Transition Metal-catalyzed Reductive Cleavage Of Carbonoxygen Bonds Relative To Lignin

The utilize of lignin remains a challenge in the chemical conversion of straw biomass. The lignin is always regarded as waste, while the other components of biomass(cellulose and hemicellulose) have achieved effective use. Especially in the paper industry, a lot of lignin is discarded, which is not only a waste of material, but also polluting environment. Lignin is the second largest source of biomass after cellulose and the most abundant natural aromatic polymer material. The lignin consists of large amounts of C-O bonds. Provided phenoxy bond or other type of carbonoxygen bonds in the main chain of lignin undergoing reductive cleavage, most lignin backbone will generate small organic molecules containing one or more benzene rings. After industrial fractionation, these small organic molecules can result in a variety of high value-added chemicals. In addition, they can generate small molecules suitable for liquid fuel after hydrodeoxygenation reforming. Above all, phenoxy bond or other type of carbon-oxygen bond is an important process of reductive cleavage of lignin to liquid fuel or high value-added chemical transformation. So the reductive cleavage of phenoxy bond or other type of carbon-oxygen bond is an important process for the chemical transformation.from lignin to liquid fuel or high value-added chemicals.In this paper, a cobalt compound as a catalyst to achieve the reductive cleavage of the lignin-related aryl carbon-oxygen bond. Moreover, lanthanum catalyst and cobalt catalyst have also been found in the absence of strong reducing agents, to achieve the reductive cleavage of the lignin-related β-O-4 type carbon-oxygen bond. The main contents are as follows:1. To Co(acac)2 as the catalyst, achieve the reductive cleavage of the ligninrelated aryl carbon-oxygen bond. The obtained optimal conditions is that 2.5 equivalents of Lithium Aluminum Hydride, 2.5 equivalents of sodium tert-butoxide, 15 mol% cobalt acetylacetonate, 2 m L toluene, 140 degrees Celsius, 24 hours, nitrogen environment. Under these reaction conditions, the broken bond of the aromatic oxygen bond of different aromatic compounds was investigated and found that under the conditions of this reaction, to achieve the reductive cleavage of aryl-oxygen bond of most diphenyl ethers compounds. In addition to the 2,2’-dimethyl diphenyl ether, the reaction result of other diphenyl ethers compounds is better. Alkyl carbon-oxygen bond of the aryl alkyl ethers has less reactivity, and the selective reductive cleavage of carbon-oxygen bond occurs in aryl carbon-oxygen bonds. However, when benzyl phenyl ether was used as the substrate, benzyl carbon-oxygen bond is broken first. When anisole was used as the substrate, the reaction hardly proceeds. Preliminary study of the mechanism indicate that the true catalytic species of the reaction may be Co(0).2. To Co(acac)2 as the catalyst, achieve the reductive cleavage of the ligninrelated β-O-4 type carbon-oxygen bond. The results show that when the reducing agent is Li Al H4, obtain phenol and phenethyl alcohol with the yield of two types of products are higher. However, when the methoxy group is introduced, the reaction has poor selectivity, and the products have more types. When the reaction atmosphere replaced with H2, obtain phenol and acetophenone products. Two products, the ketones have lower yield. When no reducing agent, the phenolic yield is high and the ketones yield is poor to different substrates.3. To La(Ac)3 as the catalyst, achieve the reductive cleavage of the lignin-related β-O-4 type carbon-oxygen bond. The obtained optimal conditions is that 2.5 equivalents of sodium tert-butoxide, 20 mol% lanthanum acetate, 40 mol% 2-phenylpyridine, 2 m L toluene, 140 degrees Celsius, 24 hours, the air environment. Under these reaction conditions, the broken bond of the lignin-related β-O-4 type carbon-oxygen bond was investigated. It was found that, although the catalytic effect of the experiment is not particularly desirable, however, compared to the last chapter of cobalt catalytic the reductive cleavage of the related carbon-oxygen bond of lignin fragments, the experiment has a certain degree of development. Compared with the experimental results of Li Al H4 as the reducing agent, the reaction selectivity is better, and the product is relatively simple. Compared with the experimental results of no reducing agent, ketones yields has increased.