Temperature Dependence of the Reaction of Chlorine Atoms with CH3OH and CH3CHO

Insight into homogeneous activation of sodium hypochlorite by dithionite coupled with dissolved oxygen (DO@NaClO/DTN) for carbamazepine degradation

Emerging contaminants (ECs) including carbamazepine (CBZ) in aquatic systems pose non-target risks to wildlife. We introduce an innovative advanced oxidation process (AOP) utilizing sodium hypochlorite (NaClO), which achieved 45.3 % degradation and mineralization of CBZ within 60 mins. Natural saturated state dissolved oxygen (DO, ∼7.5 mg·L-1) played a crucial role in synergistically activating NaClO with dithionite (DTN) without extra energy consumption. In DO@NaClO/DTN system, scavenging tests and electron spin resonance (ESR) analysis confirmed that ·OH and Cl· were dominant for CBZ degradation. The critical DO was responsible for the direct simultaneous production of ·OH and Cl·, confirmed by the greater thermodynamic data ΔG from density functional theory (DFT) calculation. These reactive species participate in subsequent transformations of SO4·-, O2·-, and 1O2. Preferential hydroxylation of CBZ first occurred due to the attacking at the reactive sites of C(21) and C(22) atoms. LC-MS/MS detection and DFT theoretical calculations also verified the sequent mechanisms of Meinwald rearrangement, deamidation and hydroxylation, cyclized hydroxylated and dehydrated with the decreasing ΔG. Ubiquitous Cl- accelerated CBZ degradation remarkably, regardless of its concentration. The significant enhancement of Cl- for CBZ degradation in DO@NaClO/DTN system suggest its promising application for ECs degradation in high-chloride seawater including offshore wastewater and tailwater in mariculture.

Reaction Kinetics of CH2OO and syn-CH3CHOO Criegee Intermediates with Acetaldehyde

Criegee intermediates exert a crucial influence on atmospheric chemistry, functioning as powerful oxidants that facilitate the degradation of pollutants, and understanding their reaction kinetics is essential for accurate atmospheric modeling. In this study, the kinetics of CH2OO and syn-CH3CHOO reactions with acetaldehyde (CH3CHO) were investigated using a flash photolysis reaction tube coupled with the OH laser-induced fluorescence (LIF) method. The experimental results indicate that the reaction of syn-CH3CHOO with CH3CHO is independent of pressure in the range of 5-50 Torr when using Ar as the bath gas. However, the rate coefficient for the reaction between CH2OO and CH3CHO at 5.5 Torr was found to be lower compared to the near-constant values observed between 10 and 100 Torr. Furthermore, the reaction of syn-CH3CHOO with CH3CHO demonstrated positive temperature dependence from 283 to 330 K, with a rate coefficient of (2.11 ± 0.45) × 10-13 cm3 molecule-1 s-1 at 298 K. The activation energy and pre-exponential factor derived from the Arrhenius plot for this reaction were determined to be 2.32 ± 0.49 kcal mol-1 and (1.66 ± 0.61) × 10-11 cm3 molecule-1 s-1, respectively. In comparison, the reaction of CH2OO with CH3CHO exhibited negative temperature dependence, with a rate coefficient of (2.16 ± 0.39) × 10-12 cm3 molecule-1 s-1 at 100 Torr and 298 K and an activation energy and a pre-exponential factor of -1.73 ± 0.31 kcal mol-1 and (1.15 ± 0.21) × 10-13 cm3 molecule-1 s-1, respectively, over the temperature range of 280-333 K.

The atmospheric relevance of primary alcohols and imidogen reactions

Organic alcohols as very volatile compounds play a crucial role in the air quality of the atmosphere. So, the removal processes of such compounds are an important atmospheric challenge. The main goal of this research is to discover the atmospheric relevance of degradation paths of linear alcohols by imidogen with the aid of simulation by quantum mechanical (QM) methods. To this end, we combine broad mechanistic and kinetic results to get more accurate information and to have a deeper insight into the behavior of the designed reactions. Thus, the main and necessary reaction pathways are explored by well-behaved QM methods for complete elucidation of the studying gaseous reactions. Moreover, the potential energy surfaces as  a main factor are computed for easier judging of the most probable pathways in the simulated reactions. Our attempt to find the occurrence of the considered reactions in the atmospheric conditions is completed by precisely evaluating the rate constants of all elementary reactions. All of the computed bimolecular rate constants have a positive dependency on both temperature and pressure. The kinetic results show that H-abstraction from the α carbon is dominant relative to the other sites. Finally, by the results of this study, we conclude that at moderate temperatures and pressures primary alcohols can degrade with imidogen, so they can get atmospheric relevance.

Towards an Understanding of Halide Interactions with the Carbonyl-Containing Molecule CH3 CHO

The anion photoelectron spectra of Cl^- ⋅⋅⋅CD₃ CDO, Cl^- ⋅⋅⋅(CD₃ CDO)₂ , Br^- ⋅⋅⋅CH₃ CHO, and I^- ⋅⋅⋅CH₃ CHO are presented with electron stabilisation energies of 0.55, 0.93, 0.48, and 0.40 eV, respectively. Optimised geometries of the singly solvated species featured the halide appended to the CH₃ CHO molecule in-line with the electropositive portion of the C=O bond and having binding energies between 45 and 52 kJ mol^-1 . The doubly solvated Cl^- ⋅⋅⋅(CH₃ CHO)₂ species features asymmetric solvation upon the addition of a second CH₃ CHO molecule. Theoretical detachment energies were found to be in excellent agreement with experiment, with comparisons drawn between other halide complexes with simple carbonyl molecules.

Acetonyl Peroxy and Hydro Peroxy Self- and Cross-Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product

Pulsed laser photolysis coupled with infrared (IR) wavelength modulation spectroscopy and ultraviolet (UV) absorption spectroscopy was used to study the kinetics and branching fractions for the acetonyl peroxy (CH₃C(O)CH₂O₂) self-reaction and its reaction with hydro peroxy (HO₂) at a temperature of 298 K and pressure of 100 Torr. Near-IR and mid-IR lasers simultaneously monitored HO₂ and hydroxyl, OH, respectively, while UV absorption measurements monitored the CH₃C(O)CH₂O₂ concentrations. The overall rate constant for the reaction between CH₃C(O)CH₂O₂ and HO₂ was found to be (5.5 ± 0.5) × 10^-12 cm³ molecule^-1 s^-1, and the branching fraction for OH yield from this reaction was directly measured as 0.30 ± 0.04. The CH₃C(O)CH₂O₂ self-reaction rate constant was measured to be (4.8 ± 0.8) × 10^-12 cm³ molecule^-1 s^-1, and the branching fraction for alkoxy formation was inferred from secondary chemistry as 0.33 ± 0.13. An increase in the rate of the HO₂ self-reaction was also observed as a function of acetone (CH₃C(O)CH₃) concentration which is interpreted as a chaperone effect, resulting from hydrogen-bond complexation between HO₂ and CH₃C(O)CH₃. The chaperone enhancement coefficient for CH₃C(O)CH₃ was determined to be k_A^″ = (4.0 ± 0.2) × 10^-29 cm⁶ molecule^-2 s^-1, and the equilibrium constant for HO₂·CH₃C(O)CH₃ complex formation was found to be K_c(R14) = (2.0 ± 0.89) × 10^-18 cm³ molecule^-1; from these values, the rate constant for the HO₂ + HO₂·CH₃C(O)CH₃ reaction was estimated to be (2 ± 1) × 10^-11 cm³ molecule^-1 s^-1. Results from UV absorption cross-section measurements of CH₃C(O)CH₂O₂ and prompt OH radical yields arising from possible oxidation of the CH₃C(O)CH₃-derived alkyl radical are also discussed. Using theoretical methods, no likely pathways for the observed prompt OH radical formation have been found and the prompt OH radical yields thus remain unexplained.