out in an inert solvent.
U.S. Pat. No. 5,574,189 relates to the hydrogenation of nitriles for preparing amines. In particular, secondary amines are to be prepared. While mainly multimetal catalysts are described, a catalyst comprising 1% of Rh on Al
2
O
3
is also described for comparison, cf Table V. The reaction is carried out at 500 psi (34 bar). Primary, secondary and also tertiary aliphatic amines are obtained.
It is an object of the present invention to provide a process for preparing secondary amines in high yields and selectivities by selecting nitrites with hydrogen in the presence of catalysts.
In particular, symmetrical secondary amines are to be prepared.
We have found that this object is achieved by a process for preparing secondary amines of the formula (II)
(X—C
2
—)
2
NH  (II)
where
X is a C
1-20
-alkyl, C
2-20
-alkenyl or C
3-8
-cycloalkyl group which may be unsubstituted or substituted by C
1-20
-alkyl, C
3-8
-cycloalkyl, C
4-20
-alkylcycloalkyl, C
4-20
-cycloalkylalkyl, C
2-20
-alkoxyalkyl, C
6-14
-aryl, C
7-20
-alkylaryl, C
7-20
-aralkyl, C
1-20
-alkoxy, hydroxy, C
1-20
-hydroxyalkyl, amino, C
1-20
-alkylamino, C
2-20
-dialkylamino, C
2-12
-alkenylamino, C
3-8
-cycloalkylamino, arylamino, diarylamino, aryl-C
1-8
-alkylamino, halogen, mercapto, C
2-20
-alkenyloxy, C
3-8
-cycloalkoxy, aryloxy and/or C
2-8
-alkoxycarbonyl,
by reacting nitriles of the formula (III)
X—CN  (III)
with hydrogen at from 20 to 250° C. and pressures of from 60 to 350 bar in the presence of an Rh-containing catalyst comprising from 0.1 to 5% by weight, based on the total weight of the catalyst, of Rh on a support to give mixtures of primary amines of the formula (I)
X—CH
2
—NH
2
  (I)
and secondary amines of the formula (II)
(X—CH
2
—)
2
NH  (II)
and returning at least part of the primary amines separated from the mixtures obtained to the reaction.
The amount of primary amines returned to the reaction is preferably selected so that it corresponds essentially to the amount of primary amines present after the reaction. This is made possible by use of the catalyst employed according to the present invention.
The process of the present invention makes it possible to prepare secondary amines in high yields, in particular without formation of primary amines which have to be discharged from the process.
According to the present invention, it has been found that the use of a catalyst as defined above for the reaction of nitriles with hydrogen to form secondary amines can also lead to a longer operating life or long-term stability of the catalyst
The catalysts used according to the present invention contain from 0.1 to 5% by weight, preferably from 0.3 to 3% by weight, particularly preferably from 0.5 to 1% by weight, of rhodium, based on the total weight of the catalyst.
In addition, they can further comprise from 0.1 to 10% by weight, preferably from 0.1 to 5% by weight, particularly preferably from 0.2 to 1% by weight, based on the total weight of the catalyst, of at least one additional metal selected from among those of groups IB and VIII of the Periodic Table of the Elements, cerium and lanthanum. It is possible to use one additional metal or a mixture of a plurality of additional metals. In this case, preference is given to copper, platinum, palladium and mixtures thereof, particularly preferably platinum.
Rh is preferably the only active component present in the catalyst. The catalyst particularly preferably consists of Rh on the support.
As support, it is possible to use all known suitable supports. For example, the support may be selected from among activated carbon, silicon carbide and metal oxides. As metal oxides, preference is given to using zeolites, aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide or mixtures thereof, which may optionally be doped with alkali metal oxides and/or alkaline earth metal oxides. Particular preference is given to using &ggr;-aluminum oxide, silicon dioxide, zirconium dioxide or titanium oxide or mixtures thereof, in particular &ggr;-Al
2
O
3
and ZrO
2
. The supports can be used in any form, for example as extrudates, pellets or tablets.
Particular preference is given to a catalyst comprising from about 0.5 to 1.0% by weight of Rh, based on the total weight of the catalyst, on &ggr;-Al
2
O
3
or ZrO
2
as support.
The catalysts can be produced by generally known methods, for example by impregnating the support with solutions of compounds of the metals used.
The supports can, for example, be coated with metal precursors. Suitable metal precursors are metal salts such as nitrates, nitrosyl nitrates, halides, carbonates, carboxylates, acetylacetonates, chloro complexes, nitrito complexes and amine complexes of rhodium. Preference is given to nitrates, chlorides, chloro complexes and amine complexes, in particular nitrates. Application of the precursors is preferably carried out by impregnation. The precursors of the metals (if a plurality of metals is present) can be applied simultaneously or in succession. The order in which the active components are applied can be chosen freely.
Preference is given to impregnating the support material with a solution of a rhodium salt in a suitable solvent, preferably in water. In the impregnation of the support material with the rhodium-containing solution, the amount of solution used can be calculated so that it corresponds to from about 80 to 100% of the water uptake capacity of the support material. The concentration of rhodium in the solution is then chosen so that the desired loading of the support material with rhodium is achieved. The impregnated support material is dried at from 50 to 200° C., preferably from 100 to 140° C. Drying can be carried out with the support material in motion or static and for a period of from 0.5 to 10 hours, preferably from 4 to 6 hours. The calcination of the dried catalyst is carried out at from 300 to 800° C., preferably from 400 to 600° C., and can likewise be carried out with the catalyst in motion or static. The calcined catalyst has to be reduced before use in the synthesis, and this can be achieved by treatment with hydrogen at from 100 to 300° C., preferably from 180 to 220° C., at atmospheric pressure for a period of from 2 to 20 hours, preferably from 8 to 14 hours, after installation of the catalyst in the synthesis reactor.
Further methods of producing the catalysts used according to the present invention are known to those skilled in the art and include vapor deposition, sputtering and coprecipitation.
The surface area, the pore volume and the pore size distribution of the catalyst are not critical within wide ranges.
The process of the present invention is carried out batchwise or preferably continuously at from 20 to 250° C., preferably from 50 to 200° C., particularly preferably from 100 to 140° C., and pressures of from 60 to 350 bar, preferably from 70 to 200 bar, particularly preferably from 70 to 120 bar, in pressure apparatuses such as autoclaves or preferably in a tube reactor. The pressure is preferably the hydrogen pressure in the reactor. When using a tube reactor, the catalyst employed can also be present in a fixed bed.
The reaction is preferably carried out in the liquid phase in the upflow or downflow mode, particularly preferably in the upflow mode. In particular, preference is given to

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