- Synergistic hydrogen atom transfer with the active role of solvent: Preferred one-step aerobic oxidation of cyclohexane to adipic acid by N-hydroxyphthalimide
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In this work, we developed an one-step aerobic oxidation of cyclohexane to prepare adipic acid, catalyzed by N-hydroxyphthalimide (NHPI) under promoter- and metal-free conditions. A significant beneficial solvent effect for synergistic reaction is observed with varying polarity and hydrogen-bonding strength: detailed study reveals that the solvent environments manipulate catalytic activity and adipic acid selectivity. Cyclic voltammetry measurements and UV–visible spectra of the NHPI catalyst are examined in various solvent environments to understand the active role of solvent in influencing the catalytic-site structure (>NOH) of the molecule. Analysis of the UV–visible spectra reveals that these differences can be rationalized by considering hydrogen-bonding with solvent molecules, which modifies the catalytic-site structure. This observation is in agreement with cyclic voltammetry results: the different reversibility of the catalytic-site (>NOH/>NO[rad]) wave shows that the catalytic activity of NHPI is related to the formation of hydrogen bonds with the active participation of solvents. Computational studies presented herein have furnished mechanistic insights into the effect of solvent environments. Specifically, we present the structures, dissociation energies, and reaction barriers from DFT studies of the reactants and reaction intermediates involved in the two types of H-abstraction on >NO[rad] catalytic-sites for the rate-determining step. The results of modeling the solvent effects using the PCM continuum solvent method predict that the resulting reaction barrier of the rate-controlling H-abstraction for cyclohexane and cyclohexanone is modified significantly: the transition state barrier of H-abstraction for cyclohexane decreases from 22.36 (in benzene) to 20.78 kcal?mol?1 (in acetonitrile); the α-H-abstraction barrier for cyclohexanone decreases from 21.45 to 20.53 kcal?mol?1. The active participation of solvent molecule results in a strong interaction between pre-reaction complex (PINO???H???C NO[rad] catalytic-sites at the transition state. The lower calculated barriers of H-abstraction for cyclohexanone oxidation approximate more closely the experimental results of the higher adipic acid selectivity. Our work provides a dimension of sustainable chemistry for the metal-free preparation of adipic acid: a conversion of 27% with 79% adipic acid selectivity is achieved over use of NHPI catalysts in CH3CN solvent.
- Liang, Futong,Zhong, Wenzhou,Xiang, Liping,Mao, Liqiu,Xu, Qiong,Kirk, Steven Robert,Yin, Dulin
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p. 256 - 269
(2019/09/30)
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- Controllable Intramolecular Unactivated C(sp3)-H Amination and Oxygenation of Carbamates
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Dual catalyst-controlled intramolecular unactivated C(sp3)-H amination and oxygenation of carbamates merging visible-light photocatalysis and earth-abundant transition metal catalysis have been reported. Useful amino alcohol and diol derivatives could be selectively obtained from readily available tertiary alcohol derivatives. The possible mechanisms have been proposed via a 1,5-HAT process followed by Lewis acid-controlled cyclization. The nickel and zinc catalysts inhibit the formation of oxygenation and amination products, respectively. An interesting phenomenon of chirality transfer is also observed.
- Guo, Qihang,Ren, Xiang,Lu, Zhan
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supporting information
p. 880 - 884
(2019/05/16)
-
- Production of 1,5-pentanediol via upgrading of tetrahydrofurfuryl alcohol
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A method of making 1,5-pentanediol from tetrahydrofurfural alcohol. The method includes the steps of dehydrating tetrahydrofurfural alcohol (THFA) to dihydropyran (DHP); hydrating at least a portion of the DHP to 2-hydroxy-tetrahydropyran (2-HY-THP) in the presence of a solid acid catalyst; and hydrogenating at least a portion of the 2-HY-THP to 1,5-pentanediol. The method can be conducted entirely in the absence of noble metal catalysts.
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Page/Page column 23
(2018/10/11)
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- Systematic Engineering of Single Substitution in Zirconium Metal-Organic Frameworks toward High-Performance Catalysis
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Zirconium-based metal-organic frameworks (Zr-MOFs) exhibit great structural tunability and outstanding chemical stability, rendering them promising candidates for a wide range of practical applications. In this work, we synthesized a series of isostructural PCN-224 analogues functionalized by ethyl, bromo, chloro, and fluoro groups on the porphyrin unit, which allowed us to explicitly study the effects of electron-donating and electron-withdrawing substituents on catalytic performance in MOFs. Owing to the different electronic properties of ethyl, bromo, chloro, and fluoro substitutes, the molecular-level control over the chemical environment surrounding a catalytic center could be readily achieved in our MOFs. To investigate the effects of these substitutes on catalytic activity and selectivity, the oxidation of 3-methylpentane to corresponding alcohols and ketones was utilized as a model reaction. Within these five analogues of PCN-224, an extremely high turnover number of 7680 and turnover frequency of 10 240 h-1 was achieved by simply altering the substitutes on porphyrin rings. Moreover, a remarkable 99% selectivity of the tertiary alcohol over the five other possible by-products are realized. We demonstrate that this strategy can be used to efficiently screen a suitable peripheral environment around catalytic cores in MOFs for catalysis.
- Huang, Ning,Yuan, Shuai,Drake, Hannah,Yang, Xinyu,Pang, Jiandong,Qin, Junsheng,Li, Jialuo,Zhang, Yingmu,Wang, Qi,Jiang, Donglin,Zhou, Hong-Cai
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supporting information
p. 18590 - 18597
(2017/12/15)
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- Photooxygenation of alkanes by dioxygen with: P -benzoquinone derivatives with high quantum yields
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Alkanes were oxygenated by dioxygen with p-benzoquinone derivatives such as p-xyloquinone in alkanes which are used as solvents to yield the corresponding alkyl hydroperoxides, alcohols and ketones under visible light irradiation with high quantum yields (Φ = 1000, 1600%). The photooxygenation is started by hydrogen atom abstraction from alkanes by the triplet excited states of p-benzoquinone derivatives as revealed by laser-induced transient absorption spectral measurements.
- Ohkubo, Kei,Hirose, Kensaku,Fukuzumi, Shunichi
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p. 731 - 734
(2016/07/06)
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- Solvent-Free Photooxidation of Alkanes by Dioxygen with 2,3-Dichloro-5,6-dicyano-p-benzoquinone via Photoinduced Electron Transfer
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Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) which acts as a super photooxidant. Solvent-free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ??, as revealed by femtosecond laser-induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ??, produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH2.
- Ohkubo, Kei,Hirose, Kensaku,Fukuzumi, Shunichi
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supporting information
p. 2255 - 2259
(2016/08/30)
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- Catalytic Pulsed Flow Hydrogenation Of Lignin Carboxylic Acid Compounds
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Renewable resources comprising bagasse, corn stover, wood sawdust and switch grass are subject to direct catalytic conversion or bio-fermentation producing ethanol leaving complex lignin compounds for disposal. Chemical conversion of lignin compounds (recoverable from digested lignin) to substituted phenols followed by a carbon steel catalyzed pulsed flow hydrogenation produces cresol and substituted creosol compounds. The pulsed flow process produced close to 100 percent reduction of the reactants compared to 25 percent with continuous flow and is applicable to aliphatic carboxylic acid compounds such as natural oils producing valued liquid hydrocarbons. Specifically reactions are taught for carbon steel catalyzed pulsed flow hydrogenation of lignin carboxylic acids comprising 4-hydroxy-3,5-dimethoxybenzoic acid, 4,5-dihydroxy-3-methoxybenzoic acid, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxybenzoic acid and substituted aliphatic carboxylic acid compounds comprising citric and oleic acids in contact with a promoter comprising an anhydrous sodium sulfate and an activator comprising Co(II)-Co(III)-Co(II) using hydrogen gas at 225° C. to 350° C. and ambient to 10 atmospheres pressure.
- -
-
Paragraph 0024
(2015/02/18)
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- Stereo- and chemoselective character of supported CEO2 catalysts for continuous-flow three-phase alkyne hydrogenation
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TiO2-, Al2O3-, and ZrO2- supported CeO2 catalysts with different Ce loadings were prepared by wet impregnation of the carriers with an acidified solution of cerium ammonium nitrate. The calcined catalysts were characterized by bulk and surface-sensitive techniques, which included microcalorimetry, and evaluated in the three-phase hydrogenation of alkynes under continuous-flow conditions at variable temperature (293-413 K) and pressure (1-90 bar). A number of acetylenic compounds, which contain terminal or internal triple bonds, conjugated unsaturations, and additional functionalities, were systematically assessed. The results revealed the full stereo- and chemoselective character of the ceria catalysts, which outperform the well-known Lindlar catalyst, and open promising perspectives for the revolutionary use of a cost-effective oxide for the production of olefinic compounds in the vitamin and fine chemical industries.
- Vile, Gianvito,Wrabetz, Sabine,Floryan, Leonard,Schuster, Manfred Erwin,Girgsdies, Frank,Teschner, Detre,Perez-Ramirez, Javier
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p. 1928 - 1934
(2014/08/05)
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- Thermal decomposition of diethylketone cyclic triperoxide in polar solvents
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The thermolysis of diethylketone cyclic triperoxide (3,3,6,6,9,9-hexaethyl- 1,2,4,5,7,8-hexaoxacyclononane, DEKTP) was studied in different polar solvents (ethanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, and acetonitrile). The rate constant values (kd) are higher for reactions performed in secondary alcohols probably because of the possibility to form a cyclic adduct with the participation of the hydrogen atom bonded to the secondary carbon. The kinetic parameters were correlated with the physicochemical properties of the selected solvents. The products of the DEKTP thermal decomposition in different polar solvents support a radical-based decomposition mechanism. CSIRO 2014.
- Barreto, Gaston P.,Alvarez, Elida E.,Eyler, Gladys N.,Canizo, Adriana I.,Allegretti, Patricia E.
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p. 881 - 886
(2014/07/07)
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- Catalytic reduction of lignin acids and substituted aliphatic carboxylic acid compounds
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Renewable resources comprising bagasse, corn stover, wood sawdust and switch grass are subject to direct catalytic conversion or bio-fermentation processes producing ethanol and organic by products leaving complex lignin compounds as waste for disposal. Chemical conversion of lignin compounds to aromatic lignin acids followed by reductive hydrogenation to cresol and substituted creosol compounds prepares these natural resources for chemical conversion to a form of gasoline and valued industrial compounds. The process disclosed herein is also applicable to organic carboxylic acid compounds such as natural oils producing valued liquid hydrocarbon fuels. Specifically catalytic reactions are taught for reductive chemical hydrogenation of lignin acids comprising 4-hydroxy-3,5-dimethoxybenzoic acid, 4,5-dihydroxy-3-methoxybenzoic acid, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxybenzoic acid and substituted aliphatic carboxylic acid comprising citric and oleic acid compounds in contact with an iron or steel metal surface, a promoter comprising an alkali metal sulfate and a catalyst comprising Co(II)—Co(III) or Mn(II)—Co(III) compound using hydrogen gas at ambient to 10 atmospheres pressure. This process readily forms valued organic compounds from waste natural materials thereby increasing their value.
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Page/Page column 3-4
(2012/05/21)
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- Tuning a P450 enzyme for methane oxidation
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A new spin: The addition of chemically inert perfluoro carboxylic acids (green; see picture) to P450 enzymes results in dramatic activation of their catalytic activity as a result of the conversion of the Fe/heme from a low-spin to a high-spin state, and the reduction of the binding-pocket size. Together these effects allow otherwise inert substrates such as propane and even methane to be oxidized. Copyright
- Zilly, Felipe E.,Acevedo, Juan P.,Augustyniak, Wojciech,Deege, Alfred,Reetz, Manfred T.
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supporting information; experimental part
p. 2720 - 2724
(2011/06/10)
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- Structural basis for the properties of two single-site proline mutants of CYP102A1 (P450BM3)
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The crystal structures of the haem domains of Ala330Pro and Ile401Pro, two single-site proline variants of CYP102A1 (P450BM3) from Bacillus megaterium, have been solved. In the A330P structure, the active site is constricted by the relocation of the Pro329 side chain into the substrate access channel, providing a basis for the distinctive C-H bond oxidation profiles given by the variant and the enhanced activity with small molecules. I401P, which is exceptionally active towards non-natural substrates, displays a number of structural similarities to substrate-bound forms of the wild-type enzyme, notably an off-axial water ligand, a drop in the proximal loop, and the positioning of two I-helix residues, Gly265 and His266, the reorientation of which prevents the formation of several intrahelical hydrogen bonds. Second-generation I401P variants gave high in vitro oxidation rates with non-natural substrates as varied as fluorene and propane, towards which the wild-type enzyme is essentially inactive. The substrate-free I401P haem domain had a reduction potential slightly more oxidising than the palmitate-bound wild-type haem domain, and a first electron transfer rate that was about 10 % faster. The electronic properties of A330P were, by contrast, similar to those of the substrate-free wild-type enzyme. Protein evolution with proline: The crystal structures of two contrasting single-site proline mutants of CYP102A1 (P450BM3) have been solved. The two mutations combine to give a variant that shows substantially enhanced catalytic activity with small non-natural substrates (see graph).
- Whitehouse, Christopher J. C.,Yang, Wen,Yorke, Jake A.,Rowlatt, Benjamin C.,Strong, Anthony J. F.,Blanford, Christopher F.,Bell, Stephen G.,Bartlam, Mark,Wong, Luet-Lok,Rao, Zihe
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experimental part
p. 2549 - 2556
(2011/10/09)
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- Salt effects on the rates and mechanisms of solvolysis reaction of organic halides and water structure distortion in N,N-dimethylformamide-and N,N-dimethylacetamide-water mixed solvents
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In 50% (v/v) DMFand DMAH2O mixed solvents, salt effects on the solvolysis reaction rates of aliphatic halides and related compounds (RX) have been examined for further exploring. Compared with previous results obtained in other organic solvent systems, such as 50% (v/v) acetone, 1,4-dioxane, or sulfolaneH2O, no exceptional behavior was observed in the "pseudo" first-order rate constants (k/s-1) of all the typical SN1 and SN2 substrates by the addition of alkali metal and alkaline earth metal perchlorates or many kinds of tetraalkylammonium salts in 50% (v/v) DMFand DMA-H2O mixed solvents. The detailed examination of Δlog(k/s-1)/Δ[LiClO4] for 1-adamantyl bromide vs. the contents of organic solvents (CH3CN, DMA, and DMSO) suggested that the observed different salt effects were caused by the different solvation abilities of the solvents toward the leaving-group anion as well as the metal cation. As a new highlight in the present paper, we were able to demonstrate a proportionality or correlation between the LiClO4 effects in the solvolysis rates and the carbocation stabilities expressed by the Gibbs free energy values (ΔGo) of RX in the gas phase. Based on the Raman spectra of DMA-H2O and DMF-D2O as well as DMF-D2O mixed solvents, we discuss the distortion of the bulk water structure.
- Hojo, Masashi,Ueda, Tadaharu,Ueno, Eriko,Hamasaki, Tensei,Nakano, Toshiyuki
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supporting information; experimental part
p. 401 - 414
(2010/07/08)
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- Selectivity as a function of nanoparticle size in the catalytic hydrogenation of unsaturated alcohols
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Layer-by-layer adsorption of poly(acrylic acid)-Pd(ll) complexes and poly(ethylenimine) on alumina powder followed by reduction of Pd(ll) with NaBH4 yields Pd-nanoparticle catalysts embedded in multilayer polyelectrolyte films. The use of different ratios of poly(acrylic acid)to Pd(ll) in deposition solutions gives a series of films with Pd nanop articles whose average diameters range from 2.2 to 3.4 nm, and the catalytic selectivities of these nanoparticles vary dramatically with their size. Turnover frequencies (TOFs) for the hydrogenation of monosubstituted unsaturated alcohols increase with decreasing average nanoparticle size, whereas multisubstituted unsaturated alcohols show the opposite trend. Hence, the ratio of TOFs for the hydrogenation of allyl alcohol and crotyl alcohol is 39 with average particle diameters of 2.2 nm and only 1.3 with average particle diameters of 3.4 nm. Ratios of TOFs for hydrogenation of allyl alcohol and β-methallyl alcohol are as high as 240 with the smallest nanoparticles, but substantial isomerization of β-methallyl alcohol complicates this comparison. Increasing selectivity with decreasing average particle size occurs with both films deposited on alumina powder and nanoparticles stabilized by polyelectrolytes in solution. Presumably, high selectivities occur on the smallest nanoparticles because the active sites on the smallest Pd nanoparticles are less available for binding and hydrogenation of multisubstituted double bonds thanare active sites on larger particles.
- Bhattacharjee, Somnath,Dotzauer, David M.,Bruening, Merlin L.
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experimental part
p. 3601 - 3610
(2009/08/14)
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- Method for producing alkane or alkene compound
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[PROBLEM TO BE SOLVED]: To provide a method for producing alkane or alkene compounds by reduction of carbon-carbon multiple bond. [SOLUTION]: The method for producing alkane or alkene compounds shown by the general formula (5)-(7) [wherein, R1, R2, R3, R4, R5, and R6 are optionally different and hydrogen etc. independently respectively] characterized by reacting either kind or these mixtures among alkene or alkyne compounds shown by general formula (1) or (2) [wherein, R1-R6 are the same as formula (5)-(7)] in the presence of at least one kind selected from groups of bromic acid and hydrogen peroxide shown by general formula (3) (wherein, M is hydrogen or metal atom; m is integer of 1-3), hydrazine compoun shown by general formula (4) [wherein, n is integer of equal to or more than 0], and acid. [EFFECT]: Alkane or alkene compounds can be produced handily without hydrogenation equipment.
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Page/Page column 16
(2008/06/13)
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- FeCl3-activated oxidation of alkanes by [Os(N)O 3]-
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Although the ion [OsVIII(N)(O)3]- is a stable species and is not known to act as an oxidant for organic substrates, it is readily activated by FeCl3 in CH2Cl2/CH 3CO2H to oxidize alkanes efficiently at room temperature. The oxidation can be made catalytic by using 2,6-dichloropyridine N-oxide as the terminal oxidant. The active intermediates in stoichiometric and catalytic oxidation are proposed to be [(O)3OsVIII≡N-Fe III] and [Cl4(O)OsVIII≡N-Fe III], respectively.
- Yiu, Shek-Man,Wu, Zhi-Biao,Mak, Chi-Keung,Lau, Tai-Chu
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p. 14921 - 14929
(2007/10/03)
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- Selective Hydrogenation by Pd Nanoparticles Embedded in Polyelectrolyte Multilayers
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Alternating adsorption of poly(acrylic acid) and a polyethylenimine?Pd(II) complex on alumina and subsequent reduction of Pd(II) by NaBH4 yield catalytic Pd nanoparticles embedded in multilayer polyelectrolyte films. The polyelectrolytes limit aggregation of the particles and impart catalytic selectivity in the hydrogenation of α-substituted unsaturated alcohols by restricting access to catalytic sites. Hydrogenation of allyl alcohol by encapsulated Pd(0) nanoparticles can occur as much as 24-fold faster than hydrogenation of 3-methyl-1-penten-3-ol. Additionally, the nanoparticle/polyelectrolyte system suppresses unwanted substrate isomerization, when compared to a commercial palladium catalyst. Selective diffusion through poly(acrylic acid)/polyethlyenimine membranes suggests that hydrogenation selectivities are due to different rates of diffusion to nanoparticle catalysts. First-order kinetics are also consistent with a diffusion-limited mechanism. Further exploitation of the versatility of polyelectrolyte films should increase selectivity in hydrogenation as well as other reactions. Copyright
- Kidambi, Srividhya,Dai, Jinhua,Li, Jin,Bruening, Merlin L.
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p. 2658 - 2659
(2007/10/03)
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- Selective liquid-phase semihydrogenation of functionalized acetylenes and propargylic alcohols with silica-supported bimetallic palladium-copper catalysts
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Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated. Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated.
- Spee,Boersma,Meijer,Slagt,Van Koten,Geus
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p. 1647 - 1656
(2007/10/03)
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- Oxidations by the system 'hydrogen peroxide-manganese(IV) complex- acetic acid' - Part II: Hydroperoxidation and hydroxylation of alkanes in acetonitrile
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Higher alkanes (cyclohexane, n-pentane, n-heptane, methylbutane, 2- and 3-methylpentanes, 3-methylhexane, cis- and trans-decalins) are oxidized at 20 °C by H2O2 in air in acetonitrile (or nitromethane) solution in the presence of the manganese(IV) salt [L2Mn2O3](PF6)2 (L = 1,4,7-trimethyl- 1,4-7-triazacyclononane) as the catalyst. An obligatory component of the reaction mixture is acetic acid. Turnover numbers attain 3300 after 2 h, the yield of oxygenated products is 46% based on the alkane. The oxidation affords initially the corresponding alkyl hydroperoxide as the predominant product, however later these compounds decompose to produce the corresponding ketones and alcohols. Regio- and bond selectivities of the reaction are high: C(1): C(2): C(3): C(4) ? 1: 40: 35: 35 and 1°: 2°: 3°is 1: (15-40): (180-300). The reaction with both isomers of decalin gives (after treatment with PPh3) alcohols hydroxylated in the tertiary positions with the cis/trans ratio of ~2 in the case of cis-decalin, and of ~30 in the case of trans-decalin (i.e. in the latter case the reaction is stereospecific). Light alkanes (methane, ethane, propane, normal butane and isobutane) can be also easily oxidized by the same reagent in acetonitrile solution, the conditions being very mild: low pressure (1-7 bar of the alkane) and low temperature (- 22 to +27°C). Catalyst turnover numbers attain 3100, the yield of oxygenated products is 22% based on the alkane. The yields of oxygenates are higher at low temperatures. The ratio of products formed (hydroperoxide: ketone: alcohol) depends very strongly on the conditions of the reaction and especially on the catalyst concentration (at higher catalyst concentration the ketone is predominantly produced).
- Shul'pin, Georgiy B.,Suess-Fink, Georg,Lindsay Smith, John R.
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p. 5345 - 5358
(2007/10/03)
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- An Efficient Aerobic Oxidation of Isobutane to t-Butyl Alcohol by N-Hydroxyphthalimide Combined with Co(II) Species
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Highly selective aerobic oxidation of isobutane to t-butyl alcohol was successfully achieved by the use of a radical catalyst, N-hydroxyphthalimide (NHPI) in the presence of Co(II) salt under relatively mild conditions. The oxidation of isobutane by NHPI combined with Co(acac)2 under a pressure of air (10 atm) in benzonitrile at 100°C gave t-butyl alcohol in high yield (84%) along with acetone (13%). The reaction is thought to proceed via hydrogen abstraction from isobutane by the phthalimidooxyl radical (PINO). which seems to be a key active species. The formation of acetone can be explained by a partial β-scission of the t-butoxy radical, generated from the redox decomposition of t-butyl hydroperoxide by cobalt ion. Alkyl-substituted butanes and pentanes were difficult to be oxidized selectively under these conditions because of easy degradation to smaller fragments of the resulting alkoxyl radical intermediates.
- Sakaguchi, Satoshi,Kato, Susumu,Iwahama, Takahiro,Ishii, Yasutaka
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p. 1237 - 1240
(2007/10/03)
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- Process for preparing alkanols
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A process for preparing tertiary alkanols which comprises the step of oxidizing with ozone a saturated hydrocarbon having a tertiary carbon center in the presence of a carboxylic acid and for a sufficient period of time and at suitable temperature and pressure to form said alkanols.
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- Effect of the Structure of Unsaturated Aliphatic Alcohols on the Hydrogenation Rate over Pd-Ru Membrane Catalyst
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It is shown that the rate of hydrogenation of substituted propargyl and allyl alcohols, as measured in the liquid phase on a membrane Pd-Ru alloy catalyst is described by the two-parameter Taft equation, which accounts for the induction and steric substituent effects.A positive induction effect of the substituent group promotes the reaction, whereas a negative one slows it down; an enhancement in the steric factor decreases the rate of conversion.Both induction and steric effects are stronger in reactions with ethylenic rather than acetylenic alcohols and for trans rather than cis isomers.
- Karavanov, A. N.,Gryaznov, V. M.,Batyrev, I. G.,Olenina, E. G.
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p. 739 - 743
(2007/10/02)
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- Enthalpies of Hydration of Alkenes. 4. Formation of Acyclic tert-Alcohols
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The enthalpies of hydration of a series of acyclic alkenes that lead to tert-alcohols were determined.Several pairs of alkenes that give the same alcohol were studied and gave the differences in enthalpy of formation of the alkenes.A consistent difference in Δ Hf of 1.84 kcal/mol was found between di- and trisubstituted alkenes.It was related to the difference in Δ Hf for pairs of exocyclic and endocyclic alkenes.The enthalpies of formation of the alcohols were obtained and were related to data for primary and secondary alcohols.
- Wiberg, Kenneth B.,Hao, Shide
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p. 5108 - 5110
(2007/10/02)
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- Hydrogenation using hydrides and acid
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A process for the non-catalytic hydrogenation of organic compounds, which contain at least one reducible functional group, which comprises reacting the organic compound, a hydride complex, preferably a transition metal hydride complex or an organosilane, and a strong acid in a liquid phase.
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- Effect of the metal catalyst on the mechanism of hydrogenation of C6 acetylenic carbinols
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The most probable mechanism of the hydrogenation of tertiary and of primary C6 acetylenic carbinols on group VIII metals are discussed.By using mathematical modelling and deuterium exchange methods we have shown that in the presence of Pd, Rh, and Pt the reaction takes place by a series mechanism, whereas on Ru black the acetylenic C6 alcohols are hydrogenated by a series-parallel scheme.
- Sokolo'skii, D. V.,Zhubanova, L. K.,Omarkulov, T. O.,Sadykov, U. A.,Korolev, A. V.
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- PHOTOSENSITIZED OXIDATION OF 3,6-DIMETHYLOCTANE
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In this paper an interesting mechanism involving a Barton reaction wich leads to a propagation of photooxidation processes between γ-positioned tertiary carbons is described.
- Rontani, J-F.,Giusti, G.
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p. 1923 - 1926
(2007/10/02)
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- Process for preparing pyrylium salts
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A process for selectively preparing isomers of polysubstituted pyrylium salts from isoolefins or isoolefin precursors comprises diacylating the isoolefin or isoolefin precursor with a carboxylic acid anhydride in the presence of an acid having a Hammett acidity function, at about 22°-25° C. when pure, between -10 and -5. This method is selective to obtain the most substituted isomer of pyrylium salt that can be obtained from the isoolefin or isoolefin precursor.
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- REACTIVITE DE LA LIAISON δ ACTINIDE-CARBONE : LE TRIS(BISTRIMETHYLSILYLAMIDO)METHYLURANIUM, UN AGENT METHYLANT NUCLEOPHILE A HAUTE SELECTIVITE
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The title compound 1 reacts with carbonyl derivatives as a very highly selective nucleophilic methylating reagent.
- Dormond, A.,Aaliti, A.,Moise,, C.
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p. 1497 - 1498
(2007/10/02)
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- Solvent effects in deamination reactions
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Nitrous acid deaminations of (S)-2-butanamine, (2R,3S)-3-methyl-2-pentanamine (8), cyclopropananmine (17) and 4,4-dimethyl-2-adamantanamine (30) have been studied in water and in a series of carboxylic acids of decreasing polarity (acetic, 3,3-dimethylbutyric, 2-ethylhexanoic acid).The stereochemistry of aqueous deaminations varies from predominant inversion to predominant retention, depending upon the structure of the substrate (steric hindrance, neighbouring-group participation, etc.).In carboxylic acid media, alcohols arise with predominant retention, i.e. by front-side attack of the "internal" nucleophile (water).Inverting displacement of nitrogen by the "external" nucleophile (carboxylic acid/carboxylate) increases with decreasing polarity of the solvent.Even cyclopropanamine yields cyclopropyl esters (2-10percent) of inverted configuration, as shown with the aid of deuterium labels.Current mechanistic concepts are modified to account for these results.
- Banert, Klaus,Bunse, Michael,Engbert, Theodor,Gassen, Karl-Rudolf,Kurnianto, Apriana W.,Kirmse, Wolfgang
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p. 272 - 278
(2007/10/02)
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- Search for New Membrane-active Substances: Synthesis of Tropan-3-ols with Alkyl, Alkenyl and Alkenynyl Groups at the Bridgehead
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The synthesis of tropan-3-ols with alkyl, alkenyl and alkynyl groups at the bridgehead is described.The new compounds have been considered as new membrane-active substances that would serve as model compounds for histrionicotoxin (1).Application of the Noyori route to 2-substituted pyrroles was unsuccessful.In order to avoid difficulties in obtaining individual long-chain 4-keto aldehydes for the Robinson condensation of each new model compound a key tropane intermediate (8) was prepared instead.The first attempts to extend the chains of the mesyl ester of the diol (8b) and iodomethyltropanol (9b) by Grignard type coupling failed.Therefore we embarked on a Wittig reaction of the tropane-1-carbaldehyde (11) synthesized in high yield from the diol (8).Indeed, both pent-1-enyl- and pentyl-tropanols, (12) and (13) were obtained.Coupling with an acetylenic phosphorane led to the pent-1-enynyltropanol (14).A further new key compound, namely 3β-acetoxytropan-1-ylacetaldehyde (15) was also synthesized as a precursor to conjugated tropanyl enynes which would more closely resemble the natural product (1).
- Dharanipragada, Ramalinga,Fodor, Gabor
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p. 545 - 550
(2007/10/02)
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- ALDEHYDSELEKTIVITAET VON ALKYLHAFNIUM-KOMPLEXEN IN ALDEHYD-KETONKONKURRENZVERSUCHEN; VERGLEICH ZU ZIRKONIUM- UND TITAN-ANALOGEN KOMPLEXEN SOWIE THEORETISCHE DEUTUNG
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Cl3Hf-Me, in contrast to MeLi is not able to attack an ester or a nitrile group and fails to discriminate in competition experiments between heptanal and diethylketone.To the contrary, Cl3Hf-Bu and (EtO)3Hf-Me are highly aldehyde-selective.An explanation of these findings in comparison with alkylzirconium and alkyltitanium complexes is given.
- Kauffmann, Thomas,Pahde, Claudia,Wingbermuehle, Dorothea
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p. 4059 - 4062
(2007/10/02)
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- UEBER DIE ALDEHYDSELEKTIVITAET VON ALKYLKOMPLEXEN VON SCANDIUM, YTTRIUM, LANTHAN UND LANTHANIDEN IN ALDEHYD/KETON-KONKURRENZVERSUCHEN
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In-situ prepared alkyl complexes Hal2M-Alk (Alk = Me, Bu) of the f-metals Ce, Pr, Nd, Sm, Gd exhibit very low selectivity in competition experiments between heptanal and diethylketone in THF, whereas the selectivity of complexes Hal2M-Me (M = Sc, Y, La) is distinctly higher with decreasing tendency in the sequence Sc>Y>La.These and previously reported results led to a general working hypothesis about the reasons of the aldehyde-selectivity of transition metal alkyls.
- Kauffmann, Thomas,Pahde, Claudia,Tannert, Annegret,Wingbermuehle, Dorothea
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p. 4063 - 4066
(2007/10/02)
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- AN EFFICIENT DEPROTECTIVE METHOD FOR ALLYLIC ALCOHOLS PROTECTED AS METHOXYETHOXYMETHYL (MEM) AND METHOXYMETHYL (MOM) ETHERS
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Methoxyethoxymethyl ethers (MEM) and methoxymethyl ethers (MOM) of allylic alcohols are readily cleaved by pyridinium paratoluenesulfonate (PPTS) in 2-butanone or t-butyl alcohol.This procedure is also efficient for deprotection of benzylic and aliphatic alcohols.
- Monti, H.,Leandri, G.,Klos-Ringuet, M.,Corriol, C.
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p. 1021 - 1026
(2007/10/02)
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- Stereochemistry of Aliphatic Carbocations, 12. Alkyl Shifts between Secondary Carbon Atoms
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Several optically active, β-branched alkylamines have been synthesized from amino acids.The corresponding amines were obtained from isobutyraldehyde and 2-methylbutanal (37), respectively.The stereochemistry at the terminus of 1,2-methyl shifts has been elucidated in the nitrous acid deaminations of 4 and 21.Predominant, although incomplete inversion at the migration terminus is consistent with conformational control rather than neighboring group participation.The deamination of 31 involves a degenerate 1,2-ethyl shift and a nondegenerate 1,2-methyl shift, the reverse holds for 44.Complete inversion at the origin of the methyl migrations and the absence of subsequent retrogressive H shifts strongly support the intermediacy of methyl-bridged carbocations.Partial racemization at the origin of the ethyl migrations has been traced to proton shifts within ethyl-bridged intermediates.Rearranged open cations contribute significantly to the overall reaction if micelles are produced by self-aggregation of the alkylammonium ions.
- Kirmse, Wolfgang,Prolingheuer, Ernst-Christoph
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p. 104 - 128
(2007/10/02)
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