Mechanism Of Thermolysis Research Articles

Effect of structure on the rate and mechanism of thermolysis of some 4-substituted 3-methylfuroxans

The gas-phase thermolysis of I proceeds as a unimolecular process and is independent of the initial vapor pressure of the substance (over 190 mm Hg) and of the ratio of the reaction vessel surface to its volume (S/V = 0.55–4.62 сm). In the melt and in solution in an inert solvent dibutylphtalate (DBP) the furazans decompose according to the first-order reaction law to the conversion level of 30–45 %. The substance content in the solution (1–10 %) does not affect the reaction rate.

Spectroscopic study of calcium sulfite thermolysis

The thermal conversion of calcium sulfite into calcium sulfate in air was studied by thermogravimetric analysis and ESR and IR spectroscopy. The water of crystallization of CaSO3 · 0.5H2O was found to be involved in the formation of the heat-generated radical ion SO2−. A thermolysis mechanism is suggested.

Kinetics and thermolysis mechanism of some 4-substituted 3-methylfuroxans

Thermolysis of the non-condensed furoxans containing two reaction centers for which the initiation of decomposition reaction is possible, has not been adequately studied. We explored kinetics of thermolysis of the furoxans such as: (1–15 wt %) and nature of inert solvent (trinitrobenzene, dibutylphthalate DBP) that is inherent in the homolytic process. Thermolysis of compound II in solution occurs with acceleration and unaffected by the ratio of substance mass to volume of reactionary vessel (m/V = 1.1×10–1.6×10 g cm). It has been established earlier [1] that opening of furoxan ring proceeds at the least strong transannular N(O)–O bond. As a result the low-stable structure forms, stabilizing into the former or isomeric furoxan. At elevated temperatures the furoxan ring opens at N(O)–O and С–С bonds to give the two nitrileoxide functions, which isomerize irreversibly into isocyanate under these conditions [1, 3].

Theoretical Studies on Thermolysis Mechanism and Stability of trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐tetraazadecalin Isomers

AbstractA systematic study on the thermolysis mechanism and stability of a series of energetic cyclic nitramines, trans‐1,4,5,8‐tetranitro‐1,4,5,8‐tetraazadecalin isomers, was performed by density functional theory (DFT) and semiempirical molecular orbital (MO) calculations. Bond dissociation energies (BDE) and activation energies (Ea) of the thermolysis processes were computed at the B3LYP/6‐31G∗︁∗︁ and PM3 levels, respectively. The effect of nitroamino groups on the thermal stability and pyrolysis mechanism of the title compounds was evaluated by the BDE and Ea. The correlations among BDE, Ea, bond overlap populations, energies of the frontier orbitals, and energy gaps were examined in detail. The results indicate that thermal stabilities and decomposition mechanisms of the title compounds derived from the BDE, Ea and static electronic parameters are basically consistent. Homolysis of the N–NO2 bond is the initial step in the thermolysis of the title compounds, the meta‐isomers are more stable than the para‐isomers, and the ortho‐isomers are the most sensitive.

Substituent effect on the molecular stability, group interaction, detonation performance, and thermolysis mechanism of nitroamino-substituted cyclopentanes and cyclohexanes

Density functional theory (DFT) method has been employed to study the effect of nitroamino group as a substituent in cyclopentane and cyclohexane, which usually construct the polycyclic or caged nitramines. Molecular structures were investigated at the B3LYP/6-31G** level, and isodesmic reactions were designed for calculating the group interactions. The results show that the group interactions accord with the group additivity, increasing with the increasing number of nitroamino groups. The distance between substituents influences the interactions. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the predicted densities and heats of formation, while thermal stability and pyrolysis mechanism were studied by the computations of bond dissociation energy (BDE). It is found that the contributions of nitroamino groups to the detonation heat, detonation velocity, detonation pressure, and stability all deviate from the group additivity. Only 3a, 3b, and 9a–9c may be novel potential candidates of high energy density materials (HEDMs) according to the quantitative criteria of HEDM (ρ ≈ 1.9 g/cm3, D ≈ 9.0 km/s, P ≈ 40.0 GPa). Stability decreases with the increasing number of N-NO2 groups, and homolysis of N-NO2 bond is the initial step in the thermolysis of the title compounds. Coupled with the demand of thermal stability (BDE > 20 kcal/mol), only 1,2,4-trinitrotriazacyclohexane and 1,2,4,5-tetranitrotetraazacyclohexane are suggested as feasible energetic materials. These results may provide basic information for the molecular design of HEDMs.

Transition-metal bimaleates and their solid solutions: Synthesis, structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C4H3O4)2 · 4H2O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.

Synthesis and thermal study of rhenium(V) coordination compounds with pyroracemic acid and phenylglyoxylic acid thiosemicarbazones

Rhenium(V) coordination compounds with pyroracemic acid and phenylglyoxylic acid thiosemicarbazones were synthesized for various metal-to-ligand ratios in 1–7 M hydrohalic acids. The composition and structure of the complexes were characterized using a set of physicochemical methods. The thermal stability of rhenium(V) complexes with pyroracemic acid and phenylglyoxylic acid thiosemicarbazones and rhenium(V) solvato complexes with pyroracemic acid thiosemicarbazone was studied thermogravimetrically. The thermolysis mechanism for the complexes was determined as follows: elimination of outer-sphere water, decarboxylation, and dehalogenation.

Study on thermal decomposition and combustion of insensitive explosive 3,3′-diamino-4,4′-azofurazan (DAAzF)

Thermal decomposition of an explosive with low sensitivity, 3,3′-diamino-4,4′-azofurazan (DAAzF), has been investigated under isothermal conditions at 200–320 °C using the thin-walled glass manometer of the compensation type. Changing the ratio of the sample weight to the vessel volume allowed us to measure the kinetic parameters of DAAzF decomposition predominantly in the solid state ( k = 5.0 × 10 11 exp(−21,320/ T), s −1) and the gas phase ( k = 3.3 × 10 12 exp(−21,020/ T), s −1). The kinetics of decomposition in solution ( k = 3.5 × 10 6 exp(−14,070/ T), s −1) have also been measured. Based on the burning rate and thermocouple measurement data, rate constants of DAAzF decomposition in the molten layer at 600–800 °C have been derived from a condensed-phase combustion model ( k = 4.6 × 10 8 exp(−16,680/ T), s −1), which is in a good agreement with kinetic data obtained in the solution at 235–260 °C. The mechanism of DAAzF thermolysis and combustion includes initial rupture of C–N bond between the azo-group and furazan ring with subsequent nitrogen evolution and decomposition of the heterocyclic ring. In the combustion wave, the heat release from decomposition of the stable furazan ring follows the heat release from azo-group decomposition, resulting in a distinct two-stage flame structure.

Theoretical predictions on the structures and properties for polynitrohexaazaadamantanes (PNHAAs) as potential high energy density compounds (HEDCs)

It is the heated point to make molecular design of high energy density compounds (HEDCs) in the world energy and resource field. However, previous works usually were ended with gas molecular design. On the other hand, most of high energy materials are in agglomerate phase, especially in crystals. In this paper, we make crystal structure predictions for the potential HEDCs, polynitrohexaazaadamantanes (PNHAAs), by choosing appropriate force field using molecular mechanics (MM) method. Based on the ab initio periodic calculations on their predicted packings, their electronic structures (density of states, DOS) and properties, such as sensitivity and thermolysis mechanism were investigated. Besides, we make comparisons between the conclusions drawn from gas and solid calculations. It is most interesting that our calculations predict that 2,4,6,8,9,10-hexanitrohexaazaadamantane may possess better properties than the well-known HEDC ε-CL-20 (hexanitrohexaazaisowurtzitane).

NMR-investigation of the mechanism of silver mercaptide thermolysis in amorphous polystyrene

Polymer-embedded silver clusters have been prepared by thermal decomposition of silver dodecylmercaptide previously dissolved in amorphous polystyrene. The morphology and structure of silver clusters have been determined by transmission electron microscopy (TEM) and large angle X-ray diffractometry (XRD), respectively. The mechanism involved in the thermolysis reaction was elucidated by different NMR techniques. The thermolysis produced thiol-derivatized silver clusters (i.e., silver clusters coated with a self-organized thiol monolayer, Agx(SC12H25)y) and had the effect of increasing the branching degree of polystyrene due to enhanced cross-linking.

Molecular modeling of the mechanisms of thermolysis of nitramino-1,2,4-triazoles

Modeling of the probable mechanisms of the thermolysis of C-and N-nitramino-1,2,4-triazoles has been carried out by methods of mathematical chemistry. It was established that the formation is possible of a more diverse spectrum of products in their destruction than was previously recorded by different experimental methods. Subsequent assessment of the thermochemical preference for pathways of decomposition of the compounds was carried out by the density functional method in the B3LYP/6-31G* approach. It was determined that the thermal destruction of C-and N-nitramino-substituted polynitrogen heterocycles, capable of tautomeric conversion, was most probably through the thermochemically least stable nitramine form. Thermal decomposition of the considered tautomers is preferred at the NNO2 fragment and not at the triazole ring. The direction of the structural stabilization of the investigated compounds has been clarified by comparison of the geometric, electronic, and thermochemical characteristics of C-NNO2-and N-NNO2-substituted 1,2,4-triazoles.

A comparative study of thermolysis characteristics and kinetics of seaweeds and fir wood

Thermal analysis and thermolysis kinetics of three kinds of seaweeds and fir wood ( M. glyptostriboides Huet Cheng), a kind of typical land plant, had been conducted. The results showed that thermal stability follows the order of Grateloupia filicina < Ulva lactuca < Dictyopteris divaricata < fir wood. A notable difference on heat flow between seaweeds and fir wood during thermolysis was that the former were mainly connected with exothermic processes at relatively lower temperature regimes, while the latter was connected with an apparent endotherm at a relatively higher temperature regime followed by a maximum exothermic peak. This suggested that the heat coupling might be realized if co-thermolysis of seaweeds and fir wood were carried out. The main devolatilization phase of each seaweed could be described by Avrami–Erofeev equation, which indicated that thermolysis of seaweeds follows the mechanism of random nucleation and nuclei growth, whereas that of fir wood by Z–L–T equation and its thermolysis mechanism was three-dimensional diffusion. The activation energies calculated for both seaweeds and fir wood increase as conversion increases. However, those for the former have wider distribution.

Kinetics and Mechanism of Thermolysis of Mixtures of Ammonium Nitrate with Polynitro Compounds

Kinetics of heat release in thermolysis of mixtures of ammonium nitrate with bis(2,2,2-trinitroethyl) succinate, tetrakis(2,2,2-trinitroethyl) orthocarbonate, technical-grade trinitrotoluene and of the individual polynitro compounds was studied. The temperature dependences of the initial rates of the processes and the time required to attain the maximal rate were determined. A thermolysis mechanism of these mixtures was suggested and the dependence of the thermolysis rate on the properties of the polynitro compounds was accounted for.

Studies on energetic compounds: Part 31. Thermolysis and kinetics of RDX and some of its plastic bonded explosives

Thermal analysis of RDX and its three plastic bonded explosives (PBXs) namely RXE 9505, RXE 9010 and RXV 9010 were done using various thermo analytical techniques, under different conditions. Although, the thermal analyses do not show any significant reduction in thermal stability of RDX, there are results, which suggest that the presence of binder alters the reaction pathways. Kinetic analysis of isothermal TG data was made by model fitting methods as well as a model free isoconversional method. The merits and demerits of both modes of kinetic approaches were evaluated critically. Conventional model fitting methods fail to describe the complex reactions during thermolysis of both RDX and its PBXs. Isoconversional method shows that the mechanisms of thermolysis of RDX and its PBXs are different, in the same temperature range. Role of binder was found to be in facilitating the reaction to take place in the condensed phase and reducing the role of competing reaction channels such as evaporation and gas phase thermolysis. Rapid thermolysis of the samples was studied by measuring ignition delay and evaluating its kinetic parameters.

Thermolysis of Organic Peroxides in Solution

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on Energetic Compounds Part 27: Kinetics and Mechanism of Thermolysis of Bis(Ethylenediamine)Metal Nitrates and Their Role in the Burning Rate of Solid Propellants

AbstractFour bis(ethylenediamine)metal(II) nitrate (BEMN) complexes, i.e. [M(EDA)2](NO3)2, where M=Cu, Co, Ni and Zn, have been prepared and characterized. Thermolysis of these complexes induced by heat and drop‐weight impact has been investigated by TG‐DTG, DTA, explosion delay (DE), explosion temperature (TE) and impact sensitivity measurement. The kinetics of early thermolysis reaction prior to fast decomposition have been evaluated. Contracting area (CA, n=2) and contracting cube (CC, n=3) equations were found to give the best fits in isothermal TG data among all tested nine mechanism‐based kinetic models. The values of activation energy (Ea), TE, DE and activation energy for explosion (E*) have been found to be quite lower for the copper complex as compared to cobalt, nickel and zinc complexes. A mechanism of thermolysis has also been proposed. All these complexes were found to be insensitive towards impact of 2 kg weight up to the height of 110 cm. These complexes were used as energetic burning rate modifiers in the combustion of hydroxy‐terminated polybutadiene (HTPB)‐ammonium perchlorate (AP) composite solid propellants. A two‐fold increase in burning rate was observed with copper and cobalt complexes at low concentration (2% by wt.). The in situ freshly formed metal oxides with large number of active sites in their crystallites seem to be better additives for combustion of propellants.

Effect of High Pressure on the Kinetics and Mechanism of Thermolysis of Organic Peroxides in Solution

AbstractFor Abstract see ChemInform Abstract in Full Text.

Primary reactions of sucrose thermal degradation

Thermal degradation of sucrose at 185 °C in a closed glassware and presence of air was studied with the help of GC/MS after acetylation of reaction products. Also model compounds were used to support the mechanism of thermolysis. Goal was to identify all the primary reactions of the process. It was observed that already after 5 min of treatment, two glucopyranose isomers were formed as products of sucrose glycosidic bond splitting. The furanose structure is probably transformed to anhydrofructoses, as 2,6-anhydrofructose was identified among the degradation products in much smaller amount than d-glucose. At longer thermolysis times some diastereoisomers of sucrose, anhydrosucroses, and anhydroderivatives of monosaccharides were identified as minor products of parallel primary and secondary reaction. After 30 min at 185 °C there was no sucrose present in the reaction mixture, but some new products with longer retention times (RT) occurred. Also isomers of levoglucosan were observed after 1 h of treatment. This indicates that splitting of glycosidic bond is the most prominent primary reaction. The dehydration towards anhydrosucroses seams to be a minor primary reaction and might proceed via configuration changes on the pyranose ring.

Effect of High Pressure on the Kinetics and Mechanism of Thermolysis of Organic Peroxides in Solution

This review analyzes published data and experimental results obtained by the authors concerning the effect of high pressure on the chemical kinetics of thermal decomposition of the main types of organic and organosilicon peroxides in solution. The volume effect of activation was found to depend on the mechanism of peroxide decomposition and on the properties of solvents.

Récupération post-exercice chez le sportif fumeur

Aim: Assess the influence of tobacco on recovery after exercise in sportsmen. Methods: Sixty-three smokers aged 18-33 years, practising soccer, participed in this study. These subjects belonged to second division congolese league clubs. Heart rate (HR) was studied during recovery of moderate exercise (Ruffier's test), but also recovery index and arterial pressure. Kinetics of the HR was studied for 7 min for recovery. A control group consisted of 50 non smokers, practising soccer at similar level. Results: Smokers showed heart rate values significantly higher (P < 0,001). Non smokers presented a low recovery index. The recovery has generally two components: the first is slow in smokers, while the second is a fast one. However, recovery rate for the smokers was more rapid during the alactic phase. There exists also differences with regards to smoking tobacco dependence: when compared to great smokers, lower smokers exhibited a faster first phase and a slower second phase. These differences were significant. Discussion and conclusion: The smokers and non smokers differences are discussed with reference to the effects of nicotinemia and carbon monoxide on sympathetic-parasympathetic balance. Cardiovascular changes during exercise have a twofold control: decrease a vagal tone and increase of sympathetic activity. The comparison of smokers and non smokers concerning recovery led to suppose that there exists a difference in regards of the catecholaminergic sensitivity. The problem of thermoregulation must not be neglected during recovery. As smokers are considered, cutaneous thermolysis is perhaps important when these subjects perform exercise in ambient hot air. Here againt, it is known that thermolysis mechanisms are not similar in smokers and non smokers. In conclusion, this study showed that smoking tobacco induce a lower physical condition in sportmen. Recovery rate after exercise may function as a predictor of fitness in smokers.