Atmospheric Reaction of Cl with 4-Hydroxy-2-pentanone (4H2P): A Theoretical Study

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C₅ aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18)  ×  10^-10 and (2.07 ± 0.14)  ×  10^-10 cm³/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C₅ aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C₅ aldehyde compounds.

Iodine-mediated formal [3 + 2] annulation for synthesis of furocoumarin from oxime esters

A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins. The reaction was proposed to undergo radical mechanism mediated by iodine, a cheap and common laboratory reagent. Mechanistic studies showed the key for the successful transformation was the presence of α-iodoimine intermediate which facilitated the ring-closing step. The developed conditions produced good functional group tolerance with a wide range of high-profile furocoumarin product. The potential for this strategy to be applied in other syntheses of heterocyclic compounds is highly achievable.

A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins.

Theoretical investigation of the mechanism, kinetics and subsequent degradation products of the NO3 radical initiated oxidation of 4-hydroxy-3-hexanone

The oxidation mechanism of 4-hydroxy-3-hexanone (CH3CH2C(O)CH(OH)CH2CH3) initiated by NO3 radicals in the nighttime is investigated systematically by applying quantum theoretical methods. According to thermodynamic research, the process of H-abstraction on the -CH- group adjacent to the hydroxyl group is the most dominant pathway with the lowest activation energy. The analysis of Mulliken charge charts and molecular electrostatic potential maps illustrate that C-H bonds are the active sites of the reaction, and the calculated C-H bond dissociation energy of the CH3CH2C(O)CH(OH)CH2CH3 molecule further confirms that α-CH is the most easily activated. Individual rate constants for five H-abstraction pathways are calculated by canonical variational theory coupled with small curvature tunneling method over the temperature range of 260-330 K, and the branching ratios are also evaluated. A total rate constant of 1.18 × 10-15 cm3 per molecule per s is obtained at 298 K, which is in good agreement with the reported experimental value. A negative temperature dependence is observed in the titular reaction. The subsequent degradation processes of the advantageous product alkyl radical (CH3CH2C˙(OH)COCH2CH3) are carried out in a NO-rich environment, and propionic acid, NO2 and ozone are obtained as the major final products. The nighttime atmospheric lifetime of 4-hydroxy-3-hexanone is estimated to be around 19 days, indicating that it has impact at night. The titular reaction rate constants are fitted to a three-parameter Arrhenius formula.