- Kinetics of the thermal isomerization of 1,1,2-trimethylcyclopropane
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The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2-trimethylcyclopropane to three isomeric methylpentenes and two dimethyl-butenes have been determined over a wide range of temperatures, 688-1124 K, using both static and shock tube reactors. For the overall loss of reactant. Ea =63.7 (±0.5) kcal/mol and log10 A= 15.28 (±0.12). These values are higher by 2.6 kcal/mol and 0.7-0.8 than previously reported from experimental work or predicted from thermochemical calculations. Ea for the formation of trans-4-methyl-2-pentene is 1.5 kcal/mol higher than Ea for the formation of the cis isomer, which is identical to the Ea difference previously reported for the formation of trans- and cis-2-butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the C - C ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclo-propanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1, 1-or 1,2-dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in C - C bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes.
- Lewis, David K.,Hughes, Steven V.,Miller, Justine D.,Schlier, Jessica,Wilkinson, Kevin A.,Wilkinson, Sara R.,Kalra, Bansi L.
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- [BO2]? as a Synthon for the Generation of Boron-Centered Carbamate and Carboxylate Isosteres
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Oxoborane carbamate and carboxylate analogues result from the in situ trapping of [BO2]? produced by elimination of 2,3-dimethyl-2-butene from a pinacolatoboryl anion.
- Hill, Michael S.,Mahon, Mary F.,McMullin, Claire L.,Pécharman, Anne-Frédérique
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- Cyclopentadienyl(allyl) (butadiene)hafnium compounds. Synthesis, crystal structure, and dynamics of cyclopentadienyl(1,2,3-trimethylallyl)(1,2-dimethylbutadiene)-hafnium and cyclopentadienyl(1,1,2-trimethylallyl)-(2,3-dimethylbutadiene)hafnium
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The reaction of CpHfCl3·2THF with 2 equiv of (1,2,3-Me3allyl)MgBr or (1,1,2-Me3allyl)MgBr yields Cp(1,2,3-Me3allyl)(1,2-Me2butadiene)Hf (3) or Cp(1,1,2-Me3allyl)(2,3-Me2butadiene)Hf (4). X-ray crystallography of 3 shows that both the allyl and butadiene ligands assume a prone orientation with respect to Cp. For 3: cell constants a = 15.109 (5), b = 7.150 (2), c = 15.587 (6) A?, β = 115.41 (1)°; space group P21/c; R = 0.0305, Rw = 0.0347. Variable-temperature 1H NMR studies indicate that compound 3 is static on the NMR time scale whereas 4 exists in two isomeric forms and undergoes three separate dynamic processes involving η3-η1 isomerization at the unsubstituted and substituted ends of the allyl ligand [ΔG? = 39.4 ± 1.0 kJ/mol and 73.4 ± 1.0 kJ/mol, respectively] and butadiene flip [ΔG?(avg) = 49.8 ± 1.0 kJ/mol].
- Prins, Thomas J.,Hauger, Bryan E.,Vance, Peter J.,Wemple, Michael E.,Kort, David A.,O'Brien, Jonathan P.,Silver, Michael E.,Huffman, John C.
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- Temperature Effect on Ion-Molecule Reaction of Hydrogen Transfer in γ-Irradiated 2,3-Dimehylbutane at 4 K and 77 K As Studied by Electron Spin Resonance Spectroscopy
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Drastic temperature effects on an ion-molecule reaction of H2 transfer in solid hydrocarbon systems were studied at 4 and 77 K by ESR spectroscopy.When a 2,3-dimethylbutane (DMB)-SF6 (0.55 mol percent)-i-C4H8 (0.55 mol percent) mixture is irradiated at 4 K, the DMB(+) ion in addition to the DMB radical is formed.The tetramethylethylene (TME) cation is produced by warming the irradiated DMB-SF6-i-C4H8 mixture from 4 to 77 K.The formation of the TME(+) ion observed at 77 K is interpreted in terms of the H2 transfer reaction between the DMB(+) ion and i-C4H8.This ion-molecule reaction is completely suppressed at 4 K.The suppression of the ion-molecule reaction is explained by failure of the formation of a reaction complex in the rigid matrix at 4 K.The amounts of TME(+) ions in the DMB-SF6-i-C4H8 mixture increase gradually upon storage of the irradiated mixture at 77 K.This result indicates that the transfer reaction occurs slowly at 77 K.
- Miyazaki, Tetsuo,Tsuruta, Haruyuki,Fujitani, Yoshiteru,Fueki, Kenji
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- Pulse Radiolysis and E.S.R. Evidence for the Formation of an Alkene Radical Cation in Aqueous Solution
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Direct pulse radiolysis evidence, complemented by e.s.r. experiments, establishes that the radical cation Me2C=-C.Me2 (λmax ca. 290 nm) is formed by acid-catalysed elimination of OH- from .CMe2CMe2OH; the radica
- Asmus, Klaus-Dieter,Williams, Peter S.,Gilbert, Bruce C.,Winter, Jeremy N.
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- Isomerization of Olefin Radical Cations in ZSM-5 Zeolites
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Variable-temperature EPR was used to investigate reactions of olefin radical cations generated radiolytically in nonacidic and acidic ZSM-5 zeolites.The olefin radical cations undergo isomerization reactions even at 4K.Radical cation reactions are presumably driven by the exothermicity of charge transfer, which is not efficiently quenched by the vibrational modes of the zeolite lattice.The observation of H-addition type radicals indicates Bronsted acid-catalyzed rearrangements prior to irradiation on the more acidic zeolites.
- Werst, D. W.,Tartakovsky, E. E.,Picos, E. A.,Trifunac, A. D.
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- Radiolytic Generation of Organic Radical Cations in Zeolite Na-Y
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Several examples of radiolytically generated organic radical cations in zeolite Na-Y are illustrated.EPR studies of organic radical cations can be carried out in a wide range of temperatures up to room temperature.In every case, monomeric radical cations were observed.Comparison to previous work in freon and xenon matrices is made, illustrating that in the zeolite Na-Y there is considerably weaker radical cation-host interaction.A mechanism of radiolytic generation of radical cations in zeolite Na-Y is proposed.
- Qin, X.-Z.,Trifunac, A. D.
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- Photocatalytic Oxidative [2+2] Cycloelimination Reactions with Flavinium Salts: Mechanistic Study and Influence of the Catalyst Structure
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Flavinium salts are frequently used in organocatalysis but their application in photoredox catalysis has not been systematically investigated to date. We synthesized a series of 5-ethyl-1,3-dimethylalloxazinium salts with different substituents in the positions 7 and 8 and investigated their application in light-dependent oxidative cycloelimination of cyclobutanes. Detailed mechanistic investigations with a coumarin dimer as a model substrate reveal that the reaction preferentially occurs via the triplet-born radical pair after electron transfer from the substrate to the triplet state of an alloxazinium salt. The very photostable 7,8-dimethoxy derivative is a superior catalyst with a sufficiently high oxidation power (E=2.26 V) allowing the conversion of various cyclobutanes (with Eox up to 2.05 V) in high yields. Even compounds such as all-trans dimethyl 3,4-bis(4-methoxyphenyl)cyclobutane-1,2-dicarboxylate can be converted, whose opening requires a high activation energy due to a missing pre-activation caused by bulky adjacent substituents in cis-position.
- Hartman, Tomá?,Reisnerová, Martina,Chudoba, Josef,Svobodová, Eva,Archipowa, Nataliya,Kutta, Roger Jan,Cibulka, Radek
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p. 373 - 386
(2021/02/01)
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- Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
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Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
- Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
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supporting information
p. 9102 - 9112
(2020/03/30)
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- Spiro[1,2]oxaphosphetanes of nonstabilized and semistabilized phosphorus ylide derivatives: Synthesis and kinetic and computational study of their thermolysis
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A series of tri- and tetrasubstituted spiro-oxaphosphetanes stabilized by ortho-benzamide (oBA) and N-methyl ortho-benzamide (MoBA) ligands have been synthesized by the reaction of Cα,Cortho-dilithiated phosphazenes with aldehydes and ketones. They include enantiopure products and the first example of an isolated oxaphosphetane having a phenyl substituent at C3 of the ring. Kinetic studies of their thermal decomposition showed that the process takes place irreversibly through a polar transition state (ρ = -0.22) under the influence of electronic, [1,2], [1,3] steric, and solvent effects, with C3/P-[1,2] interactions as the largest contribution to ΔG of olefination. Inversion of the phosphorus configuration through stereomutation has been observed in a number of cases. DFT calculations showed that oBA derivatives olefinated through the isolated (N, O)(Ph, C6H4, C) oxaphosphetanes (Channel A), whereas MoBA compounds decomposed faster via the isomer (C6H4, O)(C, N, Ph) formed by P-stereomutation involving a MB2 permutational mechanism (Channel B). The energy barrier of P-isomerization is lower than that of olefination. Fragmentation takes place in a concerted asynchronous reaction. The thermal stability of oxaphosphetanes is determined by strong C3/P-[1,2] interactions destabilizing the transition state of olefination. The effect of charge distribution and C3/C4-[1,2] and C4/P-[1,3] steric and solvent interactions on ΔG was also evaluated.
- López, Jesús García,Sansores Peraza, Pablo M.,Iglesias, María José,Roces, Laura,García-Granda, Santiago,Ortiz, Fernando López
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supporting information
p. 14570 - 14591
(2020/11/20)
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- A smarter approach to catalysts by design: Combining surface organometallic chemistry on oxide and metal gives selective catalysts for dehydrogenation of 2,3-dimethylbutane
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2,3-dimethylbutane is selectively converted into 2,3-dimethylbutenes at 500 °C under hydrogen or at 390 °C under nitrogen in the presence of bimetallic catalysts Pt-Sn/Li-Al2O3. The high stability of the catalyst along the reaction is obtained by selective modification of the Pt/Li-Al2O3 catalyst using Surface Organometallic Chemistry (SOMC).
- Rouge, Pascal,Garron, Anthony,Norsic, Sébastien,Larabi, Cherif,Merle, Nicolas,Delevoye, Laurent,Gauvin, Regis M.,Szeto, Kai C.,Taoufik, Mostafa
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- Olefin oligomerization via new and efficient Br?nsted acidic ionic liquid catalyst systems
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Olefin oligomerization reaction catalyzed by new catalyst systems (a Br?nsted-acidic ionic liquid as the main catalyst and tricaprylylmethylammonium chloride as the co-catalyst) has been investigated. The synthesized Br?nsted acidic ionic liquids were characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV), 1H nuclear magnetic resonance (NMR), and 13C NMR to analyze their structures and acidities. The influence of different ionic liquids, ionic liquid loading, different co-catalysts, catalyst ratios (mole ratio of ionic liquid to co-catalyst), reaction time, pressure, temperature, solvent, source of reactants, and the recycling of catalyst systems was studied. Among the synthesized ionic liquids, 1-(4-sulfonic acid)butyl-3-hexylimidazolium hydrogen sulfate ([HIMBs]HSO4) exhibited the best catalytic activity under the tested reaction conditions. The conversion of isobutene and selectivity of trimers were 83.21% and 35.80%, respectively, at the optimum reaction conditions. Furthermore, the catalyst system can be easily separated and reused; a feasible reaction mechanism is proposed on the basis of the distribution of experimental products.
- Wang, Guoqin,Song, Heyuan,Li, Ruiyun,Li, Zhen,Chen, Jing
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p. 1110 - 1120
(2018/05/28)
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- Alkanethiolate-capped palladium nanoparticles for selective catalytic hydrogenation of dienes and trienes
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Selective hydrogenation of dienes and trienes is an important process in the pharmaceutical and chemical industries. Our group previously reported that the thiosulfate protocol using a sodium S-alkylthiosulfate ligand could generate catalytically active Pd nanoparticles (PdNP) capped with a lower density of alkanethiolate ligands. This homogeneously soluble PdNP catalyst offers several advantages such as little contamination via Pd leaching and easy separation and recycling. In addition, the high activity of PdNP allows the reactions to be completed under mild conditions, at room temperature and atmospheric pressure. Herein, a PdNP catalyst capped with octanethiolate ligands (C8 PdNP) is investigated for the selective hydrogenation of conjugated dienes into monoenes. The strong influence of the thiolate ligands on the chemical and electronic properties of the Pd surface is confirmed by mechanistic studies and highly selective catalysis results. The studies also suggest two major routes for the conjugated diene hydrogenation: the 1,2-addition and 1,4-addition of hydrogen. The selectivity between two mono-hydrogenation products is controlled by the steric interaction of substrates and the thermodynamic stability of products. The catalytic hydrogenation of trienes also results in the almost quantitative formation of mono-hydrogenation products, the isolated dienes, from both ocimene and myrcene.
- Chen, Ting-An,Shon, Young-Seok
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p. 4823 - 4829
(2017/10/19)
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- Revealing Hydrogenation Reaction Pathways on Naked Gold Nanoparticles
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Gold nanoparticles (AuNPs) display distinct characteristics as hydrogenation catalysts, with higher selectivity and lower catalytic activity than group 8-10 metals. The ability of AuNPs to chemisorb/activate simple molecules is limited by the low coordination number of the surface sites. Understanding the distinct pathways involved in the hydrogenation reactions promoted by supported AuNPs is crucial for broadening their potential catalytic applications. In this study, we demonstrate that the mechanism of the hydrogenation reactions catalyzed by AuNPs with "clean" surfaces may proceed via homolytic or heterolytic hydrogen activation depending on the nature of the support. The synthesis of naked AuNPs employing γ-Al2O3 and ionic liquid (IL)-hybrid γ-Al2O3 supports was accomplished by sputtering deposition using ultrapure gold foils. This highly reproducible and straightforward procedure furnishes small (～6.6 nm) and well-distributed metallic gold nanoparticles (Au(0)NPs) that are found to be active catalysts for the partial and selective hydrogenation of substituted conjugated dienes, alkynes, and α,β-unsaturated carbonyl compounds (aldehydes and ketones). Kinetic and deuterium labeling studies indicate that heterolytic hydrogen activation is the primary pathway occurring on the AuNPs imprinted directly on γ-Al2O3. In contrast, AuNPs supported on IL-hybrid γ-Al2O3 materials cause the reaction to proceed via a homolytic hydrogen activation pathway. The IL layer surrounds the AuNPs and acts as a cage, influencing the frequency of the interaction of the catalytically active species and the metal surface and, consequently, the catalytic performance of the AuNPs. The IL layer is shown to improve the product selectivity by the enhancement of the substrate/product discrimination, and to decrease the catalytic activity by shifting the rate-determining step to the H2 and substrate competitive adsorption/activation on the same active sites. A series of kinetic experiments suggest that AuNPs imprinted on an IL-hybrid γ-Al2O3 support are more efficient (lower activation energy, Ea) than group 8-10 metal based catalysts for hydrogenation reactions at moderate to high temperatures (75-150 °C).
- Luza, Leandro,Rambor, Camila P.,Gual, Aitor,Alves Fernandes, Jesum,Eberhardt, Dario,Dupont, Jairton
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p. 2791 - 2799
(2017/05/31)
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- Bifunctional Catalysts Based on Tungsten Hydrides Supported on Silicated Alumina for the Direct Production of 2,3-Dimethylbutenes and Neohexene from Isobutene
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Well-defined bifunctional supported catalysts that comprise tungsten hydride moieties and Br?nsted acid sites were prepared successfully. The catalysts showed outstanding activities and selectivities toward the formation of high-value-added products, 2,3-dimethylbutenes and 3,3-dimethylbutene, through a combination of the metathesis and dimerization of isobutene. The relationship between the physicochemical properties of the catalysts and their activities and selectivities indicated that isobutene conversion increased from 4 to 95 % as a function of the silica content of the silicated alumina (obtained from Sasol). Nevertheless, the selectivity toward branched hexenes showed a volcano-shaped curve that presented a maximum for the catalyst with 5 wt % silica. Therefore, the control of the support acidity by the silica loading on alumina resulted in an increase of the selectivity toward neohexene.
- Larabi, Cherif,Garron, Anthony,Rouge, Pascal,Szeto, Kai C.,Norsic, Sébastien,De Mallmann, Aimery,Merle, Nicolas,Taoufik, Mostafa
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p. 2160 - 2166
(2017/06/27)
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- Divalent Silicon-Assisted Activation of Dihydrogen in a Bis(N-heterocyclic silylene)xanthene Nickel(0) Complex for Efficient Catalytic Hydrogenation of Olefins
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The first chelating bis(N-heterocyclic silylene)xanthene ligand [SiII(Xant)SiII] as well as its Ni complexes [SiII(Xant)SiII]Ni(η2-1,3-cod) and [SiII(Xant)SiII]Ni(PMe3)2 were synthesized and fully characterized. Exposing [SiII(Xant)SiII]Ni(η2-1,3-cod) to 1 bar H2 at room temperature quantitatively generated an unexpected dinuclear hydrido Ni complex with a four-membered planar Ni2Si2 core. Exchange of the 1,3-COD ligand by PMe3 led to [SiII(Xant)SiII]Ni(PMe3)2, which could activate H2 reversibly to afford the first SiII-stabilized mononuclear dihydrido Ni complex characterized by multinuclear NMR and single-crystal X-ray diffraction analysis. [SiII(Xant)SiII]Ni(η2-1,3-cod) is a strikingly efficient precatalyst for homogeneous hydrogenation of olefins with a wide substrate scope under 1 bar H2 pressure at room temperature. DFT calculations reveal a novel mode of H2 activation, in which the SiII atoms of the [SiII(Xant)SiII] ligand are involved in the key step of H2 cleavage and hydrogen transfer to the olefin.
- Wang, Yuwen,Kostenko, Arseni,Yao, Shenglai,Driess, Matthias
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supporting information
p. 13499 - 13506
(2017/10/05)
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- SnCl4-Zn: A novel reductive system for deoxygenative coupling of aliphatic, aromatic, chalcone epoxide, and indanone carbonyl compounds to olefins
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SnCl4-Zn complex provided a novel reductive system in the deoxygenative cross-coupling of aliphatic, aromatic, chalcone epoxide and indanone carbonyl compounds to olefins in high yield (55-86%) at reflux temperature in THF. The advantage of this reagent is inexpensive, short reaction time, and high yield compared to the reagents used in the McMurry cross-coupling reaction.
- Pathe, Gulab Khushalrao,Ahmed, Naseem
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supporting information
p. 1555 - 1561
(2015/03/14)
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- Influence of the support on the selective ring opening of methylcyclohexane and decalin catalyzed by Rh-Pd catalysts
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Rh-Pd catalysts supported on Al2O3, SiO2 and SiO2-Al2O3 (SIRAL 40) were studied for methylcyclohexane (MCH) and decalin ring opening reactions. It was found that the Rh/Pd atomic ratios were similar to the theoretically expected one and the metal dispersion values varied between 30 and 50%. On bimetallic catalysts supported on Al2O3 and SiO2, Pd and Rh were present mainly in the form of monometallic particles, whereas a heterogeneous distribution constituted of large Pd particles and small bimetallic ones were observed on SIRAL 40. Total and Bronsted acidities followed the order: SIRAL 40 >> Al2O3 > SiO2. Al2O3 supported catalysts were the most suitable for MCH ring opening, while the opening of decalin was favored by using SiO2-Al2O3 (SIRAL 40). The catalysts supported on SiO2 produced mainly dehydrogenated compounds. The higher total and Bronsted acidities of SIRAL 40 series had a great impact on the opening of bicyclic naphthenes, whereas the metal function of the catalyst and the hydrogenolytic activity of Rh had a major role during MCH reaction. Using bimetallic catalysts in the MCH reaction decreased the formation of cracking and dehydrogenated products, and the selective formation of RO products could be optimized by tuning the working temperature.
- D'Ippolito, Silvana A.,Especel, Catherine,Vivier, Laurence,Pronier, Stéphane,Epron, Florence,Pieck, Carlos L.
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p. 203 - 214
(2015/02/19)
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- Steric effects in reactions of decamethyltitanocene hydride with internal alkynes, conjugated diynes, and conjugated dienes
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Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1C≡CR2 into its Ti-H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1C=CHR 2)] (2a-e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe 3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti-H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a-4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC≡C) 2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a-2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1C=CHR2)] 3a-3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a-3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [CpTi(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a-4c, 5a, 6b, and 7.
- Pinkas, Jiri,Gyepes, Robert,Cisarova, Ivana,Kubista, Jiri,Horacek, Michal,Mach, Karel
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p. 3399 - 3413
(2014/08/05)
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- Well-defined supported mononuclear tungsten oxo species as olefin metathesis pre-catalysts
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[WOCl4] was grafted on silica dehydroxylated at 200 °C, and the structure of the surface species was elucidated by a combination of spectroscopic and theoretical methods, demonstrating the formation of [(≡SiO)2WOCl2] (1a)
- Bouhoute, Yassine,Garron, Anthony,Grekov, Denys,Merle, Nicolas,Szeto, Kai C.,De Mallmann, Aimery,Del Rosal, Iker,Maron, Laurent,Girard, Guillaume,Gauvin, Rgis M.,Delevoye, Laurent,Taoufik, Mostafa
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p. 4232 - 4241
(2015/02/19)
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- Rhodium-catalyzed hydrogenation of olefins in γ-valerolactone-based ionic liquids
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γ-Valerolactone-based ionic liquids were successfully used as the catalyst phase for [Rh(cod)2][BF4]/RP(C6H 4-m-SO3Na)2 (R = Me, Pr, Bu, Cp) catalyzed hydrogenation of different olefins. Compared to broadly used ionic liquids e.g. 1-butyl-3-methylimidazolium chloride [bmim][Cl], the turnover frequencies were significantly higher and the reaction was selective for the CC double bonds in the presence of carbonyl, cyano, and phenyl groups. The catalyst was recycled for ten consecutive runs under regular or biphasic conditions without loss of activity. The vapour pressure and viscosity of γ-valerolactone-based ionic liquids were determined as well.
- Stradi, Andrea,Molnar, Mark,Ovari, Mihaly,Dibo, Gabor,Richter, Frank U.,Mika, Laszlo T.
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p. 1857 - 1862
(2013/09/24)
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- Vanadium-catalyzed deoxydehydration of glycols
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A survey of several metavandate (VO3-) and chelated dioxovanadium derivatives shows that tetrabutylammonium dioxovanadium(v) dipicolinate most effectively catalyzes the deoxydehydration (DODH) of glycols to olefins in moderate to excellent yields with triphenylphosphine or sodium sulfite as reductants.
- Chapman Jr., Garry,Nicholas, Kenneth M.
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supporting information
p. 8199 - 8201
(2013/09/12)
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- The methylation of alkenes to triptyls with dimethyl carbonate
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A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls.
- Armitage, Gareth G.,Bonati, Matteo L. M.,Guo, Neng,Gaemers, Sander,Shabaker, John W.
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p. 370 - 374
(2013/05/21)
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- SELECTIVE DEHYDRATION OF ALCOHOLS TO DIALKYLETHERS AND INTEGRATED ALCOHOL-TO-GASOLINE PROCESSES
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The invention involves an integrated process for converting a C1-C4 alcohol to gasoline and/or diesel boiling tinge product, said process comprising: contacting a C1-C4 alcohol feed under selectively dehydrating conditions with a catalyst comprising γ-alumina which is substantially free of terminal hydroxyl groups on tetrahedrally coordinated aluminum sites of the catalyst to form a dialkylether dehydration product; and contacting the dialkylether dehydration product with a zeolite conversion catalyst under conversion conditions to form the gasoline and/or diesel boiling range hydrocarbon product.
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Paragraph 0045
(2013/04/24)
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- Stable vapor-phase catalytic conversion of pinacolone into 2,3-dimethyl-1,3-butadiene
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In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene from pinacolone over modified alumina catalysts, it was found that alumina modified with transition metals such as Co stabilized the conversion of pinacolone and produced 2,3- dimethyl-1,3-butadiene selectively under hydrogen flow conditions, whereas the catalytic activity of pure alumina was seriously deteriorated irrespective of its high initial activity.
- Sato, Satoshi,Sato, Natsumi,Yamada, Yasuhiro
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supporting information; experimental part
p. 831 - 833
(2012/09/22)
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- Accuracy of calculations of heats of reduction/hydrogenation: Application to some small ring systems
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The enthalpies of reduction of carbonyl compounds and hydrogenation of alkenes have been calculated at the HF, B3LYP, M06, MP2, G3, G4, CBS-QB3, CBS-APNO, and W1BD levels and, in the case of the first four methods, using a variety of basis sets up to aug-cc-pVTZ. The results are compared with the available experimental data, and it is found that the compound methods are generally more satisfactory than the others. Large basis sets are usually needed in order to reproduce experiments. Some C-C bond hydrogenolysis reactions also have been examined including those of bicycloalkanes and propellanes. In addition, the dimerization of the remarkably strained bicyclo[2.2.0]hex(1,4)ene was studied. The reaction forming a pentacyclic propellane was calculated to have ΔH = -57 kcal/mol, and the cleavage of the propellane to give a diene had ΔH = -71 kcal/mol. The strain energies of these compounds were estimated.
- Wiberg, Kenneth B.
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p. 10393 - 10398
(2013/01/15)
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- Process and system for the production of isoprene
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Disclosed herein is a process for producing isoprene that includes reacting a mixed C4 metathesis feed stream comprising isobutylene and at least one of 1-butene and 2-pentene in a first metathesis reactor in the presence of a first metathesis catalyst under conditions sufficient to produce an intermediate product stream comprising at least 30 wt. % 2-methyl-2-pentene based upon the olefin content of fresh feed in the mixed C4 feed stream, and at least one of ethylene and propylene, separating the 2-methyl-2-pentene, subjecting the separated 2-methyl-2-pentene to pyrolysis to produce a reaction product stream comprising isoprene, and separating the isoprene into an isoprene product stream using fractionation. A system used in producing isoprene is also disclosed.
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Page/Page column 6-7
(2011/02/26)
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- Highly active and recyclable heterogeneous iridium pincer catalysts for transfer dehydrogenation of alkanes
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Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of alkanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on γ-alumina (γ-Al2O3), through basic functional groups on the para-position of the pincer ligand. The simplest of these approaches, adsorption on γ-Al2O3, is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para-substituent and that this has only a relatively subtle and indirect influence on catalytic behavior.
- Huang, Zheng,Brookhart, Maurice,Goldman, Alan S.,Kundu, Sabuj,Ray, Amlan,Scott, Susannah L.,Vicente, Brian C.
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experimental part
p. 188 - 206
(2009/10/02)
-
- AROMATIC HYDROGENATION CATALYST AND PROCESS
-
An MCM-41 catalyst having a crystalline framework containing SiO2 and a Group IV metal oxide, such as TiO2 or ZrO2 is provided. The catalyst is low in acidity and is suitable for use in processes involving aromatic saturation of hydrocarbon feedstocks.
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Page/Page column 30; 31; 32; 33
(2009/08/14)
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- SUPPORTED IRIDIUM CATALYSTS
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A method of converting at least one first alkane to a mixture of at least one low molecular weight alkane (optionally also including additional lower and/or higher molecular weight alkanes) and at least one high molecular weight alkane, comprises: reacting a first alkane in the presence of dual catalyst system comprising a first catalyst (i.e., a hydrogen transfer catalyst) and a second catalyst (i.e., a metathesis catalyst) to produce a mixture of low and high molecular weight alkanes.
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Page/Page column 19-20
(2009/01/24)
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- Process for manufacturing neohexene
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The present invention relates to a process for manufacturing neohexene, comprising contacting isobutene with a supported catalyst comprising a tungsten compound chosen from tungsten hydrides, organometallic tungsten compounds and organometallic tungsten hydrides, and a support comprising an oxide of aluminium, so as to form a reaction mixture comprising neohexene, and preferably separating neohexene from the reaction mixture, so as to isolate it. The contacting leads to the direct production of neohexene, in particular in a single (reaction) stage and with a high molar selectivity for neohexene. The contacting can be performed at a temperature of 50 to 600 °C, under a total absolute pressure of 0.01 to 100 MPa.
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Page/Page column 15
(2008/12/06)
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- Novel photoinduced reduction of conjugate dienes by the combination of benzenethiol and diphenyl diselenide
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By using a binary system that consisted of benzenethiol and diphenyl diselenide under photoirradiation through a Pyrex vessel with a xenon lamp (λ > 300 nm), a variety of conjugate dienes could be reduced to the corresponding internal alkenes under mild conditions.
- Mitamura, Takenori,Imanishi, Yoshiaki,Nomoto, Akihiro,Sonoda, Motohiro,Ogawa, Akiya
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experimental part
p. 2443 - 2445
(2009/09/30)
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- Thermal decomposition of meso- and d,l-3,4-diethyl-3,4-dimethyldiazetine N,N′-dioxide
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Two stereochemically defined diazetine N,N′-dioxides were synthesized. Thermal decomposition at 200 °C resulted in 95% retention of stereochemistry in the alkene product relative to the starting stereochemistry. These results suggest that decomposition occurs via cleavage of the two C-N bonds either simultaneously or in rapid succession.
- Breton, Gary W.,Nickerson, Justine E.,Greene, Anna M.,Oliver, Lindsey H.
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p. 3005 - 3008
(2008/02/09)
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- Re-based heterogeneous catalysts for olefin metathesis prepared by surface organometallic chemistry: Reactivity and selectivity
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Herein we describe the catalytic activity of 1, a well-defined Re alkylidene complex supported silica, in the reaction of olefin metathesis. This system is highly active for terminal and internal olefins with initial rates up to 0.7 mol per mol Re per s. It also catalyses the self-metathesis of methyl oleate (MO) without the need of co-catalysts. The turnover numbers can reach up to 900 for MO, which is unprecedented for a heterogeneous Re-based catalyst. Moreover the use of silica as a support can bring major advantages, such as the possibility to use branched olefins like isobutene, which are usually incompatible with alumina-based supports; therefore, the formation of isoamylene from the cross-metathesis of propene and isobutene can be performed. All these results are in sharp contrast to what has been found for other silica- or alumina-supported rhenium oxide systems, which are either completely inactive (silica system) or typically need co-catalysts when functionalised olefins are used. Finally the initiation step corresponds to a cross-metathesis reaction to give a 3:1 mixture of 3,3-dimethylbutene and trans-4,4-dimethylpent-2-ene, and make this catalyst the first generation of well-defined Re-based heterogeneous catalysts.
- Chabanas, Mathieu,Coperet, Christophe,Basset, Jean-Marie
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p. 971 - 975
(2007/10/03)
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- Method for producing of 2,3-dimethylbutene-1 and 2,3-dimethylbutene-2
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There is disclosed a method for producing 2,3-dimethylbutene-1 and 2,3-dimethylbutene-2, which is characterized by the steps of (a) dimerizing propylene in a propylene-dimerization step using a nickel complex catalyst as described below as a propylene-dimerization catalyst having propylene-dimerization activity and DMB-1 selectivity, (b) rectifying the resulting reaction solution to obtain 2,3-dimethylbutene-1 as a distillate and a distillation residue containing 2,3-dimethylbutene-1 in a 2,3-dimethylbutene-1 distillation step, (c) allowing the distillation residue to contact with sulfuric acid, sulfonic acid or hetetopolyacid to isomerize 2,3-dimethylbutene-1 in said distillation residue into 2,3-dimethylbutene-2 in an isomerization step, and (d) rectifying the resulting isomerization reaction solution to obtain 2,3-dimethylbutene-2 in a 2,3-dimethylbutene-2 distillation step, wherein said nickel complex catalyst containing (A) at least one nickel compound and the like, (B) a trialkylaluminum, (C) a trivalent phosphorus compound, (D) a fluorinated isopropanol or a halogenated phenol (E) at least one sulfur compound selected from a sulfonic acid and a dialkylsulfuric acid.
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-
Page column 6; 7
(2008/06/13)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
-
Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Surface characterization of alumina-supported catalysts prepared by sol-gel method. Part I. - Acid-base properties
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SCR of NOx to N2 by hydrocarbons has received considerable attention because of its potential for applications in diesel and lean-burn engine exhausts. Various alumina-supported catalysts prepared by sol-gel method show high activity but different catalytic behavior for NO reduction by propylene. Thus, the surface characterization of Al2O3, In2O3-Al2O3, and Ga2O3-Al2O3 prepared by the sol-gel technique was carried out, with emphasis on the acid-base characterizations. Cyclohexanol conversion as a model reaction showed that acid sites were predominantly present on the surface. The presence of Lewis acid sites was confirmed by pyridine adsorption followed by FTIR spectroscopy. A certain quantity of Bronsted acid sites were also revealed by the adsorption of 2,6-dimethylpyridine (DMP). From CO adsorption, it was found that the addition of Ga2O3 into alumina results in a decrease of Lewis acid strength but to an increase of the number of sites, while In2O3 addition caused a global decrease of Lewis acidic characteristics of alumina. Using CO2 as a probe to study the basicity, the number of surface basic sites on the alumina decreased by the Ga2O3 and In2O3 additives. A good correlation between the catalytic activity for 3,3-dimethylbut-1-ene isomerization and the surface acidity estimated by CO and DMP adsorption was supposed. Detailed information on the surface acid-base characteristics were given by the combination of the model reactions and adsorption of specific probe molecules.
- Haneda,Joubert,Bion,Hamada,Menezo,Daturi,Duprez,Saussey,Barbier,Lavalley
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p. 1366 - 1370
(2007/10/03)
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- Reactions of aliphatic ketones R2CO (R = Me, Et, iPr, and tBu) with the MCl4/Li(Hg) system (M = U or Ti): Mechanistic analogies between the McMurry, Wittig, and Clemmensen reactions
-
Analysis of the products of the reactions of ketones R2CO (R = Me, Et, iPr, tBu) with the MCl4/Li(Hg) system (M = U, Ti) at 20°C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketyl radicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65°C. For R = iPr, formation of iPr2C=CiPr2 as the only coupling product, the nonproduction of this alkene by reduction of the uranium pinacolate [U]-OCR2CR2O-[U] (R = iPr) at 20°C, and the instability of the corresponding titanium pinacolate towards rupture of the pinacolic C-C bond indicated that reductive coupling of iPr2CO did not proceed by dimerization of ketyl radicals. Formation of 2,4-dimethyl-2-pentene was in favor of a carbenoid intermediate resulting from deoxygenative reduction of the ketyl. These results revealed that for sterically hindered ketones, McMurry reactions can be viewed as Wittig-like olefination reactions. For R = tBu, no coupling product was obtained and the alkane tBu2CH2 was the major product. The involvement of the carbenoid species [M]=CtBu2 was confirmed by its trapping with H2O, leading to tBu2CH2, and with the aldehydes RCHO, giving the cross-coupling products tBu2C=C(R)H (R = Me, tBu). Therefore, in the case of severely congested ketones, McMurry reactions present strong similarities to the Clemmensen reduction of ketones, owing to the involvement in both reactions of carbenoid species which exhibit similar reactivity. Wiley-VCH Verlag GmbH, 2001.
- Villiers, Claude,Ephritikhine, Michel
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p. 3043 - 3051
(2007/10/03)
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- Conrotatory photochemical ring opening of alkylcyclobutenes in solution. A test of the hot ground-state mechanism
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Quantum yields for photochemical ring opening of six alkylcyclobutenes have been measured in hexane solution using 228-nm excitation, which selectively populates the lowest π,R(3s) excited singlet states of these molecules and has been shown previously to lead to ring opening with clean conrotatory stereochemistry. The compounds studied in this work - 1,2-dimethylcyclobutene (1), cis- and trans-1,2,3,4-tetramethylcyclobutene (cis- and trans-5), hexamethylcyclobutene (8), and cis- and trans-tricyclo[6.4.0.02,7]dodec-12-ene (cis- and trans-9) - were selected so as to span a broad range in molecular weight and as broad a range as possible in Arrhenius parameters for thermal (ground-state) ring opening. RRKM calculations have been carried out to provide estimates of the rate constants for ground-state ring opening of each of the compounds over a range of thermal energies from 20 00O to 49 000 cm-1. These have been used to estimate upper limits for the quantum yields of ring opening via a hot ground-state mechanism, assuming a value of kdeact = 1011 s-1 for the rate constant for collisional deactivation by the solvent, that internal conversion to the ground state from the lowest Rydberg state occurs with close to unit efficiency, and that ergodic behavior is followed. The calculated quantum yields are significantly lower than the experimental values in all cases but one (1). This suggests that the Rydberg-derived ring opening of alkylcyclobutenes is a true excited-state process and rules out the hot ground-state mechanism for the reaction.
- Cook,Leigh,Walsh
-
p. 5188 - 5193
(2007/10/03)
-
- Flash vacuum pyrolysis and photolysis of 3,3,5,5-tetramethylpyrazolin-4- one - A matrix isolation study
-
The flash vacuum pyrolysis of 3,3,5,5-tetramethylpyrazolin-4-one (4) with subsequent trapping of the products in argon at 10 K results in the formation of a complex product mixture with tetramethylcyclopropanone (5) as one of the minor constituents. The 193 nm photochemistry of matrix-isolated 4 is much cleaner, yielding cyclopropanone 5 and allene oxide 9 as the major products. The reaction of tetramethylallene 13 with oxygen atoms yields the same product mixture of 5 and 9 and thus provides an independent route to these species. The experimental IR spectra of 5 and 9 are in good agreement with the results from DFT calculations.
- Sander, Wolfram,Wrobel, Roman,Komnick, Peter,Rademacher, Paul,Muchall, Heidi M.,Quast, Helmut
-
-
- Mechanistic studies of a linear trisazoalkane, a new azimine, and a bicyclic triaziridine. Azoalkane homolysis into seven fragments
-
An aliphatic azo compound containing three azo groups (1) has been prepared by IF5 oxidation of β-azoamine 3. The thermolysis kinetics of this vicinal trisazoalkane were investigated above 155 °C, leading to a rate constant only 5.5 times faster than that of the simple model, azo-tert- butane. Because thermolysis to form seven stable products proceeds stepwise, the rate is hardly affected by the high exothermicity of the overall reaction (-93.4 kcal/mol). Oxidation of amine 3 also afforded a cyclic azimine 5 that underwent photolysis to yield a highly strained triaziridine 9 plus an unusual triazane 10, whose structures were elucidated by detailed NMR studies. On standing at ambient temperature, 9 reverted to 5 with a half-life of about an hour.
- Engel, Paul S.,Pan, Li,Whitmire, Kenton H.,Guzman-Jimenez, Ilse,Willcott, M. Robert,Smith, William B.
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p. 1016 - 1021
(2007/10/03)
-
- Silica-supported sulfated zirconia: A new effective acid solid for etherification
-
Silica-supported sulfated zirconia exhibits a comparable and even higher ether production than a reference acid resin (Amberlyst 15) giving an ether yield of 30% at 50% conversion.
- Wang,Guin
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p. 2499 - 2500
(2007/10/03)
-
- Electrophilic reactions of carboyl compounds and derivatives thereof: XIII preparation of bifunctional compounds from aldehydes and olefins by acylation under acidic catalysis
-
The reactions of aldehydes and their O-acylated derivatives (α-chloroesters, acylals) with olefins and α-ethoxystyrene in the presence of SnCl4 and ZnCl2 were investigated. The reactions afforded various bifunctional derivatives: diols, hydroxyesters, chloroesters, 1,3-ketoalcohols.
- Luk'yanov,Koblik,Murad'yan
-
p. 1593 - 1599
(2007/10/03)
-
- Process for preparing 2,3-dimethyl-2-butene
-
2,3-Dimethyl-2-butene is prepared by isomerizing 2,3-dimethyl-1-butene using at least one acid selected from the group consisting of sulfuric acid and sulfonic acids. By this process, 2,3-dimethyl-2-butene is effectively prepared from 2,3-dimethyl-1-butene using an inexpensive catalyst such as sulfonic acid or the sulfonic acids. Further, a dimerization reaction product of propene can also be used in the isomerization step without removing the dimerization catalyst from the reaction product.
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-
-
- Synthesis of 2,3-Dimethylbutenes by Dimerization of Propene Using Highly Active Nickel-Phosphine Catalysts in the Presence of Sulfonic Acids and/or Dialkyl Sulfates
-
A nickel-phosphine catalyst system consisting of nickel naphthenate, P(cyclo-C6H11)3, AlEt3, and 2,4,6-trichlorophenol (TCP) in the presence of sulfonic acids (CF3SO3H and MeSO3H) or dialkyl sulfates (Me2SO4 and Et2SO2) exhibits remarkable catalytic activity for the dimerization of propene. The catalytic activity (turnover number (TON) for the formation of C6, olefins or 2,3-dimethylbutenes) was enhanced when the catalyst was combined with effective additives, such as Et2SO4 and MeSO3H. The reaction products consisted of 2,3-dimethyl-1-butene (DMB-1) and/or 2,3-dimethyl-2-butene (DMB-2) in high yields (selectivity of dimers based on the reacted propene = 70-80%: selectivity of 2,3-dimethylbutenes in C6 olefins = 78-80%). The ratio of DMB-1/DMB-2 could be controlled by varying the molar ratios of the catalyst ingredients without decreasing in the turnover numbers. Although CF2SO3H was found to be the best additive as far as the catalytic activity and the selectivity of dimers (94-99%) are concerned, the selectivity of 2,3-dimethylbutenes in C6 olefins decreased. The addition of a small amount of water was also effective to enhance the catalytic activity: The turnover number for the formation of 2,3-dimethylbutenes was raised from 7050 to 30360.
- Nomura, Kotohiro,Ishino, Masaru,Suzukamo, Gohfu
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p. 2671 - 2676
(2007/10/03)
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- Nickel(II) Naphthenate Complexes with Phosphorous Amides in Dimerization of Propylene
-
Dimerization of propylene in the presence of diethylaluminum chloride and nickel(II) naphthenate complexes with phosphorous amides of the general formulas (RO)2P-NR'2 and (R'2N)3P (where R = C6H5, AlkC6H4; R' = C2H5, C4H9) was studied.The catalytic activity of the systems was examined in relation to the donor properties of these ligands.The procedure for recovery of 2-methyl-2-pentene and 2,3-dimethyl-2-butene from the dimerization products was developed.
- Munshieva, M. K.
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p. 1779 - 1782
(2007/10/03)
-
- Electron Transfer Reactions and Mobile Holes in Radiolysis of Squalane. Time-Resolved FDMR Study
-
Fluorescence detected magnetic resonance (FDMR) is applied to study ion-molecule reactions in squalane (2,6,10,15,19,23-hexamethyltetracosane).Several time-resolved pulsed FDMR experiments are suggested to measure rate constants of scavenging by aromatic solutes.These constants vary from 5E8 to 1.6E9 mol-1 dm3 s-1.The ion-molecule reactions of radical cations are somewhat slower than reactions of radical anions.The scavenging of the alkane hole is significantly faster than ion-molecule reactions of molecular cations.The mobile hole decays on a time scale of several tens of nanoseconds.These FDMR results are in accord with our recent work on transient absorption spectroscopy in radiolysis of squalane.
- Shkrob, I. A.,Trifunac, A. D.
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p. 14681 - 14687
(2007/10/03)
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- Dehydration of secondary alcohols via thermolysis of in situ generated alkyl diphenyl phosphates: An inexpensive and environmentally compatible method for the preparation of alkenes
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Secondary alcohols are converted into diphenyl phosphate esters by the action of triphenyl phosphate or diphenyl phosphorochloridate in high-boiling, water-miscible solvents in the presence of base. The alkyl diphenyl phosphates undergo thermolysis to afford high yields of alkenes which distill from the reaction mixtures. Purification of the products is achieved by extraction with dilute sulfuric acid which removes traces of solvent and base that may have codistilled. The ratios of 2- (14) and 3-menthene (15), obtained from menthol (13) and neomenthol (16), and the formation of rearranged alkenes by 1,2-shifts from 3, 6, and 3,3-dimethylbutan-2-ol are consistent with ionic intermediates of the elimination reaction. The novel dehydration method offers distinct and important advantages over the existing methods.
- Quast,Dietz
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p. 1300 - 1304
(2007/10/02)
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- Synthesis of α,α-disubstituted acetic acids using low-valent titanium
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Digalogenocarbenes generated using low-valent titanium (LVT) undergo a one-pot cycloaddition to diaryl, aryl alkyl or dialkyl ketones to give α,α-disubstituted acetic acids such as (R,S)-2-arylpropanoic acids.TiI4 proved most effective in this reaction for which the product yield was optimized by use of an excess of reducing agent.
- Garcia, Mariano,Campo, Carmen del,Llama, Emilio F.,Sinisterra, Jose V.
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p. 1771 - 1774
(2007/10/02)
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- Ketone Coupling on Reduced TiO2 (001) Surfaces: Evidence of Pinacol Formation
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Reductive coupling of acetone and acetophenone was investigated in temperature-programmed desorption (TPD) studies on both reduced (Ar(1+)-bombarded) and oxidized TiO2 (001) surfaces.The principal reaction product of either ketone on the reduced surface was a symmetric olefin with twice the carbon number of the reactant. 2,3-Diphenyl-2-butene comprised over 65percent of the volatile carbon-containing species desorbed from the reduced surface following acetophenone adsorption.The main side reactions which yielded products of the same carbon number as the reactants included deoxygenation to form olefins and deoxygenation plus hydrogenation to yield saturated species.The yield of reduction products was greatly diminished on the oxidized TiO2 (001) surface; the yield of 2,3-dimethyl-2-butene, the reductive coupling product of acetone, decreased 10-fold with respect to the yield from the reduced surface.This decrease in activity for reductive coupling is similar in scale to that observed for benzaldehyde coupling on the same surfaces, supporting the conclusion that both ketone and aldehyde coupling reactions occur at ensembles of Ti cations able to undergo a four-electron oxidation.Phenyl groups adjacent to the carbonyl carbon have the greatest effect on the carbonyl coupling reaction, giving significantly higher yield of the coupled olefin product.The observation of a small amount of the pinacol, 2,3-diphenyl-2,3-butanediol, during acetophenone TPD is the first direct evidence that the carbonyl coupling reaction on reduced TiO2 surfaces proceeds through a pinacolate intermediate, as it does for the McMurry reaction carried out in liquid-solid slurries.
- Pierce, Keith G.,Barteau, Mark A.
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p. 2405 - 2410
(2007/10/02)
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- - the Wet Chemical Route to a Highly Reactive Titanium Hydride
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The reaction between catalytically prepared magnesium hydride (MgH2*) and in a molar ratio of 1.5:1 in THF yields a highly pyrophoric, X-ray amorphous titanium hydride precipitate with the composition (2).This novel titanium hydride precipitate with the composition (2).This novel titanium hydride has been characterized through hydrolysis and iodolysis, as well as through thermolysis to Ti* and H2 in the solid state and in organic solvents. 2 is slightly soluble in THF and proves itself as an active reagent in a variety of reactions. - Keywords: Magnesium Hydride, Titanium Hydride, McMurry-Reaction, Titanium
- Becker, Beate,Bogdanovic, Borislav
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p. 476 - 482
(2007/10/02)
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- Cyclobutene photochemistry. Steric effects on the photochemical ring opening of alkylcyclobutenes
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Quantum yields for photochemical ring opening and cycloreversion in hydrocarbon solution have been determined for the direct photolysis (214 nm) of six 1,2-dimethylcyclobutene derivatives which contain methyl groups at C3, and C4 in numbers varying from zero to four. As the hydrogens on C3/C4 of the parent compound (1,2-dimethylcyclobutene) are replaced with increasing numbers of methyl groups, the total quantum yield for ring opening increases to a maximum of ～0.3 and then decreases with further methyl substitution. The quantum yields for ring opening (φtotal) of hexamethylcyclobutene and 1,2-dimethylcyclobutene are nearly the same, and the lowest in the series. The maximum occurs with trans-1,2,3,4-tetramethylcyclobutene; φtotal for the cis-isomer is significantly lower, but both yield an approximate 1:1 mixture of formally allowed and forbidden diene isomers. A similar trend is observed in the relative quantum yields for ring opening and cycloreversion throughout the series. The results are interpreted in terms of a combination of bond strength and steric effects on the efficiency of the ring-opening process. Increasing methyl substitution causes an increase in φtotal through the first three members of the series owing to progressive weakening of the C3-C4 bond. Compounds containing cis-dimethyl substitution exhibit substantially reduced quantum yields for ring opening, relative to what would be expected based on bond strength effects alone. This is proposed to be due to steric effects on the efficiency of the process, suggesting that the initial stages of the photochemical ring opening of cyclobutene involve disrotatory motions on the excited singlet state potential energy surface.
- Leigh, William J.,Postigo, J. Alberto
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p. 1688 - 1694
(2007/10/02)
-
- Superbase Character of Alumina loaded with Potassium by Impregnation from Ammoniacal Solution
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Al2O3 has been loaded with potassium by impregnation from an ammoniacal solution and heated under vacuum at 573 K.The resulting catalyst showed extremely high catalytic activity for the isomerization of alkenes.These catalysts had much greater activity than that of Al2O3 loaded with alkali metals by vapour deposition.The isomerization, over K(NH3)/Al2O3, of pent-1-ene to pent-2-ene gave a 98percent yield in 6 min at 201 K.The temperature-programmed desorption and IR spectra of Al2O3 after impregnation indicated that the metal amide-like species formed on the alumina is a catalytically active species.Al2O3 loaded with KNH2 was found to be more active than K(NH3)/Al2O3 for the isomerization of 2,3-dimethylbut-1-ene.The basic strength of these catalysts was estimated to be at least H- = 37.
- Baba, Toshihide,Handa, Haruhisa,Ono, Yoshio
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p. 187 - 192
(2007/10/02)
-
