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12 results on '"Bährle, Christian"'

2. Formation, Structure, and Reactivity of Organic Radicals in Lignin and its Depolymerization Products

Author

Bährle, Christian, Wokaun, Alexander, and Jeschke, Gunnar

Subjects
LIGNIN (NATURAL SUBSTANCES), CRACKING + DEGRADATION REACTIONS (CHEMICAL REACTIONS), REACTION MECHANISMS + REACTIVITY (CHEMICAL KINETICS), KRACKEN + SPALTUNGSREAKTIONEN + ABBAUREAKTIONEN (CHEMISCHE REAKTIONEN), DENSITY FUNCTIONALS (QUANTUM CHEMISTRY AND QUANTUM MECHANICS), RADIKALE (CHEMIE), RADICALS (CHEMISTRY), PYROLYSIS (CHEMICAL ENGINEERING), Chemical engineering, DICHTEFUNKTIONALE (QUANTENCHEMIE U. QUANTENMECHANIK), ddc:660, LIGNIN (NATURSTOFFE), PYROLYSE (CHEMISCHE VERFAHRENSTECHNIK), REAKTIONSMECHANISMEN + REAKTIVITÄT (CHEMISCHE KINETIK), FOS: Chemical engineering
Published
2016
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10. High-Field Electron ParamagneticResonance and DensityFunctional Theory Study of Stable Organic Radicals in Lignin: Influenceof the Extraction Process, Botanical Origin, and Protonation Reactionson the Radical gTensor.

Author

Bährle, Christian, Nick, Thomas U., Bennati, Marina, Jeschke, Gunnar, and Vogel, Frédéric

Subjects
*LIGNINS, *ELECTRON paramagnetic resonance, *DENSITY functional theory, *RADICALS (Chemistry), *EXTRACTION (Chemistry), *PROTON transfer reactions
Abstract

The radical concentrations and gfactors of stableorganic radicals in different lignin preparations were determinedby X-band EPR at 9 GHz. We observed that the gfactorsof these radicals are largely determined by the extraction processand not by the botanical origin of the lignin. The parameter mostlyinfluencing the gfactor is the pH value during ligninextraction. This effect was studied in depth using high-field EPRspectroscopy at 263 GHz. We were able to determine the gxx, gyy, and gzzcomponentsof the gtensor of the stable organic radicals in lignin.With the enhanced resolution of high-field EPR, distinct radical speciescould be found in this complex polymer. The radical species are assignedto substituted o-semiquinone radicals and can existin different protonation states SH3+, SH2, SH1-, and S2-. The proposed model structuresare supported by DFT calculations. The gprincipalvalues of the proposed structure were all in reasonable agreementwith the experiments. [ABSTRACT FROM AUTHOR]

Published
2015
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12. Aliphatic Long‐Chain C20Polyesters from Olefin Metathesis

Author

Trzaskowski, Justyna, Quinzler, Dorothee, Bährle, Christian, and Mecking, Stefan

Abstract

Self‐metathesis of undecenoic acid with [(PCy3)2Cl2RuCHPh] (2), followed by exhaustive hydrogenation yielded pure 1,20‐eicosanedioic acid (5) (>99%) free of side‐products from isomerization. Polycondensation with eicosane‐1,20‐diol (6), formed by reduction of the diol, yielded polyester 20,20 (Tm= 108 °C). By comparison, the known ADMET polymerization of undec‐10‐enyl undec‐10‐enoate (7), and subsequent exhaustive polymer‐analogous hydrogenation yielded a polyester (poly‐8) with irregular structure of the ester groups in the polymer chain (O(CO) vs. C(O)O) (Tm= 103 °C). Hydrogenation of secondary dispersions of poly‐7yielded aqueous dispersions of the long‐chain aliphatic polyester poly‐8.

Published
2011
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