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Production and transformation of organic compounds from renewable feedstock: Catalytic approaches
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on the development of strategies for lignocellulosic biomass valorization. The thesis consists of two parts.

The first part of the presented work is related to the catalytic fractionation of biomass (lignin-first approach) and the production of monomeric compounds from lignocellulose. In the first project (Chapter 2) we have established a process to study the transformations occurring during the catalytic organosolv pulping of wood in the presence of Pd/C. This was achieved by performing a fractionation under continuous-flow conditions. In the designed process, the pulping and the transition metal catalyzed reactions were separated in space and time. Thus, the role of the solvolysis and the transfer hydrogenation reactions were studied independently. We discovered that during the solvolysis of wood, a substantial amount of monomeric lignin fragments are released into the solution. The main role of the catalyst is to stabilize these monomers and prevent their repolymerization. Based on the obtained knowledge we developed a new version of the lignin-first approach (Chapter 3). In this process zeolites were used as shape-selective catalysts. We have demonstrated that by tuning the size of pores of the catalyst the undesirable bimolecular reactions can be minimized. Furthermore, the released monomers can be converted into stable products via transfer hydrogenation reactions.  

The second part is related to studies of dimeric and trimeric lignin model compounds. In Chapter 4, the reactivity of the dibenzodioxocin motif, which is considered a main branching point in the lignin structure has been investigated. We have designed a protocol for the catalytic reductive cleavage of lignin model compounds representing this motif, in the presence of Pd/C and benign hydride donors. The cleavage of the dibenzodioxocin structure results in the formation of dimeric biaryl compounds. Unlike monomers, the valorization of lignin-derived dimers is less studied. The last chapter is focused on the transformation of biaryls into highly functionalized synthetic building blocks. This was achieved via a visible light induced dearomative spirolactonization of biaryl carboxylic acids. The synthetic value of the obtained products was demonstrated by the conversion of the products into more complex structures.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2020. , p. 70
Keywords [en]
Lignin, biomass, lignin-first, catalytic fractionation, flow reactors, dibenzodioxocin, silanes, zeolites, visible light photocatalysis, dearomatization, spirolactones
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-179101ISBN: 978-91-7911-028-4 (print)ISBN: 978-91-7911-029-1 (electronic)OAI: oai:DiVA.org:su-179101DiVA, id: diva2:1394250
Public defence
2020-05-27, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2020-05-04 Created: 2020-02-18 Last updated: 2020-05-25Bibliographically approved
List of papers
1. Pd/C-Catalyzed Hydrogenolysis of Dibenzodioxocin Lignin Model Compounds Using Silanes and Water as Hydrogen Source
Open this publication in new window or tab >>Pd/C-Catalyzed Hydrogenolysis of Dibenzodioxocin Lignin Model Compounds Using Silanes and Water as Hydrogen Source
2017 (English)In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 5, p. 3726-3731Article in journal (Refereed) Published
Abstract [en]

A mild Pd/C-catalyzed hydrogenolysis of the C-O bond of model Compounds representing the dibenzodioxocin motif in lignin using polymethylhydrosiloxane (PMHS) and water as hydrogen sources was developed. The efficiency of the reaction is highly dependent on both water Concentration and the addition of a base. The results from mechanistic studies showed that the benzylic C-O bond is cleaved faster than the terminal C-O bond, which only cleaves upon the presence of the neighboring phenol. We propose a hydrogen bond formation between an oxygen atom of an ether group and a proton of a neighboring phenol under the employed mild reaction Conditions, which facilitates cleavage of the C-O bond.

Keywords
Biomass, Lignin, Dibenzodioxocin, PMHS, Hydrogenolysis, Palladium
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-143457 (URN)10.1021/acssuschemeng.7b00428 (DOI)000400634900017 ()
Available from: 2017-06-07 Created: 2017-06-07 Last updated: 2020-03-05Bibliographically approved
2. Lignin depolymerization to monophenolic compounds in a flow-through system
Open this publication in new window or tab >>Lignin depolymerization to monophenolic compounds in a flow-through system
Show others...
2017 (English)In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 19, no 24, p. 5767-5771Article in journal (Refereed) Published
Abstract [en]

A reductive lignocellulose fractionation in a flow-through system in which pulping and transfer hydrogenolysis steps were separated in time and space has been developed. Without the hydrogenolysis step or addition of trapping agents to the pulping, it is possible to obtain partially depolymerized lignin (21 wt% monophenolic compounds) that is prone to further processing. By applying a transfer hydrogenolysis step 37 wt% yield of lignin derived monophenolic compounds was obtained. Pulp generated in the process was enzymatically hydrolyzed to glucose in 87 wt% yield without prior purification.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-151203 (URN)10.1039/c7gc02731a (DOI)000417756500003 ()
Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2020-03-05Bibliographically approved
3. Functionalized spirolactones by photoinduced dearomatization of biaryl compounds
Open this publication in new window or tab >>Functionalized spirolactones by photoinduced dearomatization of biaryl compounds
Show others...
2019 (English)In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 10, no 12, p. 3681-3686Article in journal (Refereed) Published
Abstract [en]

The idea of using biaryl structures to generate synthetic building blocks such as spirolactones is attractive because biaryl structures are abundant in biomass waste streams. However, the inertness of aromatic rings of biaryls makes it challenging to transform them into functionalized structures. In this work, we developed photoinduced dearomatization of nonphenolic biaryl compounds to generate spirolactones. We demonstrate that dearomatization can be performed via either aerobic photocatalysis or anaerobic photooxidation to tolerate specific synthetic conditions. In both pathways, dearomatization is induced by electrophilic attack of the carboxyl radical. The resulting spirodiene radical is captured by either oxygen or water in aerobic and anaerobic systems, respectively, to generate the spirodienone. These methods represent novel routes to synthesize spirolactones from the biaryl motif.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-168611 (URN)10.1039/c8sc05476b (DOI)000463759100026 ()30996963 (PubMedID)
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2020-02-25Bibliographically approved
4. Zeolite-assisted lignin-first fractionation of lignocellulose: Overcoming lignin recondensation via shape-selective catalysis
Open this publication in new window or tab >>Zeolite-assisted lignin-first fractionation of lignocellulose: Overcoming lignin recondensation via shape-selective catalysis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Organosolv pulping releases reactive monomers from both lignin and hemicellulose via the cleavage of weak C–O bonds. These monomers recombine to form undesired polymers through the formation of recalcitrant C–C bonds. Different strategies have been developed to prevent this process by stabilising the reactive monomers (i.e., lignin-first approaches). To date, all reported approaches rely on the addition of capping agents or metal-catalysed stabilisation reactions, which usually require high pressures of hydrogen gas. Herein, we report a metal- and additive-free approach that uses zeolites as acid catalysts to convert the reactive monomers into more stable derivatives under organosolv pulping conditions. Experiments with model lignin compounds showed that the recondensation of aldehydes and allylic alcohols produced by the cleavage of β-O-4′ bonds was efficiently inhibited by the use of protonic BETA zeolite. By applying a zeolite with a preferred pore size, the bimolecular reactions of reactive monomers were effectively inhibited, resulting in stable and valuable monophenolics. The developed methodology was further extended to birch wood to yield monophenolic compounds and value-added products from carbohydrates.

Keywords
zeolites, lignin, biomass, shape-selective catalysis
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-179100 (URN)
Available from: 2020-02-18 Created: 2020-02-18 Last updated: 2020-03-05Bibliographically approved

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