Ruthenium Raney catalyst

Other specialized alloys have also been used to prepare skeletal metal catalysts. Raney ruthenium has been prepared from the ruthenium aluminum alloy. 20 A colloidal platinum has been prepared by the action of acetic acid on a platinum lithium alloy. l Skeletal nickel catalysts have been made from a number of intermetallic compounds of nickel with the rare earth elements, lanthanum and samarium. The rare earth element is removed from the alloy by reaction with diiodoethane or dibromoethane which convert the rare earths to the soluble halide salts. 22 Several multicomponent catalysts have also been prepared from the corresponding aluminum alloys. 23-126... 

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. 

Hydrogenation catalysts Dichlorotris(triphenylphosphine)ruthenium. Iridium. Iridium tetrachloride-Triethyl phosphite. Iridium-BaSO, or CaC04. Lithium aluminum hydride. Nickel catalyst, Raney. Palladium hydroxide. Platinum catalysts. Potassium hydride. Trihydridobis(triphenyIphosphine)iridium (III). 

Catalytic hydrogenation is mostly used to convert C—C triple bonds into C C double bonds and alkenes into alkanes or to replace allylic or benzylic hetero atoms by hydrogen (H. Kropf, 1980). Simple theory postulates cis- or syn-addition of hydrogen to the C—C triple or double bond with heterogeneous (R. L. Augustine, 1965, 1968, 1976 P. N. Rylander, 1979) and homogeneous (A. J. Birch, 1976) catalysts. Sulfur functions can be removed with reducing metals, e. g. with Raney nickel (G. R. Pettit, 1962 A). Heteroaromatic systems may be reduced with the aid of ruthenium on carbon. 

Ruthenium is excellent for hydrogenation of aliphatic carbonyl compounds (92), and it, as well as nickel, is used industrially for conversion of glucose to sorbitol (14,15,29,75,100). Nickel usually requires vigorous conditions unless large amounts of catalyst are used (11,20,27,37,60), or the catalyst is very active, such as W-6 Raney nickel (6). Copper chromite is always used at elevated temperatures and pressures and may be useful if aromatic-ring saturation is to be avoided. Rhodium has given excellent results under mild conditions when other catalysts have failed (4,5,66). It is useful in reduction of aliphatic carbonyls in molecules susceptible to hydrogenolysis. 

The sequence has been applied to the synthesis of 1,4-cyclohexanedione from hydroquinone 10), using W-7 Raney nickel as prepared by Billica and Adkins 6), except that the catalyst was stored under water. The use of water as solvent permitted, after hltration of the catalyst, direct oxidation of the reaction mixture with ruthenium trichloride and sodium hypochlorite via ruthenium tetroxide 78). Hydroquinone can be reduced to the diol over /o Rh-on-C at ambient conditions quantitatively (20). 

When we first contemplated thermochemical products available from Glu, a search of the literature revealed no studies expressly directed at hydrogenation to a specific product. Indeed, the major role that Glu plays in hydrogenation reactions is to act as an enantioselectivity enhancer (17,18). Glu (or a number of other optically active amino acids) is added to solutions containing Raney nickel, supported nickel, palladium, or ruthenium catalysts and forms stereoselective complexes on the catalyst surface, leading to enantioselective hydrogenation of keto-groups to optically active alcohols. Under the reaction conditions used, no hydrogenation of Glu takes place. 

Raney predicted that many other metal catalysts could be prepared with this technique, but he did not investigate them [8], Copper and cobalt catalysts were soon reported by others [4,5], These catalysts were not nearly as active as Raney s nickel catalyst and therefore have not been as popular industrially however they offer some advantages such as improved selectivity for some reactions. Skeletal iron, ruthenium and others have also been prepared [9-13], Wainwright [14,15] provides two brief overviews of skeletal catalysts, in particular skeletal copper, for heterogeneous reactions. Table 5.1 presents a list of different skeletal metal catalysts and some of the reactions that are catalyzed by them. 

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

Many catalysts, certainly those most widely used such as platinum, palladium, rhodium, ruthenium, nickel, Raney nickel, and catalysts for homogeneous hydrogenation such as tris(triphenylphosphine)rhodium chloride are now commercially available. Procedures for the preparation of catalysts are therefore described in detail only in the cases of the less common ones (p. 205). Guidelines for use and dosage of catalysts are given in Table 1. 

Also, Klabunovskii reported pressure dependences of the OYs in enantio-differentiating hydrogenations of ethyl acetoacetate (EAA) with ruthenium (67), Raney cobalt (65), and RNi catalysts (69) modified with TA, c. Additives. Additives which are added to the reaction system often exert a remarkable effect on the OY of the enantio-differentiating hydrogenation of M A A (23-25). Water is one such additive. For example, in most hydrogenations with amino acid MRNis, the direction of differentiation was reversed by the addition of small amounts of water as shown in Fig. 14 (23, 25). 

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. 

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. 

Citronellal, an aldehyde with a trisubstituted double bond, was hydrogenated to citronellol over a ruthenium catalyst poisoned with lead acetate in 90-100% yields (eq. 5.22)46 or over chromium-promoted Raney Ni in 94% yield in methanol at 75°C and about 0.31 MPa H2.47 Court et al. studied the selective hydrogenation of citral (1, eq. 5.24) to citronellol over unsupported Nij. o catalysts, prepared by reduction of mixtures of metal iodides with naphthalene-sodium as reducing agent, in cyclohexane and in 2-propanol at 80°C and 1.0 MPa H2.48 Higher yields of citronellol were obtained in 2-propanol than in cyclohexane, primarily via citronellal as the predominant intermediate. The yields of citronellol for the overall hydrogenation in 2-propanol over Mo-promoted catalysts were Mo0 03 96%, Mo0 06 98%, and Mo012 96%. 

Dialkyl ketones, especially sterically hindered ones, tend to give the corresponding alcohols to significant extents under conditions of reductive amination, resulting in lower yields of amines. As in the cases of the aromatic ketones described above, the addition of small amounts of acetic acid or ammonium acetate is effective to depress the formation of alcohols, which may become a significant side reaction over those catalysts that are active for the hydrogenation of ketones to alcohols such as ruthenium, Raney Co, and Raney Ni.17 Thus, the formation of 2-nonanol could be depressed effectively in the presence of ammonium acetate in the reductive amination of 2-nonanone over these catalysts (eq. 6.7). 

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