Reaction Mechanism (reaction + mechanism)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Reaction Mechanism

  • complex reaction mechanism
  • different reaction mechanism
  • plausible reaction mechanism
  • possible reaction mechanism
  • proposed reaction mechanism

  • Selected Abstracts

    An Efficient Synthesis of Substituted meta -Halophenols and Their Methyl Ethers: Insight into the Reaction Mechanism

    Faiz Ahmed Khan
    Abstract An expeditious synthetic methodology leading to substituted meta -halophenols and their corresponding methyl ether derivatives through acid-mediated fragmentation of suitably substituted dihalonorbornyl ketones has been devised. The reaction sequence consists of TBTH-mediated (TBTH is tri- n -butyltin hydride) selective bridgehead halogen reduction of easily accessible Diels,Alder adducts derived from 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and ,-substituted vinyl acetates, with subsequent conversion into the requisite bicyclic ketones by a two-step hydrolysis/oxidation approach. An extensive mechanistic investigation based on isotope labeling and cross experiments has been carried out and plausible mechanistic pathways based on these results have been proposed. The absence of halogen atoms at the bridgehead positions steers the reaction through a novel pathway involving the incorporation of proton (or deuterium) followed by elimination of HX (or DX), so the described methodology also provides a reliable route to ortho-para dideuteratedphenolic derivatives. [source]

    ChemInform Abstract: Microwave-Assisted, Solvent-Free, Parallel Syntheses and Elucidation of Reaction Mechanism for the Formation of Some Novel Tetraaryl Imidazoles of Biological Interest.

    CHEMINFORM, Issue 37 2009
    B. R. Prashantha Kumar
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    A Theoretical Study of the Inner-Sphere Disproportionation Reaction Mechanism of the Pentavalent Actinyl Ions

    CHEMINFORM, Issue 42 2007
    Helen Steele
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    ChemInform Abstract: First Catalytic Asymmetric Aldol-Tishchenko Reaction , Insight into the Catalyst Structure and Reaction Mechanism.

    CHEMINFORM, Issue 23 2001
    Cheryl M. Mascarenhas
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Asymmetric Hydrogenation with Highly Active IndolPhos,Rh Catalysts: Kinetics and Reaction Mechanism

    Jeroen Wassenaar
    Abstract The mechanism of the IndolPhos,Rh-catalyzed asymmetric hydrogenation of prochiral olefins has been investigated by means of X-ray crystal structure determination, kinetic measurements, high-pressure NMR spectroscopy, and DFT calculations. The mechanistic study indicates that the reaction follows an unsaturate/dihydride mechanism according to Michaelis,Menten kinetics. A large value of KM (KM=5.01±0.16,M) is obtained, which indicates that the Rh,solvate complex is the catalyst resting state, which has been observed by high-pressure NMR spectroscopy. DFT calculations on the substrate,catalyst complexes, which are undetectable by experimental means, suggest that the major substrate,catalyst complex leads to the product. Such a mechanism is in accordance with previous studies on the mechanism of asymmetric hydrogenation reactions with C1 -symmetric heteroditopic and monodentate ligands. [source]

    Reaction Mechanism for the LiCl-Mediated Directed Zinc Insertion: A Computational and Experimental Study

    Ching-Yuan Liu Dr.
    Tired of wondering about the role of LiCl in the DoI reaction of zinc? Kinetic/thermodynamic competitive experiments and DFT calculations were performed to clarify the regioselectivity and reaction mechanism/pathways of lithium chloride-promoted directed zinc insertion into bromobenzenes. The results strongly suggest that the LiCl-containing "push,pull form" transition state (TSb) is formed at an early stage, thus accelerating the reaction rate of zinc insertion. (DoI=directed ortho insertion.) [source]

    PPh3 -Catalyzed Reactions of Alkyl Propiolates with N -Tosylimines: A Facile Synthesis of Alkyl 2-[aryl(tosylimino)methyl]acrylate and an Insight into the Reaction Mechanism

    Huimin Liu
    Abstract A new PPh3 -catalyzed synthesis of alkyl 2-[aryl(tosylimino)methyl]acrylates from propiolate and N -tosylimine has been developed. Deuterium-labelling experiments show that the reaction mechanism involves several hydrogen-transfer processes, which are not the turnover-limiting step and strongly rely on the nature of the reaction media. The stable phosphonium,enamine zwitterion, which was proven to play an important role in the catalytic cycle, has been isolated and characterised by X-ray analysis. [source]

    Reaction Mechanism of Porphyrin Metallation Studied by Theoretical Methods

    Yong Shen Dr.
    Abstract We have studied the reaction mechanism for the insertion of Mg2+ and Fe2+ into a porphyrin ring with density functional calculations with large basis set and including solvation, zero-point and thermal effects. We have followed the reaction from the outer-sphere complex, in which the metal is coordinated with six water molecules and the porphyrin is doubly protonated, until the metal ion is inserted into the deprotonated porphyrin ring with only one water ligand remaining. This reaction involves the stepwise displacement of five water molecules and the removal of two protons from the porphyrin ring. In addition, a step seems to be necessary in which a porphyrin pyrrolenine nitrogen atom changes its interaction from a hydrogen bond to a metal-bound solvent molecule to a direct coordination to the metal ion. If the protons are taken up by a neutral imidazole molecule, the deprotonation reactions are exothermic with minimal barriers. However, with a water molecule as an acceptor, they are endothermic. The ligand exchange reactions were approximately thermoneutral (±20 kJ,mol,1, with one exception) with barriers of up to 72 kJ,mol,1 for Mg and 51 kJ,mol,1 for Fe. For Mg, the highest barrier was found for the formation of the first bond to the porphyrin ring. For Fe, a higher barrier was found for the formation of the second bond to the porphyrin ring, but this barrier is probably lower in solution. No evidence was found for an initial pre-equilibrium between a planar and a distorted porphyrin ring. Instead, the porphyrin becomes more and more distorted as the number of metal,porphyrin bonds increase (by up to 191 kJ,mol,1). This strain is released when the porphyrin becomes deprotonated and the metal moves into the ring plane. Implications of these findings for the chelatase enzymes are discussed. [source]

    Reaction Mechanism and Dynamic Investigations of Poly-channel Decomposition Reactions of o -Pyridyl Radical

    Cheng Xue-Li
    Abstract Utilizing Gaussian94 program package, all species involved in decomposition reactions of o -pyridyl radical were optimized fully at B3LYP/6-311++G** level. Intrinsic reaction coordinate calculations were employed to confirm the connections of the transition states and products, and transition states were ascertained by the number of imaginary frequency (0 or 1). The reaction mechanism was elucidated by the vibrational mode analysis and electronic population analysis, and the reaction rate constants were calculated with transition state theory. [source]

    Complete Elucidation of Electrode Reaction Mechanisms by Using Differential Pulse Polarography

    ELECTROANALYSIS, Issue 17-18 2010
    Miguel, Rodríguez Mellado
    Abstract By exploring the different parameters of the technique, it is shown that Differential Pulse Polarography (DPP) can be used for the elucidation of the reaction mechanisms of the electrochemical processes (with the evident exception of the product and intermediate identification). So, the type of transport towards or from the electrode can be identified from the dependence of the intensities with the pulse amplitude, the electrochemical reaction order with respect to the electroactive species from the shape of the polarogram, the type of rate-determining step from the dependence of the peak potentials on the pulse duration, the electrochemical reaction order with respect to other species, such as the H+ion, from the dependence of the peak potentials on their concentrations etc. [source]

    Study of the Complexation, Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric Conditions

    ELECTROANALYSIS, Issue 19 2003
    Sylvia Sander
    Abstract The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two-step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1,:,1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1,:,2 Cr(III)/DTPA complex. The electroreduction of the DTPA-Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled. The Cr(III) ion, generated in-situ from Cr(VI) at the mercury electrode at about ,50,mV (vs. Ag|AgCl) (3,mol,L,1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in-situ built complex Cr(III) ion were found to adsorb on the mercury electrode. The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible. The proposed complex structures and an overall reaction scheme are shown. [source]

    Merging of E2 and E1cb Reaction Mechanisms: A Combined Theoretical and Experimental Study

    Edoardo Mosconi
    Abstract By combining the results of kinetic measurements with DFT calculations we provide a clear-cut evidence of the merging between the E2 and E1cb reaction mechanisms for a large series of leaving groups. Our results solve a long-debated issue in chemical reactivity with profound implications both from a fundamental and biological point of view, thus paving the way to further investigations with different substrates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Reaction Mechanisms for Renewable Hydrogen from Liquid Phase Reforming of Sugar Compounds

    A. Tanksale
    Hydrogen is anticipated to become a major source of energy in the future. Hydrogen is a clean burning fuel and has been described as a long-term replacement for natural gas. It has been demonstrated here that hydrogen can be produced from biomass in the temperature range of 185-220°C using a single batch reactor pressurised at 25-30 bar. The current work is based on sugars which are considered here as the biomass resource. Glucose, fructose and sucrose solutions were used for the liquid phase reforming using supported platinum catalyst. The sugar molecules might go through reversible dehydrogenation steps to give adsorbed species on metal sites. This adsorption might be either on CC or CO bond cleavage. Platinum is one of the best catalysts for the reforming of hydrocarbons due to its high selectivity for CC bond cleavage. The CC bond cleavage is the limiting factor for the reforming and leads to a high rate of formation of hydrogen. On the other hand CO bond cleavage results in formation of alcohols, acids and other organic groups. [source]

    Reaction mechanism of methanol decomposition on Pt-based model catalysts: A theoretical study

    Cui-Yu Niu
    Abstract The decomposition mechanisms of methanol on five different Pt surfaces, the flat surface of Pt(111), Pt-defect, Pt-step, Pt(110)(1 × 1), and Pt(110)(2 × 1), have been studied with the DFT-GGA method using the repeated slab model. The adsorption energies under the most stable configuration of the possible species and the activation energy barriers of the possible elementary reactions involved are obtained in this work. Through systematic calculations for the reaction mechanism of methanol decomposition on these surfaces, we found that such a reaction shows the same reaction mechanism on these Pt-based model catalysts, that is, the final products are all H (Hads) and CO (COads) via OH bond breaking in methanol and CH bond scission in methoxy. These results are in general agreement with the previous experimental observations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010. [source]

    Reaction mechanism of palladium-catalyzed silastannation of allenes by density functional theory

    Meiyan Wang
    Abstract The reaction mechanism of Pd(0)-catalyzed allenes silastannation reaction is investigated by the density functional method B3LYP. The overall reaction mechanism is examined. For the allene insertion step, the PdSi bond is preferred over the PdSn bond. The electronic mechanism of the allene insertion into PdSi bond to form ,-vinylpalladium (terminal-insertion) and ,-allylpalladium (internal-insertion) insertion products is discussed in terms of the electron donation and back-donation. It is found that the electron back-donation is significant for both terminal- and internal-insertion. During allene insertion into PdSi bond, internal-insertion is preferred over terminal-insertion. By using methylallene, the regio-selectivity for the monosubstituted allene insertion into PdSi and PdSn bond is analyzed. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source]

    Theory of chemical bonds in metalloenzymes.


    Abstract Reaction mechanisms of oxygen evolution in native and artificial photosynthesis II (PSII) systems have been investigated on the theoretical grounds, together with experimental results. First of all, our previous broken-symmetry (BS) molecular orbitals (MO) calculations are reviewed to elucidate the instability of the d,-p, bond in high-valent (HV) Mn(X)O systems and the d,-p,-d, bond in HV MnOMn systems. The triplet instability of these bonds entails strong or intermediate diradical characters: ,Mn(IV)O, and ,MnOMn,; the BS MO resulted from strong electron correlation, leading to the concept of electron localizations and local spins. The BS computations have furthermore revealed guiding principles for derivation of selection rules for radical reactions of local spins. As a continuation of these theoretical results, the BS MO interaction diagrams for oxygen-radical coupling reactions in the oxygen evolution complex (OEC) in the PSII have been depicted to reveal scope and applicability of local singlet diradical (LSD) and local triplet diradical (LTD) mechanisms that have been successfully utilized for theoretical understanding of oxygenation reactions mechanisms by p450 and methane monooxygenase (MMO). The manganese-oxide cluster models examined are London, Berlin, and Berkeley models of CaMn4O4 and related clusters Mn4O4 and Mn3Ca. The BS MO interaction diagrams have revealed the LSD and/or LTD mechanisms for generation of molecular oxygen in the total low-, intermediate and high-spin states of these clusters. The spin alignments are found directly corresponding to the spin-coupling mechanisms of oxygen-radical sites in these clusters. The BS UB3LYP calculations of the clusters have been performed to confirm the comprehensive guiding principles for oxygen evolution; charge and spin densities by BS UB3LYP are utilized for elucidation and confirmation of the LSD and LTD mechanisms. Applicability of the proposed selection rules are examined in comparison with a lot of accumulated experimental and theoretical results for oxygen evolution reactions in native and artificial PSII systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    Reaction mechanisms between methylamine and a few Schiff bases: Ab initio potential energy surfaces of a catalytic step in semicarbazide sensitive amino oxidases (SSAO)

    Giuliano Alagona
    Abstract The potential energy surfaces for the transamination reaction catalyzed by SSAO were explored for some of the possible reactants considered in a preliminary investigation (Comput Chem 2000, 24, 311). The proton transfer to methylamine (as a model of the catalytic base belonging to the enzyme active site),either from the keto or enol form of the reactant Schiff bases with one of the possible cofactors, pyridoxal phosphate, PLP (using as a model the pyridoxal ring protonated at N),was investigated. The enol form seems to be preferred in the region of the neutral intermediate, because even the keto form undergoes a spontaneous rearrangement to the enol form once the C, proton is delivered to methylamine, producing methylammonium. When the proton is returned back to the Schiff base (on C1), the adduct is about 1.4 kcal/mol more stable than the reactants, while a canonical electron distribution is obtainable only for the enol form. The proton transfer to methylamine was also studied in the presence of the other possible cofactor (para or ortho) topaquinone, TQ. A steep uphill pathway, similar to the keto-pyridoxal Schiff base one, is obtained using the Schiff base with pTQ, which requires a rearrangement to the final intermediate. On the contrary, using the oTQ structures with the quinonoid O on the same side of methylamine, the proton abstracted from the Schiff base goes spontaneously onto the other quinonoid oxygen. The effect on the barrier heights produced by the presence of a variety of functional groups in the vicinity of the pyridoxal ring nitrogen was also examined. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001 [source]

    Support-dependent activity of noble metal substituted oxide catalysts for the water gas shift reaction

    AICHE JOURNAL, Issue 10 2010
    Parag A. Deshpande
    Abstract The water gas shift reaction was carried out over noble metal ion substituted nanocrystalline oxide catalysts with different supports. Spectroscopic studies of the catalysts before and after the reaction showed different surface phenomena occurring over the catalysts. Reaction mechanisms were proposed based upon the surface processes and intermediates formed. The dual site mechanism utilizing the oxide ion vacancies for water dissociation and metal ions for CO adsorption was proposed to describe the kinetics of the reaction over the reducible oxides like CeO2. A mechanism based on the interaction of adsorbed CO and the hydroxyl group was proposed for the reaction over ZrO2. A hybrid mechanism based on oxide ion vacancies and surface hydroxyl groups was proposed for the reaction over TiO2. The deactivation of the catalysts was also found to be support dependent. Kinetic models for both activation and deactivation were proposed. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

    A Determination of Hydration Mechanisms for Tricalcium Silicate Using a Kinetic Cellular Automaton Model

    Jeffrey W. Bullard
    Reaction mechanisms for the early stages of hydration of tricalcium silicate (Ca3SiO5) have not been agreed upon, although theories have appeared in the literature. In this paper, a mechanistic description is proposed that is consistent with a wide range of reported experimental observations, and which is supported quantitatively by simulations using HydratiCA, a new three-dimensional microstructure model of chemical kinetics. Rate processes are quantitatively modeled using probabilistic cellular automaton algorithms that are based on the principles of transition state theory. The model can test alternate assumptions about the reaction paths and rate-controlling steps, making it a kind of experimental tool for investigating kinetics and interpreting experimental observations. It is used here to show that hydration of Ca3SiO5 is most likely controlled by nucleation and growth of a compositionally variable calcium silicate hydrate solid, mediated at very early times by a transient, thermodynamically metastable solid that rapidly covers and sharply reduces the dissolution rate of Ca3SiO5. This proposed mechanism involves important elements of two leading theories of Ca3SiO5 hydration, neither of which alone has been able to capture the full range of experimental data when tested by the model. [source]

    Hydrothermal carbonization of biomass: A summary and discussion of chemical mechanisms for process engineering

    Axel Funke
    Abstract Hydrothermal carbonization can be defined as combined dehydration and decarboxy lation of a fuel to raise its carbon content with the aim of achieving a higher calorific value. It is realized by applying elevated temperatures (180,220°C) to biomass in a suspension with water under saturated pressure for several hours. With this conversion process, a lignite-like, easy to handle fuel with well-defined properties can be created from biomass residues, even with high moisture content. Thus it may contribute to a wider application of biomass for energetic purposes. Although hydrothermal carbonization has been known for nearly a century, it has received little attention in current biomass conversion research. This review summarizes knowledge about the chemical nature of this process from a process design point of view. Reaction mechanisms of hydrolysis, dehydration, decarboxylation, aromatization, and condensation polymerization are discussed and evaluated to describe important operational parameters qualitatively. The results are used to derive fundamental process design improvements. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd [source]

    A Theoretical Study of Surface Reduction Mechanisms of CeO2(111) and (110) by H2

    CHEMPHYSCHEM, Issue 6 2007
    Hsin-Tsung Chen Dr.
    Abstract Reaction mechanisms for the interactions between CeO2(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce 4f states on the redox chemistry of H2,CeO2 interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H2 molecule at various active sites of the CeO2 surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcal,mol,1 for the (111) to 26.5 kcal,mol,1 for the (110) surface, while those at the DFT+U level are between 65.0 kcal,mol,1 for the (111) and 81.8 kcal,mol,1 for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H2O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO2 surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO2(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface. [source]

    Study of Electrochemical Processes with Coupled Homogeneous Chemical Reaction in Differential Pulse Voltammetry at Spherical Electrodes and Microhemispheres

    ELECTROANALYSIS, Issue 16 2010
    Eduardo Laborda
    Abstract Homogeneous chemical reactions coupled to oxidation-reduction processes at electrode surfaces are very common in electrochemistry. In this paper we cope with the application of Differential Pulse Voltammetry at spherical electrodes and microhemispheres for the study of this kind of systems. Analytical expressions are deduced from which the influence of the different experimental variables is examined. Several diagnostic criteria for elucidation of the reaction mechanism from DPV peak parameters are given, as well as working curves for extraction of the kinetic rate constants of the chemical reaction. [source]

    Highly Sensitive Electrogenerated Chemiluminescence Detecting Ranitidine Based On Chemically Modifying Microenvironment of the Chemiluminescence Reaction

    ELECTROANALYSIS, Issue 11 2005
    Xingwang Zheng
    Abstract Using a graphite electrode modified with vaseline and NiO, ranitidine showed a strongly ECL enhancing effect for the weak ECL signal of electrooxidation of luminol. Based on this finding, a more sensitive ECL method for ranitidine was firstly proposed. Under the optimum experimental conditions, the ranitidine hydrochloride concentration in the range of 3.0×10,8,9.0×10,6,mol/L was proportional to the enhancing ECL signal and offered a 9×10,9,mol/L detection limit for ranitidine hydrochloride. At the same time, based on the investigation on this ECL reaction mechanism, a new concept, to improve the suitable ECL reaction micro-environment with chemically modified electrode technique for the better analytical performances of ECL analysis was also firstly proposed. [source]

    Reaction with N,N -Diethyl- p -phenylenediamine: A Procedure for the Sensitive Square-Wave Voltammetric Detection of Chlorine

    ELECTROANALYSIS, Issue 8 2003
    Hugo Seymour
    Abstract The reaction of chlorine and N,N -diethyl- p -phenylenediamine has been studied as a means of generating an analytical voltammetric signal of much improved sensitivity and selectivity for the detection of the former than is possible via direct electrolysis. A reaction mechanism is suggested whereby the chlorine attacks the primary amine of DEPD to form the N -chlorinated product that shows a much enhanced signal under conditions of square-wave voltammetry than does chlorine itself. The analytical parameters were found to vary with concentration of DEPD and a linear range from 17 to 495,,M was achievable with a corresponding limit of detection of 6.8,,M [source]

    Electrocatalytic Properties of Electropolymerized Ni(II)curcumin Complex

    ELECTROANALYSIS, Issue 5-6 2003
    Aleksander Ciszewski
    Abstract The voltammetric behavior in alkaline solution of a nickel-based chemically modified electrode (poly-Ni(II)curcumin) prepared by oxidative electropolymerization of nickel-curcumin complex for electrooxidation of aliphatic alcohols was investigated by cyclic voltammetry and rotating disk technique (curcumin=1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione). The dependence of the oxidation current on the alcohol concentration and on the number of redox centers Ni(II)/Ni(III) is discussed. From the fact that the oxidation current increases with the increase of film thickness it is evident that the electrocatalytic reaction occurs inside the polymer film. The system examined is a typical example of a redox polymer with 3D properties. It is also concluded that the reaction mechanism of alcohol oxidation is the case, according to the concept of Andrieux and Saveant, where the cross-exchange reaction is the limiting step. The mechanism of modifying the film formation has also been discussed. [source]

    Experimental study of flue gas desulfurization using landfill leachate

    Ding Sang-lan
    Abstract Because of the complexity of landfill leachate's composition, the reaction mechanism of SO2 in flue gas with landfill leachate was studied. The experimental results indicated that the factors influencing SO2 absorption efficiency using landfill leachate as the scrubbing medium were, in decreasing order of importance, pH, Fe2+, Mn2+, and Cl, as catalysts and the concentration of toluene and ethanol. Experiments showed that the pH of landfill leachate was the key factor governing both SO2 absorption and ammonia stripping. With the initial pH of 8.5, the terminal pH 6.0 and L/G ratio 3 L/m3, experimental results showed that average absorption efficiency of SO2 and the stripping efficiency of ammonia were 85 and 44%, respectively. The use of catalysts such as Fe2+ and Mn2+ was important for SO2 absorption when the pH value was below 7.0. The catalytic activity of Mn2+ was greater than that of Fe2+ although the reaction steps were very similar. Ethanol inhibits HSO3,/SO32, oxidation. The HSO3,/SO32, oxidation process improves the solubility of organics such as toluene in the leachate. The solute products of organics were water-soluble and biodegradable and could be used as substrates for bacteria in the post biotreatment. The factorial experiment results showed the effect of Cl,, Fe2+, and Mn2+ as catalysts on the HSO3,/SO32, oxidation has a greater positive impact than ethanol's inhibitory effect on the HSO3,/SO32, oxidation. © 2006 American Institute of Chemical Engineers Environ Prog 26:25,32, 2007 [source]

    Electro-Organocatalysis: Enantioselective ,-Alkylation of Aldehydes

    Xuan-Huong Ho
    Abstract The asymmetric organocatalyzed ,-alkylation of aldehydes via a cationic radical enamine intermediate was performed under environmentally benign electro-oxidation conditions without the use of chemical oxidants. To promote the desired ,-alkylation reaction of aldehydes, various aldehydes with xanthene or cycloheptatriene groups were exposed to electro-organocatalytic conditions to afford optically active ,-substituted aldehydes (,-alkylated aldehydes) in good yield. A reaction mechanism involving the cationic radical enamine was proposed based on the cyclic voltammetry (CV) results, DFT calculations, and control experiments. [source]

    Unsupported Copper Nanoparticles in the 1,3-Dipolar Cycloaddition of Terminal Alkynes and Azides,

    Francisco Alonso
    Abstract Readily prepared copper nanoparticles were found to catalyse the 1,3-dipolar cycloaddition of azides and alkynes up to rates comparable to those of microwave chemistry. Both the preparation of the nanoparticles and the click reaction are carried out under mild conditions, in short reaction times and in the absence of any stabilising additive or ligand. A variety of 1,2,3-triazoles were prepared in excellent yields. A reaction mechanism was postulated on the basis of different reactivity studies and deuteration experiments. Copper(I) acetylides were demonstrated to be the real intermediate species. [source]

    A Theoretical Insight into the Mechanism of the Silver-Catalysed Transsiliranation Reaction

    José Antonio Mayoral
    Abstract DFT calculations on a silver-catalysed transsiliranation reaction (silylene transfer from a silirane to an alkene) have shown the key role of a silylenesilver ion in the catalyticcycle. Although the corresponding triflate-bound species has previously been detected by NMR and IR spectroscopy, no significant silylene-transfer activity is predicted for such a nonionised structure. Several experimental results can be explained by this new reaction mechanism. [source]

    Halodecarboxylation Reaction of 4-Alkylidene-,-lactams

    Paola Galletti
    Abstract The synthesis of halo- and dihalovinyl-,-lactams by a halodecarboxylation reaction has been developed. Optimized procedures gave good yields of dibromo-, iodo- and diiodovinyl derivatives. The unprecedented synthesis of dihalo compounds by a Hunsdieker reaction was investigated in detail by 1H NMR analysis, which allowed the formulation of a reaction mechanism and revealed the role of triethylamine as a deiodinating agent. The dibromo- and diiodoalkylidene-,-lactams obtained were tested in a cross-coupling reaction with dimethylzinc. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]