Lignin Hydrolysis and Phosphorylation Mechanism during Phosphoric Acid- Acetone Pretreatment: A DFT Study
W Qin and LN Wu and ZM Zheng and CQ Dong and YP Yang, MOLECULES, 19, 21335-21349 (2014).
The study focused on the structural sensitivity of lignin during the phosphoric acid-acetone pretreatment process and the resulting hydrolysis and phosphorylation reaction mechanisms using density functional theory calculations. The chemical stabilities of the seven most common linkages (beta-O-4, beta-beta, 4-O-5, beta-1, 5-5, alpha-O-4, and beta-5) of lignin in H3PO4, CH3COCH3, and H2O solutions were detected, which shows that alpha-O-4 linkage and beta-O-4 linkage tend to break during the phosphoric acid-acetone pretreatment process. Then alpha-O-4 phosphorylation and beta-O-4 phosphorylation follow a two-step reaction mechanism in the acid treatment step, respectively. However, since phosphorylation of alpha-O-4 is more energetically accessible than phosphorylation of beta-O-4 in phosphoric acid, the phosphorylation of alpha-O-4 could be controllably realized under certain operational conditions, which could tune the electron and hole transfer on the right side of beta-O-4 in the H2PO4- functionalized lignin. The results provide a fundamental understanding for process- controlled modification of lignin and the potential novel applications in lignin-based imprinted polymers, sensors, and molecular devices.
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