- Probing the mechanism of cyanobacterial aldehyde decarbonylase using a cyclopropyl aldehyde
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Cyanobacterial aldehyde decarbonylase (cAD) is a non-heme diiron oxygenase that catalyzes the conversion of fatty aldehydes to alkanes and formate. The mechanism of this chemically unusual reaction is poorly understood. We have investigated the mechanism of C1-C2 bond cleavage by cAD using a fatty aldehyde that incorporates a cyclopropyl group, which can act as a radical clock. When reacted with cAD, the cyclopropyl aldehyde produces 1-octadecene as the rearranged product, providing evidence for a radical mechanism for C-C bond scission. In an alternate pathway, the cyclopropyl aldehyde acts as a mechanism-based irreversible inhibitor of cAD through covalent binding of the alkyl chain to the enzyme.
- Paul, Bishwajit,Das, Debasis,Ellington, Benjamin,Marsh, E. Neil G.
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- Construction of bifunctional co/h-zsm-5 catalysts for the hydrodeoxygenation of stearic acid to diesel-range alkanes
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Bifunctional Co/H-ZSM-5 zeolites were prepared by a surface organometallic chemistry grafting route, namely, by the stoichiometric reaction between cobaltocene and the Br?nsted acid sites in zeolites. The catalyst was applied to a model reaction of the catalytic hydrodeoxygenation of stearic acid (SA). The cobalt species existed in the form of isolated Co2 + ions at the exchange positions after grafting, transformed to CoO species on the surface of the zeolite, stabilized inside the zeolite channels upon calcination in air, and finally reduced by hydrogen to homogeneous clusters of metallic cobalt species approximately 1.5 nm in size. During this process, the Br?nsted acid sites of the H-ZSM-5 zeolites were preserved with a slight-ly reduced acid strength. The as-prepared bifunctional catalyst exhibited an approximately 16 times higher activity for the hydrodeoxygenation of SA (2.11 gSA gcat1 h1) than the reference catalyst (0.13 gSA gcat1 h1) prepared by solid-state ion exchange and a high C18 /C17 ratio of approximately 24. The remarkable hydrodeoxygenation performance of the bifunctional Co/H-ZSM-5 was owed to the effective synergy between the uniformed metallic cobalt clusters and the Br?nsted acid sites in H-ZSM-5. The simplified reaction network and kinetics of the SA hydrodeoxygenation catalyzed by the as-prepared bifunctional Co/H-ZSM-5 zeolites were also investigated.
- Wu, Guangjun,Zhang, Nan,Dai, Weili,Guan, Naijia,Li, Landong
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- Photobiocatalytic decarboxylation for olefin synthesis
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Here, we describe the combination of OleTJE with a light-driven in situ H2O2-generation system for the selective and quantitative conversion of fatty acids into terminal alkenes. The photobiocatalytic system shows clear advantages regarding enzyme activity and yield, resulting in a simple and efficient system for fatty acid decarboxylation.
- Zachos, Ioannis,Ga?meyer, Sarah Katharina,Bauer, Daniel,Sieber, Volker,Hollmann, Frank,Kourist, Robert
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- Molybdenum carbide-catalyzed conversion of renewable oils into diesel-like hydrocarbons
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In the paper, we report for the first time that the conversion of renewable oils into diesel-like hydrocarbon mixtures can be realized on molybdenum carbides with high activity and selectivity. The molybdenum carbide catalyst exhibited much better resistance to leaching than noble metals and could be reused consecutively for sixteen times without deactivation. Mechanism investigations indicated that molybdenum carbide and palladium showed different reaction selectivities and it was speculated that the level of difficulty in acyl-to-alkyl rearrangement of surface acyl intermediates on molybdenum carbide and palladium resulted in the different product selectivity. Copyright
- Han, Junxing,Duan, Jinzhao,Chen, Ping,Lou, Hui,Zheng, Xiaoming
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- Fe5C2 nanoparticles: A facile bromide-induced synthesis and as an active phase for Fischer-Tropsch synthesis
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Iron carbide nanoparticles have long been considered to have great potential in new energy conversion, nanomagnets, and nanomedicines. However, the conventional relatively harsh synthetic conditions of iron carbide hindered its wide applications. In this
- Yang, Ce,Hou, Yanglong,Zhao, Huabo,Ma, Ding
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p. 15814 - 15821,8
(2012)
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Read Online
- Direct Synthesis of Polysubstituted Aldehydes via Visible-Light Catalysis
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Aldehydes are among the most versatile functional groups for synthetic chemistry. However, access to polysubstituted alkyl aldehydes is very limited and requires lengthy synthetic routes that involve multiple-step functional-group conversion. This paper reports a one-step synthesis of polysubstituted aldehydes from readily available olefin substrates using visible-light photoredox catalysis. Despite a number of competing reaction pathways, commercial styrenes react with vinyl ethers selectively in the presence of an acridinium salt photooxidant and a disulfide hydrogen-atom-transfer catalyst under blue LED irradiation. Alkyl aldehydes with different substitution patterns are prepared in good yields. This strategy can be applied to structurally sophisticated substrates.
- Wu, Fengjin,Wang, Leifeng,Chen, Jiean,Nicewicz, David A.,Huang, Yong
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- COPE elimination reaction observed in the biodegradation of quaternary ammonium surfactants
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The biodegradation of dialkyldimethylammonium compounds in aqueous solutions indicates that part of the degradation pathway includes the Cope elimination reaction, which does not occur under mild conditions in the absence of microorganisms.
- Clancy, Shaun F.,Thies, Michael,Paradies, Henrich
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- Synthesis of 2,2′-quinocyanines with long N-alkyl substituents
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2,2′-Quinocyanines with long alkyl substituents on one or both nitrogen atoms have been synthesized. 1H NMR spectroscopy has been used to study the processes occurring during the alkylation of the starting quinoline bases.
- Orlova,Kolchina,Zhuravlev,Shakirov,Gerasimova,Shelkovnikov
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Read Online
- Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydroboration and Dehydroboration
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We report a dehydroboration process that can be coupled with chain-walking hydroboration to create a one-pot, contra-thermodynamic, short-or long-range isomerization of internal olefins to terminal olefins. This dehydroboration occurs by a sequence comprising activation with a nucleophile, iodination, and base-promoted elimination. The isomerization proceeds at room temperature without the need for a fluoride base, and the substrate scope of this isomerization is expanded over those of previous isomerizations we have reported with silanes.
- Bloomer, Brandon,Butcher, Trevor W.,Ciccia, Nicodemo R.,Conk, Richard J.,Hanna, Steven,Hartwig, John F.
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supporting information
p. 1005 - 1010
(2022/02/10)
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- Effect of crystalline phases and acid sites on the dehydration of 1-octadecanol to 1-octadecene over TiO2–ZrO2 mixed oxides
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Abstract: TiO2–ZrO2 mixed oxides with different amounts of TiO2 were prepared by co-precipitation method and used to synthesize 1-octadecene from 1-octadecanol. The results show that the doping of TiO2 leads to the formation of Lewis acid sites and Br?nsted acid sites on the TiO2–ZrO2 mixed oxides. For catalysts with TiO2 doping 2 doping ≥ 3?wt.%, an amorphous structure and Ti–O–Zr bond are formed. The crystalline phase of metal oxides, amount and type of acid sites simultaneously affect the performance of the catalysts. The acid sites on TiO2–ZrO2 mixed oxides with monoclinic and tetragonal zirconia crystalline phases have much lower dehydration activity than those with an amorphous form. Lewis acid sites are responsible for both the dehydration of 1-octadecanol to form 1-octadecene and the double carbon bond migration of 1-octadecene to form 2-octadecene. Br?nsted acid sites mainly catalyze the double carbon bond migration of 1-octadecene. Graphic abstract: [Figure not available: see fulltext.]
- Duan, Tingming,Xiao, Yong,Zhang, Guoquan,Hou, Bo,Jia, Litao,Li, Debao
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- Palladium-Catalyzed Oxidative Dehydrosilylation for Contra-Thermodynamic Olefin Isomerization
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We report a newly developed, palladium-catalyzed dehydrosilylation of terminal alkylsilanes that combines with chain-walking hydrosilylation to create a one-pot isomerization of internal olefins to terminal olefins. This catalytic dehydrosilylation is one of the few examples of thermal catalytic functionalizations of unactivated alkylsilanes. The reaction involves transmetalation of an alkylsilane, β-hydride elimination, release of the terminal olefin, and reoxidation of the palladium catalyst. A variety of linear internal olefins underwent the overall isomerization to terminal olefins in good yields and in good regioselectivities. Particularly noteworthy, isomerizations occurring over seven carbon units proceeded in yields that are comparable to those of isomerizations occurring over one carbon unit.
- Butcher, Trevor W.,Hanna, Steven,Hartwig, John F.,Wills, Tyler
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p. 8736 - 8741
(2020/09/23)
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- Deoxygenation of Epoxides with Carbon Monoxide
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The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
- Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
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p. 10634 - 10640
(2020/07/30)
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- Chemoselective Hydrodeoxygenation of Carboxylic Acids to Hydrocarbons over Nitrogen-Doped Carbon-Alumina Hybrid Supported Iron Catalysts
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The establishment of catalyst systems for the chemoselective hydrodeoxygenation (HDO) of carboxylic acids to hydrocarbons, such as the HDO of long-chain fatty acids to alkanes, is important for biomass to biofuel conversion. As the most abundant and probably the cheapest transition metal on the earth, iron is a promising non-noble-metal alternative to precious metals for large-scale conversion of biomass. However, it usually suffers from unsatisfactory activity. In this work, a nitrogen-doped carbon-alumina hybrid supported iron (Fe-N-C@Al2O3) catalyst is established for chemoselective HDO of carboxylic acids to hydrocarbons. By using stearic acid HDO as the model reaction, n-octadecane and n-heptadecane are produced with yields of 91.9% and 6.0%, respectively. Triglycerides can also be converted into liquid alkanes with a total molar yield of >92%. In addition, the iron catalyst can chemoselectively catalyze the HDO of the carboxylic acid group in the presence of other functional groups such as an aromatic ring. This chemoselectivity has rarely been seen before because the aromatic ring is usually more easily hydrogenated in comparison to HDO of the carboxylic acid group. The characterization results showed that both the formation of a nitrogen-doped carbon-alumina hybrid and the iron loading are important for the Lewis basicity of these catalysts, in order to adsorb the acid substrates. The addition of melamine as the nitrogen precursor during pyrolysis eliminates undesired reactions between the iron precursor and alumina support to form an inactive hercynite phase, leading to the formation of an Fe3C active phase for the hydrogenation of -COOH to -CH2OH and the hybrid of N-C and alumina for the HDO of -CH2OH to -CH3.
- Li, Jiang,Zhang, Junjie,Wang, Shuai,Xu, Guangyue,Wang, Hao,Vlachos, Dionisios G.
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p. 1564 - 1577
(2019/02/03)
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- Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydrofunctionalization and Formal Retro-hydrofunctionalization
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We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si-F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.
- Hanna, Steven,Butcher, Trevor W.,Hartwig, John F.
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supporting information
p. 7129 - 7133
(2019/09/12)
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- Aminophosphine-based chromium catalysts for selective ethylene tetramerization
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Chromium complexes of three new ligands, Ph2PN(Me)(CH 2)2-X [X = NMe2(PNN); PPh2 (PNP); Py (PNPy)], have been examined vis-a-vis their ability to promote ethylene tetramerization, (PNN)CrCl3(L) [L = THF (1); CH3CN (2)], (PNPy)CrCl3(L) [L = THF (3); CH3CN (4)], and (PNP)CrCl3(THF) (5). In the case of 2 and 4, it was possible to grow crystals suitable for X-ray diffraction. The reaction of 3 with Et3Al afforded the dinuclear [(HN(Me)(CH2)2Py)CrCl 2Et]2 (6) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex 1 displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex 6 is not a self-activating catalyst.
- Shaikh, Yacoob,Gurnham, Joanna,Albahily, Khalid,Gambarotta, Sandro,Korobkov, Ilia
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p. 7427 - 7433,7
(2020/10/15)
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- Selective hydrogenation of alkenes under ultramild conditions
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SiliaCat Pd0 solid catalyst heterogeneously mediates at room temperature the selective hydrogenation of a wide variety of alkenes under hydrogen balloon conditions using a modest 0.1 mol % catalyst amount. The catalyst is recyclable with negligible leaching of valued palladium, providing the chemical industry with a suitable replacement for less selective metal-based catalysts.
- Pandarus, Valerica,Gingras, Genevieve,Beland, Francois,Ciriminna, Rosaria,Pagliaro, Mario
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experimental part
p. 1230 - 1234
(2012/07/28)
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- Radical reduction of epoxides using a titanocene(III)/water system: Synthesis of β-deuterated alcohols and their use as internal standards in food analysis
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We describe a comprehensive study into the Cp2TiCl-mediated reductive epoxide ring opening using either water as a hydrogen source or deuterium oxide as a deuterium source. The remarkable chemical profile of this reaction allows access to alcohols with anti-Markovnikov regiochemistry from different epoxides. The use of D2O as a deuterium source leads to an efficient synthesis of β-deuterated alcohols, including a deuterated sample of tyrosol, a bioactive compound contained in the leaves of the olive, which was successfully applied as an internal standard in food analysis.
- Jimenez, Tania,Campana, Araceli G.,Bazdi, Btissam,Paradas, Miguel,Arraez-Roman, David,Segura-Carretero, Antonio,Fernandez-Gutierrez, Alberto,Oltra, J. Enrique,Robles, Rafael,Justicia, Jose,Cuerva, Juan M.
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experimental part
p. 4288 - 4295
(2010/10/21)
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- Weakening C-O bonds: Ti(III), a new reagent for alcohol deoxygenation and carbonyl coupling olefination
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Investigations detailed herein, including density functional theory (DFT) calculations, demonstrate that the formation of either alkoxy- or hydroxy-Ti(III) complexes considerably decreases the energy of activation for C-O bond homolysis. As a consequence of this observation, we described two new synthetic applications of Nugent's reagent in organic chemistry. The first of these applications is an one-step methodology for deoxygenation-reduction of alcohols, including benzylic and allylic alcohols and 1,2-dihydroxy compounds. Additionally, we have also proved that Ti(III) is capable of mediating carbonyl coupling-olefination. In this sense, and despite the fact that for over 35 years it has been widely accepted that either Ti(II) or Ti(0) was the active species in the reductive process of the McMurry reaction, the mechanistic evidence presented proves the involvement of Ti(III) pinacolates in the deoxygenation step of the herein described Nugent's reagent-mediated McMurry olefination. This observation sheds some light on probably one of the mechanistically more complex transformations in organic chemistry. Finally, we have also proved that both of these processes can be performed catalytically in Cp 2TiCl2 by using trimethylsilyl chloride (TMSCl) as the final oxygen trap.
- Dieguez, Horacio R.,Lopez, Armando,Domingo, Victoriano,Arteaga, Jesus F.,Dobado, Jose A.,Herrador, M. Mar,Quilez Del Moral, Jose F.,Barrero, Alejandro F.
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supporting information; experimental part
p. 254 - 259
(2010/03/25)
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- Glassy carbon modified by a silver-palladium alloy: cheap and convenient cathodes for the selective reductive homocoupling of alkyl iodides
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Micrometer-thick layers of silver-palladium alloy were elaborated in order to modify the surface of glassy carbon electrodes. Such a surface modification can be readily achieved via a preliminary silver galvanostatic deposit onto carbon followed by a 'palladization' step, thanks to a simple immersion in acidic PdII-based solutions producing a displacement reaction. The as-prepared metallic interfaces exhibit outstanding catalytic capabilities especially in the cleavage of carbon-halogen bonds while being chemically/electrochemically quite stable and relatively inexpensive. More specifically, the use of such glassy carbon/Ag-Pd electrodes in dimethylformamide (DMF) containing tetraalkylammonium salts (TAA+X-) makes the one-electron reductions of primary alkyl iodides possible; this reduction leads to the formation of homodimers in high yields. Formation of a free radical as transient resulted from the homocoupling reaction.
- Poizot, Philippe,Jouikov, Viatcheslav,Simonet, Jacques
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body text
p. 822 - 824
(2009/05/07)
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- Mixed disproportionation versus radical trapping in titanocene(III)-promoted epoxide openings
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The formation of either deoxygenation products or allylic alcohols from epoxides is observed when these substrates are treated with Cp2TiCl under anhydrous conditions. It seems that processes via trisubstituted radicals give allylic alcohols whereas processes via disubstituted radicals may give deoxygenation products or allylic alcohols depending on the structure of the original epoxide. This method allows a controlled access to these functional groups, providing a useful tool in organic synthesis. A mechanistic discussion for these transformations is reported.
- Justicia, José,Jiménez, Tania,Morcillo, Sara P.,Cuerva, Juan M.,Oltra, J. Enrique
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experimental part
p. 10837 - 10841
(2010/02/28)
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- Process for hydrogenation of carboxylic acids and derivatives to hydrocarbons
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A process for hydrogenating a carboxylic acid and/or derivative thereof having a carboxylate group represented by the general formula R1COO-, which process comprises feeding hydrogen and the carboxylic acid and/or derivative thereof to a reactor and maintaining conditions within the reactor such that hydrogen reacts with the carboxylic acid and/or derivative thereof to produce a product stream comprising carbon dioxide, carbon monoxide, methane and hydrocarbons represented by general formulae R1H and R1CH3, characterised in that the molar ratio of R1H : R1CH3 is above a pre-determined value and/or the mole ratio of the sum of carbon dioxide, carbon monoxide and methane to carboxylate groups is above a pre-determined value.
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Page/Page column 7-8
(2008/06/13)
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- Unsaturated fatty alcohol derivatives as a source of substituted allylzirconocene
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(Chemical Equation Presented) From A to Z: Allylzirconocenes have been easily prepared in a one-pot procedure through a tandem allylic C-H activation-β-elimination reaction from unsaturated fatty alcohol and ether starting materials (see scheme). The reaction proceeds rapidly under mild condition and is insensitive to the length of the carbon tether between the double bond and the alcohol moiety.
- Chinkov, Nicka,Levin, Anat,Marek, Ilan
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p. 465 - 468
(2007/10/03)
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- Semivolatile and volatile compounds in combustion of polyethylene
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The evolution of semivolatile and volatile compounds in the combustion of polyethylene (PE) was studied at different operating conditions in a horizontal quartz reactor. Four combustion runs at 500 and 850°C with two different sample mass/air flow ratios and two pyrolytic runs at the same temperatures were carried out. Thermal behavior of different compounds was analyzed and the data obtained were compared with those of literature. It was observed that α,ω-olefins, α-olefins and n-paraffins were formed from the pyrolytic decomposition at low temperatures. On the other hand, oxygenated compounds such as aldehydes were also formed in the presence of oxygen. High yields were obtained of carbon oxides and light hydrocarbons, too. At high temperatures, the formation of polycyclic aromatic hydrocarbons (PAHs) took place. These compounds are harmful and their presence in the combustion processes is related with the evolution of pyrolytic puffs inside the combustion chamber with a poor mixture of semivolatile compounds evolved with oxygen. Altogether, the yields of more than 200 compounds were determined. The collection of the semivolatile compounds was carried out with XAD-2 adsorbent and were analyzed by GC-MS, whereas volatile compounds and gases were collected in a Tedlar bag and analyzed by GC with thermal conductivity and flame ionization detectors.
- Font, Rafael,Aracil, Ignacio,Fullana, Andrés,Conesa, Juan A.
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p. 615 - 627
(2007/10/03)
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- Synthesis of amphiphilic thiatrimethinecyanines
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Preparation conditions were optimized for 2-methyl-5-chlorobenzothiazolium quaternary salts with long-chain N-alkyl substituents (C12H 25, C15H31, C18H37). They were used in the synthesis of thiatrimethinecyanines conteining in the meso-position phenyl, p-chlorophenyl, or p-fluorophenyl groups.
- Orlova,Kolchina,Shakirov,Gerasimova,Shelkovnikov
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p. 228 - 231
(2007/10/03)
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- PROCESS FOR THE PRODUCTION OF A WELL FLUIDS BASE OIL VIA METATHESIS OF ALPHA-OLEFINS
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Disclosed is a process for preparation of compositions having utility as well fluid base oils. The process involves metathesis of alpha-olefins followed by isomerization of the metathesis products. The base oils resulting from the process of this invention are environmentally friendly in that they are only mildly toxic to marine life, are highly biodegradable and have very low pour point temperatures. These properties make the base oils ideal candidates for use as components of well fluids for cold climates and offshore applications.
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- Polystyrene-supported (catecholato)oxorhenium complexes: Catalysts for alcohol oxidation with DMSO and for deoxygenation of epoxides to alkenes with triphenylphosphine
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Polymer-supported catalysts offer practical advantages for organic synthesis, such as improved product isolation, ease of catalyst recycling, and compatibility with parallel solution-phase techniques. We have developed the (carboxypolystyrene-catecholato)rhenium catalyst 2 derived from tyramine (=4-(2-amino-ethyl)phenol), which is effective for alcohol oxidation with dimethylsulfoxide (DMSO) and for epoxide deoxygenation with triphenylphosphine. The supported [Re(catecholato)]catalyst 2 is air- and moisture-stable and can be recovered and used repeatedly without decreasing activity. The procedures work with non-halogenated solvents (toluene). DMSO for Re-catalyzed alcohol oxidation is inexpensive and safer for transport and storage than commonly used peroxide reagents. The oxidation procedure was best suited for aliphatic alcohols, and the mild conditions were compatible with unprotected functional groups, such as those of alkenes, phenols, nitro compounds, and ketones (see Tables 1 and 2). Selective oxidation of secondary alcohols in the presence of primary alcohols was possible, and with longer reaction time, primary alcohols were converted to aldehydes without overoxidation. Epoxides (oxirans) were catalytically deoxygenated to alkenes with this catalyst and Ph3P (see Table 3). Alkyloxiranes were converted to the alkenes with retention of configuration, while partial isomerization was observed in the deoxygenation of cis-stilbene oxide (cis-1.2-diphenyloxirane). These studies indicate that supported [Re(catecholato)] complexes are effective catalysts for O-atom-transfer reactions, and are well suited for applications in organic synthesis.
- Arterburn, Jeffrey B.,Liu, Minghua,Perry, Marc C.
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p. 3225 - 3236
(2007/10/03)
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- Porous particulate and cosmetic
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An amphoteric porous particulate containing a basic polysaccharide and a polymer of an organic acid containing a reactive vinyl group or a salt thereof and having an average particle size of 50 μm or less, is capable of adsorbing a large amount of an acid or a base that is stronger than the acid or basic groups thereof and is useful in a deodorant or a cosmetic. The amphoteric porous particulate is made by emulsifying or suspending an aqueous solution containing a basic polysaccharide and an organic acid having a reactive vinyl group in a hydrophobic solvent, followed by polymerization. A deodorant may be made of a chitosan particulate having an average particle size of 0.01 to 50 μm. A polysiloxane having long-chain alkyl groups and a melting point of 20° C. or above is useful as an oil component of a deodorant.
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- Novel tridentate diamino organomanganese(II) complexes as homogeneous catalysts in manganese(II)/copper(I) catalyzed carbon-carbon bond forming reactions
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The new, paramagnetic arylmanganese(II) complex Li[MnCl2(NCN)] (2, NCN [C6H3(CH2NMe2)2-2,6] -) has been obtained in high yield from the reaction of MnCl2 and [Li(NCN)]2 in a 2:1 molar ratio. In THF solution, 2 is likely an ionic species [Li(THF)n] [MnCl2(NCN)] (molecular weight determination and conductivity measurements), while magnetic measurements indicate that a high spin d5 manganese(II) center is present. Subsequent reaction of 2 with RLi afforded [MnR(NCN)] (R=Me (3a), n-Bu (3b)). Complex 2, using CuCl as a co-catalyst, is an effective catalyst system for cross-coupling of Grignard reagents with alkyl bromides and the 1,4-addition of organomagnesium halides to α,β-unsaturated ketones. No further additives or co-solvents are necessary. For both reactions a dramatic decrease in reaction times is observed when compared to standard manganese/copper systems. Alkyl bromides with unsaturated or heteroatom functionalities can be cross-coupled. Also, excellent reactivity towards normally unreactive β,β-disubstituted ketones has been observed in the 1,4-addition reaction.
- Donkervoort, Johannes G.,Vicario, Jose L.,Jastrzebski, Johann T.B.H.,Gossage, Robert A.,Cahiez, Gerard,Van Koten, Gerard
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- Dehydration of α-silylalcohols in the reductive conversion of esters and ketones into alkenes
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The conversion of esters and ketones into easily dehydrated α-silylated alcohols, and protodesilylation of the resultant vinylsilanes, gives alkenes under relatively mild acidic conditions.
- Chenede, Alain,Abd.Rahman, Noorsaadah,Fleming, Ian
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p. 2381 - 2382
(2007/10/03)
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- Fluorination of secondary and primary alcohols by thermal decomposition of electrochemically generated alkoxy triphenylphosphonium tetrafluoroborates
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Replacement of hydroxyl groups in secondary and primary alcohols (1) with a fluorine atom arising from tetrafluoroborate anion has been performed by the electrochemical formation of alkoxy triphenylphosphonium tetrafluoroborates (2) from 1, followed by their thermal decomposition. The procedure is quite simple, involving: (1) constant-current electrolysis of a mixture of 1, Ph3P, and Ph3PH·BF4 in CH2Cl2 in an undivided cell; (2) refluxing a tetrahydrofuran or dioxane solution of the residue afforded by evaporation of the solvent in vacuo after the electrolysis. Cyclic secondary alcohols such as 3β-hydroxy steroids and 2-adamantanol are transformed into the corresponding fluorides in satisfactory yields when the geometry of the leaving group in 2 is suitable for the substitution or an elimination process for 2 to give an alkene is stereochemically forbidden. The fluorination of steroidal alcohols and 4-phenyl-1-cyclohexanol proceeded with complete inversion, demonstrating that a fluorine atom from the tetrafluoroborate anion attacks from the side opposite to the phosphonium moiety in 2 via an SN2 mechanism rather than an SN1 mechanism. The fluorination of acyclic secondary and primary alcohols was performed by the present method in reasonable yields, although the reaction for the latter required more forcing conditions, such as refluxing in dioxane.
- Maeda, Hatsuo,Koide, Takashi,Matsumoto, Sayaka,Ohmori, Hidenobu
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p. 1480 - 1483
(2007/10/03)
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- Novel organomanganese(II) complexes active as homogeneous catalysts in manganese(II)/copper(I) catalyzed carbon-carbon bond formation reactions
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Novel organomanganese complexes 3 and 4 were prepared via transmetallation of the corresponding organolithium reagent. These new complexes are active catalysts in manganese/copper mediated cross-coupling reactions.
- Donkervoort, Johannes G.,Vicario, Jose L.,Jastrzebski, Johann T.B.H.,Cahiez, Gerard,Van Koten, Gerard
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p. 547 - 548
(2007/10/03)
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- Electrochemical Reduction of 1,6-Dihalohexanes at Carbon Cathodes in Dimethylformamide
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Cyclic voltammograms for the reduction of 1,6-dibromo-, 1,6-diiodo-, 1-bromo-6-chloro-, and 1-chloro-6-iodohexane at glassy carbon electrodes in dimethylformamide containing tetramethylammonium perchlorate exhibit single irreversible waves that correspond to the reductive cleavage of carbon-bromine or carbon-iodine bonds.When large-scale controlled-potential electrolyses of either 1,6-dibromo- or 1,6-diiodohexane are performed at reticulated vitreous carbon, the principal products are n-hexane (30-45percent), 1-hexene (28-34percent), 1,5-hexadiene (6-16percent), and cyclohexane (7percent), with n-dodecane being another significant species obtained from 1,6-diiodohexane.Because a carbon-chlorine bond is not directly reducible, 1-bromo-6-chloro- and 1-chloro-5-iodohexane give rise mainly to 1-chlorohexane (47-64percent), 6-chloro-1-hexene (20-33percent), and 1,12-dichlorododecane (2-25percent).From these product distributions, and with the aid of experiments done in the presence of deuterium-labeled reagents, we conclude that the electrolytic reduction of 1,6-diiodo- and 1-chloro-6-iodohexane involves both radical and carbanion intermediates, whereas only carbanionic pathways are important for electrolyses of 1,6-dibromo- and 1-bromo-6-chlorohexane.
- Mubarak, Mohammad S.,Peters, Dennis G.
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p. 681 - 685
(2007/10/02)
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- A Convenient and High Yielding Procedure for the Preparation of Isoselenocyanates. Synthesis and Reactivity of O-Alkylselenocarbamates.
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A high yielding one pot procedure for the preparation of isoselenocyanate from the corresponding formamide is reported.Various aromatic and aliphatic primary amines were employed in order to prepare the isoselenocyanates to establish the generality of the procedure.O-Alkylselenocarbamates of various primary, secondary and tertiary alcohols were synthesized and their stability and comparative reactivity were studied.Radical deoxygenation of the selenocarbamate of a secondary and a tertiary alcohol was accomplished under various conditions.
- Barton, Derek H. R.,Parekh, Shyamal I.,Tajbakhsh, Mahmoud,Theodorakis, Emmanouil A.,Tse, Chi-Lam
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p. 639 - 654
(2007/10/02)
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- Flame retardants compounds
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Polymeric flame retardants comprise halogenated aromatic compounds having acylamino functional groups which are chemically bonded to cyclic imide-containing or imide-forming polymers or copolymers. The polymeric flame retardants are prepared by the reaction of halogenated aromatics containing a reactive hydrazido group with some or all of the anhydride groups of an cyclic alpha, beta-unsaturated dicarboxylic acid anhydride polymer or copolymer to form pendant halogenated-aromatic-substituted imide or amic acid groups. In addition, polymeric flame retardants are used to render thermoplastic resins less flammable under conditions which promote combustion. Novel flame retardant hydrazides are disclosed.
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- TETRABUTYLAMMONIUM BIFLUORIDE: A VERSATILE AND EFFICIENT FLUORINATING AGENT
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The use of tetrabutylammonium bifluoride as stable and easily available source of fluoride ion in nucleophilic substitution processes with different substrates is reported.
- Bosch, Pilar,Camps, Francisco,Chamorro, Esther,Gasol, Vicens,Guerrero, Angel
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p. 4733 - 4736
(2007/10/02)
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- Spiro[isoxazalidine-3,2'-tricyclo[3.3.1.13,7 ] decanes]
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The compounds are of the class of adamantanyl isoxazolidine derivatives useful as anti-inflammatory, antihypoxia, antimicrobial and anticonvulsant agents. Exempliary of a species of the compounds is 2 methyl-5-n-hexyl-spiro[isoxazolidin-3,2'-tricyclo[3.3.1.13,7 ] decane].
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- The Invention of New Radical Chain Reactions. Part 12. Improved Methods for the Addition of Carbon Radicals to Substituted Allylic Groups
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Reagents for the allylation of carbon radicals derived from the esters (mixed anhydrides) of N-hydroxy-2-thiopyridone have been investigated.Because of competition between the background reaction of decarboxylative rearrangement and the desired allylation process, conventional allylation reagents give moderate yields of the desired adducts.Improved yields are secured if the β-position bears an electron withdrawing group.A concerted addition and elimination process can be postulated.
- Barton, Derek H. R.,Crich, David
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p. 1613 - 1620
(2007/10/02)
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- Liquid-Crystalline Solvents as Mechanistic Probes. 20. Crystalline and Smectic B Solvent Control over the Selectivity of Photodimerization of n-Alkyl Cinnamates
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The photodimerizations of n-octadecyl, n-hexadecyl, and n-tetradecyl esters of trans-cinnamic acid have been investigated in the crystalline, smectic B, and isotropic phases of n-butyl stearate.A strong preference for head-to-tail dimerization is found in the ordered solvent phases.Dipole-dipole-induced interactions between cinnamates and solvent-mediated solute alignments are the factors that combine to control the regioselectivity of photodimerization.The ability of cinnamate esters to be incorporated into the ordered solvent phases is extremely dependent upon the length of the n-alkyl solute chains.However, ease of incorporation has little influence upon regioselectivity.
- Ramesh, Varadaray,Weiss, Richard G.
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p. 2535 - 2539
(2007/10/02)
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- SODIUM HYDROGEN TELLURIDE AS A USEFUL NUCLEOPHILIC REAGENT FOR THE CLEAVAGE OF EPOXIDES AND OF QUATERNARY AMMONIUM SALTS
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Sodium hydrogen telluride opens many epoxides cleanly by an SN2 process to give telluro-alcohols, which by reduction with nickel boride afford alcohols.An intermediate telluro-alcohol was converted to olefin in high yield by treatment with p-toluene-sulphonyl chloride in pyridine.Quaternary ammonium salts are also cleaved efficiently by sodium hydrogen telluride.
- Barton, Derek H. R.,Fekih, Abdelwaheb,Lusinchi, Xavier
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p. 6197 - 6200
(2007/10/02)
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- Type II Photochemistry of Ketones in Liquid Crystalline Solvents. The Influence of Ordered Media on Biradical Dynamics
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The Norrish type II photochemistry of five alkylphenones, PhCO(CH2)nH (1a, n=4; 1b, n=10; 1c, n=17; 1d, n=19; 1e, n=21), 10-nonadecanone (2), and 2-undecanone (3) was studied in the isotopic, smetic, and solid phases of n-butyl stearate.The ratio of elimination-to-cyclization products for ketones 1c-e and 2 exhibits a strong phase dependence with a 7-8-fold increase in the smectic phase relative to the isotropic phase.The ratio of isomeric cyclobutanols from 2 shows a similar change.Further increases in the elimination-to-cyclization ratio are observed for 1d in the solid phase.The product ratios for ketones 1a, 1b, and 3 are the same in all the phase studied.Transient absorption studies on the intermediate 1,4-biradical produced from laser flash photolysis of 1d yield lifetimes of 64 +/- 5 and 70 +/- 5 ns in the isotopic and smectic phases, respectively.These results are explaned in terms of the structures of the various phases of n-butyl stearate and the accepted behavior of Norrish type II biradicals.
- Hrovat, David A.,Liu, Jerry H.,Turro, Nicholas J.,Weiss, Richard G.
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p. 7033 - 7037
(2007/10/02)
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- 1,3(R):4,6(R)-DI-O-BENZYLIDEN-D-MANNIT ALS AUSGANGSPRODUKT FUER DIE SYNTHESE OPTISCH AKTIVER GLYCERIN-DERIVATE
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Starting from the di-O-benzylidene-D-mannitol derivative 11, certain types of optically active glycerol derivatives can be prepared with a minimum of protecting group chemistry.This is exemplified by an efficient synthesis of 2-O-alkyl glyceric acid derivatives 22 and 23.
- Schubert, Thomas,Kunisch, Franz,Welzel, Peter
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p. 2211 - 2217
(2007/10/02)
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- AN IMPROVED METHOD FOR OLEFIN SYNTHESIS USING PYRIDYLSELENO GROUP AS A LEAVING GROUP
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Alkyl pyridyl selenides are oxidized by 1.5 equiv. of 30percent H2O2 in THF to give olefins in good to excellent yields.The yields are always higher than the case where alkyl phenyl selenides are used under the same conditions.
- Toshimitsu, Akio,Owada, Hiroto,Uemura, Sakae,Okano, Masaya
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p. 5037 - 5038
(2007/10/02)
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