Copper-chromite selective

Dicyclohexylarnine may be selectively generated by reductive alkylation of cyclohexylamine by cyclohexanone (15). Stated batch reaction conditions are specifically 0.05—2.0% Pd or Pt catalyst, which is reusable, pressures of 400—700 kPa (55—100 psi), and temperatures of 75—100°C to give complete reduction in 4 h. Continuous vapor-phase amination selective to dicyclohexylarnine is claimed for cyclohexanone (16) or mixed cyclohexanone plus cyclohexanol (17) feeds. Conditions are 5—15 s contact time of <1 1 ammonia ketone, - 3 1 hydrogen ketone at 260°C over nickel on kieselguhr. With mixed feed the preferred conditions over a mixed copper chromite plus nickel catalyst are 18-s contact time at 250 °C with ammonia alkyl = 0.6 1 and hydrogen alkyl = 1 1. 

Copper—cadmium and zinc—chromium oxides seem to provide most selectivity (38—42). Copper chromite catalysts are not selective. Reduction of red oil-grade oleic acid has been accompHshed in 60—70% yield and with high selectivity with Cr—Zn—Cd, Cr—Zn—Cd—Al, or Zn—Cd—A1 oxides (43). The reduction may be a homogeneously catalyzed reaction as the result of the formation of copper or cadmium soaps (44). 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Copper chromite 14) and barium-promoted copper chromite (75,/7) have been used for acid reductions but very high temperatures (300 C) are required. The necessary temperature is sufficiently higher than that required foresters to permit selective reduction of half-acid esters to the hydroxy acid 23). The reverse selectivity can be achieved by reduction over H Ru4 CO)a PBu3)4 at I00-200 C and 1500-3000 psig. This homogeneous catalyst will reduce acids and anhydrides, but not esters (2). 

Hydrogenolyses of carboxylic acids and esters to the corresponding aldehydes seems very attractive due to their simplicity. Copper chromites are the most widely used catalysts.15 Raney copper and zinc oxide-chromium oxide have also been used for this process.16-18 The hydrogenolysis of methyl benzoate to benzaldehyde was studied on various metal oxides at 300-350°C. ZnO, Zr02 and Ce02 presented high activities and selectivities (Scheme 4.8). 

The hydrogenation of HMF in the presence of metal catalysts (Raney nickel, supported platinum metals, copper chromite) leads to quantitative amounts of 2,5-bis(hydroxymethyl)furan used in the manufacture of polyurethanes, or 2,5-bis(hydroxymethyl)tetrahydrofuran that can be used in the preparation of polyesters [30]. The oxidation of HMF is used to prepare 5-formylfuran-2-carboxylic acid, and furan-2,5-dicarboxylic acid (a potential substitute of terephthalic acid). Oxidation by air on platinum catalysts leads quantitatively to the diacid. [32], The oxidation of HMF to dialdehyde was achieved at 90 °C with air as oxidizing in the presence of V205/Ti02 catalysts with a selectivity up to 95% at 90% conversion [33]. 

Another dehydration product from glycerol is hydroxyacetone, or acetol (Scheme 4). In one study, several catalysts were tested for this reaction. Of the tested catalysts, however, only copper-chromite appeared to be effective for this transformation. Using this catalyst, 80% selectivity towards hydroxyacetone was achieved at 86% conversion in a reactive distillation experiment carried out under a slight vacuum (98 kPa) at 240... 

We have developed a multimetallic catalyst for the large scale synthesis of sterically hindered mono-N-alkylanilines with very good selectivity and high catalytic activity. In contrast to copper chromite catalysts which allow the N-alkylation only with primary alcohols, the doubly promoted Pt/Si02 catalysts described here are useful for the reaction of ortho-substituted anilines with both primary and secondary alcohols. 

Experiments with catalysts which are known to catalyze the alkylation reaction in the liquid phase (ref. 3), showed that the desired gas-phase reaction of substituted anilines with alkoxy-alcohols occurs, but with very low yield. Pd promoted copper chromite catalysts which are able to catalyze the alkylations of sterically hindered anilines with primary alkoxyalcohols (ref. 4, 5) showed only very low activity and selectivity when secondary alcohols were used. 

Raney Ni and copper chromite are selective in forming benzylic alcohols from these compounds,... 

Alcohols from esters. The major problem is reaction selectivity. Paraffin by-product in alcohol results if the catalyst activity is too high. Yet the reduction of esters to alcohols is a difficult reaction. Copper chromite catalyst, 3000-5000 psig hydrogen, and a temperature of 270-300°C are required for the reduction. An alternate catalyst is CuO/ZnO, which is used for methyl ester reduction only. Hydrogen solubility in alcohol is limiting. 

Fatty alcohols are obtained by direct hydrogenation of fatty acids or by hydrogenation of fatty acid esters. Typically, this is performed over copper catalysts at elevated temperature (170°C-270°C) and pressure (40-300 bar hydrogen) [26], By this route, completely saturated fatty alcohols are produced. In the past, unsaturated fatty alcohols were produced via hydrolysis of whale oil (a natural wax occurring in whale blubber) or by reduction of waxes with sodium (Bouveault-Blanc reduction). Today, they can be obtained by selective hydrogenation at even higher temperatures (250°C-280°C), but lower pressure up to 25 bar over metal oxides (zinc oxide, chromium oxide, iron oxide, or cadmium oxide) or partially deactivated copper chromite catalysts [26],... 

In a series of investigations, Sakakibara and co-workers employed copper chromite as a catalyst for hydrogenolysis performed under conditions selected so as to yield dimeric and trimeric structures. The procedure described by Hwang and Sakakibara (1979) serves as a typical example. 

Ponomarev221 selectively reduced the side chain of the azomethines (16) and (17) with copper chromite or Raney nickel ... 

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

Previous works have shown that copper catalysts are selective in the dehydrogenation of esters (5-7), in the hydrolysis of nitrile (8), in the selective hydrogenation of nitrile or in alcohol amination (10). The catalyst systems such as copper chromite are often used for the preparation of substituted amines. These solids, however, are very sensitive to the presence of water and ammonia (formation of copper nitrides... 

Moreover, the catalysts promoted by alkaline or alkaline-earth species are more stable than the unpromoted CuCr. For example, barium impregnated on copper chromite increases the stability of the active CuCr02 phase (13). Furthermore, the presence of barium or calcium on copper chromite catalysts influences strongly the selectivity to the methylation of amines N-alkylation/N-methylation. 

In our laboratory, we have shown that copper chromite doped with barium, calcium or manganese can lead selectively to dimethyldodecylamine from lauronitrile, ammonia, hydrogen and methanol but not to methyldidodecylamine (14). 

In the first part of our work, we examined the properties of a copper chromite catalyst for the selective synthesis of dimethylethylamine (DMEA) from monoethyiamine (MEA) and methanol (MeOH). Under our experimental conditions at 230°C, this catalyst... 

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