Multimetallic catalyst and process for preparing substituted aromatic amines

Abstract

A multimetallic catalyst for hydrogenation of substituted nitroaromatic compounds to give the corresponding aromatic amines. By doping iridium with at least one element from the group manganese, cobalt, iron, nickel, copper and ruthenium, a catalyst is obtained which is characterized by high selectivity.

We claim:  
     
         1 . A multimetallic catalyst comprising iridium and at least one other doping element on a support, wherein said iridium is doped with at least one element selected from the group consisting of manganese, cobalt, iron, nickel, copper and ruthenium.  
     
     
         2 . The multimetallic catalyst according to    claim 1   , wherein iridium is present in an amount of 0.3 to 12 wt. % by weight of the support, and said doping element is present in an amount of 1 to 100 wt. % of doping element, based on the iridium.  
     
     
         3 . The multimetallic catalyst according to    claim 1    wherein said support for the catalyst is selected from the group consisting of activated carbon, aluminum oxide, titanium dioxide, silicon dioxide and mixed oxides thereof.  
     
     
         4 . The catalyst according to    claim 3    wherein porous or non-porous activated carbon is present, wherein at least 80 wt. % of the activated carbon particles have a particle size of less than 100 μm.  
     
     
         5 . The catalyst according to    claim 2    wherein iridium is present in an amount of from 0.5 to 7 wt. %, with reference to the support material.  
     
     
         6 . A method for preparing the catalyst of    claim 1    wherein the support is first suspended in water and impregnated by adding an aqueous salt solution and said doping element, and an iridium compound reducing said doping element using a water-soluble reducing agent at temperatures from 0 to 100° C.  
     
     
         7 . A method for preparing the catalyst for    claim 1    wherein hexachloroiridium (IV) acid is reacted with a halide salt of said doping element in an aqueous medium, adjusting the resulting suspension to an alkaline pH and reducing the resulting reactant with a sodium borohydride solution and filtering to recover the catalyst.  
     
     
         8 . A method for the hydrogenation of a substituted nitroaromatic compound comprising dissolving a nitroaromatic compound in a suitable inert solvent and carrying out the hydrogenation in the presence of a catalyst according to    claim 1    with the addition of hydrogen.  
     
     
         9 . The process according to    claim 8    wherein the substituted nitroaromatic compound is a chlorine substituted aromatic nitro compound of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are the same or different and represent hydrogen, alkyl, alkoxy, hydroxy, carboxy, carbonyl, phenyl, amino, chlorine, fluorine, alkylcarbonylamido or alkyloxycarbonylamido.  
     
     
         10 . The process according to    claim 8    wherein the inorganic solvent is an aliphatic alcohol, organic acid or aromatic hydrocarbon.  
     
     
         11 . The process according to    claim 8    which is carried out at a temperature of 40 to 200° C. at a pressure from 1 to 200 bar.  
     
     
         12 . The process according to    claim 8    wherein the temperature is from 60 to 120° C.  
     
     
         13 . The process according to    claim 8    which is carried out in the presence of an organic or inorganic basic compound.  
     
     
         14 . The process according to    claim 8    wherein triethylamine is present in the reaction.  
     
     
         15 . A method for the hydrogenation of substituted aromatic nitrogen compounds to obtain high selectivity with regard to possible dehalogenated and other undesired secondary products and to avoid the elimination of chlorine by carrying out the hydrogenation in the presence of the multimetallic catalyst according to    claim 1   .