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Ozonolysis of lignin models in aqueous solution: Anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene

Environmental Science and Technology, ISSN: 0013-936X, Vol: 43, Issue: 16, Page: 6275-6282
2009
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Article Description

The lignin models anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene were reacted with ozone in aqueous solution, and major products were identified and quantified with respect to ozone consumption when reference material was available. Hydroxylation products in yields equivalent to those of singlet oxygen and muconic products (in analogy to the Criegee mechanism) dominate. The formation of quinones points to the release of methanol. Hydroxyl radicals (OH, quantified, main precursor: O), singlet oxygen (quantified), O radicals (quantified), and as counterparts of the OH radicals radical cations of these methoxybenzenes must each play an important role as intermediates. In the case of 1,4-dimethoxybenzene, for example, the following products were identified (yields in parentheses when quantified): methyl(2Z,4E)-4-methoxy-6-oxo-hexa-2,4-dienoate 5 (52%), hydroquinone 6 (2%), 1,4-benzoquinone 7 (8%), 2,5-dimethoxyhydroquinone 8, 2,5-dimethoxy-1,4-benzoquinone 9, singlet oxygen (6%), hydrogen peroxide (56%), OH (∼17%), O (≤9%). Gibbs energies for the various potential reaction pathways were calculated with the help of the Jaguar 7.5 program. The lignin models anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene were reacted with ozone in aqueous solution, and major products were identified and quantified with respect to ozone consumption when reference material was available. Hydroxylation products in yields equivalent to those of singlet oxygen and muconic products (in analogy to the Criegee mechanism) dominate. The formation of quinones points to the release of methanol. Hydroxyl radicals (OH, quantified, main precursor: O), singlet oxygen (quantified), O radicals (quantified), and as counterparts of the OH radicals radical cations of these methoxybenzenes must each play an important role as intermediates. In the case of 1,4-dimethoxybenzene, for example, the following products were identified (yields in parentheses when quantified): methyl(2Z,4E)-4-methoxy-6-oxo-hexa-2,4- dienoate 5 (52%), hydroquinone 6 (2%), 1,4-benzoquinone 7 (8%), 2,5-dimethoxyhydroquinone 8, 2,5-dimethoxy-1,4-benzoquinone 9, singlet oxygen (6%), hydrogen peroxide (56%), OH (∼17%), O (≤9%). Gibbs energies for the various potential reaction pathways were calculated with the help of the Jaguar 7.5 program. © 2009 American Chemical Society.

Bibliographic Details

Mvula, Eino; Naumov, Sergej; von Sonntag, Clemens

American Chemical Society (ACS)

Chemistry; Environmental Science

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