V. V. Dubikhin

Thermal decomposition of 2,4,6-trinitrotoluene in melt and solutions

Thermal decomposition of 2,4,6-trinitrotoluene in the temperature range from 200 to 340 °C in melt and in solutions was studied. The main features of the process (high initial rates, activation energies lower than those in the gaseous phase, a higher acceleration at the catalytic stage, and the effect of nonpolar solvents on initial rates) are explained in terms of a kinetic scheme corresponding to a degenerate branched chain reaction.

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.

Chain and monomolecular decomposition of hexogen in solutions

The decomposition of hexogen dissolved in alkylaromatic hydrocarbons, alcohols, ketones, ethers, chloroform, and some other solvents occurs via the chain mechanism. This mechanism is supported by slowing down of the reaction when inhibitors are added, the solvent deuterium kinetic isotope effect, and the dependence of the rate on the reactivity of the C—H bond in solvents. The chain reaction propagates through the transfer of a free valence from the primary N-radicals formed by N—NO2 bond dissociation to the C-centered radicals of the solvent. The solvents are inert when the N—H bond dissociation energy is >380 or <200 kJ mol–1, and hexogen decomposition in such solvents is monomolecular.

Crystal defects and stability of RDX

NQR studies demonstrated that structure imperfection of RDX crystals is affected by impurities, the particle size, and the modes of crystallization and pressing of the sample. The initial rate of RDX decomposition depends on the same factors. In pure samples, the rate varies 1.5—2 times and is proportional to imperfection. In spite of crystal destruction, the rate of thermal decomposition in pressed samples decreases due, apparently, to strengthening of the cell effect.

Concordant mechanism for gas-phase decomposition of nitro compounds

1. n nThe kinetic parameters of the first elementary step in the decomposition of o-nitroaniline, trinitroaniline, trinitrotoluene, o-nitrophenol, ando-dinitrobenzene were obtained. These compounds decompose by a concordant mechanism, with the cleavage of an O2 molecule from the adjacent nitro groups in the case of o-dinitrobenzene, and the elimination of an OH radical in the case of the other compounds. n n n n n2. n nThe structural parameters of the transition state in the decomposition of o-nitrotoluene were estimated from the value of the kinetic isotope effect.

Radical gas-phase decomposition of nitrobenzene derivatives

1. n nKinetic characteristics for C-N bond rupture, the first elementary step in gas-phase decomposition, have been estimated for 13 derivatives of nitrobenzene. n n n n n2. n nA correlation equation relating molecular structures and rate constants has been developed for p- and m-derivatives with donor-type substituents.

Solvent and external pressure effects on the ratio of the cyanoisopropyl radical recombination and disproportionation rates

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(kdispr/krec) = −1.25 + 0.096 Pint0.5 law. This means that the activation volume corresponding to recombination is larger than that corresponding to disproportionation. It follows from the relationship log(kdispr/krec) = (ΔVrec≠ − Δvdispr≠)ΔP/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 ΔVrec≠ − ΔVdispr≠ = 8 cm3/mol.

Kinetics and mechanism of the thermal decomposition of 1-bromo-4-nitroxymethylcubane

The thermal decomposition kinetics of 1-bromo-4-nitroxymethylcubane in the liquid phase is typical of C-ONO2 bond heterolysis, which occurs if the nitro ester has a strong donor substituent. A comparison between 1-bromo-4-nitroxymethylcubane and tert-butyl nitrate shows that bromocubyl is close to the tert-butyl group in induction properties and cubyl itself is a stronger donor than this group.

Chain decomposition of 2,4,6-trinitrotoluene in hydrocarbon solvents

The rate constants for the thermal decomposition of 2,4,6-trinitrotoluene have been measured in toluene and other hydrocarbon solvents. The initial, observed rate constant (ki) increases with dilution with toluene. The concentration dependence is described by the chain decomposition scheme with the transfer of the free valence to a solvent molecule. The activation energy and logki were found to linearly correlate with the dissociation energy of the C-H bond of the solvent.