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

摘要

Density functional theory (DFT) and ab initio method are employed to elucidate the mechanisms for 03-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_3CH_2CH_2CH_2OCHO for n-BVE, (CH_3)_2CHCH_2OCHO for i-BVE and (CH_3)_3COCHO 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 r-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.