Abstract
Hydrogenolysis of the C-O bonds in lignin, which promises to be able to generate fuels and chemical feedstocks from biomass, is a particularly challenging and important area of investigation. Herein, we demonstrate a vanadium-catalyzed cleavage of a lignin model compound (2,6-dimethoxyphenol). The impact of the catalyst in the context of the temperature, reaction time, and the solvent, was examined for the cleavage of the methyl ethers in 2,6-dimethoxyphenol. In contrast to traditional catalytic transfer hydrogenolysis, which requires high pressure hydrogen gas or reductive organic molecules, such as an alcohol and formic acid, the vanadium catalyst demonstrates superior catalytic activity on the cleavage of the C-O bonds using water as a solvent. For example, the conversion of 2,6-dimethoxyphenol is 89.5% at 280°C after 48 h using distilled water. Notably, the vanadium-catalyzed cleavage of the C-O bond linkage in 2,6-dimethoxyphenol affords 3-methoxycatechol, which undergoes further cleavage to afford pyrogallol. This work is expected to provide an alternative method for the hydrogenolysis of lignin and related compounds into valuable chemicals in the absence of external hydrogen and organic solvents.
Highlights
It provides an alternative approach to addressing renewable fuel sources and their associated environmental issues that converting renewable lignocellulosic biomass to value-added chemicals and biofuels by catalyzing (Son and Toste, 2010; Ma et al, 2018; Rinesch and Bolm, 2018; Gao et al, 2019; Liu et al, 2019)
Preliminary experiments focused on the examination of the influence of the reaction time on the hydrolysis of 2,6dimethoxyphenol with catalytic vanadium metal
In order to verify the reaction path mentioned in section Transfer Hydrogenation of 2,6-Dimethoxyphenol at Different Reaction Time, that 3-methoxycatechol is intermediate product, which means vanadium can catalyze the cleavage of C-O linkage in 3-methoxycatechol to product pyrogallol
Summary
It provides an alternative approach to addressing renewable fuel sources and their associated environmental issues that converting renewable lignocellulosic biomass to value-added chemicals and biofuels by catalyzing (Son and Toste, 2010; Ma et al, 2018; Rinesch and Bolm, 2018; Gao et al, 2019; Liu et al, 2019). Strategies, such as hydrogenolysis, oxidation, hydrolysis, and pyrolysis (Chu et al, 2013; Wang et al, 2013; Dai et al, 2016; Besse et al, 2017; Lin et al, 2018), have been examined for the cleavage of the C-O bond in lignin in addition to several model compounds Among these methods, the hydrogenolysis has gained increasing attention for the degradation of lignin because of the relatively high yield and selectivity. (Liu et al, 2019) investigated the hydrogenolysis of C-O bonds using Ni@ZIF-8 as catalyst, in which they demonstrated that the C-O bonds could be cleaved in the presence of a hydrogen gas under high pressure In another variation, Jiang et al (2019) reported the cleavage of C-O bond in lignin model compounds using a Ni/Al2O3-T catalyst with isopropanol as the hydrogen source. Catalytic vanadium metal is effective for the transfer hydrogenation of benzyl phenyl ethers to furnish 4-benzylphenol and 2-benzylphenol
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