Mechanism Of Lignin Model Compounds Oxidation Catalyzed By Co-salen Complex

Lignin is one of the main components in woody plants and the structure is very complex. It is difficuclt to master the main fracture modes of some chemical bonds during reaction process of natural lignin. In order to simplify research means to obtain useful information in lignin chemical structural changes, it is necessary to use lignin model compounds as objects mimicing natural lignin in structure and molecule.Due to the increasing demand of pollution control, green process becomes more and more important. The bleaching technology of ECF arid TCF is a trend, such as the novel process of Co-salen biomimetic catalytic delignification, due to the present servious pollution of pulp and paper industry, specially the hazardous chlorine-elemental bleacing.It is convenient and feasible to synthesize the Co-salen biomimetic catalyst,and the biomimetic system composed of Co-salen, pyridine, sodium hydroxide, peroxide and dioxygen. The substrates used for Co-salen biomimetic catalytic oxidation were lignin model compounds. Two polymeric and a dimeric lignin model compounds were synthesized and the degradation mechanism was studied during Co-salen biomimetic catalytic oxidation in this thesis. Conclusions as following:1) The optimum synthesis process condition and influential factors of polymeric guaiacyl-type lignin model compound linked byβ-O-4 were studied. The optimum condition of polymerization is:time 4.5h, temperature 55℃, mass concentration of bromoacetyl guaiacol in N,N-dimethyl formamide(DMF) 22%, mass ratio of potassium carbonate to bromoacetyl guaiacol 0.7; the optimum condition of reduction is:time 10h, temperature 40℃, mass concentration of unreduced polymer in dimethyl sulfoxide(DMSO) 1.6%, mass ratio of sodium borohydride to unreduced polymer 1.4. The influence of factors on polymerization:time> temperature> mass concentration of bromoacetyl guaiacol in DMF> mass ratio of potassium carbonate to bromoacetyl guaiacol; the influence of factors on reduction:mass concentration of unreduced polymer in DMSO> mass ratio of sodium borohydride to unreduced polymer> time> temperature.2) The reactions of guaiacyl-type lignin model polymer composed ofβ-O-4 linkages in Co-salen biomimetic catalytic oxidation:the main ways of lignin model polymer degradation were involved with demethylation, formation and opening of quinone-type structures, esterification of degraded products,oxidation ofαandβposition,Cβ-amination, condensation reaction and cleavage ofβ-O-4 and carbon-carbon in side-chain, producing benzaldehyde, acetophenone, phenylethanol, benzoic acid, catechol, aromatic ester, aliphatic low molecule, furan, nitrogen-containing compounds, compounds conjugated in side-chain and biphenyl.3) This thesis improved the synthetic method of intermediate product acetosyringone during the synthesis of syringyl lignin model polymer:DMF used as a reaction solvent and CuCl as a catalyst in the process of acetosyringone synthesis. The method of ice-water treatment and ethyl acetate extraction employed for acetosyringone posttreatment instead of DMF rotary evaporation.4) The reactions of syringyl lignin model polymer composed ofβ-O-4 linkages in Co-salen biomimetic catalytic oxidation:cleavages ofβ-O-4, carbon-carbon in side-chain and Cβ-Ar, and benzene ring opening, which favorable to fragmentation of polymeric lignin model coupound; benzoquinones degradation products were formed due to the attack of Co/O2 superoxo complex in biomimetic catalytic system; further esterification and etherification reactions resulted in the esterified and etherified products;nitrogenous products were obtained due to the amidation and amination; condensation of phenol-formaldehyde and benzene rings,etherificaton and esterification of phenolic hydroxyl, demethylation and demethoxylation were also involved during the catalytic oxidation reaction.5) The reactions of dimeric lignin model compound in Co-salen biomimetic catalytic oxidation:cleavage ofβ-O-4 and Cα-Cβlinkage bonds, arylring-opening, demethylation, esterification;condensation and epoxidation. Nitrogen and cobalt-containing products were detected out,such as 2-aminophenol,β-amino-4-hydroxy-3-methoxy phenylethanol and 1,2,3,4,5-pentamethyl Cobaltocene.