scholarly journals Theoretical insight on the treatment of β-hexachlorocyclohexane waste through alkaline dehydrochlorination

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alicia Bescós ◽  
Clara I. Herrerías ◽  
Zoel Hormigón ◽  
José Antonio Mayoral ◽  
Luis Salvatella
Keyword(s):  
Density Functional ◽  
Kinetic Studies ◽  
Alkaline Treatment ◽  
Functional Study ◽  
Reaction Intermediates ◽  
Preferential Formation ◽  
Reaction Intermediate ◽  
Rate Determining Step ◽  
Dehydrochlorination Reaction ◽  
Theoretical Results

AbstractThe occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the β-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1,2,4-trichlorobenzene in the β-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1,3,5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of β-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1,2,4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the β-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates).

scholarly journals Understanding the reaction mechanism of the regioselective piperidinolysis of aryl 1-(2,4-dinitronaphthyl) ethers in DMSO: Kinetic and DFT studies

2021 ◽  
Vol 46 ◽  
pp. 146867832110274
Author(s):  
Yasmen M Moghazy ◽  
Nagwa MM Hamada ◽  
Magda F Fathalla ◽  
Yasser R Elmarassi ◽  
Ezzat A Hamed ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Density Functional ◽  
Function Analysis ◽  
Density Functional Theory Method ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Nucleophilic Attack ◽  
Common Mechanism ◽  
Slow Step ◽  
Rate Determining Step

Reactions of aryl 1-(2,4-dinitronaphthyl) ethers with piperidine in dimethyl sulfoxide at 25oC resulted in substitution of the aryloxy group at the ipso carbon atom. The reaction was measured spectrophotochemically and the kinetic studies suggested that the titled reaction is accurately third order. The mechanism is began by fast nucleophilic attack of piperidine on C1 to form zwitterion intermediate (I) followed by deprotonation of zwitterion intermediate (I) to the Meisenheimer ion (II) in a slow step, that is, SB catalysis. The regular variation of activation parameters suggested that the reaction proceeded through a common mechanism. The Hammett equation using reaction constant σo values and Brønsted coefficient value showed that the reaction is poorly dependent on aryloxy substituent and the reaction was significantly associative and Meisenheimer intermediate-like. The mechanism of piperidinolysis has been theoretically investigated using density functional theory method using B3LYP/6-311G(d,p) computational level. The combination between experimental and computational studies predicts what mechanism is followed either through uncatalyzed or catalyzed reaction pathways, that is, SB and SB-GA. The global parameters of the reactants, the proposed activated complexes, and the local Fukui function analysis explained that C1 carbon atom is the most electrophilic center of ether. Also, kinetics and theoretical calculation of activation energies indicated that the mechanism of the piperidinolysis passed through a two-step mechanism and the proton transfer process was the rate determining step.

scholarly journals Density Functional Study on Formic Acid Decomposition On Pd(111) Surface: A Revisit and Comparison with Other Density Functional Methods

2021 ◽  
Author(s):  
Ni Wang ◽  
Kai Li ◽  
Ying Wang ◽  
Zhijian Wu
Keyword(s):  
Formic Acid ◽  
Computational Methods ◽  
Density Functional ◽  
Bond Cleavage ◽  
Great Influence ◽  
Functional Study ◽  
Acid Decomposition ◽  
Rate Determining Step ◽  
Functional Methods ◽  
Formic Acid Decomposition

Abstract The mechanism of formic acid decomposition on Pd(111) surface has been investigated by several theoretical methods in previous studies, including PBE and PW91. These results indicated that the mechanism is different from different methods, and even by using the same method (i.e., PBE), the mechanism is also different. In this study, we have revisited the formic acid decomposition on Pd(111) surface by using another density functional RPBE and by including van der Waals interaction which is neglected in the previous studies. Our results showed that the formic acid is decomposed via O-H bond cleavage to form bi-HCOO*, and the most favorable pathway is HCOOH* → bi-HCOO*+H* → CO2+2H*. The energy barrier is 0.55 eV at the rate-determining step. This conclusion is consistent with one of the PBE study. This demonstrated that computational methods have great influence on the reaction mechanism, and care should be taken in selecting the appropriate computational methods.

Experimental and theoretical study of monoligand complexes of nickel atoms with simple alkynes

1994 ◽  
Vol 72 (3) ◽  
pp. 587-599 ◽  
Author(s):  
S.A. Mitchell ◽  
M.A. Blitz ◽  
R. Fournier
Keyword(s):  
Binding Energy ◽  
Ground State ◽  
Density Functional ◽  
Kinetic Studies ◽  
Binding Energies ◽  
Rate Coefficients ◽  
Similar Data ◽  
Association Reaction ◽  
Reaction Theory ◽  
Theoretical Results

Monoligand complexes of nickel atoms with simple alkynes have been investigated by kinetic studies of association reactions of nickel atoms with ethyne, propyne, and 2-butyne in the gas phase near room temperature, and by quantum chemical calculations on the Ni[C2H2] complex using a Linear Combination of Gaussian-Type Orbitals – Density Functional (LCGTO–DF) method. Experimental estimates of binding energies of the monoligand complexes have been made by using RRKM unimolecular reaction theory to model the pressure dependence of second-order rate coefficients for the association reactions: [Formula: see text] and 29 ± 5 kcal mol−1, for Ni[C2H2], Ni[propyne], and Ni[2-butyne], respectively. The trend in binding energy with methyl substitution on ethyne is discussed and compared with similar data for monoligand complexes of alkynes with copper atoms. The harmonic vibrational frequencies and binding energy for the 1A1 ground state of Ni[C2H2] have been calculated using the LCGTO–DF method, and the results are compared with experimental data on the infrared spectrum of matrix-isolated Ni[C2H2] and with the estimate of the binding energy of Ni[C2H2] from the present experimental study. There is excellent agreement between the experimental and theoretical results. The calculations indicate that at least one triplet state of Ni[C2H2] is bound relative to ground state Ni + C2H2 reactants. This is consistent with indications from the kinetic results that the association reaction occurs on more than one potential energy surface.

A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

2003 ◽  
Vol 68 (12) ◽  
pp. 2322-2334 ◽  
Author(s):  
Robert Vianello ◽  
Zvonimir B. Maksić
Keyword(s):  
Ab Initio ◽  
Spin Density ◽  
Density Functional ◽  
Radical Cations ◽  
Functional Study ◽  
Theory Approach ◽  
Functional Theory ◽  
Adiabatic Ionization Potential ◽  
Highest Occupied Molecular Orbital ◽  
Positively Charged

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.

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