17040-62-9Relevant academic research and scientific papers
Preparation of cinchonidine-modified palladium catalysts for the enantioselective hydrogenation of (E)-α-phenylcinnamic acid
Nitta,Kubota,Okmoto
, p. 2635 - 2641 (2000)
The enantioselective hydrogenation of the C=C double bond in (E)-α-phenylcinnamic acid has been studied with different supported Pd catalysts prepared by a precipitation-deposition method and modified with cinchonidine. The influences of the support materials and the texture, Pd loadings, precipitation procedures, and reduction conditions on the hydrogenation activity and enantioselectivity are described. The texture of the supports has a decisive influence on the behavior of the resulting catalysts, especially when it is pre-reduced at elevated temperatures. Nonporous titania with a relatively small specific surface area was found to be the most suitable. The use of a large excess amount of precipitant resulted in an increase in the amount of residual Na and in a drastic decrease in the amount of residual Cl, leading to a remarkable increase in the activity. The elimination of both the residual Na and Cl from the catalyst precursor was found to be preferable for the enantioselectivity. A considerable increase in the enantioselectivity was observed when a 5wt%Pd/TiO2 catalyst, prepared with nonporous titania, was reduced in a hydrogen flow at elevated temperatures up to 473 K. The influences of the surface area of nonporous supports, Pd loadings, and reduction conditions strongly suggest that the enantioselectivity of the modified Pd/TiO2 catalysts depends on the Pd dispersion; a relatively low dispersion around 0.2-0.3 was found to be optimal.
Carbonaceous materials as catalyst supports for the enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Effect of the support acidity
Trung, Tran Si Bui,Kim, Yeonwoo,Kang, Sungho,Kim, Sehun,Lee, Hangil
, p. 319 - 325 (2015)
A systematic comparative study of carbonaceous materials as catalyst supports for the asymmetric heterogeneous hydrogenation of (E)-α-phenylcinnamic acid (PCA) was performed to investigate the influence of the supports on the enantioselectivity. A series of Pd-based catalysts supported on activated carbon (AC), graphene oxide (GO), or carbon nanotubes (CNTs) was prepared using deposition methods. The hydrogenation reactions of PCA were conducted with/without the pretreatment of the prepared catalysts, and the results showed a significant drop of enantiomeric excess (ee) when the Pd/GO catalyst was used (27%) compared to that obtained from the Pd/AC (70%) and Pd/CNTs (66%) catalysts. This drop of ee values was assigned to the abundance of acidic sites present on the Pd/GO catalyst, as revealed by TGA, FT-IR, and TPD-NH3 analyses. The effect of the support acidity on the ee was ascribed to the preferential adsorption mode of cinchonidine (CD) on the GO surface via electrostatic interactions between the negatively charged oxygen functional groups present on the GO surface and the positively protonated amine groups of the CD molecule.
Conversion dependence of enantioselective hydrogenation of (E)-α-phenylcinnamic acid on cinchonidine-modified Pd/TiO2 catalyst
Nitta, Yuriko,Kobiro, Kazuya
, p. 897 - 898 (1996)
The enantioselectivity of a cinchonidine-modified Pd/TiO2 catalyst varied with the extent of conversion in the hydrogenation of (E)-α-phenylcinnamic acid. The incremental enantioselectivity reached a maximum at an early stage of the reaction Under optimized reaction conditions, optical yields of up to 72%e.e. of (S)-(+)-2,3-diphenylpropionic acid were obtained at 100% conversion.
Adsorption and performance of chiral cinchona alkaloid modifiers over Pd/C catalyst for enantioselective hydrogenation of α-phenylcinnamic acids
Nakatsuji, Makoto,Misaki, Tomonori,Okamoto, Yasuaki,Sugimura, Takashi
, p. 1187 - 1191 (2016)
The enantioselective hydrogenation reactions of α-phenylcinnamic acid (PCA) and 4,4′-dimethoxy α-phenylcinnamic acid (DMPCA) were carried out over chiral cinchona alkaloidmodified Pd/C. Two sets of the modifiers were employed to get deeper insights into the effects of relative adsorption strength between the modifier and the substrate on the enantioselectivity; cinchonidine (CD)/cinchonine (CN) and quinine (QN)/quinidine (QD). The performances of the two sets of modifiers were compared by systematically varying the modifier concentration over a wide range. It was clearly substantiated that the origin of the low selectivity observed with QN/QD at an ordinary concentration is primarily due to its weak adsorption strength on Pd metal surface, which originates from the steric hindrance of the methoxy substituent at C6. A new modifier, 6-hydroxy CD, was found to exhibit a performance comparable to that of CD, implying that the steric hindrance of the 6-methoxy group of QN/QD is much more influential than the electronic effects.
Potent new heterogeneous asymmetric catalysts
Rouzaud, Jacques,Jones, Matthew D.,Raja, Robert,Johnson, Brian F. G.,Thomas, John Meurig,Duer, Melinda J.
, p. 1753 - 1759 (2003)
A set of new, air-stable. Rh1-based heterogeneous asymmetric hydrogenation catalysts have been synthesised, characterised, and tested. Individual members of this new family all exhibit good enantioselectivity.
Hydrogen pressure dependence in enantioselective hydrogenation of α,β-unsaturated acids with cinchonidine-modified Pd/TiO2 catalyst
Nitta
, p. 1971 - 1972 (2001)
The enantioselectivity in the hydrogenation of (E)-2,3-diphenyl-2-propenoic acid with a cinchonidine-modified 5wt%Pd/TiO2 catalyst decreases with increasing pressure of hydrogen up to 5 MPa contrary to the tendency observed in the hydrogenation of aliphatic acids, probably because of the difference in the adsorption strength of the substrates on both modified and unmodified sites.
Importance of product desorption in enantioselective hydrogenation of (E)-α-phenylcinnamic acid with a cinchonidine-modified Pd/TiO2 catalyst: Effect of additives
Nitta, Yuriko
, p. 635 - 636 (1999)
Addition of amines, especially benzylamine, to the reaction mixture of (E)-α-phenylcinnamic acid with a cinchonidinemodified palladium catalyst resulted in much enhanced activities and fairly increased enantioselectivities. The preferential acceleration of the selective reaction is attributable to the effective desorption, assisted by the added base, of the hydrogenated molecules from the modified sites.
Enantioselective hydrogenation of α-phenylcinnamic acids over cinchonidine-modified Pd/C commercial catalysts
Sato, Haruka,Mameda, Takuya,Nakai, Kengo,Misaki, Tomonori,Haruyama, Yuichi,Sonobe, Seiji,Kubota, Takeshi,Okamoto, Yasuaki,Sugimura, Takashi
, p. 31 - 45 (2016)
Enantioselective hydrogenation of α-phenylcinnamic acid (PCA) and p,p′-dimethoxyphenylcinnamic acid (DMPCA) was studied over a variety of commercial 5 % Pd/C catalysts to reveal catalyst properties suitable for obtaining high enantioselectivity. The catalysts were characterized by CO adsorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). It is confirmed that pretreatment at 353 K under atmospheric pressure of H2 before modification with cinchonidine is very effective for all the Pd/C catalysts used here to improve the selectivity and reaction rate. It is suggested that the distribution of Pd metal particles is crucial to attain high selectivity (ee% = 79 ± 1 for PCA, 89 ± 2 for DMPCA): a uniform or eggshell-type distribution of Pd is more suitable than an egg-white or egg-yolk-type distribution. It is also suggested that the dispersion of Pd metal particles controls the enantioselectivity over cinchonidine (CD)-modified Pd/C catalysts. XPS techniques are proposed to provide a convenient method to find desirable catalysts. The choice of such Pd/C catalysts could facilitate high-throughput guided study on highly enantioselective hydrogenation of α,β-unsaturated carboxylic acids.
Direct synthesis of in-situ chirally modified palladium nanocrystals without capping agents and their application in heterogeneous enantioselective hydrogenations
Gao, Xiuyun,Chen, Xueying,Li, Zhen Hua,He, Heyong
, p. 6100 - 6110 (2019)
Shape-controlled metal nanocrystals possess the advantages of specific atomic arrangement on the surface and uniform size, which can act as ideal model catalysts for heterogeneous enantioselective catalytic studies. Nevertheless, capping agents are commonly retained on the surface of the as-synthesized metal nanocrystals, which may hinder the necessary interaction between the substrate and the chiral modifiers coadsorbed on the metal surface for chiral recognition. In this paper, we directly synthesized dendritic or cubic palladium nanocrystals in-situ modified by chiral modifiers such as cinchonidine (CD) or S-proline through a one-pot strategy by replacing the conventional capping agents with the chiral modifiers. The as-prepared CD-modified Pd nanodendrite catalyst already exhibits enantioselectivity in the asymmetric hydrogenation of (E)-α-phenylcinnamic acid without subsequent chiral modification processes. The in-situ S-proline-modified Pd nanocube catalyst shows higher enantioselectivity than nanocubes synthesized with polyvinylpyrrolidone (PVP) or cetyltrimethylammonium bromide (CTAB) as traditional capping agents in asymmetric hydrogenation of acetophenone. Chiral modifiers have dual functions (both shape-control agents and catalytic functional molecules), which can not only eliminate the adverse effect of traditional capping agents (such as PVP) on heterogeneous enantioselective hydrogenations but also simplify the follow-up chiral modification step of metal catalysts, providing a simple and efficient synthetic protocol to directly prepare in-situ chirally modified metal nanocrystal catalysts.
Enantioselective hydrogenation of (E)-α-phenylcinnamic acid on Pd/TiO2 catalyst modified by cinchona alkaloids : Effect of modifier structure
Nitta, Yuriko,Shibata, Akira
, p. 161 - 162 (1998)
The effect of modifier structure on enantioselectivity and activity in the hydrogenation of (E)-α-phenylcinnamic acid with cinchona-modified Pd/TiO2 catalyst has been found to be in contrast to the hydrogenation of α-ketoesters with modified platinum catalysts. It is suggested that the interaction of the hydroxyl group at C9 of cinchonidine with the carboxyl group in the substrate is crucial to induce a high enantioselectivity.
