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Green Chemistry
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organic layer was separated and dried with anhydrous Na2SO4 application, we could potentially benefit financially from the
and concentrated under vacuum. The crude product was technology discussed in this manuscript.DOI: 10.1039/D0GC03597A
purified by column chromatography on silica gel (hexane/ethyl
acetate = 2/1) to produce 1c (4.8 g, 14.4 mmol) as a white solid
Acknowledgements
This material is based upon work supported by the Great Lakes
in 75% yield.
1H NMR (500 MHz, CDCl3): 7.73 (dd, J = 8.3, 2.0 Hz, 1H), 7.66 (d,
J = 2.0 Hz, 1H), 7.02 (t, J = 8.4 Hz, 1H), 6.90 (d, J = 8.4 Hz, 1H),
6.59 (d, J = 8.5 Hz, 2H), 5.16 (s, 2H), 3.95 (d, J = 1.8 Hz, 6H), 3.82
(s, 6H); 13C NMR (126 MHz, CDCl3): 193.7, 153.4, 153.3, 153.2,
148.9, 136.6, 128.3, 124.0, 123.0, 110.6, 110.0, 105.2, 105.2,
75.2, 56.0, 56.0, 56.0, 55.9. Spectral data are in accordance with
those previously reported.38
Bioenergy Research Center, U.S. Department of Energy, Office
of Science, Office of Biological and Environmental Research
under Award Number DE-SC0018409. The authors gratefully
acknowledge Casey Johnny and Tony Schilmiller in the Research
Technology Support Facility at Michigan State University for the
GC-MS and LCMS-TOF analyses. ZF thanks Nicholas Schlecht for
help in performing selected reactions and Dr. Asmaul Hoque at
UW-Madison for running the cyclic voltammetry of 2,2’-
dithiodiethanol (Fig. S31).
Oxidation of Cu-AHP lignin
Lignin from alkaline pre-extracted hybrid poplar was isolated via
the Cu-AHP pretreatment process as previously described using
1 mM of copper and 2 mM of bipyridine.49 Hydrogen peroxide
(H2O2, 100 mg per g of biomass) was added in 10 equal aliquots
at 1 h intervals while shaking at 30 °C. DDQ-catalyzed oxidation
of Cu-AHP lignin was performed following a previous literature
Notes and references
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report.10 Briefly,
3 g of lignin was solubilized in 1,2-
dimethoxyethane/2-ethoxyethanol (v/v = 3:2, 42 mL) and then
DDQ (10 wt%) and t-BuONO (10 wt%) were added. The solution
o
was heated at 80 C overnight under an oxygen atmosphere.
The oxidized lignin product (ligninox) was precipitated by
addition of 500 mL of diethyl ether, isolated by filtration,
washed with additional diethyl ether (200 mL) and dried in
vacuo, yielding 2.7 g of light-brown ligninox was obtained.
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General procedure for thio-assisted electrolysis of ligninox
Reactions were conducted at room temperature in an H-type
electrochemical cell (separated by a Nafion 117 membrane)
with 20 mL of pH 8 phosphate buffer and 20 mL of pH phosphate
8 buffer/isopropanol in the anodic and cathodic cell, in which a
platinum wire was used as the anode and the reticulated
vitreous carbon (RVC) was employed as the cathode,
respectively. A mixture of LiBF4 (100 mg) and BHT (100 mg) was
added into the cathodic cell. After 1 h of pre-electrolysis at 20
mA (current density = 10 mA/cm2), ligninox (100 mg) and 2,2’-
dithiodiethanol (RSSR, 100 mg) were added to the catholyte and
the reaction continued at 20 mA for an additional 6 h. The
solvent was removed under a N2 flow, and the crude product
was solubilized in 20 mL EtOAc/water (1:1, v/v). The solution
was acidified with 60% H2SO4 to pH 2, precipitating insoluble
material. The precipitate was filtered, washed with water, dried
in vacuo and the remaining filtrate was extracted with 30 mL
EtOAc (3 x). The organic layers were combined, dried with
anhydrous Na2SO4 and concentrated in vacuo. In the parallel
control reaction, all set-up and work-up protocols were the
same except that the RSSR and BHT components were omitted.
17. P. R. Patwardhan; R. C. Brown; B. H. Shanks, ChemSusChem,
2011, 4 (11), 1629-1636.
Conflicts of interest
18. P. J. Deuss; K. Barta, Coord. Chem. Rev., 2016, 306, 510-532.
19. S. K. Hanson; R. T. Baker, Acc. Chem. Res., 2015, 48 (7), 2037-
2048.
A patent application has been submitted by E. L. Hegg, J. E.
Jackson, and G. E. Klinger (Methods for Lignin Depolymerization
Using Thiols - WO/2018/195000). As holders of this patent
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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