Raney copper hydrogenation, selective

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). 

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). 

Raney copper is another Raney type catalyst that is prepared from a copper-aluminum alloy. This catalyst has been used infrequently but does show some reaction selectivity not possible with other catalysts. Of particular interest is its use for the selective hydrogenation of substituted dinitrobenzenes (Eqn. 11.6).2 This catalyst, as well as Raney cobalt, generally promotes fewer side reactions than does Raney nickel. 25... 

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... 

Raney metals are attractive because thermal treatment in a gas flow is not required to produce the catalytically active metal. Storage of the pyrophoric catalyst is, moreover, easy, because the catalyst can be stored in water. Another important advantage is that the catalyst particles are heavy, which enables separation of the catalyst by settling and decantation. A final attractive feature of Raney metals is that they can be exposed to alkaline liquids. Many other metal catalysts are not stable in alkaline liquids. Most well known is Raney nickel, which is an attractive hydrogenation catalyst [11-20]. Raney copper and Raney cobalt are also frequently employed. Raney metals are mostly used for hydrogenations in the fine-chemical industry. Raney nickel and Raney cobalt often have different selectivity the reason for the difference between nickel and cobalt is often obscure, though cobalt is more liable to poisoning and oxidation. 

By using sodium haiides or sodium borate the hydrogenation of D-fructose could be carried out almost to the completion. These results are shown in Table 3. In these experiments upon using Raney-copper catalysts the highest selectivity of D-mannitol, 82.7 %, was obsen/ed over a cobalt containing catalysts in the presence of sodium borate. Even higher D-mannitol selectivity, i.e. 88.2, was observed over CPG supported copper catalyst in the presence of sodium borate. 

Raney-copper catalysts showed relatively high activity in the hydrogenation of D-fructose to D-mannitol. The selectivity of D-mannitol over these catalyst was around 60-65 %. The highest D-mannitol selectivity, i.e. values around 85-88 %, was obtained over Cu/CPQ catalyst in the presence of sodium borate. This high selectivity could be maintained up to 95-97 % conversion. 

Various other reducing methods are employed for the conversion of (3-nitro alcohols to amino alcohols, namely, electrochemical reduction.107 The selective electrohydrogenation of ni-troaliphatic and nitroaromatic groups in molecules containing other groups that are easy to hydrogenate (triple bond, nitrile, C-I) are carried out in methanol-water solutions at Devarda copper and Raney cobalt electrodes (Eq. 6.55).107... 

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]. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Imaizumi et al. studied the hydrogenation of l,4-dialkyl-l,3-cyclohexadienes over the nine group VIII (groups 8-10) metals and copper in ethanol at room temperature and atmospheric pressure.122 The selectivity for monoenes formation at 50% conversion increased in the order Os-C, Ir-C < Ru-C, Rh-C, Pt < Pd-C, Raney Fe, Raney Co, Raney Ni, Raney Cu (= 100%). The selectivity for 1,4-addition product increased in the order Os-C, Ir-C < Ru-C, Rh-C, Raney Cu, Raney Fe, Raney Ni < Raney Co, Pd-C, Pt. Extensive formation of 1,4-dialkylbenzenes (more than 50% with the 1,3-dimethyl derivative) was observed over Raney Ni and Pd-C, while they were not formed over Raney Cu, Os-C, and Ir-C. In the hydrogenation of 4-methyl-1,3-pen -tadiene (39) (Scheme 3.15) over group VIII metals in cyclohexane at room temperature and atmospheric pressure, high selectivity to monoenes was obtained with iron, nickel, cobalt, and palladium catalysts where the amounts of the saturate 2-methylpen-... 

Nitta et al. compared the selectivity of copper, cobalt, and nickel borides (Cu-B, Co-B, and Ni-B) as well as Raney Ni and Ni-B modified with copper(II) chloride, in the partial hydrogenation of acetylenic compounds.82 The selectivity at 30% conversion... 

Mitsui et al. studied the selectivity of transition metal catalysts in the hydrogenation of various pyridine V-oxides in ethanol at room temperature and atmospheric pressure with Raney Ni, Pd-C, Pt-C, Rh-C, and Ru-C, and at elevated temperatures and pressures with Raney Co, Raney Cu, and copper-chromium oxide.229 The IV-oxide groups of 4-benzyloxy- and 4-styrylpyridines were hydrogenated in preference to the other functional groups over Raney Cu, copper-chromium oxide, Raney Co, and Ru-C, similarly as over Raney Ni. Pt-C and Rh-C also showed similar selectivity in... 

Acridine. Acridine is hydrogenated to 9,10-dihydro derivative over Raney Ni at 25°C and over copper-chromium oxide at 150°C in dioxane.9101 Over Raney Ni at 100°C, acridine or 9,10-dihydroacridine is hydrogenated to a mixture of as- and s-octahydro and dodecahydro derivatives. However, over copper-chromium oxide at 190°C, as-octahydro derivative is formed in high selectivity, although a small amount of dodecahydro derivative is also formed.9 The formation of... 

The ease of hydrogenation in the five-membered ring has been explained by the formation of indolizinium ion I or II, which is a resonance-stabilized pyridinium ion conjugated with an olefinic bond (see Scheme 12.16).114 On the other hand, it is usual that the hydrogenation of indolizines with Raney Ni,113,115 copper-chromium oxide,113 or Pd-C in ethyl acetate (eq. 12.59)116 leads to the products selectively reduced in the six-membered ring. 

Note the particularly mild reaction conditions and the fact that the reaction depicted by Eq. (6) progresses without cleavage of the allylic hydroxyl group. These copper-modified nickel catalysts were found to be more selective than the analogous Cu(B) formulations derived from borohydride reduction of copper chloride [17]. Copper modification of Raney nickel has also been shown to benefit the selectivity of phenylacetylene hydrogenation, but not to the same extent as the Cu-Ni(B) catalyst. 

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