Physico-Chemical Properties of Deuterated Compounds. 5th Communication. The isotope partition coefficient in cyclohexane hydrogen and cycloheptane/hydrogen mixtures

The isotope partition coefficient α between cyclohexane, cycloheptane and hydrogen has been determined between 80 and 180° and pressures around 1 atm. The values decrease with increasing deuterium content y of the hydrogen and can be expressed by the simple equation Ina = Δ S/R + (ΔH + δ · y)/RT with an error of ±1%. However it was not possible to achieve good agreement with theoretical calculations using a unique average value for the partition function of the hydrocarbon.     

Physicochemical Properties of Deuterated Compounds. 8th Communication. The kinetic isotope effect for the reaction of hydrogen atoms with methylcyclohexane and perdeuteromethylcyclohexane in the gas phase

Using H-atoms produced in the radiolysis of water vapour, we determined the kinetic isotope effect for the reaction where RH and R′D are methylcyclohexane and perdeuterated methylcyclohexane, respectively. The result obtained from the isotope competitive method can be expressed with the Arrhenius-type equation k_H/k_D = (0.51 ± 0.04) exp[(8.58 ± 0.25) kJ mol^?1/RT] over the temperature range from 363 to 483 K. The occurrence of H abstraction from primary, secondary, and tertiary C? H bonds in methylcyclohexane is taken into consideration in the interpretation of the Arrhenius-type expression obtained. Theoretical interpretation of the kinetic isotope effect has been achieved on the basis of the transition-state theory and a semiempirical London-Eyring-Polanyi-Sato potential-energy surface. The tunnel effect is found to play a role in the H-abstraction. Several methods for estimating the tunnel correction factors have been discussed.     

Physico-chemical properties of deuteriated compounds. 6th Communication. The H/D exchange in mixtures between hydrogen and heptane,methylcyclohexane or cycloheptane over Ni-catalyst

The isotopic exchange between hydrogen and saturated hydrocarbons over Nicatalysts has been studied as a function of temperature and degree of deuteriation. The experimental results can be explained by a model containing four parameters. Two different adsorbed species are assumed: in the ‘alkyl’-species one H-atom is exchanged in a single adsorption step; the ‘olefin’-species exchanges at least two H-atoms at the same time. Both species can undergo multiple exchange per adsorption step.     

硅酸盐修饰Ni/海泡石催化剂的制备

Under the hydrothermal condition, the surface of sepiolite was restored with silicate and Ni was precipitated on the restored sepiolite by precipitating-reducing method. The surface of the samples was characterized by SEM, BET and XRD. The catalytic ability was examined by hydrogenation of toluene in gas phase over the silicate restored Ni/sepiolite catalyst. The experimental results show that distribution of Ni over the surface of the sample was even with bare aggregation and can be controlled, the ability of anti-aging of this catalyst was about ten times higher than that prepared by impregnation method at the same reactive condition.     

The renaissance of H/D exchange

The increasing demand for stable isotopically labeled compounds has led to an increased interest in H/D-exchange reactions at carbon centers. Today deuterium-labeled compounds are used as internal standards in mass spectrometry or to help elucidate mechanistic theories. Access to these deuterated compounds takes place significantly more efficiently and more cost effectively by exchange of hydrogen by deuterium in the target molecule than by classical synthesis. This Review will concentrate on the preparative application of the H/D-exchange reaction in the preparation of deuterium-labeled compounds. Advances over the last ten years are brought together and critically evaluated.     

Reductive Amination of Carbonyl Compounds over a Ni2P/SiO2 Catalyst in a Flow Mode

Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...     

Biologically Active Coordination Compounds of Germanium. Synthesis and Physicochemical Properties

Russian Journal of Organic Chemistry - A promising area of modern coordination and supramolecular chemistry is the synthesis of biologically active compounds of germanium and creation of effective...     

The gas-phase H/D exchange mechanism of protonated amino acids

A mass spectrometry and Density Functional Theory study of gas-phase H/D exchange in protonated Ala, Cys, Ile, Leu, Met, and Val is reported. Site-specific rate constants were determined and results identify the alpha-amino group as the protonation site. Lack of exchange on the Cys thiol group is explained by the absence of strong intramolecular hydrogen bonding within the reaction complex. In aliphatic amino acids the presence of a methyl group at the beta-C atom was found to lower the site-specific H/D exchange rate for amino hydrogens. Study of the exchange mechanism showed that isotopic exchange occurs in two independent reactions: in one, only the carboxylic hydrogen is exchanged and in the other, both carboxylic and amino group hydrogens exchange. The proposed reaction mechanisms, calculated structures of various species, and a number of structural findings are consistent with experimental data.     

Properties of internal heat supply with carbon dioxide reforming of methane over a Ni/Al2O3 catalyst.

An addition of 6%-oxygen into a reactant of CH₄/CO₂(1/1) gave lower operating temperature of carbon dioxide reforming of methane by 130 K in obtaining 0.029 MPa of H₂, accompanied by a more endothermic atmosphere in the catalyst bed than in the absence of oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis,characterization and catalytic activity of a heterometallic Ni/Zn compound in the H/D exchange of salicylaldehyde

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The H/D Exchange and Hydrogenolysis of Butane on an Alumina-Supported Nickel Catalyst

The exchange of butane with deuterium on a nickel/alumina catalyst is studied over a wide range of temperatures (50–230°) and for three hydrocarbon/deuterium ratios. The initial distribution is used to propose a reaction scheme by considering different adsorbed species such as: alkyl-(α), alkene-(α, β) and allyl-(α,β,γ) species, where α, β, and γ are different C-atoms. It is assumed that each adsorbed species can either desorb directly while exchanging one, two, and three H-atoms or undergo multiple exchange before desorption. It is shown that by reducing the activity of the catalyst a back-exchange of the fully deuterated species sets in a lower temperature; a systematic deviation of all model calculations for the estimation of the concentrations of the C₄HD₉ and C₄D₁₀ is, thus, explained. The exchange of CH₃CD₂CD₂CH₃ and CD₃CH₂CH₂CD₃ with H₂ and D₂ is also studied, and similar results are obtained as with exchanges of CH₃CD₂CH₃ and CD₃CH₂CD₃. With the help of very-high-resolution mass spectra, it is shown that the initial degree of deuteration, i. e. the degree of deuteration after one adsorption step, is 84% for the methylene and 57% for the methyl group respectively. The hydrogenolysis reactions of butane is studied in the same system between 180° and 230°. A wide range of conversion is covered, and the product distributions are fitted to kinetic equations in order to obtain the initial rate constants. On the nickel/alumina catalyst one or several C–C bonds are broken before the desorption of the species. Under the conditions used in these experiments, the surface cracking is the rate-limiting step. An isotope effect is observed for the decomposition in D₂, the production of propane being favored.     

Physicochemical Properties of Solutions of Amides in H2O and in D2O

Excess volume, partial molar volumes, viscosity, and ultrasound velocity in H₂O and D₂O solutions of formamide (FM), acetamide (AM), dimethylformamide (DMF), and dimethylacetamide (DMA) were studied at 20°C. The change in the excess volume of the various amide solutions on substitution of D₂O for H₂O varies both in magnitude and direction. On the other hand, the isotope effect on the ultrasound velocity behaves similarly in all cases. Its magnitude is greatest for pure water and then decreases monotonically with increasing amide concentration. Although the behavior of the concentration dependence of viscosity is similar to that for ultrasound velocity, the isotope effect on the viscosity behaves in a different way. For methyl-substitued amides, a maximum isotope effect is observed at amide mole fraction 0.2, but the isotope effect for FM and AM increases monotonically with increasing amide concentration. The differences in the behavior of amides in aqueous solution are discussed in terms of their interactions with water.     

Zintl cluster supported low coordinate Rh(i) centers for catalytic H/D exchange between H2 and D2

Ligand exchange reactions of [Rh(COD){η⁴-Ge₉(Hyp)₃}] with L-type nucleophiles such as PMe₃, PPh₃, IMe₄ (IMe₄ = 1,3,4,5-tetramethylimidazol-2-ylidene) or [W(Cp)₂H₂] result in the displacement of the COD ligand to afford clusters with coordinatively unsaturated trigonal pyramidal rhodium(i) centers [Rh(L){η³-Ge₉(Hyp)₃}]. These species can be readily protonated allowing access to cationic rhodium–hydride complexes, e.g. [RhH(PPh₃){η³-Ge₉(Hyp)₃}]⁺. These clusters act as catalysts in H/D exchange between H₂ and D₂ and alkene isomerisation, thereby illustrating that metal-functionalized Zintl clusters are active in both H–H and C–H bond activation processes. The mechanism of H/D exchange was probed using parahydrogen induced polarization experiments.

We describe the synthesis of the coordinatively unsaturated Zintl clusters [Rh(L){η³-Ge₉(Hyp)₃}] (where L = PMe₃, PPh₃, IMe₄ or [W(Cp)₂H₂]). These species are active catalysts in H/D exchange and C–H bond activation reactions.     

Physico-Chemical Properties of Deuteriated Compounds. 1st Communication. The molar volume of n-heptane

The molar volumes of mixtures of perdeuteriated and protiated heptane have been measured between -10° and 40° and expressed as a second order polynomial of the weight fraction. The difference in molar volumes of about 0.4 ml/mol decreases with temperature. The possibility of using the density measurement to determine the degree of deuteriation of mixtures of partially deuteriated heptanes was examined. The percent deuteriation calculated by this method deviates systematically from the true values.     

Dry reforming of methane over Ni/Ce0.62Zr0.38O2 catalysts: Effect of Ni loading on the catalytic activity and on H2/CO production

The activity of ceria–zirconia-supported nickel catalysts (Ni/CZ) with various loadings of nickel (2, 4 and 10 wt. %) was studied in the case of low-temperature dry reforming of methane (DRM). XRD, S_BET, SEM, TPD-CO₂ and thermogravimetry were used to determine the physicochemical properties of the catalysts and of the carbon deposits formed on the surface. It was found that the agglomerates of the Ni-active phase are formed on the surface of the support for high loadings of nickel. The best conversions of CO₂ and CH₄ and an optimum ratio H₂/CO = 1 were obtained for the catalysts with the highest Ni content. It was also found that loading has an influence on the amount of carbon deposits formed in the DRM process.     

Effect of Preparation Methods on the Physicochemical and Functional Properties of Ni/CeO2 Catalysts

Kinetics and Catalysis - The effect of preparation procedures (a polymer ester precursor method and incipient wetness impregnation) on the physicochemical and functional properties of Ni/CeO2...     

The mass spectra of organic compounds. 7th Communication. 4,4-Dimethyl-1-pentene

Loss of CH, CH₄, C₂H₄, C₃H, C₃H₆ and C₃H₇ from the molecular ions of a number of ¹³C-labeled analogs of 4,4-dimethyl-1-pentene was studied both in normal (source) 70-eV electron impact (EI) spectra dn in metastable spectra. For loss of CH in the source, 96% of the methyl comes frm positions of 5, 5′ and 5″, while the remainder comes from position 1. In the metastable spectra, loss of C-1 (16%) and C-3 (9%) is increasing in importance. The loss of ethylene is a particular case: either C-1 or C-3 are lost with any other C-atom from positions 2,5,5′, and 5″ (8 × 10%) in the metastable spectra, the probability for simultaneous loss of C-1 and C-3 being 6%. If C-1 seems to these two positions become completely equivalent in the metastable time range. The T-values (kinetic energy release) for the different positions show small, but statisticaly different values and a small isotope effect. Loss of C₃H₅ (allylic cleavage) is 100% C-1, C-2 and C-3, i.e., no evidence for skeletal rearrangement is seen. This is also true for loss of C₃C₆ (McLafferty rearrangement) within the source, but in metastable decay the other positions gain in importance. The neutral fragment C₃H appears to be the the result of consecutive loss of CH and C₃H₄, rather than a one-step loss of propyl radical or the inverse reactions sequence. No metastable reaction can be seen for this reaction. Decomposition of labeled C₆H and C₅H secondary ions occurs in an essentially random fashion.     

Physico-Chemical Properties of Deuteriated Compounds. 2nd Communication. The isotope partition coefficient in methylcyclohexane-hydrogen

The deuterium isotope partition coefficient α has been determined as a function of total pressure, temperature and degree of deuteriation for methylcyclohexane/hydrogen over Ni/Al₂O₃. Good agreement with theory has been obtained for the dependence on temperature but not for that on total pressure or on the degree of deuteriation.