A Much-Needed Mechanism and Reaction Rate for the Oxidation of Phenols with ClO2: A Joint Experimental and Computational Study

2013 ◽  
Vol 66 (7) ◽  
pp. 814 ◽  
Author(s):  
Carlos Alberto Huerta Aguilar ◽  
Jayanthi Narayanan ◽  
Mariappan Manoharan ◽  
Narinder Singh ◽  
Pandiyan Thangarasu
Keyword(s):  
Oxidation Rate ◽  
Density Functional ◽  
Reaction Rate ◽  
Computational Study ◽  
Reaction Rate Constant ◽  
Oxidation Products ◽  
Gas Chromatography Mass Spectrometry ◽  
Activation Barriers ◽  
Oxidation Of Phenols ◽  
The Right

The oxidation of phenols with chlorine dioxide, a powerful means to eliminate phenol pollutants from drinking water, is explored. Kinetic experiments reveal that 2,4,6-trichlorophenol exhibits a lower oxidation rate than other phenols because the chlorine atoms (σ = 0.22) at ortho and para-positions decrease the benzene’s electron density, in agreement with the Hammett plot. The oxidation of phenol was found to be second order with respect to phenol and first order with respect to ClO2 and a possible mechanism is proposed. The phenol/ClO2 oxidation was found to be pH-dependent since the reaction rate constant increases with increasing pH. The oxidation rate was also significantly enhanced with an increasing methanol ratio in water. The oxidation products, such as benzoquinones, were analysed and confirmed by liquid chromatography and gas chromatography–mass spectrometry. Density functional theory computations at both the B3LYP/6-311+G(d,p) and M06-2X.6-311+G(d,p) levels with the SCRF-PCM solvation model (i.e. with water) further supported the proposed mechanisms in which activation barriers predicted the right reactivity trend as shown by the kinetic experiments.

scholarly journals A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

2021 ◽  
Author(s):  
Igor Kowalec ◽  
Lara Kabalan ◽  
Richard Catlow ◽  
Andrew Logsdail
Keyword(s):  
Density Functional ◽  
Negative Charge ◽  
Computational Study ◽  
Adsorbed Species ◽  
Pd Catalysts ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rate Determining Step ◽  
Adsorption Energies ◽  
Insight Into

<p>We investigate the mechanism of direct CO<sub>2</sub> hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO<sub>2</sub> on Pd-based catalysts. The initial chemisorption of CO<sub>2</sub>, forming a partially charged CO<sub>2</sub><sup>δ-</sup>, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO<sub>2</sub><sup>δ-</sup><sub> </sub>on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO<sub>2</sub><sup>δ-</sup><sub> </sub>adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H<sub>2</sub>COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.<br></p>

scholarly journals Computational Study of Methane C–H Activation by Main Group and Mixed Main Group–Transition Metal Complexes

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2794
Author(s):  
Carly C. Carter ◽  
Thomas R. Cundari
Keyword(s):  
Transition Metal Complexes ◽  
Active Site ◽  
Density Functional ◽  
Computational Study ◽  
Divalent Metal ◽  
Main Group ◽  
Free Energies ◽  
Functional Theory ◽  
Activation Barriers ◽  
Experimental Values

In the present density functional theory (DFT) research, nine different molecules, each with different combinations of A (triel) and E (divalent metal) elements, were reacted to effect methane C–H activation. The compounds modeled herein incorporated the triels A = B, Al, or Ga and the divalent metals E = Be, Mg, or Zn. The results show that changes in the divalent metal have a much bigger impact on the thermodynamics and methane activation barriers than changes in the triels. The activating molecules that contained beryllium were most likely to have the potential for activating methane, as their free energies of reaction and free energy barriers were close to reasonable experimental values (i.e., ΔG close to thermoneutral, ΔG‡ ~30 kcal/mol). In contrast, the molecules that contained larger elements such as Zn and Ga had much higher ΔG‡. The addition of various substituents to the A–E complexes did not seem to affect thermodynamics but had some effect on the kinetics when substituted closer to the active site.

Experimental Study on the Hydrogen Storage Properties of LaNi5 Alloy in Repeated Hydriding/Dehydriding Cycles

2013 ◽  
Vol 815 ◽  
pp. 25-30 ◽  
Author(s):  
Xin Xin Cao ◽  
Fu Sheng Yang ◽  
Zhen Wu ◽  
Yu Qi Wang ◽  
Zao Xiao Zhang
Keyword(s):  
Hydrogen Storage ◽  
Reaction Rate ◽  
Plateau Pressure ◽  
Reaction Rate Constant ◽  
Oxidation Products ◽  
Equilibrium Pressure ◽  
Hydrogen Storage Properties ◽  
Jma Model ◽  
Controlling Mechanism ◽  
Storage Properties

LaNi5 alloy is one of the promising materials for hydrogen storage. It has good activation property, fast reaction rate and moderate plateau pressure. However, some of its hydrogen storage properties will change after repeated hydriding/dehydriding cycles, which limits its practical application. Therefore, this paper investigated the cycling properties of LaNi5 alloy by volumetric method. The results showed that the reaction rate increased with cycling. The hydriding/dehydriding hydrogen content decreased with cycling. For hydriding reaction, the equilibrium pressure increased with cycling, while it decreased for dehydriding at 40°C and 60°C. After 100 cycles, the LaNi5 alloy has been severely pulverized and oxygenated. The oxidation products include LaNiO2, La2NiO4, La2NiO4.18 and LaNiO3. The JMA model was found to fit the kinetic data well, suggesting a nucleation and growth controlling mechanism. The intrinsic reaction rate constant ka increases from 21.87 s-1to 24.81 s-1, while the activation energy decreases from the initial value of 19459 to 19373 J/mol after 100 cycles.

scholarly journals A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

2021 ◽  
Author(s):  
Igor Kowalec ◽  
Lara Kabalan ◽  
Richard Catlow ◽  
Andrew Logsdail
Keyword(s):  
Density Functional ◽  
Negative Charge ◽  
Computational Study ◽  
Adsorbed Species ◽  
Pd Catalysts ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rate Determining Step ◽  
Adsorption Energies ◽  
Insight Into

<p>We investigate the mechanism of direct CO<sub>2</sub> hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO<sub>2</sub> on Pd-based catalysts. The initial chemisorption of CO<sub>2</sub>, forming a partially charged CO<sub>2</sub><sup>δ-</sup>, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO<sub>2</sub><sup>δ-</sup><sub> </sub>on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO<sub>2</sub><sup>δ-</sup><sub> </sub>adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H<sub>2</sub>COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.<br></p>

scholarly journals The Impact of Secondary Coordination Sphere Nucleophiles on Methane Activation: A Computational Study

2019 ◽  
Author(s):  
Mary E. Anderson ◽  
Thomas Cundari
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Bond Activation ◽  
Computational Study ◽  
Solvent Polarity ◽  
Active Hydrogen ◽  
Functional Theory ◽  
Activation Barriers ◽  
Secondary Coordination Sphere ◽  
The Impact

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'} <p>Density functional theory and ab initio calculations indicate that nucleophiles can significantly reduce enthalpic barriers to methane C–H bond activation. Different pieces of evidence point to an electrostatic origin for the nucleophile effect such as the sensitivity of the C–H activation barriers to the external nucleophile and to continuum solvent polarity. The data further imply a transition state with significant charge build-up on the active hydrogen of the hydrocarbon substrate. From the present modeling studies, one may propose proteins with hydrophobic active sites, available nucleophiles, and hydrogen bond donors as attractive targets for the engineering of novel methane functionalizing enzymes.</p>

scholarly journals The Impact of Secondary Coordination Sphere Nucleophiles on Methane Activation: A Computational Study

2019 ◽  
Author(s):  
Mary E. Anderson ◽  
Thomas Cundari
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Bond Activation ◽  
Computational Study ◽  
Solvent Polarity ◽  
Active Hydrogen ◽  
Functional Theory ◽  
Activation Barriers ◽  
Secondary Coordination Sphere ◽  
The Impact

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'} <p>Density functional theory and ab initio calculations indicate that nucleophiles can significantly reduce enthalpic barriers to methane C–H bond activation. Different pieces of evidence point to an electrostatic origin for the nucleophile effect such as the sensitivity of the C–H activation barriers to the external nucleophile and to continuum solvent polarity. The data further imply a transition state with significant charge build-up on the active hydrogen of the hydrocarbon substrate. From the present modeling studies, one may propose proteins with hydrophobic active sites, available nucleophiles, and hydrogen bond donors as attractive targets for the engineering of novel methane functionalizing enzymes.</p>

Exo selectivity and the effect of disubstitution in the Diels–Alder reactions of butadiene with 3,3-disubstituted cyclopropenes

2004 ◽  
Vol 82 (11) ◽  
pp. 1589-1596 ◽  
Author(s):  
Tammy L Gosse ◽  
Raymond A Poirier
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Computational Study ◽  
Alder Reaction ◽  
Diels Alder ◽  
Anomeric Effect ◽  
Isodesmic Reactions ◽  
Activation Barriers ◽  
Additional Stabilization ◽  
Transition State Structures

A density functional computational study was performed to accomplish two tasks: to examine the endo–exo selectivity in the Diels–Alder reactions of 3,3-disubstituted cyclopropenes with s-cis-butadiene, and to study the effect of disubstitution on the reactivity of the cyclopropene dienophile. Cyclopropene is substituted at C-3 with CH3, SiH3, NH2, PH2, OH, SH, F, and Cl; both 3-substituted and 3,3-disubstituted ground states are examined to determine relative reactivities. The exo transition-state structures are consistently lower in energy than the endo transition-state structures for the 3,3-disubstituted cyclopropene – butadiene system, and surprisingly, both modes of addition have lower activation barriers than the syn 3-substituted cyclopropene – butadiene system. Through a series of isodesmic reactions, we have concluded that there is an additional stabilization in the transition-state structures of the 3,3-disubstituted system that can account for the lowering of the activation barriers below that of the 3-substituted cases. This stabilization is a combination of the anomeric effect and the ring relaxation that occurs in the transition-state structure.Key words: Diels–Alder reaction, cyclopropene, exo selectivity, anomeric effect.

New Procedure for Linear Sweep Voltammetric Determination of Catalytic Reaction Rate Constant. Oxidation of Some Aliphatic Alcohols with Electrolytically Generated Os(VIII)

1995 ◽  
Vol 60 (5) ◽  
pp. 795-801
Author(s):  
Dušan Bustin ◽  
Štefan Mesároš ◽  
Peter Tomčík ◽  
Miroslav Rievaj
Keyword(s):  
Catalytic Reaction ◽  
Oxidation Rate ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Reaction Rate Constant ◽  
Sufficient Accuracy ◽  
Aliphatic Alcohols ◽  
Catalytic Reactions ◽  
Linear Sweep

Oxidation rate of methanol, ethanol and 2-propanol by Os(VIII) in 1 M KOH was determined by evaluating anodic voltammograms of Os(VI) in the presence of the aliphatic alcohols. The proposed method is based on the evaluation of the change of voltammogram shape by catalytic process and on the assumption of its approximation by fractionally integrated voltammograms. This assumption has been confirmed empirically for k'f /a in the interval of <0.04,1>. The rate constants from this interval could be determined with sufficient accuracy. The method is suitable for evaluation of reaction rates slow and moderately fast catalytic reactions. It was compared with other evaluation methods from the literature.

scholarly journals Atmospheric photo-oxidation of myrcene: OH reaction rate constant, gas phase oxidation products and radical budgets

2021 ◽  
Author(s):  
Zhaofeng Tan ◽  
Luisa Hantschke ◽  
Martin Kaminski ◽  
Ismail-Hakki Acir ◽  
Birger Bohn ◽  
...  
Keyword(s):  
Gas Phase ◽  
Rate Constant ◽  
Reaction Rate ◽  
Branching Ratios ◽  
Reaction Rate Constant ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Hydrogen Shift ◽  
A Value ◽  
Radical Production

Abstract. The photo-oxidation of myrcene, a monoterpene species emitted by plants, was investigated at atmospheric conditions in the outdoor simulation chamber SAPHIR. The chemical structure of myrcene consists of one moiety that is a conjugated π-system (similar to isoprene) and another moiety that is a triple-substituted olefinic unit (similar to 2-methyl-2-butene). Hydrogen shift reactions of organic peroxy radicals RO2 formed in the reaction of isoprene with atmospheric OH radicals are known to be of importance for the regeneration of OH. Structure-activity relationships (SAR) suggest that similar hydrogen shift reactions like in isoprene may apply to the isoprenyl part of RO2 radicals formed during the OH oxidation of myrcene. In addition, SAR predicts further isomerization reactions that would be competitive with bi-molecular RO2 reactions for chemical conditions that are typical for forested environments with low concentrations of nitric oxide. Assuming that OH peroxy radicals can rapidly interconvert by addition and elimination of O2 like in isoprene, bulk isomerization rate constants of 0.21 s−1 and 0.097 s−1 (T = 298 K) for the 3 isomers resulting from the 3'-OH and 1-OH addition, respectively, can be derived from SAR. Measurements of radicals and trace gases in the experiments allowed to calculate radical production and destruction rates, which are expected to be balanced. Largest discrepancies between production and destruction rates were found for RO2. Additional loss of organic peroxy radicals due to isomerization reactions could explain the observed discrepancies. The uncertainty of the total radical (ROx = OH+HO2+RO2) production rates were high due to the uncertainty in the yield of radicals from myrcene ozonolysis. However, results indicate that radical production can only be balanced, if the reaction rate constant of the reaction between hydroperoxy (HO2) and RO2 radicals derived from myrcene is lower (0.9 to 1.6 × 10−11 cm3 s−1) than predicted by SAR. Another explanation of the discrepancies would be that a significant fraction of products (yield: 0.3 to 0.6) from these reactions include OH and HO2 radicals instead of radical terminating organic peroxides. Experiments also allowed to determine the yields of organic oxidation products acetone (yield: 0.45 ± 0.08) and formaldehyde (yield: 0.35 ± 0.08). Acetone and formaldehyde are produced from different oxidation pathways, so that yields of these compounds reflect the branching ratios of the initial OH addition to myrcene. Yields determined in the experiments are consistent with branching ratios expected from SAR. The yield of organic nitrate was determined from the gas-phase budget analysis of reactive oxidized nitrogen in the chamber giving a value of 0.13 ± 0.03. In addition, the reaction rate constant for myrcene + OH was determined from the measured myrcene concentration yielding a value of (2.3 ± 0.3) × 10−10 cm3 s−1.

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