The kinetics of the thermal decomposition of the FOX-7 compound at 155°C under semiopen conditions in vessels with a volume of V = 0.8–0.9 cm3 in an air atmosphere and the degree of filling of the vessel with substances m/V = 0.03–0.72 g/cm3 has been studied by the gravimetric method. It is found that at the largest m/V, an induction period is observed in the early stages of the reaction, during which the rate of mass loss of the sample is lower by a factor of ten than the rate of decomposition of FOX-7 in the solid phase. With a decrease in m/V, the induction period is shortened and at m/V = 0.04 g/cm3 it disappears altogether. The appearance of the induction period is due to the fact that nitronic acid, which is the only product of the first stage of decomposition of FOX-7, is well adsorbed on the surface of FOX-7 crystals. At the same time, it almost completely loses its reactivity. As a result, until the end of the adsorption process, the decomposition of FOX-7 proceeds without the formation of gaseous products, and the reaction rate is not fixed by the gravimetric method suitable for studying the kinetics of the reaction at the early stages of decomposition of FOX-7.

The pressure of 1,1-diamino-2,2-dinitroethylene (FOX-7) vapors in the temperature range 140–160°C is determined by the manometric method. The correlation dependence of log Pvap on 1/T is established, which makes it possible to estimate the value of Pvap with satisfactory accuracy in the temperature range of 100–200°C. The kinetics of the reaction in the gas phase are measured at temperatures of 200–230°C and m/V = 10–3–10–4 g/cm3. It is found that under these conditions, in parallel with the usual monomolecular isomerization reaction into the aci-form, a chain process of the direct oxidation of FOX-7 by NO2 proceeds. The consequence of this reaction is a significant decrease in the activation energy observed and the appearance of a dependence of the rate on the experimental conditions. The scheme of the main stages of the chain reaction is presented and the conditions necessary for the manifestation of this reaction are determined.

The decomposition rates of diphenylfuroxane and a number of 4-nitro-3-alkyl-furoxanes in dilute solutions are measured by the manometric and calorimetric methods. An increase in the reaction rate with an increase in the polarity of the solvent is not detected in any instance, which corresponds to the absence of an increase in the dipole moment of the molecule during the formation of a transition state (TS). Based on this result, a conclusion is made about the biradical (BR) mechanism of the decomposition of uncondensed disubstituted furoxanes (FOs) in solutions.

Выделена группа из 14 взрывчатых соединений, для которых имеются корректные данные как по чувствительности к механическим воздействиям, так и по кинетике реакции термического разложения. Оценены кинетические параметры начальной стадии разложения в твердой фазе. С использованием этих параметров по формулам, описывающим очаговый взрыв, рассчитана критическая температура самовоспламенения Т кр , критический радиус очага и объемная мощность теплового потока, вызывающего самовоспламенение. Выявлена корреляционная связь Т кр с критическим давлением Р кр , при котором происходит взрыв образца. Проведено сравнение эффективности действия на чувствительность таких факторов, как скорость реакции термического разложения и теплота взрыва.

By the example of 14 compounds representing the main classes of explosives containing H, C, N, and O, it has been shown that the impact sensitivity correlates with the critical temperature T cr of spontaneous ignition, which, in turn, is determined by the kinetic parameters and heat of the decomposition reaction. At the same time, the reaction rate is the dominant factor, and against its background the effect produced on the sensitivity by the thermophysical properties of the compounds and by the specific coefficient of friction becomes barely noticeable.

A group of 14 explosive compounds for which there are correct data on sensitivity to mechanical stress and on the kinetics of the thermal decomposition reaction is identified. The kinetic parameters of the initial stage of decomposition in the solid phase are estimated. The critical temperature of self-ignition T cr , the critical radius of the focal, and the volumetric power of the heat flux that causes self-ignition are calculated using these parameters, according to the formulas describing the focal explosion. The correlation between T cr and critical pressure P cr at which the sample explodes is revealed. The effectiveness of the effect on the sensitivity of factors such as the rate of the reaction of thermal decomposition and the heat of the explosion is compared.

The kinetics of the thermal decomposition of diazacyclic derivatives of 1,1-diamino-2,2-dinitroethylene (FOX-7) in a dilute solution of nitrobenzene and in the solid phase are studied by manometric and calorimetric methods. The activation energy data obtained for the solution are used for comparison with quantum chemical calculations and for establishing the relationship between the stability of compounds and the structure of the molecules. The decomposition of these derivatives in solution proceeds according to the same mechanism as the decomposition of FOX-7. Their activation energies decrease with the increasing C=C bond length and are in close agreement with the published data on quantum chemical calculations. By the nature of decomposition in the solid state, these compounds differ significantly from FOX-7. This difference is due to the fact that the condensed products of their decomposition are not solid but liquid compounds.

The kinetics of the thermal decomposition of 1,1-diamino-2,2-dinitroethylene (FOX-7) in solutions at temperatures of 180 to 240°C and a concentration of FOX-7 of ~1 wt % is studied by the gage and calorimetric methods. Chloro- and o-dichlorobenzene, nitrobenzene, and n-nitrotoluene are used as solvents. The dependence of the decomposition rate on the polarity of the solvent is shown, and the kinetic parameters of the reaction in the solution are determined. The data obtained are used to discuss the reaction mechanism and predict the rates of conversion of FOX-7 in the liquid and solid states.

The kinetics of the thermal decomposition of 1,1-diamino-2,2-dinitroethylene (FOX-7) in the solid state is investigated by the manometric and calorimetric methods. The conditions are found under which the solid-phase reaction and the accompanying fast side processes of substance sublimation and vapor decomposition are separated in time, and the contribution of secondary reactions to the initial rate of solid-phase decomposition is small. The rate constant of the noncatalytic stage of decomposition of the substance in the solid phase is determined under these conditions.

In the representation of the rate constant k1 of the first, noncatalytic stage of decomposition, the reference series method is developed to determine the thermal stability of explosives at temperatures below 100°C. To determine k1 at low temperatures, the most accurate published data on the kinetic parameters of decomposition in liquid or solid states and the known quantitative relations between the k1 values in the liquid and solid phases are used.

The possibility of identifying the concerted mechanism of the decomposition of C-nitro compounds according to the dependence of the reaction rate on the polarity of the solvent is studied using the example of thermal decomposition reactions of nitropyrazoles in solution.

На примере реакций термического разложения нитропиразолов в растворе изучена возможность идентификации согласованного механизма разложения С-нитросоединений по зависимости скорости реакции от полярности растворителя.

The decomposition rate of 1,1-diamino-2,2-dinitroethylene (FOX-7) at 200°C in a wide range of changes in the conditions of the experiment and methods of sample preparation is measured. The nature of the first stage of decomposition is established and the reason the reaction stopped at this stage is found.

При температурах 160–280°C изучен распад изоксазолинового кольца, образующегося при присоединении этилена к метил- и этилзамещенным бензонитрилоксидам. Реакция заключается в расщеплении изоксазолинового цикла на ацетальдегид и соответствующий ароматический нитрил. Скорость ее в расплаве и в инертных растворителях типа хлорбензола слабо зависит от строения ароматического заместителя, кинетические параметры имеют низкие значения: Е = (104 ± 8) кДж/моль и lg(А, c-1) = 7.2 ± 0.8. Только в том случае, когда бензольное кольцо содержит три этильных заместителя, разложение в расплаве идет быстрее, чем в растворе. Скорость циклораспада уменьшается при увеличении вязкости среды и увеличивается в растворителях, имеющих пониженную прочность связи C–H. Для соединений, полностью дейтерированных в изоксазолиновое кольцо, наблюдается обратный кинетический дейтериевый изотопный эффект. Полученные результаты объяснены в рамках бирадикального механизма раскрытия изоксазолинового цикла, включающего эффективную рекомбинацию бирадикала и его гибель в результате синхронной перегруппировки с выбросом ацетальдегида.

The thermal decomposition of trinitropyrazole ( I ) and its ammonium salt proceeds with a very strong self-acceleration, caused mainly by the catalytic action of the condensed products. The first-order rate constant for the initial stage k 1 describes the decomposition to a depth of conversion of 0.5% and is characterized by the following kinetic parameters E (kJ/mol) and log( A , s −1 ): 131.8 and 9.60 for the liquid phase and 116.0 and 8.57 for the solid state. The rate constant k 1 is smaller if the reaction occurs in nonpolar solvents and if I is methylated at position 1. All these data are interpreted in the framework of a mechanism according to which the reaction involves the oxidation by a nitro group of a neighboring carbon atom and proceeds through a highly polar cyclic transition state. Evaluation of the thermal stability of I is conducted using the method of a reference series composed of well-known regular HEs, which for the first time was implemented in terms of k 1 . In the temperature range 20–80°C, the stability of trinitropyrazole is close to that of nitroglycerin. Trinitropyrazole ammonium salt is severalfold more stable than trinitropyrazole itself.

The decomposition of the isoxazole ring at 160–280°C formed by the addition of ethylene to methyland ethyl–substituted benzonitrile oxides is studied. The reaction consists in the cleavage of the isoxazole ring into acetaldehyde and the corresponding aromatic nitrile. Its rate in the melt and in inert solvents, such as chlorobenzene, only weakly depends on the structure of the aromatic substituent, with the kinetic parameters having low values: E = (104 ± 8) kJ/mol and log( A , s –1 ) = 7.2 ± 0.8. Only if the benzene ring has three ethyl substituents, the decomposition of the compound in the melt proceeds faster than in solution. The rate of the decomposition of the ring decreases with increasing viscosity of the medium, being higher in solvents with a lower strength of the C–H bond. For compounds with the fully deuterated isoxazole ring, the inverse kinetic H/D isotope effect is observed. The results are explained in terms of the biradical mechanism of the opening of the isoxazole ring that involves an effective recombination of the biradical and its loss through a synchronous rearrangement with acetaldehyde release.