Catalysts with Raney nickel

Wisniak [14,15] has compared precious metal catalysts with Raney nickel in the hydrogenation of glucose, fructose and xylose. It was concluded that the activity of the catalytic metals decreased in the order... 

The Al/Ni ratio percentage in NiAIg.s was choosen to allow comparison of the supported nickel uminium catalyst with Raney nickel. The actual Al/Ni ratio is smaller than th expected, however the citronellal yield is higher than that we observed with Raney nickel prepared from a commercial alloy (84%), but the citronellol yield is smaller 81 % Instead of 86%. 

The convergent synthesis of these compounds is rather simple. On the one side, the required a-keto ester may be synthesised from diethyl oxalate by a Grignard reaction. On the other side, alanine or trifluoroacetyllysine is coupled with proline via the oxazolidine-2,5-dione (the so-called Leuchs anhydride ). The two halves are combined by reductive amination. The diastereoselectivity of the hydrogenation is dependent on the choice of catalyst. With Raney nickel, the diastereoselectivity lies in case of enalapril at 87 13 and for Iisinoprii at 95 5 in favour of the desired diastereomers. In the case of Iisinoprii, there follows a final hydrolysis of the ester and amide function. The active material is ultimately purified by crystallisation. 

P-Phenylethylamine is conveniently prepared by the hydrogenation under pressure of benzyl cyanide with Raney nickel catalyst (see Section VI,5) in the presence of either a saturated solution of dry ammonia in anhydrous methyl alcohol or of liquid ammonia the latter are added to suppress the formation of the secondary amine, di- P phenylethylamine ... 

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. 

Single-bond cleavage with molecular hydrogen is termed hydrogenolysis. Palladium is the best catalyst for this purpose, platinum is not useful. Desulfurizations are most efficiently per-formed with Raney nickel (with or without hydrogen G.R. Pettit, 1962 A or with alkali metals in liquid ammonia or amines. The scheme below summarizes some classes of compounds most susceptible to hydrogenolysis. 

The available surface area of the catalyst gready affects the rate of a hydrogenation reaction. The surface area is dependent on both the amount of catalyst used and the surface characteristics of the catalyst. Generally, a large surface area is desired to minimize the amount of catalyst needed. This can be accomphshed by using either a catalyst with a small particle size or one with a porous surface. Catalysts with a small particle size, however, can be difficult to recover from the material being reduced. Therefore, larger particle size catalyst with a porous surface is often preferred. A common example of such a catalyst is Raney nickel. 

A solution of 20 g of 2-chloro-2. nitrobenzophenone in 450 ml of ethanol was hydrogenated at normal pressure and room temperature with Raney nickel. After uptake of about 6 liters of hydrogen the catalyst was filtered off, and the alcohol then removed in vacuo. The residue was distilled in a bulb tube at 0.4 mm and a bath temperature of 150° to 165°C giving a yellow oil. The oil was dissolved in alcohol, and on addition of water, needles of 2.amino.2. chlorobenzophenone melting at 58° to 60°C were obtained. 

The 1-(N-ethyl-N-2-hydroxyethylamino)-4-pentanone from above (284.2 grams) was dissolved in 300 grams of 28% ammoniacal methanol and reduced catalytically with Raney nickel (at an initial pressure of 1,000 pounds) at room temperature. After 24 hours the catalyst was filtered off and the product distilled in vacuo through a column, yielding 254 grams of a fraction distilling at 88.5° to 96°C at 0.3 mm and comprising mainly 5-(N-ethyl-N-2-hydroxyethylamino)-2-pentylamine. An analytical sample of this fraction distilled at 93°C at 0.6 mm. 

Nickel(II) chlorophyll derivatives undergo catalytic hydrogenation with Raney nickel as catalyst to yield stereoisomeric isobacteriochlorins in which ring A of the chlorophyll derivatives is reduced.16... 

Four pilot plant experiments were conducted at 300 psig and up to 475°C maximum temperature in a 3.07-in. i.d. adiabatic hot gas recycle methanation reactor. Two catalysts were used parallel plates coated with Raney nickel and precipitated nickel pellets. Pressure drop across the parallel plates was about 1/15 that across the bed of pellets. Fresh feed gas containing 75% H2 and 24% CO was fed at up to 3000/hr space velocity. CO concentrations in the product gas ranged from less than 0.1% to 4%. Best performance was achieved with the Raney-nickel-coated plates which yielded 32 mscf CHh/lb Raney nickel during 2307 hrs of operation. Carbon and iron deposition and nickel carbide formation were suspected causes of catalyst deactivation. 

Experiment HGR-13. A 2-ft bed of commercial catalyst was tested as a packed bed of 0.25-in. pellets (see Table I for bed properties). This test was similar to experiment HGR-14 in which the catalyst bed consisted of parallel plates sprayed with Raney nickel. The experiment was... 

Experiment HGR-14. The reactor was packed with 2 ft of parallel plates sprayed with Raney nickel (Table I) catalyst spraying and activation were as described under catalyst preparation. Operating conditions were practically the same as in experiment HGR-13 except for the periodic changes in the CGR ratio (see Figure 8 for reactor conditions and Figure 9 for product gas characteristics). 

Flame-Sprayed Raney Nickel Plates vs. Pellets of Precipitated Catalyst in a Packed Bed. Experiments HGR-13 and HGR-14 demonstrated that the performance of the plates sprayed with Raney nickel catalyst was significantly better than that of the precipitated nickel catalyst pellets. The sprayed plates yielded higher production of methane per pound of catalyst, longer catalyst life or lower rate of deactivation, lower CO concentration in the product gas, and lower pressure drop across the catalyst bed. 

The bed of parallel plates coated with Raney nickel catalyst was much more reactive than the bed of precipitated nickel. This was revealed by the generally lower CO concentration in the product gas during operation with the parallel plate bed for example, after 450 hrs stream time, it was 0.01% with the bed of sprayed Raney nickel (experiment HGR-14) and 0.05% with the bed of precipitated nickel catalyst (experiment HGR-13). 

The higher reactivity of the Raney nickel coated plates is also illustrated by the plots of catalyst temperature vs. bed length (Figure 10). The maximum bed temperature (indicative of near-completion of metha-nation) was consistently reached within a shorter distance from the gas inlet, and the slopes of the curves are correspondingly steeper for the more reactive bed of parallel plates coated with Raney nickel. 

The reductive amination of ketones can be carried out under hydrogen pressure in the presence of palladium catalysts. However, if enantiopure Q -aminoketones are used, partial racemization of the intermediate a-amino imine can occur, owing to the equilibration with the corresponding enam-ine [102]. Asymmetric hydrogenation of racemic 2-amidocyclohexanones 218 with Raney nickel in ethanol gave a mixture of cis and trans 1,2-diamino cyclohexane derivatives 219 in unequal amounts, presumably because the enamines are intermediates, but with excellent enantioselectivity. The two diastereomers were easily separated and converted to the mono-protected cis- and trans- 1,2-diaminocyclohexanes 220. The receptor 221 has been also synthesized by this route [103] (Scheme 33). 

Thioacetals and thioketals can also be made to undergo desul-phurisation with Raney nickel catalyst, thus effecting, overall, the indirect conversion of C=0— CH2 ... 

Dioxane reacts with Raney nickel catalyst almost explosively above 210°C. 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

Concurrent hydrogenation of acetone (A) and cyclohexene (B) in cyclohexane occurs with Raney nickel catalyst at 25. Catalyst concentration was 2 g/liter and the product compositions also are in g/liter. Determine the orders and relate the amounts of the reactants. 

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