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1.
The thermal decomposition of cyclopentyl cyanide has been investigated in the temperature range of 905–1143 K using both conventional stirred-flow reactor and very low-pressure pyrolysis (VLPP) techniques. The results from both techniques are consistent. The main primary processes are HCN elimination to form cyclopentene: and ring fragmentation to form vinyl cyanide plus propylene and ethylene plus cyanopropenes: Under the experimental conditions cyclopentene undergoes further decomposition to cyclopentadiene plus hydrogen. There is evidence for conversion of some of the reactant to a solid residue, presumably polymer. From the stirred-flow reactor results the following Arrhenius expressions were obtained: log k1(s?1) = (12.8 ± 0.3) ? (65.6 ± 1.3)/θ and log k2(s?1) = (16.0 ± 0.3) ? (80.0 ± 1.1)/θ, where θ = 2.303RT kcal/mol. Application of RRKM theory shows that the VLPP experimental rate constants are consistent with high-pressure Arrhenius parameters given by log k1(s?1) = (12.8 ± 0.3) ? (67.8 ± 2.5)/θ for HCN elimination, and log k4(s?1) = (16.3 ± 0.3) ? (80.1 ± 2.0)/θ for the sum of the ring fragmentation pathways. The rate parameters for HCN elimination are in good agreement with previous VLPP studies of alkyl cyanides and with theoretical predictions. The difference in activation energies for the ring opening of cyclopentane and cyclopentyl cyanide is reasonably close to the established value for the cyano stabilization energy. This supports the assumption of a biradical mechanism. 相似文献
2.
The kinetics of gas-phase decomposition of methyl isocyanate have been investigated in the range of 427–548°C. Two decomposition routes are followed; the predominant one is a radical-chain process giving CO, H2, and HCN as major products, which has an order of 1.5 and an Arrhenius equation given by log k(L1/2/mol1/2·s) = (13.12 ± 0.06) ? (56,450 ± 1670) cal/mol/2.303 RT. The minor route is the bimolecular formation of N,N′-dimethylcarbodiimide and CO2, which from the low activation parameters Ea = 31.6 kcal, A = 105.30 L1/2/mol1/2·s, and the reaction order of 1.57 appears to be heterogeneous. 相似文献
3.
On the basis of an elaborate investigation of the thermal decomposition reaction for crystalline copper hypophosphite by kinetic, radiospectroscopic and optical methods, and by a study of the peculiarities of the copper hypophosphite structure and defects, it has been found possible to suggest the mechanisms by which the decomposition kinetics are regulated. 相似文献
4.
Ž. D. Živković 《Journal of Thermal Analysis and Calorimetry》1979,16(1):3-11
Results are given on the kinetics and mechanism of the processes in the thermal decomposition of lead carbonate with the application of TG and DTA experimental investigation methods.The following mechanism was established: 3 PbCO3=2 PbO.PbCO3+2 CO2 (1) 2 PbO.PbCO3=3 PbO+CO2 (2) PbO — melting (3)The following activation energy values were determined with TG methods for processes (1) and (2): 118.2 and 235.2 kJ/mole, respectively; and with DTA methods for processes (1), (2) and (3): 113.9, 246.6 and 294.9 kJ/mole, respectively.
Zusammenfassung Die an Hand der TG- und DTA-Untersuchungen erhaltenen Ergebnisse über Kinetik und Mechanismus der bei der thermischen Zersetzung von Bleicarbonat auftretenden VorgÄnge werden beschrieben.Die folgenden Mechanismen des Vorganges wurden festgestellt: 3 PbCO3=2 PbO.PbCO3 + 2 CO2 (1) 2 PbO.PbCO3=3 PbO + CO2 (2) PbO — Schmelzen (3)Die folgenden Werte der Aktivierungsenergie wurden durch TG-Versuche für die VorgÄnge (1) und (2) bestimmt: 118.2, bzw. 235.2 kJ/Mol, und durch DTA-Messungen für die VorgÄnge (1), (2) und (3): 113.9, 246.6, bzw. 294.9 kJ/Mol.
Résumé La cinétique et le mécanisme des réactions qui se déroulent lors de la décomposition thermique du carbonate de plomb ont été étudiés par TG et ATD. Les mécanismes suivants ont été établis: 3 PbCO3=2 PbO.PbCO3+2 CO2 (1) 2 PbO.PbCO3=3 PbO + CO2 (2) PbO — fusion (3)Pour les réactions (1) et (2), les valeurs de 118.2 et 235.2 kJ · mol–1 ont été trouvées à partir des résultats TG et pour les réactions (1), (2) et (3) l'ATD a fourni respectivement 113.9, 246.6 et 294.9 kJ · mol–1.
, . : 3 3=2 PbO.PbCO3+2 2 (1) 2 PbO.PbCO3=3 +O2 (2) — (3) (1) (2), 118.2 235.2 /. (1), (2) (3) : 113.9; 246.6 294.9 /.相似文献
5.
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
6.
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
7.
V. V. Dubikhin V. G. Prokudin L. D. Nazina L. B. Romanova L. T. Eremenko G. M. Nazin 《Kinetics and Catalysis》2007,48(3):345-347
The thermal decomposition kinetics of 1-bromo-4-nitroxymethylcubane in the liquid phase is typical of C-ONO2 bond heterolysis, which occurs if the nitro ester has a strong donor substituent. A comparison between 1-bromo-4-nitroxymethylcubane and tert-butyl nitrate shows that bromocubyl is close to the tert-butyl group in induction properties and cubyl itself is a stronger donor than this group. 相似文献
8.
9.
K. N. Ninan K. Krishnan V. N. Krishnamurthy 《Journal of Thermal Analysis and Calorimetry》1991,37(7):1533-1543
Thermogravimetric studies on two varieties of calcium carbonate viz., analytical reagentgrade and insitu generated from calcium oxalate monohydrate, were carried out. The kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using integral methods and the effect of procedural factors such as heating rate, sample mass and method of computation on them were also studied. The procedural variables in the range studied had no marked influence on the results; however the kinetic parameters were marginally higher for the insitu generated calcium carbonate. This trend is explained by the presence of more micropores in the insitu generated calcium carbonate as well as the mechanism of its decomposition following phase boundary reaction with cylindrical symmetry.
Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60th birthday
We thank Director, VSSC for the kind permission to publish this work. Thanks are due to Mr. A. Natarajan for the support in SEM studies. 相似文献
Zusammenfassung An zwei verschiedenen Arten von Calciumcarbonat (analytisch rein bzw. in situ hergestellt aus Calciumoxalatmonohydrat) wurden thermogravimetrische Untersuchungen durchgeführt. Die Kinetik und der Mechanismus der thermischen Feststoffzersetzungsreaktionen wurde unter Anwendung integrativer Verfahren aus TG-Daten ermittelt. Auch der Einfluß experimenteller Bedingungen, wie z.B. von Aufheizgeschwindigkeit, Probenmasse und Rechenmethode wurden untersucht. Die experimentellen Bedingungen haben im untersuchten Intervall keinen sichtlichen Einfluß auf die Ergebnisse; in jedem Falle hatten die kinetischen Parameter für in situ hergestelltes Calciumcarbonat wesentlich höhere Werte. Dies wird durch die Anwesenheit von wesentlich mehr Mikroporen in dem in situ hergestellten Calciumcarbonat erklärt. Der Reaktionsmechanismus der Zersetzung wird mittels Phasengrenzreaktionen mit zylindrischer Symmetrie erklärt.
Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60th birthday
We thank Director, VSSC for the kind permission to publish this work. Thanks are due to Mr. A. Natarajan for the support in SEM studies. 相似文献
10.
Jan Nisar Mukhtiar Ali Iftikhar Ahmad Awan 《Reaction Kinetics and Catalysis Letters》2008,95(2):399-406
The kinetics of the gas-phase thermal decomposition of cis-2-methylcyclopropane methanol was studied in the temperature range
of 483–597 K and pressures between 5–24 Torr in aged Pyrex reactions vessels. Cis-2-methylcyclopropane methanol underwent
first order, reversible geometric isomerization in competition with structural isomerization. The structural isomerization
products were identified as 2-peten-1-ol and a mixture of cis and trans-2-methyl-buten-1-ol. Arrhenius parameters were determined
for homogeneous, unimolecular formation of the isomeric products and for the overall loss of reaction. The formation of isomeric
products and the observed Arrhenius parameters are consistent with a biradical mechanism. For the overall reaction, Ea = 173.8 ± 15.5 (kJ/mol) and log10 (A, s−1) = 13.3 ± 1.5. These values are in good agreement with previously reported values for similar studies of 1,2, disubstituted
cyclopropanes. 相似文献
11.
A. I. Kazakov O. G. Ivanova L. S. Kurochkina N. A. Plishkin 《Russian Journal of Applied Chemistry》2011,84(9):1516-1523
Fundamental kinetic aspects of the decomposition of mixtures and double salts of ammonium nitrate and ammonium sulfate were
studied. The effect of water and sulfuric acid additives on the thermal decomposition rate of ammonium nitrate and sulfate
mixtures was examined. The constant of proton exchange between nitric acid and the sulfate anion in molten ammonium nitrate
was estimated. 相似文献
12.
The homogeneous gas-phase decomposition kinetics of silane has been investigated using the single-pulse shock tube comparative rate technique (T = 1035–1184?K, Ptotal ≈? 4000 Torr). The initial reaction of the decomposition SiH4 \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document} SiH2 + H2 is a unimolecular process in its pressure fall-off regime with experimental Arrhenius parameters of logk1 (sec?1) = 13.33 ± 0.28–52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM-pressure fall-off calculations for four different transition-state models are reported, and good agreement with all the data is obtained with a model whose high-pressure parameters are logA1 (sec?1) = 15.5, E1(∞) = 56.9 kcal, and ΔE0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH2 → (Si2H4)* → (SiH3SiH)* → Si2H2 + H2. The mechanism of H ? D exchange absorbed in the pyrolysis of SiD4-hydrocarbon systems is also discussed. 相似文献
13.
The homogeneous gas-phase thermal decomposition kinetics of germane have been measured in a single-pulse shock tube between 950 and 1060 K at pressures around 4000 torr. The initial decomposition is GeH4 → GeH2 + H2 in its pressure-dependent regime, with log k = 13.83 ± 0.78 – 50,750 ± 3570 cal/2.303RT. RRKM calculations suggest that the high-pressure Arrhenius parameters are log k GeH4(M → ∞) = 15.5 – 54,300 cal/2.303RT. Extrapolations to static system pyrolysis conditions (T ~ 600 K, P ~ 200 torr) give homogeneous reaction rates which are much slower than those observed, hence the static system pyrolysis of germane must be predominantly heterogeneous. Shock-initiated pyrolysis reaction stoichiometry is 2 mol H2 per mole GeH4, suggesting that the subsequent decomposition of germylene is essentially quantitative. Investigations of the hydrogen product yields for pyrolysis of GeD4 in øCH3 further indicate that the germylene decomposition reaction is mainly GeH2 → H2 + Ge, but that a small amount of reaction to H atoms may also occur. 相似文献
14.
The decomposition kinetics of ethylsilane under shock tube conditions (PT ca. 3100 torr, T ? 1080–1245 K), both in the absence and presence of silylene trapping agents (butadiene and acetylene) are reported. Arrhenius parameters under maximum butadiene inhibition are: log k(C2H5SiH3) = 15.14-64,769 ± 1433 cal/2.303 RT; log k(C2H5SiD3) = 15.29-66,206 ± 1414/2.303 RT. The uninhibited reaction is subject to silylene induced decomposition (63% lowest T -- 24% highest T). Major reaction products are ethylene and hydrogen, consistent with two dominant primary dissociation reactions: C2H5SiD3 → C2H5SiD + D2, ? ? 0.66; C2H5SiD3 → CH3CH = SiD2 + HD, ? ? 0.30. Minor products suggest several other less important primary processes: alkane elimination, ? ?0.02, and free-radical production via simple bond fission, ? ?0.02. An upper limit for the activation energy of the decomposition, C2H5SiH → C2H4 + SiH2, of E < 30 ± 4 kcal is established, and speculations on the mechanism of this decomposition (concerted or stepwise) with conclusions in favor of the stepwise path are made. Computer modeling studies for the reaction both in the absence and presence of butadiene are shown to be in good agreement with the experimental observations. 相似文献
15.
16.
A. I. Kazakov Yu. I. Rubtsov L. P. Andrienko G. B. Manelis 《Russian Chemical Bulletin》1998,47(3):379-385
The kinetic regularities of the heat release during the thermal decomposition of liquid NH4N(NO2)2 at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water
on the rate of decomposition of NH4N(NO2)2 show that the contributions of the decomposition of N(NO2)2
− and HN(NO2)2 to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition
has an autocatalytic character. The analysis of the effect of additives of HNO3 solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration
is due to an increase in the acidity of the NH4N(NO2)2 melt owing to the accumulation of HNO3 and the corresponding increase in the contribution of the HN(NO2)2 decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO3
− ions decreasing the equilibrium concentration of HN(NO2)2 in the melt.
For Part 2, see Ref. 1.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998. 相似文献
17.
《Ceramurgia International》1980,6(2):61-66
The kinetics of the solid state high-temperature transformation of kyanite (Al2SiO5Al2O3·SiO2) powders (≤40 μm) to 3:2-mullite (3Al2O3·2SiO2) and silica (SiO2 were investigated by means of quantitative X-ray diffraction techniques. The transformation interval was found to lie between about 1150 and 1350°C. The reaction law best fitting the kinetic data is: 1-α = kta. The transformation is believed to be reconstructive, with decomposition of the kyanite structure, solid-state atom diffusion, and (epitactic) rearrangement of mullite and cristobalite. Cristobalite represents part of the ⪡free⪢ silica, the rest being present as a glassy phase. Addition of Fe2O3 and TiO2 to the starting material exerts a marked decrease of the transformation temperature, with TiO2 having a somewhat stronger influence than Fe2O3. The reason may be an oxide-catalyzed reaction; the decomposition begins at nuclei formed at the surfaces of the kyanite particles, which are coated with thin layers of hematite and rutile respectively. 相似文献
18.
A. I. Kazakov Yu. I. Rubtsov G. B. Manelis L. P. Andrienko 《Russian Chemical Bulletin》1998,47(1):39-45
The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO3, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide
in aqueous HNO3 is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N4O6) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the
decomposition rates of dinitramide in solutions of HNO3 as compared to those in solutions in H2SO4 and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition
rate of nondissociated dinitramide compared to the decomposition rate of the N(NO2)2
− anion is explained by a decrease in the order of the N−NO2 bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding
value for neutral molecules is due to the dehydration mechanism of the reaction.
For Part 1, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–47, January, 1998. 相似文献
19.
R. S. Stepanov L. A. Kruglyakova A. M. Astakhov O. A. Golubtsova 《Russian Journal of General Chemistry》2004,74(10):1579-1582
Thermal decomposition of 2-substituted 5,5-dinitro-1,3-dioxanes in melt and in solution follows a homolytic mechanism with initial dissociation of the C-N bond. The reaction in solution is accompanied by oxidation of the initial compound with nitrogen dioxide formed as a result of decomposition. The rate of decomposition weakly depends on the substituent in position 2 of the heteroring. On the whole, the C(NO2)2 moiety in 1,3-dioxanes is less stable than in alkanes due to conformational features of the heteroring.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1702–1705.Original Russian Text Copyright © 2004 by Stepanov, Kruglyakova, Astakhov, Golubtsova.This revised version was published online in April 2005 with a corrected cover date. 相似文献