Mechanistic and kinetic study on the ozonolysis of 2,4-hexadienedial |
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Authors: | Li Zhong Ya Gao Xiayu Chen Wei Yao Shujin Li |
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Institution: | 1. College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123, People’s Republic of China
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Abstract: | The formation and unimolecular reactions of primary ozonides and carbonyl oxides arising from the O3-initiated reactions of 2,4-hexadienedial (HDE) have been investigated using the density functional theory and ab initio method. The activation energies of O3 cycloaddition to the >C=C< and >C=O bonds of HDE for the formation primary ozonides (POZ1 and POZ2) are 4.79 and 21.37 kcal mol?1, respectively, implying that the initial O3 to the >C=C< bond is favorable pathway. Cleavage of POZ1 to form carbonyl oxides occurs with a barrier of 12.19–21.35 kcal mol?1, and the decomposition energies range from ?1.09 to ?15.75 kcal mol?1. The CHOCHOO radical, the hydroxyl radical (OH) formation via H-migration is more favorable than the dioxirane formation via rearrangement. However, the CHOCH=CHCHOO radical, the dioxirane formation via rearrangement is more favorable than OH formation. Using the transition state theory, the rate constants of formation of POZ1 and POZ2 are 1.49 × 10?19 and 6.03 × 10?25 cm3 molecule?1 s?1 at 300 K, respectively. This study shows that the hyperconjugative effect makes O3 addition to >C=C< and >C=O bonds of HDE more difficult than to >C=C< bond of ethylene and isoprene and to >C=O bond of formaldehyde. The largest rate constants of OH formation and dioxirane formation in the unimolecular reactions of carbonyl oxides are 6.13 × 10?4 and 7.93 × 10?1 s?1 at 300 K, respectively. The dioxirane is main product in the unimolecular reaction of the carbonyl oxides arising from the O3-initiated reaction of HDE. |
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