Degradation Of Lignin And Lignin Model Via BBr₃-assisted Nucleophilic Substitution

Lignocellulosic biomass as a renewable resource contains three main components cellulose,hemicellulose and lignin,has attracted more and more attention in recent years.Lignin is aromatic-based structural integrity in plants,accounts for about 15-30%of biomass.The development of efficient degradation of lignin can not only reduce the waste of biomass,but also alleviate the supply pressure of non renewable resources such as oil.At present,some achievements have been achieved in the field of degradation lignin,such as transition metal catalyzed hydrogenolysis,degradation of the pretreated lignin and so on.However,some of the researches performed poor chemo-selectivity,overhydrogenated aromatic or residual metal in the harsh reaction conditions?high temperature and pressure?.Therefore,it is imperative to develop effective degradation ways with mild reaction conditions,high selectivity and yield.Nucleophilic substitution is one of the most classical reaction in organic reactions with the formation of new bonds and the cleavge of intrinsic bonds.Therefore the modification of raw materials can be completed via nucleophilic substitution,meanwhile,the products may possess some specific chemical properties.In the present research,BBr₃-assisted nucleophilic substitution was first applied to a variety of?-O-4 and?-O-4 model compounds for the highly effective cleavage of different C-O bonds,including C-O_?-_OH,C_?-O/C_?-O and C_Me-O bonds?<0.5 h and>99%conversion for most cases?.Without any pretreatment,the substitution proceeds at room temperature in the absence of any catalyst,or additive,selectively affording phenols and important organic synthesis reagents,aromatic alkyl bromides,in high to excellent yields?up to 98%?.Preliminary studies also highlight the prospect of this method for the effective cleavage of different types of C-O bonds in acidolysis-extracted-pine lignin?AEPL?,a total 14 wt%yield of aromatic alkyl bromide,4-?1,2-dibromo-3-hydroxypropyl?benzene-1,2-diol?10?,has been obtained from lignin through this method.Moreover,the addition of formaldehyde during the process of extrating lignin can increase the amount of dichloromethane soluble lignin from 5 wt%?per wood?to 8 wt%,and the molecular weight?M_w?of pine lignin is increased from 1724g/mol?acidolysis-extracted-pine lignin?to 5021 g/mol?formaldehyde-extracted-pine lignin?FEPL??.BBr₃-assisted nucleophilic substitution was also applied to the FEPL,GPC traces showed obvious change among the molecular weight?M_w?of such lignin,reduced from5021 g/mol?before depolymerization?to 580 g/mol?after depolymerization?.