Modified nickel catalysts

Tetrahydronaphthalene is produced by the catalytic treatment of naphthalene with hydrogen. Various processes have been used, eg, vapor-phase reactions at 101.3 kPa (1 atm) as well as higher pressure Hquid-phase hydrogenation where the conditions are dependent upon the particular catalyst used. Nickel or modified nickel catalysts generally are used commercially however, they are sensitive to sulfur, and only naphthalene that has very low sulfur levels can be used. Thus many naphthalene producers purify their product to remove the thionaphthene, which is the principal sulfur compound present. Sodium treatment and catalytic hydrodesulfuri2ation processes have been used for the removal of sulfur from naphthalene the latter treatment is preferred because of the ha2ardous nature of sodium treatment. 

Stereochemical Studies of the Enantio-differentiating Hydrogenation of Various Prochiral Ketones over Tartaric Acid-Modified Nickel Catalyst... 

The chapter Chiral Modification of Catalytic Surfaces [84] in Design of Heterogeneous Catalysts New Approaches based on Synthesis, Characterization and Modelling summarizes the fundamental research related to the chiral hydrogenation of a-ketoesters on cinchona-modified platinum catalysts and that of [3-ketoesters on tartaric acid-modified nickel catalysts. Emphasis is placed on the adsorption of chiral modifiers as well as on the interaction of the modifier and the organic reactant on catalytic surfaces. 

Enantio-Differentiating Hydrogenation of Methyl 2-Methyl-3-oxobutyrate (8) with Various Modified Nickel Catalysts ... 

As a rule, synthetic chemists will consider only those new reactions and catalysts for preparative purposes where the enantioselectivity reaches a certain degree (e.g. >80%) and where both the catalyst and the technology are readily available. For heterogeneous catalysts this is not always the case because the relevant catalyst parameters are often unknown. It is therefore of interest that two types of modified Nickel catalysts are now commercially available a Raney nickel/tartrate/NaBr from Degussa [64] and a nickel powder/tartrate/NaBr from Heraeus [65, 66]. It was also demonstrated that commercial Pt catalysts are suitable for the enantioselective hydrogenation of a-ketoesters [30, 31]. With some catalytic experience, both systems are quite easy to handle and give reproducible results. 

CHEMOSELECTIVE HYDROGENATION OF AROMATIC CHLORONITRO COMPOUNDS WITH AMIDINE MODIFIED NICKEL CATALYSTS. 

Hydroxy-2-butanone and its methyl ether were also hydrogenated in 69 and 68% ee, respectively, using the same modified nickel catalyst.211 Acetylacetone was first hydrogenated to (R)-4-hydroxy-2-pentanone in 87% ee over the Raney Ni modified by (R,R)-tartaric acid. Then the (R)-hydroxy ketone was hydrogenated to a mixture of... 

Tai A, Harada T (1986) Asymmetrically modified nickel catalysts. In Iwasawa Y (ed) Tailored metal catalysts. Reidel, Tokyo, p. 265... 

Boocock, D.G.B., Mackay, D., and Franco, H., The Production of Synthetic Liquids from Wood Using a Modified Nickel Catalyst , Paper accepted for presentation at 29th Canadian Chemical Engineering Conference, Sarnia, Ontario, 30 Sept. -3 Oct. 1979. 

Most remarkably, no codimerization involving the unsaturated ester molecule is observed, even though nickel compounds such as the acrylonitrile complex are efficient catalysts for such codimerization reactions vide infra). An additional homodimer, l,3-bis(methylene)cy-clohexane (6), is formed as a minor product with phosphane-modified nickel catalysts. Only trace amounts of product 6 are obtained with maleic anhydride as cocatalyst. 

Compared with the naked nickel reactions, reactions with phosphane-modified nickel catalysts require higher temperatures (80-100 C) in order to proceed at a reasonable rate and usually exhibit a decreased stereoselectivity. Despite these obvious drawbacks, such catalyst systems are advantageous in the case of highly electron-deficient alkenes, such as ( )-but-2-enal. ° or dialkyl fumarates, which can be readily employed as cycloaddition substrates only with modified nickel catalysts (vide supra). 

The use of relatively rigid, chiral alkenes, e.g. cycloalk-2-enones, leads to a significant stereochemical induction, i.e. face selectivity of the attack. Interestingly, 4-methylcyclopent-2-enone stereospecifically reacts to provide ejco,c -3-methyl-4-methylenehexahydropentalen-l(2//)-one (22), " a product of formal proximal ring cleavage, in the presence of a phosphane-modified nickel catalyst. 

Scheme 10.6 Enantioselective hydrogenation of MAA over tartaric acid-modified nickel catalyst.

Modified nickel catalysts were prepared from the various nickel sources (Table 1). In the case of the modified nickel catalysts prepared from NiO, e.d. ability of the catalyst depended on the NiO manufacturers. These phenomena were also observed for the e.d. hydrogenation of methyl acetoacetate (MAA) [6]. Since the method of the NiO preparation presumably affect the percentage of crystallite part of reduced Ni, the types of NiO would reflect the e.d. ability of the catalyst. On the other hand, fine nickel powder (FNiP) gave the e.d. catalyst... 

Hydrogenation of 3-alkanones The modified nickel catalyst thus obtained was used for the hydrogenation of the 3-alkanones (32 mmol) in the mixture of carboxylic acid (amount is described in the text) and THF (10 ml) under an initial hydrogen pressure of 9X10 Pa. The hydrogenation temperature was also described in the text. Simple distillation gave a product of more than 98% (GLC analyses 5% Thermon 1000 on Chromosorb W at 70-260°C). 

Keywords. 3-Functionalized ketones, a-Keto acid derivatives. Cinchona modified Pt catalysts. Chiral imprints. Chiral metal surfaces. Chiral polymers. Cyanohydrin formation. Cyclic Dipeptides, Epoxidation catalysts. Heterogeneous catalysts. Hydrogenation catalysts. Modified metal oxides. Polypeptides, Tartrate-modified Nickel catalysts... 

Asymmetric modifications of hydrovinylation are one of the earliest examples of successful asymmetric transition metal catalysis. After optimization of various dimerization and codimerization reactions using phosphane modified nickel catalysts, the first examples of asymmetric olefin codimerization were reported with n-allylnickel halides activated by organoaluminum chloride and modified by chiral phosphanes7. Thus, codimerization of 2-butene with propene using n-allylnickel chloride/A]X, (X = Cl, Br) in the presence of tris(myrtanyl)phosphane gives low yields of (—)-( )-4-methy 1-2-hexene (I) with 3% ee7,7 . 

Attempts at asymmetric, enantioselective [2 + 2] cycloadditions, using chirally modified nickel catalysts, have been reported, but without positive results27. 

Alkoxy substituents are also able to direct additions to 5-alkoxy-2(5//)-furanone44. In the following modified nickel catalyst procedure, attack of methylenecyclopropane occurs once again from the sterically least hindered face. However, the yield is poor and a mixture of type A and type B products is obtained. For comparison, the type A product obtained here as the minor isomer is the sole product observed in the TMM-Pd-mediated transformation19a. 

A heterogeneous tartaric acid modified nickel catalyst was used in the synthesis of methyl (S,.S )-3-hydroxy-2-methylbutanoate. necessary for the preparation of the sex-attractant of the pine sawfly. A syntanti ratio of 75 25 was obtained69. 

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. 

Asymmetrically Modified Nickel Catalyst (MNi) A Heterogeneous Catalyst for the Enantio-Differentiating Hydrogenations... 

Modification Method Studies for the Preparation of Tartaric acid-NaBr-Modified Nickel Catalyst for the Enantio-differentiating Hydrogenation of Methyl Acetoacetate... 

The tartaric acid-NaBr-modified nickel catalyst is one of the intensively studied enantio-differentiating solid catalysts. This catalyst has a high enantio-differentiating ability (e.d.a.) for the hydrogenation of p-ketoesters and 2-alkanones [1-7]. E.d.a. values of 80-98% were attained for the hydrogenation of various P-ketoesters and 72-85% for that of the 2-afkanones. The tartaric acid-NaBr-modified nickel catalyst can be prepared by two methods, one is a conventional pre-modification method [2, 8-13], and the other is an in-situ-... 

Preparation of tartaric ocid-NaBr-modified nickel catalyst... 

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