485-64-3Relevant academic research and scientific papers
Kinetic Studies of the Enantioselective Hydrogenation of Ethyl Pyruvate Catalyzed by a Cinchona Modified Pt/Al2O3 Catalyst
Blaser, Hans-Ulrich,Jalett, Hans-Peter,Garland, Marc,Studer, Martin,Thies, Hans,Wirth-Tijani, Amina
, p. 282 - 294 (1998)
The kinetics of the hydrogenation of ethyl pyruvate to ethyl lactate on a 5% Pt/Al2O3 catalyst in toluene was investigated both in absence and in presence of the chiral modifier 10,11-dihydrocinchonidine. It was shown that all important prerequisites for obtaining reliable kinetic data for the reaction were fulfilled. The effects on rate and enantiomeric excess of catalyst loading, modifier and substrate concentrations, hydrogen pressure, and temperature were determined for the unmodified and the modified system. The modified reaction was approximately 20-30 times faster than the unmodified reaction. A significant increase of the enantiomeric excess from 1 to 40 bar was noticed. Apparent activation energies were estimated to be 4-6 kcal/mol. Rate equations were developed for various kinetic schemes on the basis of the Langmuir-Hinshelwood-Hougen-Watson formalism and fitted to the kinetic data. Several such schemes described the measured data reasonably well and in most cases explanations other than the one considered to be the most plausible were also in agreement with our data. For the unmodified catalyst, we propose a competitive adsorption of the α-ketoester and hydrogen and the addition of the first hydrogen atom to be rate determining. On a chiral site, the rate determining step (RDS) to the major enantiomer is proposed to be the addition of the second hydrogen, whereas the RDS for the minor enantiomer remains the first H addition. On the basis of this interpretation, different proposals advanced in the literature for the mode of action of the cinchona modified Pt catalyst were compared.
Enantioselective hydrogenation of ketopantolactone
Schuerch,Schwalm,Mallat,Weber,Baiker
, p. 275 - 286 (1997)
The enantioselective hydrogenation of ketopantolactone to R-(-)-pantolactone was investigated on 5 wt% Pt/Al2O3 chirally modified with cinchonidine. The influence of catalyst pretreatment conditions, hydrogen pressure, temperature, solvent polarity, and catalyst, reactant, and modifier concentrations was studied in a slurry reactor. An enantiomeric excess (ee) of 79% at full conversion was achieved in toluene after optimization of pressure, temperature, and amount of modifier. Good ee could be obtained only after rigorous removal of traces of oxygen and water during catalyst pretreatment and from the hydrogenation reaction mixture. Molecular modeling studies (performed using molecular mechanics, semiempirical, and ab initio methods) provided a feasible structure for the diastereomeric transition complex formed between cinchonidine and ketopantolactone and an explanation for the observed enantiodifferentiation in apolar medium. The calculations indicate that formation of the complex affording R-(-)-pantolactone is energetically favored with cinchonidine, whereas the near enantiomer cinchonine favors S-pantolactone, in agreement with experimental observations. Interestingly, in apolar solvents, where the alkaloid modifier is not protonated, the modeling suggests similar structures for the diastereomeric transition complexes for the hydrogenation of ketopantolactone and methyl pyruvate.
Electrospray ionization-mass spectrometry in the enantioselective hydrogenation of ethyl pyruvate catalyzed by dihydrocinchonidine modified Pt/Al2O3 in acetic acid
Bartok, Mihaly,Balazsik, Katalin,Szoelloesi, Gyoergy,Bartok, Tibor
, p. 168 - 176 (2002)
The enantioselective hydrogenation of ethyl pyruvate (EtPy) on Pt-alumina (E 4759), Pt black, and Pt black + alumina (mixture) catalysts modified by dihydrocinchonidine (DHCD) in acetic acid was studied by electrospray ionization-mass spectrometry (ESI-MS). Application of the ESI-MS technique led to the recognition of a novel-type compound, O+[Al(OAc)2]3 (oxonium ions). The effect of the DHCD concentration, temperature, and oxonium cations on the reaction rate and the enantioselectivity has been studied. Using the Engelhard 4759 catalyst in acetic acid under mild experimental conditions (room temperature, hydrogen pressure 1 bar, DHCD concentration 0.01 mM/L) an optical yield of 92% can be achieved. The high enantioselectivity is accompanied by the following turnovers: EtPy/DHCD > 43,000, EtPy/Ptsurface > 1000, TOF = 1-2 s-1, and DHCD/Ptsurface ratio = 0.0072. The enantioselectivity reducing factor is identified by ESI-MS as the gradual hydrogenation of the quinoline skeleton of DHCD that becomes more pronounced with increasing temperature and hydrogenation time. The discovery of oxonium cations, the extremely low DHCD/Ptsurface ratio, and the new data obtained by the Pt black + alumina mixture made possible an interpretation of the mechanism of the heterogeneous enantioselective hydrogenation of α-ketoesters.
Environmentally responsible, safe, and chemoselective catalytic hydrogenation of olefins: ppm level Pd catalysis in recyclable water at room temperature
Gallou, Fabrice,Gao, Eugene S.,Lipshutz, Bruce H.,Takale, Balaram S.,Thakore, Ruchita R.
supporting information, p. 6055 - 6061 (2020/10/14)
Textbook catalytic hydrogenations are typically presented as reactions done in organic solvents and oftentimes under varying pressures of hydrogen using specialized equipment. Catalysts new and old are all used under similar conditions that no longer reflect the times. By definition, such reactions are both environmentally irresponsible and dangerous, especially at industrial scales. We now report on a general method for chemoselective and safe hydrogenation of olefins in water using ppm loadings of palladium from commercially available, inexpensive, and recyclable Pd/C, together with hydrogen gas utilized at 1 atmosphere. A variety of alkenes is amenable to reduction, including terminal, highly substituted internal, and variously conjugated arrays. In most cases, only 500 ppm of heterogeneous Pd/C is sufficient, enabled by micellar catalysis used in recyclable water at room temperature. Comparison with several newly introduced catalysts featuring base metals illustrates the superiority of chemistry in water.
Hydrogenation of Ketones on Dispersed Chiral-Modified Palladium Nanoparticles
Nindakova,Strakhov,Kolesnikov
, p. 199 - 207 (2018/03/26)
Hydrogenation of acetophenone and esters of ketoacids with molecular hydrogen in the presence of the Pd(acac)2-cinchonidine–H2 catalytic system has been studied. The dependence of the molar ratio of (–)-cinchonidine/Pd on size and shape of palladium nanoparticles, formed in the system, also on reaction rate and enantioselectivity has been established. The nature of the regularities observed for the Pd(acac)2-cinchonidine–H2 catalytic system was discussed.
Enantioselective phase-transfer catalyzed alkylation of 1-methyl-7-methoxy-2-tetralone: An effective route to dezocine
Li, Ruipeng,Liu, Zhenren,Chen, Liang,Pan, Jing,Zhou, Weicheng
supporting information, p. 1421 - 1427 (2018/06/29)
In order to prepare asymmetrically (R)-(+)-1-(5-bromopentyl)-1-methyl-7-methoxy-2-tetralone (3a), a key intermediate of dezocine, 17 cinchona alkaloid-derived catalysts were prepared and screened for the enantioselective alkylation of 1-methyl-7- methoxy-2-tetralone with 1, 5-dibromopentane, and the best catalyst (C7) was identified. In addition, optimizations of the alkylation were carried out so that the process became practical and effective.
Substrate-controlled adsorption of cinchonidine during enantioselective hydrogenation on platinum
Schmidt, Erik,Mallat, Tamas,Baiker, Alfons
experimental part, p. 140 - 150 (2010/09/09)
It is commonly accepted that the origin of enantioselection on chirally modified metals is the control of the adsorption and reactivity of the substrate by the chiral environment of the modifier. Here, we provide the first experimental evidence to a mutual process, namely, that the substrate controls the adsorption and reactivity of cinchonidine (CD) on the metal surface. Our approach is to follow the competing hydrogenation of the quinoline ring, the anchoring moiety of CD, in the presence or absence of an activated ketone substrate. On Pt/Al2O3 in the weakly interacting solvent toluene, CD (and 10,11-dihydro-CD) favors a C(4′) - pro(S) adsorption geometry and saturation of the heteroaromatic ring gives 1′,2′, 3′,4′(S),10,11-hexahydro-CD {(S)-CDH6} in excess. Addition of methyl benzoylformate, ketopantolactone, or ethyl pyruvate inverts the dominant conformation of CD to C(4′) - pro(R) as indicated by the major product (R)-CDH6, and even the rate is higher by about 30% ("inverse ligand acceleration"). Acetic acid that interacts strongly with CD exerts a similar effect on quinoline hydrogenation. In contrast, the product α-hydroxyester interacts weakly with CD, decelerates the hydrogenation of the quinoline ring and the de of CDH6 depends on the chirality of the α-hydroxyester. These unexpected observations provide a fundamentally new insight into the complexity of the surface conformation of CD and the origin of high enantioselectivity on cinchona-modified Pt.
Indium-mediated catalytic enantioselective allylation of N -benzoylhydrazones using a protonated chiral amine
Kim, Sung Jun,Jang, Doo Ok
supporting information; experimental part, p. 12168 - 12169 (2010/10/03)
A catalytic enantioselective indium-mediated allylation of N-benzoylhydrazones in conjunction with a protonated chiral amine affording enantioenriched homoallylic amines with an extremely high level of enantioselectivity and chemical yield was developed.
Polymeric chiral phase-transfer catalysts derived from cinchona alkaloids for enantioselective synthesis of α-amino acids
Lee, Jeong-Hee,Yoo, Mi-Sook,Jung, Ji-Hee,Jew, Sang-sup,Park, Hyeung-geun,Jeong, Byeong-Seon
, p. 7906 - 7915 (2008/02/09)
A series of dimeric/trimeric chiral quaternary ammonium salts derived from cinchona alkaloids were designed as efficient and practical chiral phase-transfer catalysts (PTCs). Presented are the details on the development of the dimeric PTCs for the synthesis of optically active α-amino acid derivatives and the optimization of the reaction variables suitable for the dimeric PTCs. The 1,3-phenyl- and the 2,7-naphthyl-linked dimeric PTCs showed excellent catalytic capability on the reactivity and enantioselectivity in the catalytic phase-transfer alkylation of N-(diphenylmethylene)glycine tert-butyl ester (1). A variety of α-amino acid derivatives were obtained with high enantiopurities using the dimeric PTCs, especially the 2,7-naphthyl-dimer 41, in a very practical manner.
Phase-transfer-catalyzed asymmetric acylimidazole alkylation
Andrus, Merritt B.,Christiansen, Michael A.,Hicken, Erik J.,Gainer, Morgan J.,Bedke, D. Karl,Harper, Kaid C.,Mikkelson, Shawn R.,Dodson, Daniel S.,Harris, David T.
, p. 4865 - 4868 (2008/03/14)
(Chemical Equation Presented) 2-Acylimidazoles are alkylated under phase-transfer conditions with cinchonidinium catalysts at -40°C with allyl and benzyl electrophiles in high yield with excellent enantioselectivity (79 to >99% ee). The acylimidazole substrates are made in three steps from bromoacetic acid via the N-acylmorpholine adduct. The catalyst is made in high purity allowing for S-product formation (6-20 h) under mild conditions, consistent with an ion-pair mechanism. The products are readily converted to useful ester products using methyltriflate and sodium methoxide, via a dimethylacylimidazolium intermediate without racemization. The process is efficient, direct, and amenable to other electrophiles and transformations that proceed through an enolate intermediate.
