- Selective Reduction of C=O in α,β-Unsaturated Carbonyls through Catalytic Hydrogen Transfer Reaction over Mixed Metal Oxides
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Selective reduction of α,β-unsaturated carbonyls was studied over CoO-ZrO2 using propan-2-ol as a hydrogen donor and KOH as promoter in a liquid phase reaction. The catalyst used for this synthetically useful transformation showed considerable level of reusability as well as good activity.
- Sonavane, Sachin U.,Jayaram, Radha V.
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- A simple and useful synthetic protocol for selective deprotection of tert-butyldimethylsilyl (TBS) ethers
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A wide variety of tert-butyldimethylsilyl ethers 1 can be easily cleaved to the corresponding parent hydroxyl compound 2 in the presence of 5 mol % of acetonyltriphenylphosphonium bromide (ATPB) at room temperature. In addition, tert-butyldiphenylsilyl ethers can also be cleaved by using 20 mol % of the same catalyst. Alkyl tert-butyldimethylsilyl ethers can be deprotected to the hydroxyl compounds chemoselectively in the presence of aryl tert- butyldimethylsilyl ethers. Some of the major advantages are mild reaction conditions, no aqueous workup, high efficiency and chemoselectivity and compatibility with other protecting groups; no brominations occur in the aromatic ring under these experimental conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Khan, Abu T.,Ghosh, Subrata,Choudhury, Lokman H.
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- A NOVEL REDUCING AGENT DERIVED FROM FORMIC ACID AND TWO EQUIVALENTS OF A GRIGNARD REAGENT: CHEMOSELECTIVE REDUCTION OF ALDEHYDES
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Aldehydes are reduced at a moderate rate by use of a novel reagent obtained by the addition of two molar eqivalents of ethylmagnesium bromide to formic acid in tetrahydrofuran solution.Under similar conditions the reduction of ketones proceeds quite slowly.
- Babler, James H.,Invergo, Benedict J.
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- Selective deprotection of diphenylmethylsilylethers of allylic and benzylic alcohols
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Selective deprotection of diphenylmethylsilylethers of allylic or benzylic alcohols is achieved by U.V. irradiation in presence of phenanthrene (1eq.) in methylene chloride and methanol. Under these conditions, other ethers containing the t-butyldimethylsilyl or the t-butyldiphenylsilyl group are recovered unmodified.
- Piva,Amougay,Pete
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- Ni- and pd-catalyzed synthesis of substituted and functionalized allylic boronates
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Two highly efficient and convenient methods for the synthesis of functionalized and substituted allylic boronates are described. In one procedure, readily available allylic acetates are converted to allylic boronates catalyzed by Ni/PCy3 or Ni/PPh3 complexes with high levels of stereoselectivity and in good yields. Alternatively, the borylation can be accomplished with commercially available Pd catalysts [e.g., Pd 2(dba)3, PdCl2, Pd/C], starting with easily accessed allylic halides.
- Zhang, Ping,Roundtree, Ian A.,Morken, James P.
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- Chemoselective reduction of α,β-unsaturated carbonyls over novel mesoporous CoHMA molecular sieves under hydrogen transfer conditions
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Chemoselective reduction of α,β-unsaturated carbonyls to the corresponding alcohols was achieved by a catalytic transfer hydrogenation (CTH) method using cobalt(II)-substituted hexagonal mesoporous aluminophosphate (CoHMA) molecular sieve catalyst. Further, the catalyst was found to be promising as a heterogeneous catalyst as the yield was practically unchanged after up to six cycles.
- Selvam,Sonavane,Mohapatra,Jayaram
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- FOUR ALIPHATIC ESTERS OF CHAMAEMELUM FUSCATUM ESSENTIAL OILY
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Four new aliphatic esters were isolated from the essential oil of Chamaemelum fuscatum.Three are esters of methacrylicacid with 2-methyl-2E-butenol, 2-hydroxy-2-methyl-3-butenol and 2-hydroxy-2-methyl-3-oxobutanol.The other is neryl isovalerate obtained in addition to known compounds.The structures were determined by spectral measurements and by synthesis.Key Word Index-Chamaemelum fuscatum; Compositae; essential oil; aliphatic esters.
- Pascual-T., J. De,Caballero, E.,Caballero, C.,Anaya, J.,Gonzalez, M. S.
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- Oxidation of α-hydroxy containing monoterpenes using titanium silicate catalysts: Comments on regioselectivity and the role of acidity
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The regioselective epoxidation of monoterpenes in the liquid phase has been studied using the titanosilicates TS-1 and TiAlβ. A range of oxidants (hydrogen peroxide, tert-butyl hydroperoxide and urea-hydrogen peroxide complex) have been studied in detail. The allylic alcohols linalool and geraniol have been studied alongside the non-allylic alcohol citronellol and the diene dihydromyrcene to help determine the role of the hydroxy group in these reactions. Dihydromyrcene is selectively epoxidised at the more electron rich double bond regardless of the catalyst-oxidant-solvent system used. Geraniol can undergo allylic assisted epoxidation with TS-1-acetone-hydrogen peroxide and TiAlβ-acetonitrile-urea-hydrogen peroxide. With TiAlβ-hydrogen peroxide-methanol, the reaction shows an induction period in the conversion of geraniol which is considered to be characteristic of the autocatalytic removal of titanium from the catalyst framework. Reactions with citronellol show this titanium removal is entirely due to the presence of the allylic alcohol moiety. Finally, epoxidation of linalool and the subsequent in situ conversion of the epoxide to the furano- and pyrano-oxides were studied. The ratio of furano- and pyrano-oxides formed was considered to be due, in part, to the pore geometry and the Br?nsted acidity of the catalyst.
- Schofield, Lee J.,Kerton, Owain J.,McMorn, Paul,Bethell, Donald,Ellwood, Simon,Hutchings, Graham J.
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- Method for preparing nerol from geraniol
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The invention provides a method for preparing nerol from geraniol. According to the method, calix[4] aryl zinc compound catalysts are used for catalyzing geraniol to be converted into nerol. The method is especially suitable for converting a natural or artificially synthesized mixture of nerol and geraniol in any proportion into nerol.
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Paragraph 0046-0047
(2021/01/25)
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- Metal-doped mesoporous ZrO2catalyzed chemoselective synthesis of allylic alcohols from Meerwein-Ponndorf-Verley reduction of α,β-unsaturated aldehydes
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Meerwein-Ponndorf-Verley reduction (MPVr) is a sustainable route for the chemoselective transformation of α,β-unsaturated aldehydes. However, tailoring ZrO2 catalysts for improved surface-active sites and maximum performance in the MPV reaction is still a challenge. Here, we synthesized mesoporous zirconia (ZrO2) and metal-doped zirconia (M_ZrO2, M = Cr, Mn, Fe, and Ni). The incorporation of metal dopants into zirconia's crystal framework alters its physico-chemical properties such as surface area and total acidity-basicity. The prepared catalysts were evaluated in the MPVr using 2-propanol as a hydrogen donor under mild reaction conditions. The catalysts' remarkable reactivity depends mainly on their surface mesostructure's intrinsic properties rather than the specific surface area. Cr_ZrO2, which is stable and sustainable, presented superior activity and 100% selectivity to unsaturated alcohols. The synergistic effect between Cr and Zr species in the binary oxide facilitated the Lewis acidity-induced performance of the Cr_ZrO2 catalyst. Our work presents the first innovative application of a well-designed mesoporous Cr_ZrO2 in the green synthesis of unsaturated alcohols with exceptional reactivity. This journal is
- Akinnawo, Christianah Aarinola,Bingwa, Ndzondelelo,Meijboom, Reinout
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p. 7878 - 7892
(2021/05/13)
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- A Bifunctional Copper Catalyst Enables Ester Reduction with H2: Expanding the Reactivity Space of Nucleophilic Copper Hydrides
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Employing a bifunctional catalyst based on a copper(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H2 as terminal reducing agent are facilitated. The approach taken here enables the simultaneous activation of esters through hydrogen bonding and formation of nucleophilic copper(I) hydrides from H2, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guanidinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered "soft"copper(I) hydrides to previously unreactive "hard"ester electrophiles and paves the way for a replacement of stoichiometric reducing agents by a catalyst and H2.
- Kaicharla, Trinadh,Ngoc, Trung Tran,Teichert, Johannes F.,Tzaras, Dimitrios-Ioannis,Zimmermann, Birte M.
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supporting information
p. 16865 - 16873
(2021/10/20)
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- Improved method for preparation of nerol and geraniol and catalytic system thereof
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The invention relates to a method for preparing nerol and geraniol through selective hydrogenation by taking citral as a raw material and a catalytic system for the method. The method comprises the following step: carrying out selective hydrogenation reaction on initial compound citral under the catalytic action of a homogeneous catalyst and an auxiliary agent to prepare nerol and geraniol. According to the method and the catalytic system provided by the invention, by-products citronellol and nerol isomers I-III in the reaction process are remarkably reduced, and the method has a relatively good industrial prospect.
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Paragraph 0042-0053; 0056-0059
(2020/05/01)
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- Hydroxypyridine ligand and preparation method and catalytic application thereof (by machine translation)
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The invention provides a hydroxypyridine ligand, a preparation method thereof and application, for catalyzing allyl alcohol isomerism, wherein the structural formula of the hydroxypyridine ligand is as follows : One or more, R wherein, R represents the substituent C1 - C20 selected from, alkyl, phenyl, naphthyl, heteroaryl, methoxy, fluoro, chloro, bromo, trifluoromethyl, methoxycarbonyl, amine has a higher catalytic activity, than that of a ligand 2 - such as an amine alcohol α, ω - hydroxyquinoline reported in the known literature and having a double-tooth chelating effect, and a metal tungsten bonding capability. The present invention provides, a; ligand 1,3 - and a, dihalide coupling, which can be rapidly, efficiently obtained . The, ligand has, a higher catalytic activity than the, metal tungsten bonding capability. (by machine translation)
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Paragraph 0086-0088
(2020/05/11)
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- Flat and Efficient H CNN and CNN Pincer Ruthenium Catalysts for Carbonyl Compound Reduction
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The bidentate HCNN dicarbonyl ruthenium complexes trans,cis-[RuCl2(HCNN)(CO)2] (1-3) and trans,cis-[RuCl2(ampy)(CO)2] (1a) were prepared by reaction of [RuCl2(CO)2]n with 1-[6-(4′-methylphenyl)pyridin-2-yl]methanamine, benzo[h]quinoline (HCNN), and 2-(aminomethyl)pyridine (ampy) ligands. Alternatively, the derivatives 1-3 were obtained from the reaction of RuCl3 hydrate with HCO2H and HCNN. The pincer CNN cis-[RuCl(CNN)(CO)2] (4) was isolated from 1 by reaction with NEt3. The monocarbonyl complexes trans-[RuCl2(HCNN)(PPh3)(CO)] (5-7) were synthesized from [RuCl2(dmf)(PPh3)2(CO)] and HCNN ligands, while the diacetate trans-[Ru(OAc)2(HCNN)(PPh3)(CO)] (8) was obtained from [Ru(OAc)2(PPh3)2(CO)]. Carbonylation of cis-[RuCl(CNN)(PPh3)2] with CO afforded the pincer derivatives [RuCl(CNN)(PPh3)(CO)] (9-11). Treatment of 9 with Na[BArf]4 and PPh3 gave the cationic complex trans-[Ru(CNN)(PPh3)2(CO)][BArf4] (12). The dicarbonyl derivatives 1-4, in the presence of PPh3 or PCy3, and the monocarbonyl complexes 5-12 catalyzed the transfer hydrogenation (TH) of acetophenone (a) in 2-propanol at reflux (S/C = 1000-100000 and TOF up to 100000 h-1). Compounds 1-3, with PCy3, and 6 and 8-10 were proven to catalyze the TH of carbonyl compounds, including α,β-unsaturated aldehydes and bulky ketones (S/C and TOF up to 10000 and 100000 h-1, respectively). The derivatives 1-3 with PCy3 and 5 and 6 catalyzed the hydrogenation (HY) of a (H2, 30 bar) at 70 °C (S/C = 2000-10000). Complex 5 was active in the HY of diaryl ketones and aryl methyl ketones, leading to complete conversion at S/C = 10000.
- Giboulot, Steven,Baldino, Salvatore,Ballico, Maurizio,Figliolia, Rosario,P?thig, Alexander,Zhang, Shuanming,Zuccaccia, Daniele,Baratta, Walter
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p. 1127 - 1142
(2019/03/14)
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- Supported Co–Re Bimetallic Catalysts with Different Structures as Efficient Catalysts for Hydrogenation of Citral
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Bimetallic Co–Re/TiO2 catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co-impregnation (CI), successive-impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM–energy-dispersive X-ray spectroscopy, H2 temperature-programmed reduction, temperature-programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co–Re interaction. In SI samples, the metals coexist in a Janus-type structure with a concentration of Re around Co. Decoration/core–shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO2 catalyst and the Re7+ species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)a disadvantage for the hydrogenation reaction. For SR samples, the increase of Re loading contributes to the electron transfer from Re to Co that is consistent with a change of structure from decoration to core–shell. The lack of directly accessible Co atoms for SR catalysts with fully coated structure decreases the efficiency of Re reduction. The presence of Co–Re interaction resulting from the close contact between metals plays a dominant role in the hydrogenation of citral. Nevertheless, an excessively high contact degree is unnecessary for citral hydrogenation once Co–Re interaction has formed.
- Di, Xin,Lafaye, Gwendoline,Especel, Catherine,Epron, Florence,Qi, Ji,Li, Chuang,Liang, Changhai
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p. 807 - 823
(2019/02/19)
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- Selective Hydrogenation of Citral on Pt-Containing Catalysts at Room Temperature and Atmospheric Pressure
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Abstract: It is shown that the 1% Pt/CeO2–ZrO2 (1% Pt/CZ) catalytic system allows selective hydrogenation of citral with a 94% conversion and a selectivity towards unsaturated alcohols of 59% at room temperature and atmospheric pressure. The effect of addition of alkali to the reaction mixture on the yield of the target products is studied, and the optimum conditions of the reaction are determined.
- Vikanova,Redina
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p. 2566 - 2569
(2019/12/30)
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- Three-Dimensionally Hierarchical Pt/C Nanocomposite with Ultra-High Dispersion of Pt Nanoparticles as a Highly Efficient Catalyst for Chemoselective Cinnamaldehyde Hydrogenation
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A monolithic carbon-supported Pt nanocomposite with an interconnected three-dimensionally hierarchical porous carbon framework and ultra-high dispersion of Pt nanoparticles (Pt/3DHPC) is synthesized by using an effective “liquid phase impregnation template” strategy. The obtained Pt/3DHPC possesses rich mesoporosity and a low amount of oxygen-containing functional groups, which notably improve the accessible internal surface area of macropores, number of active Pt sites, and electron transfer ability. When used as a catalyst for the selective cinnamaldehyde (CMA) hydrogenation towards cinnamyl alcohol (CMO), Pt/3DHPC exhibits high CMA conversion (92.7 %) and CMO selectivity (91.1 %) at 1 h reaction time, and the corresponding activity (1553.7 h?1) greatly surpasses not only the single-sized mesoporous carbon and microporous activated carbon-supported counterparts but also the previously reported Pt catalysts dispersed on other forms of carbon. Furthermore, Pt/3DHPC can be reused at least fifteen times without pronounced decay owing to the strong interaction between Pt and carbon. The present work demonstrates the validity of multiscale control in carbon-supported Pt catalysts by overall consideration of the mass transportation, and the accessibility, quantity, and capability of active sites towards chemoselective hydrogenation of CMA, which is expected to be extended to other catalysis-related processes.
- Hu, Duo,Fan, Wenqian,Liu, Zhi,Li, Ling
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p. 779 - 788
(2018/01/04)
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- Transfer Hydrogenation of Aldehydes and Ketones with Isopropanol under Neutral Conditions Catalyzed by a Metal-Ligand Bifunctional Catalyst [Cp?Ir(2,2′-bpyO)(H2O)]
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A Cp?Ir complex bearing a functional bipyridonate ligand [Cp?Ir(2,2′-bpyO)(H2O)] was found to be a highly efficient and general catalyst for transfer hydrogenation of aldehydes and chemoselective transfer hydrogenation of unsaturated aldehydes with isopropanol under neutral conditions. It was noteworthy that many readily reducible or labile functional groups such as nitro, cyano, ester, and halide did not undergo any change under the reaction conditions. Furthermore, this catalytic system exhibited high activity for transfer hydrogenation of ketones with isopropanol. Notably, this research exhibited new potential of metal-ligand bifunctional catalysts for transfer hydrogenation.
- Wang, Rongzhou,Tang, Yawen,Xu, Meng,Meng, Chong,Li, Feng
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p. 2274 - 2281
(2018/02/23)
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- Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles promoted by the cooperation of steric and electronic effects
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The selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols can reach high selectivity and activity at room temperature using Pt nanoparticles immobilized on a non-porous Al2O3 support stabilized by aspartic acid. Aspartic acid molecules had a significant steric effect on CC hydrogenation and could modify the electronic state of metal particles.
- Liu, Hangyu,Mei, Qingqing,Li, Shaopeng,Yang, Youdi,Wang, Yanyan,Liu, Huizhen,Zheng, Lirong,An, Pengfei,Zhang, Jing,Han, Buxing
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supporting information
p. 908 - 911
(2018/02/07)
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- Nerol and geraniol preparation method
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The invention discloses a nerol and geraniol solid-phase method production technology. The technology adopts citral, paraformaldehyde and sodium hydroxide as raw materials, adds quaternary phosphoniumsalt as an auxiliary agent, and performs a solid-phase reaction in a ball mill reactor. After completion of the reaction, the obtained slurry is subjected to sieving, centrifugation, washing, and finally distilled to obtain nerol and geraniol products. The process is the green and solid-phase synthesis process, the product is easy to separate and purify, and the by-product sodium formate is highin purity and can be directly sold. The process overcomes the disadvantages of more step, low yield, large amount of three wastes, and many impurities in products in a traditional process route, and has industrial value.
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Paragraph 0032-0046
(2019/01/08)
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- Catalytic activity of nanoscale borides: Co2B and Ni7B3 in the liquid-phase hydrogenation of citral
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Metal borides are unconventional heterogeneous catalysts. Now, two compounds – the new phase Ni7B3 and well-known Co2B – were synthesized as well-defined, nanoscale material. After characterization (X-ray diffraction, scanning electron microscopy, nitrogen physisorption) they were tested for the liquid phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) in n-hexane at different temperatures. Hydrogenation products such as geraniol, nerol, citronellal and citronellol were analyzed. The Ni-free catalyst Co2B results in the formation of nerol and geraniol or citronellol selectively, depending on the reaction time. The new compound Ni7B3 yields citronellal or citronellol, depending on the temperature. Thus, the hydrogenation potential of borides – obtained as well-characterized, unsupported heterogeneous catalysts by a one-pot synthesis procedure and post-synthetic annealing – is demonstrated. The cobalt boride preferentially hydrogenates C[dbnd]O bonds, while the nickel boride is selective for C[dbnd]C double bonds.
- Kalyon,Hofmann,Malter,Lucas,Claus,Albert
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p. 436 - 441
(2017/07/05)
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- Structure-Function Studies of Artemisia tridentata Farnesyl Diphosphate Synthase and Chrysanthemyl Diphosphate Synthase by Site-Directed Mutagenesis and Morphogenesis
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The amino acid sequences of farnesyl diphosphate synthase (FPPase) and chrysanthemyl diphosphate synthase (CPPase) from Artemisia tridentata ssp. Spiciformis, minus their chloroplast targeting regions, are 71% identical and 90% similar. FPPase efficiently and selectively synthesizes the "regular" sesquiterpenoid farnesyl diphosphate (FPP) by coupling isopentenyl diphosphate (IPP) to dimethylallyl diphosphate (DMAPP) and then to geranyl diphosphate (GPP). In contrast, CPPase is an inefficient promiscuous enzyme, which synthesizes the "irregular" monoterpenes chrysanthemyl diphosphate (CPP), lavandulyl diphosphate (LPP), and trace quantities of maconelliyl diphosphate (MPP) from two molecules of DMAPP, and couples IPP to DMAPP to give GPP. A. tridentata FPPase and CPPase belong to the chain elongation protein family (PF00348), a subgroup of the terpenoid synthase superfamily (CL0613) whose members have a characteristic α terpene synthase α-helical fold. The active sites of A. tridentata FPPase and CPPase are located within a six-helix bundle containing amino acids 53 to 241. The two enzymes were metamorphosed into one another by sequentially replacing the loops and helices of the six-helix bundle from enzyme with those from the other. Chain elongation was the dominant activity during the N-terminal to C-terminal metamorphosis of FPPase to CPPase, with product selectivity gradually switching from FPP to GPP, until replacement of the final α-helix, whereupon cyclopropanation and branching activity competed with chain elongation. During the corresponding metamorphosis of CPPase to FPPase, cyclopropanation and branching activities were lost upon replacement of the first helix in the six-helix bundle. Mutations of active site residues in CPPase to the corresponding amino acids in FPPase enhanced chain-elongation activity, while similar mutations in the active site of FPPase failed to significantly promote formation of significant amounts of irregular monoterpenes. Our results indicate that CPPase, a promiscuous enzyme, is more plastic toward acquiring new activities, whereas FPPase is more resistant. Mutations of residues outside of the α terpene synthase fold are important for acquisition of FPPase activity for synthesis of CPP, LPP, and MPP.
- Lee, J. Scott,Pan, Jian-Jung,Ramamoorthy, Gurusankar,Poulter, C. Dale
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supporting information
p. 14556 - 14567
(2017/10/24)
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- New In(OiPr)3-MCM-41 heterogeneous catalyst in MPV reductions of unsaturated carbonyl compounds: effect of mesoporous SBA-15 and MCM-41 as supporting surfaces on catalytic activity of In(OiPr)3
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Indium tri-isopropoxide, In(OiPr)3, was immobilized on mesoporous material, MCM-41, and denoted as “In(OiPr)3-MCM-41”. This new heterogeneous catalyst was characterized by XRD, 29Si NMR-, N2 adsorption–desorption isotherms and ICP-OES techniques. The new heterogeneous catalyst, In(OiPr)3-MCM-41, was tested for the capable of catalyzed Meerwein–Ponndorf–Verley (MPV) reduction of unsaturated aldehydes and ketones with low catalyst loadings under mild conditions and showed good to excellent catalytic activities. Also, effect of supporting surfaces, both of SBA-15 and MCM-41, on catalytic activity of In(OiPr)3 were examined. In(OiPr)3-SBA-15 heterogeneous catalyst in comparison with the In(OiPr)3-MCM-41 catalyst, display comparatively higher catalytic activity in the MPV reduction of unsaturated aldehydes and ketones. Also, similiar reaction times and selectivities for the unsaturated alcohols were obtained with the In(OiPr)3-SBA-15 catalyst compared with the In(OiPr)3-MCM-41 catalyst. The reason for the lower activity observed for MCM-41 sample may be due to smaller pore size of the In(OiPr)3-MCM-41 catalyst as compared with In(OiPr)3-SBA-15 catalyst can creat restrict site accessibility for the carbonyl compounds. Eventually, effect of supporting surfaces, SBA-15 and MCM-41, on catalytic activity of In(OiPr)3 insignificant for MPV reduction of unsaturated carbonyl compounds.
- Karatas, Burcu Uysal,Oksal, Birsen S.,Karatas, Erhan
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- Manufacture of Citronellal by the Rhodium-Catalyzed Homogeneous Hydrogenation of Neral
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The highly chemoselective hydrogenation of neral affording citronellal is described. The reaction has been conducted with homogeneous rhodium complexes. Among the set of ancillary diphosphane ligands tested, Xantphos was found to be superior. The relevant precatalyst has been generated from neutral metal sources such as Rh(acac)(CO)2 or the carbon monoxide-free rhodium source Rh(acac)(cod) in the absence of any base. A high activity and chemoselectivity in favor of the desired citronellal is achieved at 0.1 MPa and room temperature. Under the same conditions, geranial is also reduced to citronellal. The addition of carbon monoxide to the hydrogen stream as used in an industrial process is not necessary. (Figure presented.).
- Holz, Jens,Doerfelt, Stephan,B?rner, Armin
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p. 4379 - 4387
(2017/12/26)
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- Mechanistic Investigation of Bis(imino)pyridine Manganese Catalyzed Carbonyl and Carboxylate Hydrosilylation
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We recently reported a bis(imino)pyridine (or pyridine diimine, PDI) manganese precatalyst, (Ph2PPrPDI)Mn (1), that is active for the hydrosilylation of ketones and dihydrosilylation of esters. In this contribution, we reveal an expanded scope for 1-mediated hydrosilylation and propose two different mechanisms through which catalysis is achieved. Aldehyde hydrosilylation turnover frequencies (TOFs) of up to 4900 min-1 have been realized, the highest reported for first row metal-catalyzed carbonyl hydrosilylation. Additionally, 1 has been shown to mediate formate dihydrosilylation with leading TOFs of up to 330 min-1. Under stoichiometric and catalytic conditions, addition of PhSiH3 to (Ph2PPrPDI)Mn was found to result in partial conversion to a new diamagnetic hydride compound. Independent preparation of (Ph2PPrPDI)MnH (2) was achieved upon adding NaEt3BH to (Ph2PPrPDI)MnCl2 and single-crystal X-ray diffraction analysis revealed this complex to possess a capped trigonal bipyramidal solid-state geometry. When 2,2,2-trifluoroacetophenone was added to 1, radical transfer yielded (Ph2PPrPDI·)Mn(OC·(Ph)(CF3)) (3), which undergoes intermolecular C-C bond formation to produce the respective Mn(II) dimer, [(μ-O,Npy-4-OC(CF3)(Ph)-4-H-Ph2PPrPDI)Mn]2 (4). Upon finding 3 to be inefficient and 4 to be inactive, kinetic trials were conducted to elucidate the mechanisms of 1- and 2-mediated hydrosilylation. Varying the concentration of 1, substrate, and PhSiH3 revealed a first order dependence on each reagent. Furthermore, a kinetic isotope effect (KIE) of 2.2 ± 0.1 was observed for 1-catalyzed hydrosilylation of diisopropyl ketone, while a KIE of 4.2 ± 0.6 was determined using 2, suggesting 1 and 2 operate through different mechanisms. Although kinetic trials reveal 1 to be the more active precatalyst for carbonyl hydrosilylation, a concurrent 2-mediated pathway is more efficient for carboxylate hydrosilylation. Considering these observations, 1-catalyzed hydrosilylation is believed to proceed through a modified Ojima mechanism, while 2-mediated hydrosilylation occurs via insertion.
- Mukhopadhyay, Tufan K.,Rock, Christopher L.,Hong, Mannkyu,Ashley, Daniel C.,Groy, Thomas L.,Baik, Mu-Hyun,Trovitch, Ryan J.
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p. 4901 - 4915
(2017/04/11)
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- Chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds using potassium formate over amine-grafted Ru/AlO(OH) catalysts
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Grafting of 3-(2-aminoethylamino)propyltrimethoxysilane onto Ru/AlO(OH) resulted in an active and highly chemoselective heterogeneous catalyst for the transfer hydrogenation of α,β-unsaturated carbonyl compounds to the corresponding allylic alcohols. Potassium formate was used as a sustainable hydrogen donor. A range of substrates including cinnamaldehyde, α-amylcinnamaldehyde, citral, 3-methyl-2-butenal, trans-2-pentenal, and trans-hexenal were selectively hydrogenated at the CO moiety with >96% selectivity. In comparison, the unmodified 1 wt% Ru/AlO(OH) catalyzed hydrogenation of cinnamaldehyde at the CC bond, yielding 3-phenylpropanal as the product. Higher loaded samples with 2-10 wt% Ru exhibited 20-25% selectivity to cinnamyl alcohol. The results show that low coordination sites were more selective to hydrogenation of the internal CC than the terminal CO bond. Immobilization of the amine via chemical bonding with hydroxyl groups of the AlO(OH) support blocks adjacent exposed metal sites, increasing the chemoselective reduction of CO. Optimum results were achieved at an amine/Ru ratio of 6. The catalyst maintained high activity and chemoselectivity even after five cycles.
- Gao, Yanxiu,Wang, Jie,Han, Aijuan,Jaenicke, Stephan,Chuah, Gaik Khuan
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p. 3806 - 3813
(2016/06/13)
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- Chemoselective hydrogenation of α,β-unsaturated aldehydes on hydrogenated MoOx nanorods supported iridium nanoparticles
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As reducible supports, metal oxides present the varied charge effect after hydrogen doping and partial reduction, accomplishing the tunable metal-support interactions and the promoted catalytic turnover in heterogeneous catalysis. Herein, the one-pot fabrication of hydrogenated MoOx (H-MoOx) nanorods supported Ir (Ir/H-MoOx) was developed, which simultaneously combined the generation of active centers (Ir) and the hydrogen doping on supports (H-MoOx). Because of the accumulated electrons around MoO6 octahedras after hydrogen doping, the electronic perturbations arising from H-MoOx supports led to the negatively charge Irδ? species being beneficial for the selective hydrogenation of C[dbnd]O moiety in α,β-unsaturated aldehydes. In the hydrogenation of cinnamaldehyde to cinnamyl alcohol, Ir/H-MoOx delivered selectivity as high as ～93%, performing among the best of current metal-based catalysts. Additionally, the efficacy for various substrates with multiple groups further verified our Ir/H-MoOx system to be competitive for chemoselective hydrogenation.
- He, Sina,Xie, Lifang,Che, Minwei,Chan, Hang Cheong,Yang, Lichun,Shi, Zhangping,Tang, Yi,Gao, Qingsheng
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p. 248 - 254
(2016/10/30)
-
- Surface Lewis acid-promoted copper-based nanocatalysts for highly efficient and chemoselective hydrogenation of citral to unsaturated allylic alcohols
-
Chemoselective hydrogenation of α,β-unsaturated aldehydes or ketones to unsaturated alcohols (UAs) is one of the key processes for the production of various important intermediate chemicals. In the present work, well-dispersed ZnO-promoted supported copper nanocatalysts were generated from Cu-Zn-Al layered double hydroxide (CuZnAl-LDH) precursors for liquid-phase chemoselective hydrogenation of citral to allylic alcohols (geraniol and nerol isomers). A series of characterizations including XRD, TEM, STEM, XPS, H2-TPR, and Py-IR demonstrated that the microstructure and catalytic performance of as-formed Cu-based nanocatalysts were significantly affected by the incorporation of Zn into catalyst precursors. It was found that the addition of more ZnO to catalysts could result in better metal dispersion and an increase in the surface Cu+/(Cu+ + Cu0) ratio and surface Lewis acid sites. In liquid-phase chemoselective hydrogenation of citral, a high selectivity toward allylic alcohols (>75%) at complete citral conversion was achieved successfully on as-formed non-noble-metal Cu-based nanocatalysts with a Cu/Zn molar ratio of 2:1 under mild reaction conditions (e.g. 80°C, 1.0 MPa). The high efficiency of the catalysts was attributed mainly to both the synergism between Cu0 and Cu+ species and the promotion of surface Lewis acid sites, thereby improving the dissociation of hydrogen and facilitating the adsorption of the citral molecule and the following activation of the carbonyl group during the citral hydrogenation.
- Li, Wei,Fan, Guoli,Yang, Lan,Li, Feng
-
p. 2337 - 2348
(2016/04/26)
-
- Chemoselective Pt-catalysts supported on carbon-TiO2 composites for the direct hydrogenation of citral to unsaturated alcohols
-
A series of carbon xerogels-TiO2 composites with different TiO2 contents were prepared, exhaustively characterized and used as a Pt-support to develop selective hydrogenation catalysts. The carbon phase in the composite hinders the TiO2 crystal growth and the transformation to rutile during thermal treatments. Textural, chemical and catalytic properties are determined by the TiO2 content, with an optimum around 40 wt.% of TiO2 content. The mesoporosity of the supports, the Pt-dispersion and Pt-support interactions are favoured in this sense. During the H2-pretreatment, the Pt and TiO2 phases were simultaneously reduced and the formation of oxygen vacancies leads to the mobility of Pt-species inside the TiO2 structure, avoiding sintering in surface and strongly improving both catalytic activity and selectivity. The catalytic performance was discussed on the basis of the sample characteristics. Unsaturated alcohols were obtained as main reaction products in all cases, being the only product in the case of the optimized catalyst.
- Bailón-García, Esther,Carrasco-Marín, Francisco,Pérez-Cadenas, Agustín F.,Maldonado-Hódar, Francisco J.
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p. 701 - 711
(2016/12/09)
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- Synthesis of Co-Sn intermetallic nanocatalysts toward selective hydrogenation of citral
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In this work, three supported Co-Sn intermetallic compound (IMC) catalysts (Co2.9Sn2, CoSn and CoSn2) with a particle size of ～20 nm were prepared via a facile hydrotalcite approach, and their catalytic performances were evaluated in the selective hydrogenation of citral to unsaturated alcohols (geraniol and nerol). EXAFS, in situ CO-FTIR and DFT calculation results reveal that the introduction of Sn in Co-Sn IMCs dramatically optimizes the geometric and electronic structures of active Co, in which Sn isolates the Co active-site and electron transfer occurs from Sn to the Co atom. H2-TPD measurements indicate the presence of four different Co sites (labeled as α, β, γ and σ) on the surface of these IMCs; the sample of CoSn IMC shows the largest β/(γ + σ) ratio, which results in the highest selectivity toward unsaturated alcohols (SUA: 67.6%). DFT studies prove that the geometric and electronic effects of the CoSn IMC weaken the hydrogenation of the CC group, accounting for the largely enhanced hydrogenation selectivity of citral to unsaturated alcohols.
- Zhou, Junyao,Yang, Yusen,Li, Changming,Zhang, Shitong,Chen, Yudi,Shi, Shuxian,Wei, Min
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p. 12825 - 12832
(2018/06/26)
-
- Comparison of enzymatic and acid hydrolysis of bound flavor compounds in model system and grapes
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Four synthesized terpenyl-β-D-glycopyranosides (geranyl, neryl, citronellyl, myrtenyl) were subjected to enzymatic (AR 2000, pH 5.5) and acid (citric buffer, pH 2.5) hydrolysis. Decrease of glycosides was measured by HPLC and the volatiles released - by comprehensive gas chromatography-mass spectrometry (GC x GC-ToF-MS). Enzymatic hydrolysis performed for 21 h yielded 100% degree of hydrolysis for all glycosides but citronellyl (97%). Degree of acid hydrolysis was highly dependent on type of aglycone and the conditions. The highest degree was achieved for geraniol, followed by citronellol and nerol. Myrtenylo-β-D-glycopyranoside was the most resistant glycoside to hydrolysis. Acid hydrolysis degree was also related to temperature/time combination, the highest being for 100 °C and 2 h. In a result of enzymatic hydrolysis 85-91% of total peak areas was terpene aglycone, whereas for acid hydrolysis the area of released terpene aglycone did not exceed 1.3% of total peak area indicating almost complete decomposition/transformation of terpenyl aglycone.
- Dziadas, Mariusz,Jeleń, Henryk H.
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p. 412 - 418
(2015/06/17)
-
- Unexpectedly fast catalytic transfer hydrogenation of aldehydes by formate in 2-propanol-water mixtures under mild conditions
-
Unsaturated aldehydes were efficiently reduced by transfer hydrogenation from sodium formate in water-2-propanol mixtures using a water-soluble Ru(II)-tertiary phosphine catalyst. The reaction yielded unsaturated alcohols with complete selectivity and without hydrogenation or isomerization of CC bonds of the substrates. Very high reaction rate was observed in the transfer hydrogenation of cinnamaldehyde already at 30 °C with turnover frequency of 160 h-1 and this increased to 3800 h-1 at 70 °C. Consequently, the method is applicable to the synthesis of unsaturated alcohols in case of heat sensitive or highly volatile aldehydes, too. Based on multinuclear NMR investigations, trans-[RuH2(H2O)(mtppms)3] is suggested as the key catalytic species.
- Szatmári, Imre,Papp, Gábor,Joó, Ferenc,Kathó, ágnes
-
-
- Air-Stable Gold Nanoparticles Ligated by Secondary Phosphine Oxides as Catalyst for the Chemoselective Hydrogenation of Substituted Aldehydes: A Remarkable Ligand Effect
-
Air-stable and homogeneous gold nanoparticles (AuNPs, 1a-5a) ligated by various secondary phosphine oxides (SPOs), [R1R2P(O)H] (R1 = Naph, R2 = tBu, L1; R1 = R2 = Ph, L2; R1 = Ph, R2 = Naph, L3; R1 = R2 = Et, L4; R1 = R2 = Cy, L5; R1 = R2 = tBu, L6), with different electronic and steric properties were synthesized via NaBH4 reduction of the corresponding Au(I)-SPO complex. These easily accessible ligands allow the formation of well dispersed and small nanoparticles (size 1.2-2.2 nm), which were characterized by the use of a wide variety of techniques, such as transmission electron microscopy, thermogravimetric analysis, UV-vis, energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), and cross polarization magic angle spinning (CP MAS) NMR spectroscopy. A pronounced ligand effect was found, and CP MAS NMR experiments enabled us to probe important differences in the polarity of the P-O bond of the SPOs coordinated to the nanoparticle surface depending on the type of substituents in the ligand. AuNPs containing aryl SPOs carry only SPO anions and are highly selective for aldehyde hydrogenation. AuNPs of similar size made with alkyl SPOs contain also SPOH, hydrogen bonded to SPO anions. As a consequence they contain less Au(I) and more Au(0), as is also evidenced by XPS. They are less selective and active in aldehyde hydrogenation and now show the typical activity of Au(0)NPs in nitro group hydrogenation. (Chemical Equation Presented).
- Cano, Israel,Huertos, Miguel A.,Chapman, Andrew M.,Buntkowsky, Gerd,Gutmann, Torsten,Groszewicz, Pedro B.,Van Leeuwen, Piet W. N. M.
-
supporting information
p. 7718 - 7727
(2015/07/01)
-
- METHOD FOR PRODUCING UNSATURATED ALCOHOL
-
PROBLEM TO BE SOLVED: To provide a method for producing an unsaturated alcohol that uses an unsaturated carbonyl compound as a raw material and can produce an unsaturated alcohol in which only the carbonyl bond of the unsaturated carbonyl compound is selectively reduced with excellent reaction rate, high selectivity and high yield. SOLUTION: The process for producing an unsaturated alcohol includes a step of allowing the reductive reaction of a 3C or more unsaturated carbonyl compound having one or more carbon-carbon unsaturated bonds in the molecule with hydrogen to proceed in the presence of a catalyst comprising at least one kind of metal selected from the group consisting of cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, silver, osmium, iridium and platinum and at least one kind of metal selected from the group consisting of vanadium, chromium, manganese, iron, molybdenum, tungsten and rhenium to produce a corresponding unsaturated alcohol. COPYRIGHT: (C)2015,JPOandINPIT
- -
-
Paragraph 0074-0076
(2017/01/02)
-
- Effect of 2-propanol on the transfer hydrogenation of aldehydes by aqueous sodium formate using a rhodium(i)-sulfonated triphenylphosphine catalyst
-
In water/2-propanol mixtures [RhCl(mtppms)3] (mtppms = monosulfonated triphenylphosphine) was an efficient catalyst for the selective C=C reduction of trans-3-phenyl-2-propenal (trans-cinnamaldehyde) by hydrogen transfer from formate at temperatures as low as 30 °C. An outstandingly high catalyst turnover frequency of 1214 h-1 was determined at 70 °C. A possible mechanism of the reaction is suggested on the basis of kinetic studies and 1H- and 31P-NMR spectroscopic identification of the major Rh(i) species in the reaction mixtures as cis-mer-[H2RhX(mtppms)3] (X = HCOO- or H2O). It was established that a large part but not all of the rate increase observed in water/2-propanol mixtures in comparison with systems with neat water as solvent was the consequence of complete dissolution of trans-cinnamaldehyde on the effect of the co-solvent. Nevertheless, the rate showed a significant further increase with increasing 2-propanol concentration even in homogeneous solution and this was ascribed to changes in the solvent structure. The high catalyst activity in this solvent mixture allowed the transfer hydrogenation of citral. Although good to excellent conversions were observed at 30-70 °C, a useful degree of selectivity in hydrogenation of C=C vs. C=O bonds could not be achieved.
- Kathó, ágnes,Szatmári, Imre,Papp, Gábor,Joó, Ferenc
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p. 339 - 344
(2015/11/24)
-
- Use of short time-on-stream attenuated total internal reflection infrared spectroscopy to probe changes in adsorption geometry for determination of selectivity in the hydrogenation of citral
-
A new experimental procedure based on attenuated total reflection infrared spectroscopy has been developed to investigate surface species under liquid phase reaction conditions. The technique has been tested by investigating the enhanced selectivity in the hydrogenation of α,β-unsaturated aldehyde citral over a 5% Pt/SiO2 catalyst toward unsaturated alcohols geraniol/nerol, which occurs when citronellal is added to the reaction. The change in selectivity is proposed to be the result of a change in the citral adsorption mode in the presence of citronellal. Short time on stream attenuated total internal reflection infrared spectroscopy has allowed identification of the adsorption modes of citral. With ssno citronellal, citral adsorbs through both the C = C and C = O groups; however, in the presence of citronellal, citral adsorption occurs through the C = O group only, which is proposed to be the cause of the altered reaction selectivity.
- Daly,Manyar,Morgan,Thompson,Delgado,Burch,Hardacre
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p. 2470 - 2478
(2014/08/18)
-
- Versatile iridicycle catalysts for highly efficient and chemoselective transfer hydrogenation of carbonyl compounds in water
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Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include α-substituted ketones (α-ether, α-halo, α-hydroxy, α-amino, α-nitrile or α-ester), α-keto esters, β-keto esters and α,β-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50000 at pH 4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of β-functionalised secondary alcohols, such as β-hydroxyethers, β-hydroxyamines and β-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis. Water wonder: Iridicycle catalysts are versatile and allow the highly efficient and chemoselective transfer hydrogenation of a variety of carbonyl compounds, including problematic and challenging ones, with formate in neat water (see scheme).
- Talwar, Dinesh,Wu, Xiaofeng,Saidi, Ourida,Salguero, Noemí Poyatos,Xiao, Jianliang
-
supporting information
p. 12835 - 12842
(2015/03/30)
-
- Substrate flexibility and reaction specificity of tropinone reductase-like short-chain dehydrogenases
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Annotations of protein or gene sequences from large scale sequencing projects are based on protein size, characteristic binding motifs, and conserved catalytic amino acids, but biochemical functions are often uncertain. In the large family of short-chain dehydrogenases/reductases (SDRs), functional predictions often fail. Putative tropinone reductases, named tropinone reductase-like (TRL), are SDRs annotated in many genomes of organisms that do not contain tropane alkaloids. SDRs in vitro often accept several substrates complicating functional assignments. Cochlearia officinalis, a Brassicaceae, contains tropane alkaloids, in contrast to the closely related Arabidopsis thaliana. TRLs from Arabidopsis and the tropinone reductase isolated from Cochlearia (CoTR) were investigated for their catalytic capacity. In contrast to CoTR, none of the Arabidopsis TRLs reduced tropinone in vitro. NAD(H) and NADP(H) preferences were relaxed in two TRLs, and protein homology models revealed flexibility of amino acid residues in the active site allowing binding of both cofactors. TRLs reduced various carbonyl compounds, among them terpene ketones. The reduction was stereospecific for most of TRLs investigated, and the corresponding terpene alcohol oxidation was stereoselective. Carbonyl compounds that were identified to serve as substrates were applied for modeling pharmacophores of each TRL. A database of commercially available compounds was screened using the pharmacophores. Compounds identified as potential substrates were confirmed by turnover in vitro. Thus pharmacophores may contribute to better predictability of biochemical functions of SDR enzymes.
- Reinhardt, Nicole,Fischer, Juliane,Coppi, Ralph,Blum, Elke,Brandt, Wolfgang,Draeger, Birgit
-
-
- Hydrogenation of aldehydes and ketones to corresponding alcohols with methylamine borane in neat water
-
GRAPHICAL ABSTRACT Chemoselective hydrogenation of various aldehydes and ketones with methylamine borane (MeAB) in neat water was investigated. MeAB is suitable for green organic reactions, for MeAB is a nontoxic, environmentally benign, and easily handled reagent. Aldehydes were selectively and rapidly hydrogenated in excellent yields (86-97%) for 30 min, but hydrogenation of aromatic ketones needed over 20 h at room temperature because of their poor water solubility and steric hindrance. Thus we investigated polyethylene glycol (PEG400) and acidic cation-exchange D072 resin as catalysts to accelerate the hydrogenation reaction of aromatic ketones and achieved excellent yields within several hours. PEG 400 and D072 resin are both suitable for green organic reactions. The D072 resin was reused up to four times without any significance loss in activity.
- Duan, Yifan,Bai, Ruijiao,Tian, Jun,Chen, Ligong,Yan, Xilong
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p. 2555 - 2564
(2014/08/05)
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- Effect of the acid-base properties of the support on the performance of Pt catalysts in the partial hydrogenation of citral
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In this work, the effect that mesoporous solid materials, with different acid-base properties (Pt-1 wt%/acid or base) have over the product distribution during the partial hydrogenation of citral was evaluated. It was found that basic materials were the most active catalysts reaching a 100% citral conversion after 1 h of reaction. Regarding selectivity, in basic materials (Pt/MgAl-c and Pt/MgAl-r) citronellal was the main product, while nerol and geraniol were produced in acid solids (Pt/SiO2; Pt/SiO2-TiO2 and Pt/SiO2-ZrO2). The formation of unsaturated alcohols is related to the strength and density of the acid sites of the catalyst and in this sense the Pt/SiO2-ZrO2 gave a yield of 80%. The acidity trend is: Pt/SiO2-ZrO2 > Pt/SiO 2-TiO2 > Pt/SiO2 > Pt/MgAl-c.
- Santiago-Pedro, Smid,Tamayo-Galván, Victoria,Viveros-García, Tomas
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p. 101 - 108
(2013/08/23)
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- Rapid synthesis of unsaturated alcohols under mild conditions by highly selective hydrogenation
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Ir-ReOx/SiO2 acted as a highly active and selective heterogeneous catalyst for the hydrogenation of unsaturated aldehydes to unsaturated alcohols in water at low H2 pressure (0.8 MPa) and low temperature (303 K). The catalysis is derived from the synergy between Ir metal and ReOx.
- Tamura, Masazumi,Tokonami, Kensuke,Nakagawa, Yoshinao,Tomishige, Keiichi
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supporting information
p. 7034 - 7036
(2013/09/02)
-
- The biosynthetic origin of irregular monoterpenes in lavandula: Isolation and biochemical characterization of a novel cis-prenyl diphosphate synthase gene, lavandulyl diphosphate synthase
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Lavender essential oils are constituted predominantly of regular monoterpenes, for example linalool, 1,8-cineole, and camphor. However, they also contain irregular monoterpenes including lavandulol and lavandulyl acetate. Although the majority of genes responsible for the production of regular monoterpenes in lavenders are now known, enzymes (including lavandulyl diphosphate synthase (LPPS)) catalyzing the biosynthesis of irregular monoterpenes in these plants have not been described. Here, we report the isolation and functional characterization of a novel cis-prenyl diphosphate synthase cDNA, termed Lavandula x intermedia lavandulyl diphosphate synthase (LiLPPS), through a homology-based cloning strategy. The LiLPPS ORF, encoding for a 305-amino acid long protein, was expressed in Escherichia coli, and the recombinant protein was purified by nickel-nitrilotriacetic acid affinity chromatography. The approximately 34.5-kDa bacterially produced protein specifically catalyzed the head-to-middle condensation of two dimethylallyl diphosphate units to LPP in vitro with apparent Km and k cat values of 208 ± 12 μM and 0.1 s-1, respectively. LiLPPS is a homodimeric enzyme with a sigmoidal saturation curve and Hill coefficient of 2.7, suggesting a positive co-operative interaction among its catalytic sites. LiLPPS could be used to modulate the production of lavandulol and its derivatives in plants through metabolic engineering.
- Demissie, Zerihun A.,Erland, Lauren A.E.,Rheault, Mark R.,Mahmoud, Soheil S.
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p. 6333 - 6341
(2013/05/09)
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- Kinetic study of the hydrogenation of citral on ir promoted Au/Tio 2 catalyst
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A kinetic study of citral hydrogenation over an Au-Ir/TiO2 catalyst was performed with the aim to understand the effect of iridium on gold in this catalytic system. Au-Ir/TiO2 catalyst was prepared by co-deposition precipitation in an atomic ratio of 3/1. The effect of citral concentration, hydrogen pressure and temperature effect were also studied. The product distribution obtained is related with the proportion of Meδ+/Me0 sites. The deactivation of the catalyst occurs in the whole studied temperature range, 363 to 403 K, being more drastic as temperature increases due to the irreversible adsorbed CO blocks principally Ir0 sites. From initial reaction rates treatment an apparent global order close to 1 was determined. A Langmuir-Hinshelwood-type kinetic model involving the surface reaction as the rate limiting step between adsorbed citral and hydrogen on active sites with different nature shows good agreement with experimental initial reaction rates.
- Martinez, Jose J.,Rojas, Hugo,Reyes, Patricio
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p. 1799 - 1804
(2014/03/21)
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- New heterogeneous B(OEt)3-MCM-41 catalyst for preparation of α,β-unsaturated alcohols
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Grafting of boron tri-ethoxide on mesoporous MCM-41 resulted in a highly active catalyst for the Meerwein-Ponndorf-Verley (MPV) reduction and the catalyst denoted as B(OEt)3-MCM-41. Chemoselective reduction of α,β-unsaturated aldehydes and ketones to the corresponding α,β-unsaturated alcohols was achieved by MPV reduction reaction using a new B(OEt)3-MCM-41 catalyst. The prepared new heterogeneous catalyst, B(OEt)3-MCM-41, was characterized in detail by using XRD, 29Si NMR-, 11B NMR-, 13C NMR-, and TEM, N2 adsorption, and ICP-OES. The results demonstrated the successful homogenous distribution of the B(OEt)3 on the MCM-41 support. The heterogeneous B(OEt)3-MCM-41 catalyst, in comparison with the homogeneous B(O i Pr)3 and B(OEt)3 catalysts, displayed similiar catalytic activity in the MPV reduction of α,β-unsaturated aldehydes and ketones with alcohols as reductants. Reduced reaction times and very high selectivities for the unsaturated alcohols were obtained with the heterogenous catalyst compared with the homogeneous catalysts. The B(OEt)3-MCM-41 catalyst was found to be encouraging, as is is recyclable up to six cycles without any significant loss in its catalytic activity.
- Uysal, Burcu,Oksal, Birsen S.
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p. 3893 - 3911
(2015/06/08)
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- Reduction of citral in water under typical transfer hydrogenation conditions-Reaction mechanisms with evolution of and hydrogenation by molecular hydrogen
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The reduction of an α,β-unsaturated aldehyde, citral, was investigated over a 10 wt% Pd catalyst under transfer hydrogenation (TH) conditions in a closed system with microwave assistance. Surprisingly, it was found that hydrogen was produced quite fast under the microwave irradiation during the reaction, and the reduction of citral was proved to go mainly through consecutive pathways of hydrogen production - hydrogenation rather than those commonly considered for TH reactions. Similar reaction pathways were also observed with a homogeneous catalyst of [RuCl2(C6H 6)]2 and other typical hydrogen donors like formate salts and isopropanol, which are usually used in the typical transfer hydrogenations.
- Liu, Ruixia,Wang, Yu,Cheng, Haiyang,Yu, Yancun,Zhao, Fengyu,Arai, Masahiko
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p. 315 - 320
(2013/02/23)
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- Comparison of heterogeneous B(OiPr)3-MCM-41 and homogeneous B(OiPr)3, B(OEt)3 catalysts for chemoselective MPV reductions of unsaturated aldehydes and ketones
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Boron tri-isopropoxide, B(OiPr)3, was immobilized on mesoporous material, MCM-41, and denoted as "B(OiPr) 3-MCM-41". The prepared new heterogeneous catalyst, B(O iPr)3-MCM-41, was characterized in details by using PXRD, FT-IR-, 11B NMR-, 29Si NMR-, 13C NMR-, TEM, EDX, N2 adsorption and ICP-OES. The results demonstrated the successful homogenous distribution of the B(OiPr)3 on the MCM-41 support. Heterogeneous B(OiPr)3-MCM-41 catalyst in comparison with the homogeneous B(OiPr)3 and B(OEt) 3 catalysts, display similiar catalytic activity in the Meerwein-Ponndorf-Verley (MPV) reduction of unsaturated aldehydes and ketones with alcohols as reductants. Reduced reaction times, higher rate constants and very high selectivities for the unsaturated alcohols were obtained with the heterogenous catalyst than the homogeneous catalysts. In most cases, there were no side products other than the desired alcohol. The B(OiPr) 3-MCM-41 catalyst was found to be encouraging as the catalyst is recyclable up to six cycles without any significant loss in its catalytic activity. This work enriches the family of heterogeneous MPV catalysts for chemoselective reductions of unsaturated aldehydes and ketones.
- Uysal, Burcu,Oksal, Birsen S.
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experimental part
p. 204 - 216
(2012/10/18)
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- Hydrogenation of citral over carbon supported iridium catalysts
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Hydrogenation of citral (3,7-dimethyl-2,6-octadienal) was carried out in a batch reactor at atmospheric hydrogen pressure and 70 °C over Sibunit (mesoporous carbon) supported iridium catalysts with different metal loadings. The major products were isopropyl ethers of geraniol and nerol (2-propanol was used as solvent), but also geraniol, nerol, citronellal di-isopropyl acetal and citronellal were formed. The metal particle size was determined by CO-chemisorption and varied from 2 to 6 nm. The turnover frequency for hydrogenation reactions increased with the metal particle size.
- Bernas, Heidi,Simakova, Irina,Prosvirin, Igor P.,Maeki-Arvela, Paeivi,Leino, Reko,Murzin, Dmitry Yu
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experimental part
p. 690 - 697
(2012/09/07)
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- Selective hydrogenation of α,β-unsaturated aldehydes catalyzed by amine-capped platinum-cobalt nanocrystals
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More Greasy, More Selective: Amine-capped Pt3Co nanocatalysts were synthesized and used for the hydrogenation of cinnamaldehyde (CAL). Capping the catalysts with amines that contain long carbon chains results in an ordered surface "array" (see scheme), in which high selectivity towards Ci-O hydrogenation can be achieved because the Ci-C bond in CAL does not interact with the surface. The longer the carbon chains in the amine, the higher the selectivity. Copyright
- Wu, Binghui,Huang, Huaqi,Yang, Jing,Zheng, Nanfeng,Fu, Gang
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experimental part
p. 3440 - 3443
(2012/06/30)
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- Liquid-phase hydrogenation of citral over Pt/TiO2 and Pt-Fe/TiO2 catalysts
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The liquid phase hydrogenation of citral to unsaturated alcohol over supported platinum catalysts has been studied. The catalysts were used Pt/TiO2 reduced at low or high temperature and the bimetallic Pt-Fe/TiO2 low or high temperature catalysts. As solvent n-heptane, an equimolar mixture n-heptane-1-propanol and 1-propanol were used. The reactions were carried out at a hydrogen pressure of 8.27 bar at 363 K. In the low temperature catalyst, the catalytic activity increases upon the addition of Fe3+. This positive effect was obtained keeping constant the selectivity to the unsaturated alcohol, being high selective to the products obtained by hydrogenation of the C=O bond. In the high temperature catalysts, both the addition of Fe and the presence of TiO2 moieties generated by the strong metal support interaction (SMSI) effect, lead to an increase of surface acidity. In low or high temperature catalysts, an increase in the polarity of the solvent increases the catalytic activity. However the reaction pathway is modified by the presence of acid sites which in polar solvents allow the formation of acetals, mainly in the high temperature catalysts.
- Ananthan,Narayanan
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experimental part
p. 183 - 188
(2011/11/30)
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- A new method for the chemoselective reduction of aldehydes and ketones using boron tri-isopropoxide, B(OiPr)3: Comparison with boron tri-ethoxide, B(OEt)3
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A chemoselective Meerwein-Ponndorf-Verley reduction process of various aliphatic and allylic α,β-unsaturated aldehydes and ketones is described. This chemoselective reduction is catalysed by boron triisopropoxide B(Oi Pr)3. Kinetics of reduction of aldehydes and ketones to corresponding alcohols were also examined and rate constant of each carbonyl compounds were measured. Rate constant and reduction yield of each carbonyl compounds in the presence of B(Oi Pr)3 were compared with those in the presence of B(OEt)3. The alcohols that are the reduction product were analysed by GC-MS. The rate constants and alcohol yields were found to be higher with B(OEt)3 than with B(Oi Pr) 3. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst. Indian Academy of Sciences.
- Uysal, Burcu,Oksal, Birsen S.
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supporting information; experimental part
p. 681 - 685
(2012/06/18)
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- Catalytic performance in selective hydrogenation of citral of bimetallic Pt-Sn catalysts supported on MgAl2O4 and γ-Al 2O3
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The liquid phase citral hydrogenation, using Pt and PtSn catalysts supported on MgAl2O4 and γ-Al2O 3, was studied in a stirred reactor at 70 °C and atmospheric pressure. It was found that the addition of Sn to the Pt catalysts increases the selectivity to double unsaturated alcohols for both catalyst series. Besides, monometallic catalysts hydrogenate the α,β-unsaturation with a high selectivity in absence of cyclization secondary products. The performance of these catalysts in the citral hydrogenation was related with the characteristics of the metallic phase. Results from test reactions - cyclohexane dehydrogenation (CHD) and cyclopentane hydrogenolysis (CPH) - H2 chemisorption, 2-propanol dehydration, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS), were used to explain the influence of the support and the Sn loading and postulate the models of the catalytic metallic surface. Results indicated that, a fraction of ionic Sn would be deposited near Pt, thus increasing the polarization of the carbonyl group, and a fraction of metallic Sn could form Pt-Sn alloy phases that would hinder the hydrogenation of the olefinic bonds and would be active to the hydrogenation of the carbonyl group. Both effects contribute to a higher selectivity to unsaturated alcohols in bimetallic PtSn/Al2O3 catalysts than PtSn/MgAl2O4 ones, which display a low alloy formation.
- Zgolicz, Patricia D.,Rodríguez, Virginia I.,Vilella, Irene M.J.,De Miguel, Sergio R.,Scelza, Osvaldo A.
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experimental part
p. 208 - 217
(2011/10/31)
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- Knitting an oxygenated network-coat on carbon nanotubes from biomass and their applications in catalysis
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In this work, we presented a new way for the functionalization of carbon nanotubes (CNTs) with the use of biomass as starting materials and introduced a novel concept of knitting process in the chemistry of CNTs for the first time. A mixture of aromatic compounds obtained from the hydrothermal treatment of biomass, rather than the traditional polymer monomers, was used as the nanoscale building blocks to knit an oxygenated network-coat on the CNTs layer-by-layer. It is an effective, mild, green and easily-controlled method for the functionalization of CNTs. The obtained f-CNTs were proved to be a promising catalyst support for metal catalysts, such as Ru/f-CNTs, showed high activity and selectivity for the hydrogenation of citral to unsaturated alcohol. More importantly, we opened a pioneering way for the conversion of low-cost, abundant and renewable biomass into a hydrophilic/chemical reactive network-coat on the inert surface of a wide range of sp2 carbon materials, such as prevalent fullerene, carbon nanotubes, carbon nanohorns and hot graphene etc.
- Ming, Jun,Liu, Ruixia,Liang, Guanfeng,Cheng, Haiyang,Yu, Yancun,Zhao, Fengyu
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supporting information; experimental part
p. 10929 - 10934
(2012/05/04)
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- α-Rhamnosyl-β-glucosidase-catalyzed reactions for analysis and biotransformations of plant-based foods
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Most aroma compounds exist in vegetal tissues as disaccharide conjugates, rutinose being an abundant sugar moiety in grapes. The availability of aroma precursors would facilitate analytical analysis of plant-based foods. The diglycosidase α-rhamnosyl-β-glucosidase from Acremonium sp. DSM 24697 efficiently transglycosylated the rutinose moiety from hesperidin to 2-phenylethanol, geraniol, and nerol in an aqueous-organic biphasic system. 2-Phenethyl rutinoside was synthesized up to millimolar level with an 80% conversion regarding the donor hesperidin. The hydrolysis of the synthesized aroma precursors was not detected in an aqueous medium. However, in the presence of ethanol as a sugar acceptor, the enzyme was able to transfer the disaccharide residue forming the alkyl-rutinoside. The aroma precursors were significantly hydrolyzed (up to 3-4% in 2 h at 30 °C), which indicated the potential use of the enzyme for biotechnological applications, for example, in aroma modulation of fermented foods.
- Minig, Marisol,Mazzaferro, Laura S.,Erra-Balsells, Rosa,Petroselli, Gabriela,Breccia, Javier D.
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experimental part
p. 11238 - 11243
(2012/03/08)
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- Selective hydrogenation of citral over a carbon-titania composite supported palladium catalyst
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A novel carbon-titania composite material, C/TiO2, has been prepared by growing carbon nanofibers (CNFs) on TiO2 surface via methane decomposition using Ni-Cu as a catalyst. The C/TiO2 was used for preparing supported palladium catalyst, Pd/C/TiO2. The support and Pd/C/TiO2 catalyst were characterized by BET, SEM, XRD and TG-DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO2 catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure. A novel palladium catalyst supported on carbon-titanium composite, Pd/C/TiO 2, has been prepared via chemical reduction process. It contains 97% mesopores and exhibited higher selectivity to citronellal in citral hydrogenation compared to formed activated carbon supported palladium catalyst, which was attributed to elimination of internal diffusion limitations.
- Zhu, Jie,Lu, Mohong,Li, Mingshi,Zhu, Jianjun,Shan, Yuhua
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experimental part
p. 655 - 660
(2011/11/30)
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- Citral hydrogenation over Rh and Pt catalysts supported on TiO2: Influence of the preparation and activation protocols of the catalysts
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During citral hydrogenation, the products distribution obtained on Rh/TiO2 and Pt/TiO2 catalysts depends on their preparation and activation protocols: (i) the unsaturated alcohols (the intended products) are formed in higher quantity on samples reduced at 500 °C and more notably with Pt/TiO2 catalyst; (ii) samples prepared by impregnation of the metallic precursor salt in HCl medium and activated at 300 °C are the only ones to lead to the formation of isopulegol as by-product. On the catalysts activated at 500 °C, these results can be explained by the presence of the SMSI effect beneficial to hydrogenate selectively the CO bond of citral towards unsaturated alcohols.
- Ekou, Tchirioua,Ekou, Lynda,Vicente, Aurélie,Lafaye, Gwendoline,Pronier, Stéphane,Especel, Catherine,Marécot, Patrice
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experimental part
p. 82 - 88
(2011/04/18)
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- Transfer hydrogenation of citral to citronellol with Ru complexes in the mixed solvent of water and polyethylene glycol
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The transfer hydrogenation of citral to citronellol was studied with [RuCl2(benzene)]2 catalyst in a mixed solvent of water and polyethylene glycol (H2O-PEG). The influence of several important factors including hydrogen source, solvent, temperature and active species is discussed. Under the present conditions, citronellol was produced with an extremely high selectivity above 90%. The Ru complexes could be immobilized in the H2O-PEG phase well and separated from organic products successfully. Moreover, a stable catalytic activity was obtained after the first run, although the decomposition of Ru complexes occurred during the recycling processes. The selectivity to citronellol decreased but kept a stable level about 60% in the recycling runs. Copyright
- Cheng, Haiyang,Liu, Ruixia,Hao, Jianmin,Wang, Qiang,Yu, Yancun,Cai, Shuxia,Zhao, Fengyu
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experimental part
p. 763 - 766
(2011/06/20)
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- Enantioselective synthesis of allylboronates bearing a tertiary or quaternary B-substituted stereogenic carbon by NHC-Cu-catalyzed substitution reactions
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Allylic substitutions that afford α-substituted allylboronates bearing B-substituted tertiary or quaternary carbon stereogenic centers are presented. C-B bond-forming reactions, catalyzed by chiral bidentate Cu-NHC complexes, are performed in the presence of commercially available bis(pinacolato)diboron. Transformations proceed in high yield (up to >98%) and site selectivity (>98% SN2′), and in up to >99:1 enantiomer ratio. Trans- or cis-disubstituted alkenes can be used; alkyl- (linear as well as branched) and aryl-trisubstituted allylic carbonates serve as effective substrates. Allylboronates that bear a quaternary carbon center are air-stable and can be easily purified by silica gel chromatography; in contrast, secondary allylboronates cannot be purified in the same manner and are significantly less stable. Oxidation of the enantiomerically enriched products furnishes secondary or tertiary allylic alcohols, valuable small molecules that cannot be easily obtained in high enantiomeric purity by alternative synthesis or kinetic resolution approaches.
- Guzman-Martinez, Aikomari,Hoveyda, Amir H.
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supporting information; scheme or table
p. 10634 - 10637
(2010/11/05)
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