scholarly journals An Ab Initio Investigation of the 4,4′-Methlylene Diphenyl Diamine (4,4′-MDA) Formation from the Reaction of Aniline with Formaldehyde

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 398 ◽  
Author(s):  
R. Boros ◽  
László Farkas ◽  
Károly Nehéz ◽  
Béla Viskolcz ◽  
Milán Szőri
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Acid Strength ◽  
Standard Enthalpy Of Formation ◽  
Side Reactions ◽  
Acidic Media ◽  
Pka Calculation ◽  
Industrial Synthesis ◽  
Dead End ◽  
Competing Reactions

The most commonly applied industrial synthesis of 4,4′-methylene diphenyl diamine (4,4′-MDA), an important polyurethane intermediate, is the reaction of aniline and formaldehyde. Molecular understanding of the 4,4′-MDA formation can provide strategy to prevent from side reactions. In this work, a molecular mechanism consisted of eight consecutive, elementary reaction steps from anilines and formaldehyde to the formation of 4,4′-MDA in acidic media is proposed using accurate G3MP2B3 composite quantum chemical method. Then G3MP2B3-SMD results in aqueous and aniline solutions were compared to the gas phase mechanism. Based on the gas phase calculations standard enthalpy of formation, entropy and heat capacity values were evaluated using G3MP2B3 results for intermediates The proposed mechanism was critically evaluated and important side reactions are considered: the competition of formation of protonated p-aminobenzylaniline (PABAH+), protonated aminal (AMH+) and o-aminobenzylaniline (OABAH+). Competing reactions of the 4,4′-MDA formation is also thermodynamically analyzed such as the formation of 2,4-MDAH+, 3,4-MDAH+. AMH+ can be formed through loose transition state, but it becomes kinetic dead-end, while formation of significant amount of 2,4-MDA is plausible through low-lying transition state. The acid strength of the key intermediates such as N-methylenebenzeneanilium, PABAH+, 4-methylidenecyclohexa-2,5-diene-1-iminium, and AMH+ was estimated by relative pKa calculation.

Electron-Transfer-Induced Side-Chain Cleavage in Tryptophan Facilitated through Potassium-Induced Transition-State Stabilization in the Gas Phase

2021 ◽  
Author(s):  
Filipe Ferreira da Silva ◽  
Tiago Cunha ◽  
Andre Rebelo ◽  
Adrià Gil ◽  
Maria José Calhorda ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transition State ◽  
Gas Phase ◽  
Side Chain ◽  
Side Chain Cleavage ◽  
Transition State Stabilization ◽  
Chain Cleavage

New product from old reaction: uniform magnetite nanoparticles from iron-mediated synthesis of alkali iodides and their protection from leaching in acidic media

RSC Advances ◽  
2014 ◽  
Vol 4 (43) ◽  
pp. 22606-22612 ◽  
Author(s):  
R. P. Pogorilyi ◽  
I. V. Melnyk ◽  
Y. L. Zub ◽  
S. Carlson ◽  
G. Daniel ◽  
...  
Keyword(s):  
Magnetic Material ◽  
Magnetite Nanoparticles ◽  
Acid Leaching ◽  
New Product ◽  
Silica Coating ◽  
Acidic Media ◽  
Industrial Synthesis

Magnetic material stable to acid leaching was produced by silica coating of byproduct from the industrial synthesis of alkali iodides.

DFT calculations of the intermediate and transition state in the oxidation of NO by oxygen in the gas phase

2011 ◽  
Vol 47 (2) ◽  
pp. 93-100 ◽  
Author(s):  
I. I. Zakharov ◽  
B. F. Minaev
Keyword(s):  
Dft Calculations ◽  
Transition State ◽  
Gas Phase ◽  
Oxidation Of No

Catalytic routes to fuels from C1 and oxygenate molecules

2017 ◽  
Vol 197 ◽  
pp. 9-39 ◽  
Author(s):  
Shuai Wang ◽  
Iker Agirrezabal-Telleria ◽  
Aditya Bhan ◽  
Dante Simonetti ◽  
Kazuhiro Takanabe ◽  
...  
Keyword(s):  
Transition State ◽  
Active Sites ◽  
Aldol Condensation ◽  
Bond Formation ◽  
Transition States ◽  
Solid Acids ◽  
State Theory ◽  
Side Reactions ◽  
Oh Radicals ◽  
Acid Base

This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C1 and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C–C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C–C bond from C1 molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O2 and H2O molecules. These gaseous OH species act as strong H-abstractors and activate C–H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C–H bonds in larger alkane products than in CH4 reactants. Anhydrous carbonylation of dimethyl ether forms a single C–C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni2+ active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C–C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C1 homologation selectively forms C4 and C7 chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C–C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid–base site pairs on TiO2 and ZrO2 catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid–base pairs. Ketonization is mediated instead by C–C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H2 and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal–alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C–C bonds as skeletal isomers unattainable by other routes. Their respective transition states are of similar size, leading to selectivities that cannot sense the presence of a confining host. Prins condensation reactions benefit from weaker acid sites because their transition states are less charged than those for oligomerization and consequently less sensitive to conjugate anions that become less stable as acids weaken.

Charge development at the transition state: a second-order Moeller-Plesset perturbation study of gas-phase SN2 reactions

1991 ◽  
Vol 113 (4) ◽  
pp. 1072-1076 ◽  
Author(s):  
Zheng Shi ◽  
Russell J. Boyd
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Second Order ◽  
Sn2 Reactions

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. IV. o-Alkoxy-, Dialkylamino- and Alkylthio-1-phenylethylidenes

1979 ◽  
Vol 32 (1) ◽  
pp. 123 ◽  
Author(s):  
WD Crow ◽  
H McNab
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Side Chains ◽  
Ortho Position ◽  
No Formation ◽  
Carbene Insertion ◽  
Transition State Geometry

A series of 1-phenylethylidenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.30 mm. Carbene insertion to form five-membered heterocyclic rings predominates, with up to 20% Bamford-Stevens insertion, to give the styrenes; little or no formation of six-membered rings is observed. In cases where stereoselective insertion is possible, the trans-disubstituted heterocycle is formed preferentially, the selectivity being greatest in the case of dialkylamino substitution. The mechanisms involved are discussed in terms of transition state geometry.

A search for a gas-phase free-radical inversion displacement reaction at a saturated carbon atom

1983 ◽  
Vol 61 (5) ◽  
pp. 916-920 ◽  
Author(s):  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Side Reactions ◽  
Forward Reaction ◽  
Reaction Systems ◽  
Upper Limit ◽  
Upper Limits ◽  
Decomposition Of Methane ◽  
Simple Inversion ◽  
Saturated Carbon Atom

Five thermal and photochemical reaction systems have been examined in an attempt to detect or to place upper limits on the rates of the simple inversion reaction, CH3 + CH4 → C2H6 + H, and its reverse. No positive evidence was obtained for the occurrence of these reactions. An upper limit for the rate constant for the forward reaction of 0.063 M−1s−1 at 802 K was obtained from the thermal decomposition of methane, and upper limits of 0.044 and 0.14 at 823 and 983 K respectively were estimated from the thermal decomposition of ethane. Other systems examined were the thermal decomposition of azomethane in the presence of methane, and the mercury-photosensitized decompositions of methane and ethane, which were complicated by unexpected side reactions.

Computational Investigation of Selective MOVPE of AlxGa1-xAs in Presence of Hcl

2001 ◽  
Vol 701 ◽  
Author(s):  
Maria Nemirovskaya ◽  
Carlo Cavallotti ◽  
Klavs Jensen
Keyword(s):  
Fluid Dynamics ◽  
Monte Carlo ◽  
Transition State ◽  
Gas Phase ◽  
Kinetic Monte Carlo ◽  
Monte Carlo Model ◽  
Operating Conditions ◽  
Morphology Evolution ◽  
Computational Investigation ◽  
Dynamics Simulations

ABSTRACTThe deposition of AlGaAs in the presence of HCl was investigated at the macroscopic and mesoscopic scales. Fluid dynamics simulations were first performed in order to study the dependence of the deposition rate on the operating conditions. Unknown gas phase and surface kinetic parameters were estimated by quantum chemistry and transition state computations. The fluxes of all species to the surface were thus computed and provided the input to a kinetic Monte Carlo model used to investigate the morphology evolution of the film.

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