- Deuterium Exchange Reactions of Isobutane, n-Hexane, and n-Heptane Catalyzed over Platinum Single Crystal Surfaces
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Isotopic exchange reactions of isobutane, n-heptane, and n-hexane with deuterium gas have been investigated near atmospheric pressure in the temperature range 500-650 K over the flat (111) and kinked (10,8,7) crystal faces of platinum.The exchange kinetics at low conversion displayed zero activation energy, a first-order dependence on D2 pressure, and a strong negative-order dependence on the surface coverage by strongly bound carbonaceous species.Initial exchange rates and product distributions were not influenced appreciably by the presence of steps and kinks on the platinum surface, and the exchange product distributions varied little with temperature, D2 pressure, and surface composition.Hydrocarbon (HC) conversion and deuterium exchange rates measured simultaneously for n-hexane reactions catalyzed over Pt(111) revealed that deuterium exchange always occurs more rapidly as compared to all other competing chemical reactions.
- Davis, S. M.,Somorjai, G. A.
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- Kinetic Isotope Effects for Hydrogen Abstraction from a Series of Cycloalkanes and Branched Alkanes by Hydrogen Atoms in the Gaseous Phase
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Hydrogen atoms produced in the radiolysis of water vapor were used to determine the kinetic isotope effects for the reactions H(.) + RH(RD) -> H2(RD) + R(.) H(KD)>, where RH is a perprotiated alkane and RD is the corresponding perdeuterated alkane.The alkanes studied include a homologous series of cycloalkanes, cyclopentane through cyclododecane, and isobutane, 2,3-dimethylbutane, 2,3,4-trimethylpentane, and neopentane.The results were expressed in terms of the Arrhenius-type equation kH/kD = AH/AD expD-EH)(kJ mol-1)/RT>, over the temperature range of 363-463 K.The values for the ratio AH/AD range from 0.32 to 0.75, and the activation energy differences ED-EH vary from 6.8 to 11.0 kJ/mol, depending on the molecular structures of the reactants.The variation in the values of ED-EH was correlated with the bond dissociation energies of the C-H bond being broken.Theoretical calculations based on transition-state theory combined with the London-Eyring-Polanyi-Sato potetial energy surfaces could reproduce the major features of the experimental results when tunnel effects were taken into consideration.
- Fujisaki, Noboru,Ruf, Amanz,Gaeumann, Tino
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- Synthesis of deuterium labeled isobutane: Isobutane-2-d1, isobutane-1-d9 and isobutane-d10
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2-Methylpropane-2-d1 (isobutane-2-d1), 2-(methyl-d3)-propane-1,1,1,3,3,3-d6 (nonadeuterated isobutane) and 2-methylpropane-d10 (perdeuterated isobutane) were synthesized by using a combination of classical organic chemistry and recently developed H/D exchange processes on solid acids. Isobutane-2-d1 was synthesized from t-butyl chloride by Grignard synthesis with an overall yield of 27.0% (chemical purity: 99.9% and isotopic purity: 96.0%). Isobutane-1-d9 was prepared by H/D exchange of 2-methylpropane (isobutane) with a D2O exchanged zeolite. The deuteriated product was obtained with an overall yield of 80.0% (chemical purity: 99.9% and isotopic purity: 98.7%). Perdeuteriated isobutane was prepared by reacting isobutane-2-d1 with 98.0% deuteriated sulfuric acid and was obtained in a total yield of 98.0% (chemical purity: 99.8% and isotopic purity: 97.9%).
- Sassi,Coeppert,Sommer,Esteves,Mota
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p. 1023 - 1030
(2007/10/03)
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