25549-98-8Relevant academic research and scientific papers
H and D atom addition to ethylene on Cu(100): Absence of ethyl H/D shift and decomposition
Yang, Michael X.,Bent, Brian E.
, p. 822 - 832 (1996)
The addition of gas phase H and D atoms to unsaturated hydrocarbons physisorbed on metal surfaces is a viable synthetic route to partially-deuterated alkyl groups on the surface (Jenks, C. J.; Xi, M.; Yang, M. X.; Bent, B. E. J. Phys. Chem. 1994, 98, 2152-2157). Because these processes are exothermic by ～60 kcal/ mol, the possibility of alkyl decomposition and/or rearrangement prior to thermal accommodation with the surface (a possibility not explicitly addressed in prior studies) should be considered. In the studies here, these decomposition and rearrangement possibilities have been investigated by studying H and D atom addition to variously-deuterated ethylenes physisorbed on a Cu(100) surface. Ethyl decomposition by C-H, C-D, or C-C bond scission has been addressed and shown not to occur by comparison with results from previous studies of the surface species that would be formed by these bond scission processes. H/D shift between the two carbons of the ethyl groups has been addressed by heating the surface to induce β-hydrogen or β-deuterium elimination. The resulting alkene product ratios are compared with those for β-elimination from selectively-deuterated ethyl groups formed by an independent route, i.e., the dissociative adsorption of a labeled bromoethane. The results show that the extent of H/D shift, if it occurs at all, is H/kD) for β-hydrogen/β-deuterium elimination is 9.5 ± 0.4 at ～260 K on Cu(100). No secondary isotope effect of D for H substitution at the α-carbon is detected to within the experimental uncertainty. These results demonstrate, at least for a Cu-(100) surface, the feasibility of synthesizing selectively-labeled surface alkyl groups from H and D atom addition to alkenes.
Oxidative dehydrogenation of ethane on dynamically rearranging supported chloride catalysts
G?rtner, Christian A.,Van Veen, Andr C.,Lercher, Johannes A.
, p. 12691 - 12701 (2014)
Ethane is oxidatively dehydrogenated with a selectivity up to 95% on catalysts comprising a mixed molten alkali chloride supported on a mildly redox-active Dy2O3-doped MgO. The reactive oxyanionic OCl- species acting as active sites are catalytically formed by oxidation of Cl- at the MgO surface. Under reaction conditions this site is regenerated by O2, dissolving first in the alkali chloride melt, and in the second step dissociating and replenishing the oxygen vacancies on MgO. The oxyanion reactively dehydrogenates ethane at the melt-gas phase interface with nearly ideal selectivity. Thus, the reaction is concluded to proceed via two coupled steps following a Mars-van-Krevelen-mechanism at the solid-liquid and gas-liquid interface. The dissociation of O2 and/or the oxidation of Cl- at the melt-solid interface is concluded to have the lowest forward rate constants. The compositions of the oxide core and the molten chloride shell control the catalytic activity via the redox potential of the metal oxide and of the OCl-. Traces of water may be present in the molten chloride under reaction conditions, but the specific impact of this water is not obvious at present. The spatial separation of oxygen and ethane activation sites and the dynamic rearrangement of the surface anions and cations, preventing the exposure of coordinatively unsaturated cations, are concluded to be the origin of the surprisingly high olefin selectivity.
Experimental evidence for ethylidene-d4
Modarelli, David A.,Platz, Matthew S.
, p. 470 - 475 (1993)
Laser flash photolysis (LFP, 351 nm, XeF excimer) of 3-methyldiazirine in the presence and absence of pyridine fails to produce a UV-vis active transient intermediate. However, LFP of 3-methyldiazirine-d4 in pentane containing pyridine produces a transient absorption attributed to the ethylidene-d4-pyridine ylide. A double-reciprocal plot of the optical yield of ylide (Ay-1) versus (pyridine concentration)-1 is linear and indicates that the lifetime of ethylidene-d4 is 500 ps in pentane, assuming that the second-order rate constant of reaction of ethylidene-d4 with pyridine is 1 × 109 M-1 s-1. Laser induced fluorescence spectra of methyldiazirine and methyldiazirine-d4 are reported and discussed.
Photolysis of Thietane and Thietane-d6 in Argon Matrix: Infrared Spectra of Matrix-Isolated Thioformaldehyde and Thioformaldehyde-d2
Watanabe, Osamu,Suzuki, Eiichi,Watari, Fumio
, p. 1389 - 1391 (1991)
Argon-matrix isolated thietane at 10 K decomposed by irradiation (λ > 290 nm) to form ethylene and thioformaldehyde.The photolysis of thietane under these conditions has been shown to be a clean source of thioformaldehyde.The CH2S and CD2S molecules generated this way are indefinitely stable and their infrared spectra could be recorded.
Kinetics and mechanism of ethanol dehydration on γ-Al 2O3: The critical role of dimer inhibition
DeWilde, Joseph F.,Chiang, Hsu,Hickman, Daniel A.,Ho, Christopher R.,Bhan, Aditya
, p. 798 - 807 (2013)
Steady state, isotopic, and chemical transient studies of ethanol dehydration on γ-alumina show unimolecular and bimolecular dehydration reactions of ethanol are reversibly inhibited by the formation of ethanol-water dimers at 488 K. Measured rates of ethylene synthesis are independent of ethanol pressure (1.9-7.0 kPa) but decrease with increasing water pressure (0.4-2.2 kPa), reflecting the competitive adsorption of ethanol-water dimers with ethanol monomers; while diethyl ether formation rates have a positive, less than first order dependence on ethanol pressure (0.9-4.7 kPa) and also decrease with water pressure (0.6-2.2 kPa), signifying a competition for active sites between ethanol-water dimers and ethanol dimers. Pyridine inhibits the rate of ethylene and diethyl ether formation to different extents verifying the existence of acidic and nonequivalent active sites for the dehydration reactions. A primary kinetic isotope effect does not occur for diethyl ether synthesis from deuterated ethanol and only occurs for ethylene synthesis when the β-proton is deuterated; demonstrating olefin synthesis is kinetically limited by either the cleavage of a Cβ-H bond or the desorption of water on the γ-alumina surface and ether synthesis is limited by the cleavage of either the C-O bond of the alcohol molecule or the Al-O bond of a surface bound ethoxide species. These observations are consistent with a mechanism inhibited by the formation of dimer species. The proposed model rigorously describes the observed kinetics at this temperature and highlights the fundamental differences between the Lewis acidic γ-alumina and Bronsted acidic zeolite catalysts.
Collisional Energy Transfer in the Two-Channel Thermal Decomposition of Bromoethane-1,1,2,2-d4
Nguyen, Tam T.,King, Keiieth D.,Gilbert, Robert G.
, p. 494 - 498 (1983)
The two-channel thermal decomposition of CHD2CD2Br (products HBr + C2D4, DBr + CHDCD2), along with the decomposition of CH3CH2Br, has been studied by using the technique of very low-pressure pyrolysis (VLPP).Rate coefficients were obtained at pressures both so low that only gas/wall collisions occur (over the temperature range 950-1200 K) and dilute in various bath gases (pressures up to 10 Pa) over the range 1000-1070 K.Fitting these data by solution of the appropriate reaction-diffusion integrodifferential master equation yields the gas/wall collisional efficiency, the extrapolated high-pressure rate parameters, and the gas/gas collisional energy transfer probability function, P(E,E').The extrapolated high-pressure rate coefficients are as follows: for CHD2CD2Br, 1013.20 exp(-227.4 kJ mol-1/RT) s-1 (HBr elimination), 1013.15 exp(-230.2 kJ mol-1/RT) s-1 (DBr elimination), and 1013.6 exp(-221 kJ mol-1/RT) s-1 for CH3CH2Br, in good agreement with those obtained by other methods.Gas/wall collision efficiencies (the wall being seasoned quartz) are ca. 0.6 at 1200 K, ca. 0.8 at 1000 K (with those for the d4 species ca. 10percent less than for the d0), in accord with values estimated from the potential well depth.The data are moderately sensitive to P(E,E').Assuming this for downward transitions to be a function of E-E' alone, we found that this function falls off more steeply than exponential, as found previously for chloroethane.Average bromoethane/M downward energy transfer values ((ΔEdown)) are 250 (M = Ne), 600 (M = CO2), 850 (M = C2H4), and 1200 (M = benzene) cm-1, the variation of (ΔEdown) with temperature being less than experimental uncertainty over the small experimental temperature range.
A Comparative Analysis of the CO-Reducing Activities of MoFe Proteins Containing Mo- and V-Nitrogenase Cofactors
Lee, Chi Chung,Tanifuji, Kazuki,Newcomb, Megan,Liedtke, Jasper,Hu, Yilin,Ribbe, Markus W.
, p. 649 - 653 (2018/04/16)
The Mo and V nitrogenases are structurally homologous yet catalytically distinct in their abilities to reduce CO to hydrocarbons. Here we report a comparative analysis of the CO-reducing activities of the Mo- and V-nitrogenase cofactors (i.e., the M and V clusters) upon insertion of the respective cofactor into the same, cofactor-deficient MoFe protein scaffold. Our data reveal a combined contribution from the protein environment and cofactor properties to the reactivity of nitrogenase toward CO, thus laying a foundation for further mechanistic investigation of the enzymatic CO reduction, while suggesting the potential of targeting both the protein scaffold and the cofactor species for nitrogenase-based applications in the future.
deuterium generation ethylene preparation method
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Paragraph 0027; 0038; 0040; 0041-0049; 0056-0067, (2018/02/04)
The invention discloses a preparation method of deuteroethylene. According to the preparation method, calcium carbide is reacted with D2O to generate deuteroacetylene; a deuteration reaction is performed on the prepared deuteroacetylene and deuterium gas in the presence of a composite catalyst Cu-Ni/SiO2 to obtain the deuteroethylene; the volume ratio of the deuteroacetylene to the deuterium gas is 1: (10-60). The preparation method of the deuteroethylene is applicable to industrial production and has been verified and utilized in an industrial pilot plant already; experimental results prove that the preparation method has the advantages of simple reaction steps, mild reaction conditions, high deuteroethylene yield, recyclability of superfluous deuterium gas in the reaction as the raw material, and great reduction of the production cost.
Reaction Mechanism and Kinetics of Olefin Metathesis by Supported ReOx/Al2O3 Catalysts
Lwin, Soe,Wachs, Israel E.
, p. 272 - 278 (2016/01/12)
The self-metathesis of propylene by heterogeneous supported ReOx/Al2O3 catalysts was investigated with in situ Raman spectroscopy, isotopic switch (D-C3= → H-C3=), temperature-programmed surface reaction (TPSR) spectroscopy, and steady-state kinetic studies. The in situ Raman studies showed that two distinct surface ReO4 sites are present on alumina and that the olefins preferentially interact with surface ReO4 sites anchored at acidic surface sites of alumina (olefin adsorption: C4= > C3= > C2=). The isotopic switch experiments demonstrate that surface Re?CH3 and Re?CHCH3 are present during propylene metathesis, with Re? representing activated surface rhenia sites. At low temperatures (3=][Re?]2. At high temperatures (>100 °C), the rate-determining step is the recombination of two surface propylene molecules (rate ≈ [C3=]2[Re?]). To a lesser extent, the recombination of surface Re?CH3 and Re?CHCH3 intermediates also contributes to self-metathesis of propylene at elevated reaction temperatures.
Metathesis of C5–C8 Terminal Olefins on Re2O7/Al2O3 Catalysts
Kustov, Leonid M.,Furman, Daniil B.,Barkova, Aleksandra P.
, p. 1033 - 1039 (2016/06/01)
Abstract: Primary products of the interaction of terminal olefins C5–C8 with Re2O7/Al2O3 catalysts are established. The rupture of the C=C bond of the olefin occurs with formation of a carbene localized at a rhenium ion, with the alkylidene fragment in the produced carbene being the CH2=group of the terminal alkene molecule. Thus M=CH2 species and lower normal α-olefins are formed. Graphical Abstract: [Figure not available: see fulltext.]
