Effect of Benzyl Functionality on Microwave-Assisted Cleavage of Cα–Cβ Bonds in Lignin Model Compounds

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• 作者：Guodian Zhu ; Meilu Lin ; Di Fan ; Wenshan Ning ; Xinping Ouyang ; Yong Qian ; Xueqing Qiu
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 26, 2017
• 年：2017
• 卷：121
• 期：3
• 页码：1537-1545
• 全文大小：607K
• ISSN：1932-7455

文摘

The effect of benzylic alcohol (C_α—OH) pretreatments on microwave-assisted cleavage of C_α—C_β bonds in lignin model compounds was investigated by combining experimental results with density functional theory (DFT) calculations at the M06-2X/6-311++G(d,p) level. The oxidization of C_α—OH to benzylic ketone (C_α═O) facilitated the cleavage of the C_α—C_β bond due to a greater decomposition rate constant and a lower barrier for the decomposition-determining step. The reduction of C_α—OH to benzylic hydrogen (C_α—H) resulted in no C_α—C_β bond being cleaved. Since the C_α—OH quickly reacted with methanol solvent, the etherification of C_α—OH to benzylic ether (C_α—OCH₃) had no effect on the C_α—C_β bond cleavage. The aromatic aldehyde would be obtained from the model compounds containing C_α—OH or C_α—OCH₃, while the model compound containing C_α═O would produce aromatic ester. The research also revealed that the microwave-assisted cleavage of C_α—C_β bonds followed a first-order kinetic and radical reaction mechanism.