Raney-copper

Raney copper is prepared from the commercially available copper aluminum alloy. It does not have much to offer the synthetic chemist as only a few reactions are reported to be affected by this catalyst. Raney copper, as well as Raney cobalt, generally produces fewer side reactions than Raney nickel even though they usually require higher reaction temperatures for the same reaction. Raney copper is, however, quite usefiil for the selective hydrogenation of substituted dinitro benzenes (Eqn. 8.6) with its activity apparently increasing with continued reuse. Raney copper can also be used for the catalytic hydrolysis of hindered nitriles to the amides (Eqn. 12.13). 2 

The precipitated nickel is composed of nickel on zinc particles with a covering of zinc oxide and other zinc compounds. 2 These zinc compounds are removed by the acid wash to expose the metallic nickel. Since the presence of the zinc prevents the oxidation of the nickel when exposed to mild oxidation 

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Mitsui Toatsu Chemical, Inc. disclosed a similar process usiag Raney copper (74) shortiy after the discovery at Dow, and BASF came out with a variation of the copper catalyst ia 1974 (75). Siace 1971 several hundred patents have shown modifications and improvements to this technology, both homogeneous and heterogeneous, and reviews of these processes have been pubHshed (76). Nalco Chemical Company has patented a process based essentially on Raney copper catalyst (77) ia both slurry and fixed-bed reactors and produces acrylamide monomer mainly for internal uses. Other producers ia Europe, besides Dow and American Cyanamid, iaclude AUied CoUoids and Stockhausen, who are beheved to use processes similar to the Raney copper technology of Mitsui Toatsu, and all have captive uses. Acrylamide is also produced ia large quantities ia Japan. Mitsui Toatsu and Mitsubishi are the largest producers, and both are beheved to use Raney copper catalysts ia a fixed bed reactor and to sell iato the merchant market. 

The chemical production of aminophenols via the reduction of nitrobenzene occurs in two stages. Nitrobenzene [98-95-3] is first selectively reduced with hydrogen in the presence of Raney copper to phenylhydroxylamine in an organic solvent such as 2-propanol (37). With the addition of dilute sulfuric acid, nucleophilic attack by water on the aromatic ring of /V-phenylhydroxylamine [100-65-2] takes place to form 2- and 4-aminophenol. The by-product, 4,4 -diaminodiphenyl ether [13174-32-8] presumably arises in a similar manner from attack on the ring by a molecule of 4-aminophenol (38,39). Aniline [62-53-3] is produced via further reduction (40,41). 

In addition to the Raney nickel catalysts, Raney catalysts derived from iron, cobalt, and copper have been examined for their action on pyridine. At the boiling point of pyridine, degassed Raney iron gave only a very small yield of 2,2 -bipyridine but the activity of iron in this reaction is doubtful as the catalyst was subsequently found to contain 1.44% of nickel. Traces of 2,2 -bipyridine (detected spectroscopically) were formed from pyridine and a degassed, Raney cobalt catalyst but several Raney copper catalysts failed to produce detectable quantities of 2,2 -bipyridine following heating with pyridine. 

An alternative sequence utilized 2-oxazolidone, which was readily synthesized from urea and ethanolamine, as the glycine equivalent. Subsequent treatment with phosphorous acid and formaldehyde produced iV-phosphonomethyl-2-oxazolidone 12 (16). Upon hydrolysis, and loss of CO2,12 provided the related derivative, iV-phosphonomethylethanolamine 13, which was oxidized at high temperature with a variety of metal catalysts including cadmium oxide (16) or Raney copper (17) to give GLYH3, after acidification. A similar oxidation route has also been reported starting from iV-phosphonomethy 1-morpholine (18). 

This type of catalyst is not limited to nickel other examples are Raney-cobalt, Raney-copper and Raney-ruthenium. When dry, these catalysts are pyrophoric upon contact with air. Usually they are stored under water, which enables their use without risk. The pyrophoric character is due to the fact that the metal is highly dispersed, so in contact with oxygen fast oxidation takes place. Moreover, the metal contains hydrogen atoms and this adds to the pyrophoric nature. Besides the combustion of the metal also ignition of organic vapours present in the atmosphere can occur. Before start of the reaction it is a standard procedure to replace the water by organic solvents but care should be taken to exclude oxygen. Often alcohol is used. The water is decanted and the wet catalyst is washed repeatedly with alcohol. After several washes with absolute alcohol the last traces of water are removed. 

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). 

Wainwright, Tomsett, Trimm, and coworkers/Mellor, Copperthwaite, and coworkers—Raney copper catalysts for WGS and methanol synthesis. In 1995, Wainwright and Trimm295 reviewed Raney178 copper catalysts for both water-gas shift and methanol synthesis applications and discussed the possibility of either a redox mechanism or a formate mechanism for Raney copper catalysts. Formates, they indicated, rapidly decompose to C02 and H2 over metallic copper surface. They... 

In 1997 and 1998, the authors306 307 also examined acid leached Raney copper catalysts, whereby the alloy was leached with either nitric or perchloric acid of 5, 14, or 27.5 wt% strength. The acid solution was added dropwise over 15 min to an equal volume of deionized water containing the alloy particles. After leaching at 50 °C, the particles were removed and washed to a pH of 7. Air drying at 120 °C was then carried out for one hour. The dissolution rates of catalyst components were observed to be functions of the extraction time (Table 56). 

Table 55 Compositions and properties of Raney copper catalysts305...

Table 56 time307 Compositions of Raney copper catalysts as function of acid type and extraction ... 

J.A. Stanfield and P.E. Robbins, Raney Copper Catalysts, Proc. 2nd Int. Cong. Catal., Paris, 1960, pp. 2579-2599. 

In contrast to Raney Ni, no hydrocarbons are formed over pure Raney copper, while propane-1,2-diol is produced with a selectivity of 66% at 85% glycerol conversion at 3 MPa and 513 K. It has been verified that the excellent selectivity is due to the high stability of propane-1,2-diol under the reaction conditions. 1,3-Propanediol is not stable and converts almost quantitatively into 1-propanol... 

The Raney nickel process applied to alloys of aluminum with other metals produces Raney iron, Raney cobalt, Raney copper and Raney zinc, respectively. These catalysts are used very rarely and for special purposes only. 

Naphthol has been reduced to 1-decalol using platinum,5 Raney nickel,6 and Raney copper.7 The reactions catalyzed by nickel and copper required elevated temperatures and pressure. The present procedure allows the preparation of substantial quantities of 1-decalol under much more convenient conditions and shorter reaction times. Previous methods5-7 require costly catalysts or high-pressure equipment and frequently result in a high degree of hydrogenolysis. The submitters have found that the present method is applicable to a wide variety of aromatic nuclei, some of which are listed in Table I. 

The trail-blazing patent of Goto et al. ( ) for the oxidative dehydrogenation of aminoalcohols to the corresponding aminocarboxylic acid salts over Raney copper catalysts in strongly alkaline solutions was cast in terms of the general reaction... 

Specific examples of RWA are further described. Raney copper precursor with a small amount of Pd was prepared by this process. Rapid solidification was effective in keeping most of the added Pd dissolved in the precursor. The specific surface area of the leached specimen increased by about 3 times in comparison with that of ordinary Raney copper catalyst. The conversion from acrylonitrile to acrylamide by the hydration reaction was about 60%, or more than 20% higher than that from ordinary Raney copper catalyst. In case of Ti or V addition, the conversion increased to 70-80%. Rapid solidification was quite effective in decreasing the defect rate of Raney catalysts from some precursors. The potential for design of new catalysts may be widely extended by rapid solidification. 

The reduction of polyfunctional nitro compounds, nitroaryl as well as nitroalkyl compounds, to the corresponding amines in basic aqueous alcoholic solutions on Raney copper (RCu) is more selective if carried out by generating chemisorbed hydrogen by electroreduction of water (ECff method) than by generating it by leaching of the alloy in situ (CCff method) except in the case of o-iodonitrobenzene (2) for which the CCH method is more selective, ffowever, the most selective method in all cases studied is ECH in neutral medium (pff 3-7). 

More recent research efforts have focused on the development of other possible catalysts such as promoted Raney copper,371,403 catalysts prepared from intermetal-lic precursors,362,371 386 404-406 and catalysts that tolerate high C02 content.407 Catalyst modifications allowed to shift the selectivity to the formation of higher alcohols.208,408 110 For example, in a process developed by IFP, a multicomponent oxide catalyst is applied with copper and chromium as the main components 410 By this method, 70-75% total alcohol selectivities and 30-50% of C2 and higher alcohol selectivities can be achieved at 12-18% conversion levels (260-320°C, 60-100 atm). 

This last reaction (RM) enables us to understand the formation of products containing 3 carbon atoms (glycerol, 1,2-propanediol) from glucitol (sorbitol) but is always in competition with the two other ones (DOH, RC). The ratio of these three reactions, determining the conversion selectivity, depend widely on the copper origin (Raney, deposited on a support, impurities, activation process). So, we studied the influence of additives deposited on Raney copper on these reaction selectivities. 

Raney copper is prepared by intensive leaching of a commercial copper-aluminum alloy (50-50 wt%) washed with water until neutral. Bimetallic catalysts are obtained using an oxido-reduction method summarized as n Cu-s + 2 Mn+ -> n Cu2+ + 2 Ms... 

As shown in figure 2 for glucitol conversion at 493 K for platinum and ruthenium as additives, the first atoms exchanged with copper are strong poisons for the copper catalyst until M/Cus = 0,10 to 0,15. In the range (A), the selectivity observed is that of Raney copper (DOH mainly, RC, RM). No cyclodehydration products have been detected. 

In A, a Raney copper catalyst would be able to hydro-dehydrogenate alcoholic functions (-H, +H) on metallic copper sites. About 10 to 15% of the copper would be hydroxylated copper able to catalyze the degradation reactions DOH, RC, RM. These sites would be more reactive than Cu towards Mn + in the oxido-reduction modification of the initial Raney copper, so that, beeing first exchanged, the rates of DOH, RC, RM decrease. 

Figure 5.23 a Stoichiometric acid hydrolysis of acrylonitrile to acrylamide b Raney copper-catalyzed hydrolysis. 

Particles of Raney copper, modified by redox deposition of ruthenium, platinum, or gold were characterized by energy dispersive spectroscopy. Ruthenium is deposited preferentially on the rims of the copper particles while low Miller-index planes are totally free of deposited ruthenium atoms. For platinum or gold the deposition can occur over the whole copper surface [11]. 

Scheme 6.36 Production of acrylamide with a Raney copper catalyst.

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