Preparation of secondary amines from primary amines

Details Preparation of secondary amines from primary amines Preparation of secondary amines from primary amines

2002-06-19

2004-04-20

Davis, Brian (Department: 1621)

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

Organic compounds

Amino nitrogen containing

C564S395000, C564S399000, C564S474000, C564S475000, C564S485000

Reexamination Certificate

active

06723880

ABSTRACT:

The present invention relates to a process for preparing secondary amines from primary amines over transition metal catalysts.
Processes for preparing secondary amines from primary amines are known per se. It is prior art to convert a primary amine having the desired substituents or structural elements into the desired secondary amine under hydrogen and under the reaction conditions chosen in each case. Various catalysts are used; the pressures and temperatures employed in the reaction vary widely. A frequent problem in this synthesis of the secondary amines is that the conversion or the selectivity to the desired product frequently do not achieve the desired values. It is often also necessary to use expensive noble metal catalysts.
DE-A 30 48 832 relates to a process for preparing amines, in particular bis(3-dimethylamino)propylamine (bis-DMAPA) from 3-dimethylaminopropionitrile (DMAPN) or 3-dimethylaminopropylamine (DMAPA) or mixtures of DMAPN and DMAPA. In an example, a bis-DMAPA selectivity of 80% is achieved at a DMAPA conversion of 53% at high pressure (173 bar) over Ni—Cu—Cr
2
O
3
, while a bis-DMAPA selectivity of 88% is achieved at a DMAPA conversion of 49% over Co—Cu—Cr
2
O
3
.
It is found here that, in particular, the conversions are much too low. In addition, for environmental reasons, the use of chromium-containing catalysts is no longer acceptable.
It is an object of the present invention to provide a process for preparing secondary amines from primary amines which can be carried out using chromium-free catalysts and gives the desired secondary amines in high yields and selectivities.
We have found that this object is achieved by a process for preparing a secondary amine of the formula
where
R
1
, R
2
may be identical or different and are each, independently of one another, a linear or branched alkyl radical having from 1 to 20 carbon atoms which may bear from 1 to 5 phenyl groups as substituents or a cyclohexyl radical or together with the N atom to which they are bound form a 3- to 7-membered saturated ring which may contain further heteroatoms selected from the group consisting of N, O and S and may be substituted by from 1 to 5 alkyl groups having 1 or 2 carbon atoms,
A is a linear or branched alkylene group having from 2 to 20 carbon atoms which may have from 1 to 5 phenylene groups in its chain, or a radical of the formula
 where R
3
=H or CH
3
, X=O or S or an NR
4
group in which R
4
is H or a linear or branched alkyl group having from 1 to 4 carbon atoms, k is 1 or 2 and m is an integer from 0 to 4, or a group of the formula
where n, o and p, q are each, independently of one another, integers from 1 to 4,
by reaction of primary amines of the formula
R
1
R
2
N—A—NH
2
  (II),
where R
1
, R
2
and A are as defined for formula (I), in the presence of hydrogen and a catalyst comprising at least one element or compound of an element of groups VIII and IB of the Periodic Table of the Elements. In one embodiment of the present invention, the catalyst composition can be free of a metal of group IB or a compound thereof. In a preferred embodiment, the catalyst contains up to 50% by weight of at least one element or compound of an element of group IB of the Periodic Table of the Elements.
The catalysts used in the process of the present invention thus comprise, in the active catalyst composition, up to 100% by weight of at least one element or at least one compound of an element of groups VIII and IB of the Periodic Table of the Elements, i.e. from the group consisting of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au. In one embodiment, the active catalyst composition can contain 0% by weight, in a preferred embodiment up to 50% by weight, or at least one element or at least one compound of an element of group IB of the Periodic Table of the Elements, i.e. from the group consisting of Cu, Ag and Au, preferably Cu. The amount of metal or compound of a metal of group IB is, in a more preferred embodiment, from 1 to 30% by weight, in particular from 10 to 25% by weight, based on the total amount of active catalyst composition. In a further preferred embodiment, the active catalyst composition comprises at least one element or at least one compound of an element from the group consisting of Ni, Co, Cu, Ru, Rh, Ir, Pd, Pt, in the ratios indicated above for the general and preferred embodiments.
If compounds of the specified metals are used for preparing the catalyst, it is possible to use, for example, the oxides, nitrates, carbonates, chlorides and acetates.
In the most preferred embodiment of the present invention, the oxides of the elements employed are used for preparing the catalyst. These are then reduced before use in the reaction, preferably by treatment with hydrogen. This gives a catalyst in which the metal components employed are present in elemental, finely-divided form.
The catalysts can be used as all-active catalysts or in supported form. When using supported catalysts, the proportion of support is from 10 to 90% by weight, based on the total mass of the catalyst (active composition plus support).
As supports, it is possible to use all known suitable supports, for example, activated carbon, silicon carbide or metal oxides. The use of metal oxides is preferred. Among metal oxides, preference is given to using aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide or mixtures thereof, which may, if appropriate, be doped with alkali metal oxides and/or alkaline earth metal oxides. Particular preference is given to &ggr;-aluminum oxide, silicon dioxide, zirconium dioxide or titanium dioxide or mixtures thereof, in particular Al
2
O
3
. The supports can be used in any form, for example as extrudates (rod form), pellets, tablets, monoliths, woven meshes, knitteds or in powder form. The supported catalysts can be prepared by generally known methods. These include, for instance, impregnation of a support with solutions of compounds of the metal components used. Suitable solvents include all customary solvents, for instance water, methanol, ethanol or acetone; preference is given to using water. Furthermore, the catalyst can be prepared by coprecipitation or sequential precipitation of the catalyst components, followed by filtration and washing of the filter cake. The impregnation or precipitation is followed by a drying step (50-200° C.) and a calcination step (200-500° C.). The catalysts are then reduced at final temperatures of from 200 to 400° C. and can subsequently be passivated, since the reduced metals are pyrophoric. After installation of the catalysts in the synthesis reactor, the catalysts can be reactivated by reduction with hydrogen at from 100 to 300° C. before the reaction is started.
According to the present invention, preference is given to the use as starting materials of primary amines of the formula (I) and the synthesis of secondary amines of the formula (II) in which the substituents R
1
, R
2
and A have the following meanings:
A is a linear or branched methylene chain having from 2 to 10 carbon atoms or a group of the formula
—CH
2
—CH
2
—O—(CH
2
—CH
2
—O)
n
—CH
2
—CH
2
—,
 where n is an integer from 0 to 2,
R
1
, R
2
are identical or different and are each, independently of one another, an alkyl radical having from 1 to 12 carbon atoms or together with the nitrogen atom to which they are bound form a 5- or 6-membered saturated ring which may contain a further heteroatom selected from the group consisting of O and N.
Particular preference is given to amines of the formulae (I) and (II) in which
A is an alkylene group having from 1 to 6 carbon atoms or a group of the formula
—CH
2
—CH
2
—O—CH
2
—CH
2
—
and
R
1
and R
2
may be identical or different and are each, independently of one another, a linear or branched alkyl radical having from 1 to 4 carbon atoms or together with the nitrogen atom to which they are bound form a piperidine ring or a morpholine ring.
In particular, 3-dimethylaminopropylamine (DMAPA) is used to produce bis-3-dimethylaminopropyl

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