Process for the production of aromatic halogen-amino compounds

Details Process for the production of aromatic halogen-amino compounds Process for the production of aromatic halogen-amino compounds

1998-11-04

2001-03-06

Barts, Samuel (Department: 1621)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Organic compound containing

C502S166000, C502S209000, C556S022000, C556S136000

Reexamination Certificate

active

06197716

ABSTRACT:

The present invention relates to a hydrogenation process for the production of aromatic halogen-amino compounds. Production is effected by means of catalytic hydrogenation of the corresponding aromatic halonitro compounds in the presence of a modified noble metal catalyst and a vanadium compound. The invention also relates to catalyst systems consisting of a modified noble metal catalyst and a vanadium compound, as well as the use thereof in the hydrogenation of aromatic halonitro compounds.
It is known that aromatic nitro compounds may be reduced to aromatic amines in very good yields in the presence of noble metal catalysts and hydrogen. When further hydrogenatable groups are present simultaneously, for example halogen substituents (halonitro aromatic substances), special measures are necessary to prevent the formation of undesired by-products, which otherwise can often only be separated from the desired product at great expense or, in particularly unfavourable cases, not at all. What is particularly difficult is selective reduction, if several hydrogenatable groups are present in a compound.
Catalytic hydrogenation of aromatic nitro compounds to the corresponding aromatic amines takes place via several intermediate steps. The corresponding nitroso compounds, and in particular the hydroxylamine intermediate step, are important. In practice, the formation of hydroxylamines is a special problem, since it can accumulate in large quantities in the reaction solution under certain conditions. This applies in particular to aromatic nitro compounds, the hydrogenation of which yields relatively stable arylhydroxylamines. This is especially critical if hydrogenation is carried out in a slurry-batch reactor. In extreme cases, several tons of arylhydroxylamine may be formed in the interim.
In U.S. Pat. No. 4,020,107, phosphorous acid, hypophosphorous acid or derivatives thereof are proposed as an additive in the hydrogenation of nitro-aromatic substances, which are substituted by halogen on the aromatic substance, using Pt or Pd on activated carbon and hydrogen. These systems are selective towards the halogen substituents present in the molecule. However, they have too little reactivity, which in many cases leads to the formation of considerable quantities of undesired arylhydroxylamines [J. R. Kosak, in Catalysis of Organic Reactions, Vol 18, (1988), 135-147); idem, in Catalysis in Organic Synthesis, 1980, 107-117].
The accumulation of arylhydroxylamines is undesired for the following reasons. On the one hand, it is known that such compounds are thermally unstable, and upon heating with or without H
2
may disproportionate whilst giving off heat. Further decomposition reactions may be initiated by the heat being released, and these then may consequently give rise to occurrences of severe explosions. W. R. Tong et al, AICHE Loss Prev. 1977, (11), 71-75 describe such an occurrence during the reduction of 3,4-dichloronitrobenzene to 3,4-dichloroaniline.
In addition, arylhydroxylamines are known as strong carcinogens and represent a certain potential danger. Larger quantities formed have to be disposed of at great expense.
A third range of problems is the production of the desired pure aromatic amine. If, during hydrogenation or at the end of the reaction, significant quantities of arylhydroxylamine are present, this may lead to condensation, thus forming undesired, dyed azo or azoxy products or higher molecular weight, deeply dyed condensation products. Since the quantity of arylhydroxylamine may change from batch to batch, the product quality obtained varies in purity and appearance. Thus, complicated purifying operations are necessary, with corresponding losses in yield and problems relating to disposal of the residue.
The above-mentioned problems are intensified in such a way that the concentrations occurring or even the maximum possible concentrations of this hydroxylamine intermediate step cannot be predicted even in the case of known processes which have been studied thoroughly. The presence of traces of impurities may unpredictably initiate the spontaneous accumulation of hydroxylamine intermediate steps. For example, J. R. Kosak, in Catalysis of Organic Reactions, Vol. 18, (1988), 135, describes that the simple addition of 1% NaNO
3
increases accumulation during hydrogenation of 3,4-dichloronitrobenzene from an original <5% to approximately 30%.
It has now surprisingly been found that the catalytic hydrogenation of aromatic halonitro compounds is effected with very high selectivity, with high yields and short reaction times, if rhodium, iruthenium, ridium, platinum or palladium catalysts, which are modified with inorganic or organic phosphorus compounds with a degree of oxidation of less than 5, are used in the presence of a vanadium compound.
Surprisingly, in many cases, only small concentrations of hydroxylamine occur. Normally, the hydroxylamine concentrations observed during the entire reaction are less than 1%. In this way, it is possible to use higher concentrations or quantities of halonitro aromatic substances, which contributes towards providing an extremely economical process without endangering the required safety measures. In addition, the activity and selectivity of the catalyst systems is high.
The catalyst systems may be easily produced for example from well known, commercially available standard noble metal catalysts, for example standard Pt, Pd or Ir hydrogenation catalysts, so that a constant quality of catalyst is assured, which is of importance for large-scale production.
Frequently, in hydrogenation, a lower pressure (ca. 5 bar) and a comparatively low temperature (ca. 100°) may even be used.
A further advantage of the process also over known reduction methods, such as Bechamp reduction or sulphide reduction, is that only small quantities of product residues are obtained, which have to be disposed of. The product is obtained in high purity, since practically no azo or azoxy compounds result, and the reaction may be carried out in a highly economic manner in current reactors without having to resort to special safety measures. Hydrogenation, especially the latter phase, is quick. The outcome of this is considerable advantages as regards constant quality.
The subject matter of the invention is a process for the production of aromatic halogen-amino compounds by means of catalytic hydrogenation of corresponding aromatic halonitro compounds on noble metal catalysts, characterised in that hydrogenation is carried out in the presence of a rhodium, ruthenium, iridium, platinum or palladium catalyst, which is modified with an inorganic or organic phosphorus compound with a degree of oxidation of less than 5, and in the presence of a vanadium compound.
Preferably, the noble metal catalyst employed is a platinum or iridium catalyst, most preferably a platinum catalyst.
The noble metal catalyst is preferably employed in a quantity of 0.1 to 10% by weight, most preferably in an amount of 0.1 to 2% by weight, based on the aromatic halonitro compound employed.
It is preferable to use a noble metal catalyst which contains 1 to 10% by weight platinum. The platinum employed may be applied to a carrier as platinum black, platinum oxide or preferably in metallised or oxidised form. Especially good carriers are activated carbon, silicon dioxide in the form of silicic acid or silica gel, aluminium oxide, calcium carbonate, calcium phosphate, calcium sulphate, barium sulphate, titanium oxide, magnesium oxide or iron oxide, most preferably activated carbon, aluminium oxide or silicon dioxide. Platinum applied to the above-mentioned carrier material is available commercially, or may be produced by methods which are familiar to a person skilled in the art, as disclosed for example in DE-OS 2 042 368.
Phosphorus compounds as modifiers may be in principle any inorganic or organic phosphorus compounds, in which the phosphorus has a degree of oxidation of less than 5. Examples are most preferably phosphorous acid and derivatives of phosphorous acid, as named for example in U

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