Mechanism Of Lignin-carbohydrate Complexes Oxidation And Delignification Topchemistry Catalyzed By Co-salen Complex

Lignin has been described as a random three-dimensional network biopolymer present throughout the plant cellular structure. Lignin is removed for production of most papers. Degradation of lignin (delignification) hence constitutes an important step in paper manufacture.Data from numerous studies indicate the presence of covalent linkages between lignin and carbohydrate in plant. Structures with these type of linkages are referred to as lignin-carbohydrate complexes (LCC). Lignin-carbohydrate bonds prevent removal of lignin from carbohydrates in pulping and bleaching, decrease pulp bleachability. Consequently, the search for a selective and environmentally friendly delignification technology which can selectively oxidize lignin functionalities without harming the cellulose fibres is a current challenge for the paper industry worldwide. A very attractive attempt is to catalytically enhance the delignification with aid of oxygen and/or hydrogen peroxide in the bleaching cycle, this certainly involves the development of metal complexes. Co(salen) along with dioxygen as the oxidant constitutes the most promising biomimetic degradation of lignin.In this work, we report the oxidative mechanism of LCC in the presence of the Co-salen complex catalyst using the LCC substrates from sweet bamboo and chemically synthesis (veratrylglycerol-β-guaiacyl-a,γ-dimethylether, VGD). Several spectroscopic techniques (such as FTIR, NMR, GC-MS) were used to study the structural changes and the product formation in the reaction of O2/H2O2 with LCC catalyzed by Co-salen. The Co-salen has showed the obvious ability to catalytically degrade LCC as the aromatic-ring opening occurring. The cellulose and hemicellulose portion present in LCC was seriously degraded, such as glucuronic acid, xyloglucan. The cleavage ofβ-O-4 gave rise to the 2-methoxy phenol, and that of Ca-Cβgave the product of aldehyde. The aromatic methoxyl was removed in reaction process, however, the methoxyl in a-,γ-positions has the better stability. Some biphenyls were also found with GC-MS, possibly due to radical coupling. Similarly, from the perspective of topchemistry, the catalytic ability of Co-salen was studied with SEM-EDXA upon the delignification in microregions, such as cell corner (CC), compound middle lamella (CML), secondary wall (S).