Notizen: Oxidation of Tetraline by Dioxygen. Effect of Fe(acac)3 on the Thermal and Photoinitiated Reactions

1983 ◽  
Vol 38 (10) ◽  
pp. 1293-1294 ◽  
Author(s):  
Stanislav Luňák ◽  
Marie Vašková ◽  
Josef Vepřek-Šiška
Keyword(s):  
Reaction Rate ◽  
Thermal Reaction ◽  
Photochemical Oxidation ◽  
Rate Determining Step

Abstract The photochemical oxidation of tetraline by dioxygen is catalyzed by ferric acetylacetonate (iron(III) 2,4-pentadionate), the reaction rate increasing markedly with temperature. The rate-determining step of the photochemical oxidation is presumably a catalyzed thermal reaction.

Kinetics of carbon monoxide methanation on a Ni/SiO2 catalyst

1990 ◽  
Vol 55 (7) ◽  
pp. 1678-1685
Author(s):  
Vladimír Stuchlý ◽  
Karel Klusáček
Keyword(s):  
Carbon Monoxide ◽  
Reaction Rate ◽  
Catalyst Activity ◽  
Adsorbed Hydrogen ◽  
Reaction Products ◽  
Co Methanation ◽  
Molar Ratios ◽  
Rate Determining Step ◽  
Higher Temperature ◽  
Kinetics Of

Kinetics of CO methanation on a commercial Ni/SiO2 catalyst was evaluated at atmospheric pressure, between 528 and 550 K and for hydrogen to carbon monoxide molar ratios ranging from 3 : 1 to 200 : 1. The effect of reaction products on the reaction rate was also examined. Below 550 K, only methane was selectively formed. Above this temperature, the formation of carbon dioxide was also observed. The experimental data could be described by two modified Langmuir-Hinshelwood kinetic models, based on hydrogenation of surface CO by molecularly or by dissociatively adsorbed hydrogen in the rate-determining step. Water reversibly lowered catalyst activity and its effect was more pronounced at higher temperature.

The dehydrogenation of 1,4-dihydronaphthalene by tetrachloro-p-benzoquinone

1976 ◽  
Vol 54 (14) ◽  
pp. 2261-2265 ◽  
Author(s):  
Z. M. Hashish ◽  
I. M. Hoodless
Keyword(s):  
Electron Transfer ◽  
Charge Transfer ◽  
Reaction Rate ◽  
Second Order ◽  
Charge Transfer Complexes ◽  
Ion Transfer ◽  
Hydride Ion ◽  
Rate Determining Step ◽  
Hydride Ion Transfer

The dehydrogenation of 1,4-dihydronaphthalene by tetrachloro-p-benzoquinone in phenetole solution has been investigated. The present work does not fully confirm earlier studies which report that the reaction follows second-order kinetics and that the hydride ion transfer is rate determining. In the investigations described in this paper second-order kinetics are only observed in the later stages of the reaction and a 1:1 stoichiometry of the reactants in the process is not obtained. Substitution of tritium in the 1,4-positions of the hydrocarbon appears to not significantly affect the reaction rate. The present results indicate that charge-transfer complexes are formed in the reaction and it is suggested that electron transfer within these complexes could be the rate-determining step in the dehydrogenation.

scholarly journals Kinetics and mechanism of cetyltrimethylammonium bromide catalyzed oxidation of diethylene glycol by chloramine-T in acidic medium

2003 ◽  
Vol 68 (7) ◽  
pp. 535-542 ◽  
Author(s):  
V.W. Bhagwat ◽  
J. Tiwari ◽  
A. Choube ◽  
B. Pare
Keyword(s):  
Diethylene Glycol ◽  
Acidic Medium ◽  
Cetyltrimethylammonium Bromide ◽  
Reaction Rate ◽  
Chloride Ions ◽  
Kinetics And Mechanism ◽  
Product Analysis ◽  
Rate Determining Step ◽  
Chloramine T ◽  
Catalyzed Oxidation

The kinetics and mechanism of the C16TABcatalyzed oxidation of diethylene glycol (2,2?-oxydiethanol) by chloramine-T in acidic medium has been studied. The reaction has a first-order dependence on chloramine-T. With excess concentrations of other reactants, the reaction rate follows fractional order kinetics with respect to [diethylene glycol]. The micellar effect due to cetyltrimethylammonium bromide, a cationic surfactant, has been studied. The reaction is catalyzed by chloride ions as well. The small salt effect and increase in the reaction rate with increasing dielectric constant suggest the involvement of neutral molecules in the rate determining step. Addition of p-toluenesulfonamide retards the reaction rate. On the basis of product analysis, a pertinent mechanism is proposed.

Homogeneous Catalysis of Hydrogen Isotope Exchange Between D2 and Ethanol by Chlorotris(triphenyIphosphine)rhodium(I). II. In Chloroform-Ethanol

1974 ◽  
Vol 52 (12) ◽  
pp. 2226-2235 ◽  
Author(s):  
Graeme Strathdee ◽  
Russell Given
Keyword(s):  
Activation Energy ◽  
Computer Simulation ◽  
Exchange Reaction ◽  
Homogeneous Catalysis ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Reaction Rate ◽  
Side Reaction ◽  
Rate Determining Step ◽  
Inverse Isotope Effect

The kinetics and mechanism of D2 exchange catalyzed by RhCl(PPh3)3 have been studied in chloroform–ethanol solutions. Interpretation of the results was complicated by a side reaction of the solvent to yield HCl, RhHCl2(PPh3)2, C2H5Cl, CH2Cl2, Ph3PO, and other phosphorus(V) species. Computer simulation of the exchange reaction was used to show that the observed inverse isotope effect [Formula: see text] could arise only if the rate determining step was the activation of D2, HD, and H2 by RhCl(PPh3)3.The D2 exchange reaction rate was extremely dependent on solvent composition and decreased 30 times between 6 and 96 mol% C2H5OH. The activation energy for D2 exchange was 101 ± 9 kJ mol−1 at 58 mol% C2H5OH, and 86 ± 8 kJ mol−1 at 6 mol% C2H5OH. These data suggested that solvent–catalyst bonding interactions were important.

Kinetics of the Substitution of Norbornadiene in Tetracarbonyl(norbomadiene)molybdenum(0) by 2,2'-Bipyridine

2001 ◽  
Vol 56 (3) ◽  
pp. 281-286 ◽  
Author(s):  
Ceyhan Kayran ◽  
Eser Okan
Keyword(s):  
Reaction Rate ◽  
Activation Parameters ◽  
Bipy Ligand ◽  
First Order ◽  
Rate Determining Step ◽  
Vis Spectroscopy ◽  
Different Temperatures ◽  
Ft Ir ◽  
Thermal Substitution ◽  
Kinetics Of

Abstract The kinetics of the thermal substitution of norbornadiene (nbd) by 2,2'-bipyridine (2,2'-bipy) in (CO)4Mo(C7H9) was studied by quantitative FT-IR and UV-VIS spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of both leaving nbd and entering 2,2'-bipy ligand. The mechanism was found to be consistent with the previously proposed one, where the rate determining step is the cleavage of one of the two Mo-olefin bonds. The reaction was performed at four different temperatures (35 -50 °C) and the evaluation of the kinetic data gives the activation parameters which now support states.

Kinetics of heterogeneous processes

2005 ◽  
Author(s):  
Boris S. Bokstein ◽  
Mikhail I. Mendelev ◽  
David J. Srolovitz
Keyword(s):  
Oxide Layer ◽  
Atomic Oxygen ◽  
Reaction Rate ◽  
Heterogeneous Reaction ◽  
Effective Rate Constant ◽  
Internal Oxide ◽  
Reactant Concentration ◽  
Rate Determining Step ◽  
Oxidation Reduction ◽  
Heterogeneous Processes

Most practical reactions that occur in synthesizing or processing materials are heterogeneous. These include oxidation, reduction reactions, dissolution of solids in liquids, and most solid-state phase transformations. Consider the oxidation of a metal by exposure of a solid metal to an atmosphere with a finite partial pressure of oxygen. In order for oxidation to occur, molecular oxygen must dissociate into atomic oxygen on the metal surface. In some cases, atomic oxygen diffuses into the metal and reacts to form an internal oxide, while in others, the reaction occurs at the surface. In the latter case, thickening of the oxide layer requires either metal or oxygen diffusion through the growing oxide layer. This example demonstrates that heterogeneous processes commonly involve several steps. The first step is usually the transport of a reactant through one of the phases to the interface. The second is the adsorption (segregation) or chemical reaction on the interface. Finally, the last third step is the diffusion of the products into the growing phase or the desorption of the product. Since the entire heterogeneous process is a type of complex reaction, there is usually one step that controls the rate of the process, that is, is the rate-determining step. Recall that the rate-determining step is the slowest (fastest) step for a consecutive (parallel) reaction (see Sections 8.2.1 and 8.2.2). Consider the case of a consecutive heterogeneous reaction in which one of the reactants is transported through the fluid phase to the solid–fluid interface, where a first-order reaction takes place. The reaction rate ωr in such a case is ωr=kcx, where cx is the concentration of the reactant on the interface. Since the reactant is consumed at the interface, cx is smaller than the reactant concentration far from the interface, c0. It is usually easier to measure the reactant concentration in the bulk fluid. Therefore, it is convenient, to rewrite the reaction rate in terms of the bulk concentration in the fluid and an effective rate constant . . . ωr = kcx = keffc0. (11.1) . . . It is easiest to see the relation between keff and k by considering the steady-state case.

The photochemistry of complex ions: photochemical and thermal decomposition of the trioxalatocobaltate III complex

1955 ◽  
Vol 228 (1173) ◽  
pp. 252-263 ◽  
Keyword(s):  
Quantum Efficiency ◽  
Reaction Rate ◽  
Ultra Violet ◽  
Reaction Scheme ◽  
Thermal Reaction ◽  
Water Molecules ◽  
Back Reaction ◽  
Complex Ions ◽  
Excited Complex ◽  
Photochemical Quantum Yield

The photochemistry of the trioxalatocobaltate III complex was studied. It was shown that both the peak in the ultra-violet region (attributed to electron transfer) and that in the blue (attributed to d->d transitions) are photochemically active. Primary quantum efficiencies were found for various lines to be: 313 m μ , 0.365; 365 m μ , 0.345; 405 m μ , 0.085; 435 m μ , 0.06. The quantum efficiency of cobaltous ion formation is twice the primary quantum efficiency. No temperature dependence was detected. Ethyl alcohol (up to 75%) and acetone (up to 60%) did not effect the photochemical quantum yield. The radical C 2 O 4 - is postulated as intermediate capable of reducing mercuric chloride in the course of the reaction. The reaction scheme consists of photo-excitation, primary dark back-reaction, dissociation of excited complex and non-rate-determining oxidation of the C 2 O 4 - ion. The thermal reaction was also studied. It was found that the reaction rate could be presented by -d[Co Ox 3- 3 ]/d t = k 1 [Co Ox 3- 3 ]+ k 2 [H + ][Co Ox 3- 3 ] k 1 and k 2 were evaluated as 1.62 x 10 18 exp ( - 33 600/ RT ) s -1 and 1.77 x 10 19 exp ( - 32500/ RT ) s -1 (mol./l.) -1 respectively. Both the neutral and acid reactions were, however, postulated to proceed through a pseudomonomolecular mechanism involving water molecules with the [H + ] ion effecting the level of the transition state. Activation energies are discussed and finally the suitability of the trioxalatocobaltate III complex for chemical actionometry is analyzed.

scholarly journals Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Triethylene glycol by Chloramine-T in Acidic Medium

2008 ◽  
Vol 5 (4) ◽  
pp. 894-903 ◽  
Author(s):  
Vandana Sharma ◽  
K. V. Sharma ◽  
V. W. Bhagwat
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Reaction Rate ◽  
Catalytic Effect ◽  
Triethylene Glycol ◽  
Chloride Ion ◽  
Effect Of Temperature ◽  
Rate Determining Step ◽  
Excess Concentration ◽  
Chloramine T ◽  
Catalyzed Oxidation

The kinetics and mechanism of cetyltrimethylammonium bromide catalyzed oxidation of triethylene glycol [2,2'-ethylene diqxybis(ethanol)] by chloramine-T in acidic acid medium have been investigated. The reaction is first order dependence on chloramine-T and fractional order for triethylene glycol with excess concentration of other reactants. The catalytic effect due to cetyletrimethylammonium bromide has been studied. The small salt effect and increase in the reaction rate with increasing dielectric constant suggest the involvement of neutral molecule in the rate-determining step. The addition ofp-toluene sulfonamide retards the reaction rate. The effect of chloride ion on the reaction also studied. The effect of temperature on the reaction has been investigated in the temperature range 313-333K and thermodynamic parameters were calculated from the Arrhenious plot. A tentative mechanism consistent with the experimental results has been proposed.

Kinetics of Photochemical Oxidation of Glucose by Chloramine-T in Acidic Medium: A Mechanistic Approach

2013 ◽  
Vol 816-817 ◽  
pp. 7-12
Author(s):  
Meena Wadhwani ◽  
Shubha Jain
Keyword(s):  
Acidic Medium ◽  
Reaction Rate ◽  
Accurate Method ◽  
Photochemical Oxidation ◽  
First Order ◽  
Mechanistic Approach ◽  
Excess Concentration ◽  
Chloramine T ◽  
Kinetics Of ◽  
Oxidation Of Glucose

A simple, convenient and accurate method for the kinetic study of photochemical oxidation of glucose by chloramine-T in acidic medium is described. The kinetic investigation shows the first order dependence of reaction rate on chloramine-T. With excess concentration of other reactants the reaction rate follows fractional order kinetics with respect to substrate. The reaction is catalyzed by H+ ions as well. A small salt effect and increase in reaction rate with increasing the intensity of light source is also observed. Addition of p-toluene sulphonamide retards the reaction rate. A suitable mechanism in agreement with observed kinetics has been proposed

scholarly journals A theoretical study of abiotic methylation reactions of gaseous elemental mercury by halogen containing molecules

2010 ◽  
Vol 10 (9) ◽  
pp. 22369-22394 ◽  
Author(s):  
L. Castro ◽  
A. Dommergue ◽  
C. Larose ◽  
C. Ferrari ◽  
L. Maron
Keyword(s):  
Experimental Data ◽  
Reaction Rate ◽  
Theoretical Study ◽  
Elemental Mercury ◽  
Thermal Reaction ◽  
Visible Range ◽  
Electronic Data ◽  
Subsequent Formation ◽  
Gaseous Elemental Mercury ◽  
Methyl Transfer

Abstract. Methylation reactions of gaseous elementary mercury by halogen containing molecules such as halogenomethane species CH3X (with X=Cl, Br and I) and the dimethylchlorinium ion CH3ClCH3+ were investigated at the DFT level. With CH3X, the reaction is predicted to be almost athermic and kinetically demanding for a thermal reaction. The reaction can proceed photochemically in the visible range; therefore sunlight may increase the reaction rate. These results compare well with the experimental data. Consecutive methylation of the CH3HgX products (with X=Cl, Br and I) and subsequent formation of CH3HgCH3 were also studied. These reactions are predicted to be kinetically inaccessible and thermodynamically unfavorable. With CH3ClCH3+, the reaction is predicted to be athermic but kinetically easy. This is due to the suitability of the methyl transfer reagent. Geometrical and electronic data were systematically analyzed in order to rationalize the results.

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