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Palladium-catalyzed lignin valorization: Towards a lignin-based biorefinery
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Synthetical Organic Chemistry.ORCID iD: 0000-0001-6543-7674
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work described in this thesis focuses on the cleavage of the β-O-4′ bond, which is the most abundant interunit linkage in the lignin polymer.

In the first part, three methods based on palladium catalysis have been developed and their applicability has been verified using lignin model compounds. A transfer hydrogenolysis of the β-O-4′ bond using formic acid as a mild hydrogen donor together with a base. An aerobic oxidation of the benzylic alcohol motif in the β-O-4′ linkage to generate a key intermediate in the cleavage reaction was performed. A redox neutral cleavage of the β-O-4′ bond was accomplished in which no stoichiometric reducing or oxidizing agents were added.

In the second part of the thesis, a mechanistic study is presented. The corresponding ketone from a dehydrogenation reaction of the benzylic alcohol motif was identified to be the key intermediate. This ketone and its enol tautomer was found to be responsible for the β-O-4′ bond cleavage reaction under the employed reaction conditions.

In the final part of this thesis, the methodologies have been applied to native lignin. The depolymerization reaction was combined with organosolv pulping. This approach was successful, and together with cellulose and hemicellulose, propenyl aryls were generated in excellent yields directly from wood. In this transformation, the lignin derived molecules have been reduced by an endogenous hydrogen donor from the wood.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1310
Keyword [en]
Lignin, Heterogeneous Catalysis, Palladium, Biomass, Depolymerization, Reduction, Oxidation, Biorefinery, Transfer Hydrogenolysis
National Category
Organic Chemistry Polymer Chemistry Wood Science
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-265315ISBN: 978-91-554-9393-6 (print)OAI: oai:DiVA.org:uu-265315DiVA: diva2:865155
Public defence
2015-12-14, B:22, Uppsala Biomedical Centre (BMC), Husargatan 3, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2015-11-23 Created: 2015-10-27 Last updated: 2016-01-13
List of papers
1. Mild Heterogeneous Palladium-Catalyzed Cleavage of beta-O-4 '-Ether Linkages of Lignin Model Compounds and Native Lignin in Air
Open this publication in new window or tab >>Mild Heterogeneous Palladium-Catalyzed Cleavage of beta-O-4 '-Ether Linkages of Lignin Model Compounds and Native Lignin in Air
Show others...
2014 (English)In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, no 1, 179-184 p.Article in journal (Refereed) Published
Abstract [en]

A mild and robust heterogeneous palladium-catalyzed CO bond cleavage of 2-aryloxy-1-arylethanols using formic acid as reducing agent in air was developed. The cleaved products were isolated in 92-98% yield; and by slightly varying the reaction conditions, a ketone, an alcohol, or an alkane can be generated in near-quantitative yield. This reaction is applicable to cleaving the -O-4-ether bond found in lignin polymers of different origin. The reaction was performed on a lignin polymer model to generate either the monomeric aryl ketone or alkane in a quantitative yield. Moderate depolymerization was achieved with native lignin at similar reaction conditions. Mechanistic studies under kinetic control indicate that an initial palladium-catalyzed dehydrogenation of the alcohol is followed by insertion of palladium to an enol equivalent. A palladium-formato complex reductively cleaves the palladium-enolate complex to generate the ketone.

Keyword
heterogeneous catalysis, cleavage reactions, green chemistry, palladium, polymers, lignin
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-220309 (URN)10.1002/cctc.201300540 (DOI)000330636800023 ()
Note

De två första författarna delar första författarskapet.

Available from: 2014-03-17 Created: 2014-03-12 Last updated: 2017-12-05Bibliographically approved
2. Selective Aerobic Benzylic Alcohol Oxidation of Lignin Model Compounds: Route to Aryl Ketones
Open this publication in new window or tab >>Selective Aerobic Benzylic Alcohol Oxidation of Lignin Model Compounds: Route to Aryl Ketones
2015 (English)In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 7, no 3, 401-404 p.Article in journal (Refereed) Published
Abstract [en]

A mild and chemoselective oxidation of the -alcohol in -O-4-ethanoaryl and -O-4-glycerolaryl ethers has been developed. The benzylic alcohols were selectively dehydrogenated to the corresponding ketones in 60-93% yield. A one-pot selective route to aryl ethyl ketones was performed. The catalytic system comprises recyclable heterogeneous palladium, mild reaction conditions, green solvents, and oxygen in air as oxidant. Catalytic amounts of a coordinating polyol were found pivotal for an efficient aerobic oxidation.

Keyword
biomass valorization, heterogeneous catalysis, lignin, oxidation, palladium
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-246820 (URN)10.1002/cctc.201402825 (DOI)000349147100005 ()
Available from: 2015-03-11 Created: 2015-03-10 Last updated: 2017-12-04Bibliographically approved
3. Mild and Robust Redox-Neutral Pd/C-Catalyzed Lignol -O-4 Bond Cleavage Through a Low-Energy-Barrier Pathway
Open this publication in new window or tab >>Mild and Robust Redox-Neutral Pd/C-Catalyzed Lignol -O-4 Bond Cleavage Through a Low-Energy-Barrier Pathway
2015 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 8, no 13, 2187-2192 p.Article in journal (Refereed) Published
Abstract [en]

A Pd/C catalyzed redox neutral CO bond cleavage of 2-aryloxy-1-arylethanols has been developed. The reactions are carried out at 80 degrees C, in air, using a green solvent system to yield the aryl ketones in near quantitative yields. Addition of catalytic amounts of a hydrogen source to the reaction mixture activates the catalyst to proceed through a low energy barrier pathway. Initial studies support a transfer hydrogenolysis reaction mechanism that proceeds through an initial dehydrogenation followed by an enol adsorption to Pd/C and a reductive CO bond cleavage.

Keyword
heterogeneous catalysis, lignin, palladium, reaction mechanisms, transfer hydrogenolysis
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-259649 (URN)10.1002/cssc.201500117 (DOI)000357619000004 ()25925736 (PubMedID)
Funder
Swedish Energy Agency
Available from: 2015-08-20 Created: 2015-08-10 Last updated: 2017-12-04Bibliographically approved
4. Selective Route to 2-Propenyl Aryls Directly from Wood by a Tandem Organosolv and Palladium-Catalysed Transfer Hydrogenolysis
Open this publication in new window or tab >>Selective Route to 2-Propenyl Aryls Directly from Wood by a Tandem Organosolv and Palladium-Catalysed Transfer Hydrogenolysis
2014 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 7, no 8, 2154-2158 p.Article in journal (Refereed) Published
Abstract [en]

A tandem organosolv pulping and Pd-catalysed transfer hydrogenolysis depolymerisation and deoxygenation has been developed. The tandem process generated 2-methoxy-4-(prop-1-enyl)phenol in 23 % yield (92 % theoretical monomer yield) starting from pine wood and 2,6-dimethoxy-4-(prop-1-enyl)phenol in 49 % yield (92 % theoretical monomer yield) starting from birch wood. Only endogenous hydrogen from wood was consumed, and the reaction was performed using green solvents.

Keyword
Biomass, Lignin Green, Chemistry, Palladium, catalysis
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-226637 (URN)10.1002/cssc.201402017 (DOI)000340519500016 ()
Funder
Swedish Energy Agency
Available from: 2014-06-18 Created: 2014-06-18 Last updated: 2017-12-05Bibliographically approved

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