Thermal decomposition of solid azobisisobutyronitrile

The rate of the thermal decomposition of solid azobisisobutyronitrile was measured under conditions such that the side processes, such as gas-phase decomposition, the formation of liquid products, crystal cracking, and polymorphic transitions, had no effect on the process rate. The reaction occurs on the inner crystal surface, and its rate depends on the method of crystallization. The sample crystallized under conditions of low supersaturation is the most stable. The kinetic parameters of the reaction are E = 134.9 ± 3.5 kJ/mol and log A = 14.12 ± 1.5 [s^?1]. The decomposition rate constant of solid azobisisobutyronitrile is 50 times lower than that of azobisisobutyronitrile in benzene solution. The low reaction rate in the solid phase is explained in terms of the additional-volume model proposed for unimolecular reactions in molecular crystals.     

Influence of purity on the thermal stability of solid organic compounds

DSC method was used to study thermal stability of nitrocompounds. It was assumed the model to estimate stability of solid phase in which perfect solid phase is totally stable and amorphous-liquid domains connected with impurities decompose according to the kinetic model determined for the liquid phase above the melting point. The influence of sample purity on relative stability, which is k _l/k _s — ratio of decomposition rate constants in liquid and solid phase, at temperature 20 K below the melting point was predicted. The increase of liquid domains in solid phase causes decrease of k _l/k _s ratio (relative stability) at chosen temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N₂ amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO₂ group remains in the residue, which contains amino groups and no C−H bonds. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 815–821, May, 2000.     

Thermal decomposition of N-2,4,6-tetranitro-N-methylaniline

Purity determination by calorimetry has been used to determine the rate constant of thermal decomposition of N-2,4,6-tetranitro-N-methylaniline in liquid and solid states. The ratios of the initial rates of decomposition in solid and liquid decrease when temperature increases in the region not far below the melting point. The predicted rate constants in solid state are about 10 times greater than the one estimated by Wiseman. The thermal decomposition process at lower temperatures has been used to determine the rate constant in the decay phase. Activation energy and pre-exponential factor are also presented.     

Kinetics of Thermal Decomposition of Solid Propellant Based on Aluminum and Ammonium Perchlorate

Kinetic regularities of the mass loss and heat and-gas release were studied in the thermal decomposition of a solid propellant composed of aluminum, ammonium perchlorate, and a polymer binder. It was shown that, under heating from 40 to 340°C under permanent vacuum conditions, propellant samples decompose without ignition, with the limiting mass loss in the decomposition being 48%. When experiments were performed in air, the propellant formulation decomposes with sharp ignition, with the inflammation temperature (270–287°C) and amount of volatiles released by this instant of time (10–16 wt %) dependent on the heating rate. The kinetic regularities of the mass loss in the decomposition of a solid propellant were described in terms of the polychromatic kinetics model that assumes that the reaction system has ensembles of particles differing in reactivity. The distribution functions of the mass fractions of the propellant by activation energies of decomposition were calculated. The heat release kinetics in the decomposition of a propellant formulation in the temperature range 153–270°C in a closed evacuated system is described by a sum of equations for two parallel reactions: 1st-order reaction with a heat effect Q₁ = 200 ± 5 kJ kg^–1 and 1st-order autocatalysis with heat effect Q₂ = 1900 ± 50 kJ kg–1. The rate constants and the activation parameters of the process were determined.

     

Thermal and dissolution kinetics of ampicillin drug and capsules

This work aims to compare the thermal decomposition and dissolution kinetics of ampicillin drug and products A, B and C. The thermal decomposition reaction rate constants (kT) were determined by isothermal thermogravimetric method using the classical Arrhenius equations. The dissolution profiles were obtained using USP 23 method and rate constants (kD) were determined by Kitazawa equation. The results showed correlation between kT and kD can be used in the study of preformulation of drugs and also as a parameter in the studies of pharmaceutical equivalence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nonintegral and integral folding crystal growth in low-molecular mass poly (ethylene oxide) fractions. III. Linear crystal growth rates and crystal morphology

Correlations of the linear crystal growth rates with the change in crystal morphology for poly (ethylene oxide) (PEO) (MW 3000) and α,ω--methoxy-poly (ethylene oxide) (MPEO) (MW 3000) fractions have been established over a wide range of supercooling (ΔT = 25 K). Two linear crystal growth rates were measured, namely, the linear crystal growth rate of spherulites or hedrites and the lateral (linear) crystal growth rate of single lamellar crystals along different crystalline planes (below ΔT = 11–12 K). At a low supercooling of 5 K, the crystal growth rate of the MPEO fraction passes through a minimum. Subsequently, the rate increases abnormally and reaches a maximum at even lower supercooling. This crystal growth retardation has been attributed to the competition between differing chain conformations during crystal growth. In this case, particularly, these conformations are the extended chain and the once-folded chain conformations. This retardation is not observed in the PEO fraction, since in this low supercooling region any once-folded chain conformations formed during crystal growth are of the double-layer lamella type. The change in morphology in this region supports this judgement. Above ΔT = 7.6 K, the crystal growth behavior in these two fractions can be described by the present nucleation theory on flat crystal growth faces. Below that ΔT, however, different crystal growth mechanisms can be clearly seen. This may be associated with the crystal growth on the highly serrated growth faces in these two fractions.     

Kinetics of the reaction of sodium arylthiolates with nitro-carboxybenzyl halide derivatives

The rate constants for the reactions of 4-halomethyl-3-nitrobenzoic acids, the nonnitro derivatives, and their ethyl esters with arylthiolates were measured at different temperatures. It was found that the retardation in rate constants compared to benzyl halides is due to the electrostatic repulsion between the electronegative substituents (COO⁻ and/or NO₂) in the substrates and thiolate ions. Good correlations between log k₂ values of the acids and carbon basicities of thiolates were found while log k₂ values of the esters show good straight lines with Hammett σ constants, pk_a, and carbon basicities of arylthiolates. © 1996 John Wiley & Sons Inc     

Germa‐closo‐dodecaborate: A New Ligand in Transition‐Metal Chemistry with a Strong trans Influence

The strong nucleophilic character of germa‐closo‐dodecaborate towards late transition metal centres is described. The synthesis and characterisation of the first germa‐closo‐dodecaborate complexes are presented, and the solid state structures of the germaborate transition metal complexes were determined by X‐ray crystal structure analyses. The strong trans influence of the new germaborate ligand was determined by IR spectroscopy and NMR coupling constants.     

Influence of heating rate on kinetic quantities of solid phase thermal decomposition

Thermogravimetric analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion) of 9 different samples were carried out in dynamic conditions at different heating rates. The kinetic parameters (E, A and k_m) of thermal decomposition were determined and interrelations between the parameters and heating rate q were analyzed. There were also relations between Arrhenius and Eyring equations analyzed for thermal decomposition of solid phase. It was concluded that Eyring theory is an element, which interconnects used thermokinetic equations containing Arrhenius law and suggests considering kinetic quantities in way relative to 3 kinetic constants (E, A and k_m). Analysis of quantities other than km (i.e. E, A, Δ⁺H, Δ⁺S) in relation to heating rate is an incomplete method and does not lead to unambiguous conclusions. It was ascertained that in ideal case, assuming constant values of kinetic parameters (E and A) towards heating rate and satisfying both Kissinger equations, reaction rate constant k_m should take on values intermediate between constants (k_m)₁ and (k_m)₂ determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation k_m vs. q in the background of (k_m)₁ and (k_m)₂ made possible classification of differences between thermal decomposition processes taking place in oxidizing and oxygen-free atmosphere.     

Chemically activated 3-methyl-l-butene and 2-methyl-l-butene from photolysis of diazomethane–isobutene–neopentane–oxygen mixtures

An experimental study of the decomposition kinetics of chemically activated 2-methyl-l-butene and 3-methyl-l-butene produced from photolysis of diazomethane-isobutene-neopentane-oxygen mixtures is reported. The experimental rate constants for 3-methyl-l-butene decomposition were 1.74 ± 0.44 × 10⁸ sec^?1 and 1.01 ± 0.25 × 10⁸ sec^?1 at 3660 and 4358 Å, respectively. 2-Methyl-l-butene experimental decomposition rate constants were found to be 5.94 ± 0.59 × 10⁷ sec^?1 at 3660 Å and 3.42 ± 0.34 × 10⁷ sec^?1 at 4358 Å. Activated complex structures giving Arrhenius A-factors calculated from absolute rate theory of 10^{16.6 ± 0.5} sec^?1 for 3-methyl-l-butene and 10^{16.2 ± 0.4} sec^?1 for 2-methyl-l-butene, both calculated at 1000°K, were required to fit RRKM theory calculated rate constants to the experimental rate constants at reasonable E₀ and E* values. Corrected calculations (adjusted E₀ values) on previous results for 2-pentene decomposition gave an Arrhenius A-factor of 10^{16.45 ± 0.35} sec^?1 at 1000°K. The predicted A-factors for these three alkene decompositions giving resonance-stabilized methylully radicals are in good internal agreement. The fact that these A-factors are only slightly less than those for related alkane decompositions indicates that methylallylic resonance in the decomposition products leads to only a small amount of tightening in the corresponding activated complexes. This tightening is a significantly smaller factor than the large reduction in the critical energy due to resonance stabilization.     

Very low-pressure pyrolysis. VII. The decomposition of methylhydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine,and tetramethylhydrazine. Concerted deamination and dehydrogenation of methylhydrazine

The rate constants (k_uni) for the first-order disappearance of the title molecules have been determined under VLPP conditions. The k_uni are not the rate constants of ultimate interest since they reflect the fact that energy transfer competes with the chemical decomposition. Use of the Rice-Ramsperger-Kassel-(Marcus) [RRK(M)] theory allows the determination of the high-pressure rate constants (k_α), if the mode of decomposition is known. The heats of formation of the radicals NH₂, CH₃NH, and (CH₃)₂N are known. These values should be usable for prediction of the activation energy for N? N bond homolysis in the hydrazines. Measured rate constants for UDMH and TMH bear this out, but the rate constant for MMH does not. This and other evidence lead to the conclusion that MMH decomposes via molecular concerted elimination of NH₃ and H₂ not and by N? N bond scission. The following values are preferred from this work (θ = 2.303RT in kcal/mole). Mode of decomposition is N—N bond scission unless noted otherwise in parenthesis: .     

Kinetics and mechanism of free-surface vaporization of zinc, cadmium and mercury oxides analyzed by the third-law method

On the basis of critical comparison of experimental and theoretical values of the E parameter and investigation of the retardation effect of oxygen on the evaporation rate of ZnO, CdO and HgO, it was concluded that the dissociative evaporation of ZnO and HgO proceeds with releasing of atomic oxygen (O) as a primary product of decomposition. By contrast, the mechanism of dissociative evaporation of CdO corresponds to the equilibrium reaction with releasing of molecular oxygen (O₂) as a primary product of decomposition. As was shown, this difference in mechanisms is not related with interatomic OO distances in these oxides. From the analysis of crystal structure for 12 different oxides, which evaporate with releasing of atomic oxygen, and for 13 compounds, which evaporate with releasing of molecular oxygen, it was revealed that the first mechanism is observed for all oxides with the cubic crystal structure. It was proposed that a decisive role in this difference belongs to a local symmetry in the position of O atoms.     

On the estimation of the reaction mechanisms of thermal decomposition of solids from the fraction reacted at the maximum reaction rate

A procedure is developed for determining equilibrium constants of reactions of the type: A (solid) ? B (solid) + C (gas) from TG data. The method is based upon the overlapping of both formation and decomposition TG diagrams when an appropriate heating rate is applied.     

Radiation-induced bulk polymerization of maleimide

Radiation-induced bulk polymerization of maleimide in both solid and liquid states was studied. Benzoquinone inhibited the liquid-state polymerization and retarded solid-state polymerization. The results of ESR study showed that solid monomer irradiated at 61°C. gave a spectrum, the concentration of which slowly decreased without changing the shape at 61°C. The radical detected at 61°C. was shown not to be the main propagating species. Overall rate polymerizations in the liquid and solid states were expressed, respectively, by first-order and zero-order rate equations with respect to the concentration of monomer. The overall rate constants in liquid and solid states were proportional to I^0.9 and I^1.0, respectively.     

Kinetics of photochromic reactions in condensed phases

A review of kinetic data reported for a few organic photochromic systems is given. The kinetics of processes taking place in solid matrices and in crystals was briefly discussed. The effect of solid matrices manifests itself in the kinetics being controlled by distributions rather than by discrete rate constants. The photochromic reactions often require a substantial free volume to occur, hence they seldom take place in crystals without a destruction of the crystal lattice. The activation energies of thermally driven reactions are in this case related rather to crystal parameters than to the reactions themselves.     

Thermal decomposition behaviors of β-cyclodextrin,its inclusion complexes of alkyl amines,and complexed β-cyclodextrin at different heating rates

The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin (CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant (k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies (E _a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when the decomposition reaction of the complexed β-CD encountered a large value of E _a, such as that in Dta–β-CD system, an apparent compensation effect of A on E _a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation.     

The cycloaddition of ethylene to butene-2. I. Stereochemistry of the reaction

The rate of the thermal cycloaddition of ethylene to cis and trans butene-2 has been measured at 693°K and at pressures of about 12 atmospheres. The ratio of trans- to cis-1,2-dimethylcyclobutane from the reaction of trans-butene-2 with ethylene was 5.1, obtained from the initial rates of formation of the products. Similarly, the ratio of cis- to trans-1,2-dimethyl-cyclobutane from the reaction of cis-butene-2 with ethylene was 2.8. The results show that the cycloaddition reactions are the reverse of the decomposition reactions of the dimethyl-cyclobutanes and may be interpreted in terms of a biradical intermediate. Several ratios of rate constants have been measured as well as the rate constants for the reaction of the olefins to form the intermediate biradical.