- Reductive amination of isopropanol to monoisopropylamine over Ni-Fe/Γ-Al2O3 catalysts: Synergetic effect of Ni-Fe alloy formation
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We herein reported the syntheses of 17?wt% Ni-xFe/γ-Al2O3 catalysts containing different Fe/Ni molar ratios (x?=?0–0.7) via an incipient wetness impregnation method, followed by subsequent investigation of their catalytic properties in the reductive amination of isopropanol (IPA). We attempted to reveal the synergetic effect of bimetallic Ni-Fe on γ-Al2O3 support through characterization of the catalysts by N2-sorption, X-ray diffraction, H2-temperature-programmed reduction, and X-ray photoelectron spectroscopy. We found that conversion and selectivity to monoisopropylamine (MIPA) through the reductive amination of IPA was influenced by the reducibility of the catalysts. In addition, the surface Ni0 content increased upon the addition of Fe species, with a maximum Ni0 content being reached at a Fe/Ni molar ratio of 0.3. This molar ratio also yielded the highest conversion and MIPA selectivity, and no deactivation was observed for 100?h on stream in the presence of hydrogen gas. In addition, reaction parameters, such as the partial pressures of H2 and NH3, the space velocity, and the reaction temperature were also examined to optimize the experimental conditions.
- Hong, Eunpyo,Bang, Seonu,Cho, Jun Hee,Jung, Kwang Deog,Shin, Chae-Ho
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Read Online
- Development and Application of Efficient Ag-based Hydrogenation Catalysts Prepared from Rice Husk Waste
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The development of strategies for the sustainable management and valorization of agricultural waste is of outmost importance. With this in mind, we report the use of rice husk (RH) as feedstock for the preparation of heterogeneous catalysts for hydrogenation reactions. The catalysts were prepared by impregnating the milled RH with a silver nitrate solution followed by carbothermal reduction. The composition and morphology of the prepared catalysts were fully assessed by IR, AAS, ICP-MS, XPS, XRD and STEM techniques. This novel bio-genic silver-based catalysts showed excellent activity and remarkable selectivity in the hydrogenation of nitro groups in both aromatic and aliphatic substrates, even in the presence of reactive functionalities like halogens, carbonyls, borate esters or nitriles. Recycling experiments showed that the catalysts can be easily recovered and reused multiple times without significant drop in performance and without requiring re-activation.
- Unglaube, Felix,Kreyenschulte, Carsten Robert,Mejía, Esteban
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p. 2583 - 2591
(2021/04/09)
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- A Lewis Base Nucleofugality Parameter, NFB, and Its Application in an Analysis of MIDA-Boronate Hydrolysis Kinetics
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The kinetics of quinuclidine displacement of BH3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale (NFB), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R′3-nRnX (X = P, N; R′ = aryl, alkyl) has allowed the formulation of related substituent parameters (nfPB, nfAB), providing a means of calculating NFB values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nfPB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.
- García-Domínguez, Andrés,Gonzalez, Jorge A.,Leach, Andrew G.,Lloyd-Jones, Guy C.,Nichol, Gary S.,Taylor, Nicholas P.
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supporting information
(2022/01/04)
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- Rapid and Quantitative Profiling of Substrate Specificity of ω-Transaminases for Ketones
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ω-Transaminases (ω-TAs) have gained growing attention owing to their capability for asymmetric synthesis of chiral amines from ketones. Reliable high-throughput activity assay of ω-TAs is essential in carrying out extensive substrate profiling and establishing a robust screening platform. Here we report spectrophotometric and colorimetric methods enabling rapid quantitation of ω-TA activities toward ketones in a 96-well microplate format. The assay methods employ benzylamine, a reactive amino donor for ω-TAs, as a cosubstrate and exploit aldehyde dehydrogenase (ALDH) as a reporter enzyme, leading to formation of benzaldehyde detectable by ALDH owing to concomitant NADH generation. Spectrophotometric substrate profiling of two wild-type ω-TAs of opposite stereoselectivity was carried out at 340 nm with 22 ketones, revealing subtle differences in substrate specificities that were consistent with docking simulation results obtained with cognate amines. Colorimetric readout for naked eye detection of the ω-TA activity was also demonstrated by supplementing the assay mixture with color-developing reagents whose color reaction could be quantified at 580 nm. The colorimetric assay was applied to substrate profiling of an engineered ω-TA for 24 ketones, leading to rapid identification of reactive ketones. The ALDH-based assay is expected to be promising for high-throughput screening of enzyme collections and mutant libraries to fish out the best ω-TA candidate as well as to tailor enzyme properties for efficient amination of a target ketone.
- Han, Sang-Woo,Shin, Jong-Shik
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p. 3287 - 3295
(2019/06/21)
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- Catalytic amino acid production from biomass-derived intermediates
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Amino acids are the building blocks for protein biosynthesis and find use in myriad industrial applications including in food for humans, in animal feed, and as precursors for bio-based plastics, among others. However, the development of efficient chemical methods to convert abundant and renewable feedstocks into amino acids has been largely unsuccessful to date. To that end, here we report a heterogeneous catalyst that directly transforms lignocellulosic biomass-derived α-hydroxyl acids into α-amino acids, including alanine, leucine, valine, aspartic acid, and phenylalanine in high yields. The reaction follows a dehydrogenation-reductive amination pathway, with dehydrogenation as the rate-determining step. Ruthenium nanoparticles supported on carbon nanotubes (Ru/CNT) exhibit exceptional efficiency compared with catalysts based on other metals, due to the unique, reversible enhancement effect of NH3 on Ru in dehydrogenation. Based on the catalytic system, a two-step chemical process was designed to convert glucose into alanine in 43% yield, comparable with the well-established microbial cultivation process, and therefore, the present strategy enables a route for the production of amino acids from renewable feedstocks. Moreover, a conceptual process design employing membrane distillation to facilitate product purification is proposed and validated. Overall, this study offers a rapid and potentially more efficient chemical method to produce amino acids from woody biomass components.
- Deng, Weiping,Wang, Yunzhu,Zhang, Sui,Gupta, Krishna M.,Hülsey, Max J.,Asakura, Hiroyuki,Liu, Lingmei,Han, Yu,Karp, Eric M.,Beckham, Gregg T.,Dyson, Paul J.,Jiang, Jianwen,Tanaka, Tsunehiro,Wang, Ye,Yan, Ning
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p. 5093 - 5098
(2018/05/23)
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- A hydrogenation of acetone ammonia synthesis isopropylamine method (by machine translation)
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The invention discloses a method for hydrogenation of acetone ammonia synthesis isopropylamine method, the reaction feeding before replace the nitrogen in the reactor of the air, and then the preheating of the hydrogen is introduced in the reactor, the catalyst in the reactor temperature is raised to 90 - 180 °C, in the reactor pressure to rise to 0.2 - 1.8 mpa; after preheating into acetone, hydrogen, and ammonia are mixed in the material into the reactor, the catalyst in the presence of 0.2 - 1.8 mpa, 90 - 180 °C hydrogenated ammoniation reaction, to get the crude product, prepared by precipitating the crude product after cooling separator for separating gas and liquid, liquid is rough isopropylamine. The invention make coarse isopropylamine in isopropylamine content is high, acetone conversion rate 100%, isopropylamine selectively in 99.7% or more. (by machine translation)
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Paragraph 0030; 0031; 0032; 0033; 0034; 0035; 0036-0040
(2017/03/14)
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- NHC-based coordination polymers as solid molecular catalysts for reductive amination of biomass levulinic acid
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A class of robust solid molecular NHC-based catalysts were readily fabricated via self-assembly from a p-phenylene-bridged bis-benzimidazolium salt with selected metal precursors. Among them, the NHC-Ru polymer demonstrated high catalytic activity and excellent stability as a solid molecular catalyst for the solvent-free reductive amination of biomass levulinic acid with inexpensive ammonium formate, furnishing a challenging unprotected 5-methyl-2-pyrrolidone quantitatively at a 0.15 mol% catalyst loading. The solid catalyst was readily recovered and reused for 37 runs without obvious loss of activity. Remarkably, a TON value up to 6.7 × 104 was achieved in a molar-scale reaction with a catalyst loading at 0.001 mol%. Inspired by the results of a preliminary mechanistic study, notably, one-pot tandem reductive reactions of LA with aldehydes or ketones were successfully developed, affording a variety of structurally intriguing and functional N-substituted 5-methyl-2-pyrrolidones in high chemo-selectivity with good to excellent yields.
- Sun, Zheming,Chen, Jiangbo,Tu, Tao
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p. 789 - 794
(2017/08/18)
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- METHOD FOR PRODUCING N-ETHYL-DIISOPROPYLAMINE
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A process for preparing N-ethyldiisopropylamine by reacting acetaldehyde with diisopropylamine and hydrogen at elevated temperature and under pressure in the presence of a heterogeneous hydrogenation catalyst, the catalyst being a supported transition metal catalyst comprising Pd and/or Pt as catalytically active metal, wherein the diisopropylamine used has a purity of 58% to 94% by weight and impurities as follows: 3% to 20% by weight of water, 3% to 20% by weight of isopropanol, 0% to 2% by weight of others.
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Paragraph 0070-0076
(2017/01/26)
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- Porous silica-encapsulated and magnetically recoverable Rh NPs: A highly efficient, stable and green catalyst for catalytic transfer hydrogenation with "slow-release" of stoichiometric hydrazine in water
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A core-shell structured nanocatalyst (Fe3O4@SiO2-NH2-RhNPs@mSiO2) that is encapsulated with porous silica has been designed and prepared for catalyzing the transfer hydrogenation of nitro compounds into corresponding amines. Rh nanoparticles serve as the activity center, and the porous silica shell plays an important role in the "slow-release" of the hydrogen source hydrazine. This reaction can be carried out smoothly in the green solvent water, and the atom economy can be improved by decreasing the amount of hydrazine hydrate used to a stoichiometric 1.5 equivalent of the substrate. Significantly, high catalytic efficiency is obtained and the turnover frequency (TOF) can be up to 4373 h-1 in the reduction of p-nitrophenol (4-NP). A kinetics study shows that the order of reaction is ~0.5 towards 4-NP, and the apparent active energy Ea is 58.18 kJ mol-1, which also gives evidence of the high catalytic efficiency. Additionally, the excellent stability of the catalyst has been verified after 15 cycles without any loss of catalytic activity, and it is easily recovered by a magnet after reaction due to the Fe3O4 nucleus.
- Zhou, Junjie,Li, Yunong,Sun, Hong-Bin,Tang, Zhike,Qi, Li,Liu, Lei,Ai, Yongjian,Li, Shuang,Shao, Zixing,Liang, Qionglin
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supporting information
p. 3400 - 3407
(2017/07/28)
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- Versatile Dynamic Covalent Assemblies for Probing π-Stacking and Chirality Induction from Homotopic Faces
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Herein we report for the first time the use of dynamic covalent reactions (DCRs) for building a π-stacking model system and further quantifying its substituent effects (SEs), which remain a topic of debate despite the rich history of stacking. A general DCR between 10-methylacridinium ion and primary amines was discovered, in which π-stacking played a stabilizing role. Facile quantification of SEs with in situ competing π-stacking systems was next achieved in the form of amine exchange exhibiting structural diversity by simply varying components. The linear correlation with σm in Hammett plots indicates the dominance of purely electrostatic SEs, and the additivity of SEs is in line with the direct interaction model. With α-chiral amines π-stacking within the adduct enabled chirality transfer from homotopic faces. The strategy of dynamic covalent assembly should be appealing to future research of probing weak interactions and manipulating chirality.
- Ye, Hebo,Hai, Yu,Ren, Yulong,You, Lei
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supporting information
p. 3804 - 3809
(2017/03/27)
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- O -Phthalaldehyde catalyzed hydrolysis of organophosphinic amides and other P(O)-NH containing compounds
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Over 50 years ago, Jencks and Gilchrist showed that formaldehyde catalyses the hydrolysis of phosphoramidate through electrophilic activation, induced by covalent attachment to its nitrogen atom. Given our interest in the use of aldehydes as catalysts, this work was revisited to identify a superior catalyst, o-phthalaldehyde, which facilitates hydrolyses of various organophosphorus compounds bearing P(O)-NH subunits under mild conditions. Interestingly, chemoselective hydrolysis of the P(O)-N bonds could be accomplished in the presence of P(O)-OR bonds.
- Li, Bin-Jie,Simard, Ryan D.,Beauchemin, André M.
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supporting information
p. 8667 - 8670
(2017/08/10)
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- Graphene-Supported NiPd Alloy Nanoparticles for Effective Catalysis of Tandem Dehydrogenation of Ammonia Borane and Hydrogenation of Nitro/Nitrile Compounds
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Monodisperse NiPd alloy nanoparticles (NPs) are synthesized and assembled on graphene (G) or other support to provide clean, efficient catalysis of tandem reactions—dehydrogenation of ammonia borane (AB) and hydrogenation of R—NO2 and/or R—CN to R—NH2. The tandem reactions proceed quickly and with high efficiency in aqueous methanol solutions at room temperature, and the supported catalyst is readily recovered for re-use, providing a simple, efficient and ‘green’ route to the preparation of many common pharmaceutical, dye or other chemical products. NiPd alloy NPs of 3.4 nanometer size were prepared by co-reduction of nickel(II) acetate and palladium(II) acetlyacetonate by borane-tert-butylamine in oleylamine and deposited on G via a solution phase self-assembly process. The G-NiPd showed composition-dependent catalysis on the tandem reaction with G-Ni30Pd70 being the most active. A variety of R—NO2 and/or R—CN derivatives (R alkyl or aryl) were reduced selectively into R—NH2 via G-Ni30Pd70 catalyzed tandem reaction in short (5-30 minute) reaction times with conversion yields reaching up to 100%, demonstrating a new approach to G-NiPd-catalyzed dehydrogenation of AB and hydrogenation of R—NO2 and R—CN. The G-NiPd NP catalyst is efficient and is reusable; thus the reaction can be performed in an environment-friendly process with short reaction times and high yields.
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Paragraph 0022
(2016/10/17)
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- Effect of polyamide on selectivity of its supported Raney Ni catalyst
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A newly-developed polyamide supported Raney Ni catalyst, which is suitable for use in fix-bed reactions with high selectivity, was studied in this paper. Selective hydrogenation of acetone to isopropanol was chosen as a probe reaction. It has been found that clean preparation of isopropanol could be achieved, that is to say, the two main byproducts (isopropyl ether and methyl- iso-butyl carbinol) could be eliminated with the newly-developed polyamide supported Raney Ni catalyst. The elimination of these side reactions was attributed to the adsorption effect of polyamide support and a model was proposed. The proposed model was further proved by hydroamination reaction of acetone. According to this model, catalyst support can play an important role in chemical reactions. Different products could be produced when different catalyst support is used, the main reaction and side reactions can even be reversed sometimes when the chemicals, active component of catalyst and reaction condition are the same. This model could help to improve catalytic selectivity of many Raney metal catalysts used routinely in chemical and oil refining industry, and is also useful for hydrogenation reactions in pharmaceutical and food industry.
- Jiang, Haibin,Lu, Shuliang,Zhang, Xiaohong,Tian, Baoliang,Peng, Hui,Dai, Wei,Qiao, Jinliang
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p. 776 - 780
(2016/07/06)
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- Effect of an Alumina Phase on the Reductive Amination of 2-Propanol to Monoisopropylamine over Ni/Al2O3
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Various single-phase aluminum oxides were prepared through the thermal decomposition of bayerite, boehmite, and gibbsite. Ni/γ-Al2O3 and Ni/δ-Al2O3 catalysts exhibited higher monoisopropylamine (MIPA) selectivity than the η-, θ-, and κ-Al2O3 supported Ni catalysts for the reductive amination of 2-propanol (IPA) in the presence of hydrogen and ammonia. FT-IR spectra after pyridine adsorption showed that a high number of Lewis acid sites could be correlated with enhancement in MIPA selectivity. Ni/η-Al2O3 and Ni/γ-Al2O3 catalysts exhibited the highest catalytic activity arising from differences in the metallic surface area. Both catalyst activity and selectivity with regards to reductive amination were strongly affected by the nature of the support.
- Cho, Jun Hee,An, Sang Hee,Chang, Tae-Sun,Shin, Chae-Ho
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p. 811 - 819
(2016/03/19)
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- Aminophobanes: Hydrolytic stability, tautomerism and application in Cr-catalysed ethene oligomerisation
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9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR′; R = Me or iPr) are readily prepared by aminolysis of PhobPCl and are significantly less susceptible to hydrolysis than the acyclic analogues Cy2PNHR′. Treatment of Cy2PNHMe with Cy2PCl readily gave Cy2PNMePCy2. By contrast, treatment of PhobPCl with PhobPNHMe in the presence of Et3N does not afford PhobPNMePPhob but instead the salt [PhobP(NMeH)PPhob]Cl is formed which, upon addition of [PtCl2(NCtBu)2] gives the zwitterionic complex [PtCl3(PhobP(NMeH)PPhob)]. The neutral PhobP(NMe)PPhob is accessible from PhobNMeLi and is converted to the chelate [PdCl2(PhobPNMePPhob)] by addition of [PdCl2(cod)]. The anomalous preference of the PhobP group for the formation of PPN products is discussed. The unsymmetrical diphos ligands PhobPNMePAr2 (Ar = Ph, o-Tol) are prepared, converted to [Cr(CO)4(PhobPNMePAr2)] and shown to form Cr-catalysts for ethene oligomerisation, producing a pattern of higher alkenes that corresponds to a Schulz-Flory distribution overlaid on selective tri/tetramerisation.
- Haddow, Mairi F.,Jaltai, Judit,Hanton, Martin,Pringle, Paul G.,Rush, Laura E.,Sparkes, Hazel A.,Woodall, Christopher H.
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p. 2294 - 2307
(2016/02/09)
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- Thermal behavior of the β-blocker propranolol
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The thermal behavior of the β-blocker anti-hypertensive drug propranolol was investigated using thermoanalytical techniques TG-DTA, DSC and the evolved gas analysis by TG-FTIR, providing information regarding thermal stability, decomposition steps, melting point and heat of fusion of the compound. The results pointed for the decomposition in a single mass loss step, after melting. DSC data revealed that cold crystallization occurred in heat-cool-heat cycles, around 165 °C. TG-FTIR presented 1-naphthol, isopropylamine and HCl as principal decomposition products. A tentative mechanism for the thermal behavior of propranolol is presented.
- Ambrozini, Beatriz,Cervini, Priscila,Cavalheiro, éder Tadeu Gomes
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p. 1013 - 1017
(2016/01/25)
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- Asymmetric Amination of Secondary Alcohols by using a Redox-Neutral Two-Enzyme Cascade
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Multienzyme cascade approaches for the synthesis of optically pure molecules from simple achiral compounds are desired. Herein, a cofactor self-sufficient cascade protocol for the asymmetric amination of racemic secondary alcohols to the corresponding chiral amines was successfully constructed by employing an alcohol dehydrogenase and a newly developed amine dehydrogenase. The compatibility and the identical cofactor dependence of the two enzymes led to an ingenious in situ cofactor recycling system in the one-pot synthesis. The artificial redox-neutral cascade process allowed the transformation of racemic secondary alcohols into enantiopure amines with considerable conversions (up to 94 %) and >99 % enantiomeric excess at the expense of only ammonia; this method thus represents a concise and efficient route for the asymmetric synthesis of chiral amines. If you know what amine: A redox-neutral two-enzyme cascade encompassing an alcohol dehydrogenase (ADH) and an amine dehydrogenase (AmDH) is constructed for the synthesis of chiral amines from the corresponding racemic alcohols in one pot to afford considerable conversions (up to 94 %) and high enantiomeric excess values (>99 %) at the expense of only ammonia.
- Chen, Fei-Fei,Liu, You-Yan,Zheng, Gao-Wei,Xu, Jian-He
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p. 3838 - 3841
(2016/01/26)
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- Method for producing and phenoxyethylamine monoisopropylamine (MIPA)
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Method for producing ethylamines and monoisopropylamine (MIPA), in which bioethanol is reacted with ammonia in the presence of hydrogen and a heterogeneous catalyst to form ethylamines, wherein the bioethanol contains sulphur and/or sulphur-containing compounds of >= 0.1 ppm by weight (calculated S), and then in the presence of the same catalyst, isopropanol is reacted with ammonia in the presence of hydrogen to form MIPA.
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Paragraph 0113; 0115; 0116
(2016/12/26)
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- Method for manufacturing ammonia-N
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PROBLEM TO BE SOLVED: To provide a method for producing an N-alkyl hydroxylamine, which produces a pure N-alkyl hydroxylamine in a high yield under a mild condition by a simple method, does not require a strict time management and is advantageous for industrial-scale production. SOLUTION: The method for producing an N-alkyl hydroxylamine includes bringing an N-alkyl nitro compound into contact with a hydrogen source in the presence of a solid catalyst supporting palladium on silica and in the absence of a significant quantity of a fourth reaction component. The method for producing an N-alkyl hydroxylamine includes bringing (A) an N-alkyl nitro compound into contact only with (B) a hydrogen source and (C) a solid catalyst supporting palladium on silica, or bringing (A) an N-alkyl nitro compound into contact only with (B) a hydrogen source, (C) a solid catalyst supporting palladium on silica and (D) a solvent that does not deactivate catalytic activity and has a pKa of ≥12. COPYRIGHT: (C)2012,JPOandINPIT
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Paragraph 0075-0076; 0083-0084
(2018/12/01)
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- η3-silaallyl/alkenylsilyl molybdenum complex: Synthesis, structure, and reactivity toward primary amines to form Mo-N-Si three-membered cyclic complexes
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The new η3-silaallyl/alkenylsilyl molybdenum complex CpMo(CO)2(η3-Ph2SiCHCMe2) (3) was synthesized by the reaction of CpMo(CO)2(py)Me with Ph2HSiCH-CMe2. Reactions of 3 with primary amines RNH2 (R = tBu, iPr, Et) gave Mo-N-Si three-membered cyclic complexes CpMo(CO)2(η2-N,Si-RHNSiPh2) (5a, R = tBu; 5b, R = iPr; 5c, R = Et) with elimination of isobutene. In NMR tube reactions using iPrNH2 and EtNH2, the Mo-N-Si-C four-membered cyclic complexes CpMo(CO)2(η2-N,C-RHNSiPh2CHiPr) (4b, R = iPr; 4c, R = Et) were observed as intermediates leading to 5b and 5c, respectively. Complex 4c was successfully isolated in a preparative reaction. The molecular structures of 3, 4c, and 5b were determined by X-ray crystal analyses. Interestingly, the contribution of silylene character was suggested for the SiPh2 moiety of 5b from the X-ray structure. The reaction of 5b with MeOH gave the dinuclear complex Cp(CO)2Mo(η-OMe)(η -H)Mo(CO)2Cp as a major product.
- Sakaba, Hiroyuki,Tonosaki, Hiroki,Isozaki, Kazuyoshi,Kwon, Eunsang
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p. 1029 - 1037
(2015/03/31)
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- Deciphering ligands' interaction with Cu and Cu2O nanocrystal surfaces by NMR solution tools
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The hydrogenolysis of [Cu2{(iPrN)2(CCH3)}2] in the presence of hexadecylamine (HDA) or tetradecylphosphonic acid (TDPA) in toluene leads to 6-9 nm copper nanocrystals. Solution NMR spectroscopy has been used to describe the nanoparticle surface chemistry during the dynamic phenomenon of air oxidation. The ligands are organized as multilayered shells around the nanoparticles. The shell of ligands is controlled by both their intermolecular interactions and their bonding strength on the nanocrystals. Under ambient atmosphere, the oxidation rate of colloidal copper nanocrystals closely relies on the chemical nature of the employed ligands (base or acid). Primary amine molecules behave as soft ligands for Cu atoms, but are even more strongly coordinated on surface CuI sites, thus allowing a very efficient corrosion protection of the copper core. On the contrary, the TDPA ligands lead to a rapid oxidation rate of Cu nanoparticles and eventually to the re-dissolution of CuII species at the expense of the nanocrystals.
- Glaria, Arnaud,Cure, J??r??my,Piettre, Kilian,Coppel, Yannick,Turrin, C??dric-Olivier,Chaudret, Bruno,Fau, Pierre
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supporting information
p. 1169 - 1178
(2015/03/05)
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- Insight into the mechanism of hydrogenation of amino acids to amino alcohols catalyzed by a heterogeneous MoOx-modified Rh catalyst
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Hydrogenation of amino acids to amino alcohols is a promising utilization of natural amino acids. We found that MoOx-modified Rh/SiO2 (Rh-MoOx/SiO2) is an efficient heterogeneous catalyst for the reaction at low temperature (323 K) and the addition of a small amount of MoOx drastically increases the activity and selectivity. Here, we report the catalytic potential of Rh-MoOx/SiO2 and the results of kinetic and spectroscopic studies to elucidate the reaction mechanism of Rh-MoOx/SiO2 catalyzed hydrogenation of amino acids to amino alcohols. Rh-MoOx/SiO2 is superior to previously reported catalysts in terms of activity and substrate scope. This reaction proceeds by direct formation of an aldehyde intermediate from the carboxylic acid moiety, which is different from the reported reaction mechanism. This mechanism can be attributed to the reactive hydride species and substrate adsorption caused by MoOx modification of Rh metal, which results in high activity, selectivity, and enantioselectivity.
- Tamura, Masazumi,Tamura, Riku,Takeda, Yasuyuki,Nakagawa, Yoshinao,Tomishige, Keiichi
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p. 3097 - 3107
(2015/02/05)
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- Amination of alcohols with ammonia in water over Rhin catalyst
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Amination of various C3 alcohols such as 1,2-propanediol with ammonia was catalyzed by RhIn/C in water while Rh/C was totally inactive. Activated carbon FAC-10 was the best support in terms of activity and resistance to metal leaching. In the amination of 1,2-propanediol, RhIn/C produced amino alcohols in 68% total selectivity and 38% conversion. XRD and TEM measurements showed that RhIn alloy particle with size of 34 nm was formed on the carbon support.
- Takanashi, Tsukasa,Nakagawa, Yoshinao,Tomishige, Keiichi
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p. 822 - 824
(2014/06/23)
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- Polymethylhydrosiloxane derived palladium nanoparticles for chemo- and regioselective hydrogenation of aliphatic and aromatic nitro compounds in water
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Chemo- and regioselective hydrogenation of a wide range of aliphatic, unsaturated, aromatic and heteroaromatic nitro compounds into their corresponding amines has been achieved with highly efficient polysiloxane-stabilised "Pd" nanoparticles on NAP-magnesium oxide supports using an environmentally friendly hydrogenating agent, polymethylhydrosiloxane [PMHS] in water. Highly stable and active Pd nanoparticles were prepared by the reduction of NAP-Mg-PdCl4 with PMHS, which serves as a reducing agent as well as a capping agent. The well-dispersed palladium nanoparticles on NAP-MgO catalysts also exhibit excellent regioselectivity in the hydrogenation of dinitrobenzenes to the corresponding nitroanilines. The catalyst has high durability against sintering during the hydrogenation reaction and can be reused with no loss in its activity. This journal is the Partner Organisations 2014.
- Damodara, Dandu,Arundhathi, Racha,Ramesh Babu, T. Venkata,Legan, Margaret K.,Kumpaty, Hephzibah J.,Likhar, Pravin R.
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p. 22567 - 22574
(2014/06/23)
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- Aerobic oxidative N-dealkylation of secondary amines in aqueous solution catalyzed by rhodium porphyrins
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N-dealkylation demonstrates an important biochemical oxidation reaction by cytochrome P450 and other monooxygenases. In this article, catalytic oxidative N-dealkylation of secondary amines was achieved using rhodium(III) tetra (p-sulfonato-phenyl) porphyrin ((TSPP)RhIII) in aqueous solution with oxygen as the sole oxidant. Addition of benzaldehyde to trap primary amine product inhibited catalyst deactivation and dramatically increased reaction turnover numbers (TONs). Substrate scope examination suggested the reaction was performed with a preference for bulkier secondary amines. Kinetic study exhibited first-order kinetics with regard of (TSPP)RhIII catalyst. Results from the Hammett study gave a ρ value of -1.38, suggesting formation of an iminium ion intermediate in the rate determining step.
- Yun, Lin,Zhen, Ling,Wang, Zikuan,Fu, Xuefeng
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p. 937 - 943
(2015/06/16)
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- Aerobic oxidative N-dealkylation of secondary amines in aqueous solution catalyzed by rhodium porphyrins
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N-dealkylation demonstrates an important biochemical oxidation reaction by cytochrome P450 and other monooxygenases. In this article, catalytic oxidative N-dealkylation of secondary amines was achieved using rhodium(III) tetra (p-sulfonato-phenyl) porphyrin ((TSPP)RhIII) in aqueous solution with oxygen as the sole oxidant. Addition of benzaldehyde to trap primary amine product inhibited catalyst deactivation and dramatically increased reaction turnover numbers (TONs). Substrate scope examination suggested the reaction was performed with a preference for bulkier secondary amines. Kinetic study exhibited first-order kinetics with regard of (TSPP)RhIII catalyst. Results from the Hammett study gave a σ value of -1.38, suggesting formation of an iminium ion intermediate in the rate determining step.
- Yun, Lin,Zhen, Ling,Wang, Zikuan,Fu, Xuefeng
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p. 937 - 943
(2015/05/27)
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- Transfer of 1-alkenyl groups between secondary amines. Relative stability and reactivity of enamines from popular organocatalysts
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Enamines from 3-methylbutanal and several Pro- and Phe-derived secondary amines were prepared in DMSO-d6, CD3CN, and CDCl 3. For the first time, the relative thermodynamic stabilities of these and other enamines were compared, and rapid exchanges of 1-alkenyl groups were demonstrated. Competition experiments showed that the most favored enamines (without significant steric inhibition of resonance) react more rapidly with electrophiles.
- Carneros, Hector,Sanchez, Dani,Vilarrasa, Jaume
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p. 2900 - 2903
(2014/06/23)
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- Catalytic hydrogenation of amino acids to amino alcohols with complete retention of configuration
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Rh-MoOx/SiO2 is an effective heterogeneous catalyst for selective hydrogenation of amino acids to amino alcohols in a water solvent. MoOx modification of Rh drastically enhanced the activity and improved the selectivity and ee. Various amino alcohols were obtained in high yields (90-94%) with complete retention of configuration. This journal is the Partner Organisations 2014.
- Tamura, Masazumi,Tamura, Riku,Takeda, Yasuyuki,Nakagawa, Yoshinao,Tomishige, Keiichi
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supporting information
p. 6656 - 6659
(2014/06/10)
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- Reductive amination of 2-propanol to monoisopropylamine over Ni/γ-Al2O3 catalysts
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Ni/γ-Al2O3 catalysts with different nickel loadings (4-27 wt%) were used for the synthesis of monoisopropylamine by the reductive amination of 2-propanol in the presence of hydrogen and ammonia. H2-chemisorption analysis i
- Cho, Jun Hee,Park, Jung-Hyun,Chang, Tae-Sun,Kim, Jin-Eok,Shin, Chae-Ho
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p. 1319 - 1327
(2014/01/06)
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- Reductive amination of 2-propanol to monoisopropylamine over Co/γ-Al2O3 catalysts
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Co/γ-Al2O3 catalysts with 4-27 wt% cobalt loadings were prepared by incipient-wetness impregnation and used to catalyze the synthesis of monoisopropylamine by the reductive amination of 2-propanol in the presence of hydrogen and ammonia. The catalysts were characterized by X-ray diffraction, H2-temperature programmed reduction, N 2-sorption, and H2-chemisorption. 23 wt% Co loading resulted in the highest catalytic activity and a long-term stability of up to 100 h on stream. 2-Propanol conversion was related to the exposed metal surface area and the number of exposed cobalt atoms. In the absence of hydrogen, the catalyst was progressively deactivated; its initial activity and selectivity were completely recovered upon re-exposure to hydrogen. The deactivation was due to the formation of metal nitride caused by the strong adsorption of ammonia on the surface of the metal phase. Excess hydrogen hindered the phase transition to metal nitride, preventing deactivation.
- Cho, Jun Hee,Park, Jung Hyun,Chang, Tae-Sun,Seo, Gon,Shin, Chae-Ho
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experimental part
p. 313 - 319
(2012/05/04)
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- Synthesis, characterization, and photophysical study of fluorescent N-substituted benzo[ghi]perylene "swallow tail" monoimides
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A set of N-substituted benzoperylene monoimide (BPI) fluorophores was synthesized and characterized structurally and photophysically. Condensation of benzo[ghi]perylene-1,2-dicarboxylic anhydride in the presence of "swallow tail" alkyl amines produced fluorophores that are soluble in a range of organic solvents, highly absorbing in the near-UV (ε334 = 79 000 M-1cm-1), and fluorescent in the visible range. Photophysical behavior of the compounds was studied with steady-state and time-correlated single photon counting. The synthesized BPIs exhibit positive solvachromatic emission (λem (hexane) = 469 nm; λem (ethanol) = 550 nm) as a function of solvent polarity with little change in their excited-state lifetime (9.6-6.5 ns) and fluorescence quantum yield (0.27-0.44) over the polarity range studied. Solvachromatic shifts were analyzed using the Lippert-Mataga approach. In nonpolar hydrocarbon solvents evidence of dual emission from closely spaced (562 cm-1) S1 and S2 excited states is observed. Preliminary peak assignments for the anomalous S2 emission are made.
- Manning, Steven J.,Bogen, William,Kelly, Lisa A.
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scheme or table
p. 6007 - 6013
(2011/10/09)
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- Convenient reduction of nitro compounds to their corresponding amines with promotion of NaBH4/Ni(OAc)2.4H2O system in wet CH3CN
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NaBH4 in the presence of catalytic amounts of Ni(OAc) 2.4H2O reduces varieties of nitro compounds to their corresponding amines. Reduction reactions were carried out in a mixture of CH3CN and H2O (3.0:0.3 ml) at room temperature with high to excellent yields of products.
- Setamdideh, Davood,Khezri, Behrooz,Mollapour, Manouchehr
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experimental part
p. 991 - 996
(2012/03/27)
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- Synthesis of primary amines from secondary and tertiary amines: Ruthenium-catalyzed amination using ammonia
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Splitting of secondary and tertiary amines! The first selective catalytic synthesis of primary amines from secondary and tertiary amines with ammonia is reported. The products are obtained in yields up to 84 %. Copyright
- Baehn, Sebastian,Imm, Sebastian,Neubert, Lorenz,Zhang, Min,Neumann, Helfried,Beller, Matthias
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experimental part
p. 4705 - 4708
(2011/05/12)
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- METHOD FOR PRODUCING AMINES FROM GLYCERIN
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The present invention relates to a process for preparing amines by reacting glycerol with hydrogen and an aminating agent from the group of ammonia and primary and secondary amines in the presence of a catalyst at a temperature of from 100° C. to 400° C. and a pressure of from 0.01 to 40 MPa (from 0.1 to 400 bar). Preference is given to using glycerol based on renewable raw materials. The catalyst preferably comprises one metal or a plurality of metals or one or more oxygen compounds of the metals of groups 8 and/or 9 and/or 10 and/or 11 of the Periodic Table of the Elements. The invention further relates to the use of the reaction products as an additive in cement or concrete production and in other fields of use. This invention further provides the compounds 1,2,3-triaminopropane, 2-aminomethyl-6-methylpiperazine, 2,5-bis(aminomethyl)piperazine and 2,6-bis(aminomethyl)piperazine.
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Page/Page column 12
(2010/10/03)
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- A new acylamidase from Rhodococcus erythropolis TA37 can hydrolyze N-substituted amides
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A new acylamidase was isolated from Rhodococcus erythropolis TA37 and characterized. N-Substituted acrylamides (isopropyl acrylamide, N,N-dimethyl-aminopropyl acrylamide, and methylene-bis-acrylamide), acid para-nitroanilides (4′-nitroacetanilide, Gly-pNA, Ala-pNA, Leu-pNA), and N-acetyl derivatives of glycine, alanine, and leucine are good substrates for this enzyme. Aliphatic amides (acetamide, acrylamide, isobutyramide, n-butyramide, and valeramide) are also used as substrates but with less efficiency. The enzyme subunit mass by SDS-PAGE is 55 kDa. Maximal activity is exhibited at pH 7-8 and 55°C. The enzyme is stable for 15 h at 22°C and for 0.5 h at 45°C. The Michaelis constant (K m) is 0.25 mM with Gly-pNA and 0.55 mM with Ala-pNA. The acylamidase activity is suppressed by inhibitors of serine proteases (phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate) but is not suppressed by inhibitors of aliphatic amidases (acetaldehyde and nitrophenyl disulfides). The N-terminal amino acid sequence of the acylamidase is highly homologous to those of two putative amidases detected from sequenced R. erythropolis genomes. It is suggested that the acylamidase together with the detected homologs forms a new class within the amidase signature family.
- Lavrov,Zalunin,Kotlova,Yanenko
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experimental part
p. 1006 - 1013
(2011/11/06)
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- Molecular cloning and characterization of γ-Glutamyltranspeptidase from pseudomonas nitroreducens IFO12694
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y-Glutamyltranspeptidase from Pseudomonas nitroreducens IFO12694 (PnGGT) exhibited higher hydro-lytic activity than transfer activity, as compared with other y-glutamyltranspeptidases (GGTs). PnGGT showed little activity towards most of L-amino acids and towards glycyl-glycine, which is often used as a standard y-glutamyl accepter in GGT transfer reactions. The preferred substrates for PnGGT as a y-glutamyl accepter were amines such as methylamine, ethylamine, and isopropylamine.
- Imaoka, Masashi,Yano, Shigekazu,Okumura, Masashi,Hibi, Takao,Wakayama, Mamoru
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experimental part
p. 1936 - 1939
(2011/06/11)
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- Dual mechanisms of HNO generation by a nitroxyl prodrug of the diazeniumdiolate (NONOate) class
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Here we describe a novel caged form of the highly reactive bioeffector molecule, nitroxyl (HNO). Reacting the labile nitric oxide (NO)- and HNO-generating salt of structure iPrHN-N(O)=NO-Na+ (1, IPA/NO) with BrCH2OAc produced a stable derivative of structure iPrHN-N(O)=NO-CH2OAc (2, AcOM-IPA/NO), which hydrolyzed an order of magnitude more slowly than 1 at pH 7.4 and 37 °C. Hydrolysis of 2 to generate HNO proceeded by at least two mechanisms. In the presence of esterase, straightforward dissociation to acetate, formaldehyde, and 1 was the dominant path. In the absence of enzyme, free 1 was not observed as an intermediate and the ratio of NO to HNO among the products approached zero. To account for this surprising result, we propose a mechanism in which base-induced removal of the N-H proton of 2 leads to acetyl group migration from oxygen to the neighboring nitrogen, followed by cleavage of the resulting rearrangement product to isopropanediazoate ion and the known HNO precursor, CH3-C(O)-NO. The trappable yield of HNO from 2 was significantly enhanced over 1 at physiological pH, in part because the slower rate of hydrolysis for 2 generated a correspondingly lower steady-state concentration of HNO, thus, minimizing self-consumption and enhancing trapping by biological targets such as metmyoglobin and glutathione. Consistent with the chemical trapping efficiency data, micromolar concentrations of prodrug 2 displayed significantly more potent sarcomere shortening effects relative to 1 on ventricular myocytes isolated from wild-type mouse hearts, suggesting that 2 may be a promising lead compound for the development of heart failure therapies.
- Andrei, Daniela,Salmon, Debra J.,Donzelli, Sonia,Wahab, Azadeh,Klose, John R.,Citro, Michael L.,Saavedra, Joseph E.,Wink, David A.,Miranda, Katrina M.,Keefer, Larry K.
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scheme or table
p. 16526 - 16532
(2011/02/23)
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- Nanocrystalline magnesium oxide-stabilized palladium(0): An efficient and reusable catalyst for selective reduction of nitro compounds
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An efficient, mild and selective synthesis of aromatic and aliphatic amines from the corresponding nitro compounds has been realized by using a ligand-free heterogeneous nanocrystalline magnesium oxide-stabilized palladium(0) catalyst, employing molecular hydrogen as the reductant. The catalyst is recovered quantitatively by simple filtration and was reused for several cycles with consistent activity.
- Kantam, M. Lakshmi,Chakravarti, Rajashree,Pal, Ujjwal,Sreedhar,Bhargava, Suresh
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experimental part
p. 822 - 827
(2009/04/10)
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- Kinetics and mechanism of Ru(III) catalyzed and uncatalyzed oxidation of atenolol by chloramine-T in perchloric acid medium
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The kinetics and mechanism of chloramine-T (CAT)-oxidation of atenolol (ATN) in aqueous perchloric acid medium have been studied at 26 ± 0.1°C in the presence and absence of Ru(III) catalyst. Under identical experimental conditions, the reaction shows a first-order dependence on [CAT]0, a zero-order dependence on [ATN]0 and an inverse fractional-order dependence on [H+] for both the Ru(III) catalyzed and uncatalyzed reactions. The order with respect to Ru(III) is unity. Variation of ionic strength and addition of p-toluenesulfonamide or chloride ion have no effect on the rate. Decrease in dielectric constant of the reaction medium decreases the rate constant in both cases. Activation parameters have been computed. The stoichiometry of the reaction is found to be 1:4 and the main oxidation products are identified as 4-acetamidobenzencoxyacetic acid and isopropyl amine. Based on the kinetic data, the conjugate acid, CH 3C6H4SO2NHCl, is assumed to be the reactive oxidizing species in both cases. The Ru(III) catalyzed reactions are 2-3 times faster than the uncatalyzed reactions. Mechanisms consistent with the observed rate laws have been proposed.
- Puttaswamy,Suresha
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body text
p. 1649 - 1655
(2009/06/28)
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- METHOD FOR THE CONTINUOUS PRODUCTION OF AN AMINE
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The invention relates to a method for the continuous production of an amine by reacting a primary or secondary alcohol, aldehyde and/or ketone with hydrogen and a nitrogen compound, selected from the group containing ammonia and primary and secondary amines, at a temperature that ranges between 60 and 300 °C in the presence of a catalyst containing copper. According to the invention, the catalytically active mass of the catalyst contains the following prior to its reduction with hydrogen: 20 to 85 wt. % aluminium oxide (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2) and/or silicon dioxide (SiO2); 1 to 70 wt. % copper compounds containing oxygen, calculated as CuO; 0 to 50 wt. % magnesium compounds containing oxygen, calculated as MgO; chromium compounds containing oxygen, calculated as Cr2O3; zinc compounds containing oxygen, calculated as ZnO; barium compounds containing oxygen, calculated as BaO; and/or calcium compounds containing oxygen, calculated as CaO; and less than 30 wt. % nickel compounds containing oxygen, calculated as NiO, in relation to the copper compounds containing oxygen, calculated as CuO. The reaction in the gas phase takes place isothermally in a tubular reactor.
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Page/Page column 25; 26
(2008/06/13)
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- Mechanistic investigation of oxidation of atenolol by N-chloro-p- toluenesulfonamide in alkaline medium: A kinetic approach
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Kinetic studies of the oxidation of atenolol (ATN) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of NaOH at 26.0 ± 0.1°C follows the rate law -d[CAT]/dt = k[CAT][ATN] x[OH]-y, where x and y are less than unity. The variation of ionic strength and addition of the reaction product, p-toluenesulfonamide and Cl- ion had no pronounced effect on the reaction rate. Decrease of dielectric constant of the medium by increasing the MeOH content decreased the rate. Composite activation parameters for the reaction have been computed from Arrhenius plot. Michaelis-Menten type of kinetics is observed and activation parameters for rate limiting step have been computed. Formation and decomposition constants of CAT-ATN complexes in the reaction scheme have been determined. The conjugate acid, CH3C6H4SO 2NHCl is assumed to be the reactive species. 4-Acetamido-benzene-oxy- acetic acid and isopropyl amine were found to be the main oxidation products of atenolol. The proposed mechanism and derived rate law are consistent with the observed kinetic data.
- Puttaswamy,Suresha,Jagadeesh
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p. 903 - 908
(2007/10/03)
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- Fused pyrazole derivatives bieng protein kinase inhibitors
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Compounds of Formula (I): salts or solvates or physiologically functional derivatives thereof, wherein Z is CH or N, and R1, (R2, and R4 are various substituent groups, are protein kinase inhibitors.
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- Process of preparation of aliphatic amines
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Aliphatic amines are obtained by continuous addition of ammonia to C2- to C8-alkenes in the presence of a heterogeneous or homogeneous catalyst at a pressure of 2 to 8 MPa, a temperature of 220 to 320° C. and a molar ratio of ammonia to the alkene of 1.5 to 20, while the gaseous reaction mixture which leaves the second section, is cooled to a temperature near the dew point, it is led to the enrichment part of the first section, where it is sprayed in counterflow with a liquid mixture consisting of the starting substances. The unreacted starting substances thus disposed of the most of the amine formed are recycled under pressure in gaseous state to the second section, the liquid mixture in the impoverishment part of the section gets rid of the unreacted starting substances, and from the bottom of the first section the concentrate is conducted to further processing.
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- Magnesium-Catalyzed Proficient Reduction of Oximes to Amines Using Ammonium Formate
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Various aldoximes and ketoximes were selectively reduced to the corresponding amines by catalytic transfer hydrogenation employing low cost magnesium powder and ammonium formate at room temperature. Many other functionalities such as halogens, -OH, -OCH3, -COOH and -CH 3 remained unaffected. The hydrogenation is fast, mild, clean, cost effective and high yielding.
- Abiraj,Gowda, D. Channe
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p. 599 - 605
(2007/10/03)
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- Spectroscopy of Hydrothermal Reactions, Part 26: Kinetics of Decarboxylation of Aliphatic Amino Acids and Comparison with the Rates of Racemization
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The kinetics of decarboxylation of six α-amino acids (glycine, alanine, aminobutyric acid, valine, leucine, and isoleucine) and β-aminobutyric acid were studied in aqueous solution at 310-330 deg C and 275 bar over the pH25 range 1.5-8.5 by using an in situ FT-IR spectroscopy flow reactor. Based on the rate of formation of CO2, the first-order or pseudo-first-order rate constants were obtained along with the Arrhenius parameters. The decarboxylation rates of amino acids follow the order Gly > Leu ca. Ile ca. Val > Ala > α-Aib > β-Aib. Differences in the concentration between 0.05 and 0.5 m had only a minor effect on the decarboxylation rate. The effect of the position of the amino group on the decarboxylation rate was investigated for α-, β-, and γ-aminobutyric acid and the order was found to be α > β >> γ. Although the pH dependence is complex, the decarboxylation rates of α-amino acids qualitatively have the inverse trend of the racemization rates.
- Li, Jun,Brill, Thomas B.
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p. 602 - 610
(2007/10/03)
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- Substituted pyridines useful for inhibiting cholesteryl ester transfer protein activity
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A class of substituted pyridines that are useful for inhibiting the activity of cholesteryl ester transfer protein, and have the structural formula (IA), wherein R2, R3, R4, R5, and R6are defined in the claims.
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- First and efficient method for reduction of aliphatic and aromatic nitro compounds with zinc borohydride as pyridine zinc tetrahydroborato complex: A new stable ligand-metal borohydride
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Pyridine zinc tetrahydroborate, [(Py)Zn(BH4)2], as a new stable ligand-metal borohydride, is prepared quantitatively by complexation of 1:1 zinc borohydride and pyridine at room temperature. This reagent efficiently reduces different aromatic and aliphatic nitro compounds to their primary amines in refluxing THF. In addition, the reduction shows chemoselectivity for aliphatic nitro compounds over the aromatic nitro compounds.
- Zeynizadeh, Behzad,Zahmatkesh, Karam
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p. 267 - 271
(2007/10/03)
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- Polymer supported palladium (II) complexes as hydrogenation catalysts
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Dihydrogen reduction of aliphatic and aromatic nitrocompounds, alkenes, alkynes, nitriles and Schiff bases to their corresponding saturated products is efficiently carried out using the soluble and polymer anchored palladium (II) complexes. The immobilization of the palladium (II) complexes in the polymer matrix slightly decreased the catalytic activities on the basis of metal content but improved the thermal and chemical stabilities and product selectivities relative to those of the corresponding homogeneous ones. The soluble catalyst has the propensity to decompose under high pressure, high temperature conditions but the immobilized ones can be used repeatedly and can be stored for long periods without any appreciable loss of catalytic activity. XPS study indicates the presence of palladium (II) in the fresh and used catalyst and a plausible reaction mechanism has been suggested on the basis of experimental findings.
- Mukherjee, Debkumar
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p. 346 - 352
(2007/10/03)
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- Zinc/ammonium formate: A new facile system for the rapid and selective reduction of oximes to amines
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Various oximes, both aldoximes and ketoximes, are selectively reduced to corresponding amines employing low cost zinc dust and ammonium formate despite presence of other functional groups such as halogens, -OH, -OCH3, -COOH, -CN, > C = C 3.
- Abiraj,Gowda, D. Channe
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p. 332 - 334
(2007/10/03)
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- Orally active iron (III) chelators
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A compound of formula I wherein R is hydrogen or a group that is removed by metabolism in vivo to provide the free hydroxy compound, R1is an aliphatic hydrocarbon group or an aliphatic hydrocarbon group substituted by a hydroxy group or a carboxylic acid ester, sulpho acid ester or a C1-6alkoxy, C6-aryloxy or C7-10aralkoxy ether thereof, and R3is selected from hydrogen and C1-6alkyl; characterized in that R2is selected from groups (i) —CONH—R5(ii)—CR6R6OR7(iii) —CONHCOR5and (iv) —CON(CnH2n+1)2 R4is selected from hydrogen, C1-6alkyl and a group as described for R2; R5is selected from hydrogen and optionally hydroxy, alkoxy, aryloxy or aralkoxy substituted C1-13alkyl, aryl and C7-13alkyl R6is independently selected from hydrogen and C1-13alkyl, R7is selected from hydrogen, C1-13alkyl, aryl and C7-13aralkyl or a pharmaceutically acceptable salt of any such compound and CnH2n+1is C1-6alkyl with the proviso that the compound is not one of 1-ethyl-2-(1′-hydroxyethyl)-3-hydroxypyridin-4-one and 1-methyl-2-hydroxymethyl-3-hydroxypyridoin-4-one.
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