Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-05-22
2001-04-03
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S301000
Reexamination Certificate
active
06211410
ABSTRACT:
Various processes have been described for preparing organic hydroxylamines, e.g. the electrochemical reduction of nitro compounds or the reduction of nitro compounds using metals such as zinc or amalgams. On an industrial scale, it is particularly the selective catalytic hydrogenation of organic nitro compounds which is utilized.
In the case of nitroaromatics, it is known that the catalytic hydrogenation proceeds via a number of stages. It is frequently not possible to isolate the nitrosoaromatics and arylhydroxylamines which occur as intermediates, since further reduction to the stable aniline derivative occurs.
In addition, selective preparation of arylhydroxylamines is made more difficult by secondary reactions. Thus, arylhydroxylamines disproportionate to form the corresponding nitrosoaromatics and aniline derivatives. These intermediates can undergo further reactions which lead to dimeric compounds such as azoxybenzenes, azobenzenes and hydrazobenzenes.
Suitable additives allow disproportionation and over-reduction to be suppressed in the hydrogenation of nitroaromatics, so that a selective preparation becomes possible.
DE-A-2118369 (corresponds to U.S. Pat. No. 3,694,509; inventors: P. N. Rylander et al.) describes a method for the selective preparation of arylhydroxylamines, in which nitroaromatics are hydrogenated by means of hydrogen in a neutral solvent in the presence of from 0.1 to 100 mol of dimethyl sulfoxide per mole of catalyst. The selectivity of the hydrogenation under these conditions is about 85%, so that the arylhydroxylamines obtained are still contaminated with large amounts of the corresponding aniline derivatives and the total yields of the arylhydroxylamines are low.
In EP-A-212375 (inventor: G. C. Davis), phosphines, phosphates, sulfides, sulfoxides and heterocyclic nitrogen compounds in the presence of up to 0.4 equivalents of a protic acid per mole of the nitro-aromatic compound are used as additives. In the case of the hydrogenation of ethyl p-nitrobenzoate, selectivities of up to 99% can be achieved. Further nitro compounds are not described. However, the addition of acids required in this method has an adverse effect on the preparation of acid-sensitive arylhydroxylamines.
EP-A-86363 (inventors: D. C. Caskey, D. W. Chapman) describes the use of divalent sulfur compounds in combination with ammonia, aliphatic amines, phosphine, aliphatic phosphines, arylphosphines and phosphite esters as reaction moderators for the selective hydrogenation of nitroaromatics to arylhydroxylamines. The achievable selectivities are in the range 89-92%. The inactivation or poisoning of the catalysts, in particular by means of sulfur-containing additives, leads to the catalysts usually losing a large part of their activity after only one cycle and having to be replaced or regenerated at considerable cost.
JP 54-24837 (inventor: T. Tsurutani) (C.A. 91,56604) discloses a process in which arylhydroxylamines are obtained by catalytic hydrogenation of unsubstituted or substituted nitrobenzenes in alcohols or ethers in which phosphorous acid, alkali metal salts of phosphorous acid, phosphorous esters, thiophosphorous esters, alkylphosphines or arylphosphines, alkyl or aryl aminophosphines, alkyl or aryl sulfides, carboalkoxyalkyl sulfides, alkyl or aryl mercaptans or thiophenes are present. In this process, the hydrogenation has to be stopped after consumption of two equivalents of hydrogen, based on the nitro compound, in order to avoid over-reduction to the corresponding anilines. The achievable selectivity is 67-98%.
A selective hydrogenation of nitrobenzenes using platinum or palladium catalysts in the presence of organic bases whose pK is less than 3.2 is described in DE-A-2327412 (corresponds to CA-A-1001658; inventor: J. le Ludec) and DE-A-2357370 (corresponds to GB-A-1428226; inventor: J. le Ludec). The organic base has to be used in excess relative to the nitro compound. In the case of the preferred bases piperidine and diethylamine, only modest yields of simply structured arylhydroxylamines can be achieved after work-up and purification: N-phenylhydroxylamine was able to be isolated in a yield of only 52% after hydrogenation of nitrobenzene in diethylamine as solvent (DE-A-2327412).
Further organic bases described for this type of catalytic hydrogenation of nitroaromatics are N-alkylated piperidines which may also be alkylated on the carbon atoms of the ring, pyrrolidines alkylated on the nitrogen atom and/or the carbon atoms of the ring, N-alkylated or N-cycloalkylated anilines which may also be alkylated on the carbon atoms of the ring and pyridine, alkylated pyridines, quinoline and isoquinoline (DE-A-2455238, corresponds to U.S. Pat. No. 3,927,101; inventor: J. le Ludec) and also, for the selective hydrogenation of chloronitro-aromatics, secondary and tertiary monoamines which bear alkyl or cycloalkyl groups (DE-A-2455887, corresponds to U.S. Pat. No. 3,992,395; inventor: J. le Ludec). Using pyridine as solvent, N-phenylhydroxylamine was able to be isolated in a yield of 83% (DE-A-2455238).
DE-A-19502700 (corresponds to ZA-A-9600610; inventors: N. Götz et al.) describes a method of selectively hydrogenating nitroaromatics using platinum catalysts or sulfur- or selenium-doped palladium catalysts, in which nitroaromatics are hydrogenated in the presence of an excess of N-substituted morpholines as reaction moderators. The selectivities described are up to 98%. A disadvantage of this process is the high price of the bases which are used in excess. Owing to the high boiling point of N-alkylated morpholines, removal of these bases requires a relatively high temperature.
Nitroaromatics and nitroaliphatics are reduced in inert solvents to the corresponding arylhydroxylamines or alkylhydroxylamines in the presence of less than 10% by weight of organic base (based on the mass of the nitro derivative) and with addition of trivalent or pentavalent organic phosphorus compounds (EP-A-0147879; inventors: A. H. Sharma, P. Hope). Good yields of arylhydroxylamines are obtained, in particular, when using the costly DMAP (N,N-dimethylaminopyridine) instead of pyridine (yield of N-phenylhydroxylamine is 88% when using DMAP, 76% when using pyridine). Here too, a disadvantage is again that high selectivities are achieved only when using costly bases which have high boiling points and are therefore difficult to separate off. When using organic bases in amounts of less than 10% by weight based on the nitroaromatics, large amounts of trivalent phosphorus compounds (0.1-5% by weight) are required for a selective reaction. This results in rapid deactivation of the catalyst.
U.S. Pat. No. 3,441,610 (inventors: J. W. Dietz, J. R. McWorther) describes the catalytic hydrogenation of nitroalkanes to give N-alkylhydroxylamines. Here, the hydrogenation is carried out using a palladium catalyst with addition of iron, cobalt or nickel cations in a liquid two-phase system comprising aqueous sulfuric acid and an immiscible organic solvent. Under such strongly acidic conditions, the loss of catalyst is considerable. In addition, such mixtures have a strongly corrosive action on the apparatuses used.
EP-A-0321219 (inventors: M. B. Sherwin, P. Pichaichanarong) describes a process for preparing aqueous solutions of alkylhydroxylamines which are stable on storage under anaerobic conditions by reduction of nitroaliphatics having 1-18 carbon atoms with addition of complexing agents such as EDTA. The storage stability of such solutions is achieved by reducing the concentration of transition metal ions present to less than 20 ppm.
It is an object of the invention to provide a process for preparing organic hydroxylamines which avoids the disadvantages mentioned in the discussion of the prior art, can be carried out simply and inexpensively in industry, gives high selectivities and yields and makes it possible to isolate the organic hydroxylamines under gentle conditions.
This object is achieved by a process in which at least one organic nitro compound is partially hydrogenated in the presence of an organic
Freudenreich Johannes
Stohrer Jurgen
Barts Samuel
Collard & Roe P.C.
Consortium fur Elektrochemische Industrie GmbH
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