Study of Mechanism and Improvement of the Process of Oxidative Cleavage of Lignins into the Aromatic Aldehydes
VALERI E. TARABANKO and DMITRIY V. PETUKHOV
Institute of Chemistry and Chemical Technology, Siberian Branch of the Russian Academy of Sciences, Ul. K. Marxa 42, Krasnoyarsk 660049 (Russia) E-mail: veta@icct.ru
Pages: 655-667
Abstract
Known hypotheses concerning the mechanism of formation of aromatic aldehydes (vanillin and syringaldehyde) in the processes of oxidative cleavage of lignins are discussed. A new mechanism of lignin oxidation is described, which starts from the formation of phenoxyl radical and is completed by the formation of vanillin through the retro-aldol cleavage of substituted coniferyl aldehyde. Oxidation of the model compounds is studied and experimental confirmations of the proposed mechanism are obtained. Coniferyl alcohol, the postulated intermediate of eugenol oxidation, was detected by GC-MS. Comparison of the kinetics and oxidation products of vanillidenacetone and lignosulphonates, eugenol and isoeugenol, guaiacyl ethanol and quaiacyl propanol confirms the proposed mechanism. On its basis, possibilities are found to elevate the selectivity of lignin oxidation by oxygen into aromatic aldehydes by accelerating the process due to tightening conditions.
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