Kinetics and mechanism of the thermal decomposition of cyclopentyl cyanide

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.     

Kinetics and mechanism of the thermal decomposition of methyl isocyanate

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(L^1/2/mol^1/2·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 E_a = 31.6 kcal, A = 10^5.30 L^1/2/mol^1/2·s, and the reaction order of 1.57 appears to be heterogeneous.     

Kinetics and mechanism of thermal decomposition of copper hypophosphite

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.     

Kinetics and mechanism of thermal decomposition of lead carbonate

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.

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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.

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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.

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, . : 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 /.

     

Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate

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.     

Kinetics and mechanism of the thermal decomposition of barium titanyl oxalate

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 60^th birthday of Dr. Andrew K. Galwey     

Kinetics and mechanism of the thermal decomposition of 1-bromo-4-nitroxymethylcubane

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.     

Kinetics and mechanism of thermal decomposition of insitu generated calcium carbonate

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.

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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.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday

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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.     

Kinetics and mechanism of the gas-phase thermal decomposition of cis-2-methylcyclopropane methanol

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, E_a = 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.     

Kinetics and mechanism of thermal decomposition of ammonium nitrate and sulfate mixtures

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.     

Kinetics and mechanism of the silane decomposition

The homogeneous gas-phase decomposition kinetics of silane has been investigated using the single-pulse shock tube comparative rate technique (T = 1035–1184?K, P_total ≈? 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, E_1(∞) = 56.9 kcal, and ΔE^0±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.     

Kinetics and mechanism of the germane decomposition

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.     

The kinetics and mechanism of the shock induced gas phase decomposition of ethylsilane

The decomposition kinetics of ethylsilane under shock tube conditions (P_T 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.     

Kinetics of the thermal decomposition of dinitramide

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.     

Kinetics of the thermal decomposition of kyanite

The kinetics of the solid state high-temperature transformation of kyanite (Al₂SiO₅Al₂O₃·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 = kt^a. 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.     

Kinetics of the thermal decomposition of dinitramide

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.     

Kinetics and mechanism of thermal decomposition of 2-substituted 5,5-dinitro-1,3-dioxanes

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.