On the non-isothermal determination of activation energy for thermal decomposition reactions

Attention is called to the frequently encountered linear sector in the isothermal course of the topochemical processes which is used in the kinetic treatment of the differential curves of thermal CoOOH decomposition. The effect of sample weight and heating rate on the values of the activation energy of this process under polythermal conditions has been investigated. Most of the values obtained are in good agreement among themselves as well as with those found isothermally. Existing differences have been explained satisfactorily.     

Computational study of the thermal decomposition of 2-methylbutyraldehyde and 2-pentanone through retro-ene reactions

In this work, a theoretical study at the MP2/6-31G(d) level of the thermal decomposition retro-ene reaction of 2-methylbutyraldehyde was carried out at a pressure of 1.5 atm. and temperatures ranging from 1110 to 1190 K. The progress of the reaction has been followed by means of the Wiberg bond indices which in turn allowed the calculation of the reaction synchronicity. Transition state theory was used to calculate the theoretical rate constant at 1150 K which was compared with the previously reported experimental value at the same conditions. We found that both values show a close agreement. The obtained computational evidence allowed us to support a reaction mechanism which proceeds in two steps: the first one with the formation of ethylene and 1-propenol via a six-membered cyclic transition state and the second one involving keto-enol equilibrium of 1-propenol to propionaldehyde via a four-membered cyclic transition state. It was found that the reaction is a highly synchronous and concerted process. The results obtained for the thermolysis of 2-methylbutyraldehyde were compared with those obtained for the thermolysis of 2-pentanone. A comparison of our results with those reported for their corresponding β-hydroxy counterparts, 3-hydroxy-2-methylpropionaldehyde and 4-hydroxy-2-butanone has also been made. A study of the thermochemistry of the compounds involved in the reactions studied has been carried out at the G3 level.     

Theory of solid-state thermal decomposition reactions

A case is presented to recommend strongly that scientists interested in thermal chemistry should make comprehensive, conscientious, clinical and critical analyses of the strengths and weaknesses of The L??vov Thermochemical Theory (L??vov, Thermal decomposition of solids and melts??new thermochemical approach to the mechanism, kinetics and methodology, Springer, Berlin, 2007), used to interpret the kinetics and mechanisms of reactions that occur on heating. The shortcomings underlying the theory (some originally developed for solid decompositions) currently uncritically accepted in this field are reviewed, and these deficiencies are contrasted with the successes of L??vov??s approach. To promote the use of this alternative theory, features that may have discouraged researchers unfamiliar with its assumptions, methodology and applications are discussed here. A new scientific theory cannot be ignored or discounted without adequate consideration and testing, particularly in a stagnant area of chemistry that lacks guiding principles and unifying concepts. Novel ideas in the literature (L??vov 2007) deserve recognition, critical appraisal and, if possible, exploitation to maintain the progress of scientific research.     

Kinetic analysis of thermal decomposition reactions

The effect of⁶⁰C0-gamma radiation on the kinetic parameters of the thermal decomposition of potassium bromate crystals has been investigated. Radiation did not modify the mechanism of thermal decomposition reaction, but resulted in a decrease in activation energy and frequency factor with a rate which is large at small doses and decreases at higher doses. The results showed that the increase in the concentration of decomposition nuclei tends to be more important than the increase in the porous character of the solid.     

Kinetics of solid state thermal decomposition reactions

The author wishes to thank Prof. C. G. R. Nair, Dr. V. R. Gowarikar, Mr. M. R. Kurup and Dr. K. V. C. Rao for their encouragements. Thanks are due to Prof. P. M. Madhusudanan and Dr. K. Krishnan for helpful discussions and to Director, VSSC for the kind permission to publish this work.     

Activation energy of the thermal decomposition of ammonium metavanadate. A thermogravimetric study

The thermogravimetric curves of the title compound (AMV), recorded at two rates of heating (10 and 1.25 deg min^–1), exhibited two separate steps of weight loss (at 423–513 and 513–613 K). The TG curves were analysed by testing 18 solid-state reaction equations associated with the methods of Coats and Redfern (1964), atava and kvára (1969) and Blazejowski et al. (1983). On the basis of linearization procedures, high-order reactions with n=1.5 and 2.0 best described the two TG steps. The activation energies of the two conversion stages are: first stage: 163.6 and 152.6 kJ mol^–1, and second stage: 238.1 and 167.7 kJ mol^–1 (low and high heating rates, respectively).

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Zusammenfassung Die thermogravimetrische Untersuchung der Titelverbindung (AMV) ergab bei zwei Aufheizgeschwindigkeiten (10 und 1,25 deg·min^–1) zwei verschiedene Gewichtsverlustintervalle (423–513 und 513–613 K). Die Analyse der TG-Kurven wurden anhand der Gleichungen von 18 Festkörperreaktionen mittels der Coats-Redfern Methode (1964), der Methode von atava und kvára (1969) sowie der Methode von Blazejowski und Mitarb. (1983) durchgeführt. Auf Grund des Linearisierungsverfahrens erwiesen sich höhere Reaktionsordnungen mit n=1,5 und 2 am geeignetsten zur Beschreibung beider TG-Kurven. Die Aktivierungsenergie der beiden Konversionsschritte (für die kleinere und größere Aufheizgeschwindigkeit) beträgt: 1. Schritt: 163,6, 152,6 und 2. Schritt: 238,1 und 167,7 kJ·mol^–1.

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, (10 1,25 ·^–1), 423–513 513–613 . 18 , - , -, . , =1,5 2,0 . , , , 163,6 152,6 ·^–1, – 238,1 167,7 ·^–1.

     

The sources of thermal energy exchange accompanying microbial anabolism

Calculations are made of the thermal energy exchanges accompanying the anabolism of Saccharomyces cerevisiae of four substrates using the equations and . Contrary to a previous postulate cited in the Discussion, the free-energy changes accompanying anabolism are not zero, but can be either positive or negative. However, their magnitude with either sign is small compared to that of catabolism of the same substrates, so that even with free energy changes that are negative it is unlikely anabolism can be considered a spontaneous process.     

Superfast thermal decomposition reactions of polymers and crystallohydrates

Evidence of the existence of a high-limit degradation temperature for polymers is reported. At this high-limit temperature, the rate of polymer thermolysis exceeds the reaction rate predicted by the Arrhenius law by many orders of magnitude. An explanation is proposed for the observed behaviour, based on the disappearance of intermolecular interactions. For the study of degradation reactions under high-limit temperature conditions, new methods of fast (pulsed) thermal analysis are presented. The investigated samples, as very thin films, are brought into tight contact with a hot moving metal surface. Under these conditions, the heating rate exceeds 10⁴ deg/s, allowing estimation of accompanying decomposition rates for heating times of the order of 0.01 s.     

Collisional energy transfer in the thermal decomposition of oxetane

The first order rate coefficient for the thermal decomposition of oxetane and oxetane-d₂ has been investigated at two temperatures as a function of pressure. Gas phase collisional relaxation results are obtained by using RRKM theory and various energy tranfer probability models.

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-d₂ . , RRKM .

     

Ring-expansion reactions in the thermal decomposition of tert-butyl-1,3-cyclopentadiene

The thermal decomposition of tert-butyl-1,3-cyclopentadiene has been investigated in single-pulse shock-tube studies at shock pressures of 182-260 kPa and temperatures of 996-1127 K. Isobutene (2-methylpropene), 1,3-cyclopentadiene, and toluene were observed as the major stable products in the thermolysis of dilute mixtures of the substrate in the presence of a free-radical scavenger. Hydrogen atoms were also inferred to be a primary product of the decomposition and could be quantitatively determined on the basis of products derived from the free-radical scavenger. Of particular interest is the formation of toluene, which involves the expansion of the ring from a five- to a six-membered system. The overall reaction mechanism is suggested to include isomerization of the starting material; a molecular elimination channel; and C-C bond fission reactions, with toluene formation occurring via radical intermediates formed in the latter pathway. These radical intermediates are analogous to those believed to be important in soot formation reactions occurring during combustion. Molecular and thermodynamic properties of key species were determined from G3MP2B3 quantum chemistry calculations and are reported. The temperature dependence of the product spectrum was fit with a detailed chemical kinetic model, and best-fit kinetic parameters were derived using a Nelder-Mead simplex minimization algorithm. Our mechanism and rate constants are consistent with and provide experimental support for the H-atom-assisted routes to the conversion of fulvene to benzene that have been proposed in the literature on the basis of theoretical investigations.     

Application of programmed temperature decomposition to the study of solid decomposition reactions taking place through the prout and tompkins mechanism

A method has been developed to allow kinetic analysis of the Prout and Tompkins mechanism of solid decomposition reactions using a single TG diagram obtained in a linear heating program. On the other hand, provided that the nickel formate decomposition follows such a mechanism, this reaction has been used for checking the kinetic equation obtained.     

The catalytic effects of metal oxides on thermal decomposition reactions,III

The catalytic activity of a series of iron oxides on the thermal decomposition of potassium chlorate was investigated by methods of thermal analysis. Structural and electronic defects were introduced into the oxide by doping, heat treatment in different atmospheres, and irradiation with-rays. These induced defects changed in a systematic way the conductive properties of the iron oxides and correspondingly, their catalytic activity. The results are consistent with ann-type semiconductive behavior of the oxides.

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Zusammenfassung Die katalytische Aktivität einer Reihe von Eisenoxiden gegenüber der thermischen Zersetzung von Kaliumchlorat wurde durch Methoden der Thermoanalyse untersucht. Strukturelle und elektronische Defekte wurden in das Oxid durch Dosierung, Wärmebehandlung in verschiedenen Atmosphären und Bestrahlung mit-Strahlen eingebaut. Diese induzierten Defekte änderten systematisch die Leitfähigkeitseigenschaften der Eisenoxide und dementsprechend ihre katalytische Aktivität. Die Ergebnisse stimmen mit dem Halbleiterverhalten desn-Typs der Oxide gut überein.

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. , . , , . , n-.

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This work was supported by the U.S. Army Edgewood Arsenal under Project No. DA-18-035-AMC-341(A). The authors are grateful to Mr. B. Zeffert and Mr. Harry A. Brown for valuable discussions and useful suggestions.

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The authors also wish to acknowledge Brent Boldt for the laboratory work which he conducted on this program.     

Activation energy for thermal decomposition of nitric oxide

Variation of the reaction mechanism for homogeneous thermal decomposition of NO into N₂ and O₂ in the temperature range between 1000 and 4000 K is studied. The decomposition always proceeds through an atomic chain mechanism initiated by formation of oxygen atom. However the step of the oxygen atom initiation depends on the reaction condition, i.e., collision between two NO molecules at low conversions (when P_O2/P_NO ratio≪ ≪ 1) and collision between NO and O₂ and/or unimolecular decomposition of O₂ at high conversions (after substantial O₂ has been accumulated from the reaction). In this study, apparent activation energy (E_app) of the decomposition reaction has been theoretically determined on the basis of our proposed mechanisms. The E_app thus determined varies widely (from 254 to 401 kJ mol⁻¹) with the accepted step of initiation. This variation can account for the variations among experimental activation energies for the decomposition reaction in the literature. © 1996 John Wiley & Sons, Inc.     

Mechanistic study of the decomposition reactions of azobenzene

The electron impact-induced fragmentation of azobenzenes and its d₁, d₂, d₅, d₁₀, and ¹⁵N analogues was studied by mass Spectrometry and ion kinetic energy spectroscopy. The main fragment ions found in the mass spectrum of azobenzene are due to two parallel stepwise processes from the molecular ion: the expulsion of N₂ and two hydrogen radicals producing an ion at m/z 152 having possibly a biphenylene radical cation structure and loss of C₆H₅? and N₂. Except in the elimination of two hydrogen atoms from [M ? N₂]^+· ions, hydrogen scrambling between the phenyl rings does not feature in azobenzene upon electron impact.     

NMR studies of the thermal decomposition and branching reactions of aromatic esters

Poly(chlorophydroquinone terephthalate) is an aromatic polyester containing mainly chlorohydroquinone and terephthalate. Thermal stability of this aromatic polyester has been a problem during the processing. In order to characterize the melt reactions of this polyester, the thermal degradation of the model compound chlorohydroquinone dibenzoate was studied. The chlorohydroquinone dibenzoate was characterized by high resolution ¹³C-NMR. All experiments for studyng degradation of chlorohydroquinone dibenzoate were designed to test the following environmental parameters: (1) atmosphere, (2) temperature, (3) time, (4) additives, (5) container material. The analysis of the degradation products were carried out mainly using NMR; in some cases GC/MS and HPLC were also used to aid in separation and identification of the degradation products. The major degradation products produced in various experimental conditions were identified as chlorohydroquinone benzoates, hydroquinone dibenzoate, dichlorohydroquinone dibenzoate, 9-fluorenone, benzoic acid, Fries products, and hydrogen chloride     

Continuous determination of carbon monoxide evolved during thermal decomposition reactions

A device suitable for the continuous detection of carbon monoxide evolved during themal decomposition processes is described. The detector can be connected directly to thermoanalytical equipment of controlled gas atmosphere. Carbon monoxide collected by the carrier gas is passed through the device containing hopcalite catalyst. In the presence of oxygen carbon monoxide is converted to carbon dioxide in the cell and the temperature change caused by the heat of reaction is measured. According to experience, the change of temperature is linearly proportional to the amount of carbon monoxide released.The signal curve of the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which carbon monoxide was released.The detector is not completely selective to carbon monoxide, but in most cases the interferring gases can be removed from the carrier gas by various packings placed between the detector and the thermoanalytical equipment.

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Zusammenfassung Es wird ein geeignetes GerÄt zur kontinuierlichen Detektierung von in thermischen Zersetzungsprozessen freigesetztem Kohlenmonoxid beschrieben. Der Detektor kann direkt an eine thermoanalytische Apparatur mit überwachter GasatmosphÄre angeschlossen werden. Das vom Carriergas aufgenommene Kohlenmonoxid wird durch das GerÄt geleitet, das einen Hopcalit-Katalysator enthÄlt. In Gegenwart von Sauerstoff wird das Kohlenmonoxid in Kohlendioxid überführt und die durch die ReaktionswÄrme verursachte TemperaturÄnderung gemessen. ErfahrungsgemÄ\ ist die TemperaturÄnderung proportional der entwickelten Menge Kohlenmonoxid.Das Detektorsignal kann mit den gleichzeitig aufgezeichneten thermoanalytischen Kurven verglichen und zur Bestimmung dessen benutzt werden, in welchem Teilschritt Kohlenmonoxid freigesetzt wird.Der Detektor zeigt keine vollstÄndige SelektivitÄt, jedoch können Störgase durch verschiedene Füllungen zwischen Thermoanalysator und Detektor vom Carriergas getrennt werden.

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The authors thank Dr. A. Felinger for his kind help in the computer processing of the recordings.