scholarly journals Urethane Formation with an Excess of Isocyanate or Alcohol: Experimental and Ab Initio Study

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1543 ◽  
Author(s):  
Wafaa Cheikh ◽  
Zsófia Borbála Rózsa ◽  
Christian Orlando Camacho López ◽  
Péter Mizsey ◽  
Béla Viskolcz ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Activation Energies ◽  
Phenyl Isocyanate ◽  
Point Of View ◽  
Fourth Generation ◽  
Implicit Solvent ◽  
Stoichiometric Ratio ◽  
Urethane Formation ◽  
Solvent Model ◽  
Mechanistic Investigation

A kinetic and mechanistic investigation of the alcoholysis of phenyl isocyanate using 1-propanol as the alcohol was undertaken. A molecular mechanism of urethane formation in both alcohol and isocyanate excess is explored using a combination of an accurate fourth generation Gaussian thermochemistry (G4MP2) with the Solvent Model Density (SMD) implicit solvent model. These mechanisms were analyzed from an energetic point of view. According to the newly proposed two-step mechanism for isocyanate excess, allophanate is an intermediate towards urethane formation via six-centered transition state (TS) with a reaction barrier of 62.6 kJ/mol in the THF model. In the next step, synchronous 1,3-H shift between the nitrogens of allophanate and the cleavage of the C–N bond resulted in the release of the isocyanate and the formation of a urethane bond via a low-lying TS with 49.0 kJ/mol energy relative to the reactants. Arrhenius activation energies of the stoichiometric, alcohol excess and the isocyanate excess reactions were experimentally determined by means of HPLC technique. The activation energies for both the alcohol (measured in our recent work) and the isocyanate excess reactions were lower compared to that of the stoichiometric ratio, in agreement with the theoretical calculations.

scholarly journals Computational Study of Catalytic Urethane Formation

Polymers ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 8
Author(s):  
Hadeer Q. Waleed ◽  
Marcell Csécsi ◽  
Rachid Hadjadj ◽  
Ravikumar Thangaraj ◽  
Dániel Pecsmány ◽  
...  
Keyword(s):  
Computational Study ◽  
Phenyl Isocyanate ◽  
Catalyst Design ◽  
Implicit Solvent ◽  
Proton Affinities ◽  
Urethane Formation ◽  
Solvent Model ◽  
Nitrogen Containing Compounds ◽  
Near Future ◽  
Pu Foams

Polyurethanes (PUs) are widely used in different applications, and thus various synthetic procedures including one or more catalysts are applied to prepare them. For PU foams, the most important catalysts are nitrogen-containing compounds. Therefore, in this work, the catalytic effect of eight different nitrogen-containing catalysts on urethane formation will be examined. The reactions of phenyl isocyanate (PhNCO) and methanol without and in the presence of catalysts have been studied and discussed using the G3MP2BHandHLYP composite method. The solvent effects have also been considered by applying the SMD implicit solvent model. A general urethane formation mechanism has been proposed without and in the presence of the studied catalysts. The proton affinities (PA) were also examined. The barrier height of the reaction significantly decreased (∆E0 > 100 kJ/mol) in the presence of the studied catalysts, which proves the important effect they have on urethane formation. The achieved results can be applied in catalyst design and development in the near future.

Theoretical and experimental studies of palladium-catalyzed site-selective C(sp3)−H bond functionalization enabled by transient ligands

2017 ◽  
Author(s):  
Haibo Ge ◽  
Lei Pan ◽  
Piaoping Tang ◽  
Ke Yang ◽  
Mian Wang ◽  
...  
Keyword(s):  
Bond Activation ◽  
Theoretical Calculations ◽  
Experimental Studies ◽  
Bond Functionalization ◽  
Aliphatic Ketones ◽  
Site Selectivity ◽  
Mechanistic Investigation ◽  
Palladium Catalyzed ◽  
Metal Catalyzed ◽  
Site Selective

Transition metal-catalyzed selective C–H bond functionalization enabled by transient ligands has become an extremely attractive topic due to its economical and greener characteristics. However, catalytic pathways of this reaction process on unactivated sp<sup>3</sup> carbons of reactants have not been well studied yet. Herein, detailed mechanistic investigation on Pd-catalyzed C(sp<sup>3</sup>)–H bond activation with amino acids as transient ligands has been systematically conducted. The theoretical calculations showed that higher angle distortion of C(sp2)-H bond over C(sp3)-H bond and stronger nucleophilicity of benzylic anion over its aromatic counterpart, leading to higher reactivity of corresponding C(sp<sup>3</sup>)–H bonds; the angle strain of the directing rings of key intermediates determines the site-selectivity of aliphatic ketone substrates; replacement of glycine with β-alanine as the transient ligand can decrease the angle tension of the directing rings. Synthetic experiments have confirmed that β-alanine is indeed a more efficient transient ligand for arylation of β-secondary carbons of linear aliphatic ketones than its glycine counterpart.<br><br>

Temperature dependence of the optical properties in p-Cd0.96Zn0.04Te single crystals

2001 ◽  
Vol 16 (8) ◽  
pp. 2196-2199 ◽  
Author(s):  
H. Y. Lee ◽  
T. W. Kang ◽  
T. W. Kim
Keyword(s):  
Optical Properties ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Reasonable Agreement ◽  
Theoretical Calculations ◽  
Optoelectronic Devices ◽  
Activation Energies ◽  
Acoustic Parameters ◽  
Longitudinal Acoustic ◽  
Pl Spectra

Photoluminescence (PL) measurements were performed on p-Cd0.96Zn0.04Te single crystals to investigate the dependence of the excitons on temperature. The activation energies and the longitudinal acoustic parameters of the excitons were determined from the temperature dependence of the PL spectra and were in reasonable agreement with the theoretical calculations. These results can help improve understanding for the application of p-CdxZn1–xTe single crystals in optoelectronic devices.

scholarly journals Influence of TEM-1 β-Lactamase on the Pharmacodynamic Activity of Simulated Total versus Free-Drug Serum Concentrations of Cefditoren (400 Milligrams) versus Amoxicillin-Clavulanic Acid (2,000/125 Milligrams) against Haemophilus influenzae Strains Exhibiting an N526K Mutation in the ftsI Gene

2007 ◽  
Vol 51 (10) ◽  
pp. 3699-3706 ◽  
Author(s):  
M. Torrico ◽  
L. Aguilar ◽  
N. González ◽  
M. J. Giménez ◽  
O. Echeverría ◽  
...  
Keyword(s):  
Haemophilus Influenzae ◽  
Oral Administration ◽  
Clavulanic Acid ◽  
Bactericidal Activity ◽  
Theoretical Calculations ◽  
Point Of View ◽  
Release Formulation ◽  
Extended Release Formulation ◽  
Amoxicillin Clavulanic Acid ◽  
Free Serum

ABSTRACT The aim of this study was to explore bactericidal activity of total and free serum simulated concentrations after the oral administration of cefditoren (400 mg, twice daily [bid]) versus the oral administration of amoxicillin-clavulanic acid extended release formulation (2,000/125 mg bid) against Haemophilus influenzae. A computerized pharmacodynamic simulation was performed, and colony counts and β-lactamase activity were determined over 48 h. Three strains were used: ampicillin-susceptible, β-lactamase-negative ampicillin-resistant (BLNAR) (also resistant to amoxicillin-clavulanic acid) and β-lactamase-positive amoxicillin-clavulanic acid-resistant (BLPACR) strains, with cefditoren MICs of ≤0.12 μg/ml and amoxicillin-clavulanic acid MICs of 2, 8, and 8 μg/ml, respectively. Against the ampicillin-susceptible and BLNAR strains, bactericidal activity (≥3 log10 reduction) was obtained from 6 h on with either total and free cefditoren or amoxicillin-clavulanic acid. Against the BLPACR strain, free cefditoren showed bactericidal activity from 8 h on. In amoxicillin-clavulanic acid simulations the increase in colony counts from 4 h on occurred in parallel with the increase in β-lactamase activity for the BLPACR strain. Since both BLNAR and BLPACR strains exhibited the same MIC, this was due to the significantly lower (P ≤ 0.012) amoxicillin concentrations from 4 h on in simulations with β-lactamase positive versus negative strains, thus decreasing the time above MIC (T>MIC). From a pharmacodynamic point of view, the theoretical amoxicillin T>MIC against strains with elevated ampicillin/amoxicillin-clavulanic acid MICs should be considered with caution since the presence of β-lactamase inactivates the antibiotic, thus rendering inaccurate theoretical calculations. The experimental bactericidal activity of cefditoren is maintained over the dosing interval regardless of the presence of a mutation in the ftsI gene or β-lactamase production.

The fifth force: An enigma in this Universe

2019 ◽  
Vol 34 (09) ◽  
pp. 1950056 ◽  
Author(s):  
Koijam Manihar Singh ◽  
Kangujam Priyokumar Singh
Keyword(s):  
Theoretical Calculations ◽  
Point Of View ◽  
Theoretical Point ◽  
Experimental Proof ◽  
Fifth Force ◽  
Theory Of Everything ◽  
Discovery Science ◽  
Near Future ◽  
The Universe ◽  
High Hope

In an attempt to explain some of the unknown phenomena of nature, including dark energy and dark matter, we explore the possibility of the existence of a fifth fundamental force of nature as also cited by some researchers. With the inclusion of such a force in the system, some of the vague things can be explained and there is high hope of its importance in building up a “theory of everything”. With this intention, we investigate some manifestations of the fifth force which stand from theoretical calculations or from theoretical point of view, though till now there is less experimental proof. However, the theoretical results obtained indicate the existence of a fifth force which will lead to the completion in defining the laws of physics and nature. With this discovery, science may be able to explain the whole complexity of the Universe in near future.

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