scholarly journals Direct carbon-carbon coupling of furanics with acetic acid over Brønsted zeolites

2016 ◽  
Vol 2 (9) ◽  
pp. e1601072 ◽  
Author(s):  
Abhishek Gumidyala ◽  
Bin Wang ◽  
Steven Crossley
Keyword(s):  
Acetic Acid ◽  
Density Functional ◽  
Reaction Rate ◽  
Activation Barrier ◽  
Density Functional Theory Calculations ◽  
Step Change ◽  
Functional Theory ◽  
Transportation Fuels ◽  
Bond Forming ◽  
Direct Acylation

Effective carbon-carbon coupling of acetic acid to form larger products while minimizing CO2emissions is critical to achieving a step change in efficiency for the production of transportation fuels from sustainable biomass. We report the direct acylation of methylfuran with acetic acid in the presence of water, all of which can be readily produced from biomass. This direct coupling limits unwanted polymerization of furanics while producing acetyl methylfuran. Reaction kinetics and density functional theory calculations illustrate that the calculated apparent barrier for the dehydration of the acid to form surface acyl species is similar to the experimentally measured barrier, implying that this step plays a significant role in determining the net reaction rate. Water inhibits the overall rate, but selectivity to acylated products is not affected. We show that furanic species effectively stabilize the charge of the transition state, therefore lowering the overall activation barrier. These results demonstrate a promising new route to C–C bond–forming reactions for the production of higher-value products from biomass.

The Role of SiH3 Diffusion in Determining the Surface Smoothness of Plasma-Deposited Amorphous Si Thin Films: An Atomic-Scale Analysis

2005 ◽  
Vol 862 ◽  
Author(s):  
Mayur S. Valipa ◽  
Tamas Bakos ◽  
Eray S. Aydil ◽  
Dimitrios Maroudas
Keyword(s):  
Thin Films ◽  
Density Functional ◽  
Activation Barrier ◽  
Density Functional Theory Calculations ◽  
Atomic Scale ◽  
Functional Theory ◽  
Weak Adsorption ◽  
Dynamics Simulations ◽  
Hydrogenated Amorphous

AbstractDevice-quality hydrogenated amorphous silicon (a-Si:H) thin films grown under conditions where the SiH3 radical is the dominant deposition precursor are remarkably smooth, as the SiH3 radical is very mobile and fills surface valleys during its diffusion on the a-Si:H surface. In this paper, we analyze atomic-scale mechanisms of SiH3 diffusion on a-Si:H surfaces based on molecular-dynamics simulations of SiH3 radical impingement on surfaces of a-Si:H films. The computed average activation barrier for radical diffusion on a-Si:H is 0.16 eV. This low barrier is due to the weak adsorption of the radical onto the a-Si:H surface and its migration predominantly through overcoordination defects; this is consistent with our density functional theory calculations on crystalline Si surfaces. The diffusing SiH3 radical incorporates preferentially into valleys on the a-Si:H surface when it transfers an H atom and forms a Si-Si backbond, even in the absence of dangling bonds.

scholarly journals Carbon Dioxide Activation by a Palladium Terminal Imido Complex

2019 ◽  
Vol 72 (11) ◽  
pp. 900 ◽  
Author(s):  
Stephen J. Goodner ◽  
Annette Grünwald ◽  
Frank W. Heinemann ◽  
Dominik Munz
Keyword(s):  
Carbon Dioxide ◽  
Nitrogen Atom ◽  
Density Functional ◽  
Reaction Rate ◽  
Density Functional Theory Calculations ◽  
Nucleophilic Attack ◽  
Functional Theory ◽  
Highest Occupied Molecular Orbital ◽  
Nucleophilic Reactivity ◽  
Complex Features

We recently reported the first example of a palladium(ii) terminal imido complex. We proposed that this complex features exceptional high nucleophilicity at the nitrogen atom and a peculiar zwitterionic electronic structure with an anti-bonding highest-occupied molecular orbital (HOMO). This complex swiftly activated moderately acidic CH, OH, and NH bonds and also reacted with dihydrogen. However, unambiguous nucleophilic reactivity with substrates not featuring a hydrogen atom could not be observed. Herein, we now show that this nucleophilic complex also reacts with CO2 to give a ring-strained four-membered palladium(ii) carbamate complex. Remarkably, the same product is obtained in the reaction of the related bisamido complex, albeit at a slower reaction rate. Density functional theory calculations indicate that the addition of CO2 does not proceed via initial 1,2-addition across the Pd–N bond, but instead through nucleophilic attack by the imido (amido respectively) nitrogen atom.

scholarly journals Surprisingly facile CO2 insertion into cobalt alkoxide bonds: A theoretical investigation

2015 ◽  
Vol 11 ◽  
pp. 1340-1351 ◽  
Author(s):  
Willem K Offermans ◽  
Claudia Bizzarri ◽  
Walter Leitner ◽  
Thomas E Müller
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Density Functional Theory ◽  
Theoretical Investigation ◽  
Density Functional ◽  
Activation Barrier ◽  
Density Functional Theory Calculations ◽  
Reaction Energy ◽  
Reaction Step ◽  
Functional Theory

Exploiting carbon dioxide as co-monomer with epoxides in the production of polycarbonates is economically highly attractive. More effective catalysts for this reaction are intensively being sought. To promote better understanding of the catalytic pathways, this study uses density functional theory calculations to elucidate the reaction step of CO2 insertion into cobalt(III)–alkoxide bonds, which is also the central step of metal catalysed carboxylation reactions. It was found that CO2 insertion into the cobalt(III)–alkoxide bond of [(2-hydroxyethoxy)CoIII(salen)(L)] complexes (salen = N,N”-bis(salicyliden-1,6-diaminophenyl)) is exothermic, whereby the exothermicity depends on the trans-ligand L. The more electron-donating this ligand is, the more exothermic the insertion step is. Interestingly, we found that the activation barrier decreases with increasing exothermicity of the CO2 insertion. Hereby, a linear Brønsted–Evans–Polanyi relationship was found between the activation energy and the reaction energy.

Modeling Reaction Kinetics of Twin Polymerization via Differential Scanning Calorimetry

2018 ◽  
Vol 43 (4) ◽  
pp. 347-357
Author(s):  
Janett Prehl ◽  
Robin Masser ◽  
Peter Salamon ◽  
Karl Heinz Hoffmann
Keyword(s):  
Reaction Mechanism ◽  
Density Functional ◽  
Reaction Rate ◽  
Density Functional Theory Calculations ◽  
Scanning Calorimetry ◽  
Functional Theory ◽  
Reaction Rate Constants ◽  
Acid Catalyzed ◽  
Kinetics Of ◽  
Derivatives Of

Abstract We present a kinetic model for the reaction mechanism of acid-catalyzed twin polymerization. Our model characterizes the reaction mechanism not by the reactants, intermediate structures, and products, but via reaction-relevant moieties. We apply our model for three different derivatives of 2,2’-Spirobi[4H-1,3,2-benzodioxasiline] and determine activation energies, reaction enthalpies, and reaction rate constants for the reaction steps in our mechanism. We compare our findings to previously reported values obtained from density functional theory calculations. Furthermore, with this approach we are also able to follow the time development of the concentrations of the reaction-relevant moieties.

scholarly journals Direct Metal-Free Transformation of Alkynes to Nitriles: Computational Evidence for the Precise Reaction Mechanism

2021 ◽  
Vol 22 (6) ◽  
pp. 3193
Author(s):  
Lucija Hok ◽  
Robert Vianello
Keyword(s):  
Reaction Mechanism ◽  
Density Functional ◽  
Activation Barrier ◽  
Solvent Polarity ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Metal Free ◽  
Nitrogen Donor ◽  
Reaction Free Energy ◽  
Electron Donating Groups

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN3) as a nitrogen donor. The reaction requires six steps with the activation barrier ΔG‡ = 33.5 kcal mol−1 and a highly exergonic reaction free-energy ΔGR = −191.9 kcal mol−1 in MeCN. Reaction profiles agree with several experimental observations, offering evidence for the formation of molecular I2, interpreting the necessity to increase the temperature to finalize the reaction, and revealing thermodynamic aspects allowing higher yields for alkynes with para-electron-donating groups. In addition, the proposed mechanism indicates usefulness of this concept for both internal and terminal alkynes, eliminates the option to replace NIS by its Cl- or Br-analogues, and strongly promotes NaN3 as an alternative to TMSN3. Lastly, our results advise increasing the solvent polarity as another route to advance this metal-free strategy towards more efficient processes.

Ligand Exchange Processes on the Solvated Zinc Cation II. [Zn(H2O)4L]2+·2H2O with L = NH3, NH2(CH3), NH(CH3)2, and N(CH3)3

2010 ◽  
Vol 63 (2) ◽  
pp. 236 ◽  
Author(s):  
Basam M. Alzoubi ◽  
Ralph Puchta ◽  
Rudi van Eldik
Keyword(s):  
Density Functional ◽  
Water Exchange ◽  
Activation Barrier ◽  
Density Functional Theory Calculations ◽  
Exchange Reactions ◽  
Functional Theory ◽  
Zinc Cation ◽  
Exchange Processes ◽  
The Stability ◽  
Electronic And Steric Effects

Water-exchange mechanisms for the complexes [Zn(H2O)4L]2+·2H2O, L = NH3, NH2CH3, NH(CH3)2, and N(CH3)3, have been studied by density functional theory calculations (B3LYP/6–311+G**). The water-exchange reactions follow an associative (A) pathway involving formation of a six-coordinate intermediate [Zn(H2O)5L]2+·H2O. Electronic and steric effects of the amine ligands influence the activation barrier and the stability of the six-coordinate intermediate.

Reaction Prediction using Density Functional Theory Calculations: A Study into the Synthesis of Safranal via Diels-Alder Reactions

2011 ◽  
Vol 66 (11) ◽  
pp. 1141-s1241
Author(s):  
Gabriele Wagner ◽  
Nadia Vahdati ◽  
Ashley Howkins ◽  
Louisa Cubitt
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Activation Barrier ◽  
Exothermic Reaction ◽  
Density Functional Theory Calculations ◽  
Alder Reaction ◽  
Diels Alder ◽  
Functional Theory ◽  
Diels Alder Reaction ◽  
High Activation Barrier

Two pathways for the synthesis of safranal (2,6,6-trimethyl-cyclohexa-1,3-diene-1-carbaldehyde) via a Diels-Alder reaction are proposed and analyzed for their feasibility by Density Functional Theory (DFT) calculations on a B3LYP/6-31G* level of theory. Pathway A involving the reaction of 3-methyl-2-butenal with 4-methoxypenta-1,3-diene is predicted to produce the desired regioisomers, although with low stereoselectivity. Due to the high activation barrier (23 kcal mol−1), the reaction will require harsher conditions than the related known reaction of Z-2-butenal and 1-methoxy-1,3- butadiene with a calculated ΔEa of 17 kcal mol−1. Replacement of the methoxy group at the diene by OAc, OSiMe3 or pyrrolidinyl does not enhance the reactivity any further. Preliminary experiments confirm these results, although the reaction conditions need to be improved for the reaction to be of synthetic use. In the reaction of methoxyethene with 3-formyl-2,4-dimethylpenta-1,3-diene (pathway B), the homo- and hetero-Diels-Alder pathways were compared. The desired homo-Diels-Alder reaction is predicted to give the correct regioisomer in an exothermic reaction. However, the activation barrier is high (30 kcal mol−1) and the reaction unlikely to proceed. The hetero-Diels-Alder reaction requires less activation energy (23 kcal mol−1) and is expected to dominate, although the thermodynamic driving force is low. The preferred regioisomeric product is the 2-methoxy-3,4-dihydropyran, in agreement with related reactions studied experimentally

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