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1.
Edgar Marquez Tania Cordova Gabriel Chuchani 《International journal of quantum chemistry》2012,112(3):724-730
The mechanism of the gas‐phase elimination kinetics of 2‐ethoxypyridine has been studied through the electronic structure calculations using density functional methods: B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), B3PW91/6‐31G(d,p), B3PW91/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p), PBEPBE/6‐31G(d,p), PBEPBE/6‐31++G(d,p), PBE1PBE1/6‐31G(d,p), and PBE1PBE1/6‐31++G(d,p). The elimination reaction of 2‐ethoxypyridine occurs through a six‐centered transition state geometry involving the pyridine nitrogen, the substituted carbon of the aromatic ring, the ethoxy oxygen, two carbons of the ethoxy group, and a hydrogen atom, which migrates from the ethoxy group to the nitrogen to give 2‐pyridone and ethylene. The reaction mechanism appears to occur with the participation of π‐electrons, similar to alkyl vinyl ether elimination reaction, with simultaneous ethylene formation and hydrogen migration to the pyridine nitrogen producing 2‐pyridone. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
2.
Elisey Mazilov Evgeniya Ogurtsova Alexander Shamov Grigorii Khrapkovskii 《International journal of quantum chemistry》2010,110(4):939-945
Using nonempirical methods and DFT‐methods the geometrical parameters formation enthalpies of molecules and radicals, energies dissociation of N? NO2 bonds of primary and secondary N‐nitramines have been investigated. The basic tendencies in the changes of the geometrical and electronic structures, formation enthalpies, and dissociation energies have been analyzed in basic homologous series of nitramines. Various alternative mechanisms of the gas‐phase monomolecular thermal decomposition have been studied by of the example of N‐methylnitramine. The process of the aci‐form formation and its further multistage destruction is the most advantageous way of decomposition of the primary N‐nitramines. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
3.
Dana Bogdan J. P. Aycard Mohamed Hnach Elena Volanschi Mihaela Hillebrand V. Badescu N. Dragoe E. Segal 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1729-1740
The thermal behaviour of some compounds derived from 5-phenylfuran-2,3-dione was studied. The thermoanalytical data relating to the decomposition steps and intermediates were completed with mass spectrometric analysis and infrared spectroscopy results. For some of the investigated reactions, the kinetic and structural data correlated satisfactorily. 相似文献
4.
Oriana Brea Marcos Loroño Edgar Marquez Jose R. Mora Tania Cordova Gabriel Chuchani 《International journal of quantum chemistry》2012,112(12):2504-2514
The unimolecular gas‐phase elimination kinetics of 2‐methoxy‐1‐chloroethane, 3‐methoxy‐1‐chloropropane, and 4‐methoxyl‐1‐chloroburane has been studied by using density functional theory (DFT) methods to propose the most reasonable mechanisms of decomposition of the aforementioned compounds. Calculation results of 2‐methoxy‐1‐chloroethane and 3‐methoxy‐1‐chloropropane suggest dehydrochlorination through a concerted nonsynchronous four‐centered cyclic transition state (TS) to give the corresponding olefin. In the case of 4‐methoxyl‐1‐chloroburane, in addition to the 1,2‐elimination mechanism, the anchimeric assistance by the methoxy group, through a polar five‐centered cyclic TS, provides additional pathways to give 4‐methoxy‐butene, tetrahydrofuran and chloromethane. The bond polarization of the C? Cl, in the direction of Cδ+ ··· Clδ?, is the limiting step of these elimination reactions. The significant increase in rate together with the formation of a cyclic product tetrahydrofuran in the gas‐phase elimination of 4‐methoxyl‐1‐chloroburane is attributed to neighboring group participation of the oxygen of the methoxy group in the TS. The theoretical calculations show a good agreement with the reported experimental results. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
5.
By means of TG, the thermal decomposition of the powdered CaCO3 was tested with its various dispersities, range of size, and the different content of CO2 in flowing nitrogen. Formulae for calculating the rate and time of decomposition were obtained. 相似文献
6.
Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition
process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements.
A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation
and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous
hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition
processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were
estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic
analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate
the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for
the decarbonation process. 相似文献
7.
《中国科学B辑(英文版)》2008,(11)
N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by 1H-NMR, Fourier transform in-frared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The ki-netic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1-α) 1/3-1]-1, 203.75 kJ-mol-1 and 1017.95s-1, respec-tively. The values of ΔS≠, ΔH≠ andΔG≠ of the reaction are 94.28 J-mol-1-K-1, 203.75 kJ-mol-1 and 155.75 kJ-mol-1, respectively. 相似文献
8.
氢氧化镁分解动力学的研究 总被引:1,自引:0,他引:1
以硼泥为原料与硫酸反应制备出七水硫酸镁,以氢氧化钠为沉淀剂制备出符合标准HG/T 3607-2000的氢氧化镁.利用XRD,SEM和TEM对氢氧化镁进行了表征,DTA-TG对氢氧化镁的热分解动力学进行了研究.XRD结果表明:制备粉体为单一Mg(OH)2.SEM和TEM结果表明:样品为片状或针状纤维,片直径大小不一,在20~50 nm之间,针状纤维形状不规则,大小不一致,长度在20~100 nm之间.利用Kissinger法和Ozawa法计算出的氢氧化镁热分解反应活化能分别为135.14和141.61 kJ·mol-1.利用Coats-Redfern法和Dolye法判断氢氧化镁热分解反应机理函数为A1.5. 相似文献
9.
J. Straszko J. Możejko M. Olszak-Humienik 《Journal of Thermal Analysis and Calorimetry》1995,45(5):1109-1116
The paper describes the kinetics of all the recorded steps of thermal decomposition of nickel sulfate hexahydrate in air. The thermal decomposition of the salt in air led to NiO at about 1060 K. The kinetic parameters, the activation energyE and the preexponential factorA, and the thermodynamic parameters, the entropy, enthalpy and free energy of activation were evaluated for the dehydration and decomposition reactions. Tentative reaction mechanisms are suggested for each step of the thermal decomposition. 相似文献
10.
11.
The reaction pathway of the thermal decomposition of synthetic brochantite, Cu4(OH)6SO4, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu4O(OH)4SO4. The dehydrated sample, Cu4O3SO4, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO4 at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO3, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom. 相似文献
12.
The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO3 formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N2O3 and NH3OH+, whereas the subsequent acceleration is due to oxidation of NH3OH+ by nitrogen oxides formed as well as by nitrous acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1897–1901, November, 1993. 相似文献
13.
Thermal analysis of barium titanyl oxalate reveals that the decomposition proceeds through four distinct rate processes. Among
them, the decomposition of oxalate occurs in the temperature range 230–350°C, and has been studied by TG and gas pressure
measurements, supplemented by IR spectroscopy, electron microscopy and chemical analysis. Oxalate decomposition proceeds differently
in vacuum and in flowing gas atmospheres. Analytical results indicate the formation of a complex carbonate together with CO,
CO2 and water vapour below 400°C. Schemes for each type of decomposition are proposed and discussed. For decomposition in vacuum,
kinetic observations fitted the three-dimensional, diffusion controlled, rate equation for almost the entire α-range (0.028≤α≤0.92).
The activation energy is calculated to be3 189±6 kJ mol−1.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献
14.
《International journal of quantum chemistry》2018,118(11)
The 1,3‐dipolar cycloaddition (13DC) reactions of nitrile‐oxide NO 1 with two ethylenes, enamine 2a and enamine 2b , were computationally studied using B3LYP/6‐31G(d) DFT methods. The two possible ortho and meta regioselective channels were characterized and analyzed. The moderate polarity of these 13DC reactions is related to the high nucleophilic character of both ethylenes, and the moderate electrophilic nature of the NO 1 , that accounts for the relatively low calculated activation energies. Analysis of different forms of energies along the different reaction channels indicates that the present 13DC reactions are completely ortho regioselective, accordingly to the experimental outcomes. Electron localization function analysis indicates that these 13DC reactions proceed via a nonconcerted (two‐stage) one‐step mechanism. 相似文献
15.
A. I. Kazakov Yu. I. Rubtsov G. B. Manelis L. P. Andrienko 《Russian Chemical Bulletin》1997,46(12):2015-2020
Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide
temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition
of different forms of dinitramide as the acidity of the medium increases: first, N(NO2)− anions, then HN(NO2)2 molecules, and finally, protonated H2N(NO2)2
+ cations. The temperature dependences of the rate constants of the decomposition of N(NO2)− (k
an) and HN(NO2)2 (k′ac) and the equilibrium constant of dissociation of HN(NO2)2 (K
a) were determined:k
an=1.7·1017 exp(−20.5·103/T), s−1,k′ac=7.9·1016 exp(−16.1·103/T), s−1, andK
a=1.4·10 exp(−2.6·103/T). The temperature dependences of the decomposition rate constant of H2N(NO2)2
+ (k
d) and the equilibrium constant of the dissociation of H2N(NO2)2
+ (K
d) were estimated:k
d=1012 exp(−7.9·103/T), s−1 andK
d=1.1 exp(6.4·103/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions
in a wide range of temperatures and acidities of the medium.
In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978
and not published previously.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997. 相似文献
16.
R. N. Zaripov R. L. Safiullin E. I. Yaubasarova A. A. Mukhametzyanova V. D. Komissarov 《Russian Chemical Bulletin》1997,46(5):895-897
The kinetics of the decomposition of acetylcyclohexylsulfonyl peroxide (ACSP) in CCl4, benzene, toluene, ethylbenzene, cumene, acetonitrile, ethanol, and 2-propanol in an atmosphere of O2 were studied at 40–70 °C. The rate constants (k
0) and activation parameters of the monomolecular decomposition of ACSP were determined. A linear dependence between logA
0 and activation energyE
0 (compensation effect) was established. The dependence ofk
0 on the nature of a solvent is described by the four-parameter Koppel-Palm equation.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 935–937, May 1997. 相似文献
17.
The kinetics of induced decomposition of potassium peroxomonosulphate (PMS) by the phase transfer catalysts (PTC), viz. tetrabutylammonium
chloride [TBAC] and tetrabutylphosphonium chloride [TBPC] have been investigated. The effect of [PMS], [PTC], ionic strength
of the medium and temperature on the rate of decomposition of PMS was studied. The rate of decomposition of PMS was monitored
under pseudo-first-order condition at a constant temperature (50 ± 0.1 °C). The rate of decomposition was first order with
respect to PMS for TBAC and half order for TBPC. The order with respect of PTC was found to be unity for TBAC and half order
for TBPC. A suitable kinetic scheme has been proposed to account for the experimental data and its significance is discussed. 相似文献
18.
Density functional theory has been used to study the mechanism of the decomposition of peroxyacetyl nitrate (CH3C(O)OONO2) in hydrogen fluoride clusters containing one to three hydrogen fluoride molecules at the B3LYP/6‐311++G(d,p) and B3LYP/6‐311+G(3df,3pd) levels. The calculations clarify some of the uncertainties in the mechanism of PAN decomposition in the gas phase. The energy barrier decreases from 30.5 kcal mol?1 (single hydrogen fluoride) to essentially 18.5 kcal mol?1 when catalyzed by three hydrogen fluoride molecules. As the size of the hydrogen fluoride cluster is increased, PAN shows increasing ionization along the O? N bond, consistent with the proposed predissociation in which the electrophilicity of the nitrogen atom is enhanced. This reaction is found to proceed through an attack of a fluorine to the PAN nitrogen in concert with a proton transfer to a PAN oxygen. On the basis of our calculations, an alternative reaction mechanism for the decomposition of PAN is proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
19.
研究了过氧化苯甲酸叔丁酯的热分解动力学及不同包装规格下的自加速分解温度(SADT),利用C600微量热仪测试了过氧化苯甲酸叔丁酯的热分解特征,得到升温速率分别为0.1 K/min、0.2 K/min、0.5 K/min、1 K/min下热流随时间的变化曲线,并使用Friedman等转化率法对所得的实验数据进行分析处理,得到了过氧化苯甲酸叔丁酯的分解反应活化能、指前因子等热动力学参数,推算了不同包装规格的过氧化苯甲酸叔丁酯的SADT。结果表明TBPB分解活化能及指前因子随转化率变化而变化,活化能范围为42-135.5 kJ/mol,指前因子范围为0.25-33.5,在25L聚乙烯桶包装下的SADT为59℃,50L下为52℃,200L下为46℃。 相似文献
20.
F. A. López M. C. Ramirez J. A. Pons A. López-Delgado F. J. Alguacil 《Journal of Thermal Analysis and Calorimetry》2008,94(2):517-522
This study presents an evaluation of the decomposition kinetic of low-grade nickeliferous laterite by thermogravimetric analysis.
Kinetic parameters were calculated using the Ozawa and the iso-conversional Friedman methods. Simplified kinetics models like
those based on the reaction order were also applied for the simulations. Two-dimensional shrinkage models of the reaction
interface mechanism were adopted as describing the thermal transformation process from non-isothermal kinetic analysis. The
iso-conversional method (model-free kinetics) reveals that the decomposition of low-grade nickeliferous laterite does not
follow a single mechanism because the determined activation energies and pre-exponential factor are not constant during the
course of the reaction. 相似文献