The role of alkali halides in the enantioselective hydrogenation of a prochiral keto compound over modified nickel catalysts

doi:10.1016/0304-5102(84)85098-1

Journal of Molecular Catalysis

Volume 27, Issue 3, December 1984, Pages 387-395

https://doi.org/10.1016/0304-5102(84)85098-1 Get rights and content

Abstract

Influences of alkali halides on the catalysis of tartrate-modified nickel in the asymmetric hydrogenation of a prochiral keto compound have been studied. The effects are shown to be dependent on the concentration of these salts in the reaction mixture. At low concentrations of Na or K halides the selectivity is enhanced, but at higher concentrations it drops below the value found in the absence of alkali halides. The concentration required for the selectivity maximum is two orders of magnitude higher for NaBr than for NaI, in accordance with the much stronger adsorption of the latter, found by direct determination of the adsorbed quantities. For a given anion, the effects on the selectivity strongly depend on the nature of the cation. The results are rationalized tentatively by assuming that alkali ions, by coordination with tartrate and substrate oxygens, modify the stereochemistry of the product-determining surface complex.

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Cited by (27)

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Citation Excerpt :
With the exception of the material with Ni/Zn ratio equal to 2.94, Ni leaching was diminished when using NaBr. According to Bostelaar and Sachtler [52], NaBr lowers the solubility of adsorbed species resulting in an increased stability of the complexed Ni on the surface. This is supported by Kukula et al. [53], who speculated that the use of a salt would diminish the possibility for Ni and its compounds to leach out from the surface.
The catalytic properties of tartaric acid–nickel supported catalysts obtained from hydrotalcite-like compounds have been assessed in the enantioselective hydrogenation of methyl acetoacetate. Ni particle size above a minimum threshold of ca. 20 nm was found to influence enantioselectivity. For materials with similar Ni crystallite size, e.e. progressively lowers as Mg is incorporated to Ni/Al, whereas incorporation of Zn improves e.e. for all Ni/Zn ratios. In general, activity is higher on Ni/Mg/Al than on Ni/Zn/Al series. Moreover, the synthetic method to obtain hydrotalcite-like compounds affects the catalytic properties of the resultant catalysts. For a series of materials of the same composition, the urea hydrolysis method leads to catalysts with enantiodifferentiation ability, whereas the coprecipitation method does not. Variables of reaction during chiral modification, such as pH and tartaric acid concentration, proved not to have a major effect on enantioselectivity. Furthermore, no direct correlation between the amount of tartaric acid adsorbed onto, or Ni leached from the surface, and the enantiodifferentiation ability of the catalysts was found.
Application of an in situ modification of nickel catalysts to the enantio-differentiating hydrogenation of methyl acetoacetate
2001, Journal of Molecular Catalysis A: Chemical
In situ modification ((R,R)-tartaric acid and NaBr were directly added to the reaction media) of fine Ni powder (FNiP) and reduced Ni catalysts was applied to the enantio-differentiating hydrogenation of methyl acetoacetate (MAA). The high optical yield of 89% was attained by the reduced Ni catalyst. This is the highest value reported so far for the hydrogenation of methyl acetoacetate using the in situ modification. The addition of a small amount of NaBr to the reaction media increased both the optical yield and hydrogenation rate, while the hydrogenation rate decreased with the addition of NaBr to the modification solution for the conventional modification method. NaBr added to the reaction media for the in situ modification would have both of the following roles: (i) Na⁺ increased the optical yield and the hydrogenation rate; and (ii) Br⁻ increased the optical yield and decreased the hydrogenation rate.
Enantio-differentiating hydrogenation of methyl acetoacetate over tartaric acid-NaBr-modified supported nickel catalyst prepared from nickel acetylacetonate
2000, Journal of Molecular Catalysis A: Chemical
Supported nickel catalysts were prepared from nickel acetylacetonate, and then modified in a solution containing tartaric acid and sodium bromide. The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over this catalyst. The effects of the preparation variables of the supported nickel catalysts on the optical yield and the effects of the conditions for the nickel surface modification on the optical yield were examined. The catalysts were also characterized by XRD and TEM.
The maximal optical yield of 87% was attained when crystallized α-alumina (sumico rundum) was used as a support.
New preparation method of asymmetrically modified supported nickel catalysts for the enantio-differentiating hydrogenation of methyl acetoacetate
1998, Studies in Surface Science and Catalysis
Supported nickel catalysts were prepared from nickel acetylacetonate, and then modified in a solution containing tartaric acid and NaBr. The effects of the catalyst preparation conditions on the optical yields and those of the Ni surface modification process on optical yields were examined in the enantio-differentiating hydrogenation of methyl acetoacetate. The maximal optical yield of 86% was attained when zeolite was used as the support.
Enantio-differentiating hydrogenation of prochiral ketones over modified nickel
1997, Catalysis Today
This article reviews the enantio-differentiating hydrogenation of prochiral ketones over a asymmetrically modified catalyst, focusing on the hydrogenation of simple prochiral alkanones. The parameters affecting catalytic activity and enantiodifferentiating ability are considerable in number, and each parameter should be optimized in order to attain a highperformance enantio-differentiating catalyst. Optimization of the parameters and the mode of enantio-differentiation are discussed and compared with the enantio-differentiating hydrogenation of β-ketoesters.
The liquid-phase hydrogenation of methyl acetoacetate using nickel-exchanged Y zeolite catalysts: Part III. The role of surface acidity
1993, Zeolites
The liquid-phase hydrogenation of methyl acetoacetate (MAA) in n-butanol was investigated using a range of nickel-exchanged Y zeolites with different nickel loadings and enriched to various levels with Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ cocations. While the supported nickel metal promoted the formation of methyl 3-hydroxybutyrate (MHB), the β-keto ester also underwent a transesterification with n-butanol at the acid sites to form n-butyl acetoacetate (BAA). Butyl 3-hydroxybutyrate (BHB) was also isolated in the product mixture and it is posited that BHB is produced at the metal sites by the hydrogenation of BAA and at the acid sites by the transesterification of MHB with n-butanol. The composition of the product mixture is correlated to the reaction time and temperature and the number, location, and strength of the large cage acid sites. It was found that ethyl acetoacetate (EAA) underwent transesterification to a greater extent than was observed for MAA. The transesterification step is proposed to proceed via a carbenium ion intermediate where the β-keto ester is adsorbed dissociatively at the supercage Bronsted acid sites. Transesterification activity was totally suppressed by treating the catalysts with ammonia and pyridine.

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The role of alkali halides in the enantioselective hydrogenation of a prochiral keto compound over modified nickel catalysts

Abstract

J. Catal.

Inorg. Chem.

Pure Appl. Chem.

Chem. Lett.

Bull. Chem. Soc. Jpn.

Bull. Chem. Soc. Jpn.

J. Mol. Catal.