Oxidative Lignin-Spaltung und die Verwertung der resultierenden Produkte

Abstract

The presented thesis aimed at finding reactions that would leave to the oxidative cleavage of Lignin. An abundant structural motive in the very heterogenic composition of Lignin is the aromatic ring. Cyclohexylbenzene and Veratrole alcohol were used as model compounds. Ozonolysis of these compounds in ionic liquids (ILs) as solvent and in common solvents did not lead to aromatic cleavage. Furthermore Potassium persulfate and Rutheniumtetroxid (RuO4) have been used. Optimized reaction conditions, using Ruthenium(III) chloride as catalyst, Sodium hypochlorite as oxidizing agent and Acetonitrile/Water as solvent could be found. A third solvent, e.g. DCM was only needed, when the starting material was insoluble in CH3CN/H2O. If this reaction was allowed to run 70 hours or more, the starting material Veratrole alcohol reacted to the supramolecule Cyclotriveratrylene (CTV). To my knowledge this is the first alkaline reaction to yield CTV. It was tried to optimize this reaction and to use it on different starting materials. 4-(Tert-butoxymethyl)-1,2-dimethoxybenzene yielded CTV up to 80 %. Butyl (3,4-dimethoxybenzyl)carbamate did not react under the applied conditions. 3,4-Dimethoxybenzyl methyl carbonate yielded its dimer. 3,4-Dimethoxybenzyl 3,5-Dinitrobenzoate and (3,4-Dimethoxyphenyl) methanamine each yielded a mixture of products with different ratios of Veratraldehyde, Veratrole alcohol and 1,2-Dimethoxybenzene.The experiment oxidative cleavage of (1S,2R)-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol as a model compound with Manganese based catalysts failed.Additionally this thesis aimed at transforming the Lignin cleavage products to more valuable chemicals. Electron-rich arenes were successfully sulfenylated by silver catalysts. Guaiacol was successfully iodinated with Barluenga reagent and subsequently cross-coupled in a one-pot reaction.1,3-Dimethylimidazolium dimethyl phosphate ([DMIM]DMP) and 1-Ethyl-3-methylimidazolium acetate ([EMIM]Ac) solve biomass quite well. Therefore these ILs could be used in a biomass disintegration process. For this purpose the ILs need to show great long-term stability at high temperatures. Tests to examine the long-term stability over 3 months have been conducted in collaboration with the AVT. Although the large majority of the probes kept their ability to disintegrate biomass at the end of the test, signs of aging, shown in NMR, IR and Raman spectra, make an economic deployment less likely