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.

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 Chemical Reaction of Soybean Flavonoids with DNA: A Computational Study Using the Implicit Solvent Model

2012 ◽  
Vol 13 (2) ◽  
pp. 1269-1283 ◽  
Author(s):  
Hassan H. Abdallah ◽  
Janez Mavri ◽  
Matej Repič ◽  
Vannajan Sanghiran Lee ◽  
Habibah A. Wahab
Keyword(s):  
Chemical Reaction ◽  
Computational Study ◽  
Implicit Solvent ◽  
Implicit Solvent Model ◽  
Solvent Model

Redshift or Adduct Stabilization—A Computational Study of Hydrogen Bonding in Adducts of Protonated Carboxylic Acids

2009 ◽  
Vol 15 (2) ◽  
pp. 239-248 ◽  
Author(s):  
Solveig Gaarn Olesen ◽  
Steen Hammerum
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Bond Strength ◽  
Bond Length ◽  
Carboxylic Acids ◽  
Computational Study ◽  
Proton Affinities ◽  
Oh Groups ◽  
Hydrogen Bond Strength ◽  
Length Changes

It is generally expected that the hydrogen bond strength in a D–H•••A adduct is predicted by the difference between the proton affinities (Δ PA) of D and A, measured by the adduct stabilization, and demonstrated by the infrared (IR) redshift of the D–H bond stretching vibrational frequency. These criteria do not always yield consistent predictions, as illustrated by the hydrogen bonds formed by the E and Z OH groups of protonated carboxylic acids. The Δ PA and the stabilization of a series of hydrogen bonded adducts indicate that the E OH group forms the stronger hydrogen bonds, whereas the bond length changes and the redshift favor the Z OH group, matching the results of NBO and AIM calculations. This reflects that the thermochemistry of adduct formation is not a good measure of the hydrogen bond strength in charged adducts, and that the ionic interactions in the E and Z adducts of protonated carboxylic acids are different. The OH bond length and IR redshift afford the better measure of hydrogen bond strength.

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