Kinetic studies of the gas phase reaction of 1,2-propylene oxide with the OH radical over a temperature range of 261–335 K

Bedjanian

et al. 2021

ACS Earth Space Chem.

Epoxides have many primary and secondary atmospheric sources. As with other oxygenates, they exhibit a complex temperature-dependent reaction with OH, whose full description is necessary in order to understand their interactions in atmospheric and combustion environments. We measured the kinetics of the title reaction using two complementary absolute methods: pulsed-laser photolysis–laser-induced fluorescence (PLP–LIF) and a discharge-flow mass spectrometric system (DF-MS), both monitoring temporal decays in OH. In addition, two relative methods employing the DF-MS as a function of temperature as well as several simulation chamber experiments at room temperature were performed. A very weak negative temperature dependence was observed at T ≤ 285 K, and only through the combination of precise data and a large temperature range were we able to discern the transition toward positive temperature dependence found at T ≥ 295 K. The non-Arrhenius temperature dependence of OH + 1,2-epoxybutane implies the agency of prereactive complexes in this reaction mechanism, albeit with a smaller effect than that with its acyclic ether analogues. This will have implications for understanding the chemical fate of epoxides within oxidizing environments.

Section: Pulsed-laser Photolysis-laser-induced By Fluorescence Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gas-Phase Rate Coefficient of OH + 1,2-Epoxybutane Determined between 220 and 950 K

Othmani

Bedjanian

et al. 2021

ACS Earth Space Chem.

“…Cyclohexene oxide (1,2-epoxycyclohexane) is larger than those epoxides studied previously [10][11][12][13], and, by virtue of the fact that it contains more C-H bonds than other epoxides found in the kinetic database [9], is expected to react comparatively rapidly with OH and be lost primarily through Reaction (1) under atmospheric conditions. The bicyclic structure of cyclohexene oxide also contrasts with previously studied epoxides, and may influence its reaction with OH.…”

Section: Introductionmentioning

confidence: 93%

Gas-phase rate coefficient of OH + cyclohexene oxide measured from 251 to 373 K

Othmani

Chemical Physics Letters

Mellouki

et al. 2021

Absolute measurements of the rate coefficient of the title reaction are reported from 251-373 K using the laser-induced fluorescence-pulsed-laser photolysis technique, together with room-temperature relative rate determinations using a simulation chamber. These are the first reported values of this rate coefficient, which demonstrates a predominantly negative temperature dependence that is more pronounced than with other epoxides, suggesting that pre-reactive complexes contribute to the overall reactivity, and that these complexes are comparatively stable for OH + cyclohexene oxide, which may result from its bicyclic structure. This work provides new insights into the lesser-studied reactivity of the epoxide functionality.

“…7, increasing OH À concentration in the solution can promote the formation of hydroxyl radicals according to Equations ( 6) and (7 8)-( 13)). Therefore, the pH of the solution played an important role in diatrizoate degradation during ozonation (Gunten 2003;Virmani et al 2020).…”

Section: Effect Of Solution Ph On the Degradation Of Diatrizoate During Ozonationmentioning

confidence: 99%

Kinetics of diatrizoate degradation by ozone and the formation of disinfection by-products in the sequential chlorination

Journal of Water Reuse and Desalination

Lin³

et al. 2021

In this study, we studied the degradation kinetics of a common iodine contrast agent, diatrizoate, by ozone and the formation of disinfection by-products (DBPs) in the sequential chlorination. Effects of ozone concentration, solution pH, and bromide concentration on diatrizoate degradation were evaluated. The results indicate that diatrizoate can be effectively degraded (over 80% within 1 h) by ozone, and the degradation kinetics can be well described using the pseudo-first-order kinetic model. The pseudo-first-order rate constant (kobs) of diatrizoate degradation significantly increased with increasing ozone concentration and decreasing bromide concentration. The kobs kept increasing with the increase of pH value and reached a maximum of 6.5 (±0.05) × 10−2 min−1 at pH 9. As the ozone concentration gradually increased from 0.342 to 1.316 mg/L, the corresponding kobs of diatrizoate degradation increased from 1.76 (±0.20) × 10−3 to 4.22 (±0.3) × 10−2 min−1. The bromide concentration exhibited a strong inhibitory effect on diatrizoate degradation because of the competition for ozone with diatrizoate. Trichloromethane was the only detected DBP in the subsequent chlorination in the absence of bromide. However, in the presence of bromide, six other DBPs were detected, and bromochloroiodomethane and tribromomethane became the major products with concentrations 1–2 orders higher than those of the other DBPs. In order to provide safe drinking water to the public, water should be maintained at circumneutral pH values and low bromine concentrations (<5 μM) before reaching the chlorine disinfection process to effectively control the formation of DBPs.