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.

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 mono-, di-, and trinitropyrazole derivatives in the condensed state was studied by the manometric method. The reaction rate depends on the number and position of nitro groups in the pyrazole cycle and on the polarity of the medium and aggregate state of the substance. The activation energy of the initial non-catalytic stage of decomposition Е 1 decreases on going from monoto trinitropyrazoles from 142 to 132 kJ mol −1 , and the preexponential factor is 10 9±0.5 s −1 . In a diphenyl solution the decomposition rate is lower than that in the melt, and this difference decreases with increasing in the number of nitro groups in the molecule. For the decomposition of trinitropyrazole in the solid state, Е 1 decreases by 10 kJ mol −1 . All these facts are explained in terms of the mechanism, according to which the reaction occurs as the oxidation of the adjacent carbon atom by the nitro group and proceeds via a strongly polar cyclic transition state.

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.

Термическое разложение тринитропиразола (I) и его аммониевой соли протекает с очень сильным самоускорением, вызванным в основном каталитическим действием конденсированных продуктов. Константа скорости первого порядка начальной стадии (k1) описывает разложение до глубины в 0.5% и характеризуется кинетическими параметрами Е (кДж/моль) и lg(A, c-1): соответственно 131.8 и 9.60 в жидкой фазе и 116.0 и 8.57 в твердом состоянии. Константа k1 уменьшается при проведении реакции в неполярных растворителях и при метилировании I в положение 1. Все эти данные объяснены в рамках механизма, согласно которому реакция заключается в окислении нитрогруппой соседнего атома углерода и идет через сильно полярное циклическое переходное состояние. Оценка термической стабильности I проведена методом опорного ряда, который составлен из широко известных штатных ВВ и впервые представлен в формате k1. В области температур 20–80°С тринитропиразол по стабильности близок к нитроглицерину. Аммониевая соль в несколько раз стабильнее, чем сам тринитропиразол.

The method of cross-recombination of isotopically labeled NC(CH3)2C and NC(CD3)2C radicals with equal free-valence reactivity is applied to measure the cage effect, F = k rec/(k rec + k dif), in the thermal decomposition of azobis(isobutironitrile) in isomorphic crystals consisting by half of fully deuterated molecules of the initial substance. It is shown that the decomposition occurs at crystal lattice defects. The products are analyzed by chromatography-mass spectrometry at the degree of conversion of 1% at 70°C. The CE effect and diffusion coefficient at 70°C have been found to be F = 0.87 and D = 7.7 · 10−7 cm2/s. These results are indicative of a high mobility of molecules on the inner surface of the crystal.

A GC-MS analysis of the azobisisobutyronitrile thermal decomposition products of in solutions at 80°C showed that the ratio of recombination and disproportionation rates of the cyanoisopropyl radical does not depend on the medium viscosity, but increases when the internal pressure of the solvent increases according to the log( k dispr / k rec ) = −1.25 + 0.096 P int 0.5 law. This means that the activation volume corresponding to recombination is larger than that corresponding to disproportionation. It follows from the relationship log( k dispr / k rec ) = (Δ V rec ≠ − Δ v dispr ≠ )Δ P/RT that, for the decomposition of the substrate in benzene under a pressure of 0.5–4.0 kbar, the difference between the activation volumes is Δ V rec ≠ − Δ V dispr ≠ = 8 cm 3 /mol.

The fact of the constancy of activation entropy of N-NO2 bond homolysis in a series of secondary nitramines was utilized for correction of the experimental values of activation energy E of this process proceeding from the reliable data for the rate constants of the nitramines decomposition in solutions. When comparing the refined values of E (kJ mol−1) with the N-N bond length d N-N (Å) the following correlations were obtained: for cyclic and framework nitramines E = 663 − 356d N-N, and for the aromatic nitramines E = 1810 − 1227d N-N. A linear relationship between E and d is observed in the series of similar compounds. It depends on the electronic and steric effects of substituents.

Измерена скорость термического разложения твердого азо-бис-изобутиронитрила в условиях, когда побочные процессы, такие как разложение через газовую фазу, появление жидких продуктов, растрескивание кристаллов или полиморфный переход, не влияют на скорость процесса. Реакция протекает на внутренней поверхности кристалла, и скорость ее зависит от способа кристаллизации. Наиболее стабильным является образец, кристаллизованный в условиях низкого пересыщения. Кинетические параметры реакции равны: Е = 134.9 ± 3.5 кДж/моль, lgA = 14.12 ± 1.5 [c-1]. Константа скорости разложения в твердой фазе в 50 раз меньше, чем в бензоле. Низкая скорость реакции в твердой фазе находит объяснение в рамках модели “добавочного объема”, предложенной для мономолекулярных реакций в молекулярных кристаллах.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Structure of isoxazoline compounds formed via the reaction of alkyl-substituted benzonitrile oxides with ethylene was determined by X-ray diffraction method. Isoxazoline ring is flattened, the bond lengths in it depend slightly on the nature of substituents (CH 3 , C 2 H 5 ) and their position in the benzene ring and the angle of rotation relative to the isoxazoline ring. The connection N-O has a length 1.422 Å. Thermal decomposition of isoxazolines in a liquid phase (160–280°C) is accompanied by the release of acetaldehyde and aromatic nitrile. Both the structure of the cycle and its stability is practically independent of the structure of an aromatic substituent. The rate constant of the initial stage is characterized by the low significance of kinetic parameters, E = 104°8 kJ mol −1 and log a (A/ c ) = 7.2±0.8. The results obtained are rationalized in terms of biradical mechanism of isoxazoline ring-opening that includes an efficient recombination of the biradical and its disappearance as a result of synchronous multi-center rearrangement with the release of acetaldehyde.