- Collisional Energy Transfer in the Two-Channel Thermal Unimolecular Reaction of Bromoethane-2-d
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Unimolecular thermal decomposition in the two-channel bromoethane-2-d system was studied over the temperature range of 660-706 K in the presence of CF4 and He bath gases.The C2H5Br system was also studied as a reference process.The average energy removed per collision from energized bromoethane-2-d by a bath gas down is as follows: by the substrate, 1100 cm-1 (stepladder model); by CF4, 675 cm-1 (exponential model, EXP); by He, 215 cm-1 (EXP).Comparison is made with recent studies of direct measurements.The relative rate ratio of two-channel reaction has been expressed in terms of microscopic rate ratio and distribution function of the reacting molecule.Arrhenius parameters, i.e., log A and Ea (kcal/mol), at ca. 50 Torr of total pressure were found to be as follows: for C2H5Br, 13.37 +/- 0.18, 53.36 +/- 0.55; for CH2DCH2Br, 13.16 +/- 0.16 and 53.30 +/- 0.51 (HBr elimination) and 12.83 +/- 0.30 and 54.29 +/- 0.92 (DBr elimination).
- Jung, Kyung-Hoon,Kang, Sung Hoon,Ro, Chul Un,Tschuikow-Roux, E.
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- ACTIVATION OF ENCAPSULATION SYSTEM MoO3SnO2 FOR OLEFIN METATHESIS BY SnMe3.
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Inactive MoO//3/SnO//2 was changed to a metathesis catalyst by treating the surface with tetramethyltin (SnMe//4) at room temperature. On the catalyst olefin metathesis proceeded selectively without accompanying side reactions such as hydrogen scrambling. During the treatment of MoO//3/SnO//2 with SnMe//4, a small amount of methane formed concurrent with decomposition of SnMe//4. Decomposition of tetraethyltin (SnEt//4) also occurred in MoO//3/SnO//2; however, the surface showed no metathesis activity. From these results, it was concluded that the cause for activation of MoO//3/SnO//2 by SnMe//4 is attributed not to reduction of Mo species or the presence of Sn but to the formation of CH//2 species pivotal to the catalytic olefin metathesis cycle.
- Tanaka,Sasaki,Toyoshima
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- Gold(I) Carbenoids: On-Demand Access to Gold(I) Carbenes in Solution
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Chloromethylgold(I) complexes of phosphine, phosphite, and N-heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors. Activation of these gold(I) carbenoids with a variety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene, olefin cyclopropanation, and Buchner ring expansion of benzene.
- Sarria Toro, Juan M.,García-Morales, Cristina,Raducan, Mihai,Smirnova, Ekaterina S.,Echavarren, Antonio M.
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supporting information
p. 1859 - 1863
(2017/02/05)
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- Inorganic clusters with a [Fe2MoOS3] core - A functional model for acetylene reduction by nitrogenases
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We report the first example of a wholly inorganic mimic of a part of the FeMoco active centre of nitrogenases. We detail the synthesis, characterisation and reactivity of two related, transient hydride-containing inorganic clusters, a dihydride complex and a vinyl monohydride complex, which bear the [Fe2MoOS3] portion of FeMoco. The dihydride complex is capable of reducing acetylene to ethylene via the vinyl monohydride complex. In the reaction cycle, a transient low-valent complex was generated by the reductive elimination of H2 or ethylene from dihydride or vinyl monohydride complexes, respectively.
- Yoshimoto, Koji,Yatabe, Takeshi,Matsumoto, Takahiro,Tran, Viet-Ha,Robertson, Andrew,Nakai, Hidetaka,Asazawa, Koichiro,Tanaka, Hirohisa,Ogo, Seiji
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p. 14620 - 14627
(2016/09/28)
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- The first ruthenium-silsesquioxyl complexes-synthesis, structure and mechanistic implications in silylative coupling
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The first ruthenium-silsesquioxyl complexes have been synthesised and characterized via spectroscopic and X-ray methods. Mechanistic studies were performed and the complexes obtained were proved to be intermediates in the catalytic cycle of silylative coupling of olefins with vinylsilsesquioxane. Moreover, a mechanism for silylative coupling of styrene with vinylsilsesquioxanes was proposed. This journal is the Partner Organisations 2014.
- Zak, Patrycja,Kubicki, Maciej,Marciniec, Bogdan,Rogalski, Szymon,Pietraszuk, Cezary,Frackowiak, Dawid
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p. 7911 - 7916
(2014/05/20)
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- Decomposition of 1,1-dimethyl-1-silacyclobutane on a tungsten filament - Evidence of both ring C-C and ring Si-C bond cleavages
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The decomposition of 1,1-dimethyl-1-silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time-of-flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1-dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si-CH3 bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C-C bond and a ring Si-C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C-C bond is dominant over that of propene via an initial cleavage of a ring Si-C bond. When the collision-free condition is voided, secondary reactions in the gas-phase produce various methyl-substituted 1,3-disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3-tetramethyl-1,3-disilacyclobutane originated from the dimerization of 1,1-dimethylsilene. Copyright
- Tong,Shi
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experimental part
p. 215 - 222
(2010/10/04)
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- Efficient functionalisation of cubic monovinylsilsesquioxanes via cross-metathesis and silylative coupling with olefins in the presence of ruthenium complexes
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Monovinylheptaisobutylsilsesquioxane undergoes efficient cross-metathesis and silylative coupling with styrenes. Allyl derivatives were successfully tested in cross-metathesis in the presence of first generation Grubbs' catalyst, while heteroatom-substitu
- Zak, Patrycja,Pietraszuk, Cezary,Marciniec, Bogdan,Spolnik, Brzegorz,Danikiewicz, Witold
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body text
p. 2675 - 2682
(2010/04/05)
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- Thermal chemistry of bicyclo[4.2.0]oct-2-enes
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At 300 °C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered Stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is ~1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.
- Powers, David C.,Leber, Phyllis A.,Gallagher, Sarah S.,Higgs, Andrew T.,McCullough, Lynne A.,Baldwin, John E.
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p. 187 - 194
(2007/10/03)
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- The effect of substituents at silicon on the cross-metathesis of trisubstituted vinylsilanes with olefins
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Efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first and second generation Grubbs catalyst and Hoveyda-Grubbs catalyst is described. On the basis of the results of equimolar reactions of vinylsilanes with ruthenium alkylidene complexes and experiments with deuterium-labelled reagents, a general, metallacarbene mechanism for the cross-metathesis of trisubstituted vinylsilanes with olefins has been suggested. Reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives.
- Pietraszuk, Cezary,Fischer, Helmut,Rogalski, Szymon,Marciniec, Bogdan
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p. 5912 - 5921
(2007/10/03)
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- Reaction of Hydrogen Peroxide with Organosilanes under Chemical Vapour Deposition Conditions
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When a stream of vapour at low pressure which contained a mixture of H2O2 with an organosilane, RSiH3 (R = alkyl or alkenyl), impinged on a silicon wafer, deposition of oxide films of nominal composition RxSiO(2-0.5x), where x 3 or higher alkenyl groups. or higher alkenylgroups. Possible mechanism for the Si-C bond cleavage reaction are discussed, with energetic rearrangement of radical intermediates of type Si(H)(R)(OOH)' being favoured.
- Moore, Darren L.,Taylor, Mark P.,Timms, Peter L.
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p. 2673 - 2678
(2007/10/03)
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- Stereochemistry of the thermal conversion of 1-vinyl-2,3-cis-dideuteriocyclobutane to butadiene and 1,2-dideuterioethylenes
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This study has examined the stereochemistry of the decomposition at 900-1000 K in a single-pulse shock tube of 1-vinyl-2,3-cis-dideuteriocyclobutane to ethylenes and buta-1,3-dienes. The deuterated ethylenes formed during the decomposition, CHD=CH2, (E)-CHD=CHD, and (Z)-CHD=CHD, were quantified via two independent techniques, FTIR and IR absorption spectroscopy using a tunable diode laser spectrometer. The results of both analyses indicated that equal amounts of (E)-CHD=CHD and (Z)-CHD=CHD were formed from the cis-labeled reactant. In an earlier shock tube study of the decomposition at 1000-1200 K of two deuterium-labeled cyclohexenes to ethylenes plus buta-1,3-dienes, a pathway via a vinylcyclobutane intermediate was implicated in a significant fraction of the decomposition events; the measured ratios of (E)-CHD=CHD to (Z)-CHD=CHD in that study were consistent with a complex mechanistic model in which the stereochemistry of deuterium labels in the cyclohexene reactant was lost in ethylene products formed via vinylcyclobutane. The present results provide additional support for that model.
- Lewis, David K.,Hutchinson, Avery,Lever, Steven J.,Spaulding, Eric L.,Bonacorsi Jr., Samuel J.,Baldwin, John E.
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p. 233 - 237
(2007/10/03)
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- 70. Site-Specific, Oxidative Addition of C-C Bonds by 'Anchored' Bare Fe(I) Cations Prior to C-H Bond Activation
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Evidence is presented for the first time that 'naked' Fe+ ions, complexed to the NH2 group of primary amines, are capable of intramolecularly activating C-C bonds in a highly specific mode without preceding C-H activation.
- Karrass, Sigurd,Schwarz, Helmut
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p. 633 - 637
(2007/10/02)
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- Hydrocarbon Activation by Gas-Phase Lanthanide Cations: Interaction of Pr+, Eu+, and Gd+ with Small Alkanes, Cycloalkanes, and Alkenes
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We describe ion beam studies of the interaction of gas-phase lanthanide ions, praseodymium (Pr+), europium (Eu+), and gadolinium (Gd+), with small alkanes, cycloalkanes, alkenes, and several oxygen-containing compounds.Only Gd+ is seen to activate C-H and C-C bonds of alkanes.The ground-state electronic configuration of Gd+ (4f75d16s1) is different from those of Pr+ (4f36s1) and Eu+ (4f76s1), leading to the conclusion that the f electrons play little part in the metal ion reactivity.Gd+ can be thought of as having two valence electrons, and indeed it reacts similarly to Sc+ and the other group 3 metal ions Y+ and La+, yielding products corresponding to elimination of hydrogen, alkanes, and alkenes.The elimination of neutral alkenes in the reaction of Gd+ with alkanes results in the formation of metal dialkyl or hydrido-alkyl complexes.This finding leads to estimates for the sum of two Gd+ ? bond dissociation energies of between 110 and 130 kcal/mol.Gd+ and Pr+ react readily with alkenes, yielding mostly dehydrogenation products along with smaller amounts of C-C bond cleavage products.Reactions of Gd+ and Pr+ with oxyen-containing species such as nitric oxide, formaldehyde, acetaldehyde, and acetone yield primarily the metal oxide ions and provide a lower limit for D(M+-O) of 179 kcal/mol, in good agreement with literature values of D(Pr+-O) = 188.4 +/- 5.2 kcal/mol and D(Gd+-O) = 181.0 +/- 4.4 kcal/mol.In keeping with the strong metal ? bonds, Gd+ is also seen to readily react with formaldehyde to eliminate CO and form GdH2+.
- Schilling, J. Bruce,Beauchamp, J. L.
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- Diode laser probes of vinyl radical kinetics: The reaction of C2H3 with HCl and DCl
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A tunable diode laser probe is used to measure the rate of reaction of vinyl radicals with HCl and DCl at room temperature.Rate constants for reaction with HCl and DCl are (1.3 +/- 0.3) * 10-12 and (7.8 +/-1.6) * 10-13 cc/molecule s, respectively.These rate constants are about five orders of magnitude faster than the estimated rate constant for reaction of vinyl radicals with H2, and potential reasons for these differences are considered within the context of the BSBL (bond strength-bond length) model of atom abstraction reactions.The rate constant for reaction of C2H3 with O2 is determined to be (1.0 +/- 0.4) * 10-11 cc/molecule s, in excellent agreement with a previous determination.Finally, the temperature dependence of the vinyl radical + HCl rate constant is reported.The rate constant is found to decrease by approximately 33percent over the temperature range of 278-370 K.This change, however, is within the experimental error of the measured rate constants.From these measurements, an activation energy of - 840 +/- 1400 (2?) cal/mol is obtained.
- Krueger, Herman,Weitz, Eric
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p. 1608 - 1616
(2007/10/02)
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- Activation and Chain-carrying CH2 Species in Terminal Alkene Metathesis on Molybdena-Titania Catalysts
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The metathesis reaction of terminal alkenes other than isobutene took place on MoO3-x/TiO2, whereas that of isobutene proceeded in the presence of ethylene and following treatment of the catalyst with SnMe4 at room temperature.These results infer that chain-carrying CH2 species are generated to only a small extent by the adsorption of isobutene on MoO3-x/TiO2, although they are formed by the adsorption of alk-1-enes and SnMe4.The metathesis-inactive material, fully oxidized MoO3/TiO2, was changed to a metathesis-active catalyst by treating it with SnMe4.This suggests that MoO3/TiO2 has no ability to yield CH2 species with terminal alkenes but that these species can be supplied with SnMe4.An analysis by X-ray photoelectron spectroscopy infers that SnMe4 adsorbed on MoO3/TiO2 releases methyl groups concomitant with the oxidation of Sn.
- Tanaka, Katsumi,Tanaka, Ken-ichi
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p. 601 - 608
(2007/10/02)
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- Thermal Reactions of Pyrrolidine at Elevated Temperatures. Studies with a Single-Pulse Shock Tube
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The thermal decomposition of pyrrolidine was studied behind reflected shocks in a single-pulse shock tube over the temperature range 900-1400 K and overall densities of ca. 3 x 1E-5 mol/cm3.Under these conditions the following reaction products were found in the postshock mixtures: H2, CH4, C2H4, C2H6, C2H2, C3H6, CH2=C=CH2, CH3CCH, CH2=CHCH2CH3, HCN, CH3CN, CH2=CHCN, C2H5CN, and small quantities of pyrrole and butadiene.Studies with a mixture of pyrrolidine and pyrrolidine-d9 show that C2H4 and C3H6 are produced by direct ring cleavage with the following rate parameters: pyrrolidine -> C2H4 + (CH2)2-NH, k = 3.42 x 1E16 exp(-75.2 x 1E3/RT) s-1 and pyrrolidine -> C3H6 + CH2=NH, k = 1.35 x 1E16 exp(-80.4 x 1E3/RT) s-1, where R is expressed in units of cal/(K mol).Hydrogen cyanide has the highest concentration among the nitrogen-containing products, followed by acetonitrile.No reaction products resulting from pyrrolidine isomerization were observed.
- Lifshitz, Assa,Bidani, Menashe,Agranat, Ahuva,Suslensky, Aya
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p. 6043 - 6048
(2007/10/02)
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- Thermolysis of (1R,2R)-1,2-Dideuteriocyclobutane. An Application of Vibrational Circular Dichroism to Kinetic Analysis
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The relative rates of geometric isomerization to racemization have been studied for the title compound by using a combination of infrared (IR) and vibrational circular dichroism (VCD) spectroscopies, respectively.The results are interpreted with a kinetic and mechanistic scheme which parallels that used by Berson, Pedersen, and Carpenter on a similar study of chiral cyclopropane-d2 thermolysis.Relative rates of isomerization to stereomutation of 1.5+/-0.4 were obtained which can be interpreted to be consistent with a mechanism best described by random methylene rotation in tetramethylene-d2.This is the first application of VCD to kinetic analysis, and the advantages of IR techniques over the more usually employed UV spectroscopies to this type of basic mechanistic problem are illustrated.
- Chickos, James S.,Annamalai, A.,Keiderling, T. A.
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p. 4398 - 4402
(2007/10/02)
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- Reactions of FeCH2(1+) and CoCH2(1+) with Olefins in the Gas Phase. Studies Involving Olefin Metathesis
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Reactions of the title carbenes with several olefins and alkynes are reported.Ethene reacts with MCH2(1+) yielding exclusively M(1+) formation (C3H6 elimination).Reaction of ethene with MCD2(1+) yields the metathesis products FeCH2(1+) and CoCH2(1+) in 20percent and 2percent yields, respectively.Formation of the metathesis product MC2H4(1+) dominates for propene with no MCH2(1+) produced from MCD2(1+).Formation of MC2H4(1+) is believed to proceed through an ethene-ethylidene intermediate that rearranges to a bis(ethene) complex followed by elimination of ethene.Absence of MCH2(1+) formation from reaction of MCD2(1+) with propene suggests that the alkene-alkylidene conversion is the key step in metathesis of olefins larger than ethene.Several other pathways compete with metathesis such as cyclopropanation, olefin homologation, dehydrogenation, and various C-C bond cleavages.Both carbenes react with butadiene, generating M-c-C5H6(1+) and M-c-C5H5(1+), implying D0(Co(1+)-C5H5) > 76+/- 7 kcal/mol and D0(Fe(1+)-C5H5) > 87 +/- 5 kcal/mol.Finally, ethyne and propyne react with MCH2(1+) to yield M(1+) as the only product.
- Jacobson, D. B.,Freiser, B. S.
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p. 2605 - 2612
(2007/10/02)
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- La photolyse du cyclohexene gazeux a 184,9 nm
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We have studied the 184.9 nm photolysis of gaseous cyclohexene either in the absence or in the presence of radical scavengers such as O2, NO, H2S, or HI at pressures between 1 and 70 Torr.Propane and sulfur hexafluoride has also been used as stabilizing agent.In all cases, ethylene and 1,3-butadiene have rather high quantum yields (Φ>/=0.5).The isotopic analysis of the ethylene formed in the photolysis of cyclohexene-3,3,6,6-d4 shows the high importance of the perhydrogenated species.These results, together with others taken from the literature, favor a one-step fragmentation mechanism or a double-step mechanism involving an intermediate which has a lifetime shorter than that of the photoexcited molecule.
- Collin, Guy J.,Deslauriers, Helene
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p. 1970 - 1972
(2007/10/02)
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- Hydrogenation of Ethylene on Metal Electrodes. Part 5. Reduction of Light Ethylene on Pt in Deuteroperchloric Acid Solution and the Dual-pathway Mechanism
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Electroreduction of light ethylene on a platinum electrode was conducted in a heavy-water solution of deuteroperchloric acid.Deuterium-atom distributions in the product, ethane, support the previous conclusion that ethylene diffusion is rate-controlling at potentials less positive than ca. 100 mV, whereas the surface reaction is rate-controlling at more positive potentials where the Tafel line holds.The D-atom distribution in the latter potential region reveals double maxima at - and -ethanes.This distribution is explained by the dual-pathway mechanism which assumes two reaction rates for the step C2H4(a) + H(a) C2H5(a).The difference in the reaction rate will be attributed to the difference in the adsorption state of C2H4(a) but not of H(a), since only the weakly adsorbed hydrogen atoms are active in the hydrogenation.Reduction of light ethylene with D2 on platinum in deuteroperchloric acid solution gives the same results.A computer simulation based on the above mechanism can reproduce quantitatively not only the present distributions but also others given in the literature, even those observed for the gas-phase heterogeneous reduction.
- Fujikawa, Keikichi,Kita, Hideaki,Sato, Shinri
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p. 3055 - 3072
(2007/10/02)
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