Modified Raney Nickel Research Articles

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXVI. Asymmetric Hydrogenation of β-Keto Esters

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXVI. Asymmetric Hydrogenation of β-Keto Esters

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXVII. Asymmetric Hydrogenation of Acetylacetone

Abstract The asymmetric (enantioselective) hydrogenation process of acetylacetone (AA), which is a highly enolized compound, was studied by the use of catalysts modified with d-tartaric acid, and l-glutamic acid. AA corroded the Raney nickel catalyst during the hydrogenation. The modification protected the catalyst from corrosion, and the protective effects by the amino acids were greater than that by the hydroxy acid. The modification with tartaric acid increased the hydrogenation velocity of AA, but the amino acid hardly affected the hydrogenation velocity. The glutamic acid on the catalyst surface reacted with AA to form a Schiff base during the hydrogenation. The hydrogenation proceeded mainly by means of a two-step process via 2-pentanol-4-on. The modifying pH and temperature affected the asymmetric activity of the catalyst. In the first step of the hydrogenation, the catalyst modified with d-tartaric acid showed a high asymmetric activity, but the one modified with l-glutamic acid exhibited a low asymmetric activity as a result of the Schiff base formation. In the second step, the modification with d-tartaric acid promoted the formation of racemic 2,4-pentanediol (II), and the l-glutamic acid increased the production of meso II.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel Catalyst. XXV. Contributions of pH-Adjusting Reagents in the Asymmetric Hydrogenation

Abstract In the asymmetric hydrogenation of methyl acetoacetate with modified Raney nickel catalysts, the effects of pH-adjusting reagents were studied using ds-tartaric acid, ls-2-hydroxyisovaleric acid, l-glutamic acid, and l-aspartic acid as the modifying reagents. The effects of various metal ions and ammonium ions were investigated at pH 5.0. The asymmetric activity of the catalyst modified with the 2-hydroxy monocarboxylic acid or 2-amino dicarboxylic acid was not affected by the pH-adjusting reagents. However, 2-hydroxy dicarboxylic acid was markedly influenced by the reagents. The univalent metal ion was more effective than divalent or ammonium ions. Sodium hydroxide was the best pH-adjusting reagent. The adsorption state of the modifying reagent was discussed on the basis of the effects of the pH-adjusting reagent.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXIV. The Effect of Unsaturated Compounds on the Asymmetric Activity of the Catalyst

Abstract Dehydroacetic acid and methyl cis-3-acetoxycrotonate were picked out as trace impurities of the substrate, methyl acetoacetate. The effects of dehydroacetic acid, methyl cis-3-acetoxycrotonate, and diketene, which is the starting material for the preparation of methyl acetoacetate, on the asymmetric activities of catalysts modified with l-amino acids were examined in the hydrogenation of methyl acetoacetate. The above three compounds, when added to the hydrogenation system, raised the asymmetric activity of the catalyst. Also, simple unsaturated compounds, such as acetone and diethyl maleate, has a similar effect on the catalyst. The effects of the above unsaturated compounds on the asymmetric activities of the catalysts modified with l-amino acids were discussed, and it was suggested that the unsaturated compounds adsorb on the catalyst surface and might scavenge the asymmetrically uncontrolled active hydrogen absorbed on the catalyst surface.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXII

Abstract The state of the amino acid molecule used as a modifying reagent on a catalyst surface was investigated. From the relationship between the asymmetric activities of the catalysts modified with l-valine and its derivatives and the stability constants of the nickel chelates of l-valine and its derivatives, it was concluded that l-valine adsorbs like a ligand of the chelate on the catalyst surface. This conclusion was also supported by the finding that the asymmetric activity of the catalyst modified with the nickel l-valine chelate was higher than those of the catalysts modified with l-valine and its derivatives. Also, the asymmetric activities of the catalysts modified with l-histidine, l-serine, and l-proline, and with the nickel chelates of the above three l-amino acids were discussed on the basis of the stability constants of the nickel chelates of the above three l-amino acids, it was concluded that two conditions at least are necessary for the modifying reagent to be effective; it must adsorb stably on the catalyst surface, and it must have a structure affording effective asymmetric control of the substrate.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXI. The Effect of Water on the Asymmetric Activity of the Catalyst

Abstract The effect of water added to the hydrogenation system of methyl acetoacetate was investigated on catalysts modified with l-amino acids, their derivatives, and d- or l-hydroxy acids. In the absence of water, catalysts modified with all l-amino acids except l-serine and l-proline gave methyl ds(−)-3-hydroxybutyrate, and in the presence of water all the catalysts modified with l-amino acids gave methyl ls(+)-3-hydroxybutyrate. On the other hand, the catalysts modified with l- or d-hydroxy acids were not affected by the addition of water and gave an ls(+) or ds(−) hydrogenation product respectively. In the presence of water, the catalyst modified with the l-valine methyl ester gave an ls(+) product, while the catalysts modified with N-acetyl l-amino acids were not affected by water. As a whole, it was concluded that water added to the hydrogenation system affected the amino group of the modifying reagent on the catalyst surface, which might play an important role in the asymmetric control of the substrate approaching the catalyst surface. The water in the hydrogenation system also promoted the hydrogenation rate, regardless of the modifying reagents.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel Catalyst. XXIII

Abstract The ultraviolet spectra of acetylacetone and methyl acetoacetate adsorbed on evaporated nickel film modified with amino or hydroxy acid were measured. The spectroscopic data suggested that the adsorbed species of acetylacetone was affected by the modifying pH, that the interaction between acetylacetone and the hydroxy acid was different from that between acetylacetone and the amino acid, and also that methyl acetoacetate, similar to acetylacetone, chemisorbed with a pseudo aromatic ring on the nickel surface. Consequently, the above results strongly support the theory that in the asymmetic hydrogenation, the substrate, acetylacetone or methyl acetoacetate, approaches the catalyst surface in a form like a pseudo aromatic ring, that it is asymmetrically controlled by the modifying reagent adsorbed on the catalyst surface, and, further, that the ease of the adsorption of the substrate onto the catalyst determines the rate of asymmetric hydrogenation.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XVIII

Abstract The asymmetric activities of the catalysts modified with l-α-amino and l-α-hydroxy acids, which have two asymmetric centers on α, β and α, γ-carbons were studied, and the participation of the β- and γ-configurations to the asymmmetric activity of the catalyst was made clear. It was found that the S:β-configuration and the S:γ-configuration increase the asymmetric activity of the + and − directions respectively.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XX. The Effect of Additives on the Asymmetric Activity

Abstract The effects of various additives in methyl acetoacetate were tested in the asymmetric hydrogenation reaction. Among them, water has a particular effect on the asymmetric activities of the catalysts; in the presence of a certain amount of water, the catalysts modified with l-Glu, l-Val, and l-Ala hydrogenated methyl acetoacetate to methyl ls(+)3-hydroxybutyrate, while, without the addition of water, the catalysts promoted the hydrogenation to yield methyl ds(−)3-hydroxybutyrate. The catalyst modified with l-Ala at pH 6.0 and the catalyst modified with l-Glu at pH 5.0 and 100°C were especially sensitive to water, and both catalysts showed (+) asymmetric activity when a trace of water was also present. Even in the hydrogenation without the addition of water, the recovered catalysts modified with l-Glu, l-Val, and l-Ala from the hydrogenation in the presence of water gave results similar to those in the hydrogenation in the presence of water. The effect of water as an additive was discussed, and it was concluded that the water affects the asymmetric site of the catalyst rather than the keto-enol equilibrium of the substrate.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIX

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIX

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XVII

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XVII

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel Catalyst. XVI

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel Catalyst. XVI

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XV. Asymmetric Hydrogenation of Metal Chelate Compound

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XV. Asymmetric Hydrogenation of Metal Chelate Compound

Asymmetric Hydrogenation of C=N Double Bond with Modified Raney Nickel 1. New Determination Method for the Reaction Mechanism Using Asymmetric Catalyst

Abstract The hydrogenation process of ethyl 2-acetoximinopropionate was investigated by means of a novel technique using asymmetric hydrogenation with an asymmetrically modified R–Ni catalyst. It was found that the hydrogenation of ethyl 2-acetoximinopropionate to ethyl alaninate proceeded in two steps through ethyl acetoxyalaninate, and that the asymmetric hydrogenation was performed in the step of the formation of ethyl acetoxyalaninate from ethyl 2-acetoximinopropionate. Besides, the asymmetric reductive amination of ethyl pyruvate was tested with an asymmetrically modified R–Ni catalyst.

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIV

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIV

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIII. Modification with Peptides

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XIII. Modification with Peptides

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XII

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XII

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XI

Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XI

Asymmetric Hydrogenation with Modified Raney Nickel. X. Effect of the β-Substituent of α-Amino Acid as a Modifying Reagent

Asymmetric Hydrogenation with Modified Raney Nickel. X. Effect of the β-Substituent of α-Amino Acid as a Modifying Reagent

Asymmetric Hydrogenation with Modified Raney Nickel. IX

Abstract The asymmetric hydrogenation catalysts were prepared from the Raney nickel catalyst by modifying it with ls-3,3-dimethyl-2-hydroxybutyric acid and the corresponding amino acid, l-t-leucine, which have most methyl groups at the β-position. The asymmetric activities of the catalysts were measured by the hydrogenation of the methyl acetoacetate to methyl 3-hydroxybutyrate. The asymmetric activity of the catalyst modified with an aqueous solution of ls-3,3-dimethyl-2-hydroxybutyric acid was very low, and the direction of asymmetric activity at pH 5.0 was inverted by the temperature of the modifying solution. However, there was a high asymmetric activity in the catalyst modified with l-t-leucine, and this activity was not so influenced by the temperature of the modifying solution. The aysmmetric activities of catalysts modified with α-hydroxy acids and the corresponding amino acids reported in this paper and the previous papers are compared, and the effect of the bulk of the α-alkyl substituent of the modifying reagent upon the asymmetric activity of the catalyst is discussed.