Unexpected Primary Reactions for Thermolysis of 1,1-Diamino-2,2-dinitroethylene (FOX-7) Revealed by <i>ab Initio</i> Calculations

The primary thermolysis reactions of a promising insensitive explosive 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) have been studied in the gas phase at a high level of theory (CCSD­(T)-F12/aVTZ). Our calculations revealed that none of the conventional reactions (C–NO₂ bond fission, nitro-nitrite and nitro-aci-nitro rearrangements) dominate thermolysis of FOX-7. On the contrary, two new decomposition pathways specific for this particular species that commenced with enamino–imino isomerization and intramolecular cyclization were found instead to be more feasible energetically. The activation barriers of these primary isomerization reactions were calculated to be 48.4 and 28.8 kcal/mol, while the activation energies of the overall decomposition pathways are predicted to be ∼49 and ∼56 kcal/mol, respectively. The new pathways can also be relevant for a wide series of unsaturated hydrocarbons substituted with both nitro- and amino-groups (e.g., triaminotrinitrobenzene, TATB)

Comment on “Studies on Thermodynamic Properties of FOX‑7 and Its Five Closed-Loop Derivatives”

Comment on “Studies on Thermodynamic Properties of FOX‑7 and Its Five Closed-Loop Derivatives

Decomposition Pathways of Titanium Isopropoxide Ti(OⁱPr)₄: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

The UV-photodissociation at 266 nm of a widely used TiO₂ precursor, titanium tetraisopropoxide (Ti­(OⁱPr)₄, TTIP), was studied under molecular-beam conditions. Using the MS-TOF technique, atomic titanium and titanium­(II) oxide (TiO) were detected among the most abundant photofragments. Experimental results were rationalized with the aid of quantum chemical calculations (DLPNO–CCSD­(T) and DFT). Contrary to the existing data in the literature, the new four-centered acetone-elimination reaction was found to be the primary decomposition process of TTIP. According to computational results, the effective activation barrier of this channel was ∼49 kcal/mol, which was ∼13 kcal/mol lower than that of the competing propylene elimination. The former process, followed by the dissociative loss of an H atom, was a dominating channel of TTIP unimolecular decay. The sequential loss of isopropoxy moieties via these two-step processes was supposed to produce the experimentally observed titanium atoms. In turn, the combination of these reactions with propylene elimination can lead to another detected species, TiO. These results indicate that the existing mechanisms of TTIP thermal and photoinitiated decomposition in the chemical-vapor deposition (CVD) of titanium dioxide should be reconsidered

Thermochemistry, Tautomerism, and Thermal Decomposition of 1,5-Diaminotetrazole: A High-Level ab Initio Study

Thermochemistry, kinetics, and mechanism of thermal decomposition of 1,5-diaminotetrazole (DAT), a widely used “building block” of nitrogen-rich energetic compounds, were studied theoretically at a high and reliable level of theory (viz., using the explicitly correlated CCSD­(T)-F12/aug-cc-pVTZ procedure). Quantum chemical calculations provided detailed insight into the thermolysis mechanism of DAT missing in the existing literature. Moreover, several contradictory assumptions on the mechanism and key intermediates of thermolysis were resolved. The unimolecular primary decomposition reactions of the seven isomers of DAT were studied in the gas phase and in the melt using a simplified model of the latter. The two-step reaction of N₂ elimination from the diamino tautomer was found to be the primary decomposition process of DAT in the gas phase and melt. The effective Arrhenius parameters of this process were calculated to be <i>E</i>_<i>a</i> = 43.4 kcal mol^–1 and log­(<i>A</i>/s^‑1) = 15.2 in a good agreement with the experimental values. Contrary to the existing literature data, all other decomposition channels of DAT isomers turned out to be kinetically unimportant. Apart from this, a new primary decomposition channel yielding N₂, cyanamide, and 1,1-diazene was found for some H-bonded dimers of DAT. We also determined a reliable and mutually consistent set of thermochemical values for DAT (Δ_<i>f</i><i>H</i>_<i>solid</i>⁰ = 74.5 ± 1.5 kcal·mol^–1) by combining theoretically calculated (W1 multilevel procedure along with an isodesmic reaction) gas phase enthalpy of formation (Δ_<i>f</i><i>H</i>_<i>gas</i>⁰ = 100.7 ± 1.0 kcal·mol^–1) and experimentally measured sublimation enthalpy (Δ_<i>sub</i><i>H</i>⁰ = 26.2 ± 0.5 kcal·mol^–1)

Metal-Free Reversible Double Cyclization of Cyanuric Diazide to an Asymmetric Bitetrazolate via Cleavage of the Six-Membered Aromatic Ring

Crystallization of the reaction mixture of 2-amino-4,6-diazido-1,3,5-triazine and excess tert-butylamine results in the isolation of tert-butylammonium N,N-[1′H-(1,5′-bitetrazol)-5-yl]­cyanamidate, suggesting a complex decyclization/cyclization rearrangement involving breakage of the six-membered aromatic ring and the formation of two new five-membered azole rings mediated by deprotonation of the precursor by the amine. The addition of tert-butylamine to 2-amino-4,6-diazido-1,3,5-triazine gives spectroscopic indication of thermodynamically unfavorable reactivity in low-dielectric solvents, and high-level quantum chemical computations also suggest its formation to be unfavorable. A computed interconversion pathway describes the likely reaction mechanism and supports the general thermodynamic unfavorability of the reaction and the requirement for a high-dielectric environment to template formation of the ionic product and its trapping by crystallization