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Reaction Channel (reaction + channel)
Selected AbstractsAnalysis of Reaction Channels for Alkane Hydroxylation by Nonheme Iron(IV),Oxo Complexes,ANGEWANDTE CHEMIE, Issue 33 2010Caiyun Geng Neue High-Spin-Pfade: Die vier plausiblen Reaktionspfade der Alkanhydroxylierung durch Nichthäm-Eisen(IV)-Oxo-Komplexe wurden rechnerisch untersucht. Der Triplett-,-Pfad ist energetisch zu hoch, um an einer C-H-Aktivierung beteiligt zu sein , jedoch konkurriert die Reaktivität des Quintett-,-Kanals mit dem Triplett-Pfad, was einen neuen Ansatz für die spezifische C-H-Aktivierung durch Eisen(IV)-Oxo-Spezies bieten könnte (siehe Schema). [source] Catalytic cracking, dehydrogenation, and aromatization of isobutane over Ga/HZSM-5 and Zn/HZSM-5 at low pressuresINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2002Yanping Sun Isobutane cracking, dehydrogenation, and aromatization over Ga/HZSM-5 and Zn/HZSM-5 has been investigated in a Knudsen cell reactor and the kinetics of the primary reaction steps for isobutene and propene formation have been accurately determined. Although cracking is the dominant reaction channel, with propene and methane being primary products, methane formation is significantly less than propene formation. This indicates that a proportion of the cracking proceeds via Lewis acid attack at CC bonds, and not just via alkanium ion formation at Bronsted acid sites. This is particularly apparent over Zn/HZSM-5. Intrinsic rate constants for cracking, calculated from the rate of propene formation, are and for dehydrogenation, calculated from the rate of isobutene formation, are Large preexponential factors for cracking and dehydrogenation over Ga/HZSM-5 indicate that either the coverage of active sites is significantly less than the coverage of exposed sites or the intrinsic reaction step involves a large entropy change between reactant and transition state. For Zn/HZSM-5 the small preexponential factors suggest either small entropy changes during activation, perhaps initiated by Lewis acid sites, or a steady-state distribution of active and exposed sites is rapidly reached. Differences in intrinsic activation energies may reflect the ratio of Lewis and Bronsted acid sites on the respective catalyst surfaces. Aromatization is more prolific over Ga/HZSM-5 than over Zn/HZSM-5 under the low-pressure conditions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 467,480, 2002 [source] A phase-space method for arbitrary bimolecular gas-phase reactions: Theoretical descriptionINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2001A. Gross Abstract A theoretical model for the calculation of rate constants for arbitrary bimolecular gas-phase reactions was developed. The method is based on the phase-space statistical method developed by Light and co-workers 1,6. In the present article this method is extended to arbitrary molecular systems. The new method requires knowledge of the molecular properties in the reaction and products channels of the chemical system. The properties are the vibrational frequencies, moments of inertia, and potential energy for the interacting species in their ground state equilibrium configuration. Furthermore, we have to calculate either the energy barrier or the long-range potential for the chemical system (if the reaction channel does not have an energy barrier). The usefulness of the method is that it can be applied to all bimolecular reactions, trimolecular reactions, and even reactions of higher orders. Therefore, it can be applied to cases where rate constants of complex chemical reactions are required, but reliable laboratory measurements or other means to estimate rate parameters are not yet possible. Even if spectroscopic data are not available for the reactants and products, it is possible to use electronic structure theory to calculate the required data. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source] Investigation of multiphase hydrogenation in a catalyst-trap microreactorJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2009S. McGovern BACKGROUND: Multiphase hydrogenation plays a critical role in the pharmaceutical industry. A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport. To this end, the small-scale and large surface-to-volume ratios of microreactor technology would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate mass transfer in a catalytic hydrogenation reaction. The reactor design is such that solid catalyst is suspended in the reaction channel by an arrangement of catalyst traps. The design supports the use of commercial catalyst and allows control of pressure drop across the bed by engineering the packing density. RESULTS: This paper discusses the design and operation of the reactor in the context of the liquid-phase hydrogenation of o-nitroanisole to o-anisidine. A two-phase ,flow map' is generated across a range of conditions depicting three flow regimes, termed gas-dominated, liquid-dominated, and transitional, all with distinctly different mass transfer behavior. Conversion is measured across the flow map and then reconciled against the mass transfer characteristics of the prevailing flow regime. The highest conversion is achieved in the transitional flow regime, where competition between phases induces the most favorable gas,liquid mass transfer. CONCLUSION: The results are used to associate a mass transfer coefficient with each flow regime to quantify differences in performance. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro-scale production reactors. Copyright © 2008 Society of Chemical Industry [source] Ab initio direct dynamics studies on the reactions of chlorine atom with CH3,nFnCH2OH (n = 1,3)JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2007Ying Wang Abstract The hydrogen abstraction reactions of Cl atom with a series of fluorinated alcohols, i.e., CH3,nFnCH2OH + Cl (n = 1,3) (R1,R3) have been studied systematically by ab initio direct dynamics method and the canonical variational transition state theory (CVT). The potential energy surface information is calculated at the MP2/6-311G(d,p) level. Energies along the minimum energy paths are improved by a series of single-point calculations at the higher modified GAUSSIAN-2 (G2M) level of theory. Theoretical analysis shows that three kinds of hydrogen atoms can be abstracted from the reactants CH2FCH2OH and CHF2CH2OH, and for CF3CH2OH, two possible pathways are found. The rate constants for each reaction channel are evaluated by CVT with the small-curvature tunneling correction (SCT) over a wide range of temperature from 200 to 2000 K. The calculated CVT/SCT rate constants are in good agreement with the available experimental values for the reactions CHF2CH2OH + Cl and CF3CH2OH + Cl. However, for the reaction CH2FCH2OH + Cl, there is negative temperature dependence below 500 K, which is different from the experimental fitted. It is shown that in the low temperature ranges, the three reactions all proceed predominantly via H-abstraction from the methylene positions, and with the increase of the temperature the H-abstraction channels from the fluorinated-methyl positions should be taken into account, while the H-abstraction channels from the hydroxyl groups are negligible over the whole temperature ranges. Also, the reactivity decreases substantially with fluorine substitution at the methyl position of alcohol. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Modified Gaussian-2 level investigation of the identity ion-pair SN2 reactions of lithium halide and methyl halide with inversion and retention mechanismsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2004Yi Ren Abstract Identity ion-pair SN2 reactions LiX + CH3X , XCH3 + LiX (X = F, Cl, Br, and I) have been investigated in the gas phase and in solution at the level of the modified Gaussian-2 theory. Two possible reaction mechanisms, inversion and retention, are discussed. The reaction barriers relative to the complexes for the inversion mechanism [,H(inv)] are found to be much higher than the corresponding values for the gas phase anionic SN2 reactions, decreasing in the following order: F (263.6 kJ mol,1) > Cl (203.3 kJ mol,1) > Br (174.7 kJ mol,1) > I (150.7 kJ mol,1). The barrier gaps between the two mechanisms [,H (ret) , ,H (inv)] increase in the order F (,62.7 kJ mol,1) < Cl (4.4 kJ mol,1) < Br (24.9 kJ mol,1) < I (45.1 kJ mol,1). Thus, the retention mechanism is energetically favorable for fluorine and the inversion mechanism is favored for other halogens, in contrast to the anionic SN2 reactions at carbon where the inversion reaction channel is much more favorable for all of the halogens. The stabilization energies for the dipole,dipole complexes CH3X · · · LiX (,Hcomp) are found to be similar for the entire set of systems with X = F, Cl, Br, and I, ranging from 53.4 kJ mol,1 for I up to 58.9 kJ mol,1 for F. The polarizable continuum model (PCM) has been used to evaluate the direct solvent effects on the energetics of the anionic and ion-pair SN2 reactions. The energetic profiles are found to be still double-well shaped for most of the ion-pair SN2 reactions in the solution, but the potential profile for reaction LiI + CH3I is predicted to be unimodal in the protic solvent. Good correlations between central barriers [,H (inv)] with the geometric looseness of the inversion transition state %C,X,, the dissociation energies of the C,X bond (DC,X) and Li,X bond (DLi,X) are observed, respectively. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 461,467, 2004 [source] Hydrogenation of 2-ethylanthraquinone under Taylor flow in single square channel monolith reactorsAICHE JOURNAL, Issue 3 2009Dingsheng Liu Abstract The hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz-glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas-liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two-phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi-empirical formula were used to predict gas-solid, gas-liquid, and liquid-solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Radical clocks and electron transfer.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2005Comparison of crown ether effects on the reactivity of potassium, magnesium towards 1-bromo-2-(3-butenyl)benzene. Abstract The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis -dicyclohexano-18-crown-6 or tert -butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia,33% tert -butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal,solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd. [source] A Time-Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3,,5,-Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction PathwayCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2010Chensheng Ma Dr. Abstract 3,,5,-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3,,5,-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH3CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di- meta -methoxybenzylic moieties, for the DMBDP deprotection, comparative fs-TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3,,5,-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady-state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR3 results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection,cyclization mechanism for DMBDP in CH3CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be ,1,ns. This indicates that there is little relevance for the long-lived intermediates (>10,ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3,,5,-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (,2,ps) heterolytic bond cleavage after photoexcitation of meta -methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. [source] Photoinduced Oxidation Reaction of Benzotrifluoride with OH Radical by the Laser Flash MethodCHINESE JOURNAL OF CHEMISTRY, Issue 1 2008Ren-Xi ZHANG Abstract The optical transient and kinetics characterizations of the transients formed in the reaction of OH with benzotrifluoride (BTF) were performed by a laser flash photolysis technique. The results indicated that the formation of ,-type adduct of C6H5(OH)CF3 was the major reaction channel, and the ,-type adduct of C6H5CF3OH formation was an additional minor process in the oxidation reaction of BTF attacked by OH radicals yielded from the photolysis of H2O2. Addition of OH to the CF3 group led to the fluoride ion elimination to yield ,,, -difluorophenylcarbinol (C6H5CF2OH). Trifluoromethylphenol (HOC6H4CF3) of meta -, para - and ortho -substituted isomers resulted from the addition of OH to the BTF aromatic ring. [source] Gas-Phase Chemistry of Vanadium Oxide Cluster Cations VmOn+ (m = 1,4; n = 1,10) with Water and Molecular OxygenEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2008Sandra Feyel Abstract Bare vanadium oxide cluster cations VmOn+ (m = 1,4; n =1,10) generated by electrospray ionization are investigated with respect to their reactivity toward water and molecular oxygen by using mass spectrometric techniques. Besides ion hydration, the ion/molecule reactions of VmOn+ with oxygen-labeled water (H218O) also lead to 16O/18O exchange reactions of the vanadium oxide clusters cations. Although the probability of degenerate 16O/18O exchange between VmOn+ and water is fairly high for the cluster cations with a medium valence state of vanadium, oxygen-atom exchange reactions between VmOn+ and 18O2 can only be accomplished by VO+, V3O6+, and V4O8+. Particularly interesting is the fact that not only oxygen atoms from vanadyl units are exchanged in the cluster cations, but bridging oxygen atoms are also most likely involved in the processes. Other reaction channels for the interaction of VmOn+ cluster cations with molecular oxygen are reported as well, such as oxidative degradation of the low-valent cluster cations upon collision with O2 and formation of association complexes for the high-valent cluster cations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Ab initio chemical kinetics for the NH2 + HNOx reactions, part II: Kinetics and mechanism for NH2 + HONOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Shucheng Xu The kinetics and mechanism for the reaction of NH2 with HONO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The reaction producing the primary products, NH3 + NO2, takes place via precomplexes, H2N,,,c -HONO or H2N,,,t -HONO with binding energies, 5.0 or 5.9 kcal/mol, respectively. The rate constants for the major reaction channels in the temperature range of 300,3000 K are predicted by variational transition state theory or Rice,Ramsperger,Kassel,Marcus theory depending on the mechanism involved. The total rate constant can be represented by ktotal = 1.69 × 10,20 × T2.34 exp(1612/T) cm3 molecule,1 s,1 at T = 300,650 K and 8.04 × 10,22 × T3.36 exp(2303/T) cm3 molecule,1 s,1 at T = 650,3000 K. The branching ratios of the major channels are predicted: k1 + k3 producing NH3 + NO2 accounts for 1.00,0.98 in the temperature range 300,3000 K and k2 producing OH + H2NNO accounts for 0.02 at T > 2500 K. The predicted rate constant for the reverse reaction, NH3 + NO2 , NH2 + HONO represented by 8.00 × 10,26 × T4.25 exp(,11,560/T) cm3 molecule,1 s,1, is in good agreement with the experimental data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 678,688, 2009 [source] Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with ClINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2007Lei Yang A dual-level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF2CF2OCH3 (HFE-254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6-311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H-abstraction channels have been identified. For the reactant CHF2CF2OCH3 and the two products, CHF2CF2OCH2 and CF2CF2OCH3, the standard enthalpies of formation are evaluated with the values of ,256.71 ± 0.88, ,207.79 ± 0.12, and ,233.43 ± 0.88 kcal/mol, respectively, via group-balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition-state theory (CVT) including the small-curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k1 = 9.22 × 10,19 T2.06 exp(219/T), k2 = 4.45 × 10,14T0.90 exp(,2220/T), and k = 4.71 × 10,22 T3.20) exp(543/T) cm3 molecule,1 s,1. Our results indicate that H-abstraction from CH3 group is the main reaction pathway in the lower temperature range, while H-abstraction from CHF2 group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221,230, 2007 [source] Kinetics and mechanism for the CH2O + NO2 reaction: A computational studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2003Z. F. Xu The reactants, products, and transition states of the CH2O + NO2 reaction on the ground electronic potential energy surface have been searched at both B3LYP/6,311+G(d,p) and MPW1PW91/6,311+G(3df,2p) levels of theory. The forward and reverse barriers are further improved by a modified Gaussian-2 method. The theoretical rate constants for the two most favorable reaction channels 1 and 2 producing CHO + cis -HONO and CHO + HNO2, respectively, have been calculated over the temperature range from 200 to 3000 K using the conventional and variational transition-state theory with quantum-mechanical tunneling corrections. The former product channel was found to be dominant below 1500 K, above which the latter becomes competitive. The predicted total rate constants for these two product channels can be presented by kt (T) = 8.35 × 10,11T6.68 exp(,4182/T) cm3/(mol s). The predicted values, which include the significant effect of small curvature tunneling corrections, are in quantitative agreement with the available experimental data throughout the temperature range studied (390,1650 K). © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 184,190, 2003 [source] Theoretical study of stabling function of the NO to the (CH3)3CO · radicalINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2005Hongmei Zhao Abstract The stabling function of the NO to the (CH3)3CO · radical has been theoretically investigated. Density functional theory (DFT) calculations are performed to optimize the geometries of relevant species. The single-point energy is evaluated at CCSD(T)/6-31++G** level. Three reaction channels of (CH3)3CO · + NO in the singlet state are considered. The calculations indicate that NO is a stable reagent of active radical (CH3)3CO. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Theoretical study on the Br + CH3SCH3 reactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2007Hui Zhang Abstract The multiple-channel reactions Br + CH3SCH3 , products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6-31+G(d,p) level, and energetic information is further refined by the G3(MP2) (single-point) theory. The rate constants for every reaction channels, Br + CH3SCH3 , CH3SCH2 + HBr (R1), Br + CH3SCH3 , CH3SBr + CH3 (R2), and Br + CH3SCH3 ,CH3S + CH3Br (R3), are calculated by canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200,3000 K. The total rate constants are in good agreement with the available experimental data, and the two-parameter expression k(T) = 2.68 × 10,12 exp(,1235.24/T) cm3/(molecule s) over the temperature range 200,3000 K is given. Our calculations indicate that hydrogen abstraction channel is the major channel due to the smallest barrier height among three channels considered, and the other two channels to yield CH3SBr + CH3 and CH3S + CH3Br are minor channels over the whole temperature range. © 2007 Wiley Periodicals, Inc. J Comput Chem 2007 [source] Hydrogenation of 2-ethylanthraquinone under Taylor flow in single square channel monolith reactorsAICHE JOURNAL, Issue 3 2009Dingsheng Liu Abstract The hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz-glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas-liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two-phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi-empirical formula were used to predict gas-solid, gas-liquid, and liquid-solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] CH3CH2SCH3,+,OH radicals: temperature-dependent rate coefficient and product identification under atmospheric pressure of air,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Gabriela Oksdath-Mansilla Abstract Relative rate coefficients have been determined for the gas-phase reaction of hydroxyl (OH) radicals with ethyl methyl sulfide (EMS) using isobutene as a reference compound. The experiments were performed in a 1080,L quartz glass photoreactor in the temperature range of 286,313,K at a total pressure of 760,±,10,Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants and products. OH radicals were produced by the 254,nm photolysis of hydrogen peroxide (H2O2). The kinetic data obtained were used to derive the following Arrhenius expression valid in the temperature range of 286,313,K (in units of cm3,molecule,1,s,1): The rate coefficient displays a negative temperature dependence and low pre-exponential factor which supports the existence of an addition mechanism for the reaction involving reversible OH-adduct formation. The results are compared with previous data of other sulfides from the literature and are rationalized in terms of structure,reactivity relationships. Additionally, product identification of the title reaction was performed for the first time by the FTIR technique under atmospheric conditions. Sulfur dioxide, formaldehyde, and formic acid were observed as degradation products in agreement with the two possible reaction channels (addition/abstraction). Copyright © 2010 John Wiley & Sons, Ltd. [source] Theoretical Study on Proton-Transfer Reaction of Intracellular Second-messenger 3,,5,-Cyclic NucleotideCHINESE JOURNAL OF CHEMISTRY, Issue 8 2008Ai-Hua ZHANG Abstract The gas-phase proton-transfer reaction mechanism of intracellular second-messenger 3,,5,-cyclic nucleotide (cAMPm) has been theoretically investigated at the B3LYP/6-31G, , level. One or two H2O molecules have been used to simulate the catalyst. It is found that H shift reaction between conformation Bm and conformation Dm of cAMPm involves a cyclic transition state with one or two water molecules as a shuttle. Furthermore, H shift reaction proceeds easily with the participation of two water molecules. The results provide evidence in theory to study proton-transfer reaction mechanism of related phosphodiesters. Our present calculations have rationalized all the possible reaction channels. [source] Metabolic reconstruction of aromatic compounds degradation from the genome of the amazing pollutant-degrading bacterium Cupriavidus necator JMP134FEMS MICROBIOLOGY REVIEWS, Issue 5 2008Danilo Pérez-Pantoja Abstract Cupriavidus necator JMP134 is a model for chloroaromatics biodegradation, capable of mineralizing 2,4-D, halobenzoates, chlorophenols and nitrophenols, among other aromatic compounds. We performed the metabolic reconstruction of aromatics degradation, linking the catabolic abilities predicted in silico from the complete genome sequence with the range of compounds that support growth of this bacterium. Of the 140 aromatic compounds tested, 60 serve as a sole carbon and energy source for this strain, strongly correlating with those catabolic abilities predicted from genomic data. Almost all the main ring-cleavage pathways for aromatic compounds are found in C. necator: the ,-ketoadipate pathway, with its catechol, chlorocatechol, methylcatechol and protocatechuate ortho ring-cleavage branches; the (methyl)catechol meta ring-cleavage pathway; the gentisate pathway; the homogentisate pathway; the 2,3-dihydroxyphenylpropionate pathway; the (chloro)hydroxyquinol pathway; the (amino)hydroquinone pathway; the phenylacetyl-CoA pathway; the 2-aminobenzoyl-CoA pathway; the benzoyl-CoA pathway and the 3-hydroxyanthranilate pathway. A broad spectrum of peripheral reactions channel substituted aromatics into these ring cleavage pathways. Gene redundancy seems to play a significant role in the catabolic potential of this bacterium. The literature on the biochemistry and genetics of aromatic compounds degradation is reviewed based on the genomic data. The findings on aromatic compounds biodegradation in C. necator reviewed here can easily be extrapolated to other environmentally relevant bacteria, whose genomes also possess a significant proportion of catabolic genes. [source] | |||||||||||||||||||||||||