Atmospheric reaction of hydrazine plus hydroxyl radical

Abstract

Understanding the mechanism of hydrazine oxidation reaction by OH radical along with the rate constants of all possible pathways leads to explain the fate of hydrazine in the atmosphere. In this article, the comprehensive mechanisms and kinetics of the hydrazine plus hydroxyl radical reaction have been investigated theoretically at different temperatures and pressures. To achieve the main goals, a series of high levels of quantum chemical calculations have been widely implemented in reliable channels of the H-abstraction, SN2, and addition/elimination reactions. The energy profile of all pathways accompanied by the molecular properties of the involved stationary points has been characterized at the MP2, M06-2X, and CCSD(T)/CBS levels. To estimate accurate barrier energies of the H-abstraction channels, large numbers of the CCSD (T) calculations in conjunction with various augmented basis sets have been implemented. The direct dynamic calculations have been carried out using the validated M06-2X/maug-cc-pVTZ level, and also by the CCSD(T) (energies) + MP2 (partition functions) level. The pressure-dependent rate constants of the barrierless pathways have been investigated by the strong collision approach. Therefore, the main behaviors of the N2H4 + OH reaction have been explored according to the influences of temperature and pressure on the computed rate coefficients within the well-behaved theoretical frameworks of the TST, VTST, and RRKM theories. It has been found that the H-abstraction mechanism (to form N2H3) is dominant relative to the SN2 reaction and OH-addition to the N center of N2H4 moiety (to form H2NOH + NH2). The computed high pressure limit rate constant of the main reaction pathway, k(298.15) = 7.31 × 10–11 cm3 molecule−1 s−1, has an excellent agreement with the experimental value (k (298.15) = (6.50 ± 1.3) × 10–11 cm3 molecule−1 s−1) recommended by Vaghjiani. Also, the atmospheric lifetime of hydrazine degradation by OH radicals has been demonstrated to be 32.80 to 1161.11 h at the altitudes of 0–50 km. Finally, the disagreement in the calculated rate constants between the previous theoretical study and experimental results has been rectified.

The atmospheric relevance of primary alcohols and imidogen reactions

“…Here, we briefly discuss the sinks of these species in the air. It is well affirmed that gaseous hydroxyl radical has high reactivity 49 , 50 and concentration 51 , 52 than all present active species in our ambient. So, this radical plays a crucial role in the removal processes of atmospheric pollutants.…”

“…The used basis set for the M06-2X method is the Pople double zeta 6–31 + G(d,p) type 163 . Our recent investigations demonstrated that the structures involved in the reaction pathways and also the kinetic analysis of the H abstraction mechanism in the gas phase reactions can obtain with high accuracy by employing the M06-2X method 164 , 165 . After predicting reliable structures, the most popular composite method, CBS-QB3 166 , is used to calculate more precise energetic parameters.…”

Organophotoredox-Catalyzed C–H Functionalizations of Benzophospholes

“…14 As mentioned in Scheme 2d, the in situ generated SO 4 −• is considered to be a HAT reagent, thus suggesting its capability of homolytically cleaving other C−H or heteroatom−H bonds with bond dissociation energies (BDEs) similar to carbazate N−H (∼83 kcal/mol). 15 After additional optimization studies, pleasingly, we also found secondary phosphine oxides (BDE of P−H ≃ 79 kcal/mol) 16 and alkyl ethers (BDE of αC−H ≃ 92 kcal/mol) 17 to serve as the effective coupling partners under slightly modified conditions using Eosin Y and blue LED in place of Rose bengal and green LED (Scheme 3). For example, the dehydrogenative C2 phosphinylation of 1a with 4a proceeded smoothly to afford 5aa in 71% yield (Scheme 3a).…”

To Infinity and Beyond: An Optimization Study of Kerosene and Hydrogen Peroxide Bipropellant Fuels

“…In past hydrazine spills, cleanup has been monumentally difficult with largely irreversible damage to ecosystems (Kovshov, 2015). Additionally, being carcinogenic and toxic while also extremely volatile, transportation of hydrazine poses a risk to everyone involved and their surroundings (Douroudgari et al, 2021;Ingenito 2018). Even after being burned as fuel, hydrazine remains in the upper atmosphere for 32.8 to 1161.11 hours and in the lower atmosphere for 6.6 hours before degradation.…”

“…Besides having an acute impact on the ecosystems around these affected areas, hydrazine does not break down into a safe, biodegradable molecule and instead remains in the atmosphere as a byproduct for extended periods of time (Douroudgari et al, 2021). The proposed alternative fuels do not have this problem; instead, they tend to break apart into simple molecules such as water, oxygen, and common polyatomic ions rather than long, stringy organic compounds that are unnatural in the Earth's atmosphere.…”