5 research outputs found
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 (CCSDĀ(T)-F12/aVTZ). Our calculations
revealed that none of the conventional reactions (CāNO<sub>2</sub> 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
enaminoāimino 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 ā¼49 and
ā¼56 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 āStudies on Thermodynamic Properties of FOXā7 and Its Five Closed-Loop Derivativesā
Comment on āStudies on Thermodynamic Properties of FOXā7 and Its Five Closed-Loop Derivatives
Decomposition Pathways of Titanium Isopropoxide Ti(O<sup>i</sup>Pr)<sub>4</sub>: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations
The
UV-photodissociation at 266 nm of a widely used TiO<sub>2</sub> precursor,
titanium tetraisopropoxide (TiĀ(O<sup>i</sup>Pr)<sub>4</sub>, TTIP),
was studied under molecular-beam conditions. Using the MS-TOF
technique, atomic titanium and titaniumĀ(II) oxide (TiO) were detected
among the most abundant photofragments. Experimental results were
rationalized with the aid of quantum chemical calculations (DLPNOāCCSDĀ(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 ā¼49 kcal/mol,
which was ā¼13 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 ābuilding blockā
of nitrogen-rich energetic compounds, were studied theoretically at
a high and reliable level of theory (viz., using the explicitly correlated
CCSDĀ(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 N<sub>2</sub> 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><sub><i>a</i></sub> = 43.4 kcal mol<sup>ā1</sup> and logĀ(<i>A</i>/s<sup>ā1</sup>) = 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 N<sub>2</sub>, 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 (Ī<sub><i>f</i></sub><i>H</i><sub><i>solid</i></sub><sup>0</sup> = 74.5 Ā± 1.5
kcalĀ·mol<sup>ā1</sup>) by combining theoretically calculated
(W1 multilevel procedure along with an isodesmic reaction) gas phase
enthalpy of formation (Ī<sub><i>f</i></sub><i>H</i><sub><i>gas</i></sub><sup>0</sup> = 100.7 Ā± 1.0 kcalĀ·mol<sup>ā1</sup>) and experimentally measured sublimation enthalpy (Ī<sub><i>sub</i></sub><i>H</i><sup>0</sup> = 26.2 Ā± 0.5
kcalĀ·mol<sup>ā1</sup>)
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-[1ā²H-(1,5ā²-bitetrazol)-5-yl]Ācyanamidate,
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