Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-06-02
2002-01-01
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
Reexamination Certificate
active
06335470
ABSTRACT:
The invention relates to a process for preparing mixtures of substituted or unsubstituted cyclohexylamine and substituted or unsubstituted dicyclohexylamine in variable ratios by catalytic hydrogenation of substituted or unsubstituted aniline by means of hydrogen at elevated temperature and elevated pressure using catalysts comprising a support which may be doped with oxides, hydroxides and hydrated oxides of the rare earths (REs) and of manganese and to which Ru and Pd have been applied, the catalysts being characterized in that they contain no halogen or sulphur compounds. Substituted or unsubstituted cyclohexylamines and dicyclohexylamines are used for producing ageing inhibitors for rubbers and plastics, as corrosion inhibitors in aqueous solution and as intermediates for textile assistants and crop protection agents.
It is known that cyclohexylamine can be prepared by pressure hydrogenation of aniline. This hydrogenation is carried out using mainly noble metal catalysts, for example an Ru catalyst moderated with alkali metal as described in U.S. Pat. No. 3,636,108, where NH
3
and preferably a solvent are additionally used. A further process for the pressure hydrogenation of aniline to give cyclohexylamine is described in DE-B 1 106 319, in which an Ru catalyst is likewise used. In this process, dicyclo-hexylamine formed as coproduct is added to the starting, material again. However, owing to the simultaneous formation of cyclohexane, the process achieves only a moderate yield. According, to EP-A 53 818, supported Pd catalysts are better than Ru catalysts; the catalysts described there contain additives which either come from a group of basic compounds of the alkali metals, alkaline earth metals and rare earth metals or a group consisting of the metals Fe, Ni, Co, Mn, Zn, Cd and Ag. These catalysts allow the reduction of substituted anilines to give the corresponding cyclohexylamines; however, the corresponding dicyclohexylamines are completely absent. This applies similarly to Co catalysts containing a basic additive (GB 969 542) and to Raney Co (JP 68/03 180).
In the processes for the pressure hydrogenation of aniline which have been described, the dicyclohexylamine is formed only as by-product in addition to cyclohexylamine or not at all. In order to obtain dicyclohexylamine in larger amounts, it is prepared by separate processes. Thus, for example, it can be obtained by pressure hydrogenation of diphenylamine using an Ru/Al
2
O
3
catalyst (DE-B 1 106 319 above). Dicyclo-hexylamine is also formed in the reaction of cyclohexanone with cyclohexylamine in the presence of Pd on carbon under a hydrogen pressure of 4 bar (ER 1 530 477). In a cumbersome process, dicyclohexylamine can be isolated from the hydrogenation product of aniline over an Ni catalyst by fractional condensation. From the residual mixture, part of the ammonia also formed is removed and the remainder is returned to the reaction (DE-C 805 518).
EP-A 501 265 discloses a process for preparing substituted or unsubstituted cyclo-hexylamine and substituted or unsubstituted dicyclohexylamine by catalytic hydro-genation of substituted or unsubstituted aniline using a catalyst containing Ru, Pd or a mixture of both metals which have been applied to a support comprising niobic acid or tantalic acid or to a mixture of both. EP-A 503 347 discloses a further process for preparing substituted or unsubstituted cyclohexylamine and substituted or unsubstituted dicyclohexylamine by hydrogenation of an appropriately substituted aniline using a catalyst formed by first treating an &agr;- or &ggr;-Al
2
O
3
as support with at least one compound of rare earth metals and with at least one compound of manganese and then treating this with at least one Pd compound.
However, all catalysts and processes mentioned still have disadvantages in respect of conversion, selectivity, catalyst life, necessity of using NH
3
, etc.
The problems which still occur today despite the progress which has occurred are demonstrated by EP 560 127 filed in 1992: the Ru—Pd catalysts on alkaline supports used here can hydrogenate aromatic amines at low pressure, but only a small throughput of from 0.03 to 0.05 g/ml of catalyst and hour is possible, which requires large amounts of catalyst and large reactors; NH
3
has to be added in large amounts and the temperatures are held in the vicinity of 160° C. Nevertheless, hydrogenolysis still occurs at continuing incomplete conversion, recognizable by the formation of benzene and cyclohexane; the selectivity leaves something to be desired and the operating life of the catalysts is significantly less than, for example, that in EP 324 983. The commencement of deactivation of the catalyst is indicated by the slowly falling conversion.
It was therefore an object of the invention to provide catalysts for the industrial hydrogenation of aromatic amines to give cycloaliphatic amines, which catalysts, at a high space velocity over the catalyst, give complete conversion, have high selectivity in respect of the formation of primary and secondary cycloaliphatic amines, have a long life and, in particular, no longer trigger hydrogenolysis and methanization of the substrates.
It has been found that these requirements can be met when use is made of catalysts which contain Ru and Pd and are preferably applied to supports or to RE-Mn-doped supports and are strictly halogen-free and sulphur-free. The invention is surprising in that the influence of halogen and sulphur compounds on the catalytically active Ru in the abovementioned sense of undesired over-activation which causes hydrogenolysis and methanization was not known. The invention is also surprising since, obviously, even small residual amounts of halogen and sulphur compounds which remain in the catalyst after the preparation of such catalysts from starting materials containing halogen and sulphur compounds cause this undesirable property.
The invention provides a process for preparing mixtures of cyclohexylamines (II) and dicyclohexylamines (III) of the formulae:
in variable ratios by catalytic hydrogenation of aromatic amines of the formula (I):
where, in the formulae, R
1
and R
2
are independently hydrogen, C
1
-C
4
-alkyl or C
1
-C
4
-alkoxy,
at a reaction temperature of from 100 to 350° C. and a pressure of from 10 to 400 bar, which is characterized in that the catalysts used are fixed-bed catalysts which contain, as active constituents, a total of from 0.05 to 10% by weight of Ru and Pd in a ratio Ru:Pd=1:30-30:1 on supports and are free of halogen and sulphur compounds.
For the purposes of the invention, halogen-free means that the catalysts contain no halogen, i.e. no F, I, Br and particularly no Cl, and are therefore advantageously prepared from starting materials which do not contain halogen. For the purposes of the invention, free of sulphur compounds means that the catalysts contain no S and are therefore advantageously prepared from starting materials which are free of sulphur compounds. The sum of the halogen and sulphur contents of all starting materials for preparing the catalyst is therefore <0.8% by weight, preferably <0.3% by weight, particularly preferably <0.1% by weight, with inclusion of the complete absence of halogen and sulphur, based on their total amount. This means that the catalytically active positions, in particular the RE—Mn coating and the noble metals, are halide-free and free of sulphur compounds.
Starting compounds for preparing the catalysts used according to the invention are therefore halogen-free and sulphur-free compounds of Ru and Pd and, if they are present, of REs and Mn or low-halogen/low-sulphur compounds within the above-mentioned specification. Examples which may be mentioned are the nitrates, acetates, organic complexes with acetylacetone or amino acids.
Supports for the catalysts used according to the invention are aluminas, Al
2
O
3
in its various modifications (&agr;, &zgr;, &eegr;, &ggr;), preferably the &ggr; modification, also supports otherwise customary for noble metals, e.g. TiO
2
, kiesel
Darsow Gerhard
Langer Reinhard
Davis Brian J.
Gil Joseph C.
Henderson Richard E. L.
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