Oxidative Spaltung von Lignin und Lignin-Modellverbindungen und Funktionalisierung der Spaltprodukte

  • Oxidative cleavage of lignin and lignin-model-compounds and functionalization of the cleavage products

Rinesch, Torsten; Bolm, Carsten (Thesis advisor); Albrecht, Markus (Thesis advisor)

1. Auflage. - München : Verlag Dr. Hut (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

The present dissertation titled „Oxidative Cleavage of Lignin and Lignin-Model-Compounds and Functionalization of the Cleavage Products“ deals with the investigation of a range of transition-metal catalyzed systems for the cleavage of lignin-model-compounds and the native lignin polymer. The biopolymer lignin is one of the main constituents of lignocellulosic biomass and is formed as the main side product in the industrial production of paper. Today, lignin is primarily used for the production of energy by direct combustion. In this instance the scientific valorization of the lignin polymer as are newable resource has gained more and more interest for the sustainable production of platform chemicals or new functional materials. Because of the structural complexity of the lignin polymer simplified compounds of low molecular weight such as 1,3-dilignol-b-O-4-lignin-model-compounds are applied instead. The use of such model systems enables an easier analysis and therefore offers a possibility for mechanistic investigations on the molecular level. In the first two projects the transition metal iron and a combination of copper/vanadium were utilized. Based on preliminary work of our group the projects were extended and finalized during this dissertation. The iron-catalyzed system is a combination of iron and different peroxides. In this case it was possible to extend the scope of the catalytic system to different b-O-4-lignin-model-compounds and two lignin polymer samples. The latter ones were successfully analyzed by 2D-NMR-HSQC und GPC analysis. Furthermore the methyl radical ∙CH3 was verified as the active radical species. The reactions with the copper/vanadium system offered insight into the reaction mechanism. Furthermore a reaction pathway was revealed by the use of substituted lignin-model-compounds. In addition, a correlation of the model studies and the cleavage of the biopolymer lignin could be achieved by analysis of the cleavage products with GC-MS. Three additional projects on the basis of the transition metals copper, cobalt and vanadium were investigated. Here, the copper system required an acidic additive, but only showed an overall low yield towards benzaldehyde derivatives. The transition metal cobalt was used in combination with the organic oxidizing agent N-hydroxyphthalimide. In this case no cleavage of the investigated b-O-4-bonds in bothlignin-model-compounds and lignin polymer samples could be obtained. The main resulting products were the a-oxidation products of these b-O-4-bonds. An extension of this project was studied by its transfer towards a heterogeneous catalytic system based on metal organic frameworks (MOF). Finally, avanadium catalyzed cleavage reaction with a consecutive functionalization of the resulting products was analyzed. Here the reaction was performed in a one-pot manner on simple monomeric b-1- and b-O-4-lignin-model-compounds towards benzimidazole type products.

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