Method for hydrogenating unsaturated heterocyclic compounds

Details Method for hydrogenating unsaturated heterocyclic compounds Method for hydrogenating unsaturated heterocyclic compounds

2001-01-17

2003-06-24

Chang, Ceila (Department: 1625)

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06583286

ABSTRACT:

The present invention relates to a process for hydrogenating unsaturated heterocyclic compounds by contacting one or more unsaturated heterocylic compounds, especially pyridine or its derivatives, with a hydrogen-containing gas in the presence of a macroporous catalyst.
DE-A 16 20 664 relates to a process for preparing piperidine and its alkyl homologs by catalytic hydrogenation of pyridine and its alkyl homologs at temperatures from 100 to 200° C. and pressures of up to 200 bar in the presence of nickel catalysts comprising at least 30% by weight of nickel on active Al
2
O
3
or chromium oxide.
JP 52 148 083 describes the preparation of piperidine from pyridine at from 100 to 200° C. in the presence of hydrogenation catalysts comprising ruthenium. The catalysts described therein are pretreated with sulfur compounds, such as mercaptans, thiophenes and sulfolanes, for example, prior to hydrogenation. This pretreatment with sulfur compounds, however, is comparatively laborious and impacts negatively on the hydrogenation activity of the catalysts used.
Pyridine can also be hydrogenated to piperidine over a supported ruthenium catalyst whose support comprises carbon or &ggr;-Al
2
O
3
with approximately 5% of ruthenium at from 80 to 130° C. and from 20 to 120 bar, as is described in SU 255 940. According to the process described therein, however, high metal loadings of 5% by weight or more are required to achieve high hydrogenation activities.
According to U.S. Pat. No. 1,315,260, pyridines and their acid addition salts are converted to the corresponding piperidines and their salts in the presence of from 0.05 to 2% by weight of ruthenium, which can be present as the finely divided metal on a support or as the dioxide, at from 60 to 90 bar and from 70 to 100° C., preferably in an inert solvent. A disadvantage of this process is that an inert solvent must be used in order to obtain high selectivities.
Similarly, 2-alkylpiperidines can be prepared without using a solvent by employing a catalyst comprising from 0.1 to 10% by weight of ruthenium or RuO
2
on Al
2
O
3
or activated carbon, as is described in DE-A 25 50 716. According to this document, the hydrogenation is conducted at pressures <50 bar and at a temperature of from 160 to 180° C. The selectivity of this process, however, is inadequate. A further disadvantage is that the use of this process is limited to alkyl-substituted pyridines; under the conditions indicated therein and using the catalyst described therein it is not possible to hydrogenate pyridine to piperidine.
It is an object of the present invention to provide an improved process for selectively hydrogenating unsaturated heterocyclic compounds, especially pyridine and/or its homologs, to piperidine and/or its homologs, achieving very high yields and virtually complete conversion.
It is also an object of the present invention to provide such a process in which only a minimal fraction of byproducts and decomposition products is obtained during the hydrogenation. In addition, it should be possible to conduct the process of the invention with an extremely high turnover number under conditions of high space velocities and long service lives for the catalyst, with the corresponding hydrogenation products being obtained in high yield and high purity.
We have found that these objects, and others, are achieved by the process provided by this specification.
The present invention accordingly provides a process for hydrogenating an unsaturated heterocyclic compound or a mixture of two or more thereof by contacting the unsaturated heterocyclic compound or the mixture of two or more thereof with a hydrogen-containing gas in the presence of a catalyst whose active metal comprises at least one metal from transition group VIII of the Periodic Table, applied to a support, wherein said support has macropores.
In one preferred embodiment the present invention provides a process as defined above wherein the catalyst comprises as active metal at least one metal from transition group VIII of the Periodic Table alone or together with at least one metal from transition group I or VII if the Periodic Table, applied to a support, said support having an average pore diameter of at least 50 nm and a BET surface area of not more than 30 m
2
/g and the amount of said active metal being from 0.01 to 30% by weight based on the overall weight of the catalyst (catalyst 1).
The invention also provides such a process wherein the catalyst comprises as active metal at least one metal from transition group VIII of the Periodic Table alone or together with at least one metal from transition group I or VII of the Periodic Table in an amount of from 0.01 to 30% by weight, based on the overall weight of the catalyst, applied to a support, from 10 to 50% of the pore volume of the support being formed by macropores having a pore diameter in the range from 50 nm to 10,000 nm and from 50 to 90% of the pore volume of the support being formed by mesopores having a pore diameter in the range from 2 to 50 nm, the sum of the pore volumes adding to 100% (catalyst 2).
In a further preferred embodiment the present invention provides a process as defined above wherein the catalyst (catalyst 3) comprises as active metal at least one metal from transition group VIII of the Periodic Table alone or together with at least one metal from transition group I or VII of the Periodic Table in an amount of from 0.01 to 30% by weight, based on the overall weight of the catalyst, applied to a support, said-support having an average pore diameter of at least 0.1 &mgr;m and a BET surface area of not more than 15 m
2
/g.
As active metals it is preferred to employ platinum, rhodium, palladium, cobalt, nickel or ruthenium or a mixture of two or more thereof, ruthenium in particular being used as active metal. Among the metals which can likewise be used from transition group I or VII, or else from transition groups I and VII, of the Periodic Table, all of which can likewise be used in principle, preference is given to employing copper and/or rhenium.
The terms “macropores” and “mesopores” are used in the context of the present invention as they are defined in Pure Appl. Chem., 45 (1976) 79, namely as pores whose diameter is above 50 nm (macropores) or whose diameter is between 2 nm and 50 nm (mesopores).
The active metal content is generally from approximately 0.01 to approximately 30% by weight, preferably from approximately 0.01 to approximately 5% by weight, and in particular, from approximately 0.1 to approximately 5% by weight, based in each case on the overall weight of the catalyst used. For catalysts 1 to 3 employed with preference, which are described below, the active metal contents used with preference are stated again individually in the context of the discussion of these catalysts.
The term “heterocyclic unsaturated compound” used according to the invention embraces all cyclic compounds having at least one heteroatom, i.e., all compounds having at least one nitrogen, phosphorus, oxygen or sulfur atom, which are also unsaturated. In this context the term “unsaturated” embraces both cyclic compounds having isolated or conjugated double bonds and aromatic compounds. Owing to the selective hydrogenation capacity of the catalysts used herein, the compounds to be hydrogenated may also carry functional groups which can in principle be hydrogenated or reduced, respectively, such as —CHO, —CH
2
OH, —COOH, —COOR (R=alkyl), —CH
2
COOH, —CH
2
COOR (R=alkyl), etc. It is of course also possible to hydrogenate compounds of the above type which are substituted by nonreducible groups, such as alkylpyridines, for example.
The compounds employed in each case are then reacted selectively to form the corresponding ring-hydrogenated compounds.
Particular mention may be made of the following compounds and classes of compounds: pyridines, pyrans, thiopyrans, picolines, pyrroles, furans, thiophenes, indoles, pyrazoles, imidazoles, azepines, thiazoles and pyrazines.
The following reactions in particular are conducted with the presen

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