Dandan Han

Mechanical and Kinetic Studies of the Formation of Polyhalogenated Dibenzo-p-dioxins from Hydroxylated Polybrominated Diphenyl Ethers and Chlorinated Derivatives

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs),which may be generated from PBDEs, are more toxic than their matrix and have been detected in organisms. In this article, we have focused on the gas phase formation of polyhalogenated dibenzo-p-dioxins from several OH-PBDEs and their chlorinated derivatives. All of the geometries and frequencies are calculated at the MPWB1K/6-31+G(d,p) level of theory. The single point energy is obtained at the MPWB1K/6-311+G(3df,2p) level. Rate constants of each step have been calculated over a wide range of 200-2000 K using the canonical variational transition state (CVT) theory with small curvature tunneling (SCT) contribution. The rate equations are shown through Arrhenius formulas. The presence of chlorine atoms increases the reaction barrier for the formation of major products.

Theoretical investigation on the mechanisms and kinetics of OH-initiated photooxidation of dimethyl phthalate (DMP) in atmosphere

The atmospheric OH-initiated degradation mechanisms of dimethy phthalate (DMP) are analyzed at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. The principal products detected experimentally are confirmed by this study while several major intermediates are reported for the first time. Additionally, the pathway scheme of hydroxylation reaction of DMP is proposed. The results about initial steps indicate that hydroxyl radical is most likely to be added to the ortho-carbon atom among additional reactions, while H atoms in methyl group are the most favorable to be abstracted by the OH radical. The rate constants of the elementary reactions over the temperature of 200-400 K were deduced using RRKM theory. The overall rate constant of the title reaction is 1.18×10(-12) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr while H abstraction reactions predominate. According to the rate constants given at different temperatures, the Arrhenius equation is fitted. The atmospheric half life of DMP with respect to OH is estimated to be 6.8 days.

Mechanistic and kinetic study on the ozonolysis of n-butyl vinyl ether, i-butyl vinyl ether and t-butyl vinyl ether

Density functional theory (DFT) and ab initio method are employed to elucidate the mechanisms for O(3)-initiated oxidation of n-butyl vinyl ether (n-BVE) and its isomers (i-BVE and t-BVE). For each BVE, the reactions proceed via O(3) cycloaddition resulting in the formation of primary ozonides (POZs) and then two self-decomposition pathways of POZs are followed. Major products are identified to be formaldehyde and butyl formates (CH(3)CH(2)CH(2)CH(2)OCHO for n-BVE, (CH(3))(2)CHCH(2)OCHO for i-BVE and (CH(3))(3)COCHO for t-BVE). The total and individual rate constants for main product channels have been calculated using the modified multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) approach. At 298 K and 101 kPa, the calculated total rate constants are 2.50×10(-16), 3.41×10(-16) and 4.17×10(-16) cm(3) molecule(-1) s(-1) for n-BVE+O(3), i-BVE+O(3) and t-BVE+O(3), respectively, which are in perfect agreement with experimental results. The total rate coefficients are almost pressure independent in the range of 0.001-101 kPa but obviously positive temperature dependent over the whole study temperature range (200-400 K). Also, the favorable reaction pathways have been determined through the estimation of branching ratios. Moreover, the influence of alkoxy group structure on the reactivity of vinyl ethers was examined.

Computational study on the mechanisms and rate constants of the Cl-initiated oxidation of methyl vinyl ether in the atmosphere.

The Cl-initiated oxidation reactions of methyl vinyl ether (MVE) are analyzed by using the high-level composite method CBS-QB3. Detailed chemistry for the reactions of MVE with chlorine atoms is proposed according to the calculated thermodynamic data. The primary eight channels, including two Cl-addition reactions and six H-abstraction reactions, are discussed. In accordance with the further investigation of the two dominant additional routes, formyl chloride and formaldehyde are the major products. Over the temperature range of 200-400 K and the pressure range of 100-2000 Torr, the rate constants of primary reactions are calculated by employing the MESMER program. H-abstraction channels are negligible according to the value of rate constants. During the studied temperature range, the Arrhenius equation is obtained as ktot = 5.64 × 10(-11) exp(215.1/T). The total rate coefficient is ktot = 1.25 × 10(-10) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr. Finally, the atmospheric lifetime of MVE with respect to Cl is estimated to be 2.23 h.

Computational study on the mechanisms and rate constants of the OH-initiated oxidation of ethyl vinyl ether in atmosphere.

The hydroxylation reactions of ethyl vinyl ether (EVE) in the present of O2 and NO are analyzed by using MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. According to the calculated thermodynamic data, the detailed reaction mechanisms of EVE and OH are proposed. All of the ten possible reaction pathways are discussed. The major products of the title reaction are ethyl formate and formaldehyde, which is in accordance with experimental detection. The rate constants of the primary reactions over the temperature of 250-400K and the pressure range of 100-2000Torr are computed by employing MESMER program. At 298K and 760Torr, OH-addition channels are predominate and the total rate constant is ktot=4.53×10(-11)cm(3)molecule(-1)s(-1). The Arrhenius equation is obtained as ktot=6.27×10(-12)exp(611.5/T), according to the rate constants given at different temperatures. Finally, the atmospheric half life of EVE with respect to OH is estimated to be 2.13h.