Urushibara hydrogenation catalysts

Urushibara Co catalysts can be prepared exactly in the same way as the corresponding Ni catalysts, using cobalt chloride hexahydrate instead of nickel chloride hexahydrate as starting material. Similarly as with Raney catalysts, Urushibara Co has been found to be more effective and selective than Urushibara Ni in the hydrogenation of nitriles, affording high yields of primary amines.105,106... 

Because of their reactivity, aryl hydroxylamines can sometimes be trapped by further reaction with another material present in the hydrogenation system. Aryl nitrones such as 17 are produced by the in situ condensation of the aryl hydroxylamine with an aldehyde which is present in the reaction medium (Eqn. 19.16).35 These reactions take place in good yield over a Urushibara nickel catalyst (Chapter 12) in aqueous alcohol at room temperature and four... 

HYDROGENATION, ASYMMETRIC (-)-and (+)-2,3-0-IsopropyIidene-2,3-dihydroxy-l,4-bis(diphenyIphosphine)butane. Neomenthyldiphenylphosphine. HYDROGENATION CATALYSTS frthap/o-AlIyltris(trimethylphosphite)cobalt(I). Lindlar catalyst. Palladium catalysts. Palladium(II) chloride. Rhodium-on-carbon. Tris(triphenylphosphine)chlotorhodium. Tris(triphenylphosphine)ruthenium dl-chloride. Urushibara catalysts. 

Hydrogenation over nickel catalyst at high temperatures and pressures affects aromatic rings. Over Urushibara nickel at 106-150° and 54atm, ethyl benzoate gave ethyl hexahydrobenzoate in 82% yield [48]. 

Various active nickel catalysts obtained not via reduction of nickel oxide with hydrogen have been described in the literature. Among these are the catalysts obtained by the decomposition of nickel carbonyl 10 by thermal decomposition of nickel formate or oxalate 11 by treating Ni-Si alloy or, more commonly, Ni-Al alloy with caustic alkali (or with heated water or steam) (Raney Ni) 12 by reducing nickel salts with a more electropositive metal,13 particularly by zinc dust followed by activation with an alkali or acid (Urushibara Ni) 14-16 and by reducing nickel salts with sodium boro-hydride (Ni boride catalyst)17-19 or other reducing agents.20-24... 

Urushibara Ni A (U-Ni-A) 6 The solids prepared by the reaction of zinc dust with aqueous nickel chloride solution, in the same way as described above, are transferred into 160 ml of 13% acetic acid and digested at 40°C until the evolution of hydrogen gas subsides or the solution becomes pale green. The catalyst can be washed with water on a glass filter under gentle suction with care to prevent the catalyst from contacting air, and then with the solvent for hydrogenation. 

Iron catalysts have found only limited use in usual hydrogenations, although they play industrially important roles in the ammonia synthesis and Fischer-Tropsch process. Iron catalysts have been reported to be selective for the hydrogenation of alkynes to alkenes at elevated temperatures and pressures. Examples of the use of Raney Fe, Fe from Fe(CO)5, and Urushibara Fe are seen in eqs. 4.27,4.28, and 4.29, respectively. 

Unhindered simple olefins are usually rapidly hydrogenated under very mild conditions over platinum metal catalysts such as platinum, palladium, and rhodium as well as over active nickel catalysts such as Raney Ni, nickel boride, and Urushibara Ni. For example, 0.1 mol of cyclohexene is hydrogenated in 7 min over 0.05 g of Adams platinum oxide in ethanol at 25°C and 0.2-0.3 MPa H2 (eq. 3.1).5 1-Octene and cyclopentene (eq. 3.2) are hydrogenated in rates of 11.5 and 8.6 mmol (258 and 193 ml H2 at STP) g Ni 1-min 1, respectively, over P-1 Ni in ethanol at 25°C and 1 atm H2.18 Hydrogenation of cyclohexene over active Raney Ni proceeds at rates of 96-100 ml H2 at STP (4.3-4.5 mmol) g Ni min-1 in methanol at 25°C and 1 atm H2 49,50 and can be completed within a short time, although usually larger catalyst substrate ratios than required for platinum catalyzed hydrogenations are employed (eq. 3.3).50... 

The C-C double bonds conjugated with carboxyl functions are usually much more readily hydrogenated than usual olefinic bonds, especially with nickel and palladium catalysts. Ethyl cinnamate is rapidly hydrogenated over Raney Ni under mild conditions (eq. 3.19).115 It is also hydrogenated over palladium oxide much faster (eq. 3.20) than over platinum oxide with which 2.9 h were required under the same conditions.5 Cinnamic acid was hydrogenated smoothly to dihydocinnamic acid as the sodium salt over Urushibara Ni in water under ordinary conditions (eq. 3.21).116... 

Taira hydrogenated 2-butyne-1,4-diol using Urushibara Fe as catalyst in ethanol at 80-100°C and an initial hydrogen pressure of 5-7 MPa until the hydrogen uptake ceased and obtained cw-2-butene-1,4-diol in 70-75% yield (eq. 4.29).89... 

On the other hand, 50-cholestan-3-one was hydrogenated to the axial alcohol, 50-cholestan-30-ol, in 99% yield (GC) over Urushibara cobalt A (U-Co-A) in methanol as solvent (eq. 5.45) and in 72% yield (GC) over U-Ni-A.170 In these cases the yields decreased in less polar solvents over both catalysts. 

Orito and Imai have shown that the hydrogenation of benzene over nickel and cobalt catalysts is inhibited by alcoholic solvents and some ethers.5 As seen from the results shown in Table 11.2, benzene is hydrogenated extremely slowly or not at all in primary alcohols but very rapidly without solvent or in hydrocarbons. Benzene is hydrogenated at a considerable rate at 110°C even over Urushibara Ni A, which is known to be a poor catalyst toward the hydrogenation of aromatic nucleus,10 when used without solvent or in hydrocarbons after the water or alcohol on the catalyst has been carefully removed. 

Benzene (60 ml without solvent or 20 ml with 40 ml solvent for the supported catalysts 45 ml without solvent or 15 ml with 30 ml solvent for Raney and Urushibara catalysts) was hydrogenated at initial hydrogen pressure of 4 MPa. The rates (ml H2 min-1) were obtained at initial stages for unsupported catalysts or as average values at H2 pressure drop from 4 to 3 MPa for Raney and Urushibara catalysts. 

Hydrogenation of 3-keto steroids. Urushibara nickel A is the best catalyst for reduction of cholestane-3-one to the 3a-ol. The ratio of epicholestanol to... 

Selective hydrogenations, Japanese chemists have prepared (3) by hydrogenation with Urushibara nickel A catalyst of either (1) or (2). ... 

Benzonitrile added to Urushibara nickel-zinc catalyst (s. Synth. Meth. 12, 93) in water, and refluxed ca. 8hrs. until the oil drops of benzonitrile on the water have disappeared benzamide. Y 78%. — Water as solvent suppresses the activity of the catalyst for hydrogenation but promotes the activity for hydration. F. e. s. K. Watanabe, Bull. Ghem. Soc. Japan 37, 1325 (1964). 

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