Valorization of Lignin
M2 Watanabe
11/30/2017

1.Introduction
2.Chemical degradation
2-1. aryl C-O bond cleaverage of lignin
Hartwig’ work
2-2. alkyl C-O bond cleaverage of lignin
3. Problem of lignin separation

Introduction 1• Petroleum supplies are finite.
• utilization of biomass mitigates the release of greenhouse gas emissions.

（https://ja.wikipedia.org/wiki/地球温暖化）

David Martin Alonso, Jesse Q. Bond and James A. Dumesic. Green Chem., 2010, 12, 1493

Introduction 2• Lignin utilization is to burn it directly for the production of heat and electricity.
David Martin Alonso, Jesse Q. Bond and James A. Dumesic. Green Chem., 2010, 12, 1493

Introduction 4extraction• 50% of its components are aromatic hydrocarbons
which can be a potentially attractive source offuels and chemicals• Research on lignin deconstruction has recently
become the center of interest.
• No selective C-O bond cleavage with hydrogen.
Fedorov,
A.; Toutov,
A.Swisher,A.; Swisher,
N.Grubbs,A.; Grubbs,H. Chem.
2013,
4, 1640
Fedorov,A.; Toutov,A. A.;
N. A.;
R. H.R.Chem.
Sci. Sci.
2013,
4, 1640

Strategy of chemical depolymerization

α- O-4 (3-12%)

45-62%

Strategy 1• β-O-4motif is the most prevent in native lignin

Strategy 2

2-1. aryl C-O bond cleaverage of lignin
Hartwig’ work

Difficulty of selective hydrogenolysis of aromatic C-O bond

E. M. Van Duzee, H. Adkins, J. Am. Chem. Soc. 57, 147 (1935).
• Cleavage of C-O bond need high temperature and occur with poor selectivity.

A. Maercker, Angew. Chem. Int. Ed. Engl. 26, 972 (1987).
• Expensive and difficult to conduct on a large scale.

History of aryl C-O cleavage reaction① Wenkert’s Pioneer work ~unprecedent OMe replacement~•••

Simple phenyl ethers afforded low yields .
No reaction occurred with ortho substitution (strong stericeffect).
Alkyl Grignard with β-hydrogens.

Wenkert, E.; Michelotti, E. L.; Swindell, C. S. J. Am. Chem. Soc.1979, 101, 2246
② Dankwardt extended the scope of this reaction.
•••

Better σ donor was favorable.
Non-π extended conjugation, phenols,Alcohols, amines, N-heterocycles

Dankwardt, J. W. Angew. Chem., Int. Ed. 2004, 43, 2428
③ Chatani and Tobisu extended the scope of ketone and ester.
••Tolerance of functional group,
such as ketones and esters.
A base and bulky and electronrich Phosphine ligand wereessential.

Smiasaki, T.; Tobisu, M.; N. Chatani, N. Angew. Chem. Int. Ed. 2008, 47, 4866

First catalytic reductive cleavage of aryl C-O bond

< Initial proposed mechanism>< isotope labeling experiment>• An alternative to alkali metal• Ester, amide, acetal, tertiary amine,heterocycle could all be tolerated.
• Simple anisole needed ortho-directinggroup.
Alvarez-Bercedo, P.; ;Martin, R. J. Am. Chem. Soc. 2010, 132, 17352

Hartwig’s work ~Nickel-catalyzed hydrogenolysis of Aryl Ether~ 1Harsh condition lead to reduction of catalyst itself.
More tight ligand was necessary.
Sergeev, A. G.; Hartwig, J. F. Science 2011, 332, 439−443

Hartwig’s work ~Nickel-catalyzed hydrogenolysis of Aryl Ether~ 2• Excess base is needed fordesired reactivity.

• AlMe3 is needed toactivate C-O(alkyl)• relative reactivity was found to be Ar−OAr> Ar−OMe > ArCH2−OMe

Sergeev, A. G.; Hartwig, J. F. Science 2011, 332, 439−443

Hartwig’s work ~Nickel-catalyzed hydrogenolysis of Aryl Ether~ 3Hartwig validated the synthetic utility on depolymerization of lignin model.
but the catalyst loading and temperature for the current reaction are too highfor the reaction to be applicable on a large scalethese reported molecular catalysts are sensitive to large concentrations ofwater, which is costly to separate from raw biomass.
Sergeev, A. G.; Hartwig, J. F. Science 2011, 332, 439−443

Mechanism of Ni-NHC Catalyzed Hydrogenolysis of Aryl Ethers

Since the mechanism above does not require H2 forthe conversion of aryl ether to arene, the catalytic
trials were also performed in the absence of H2; <5%conversion was observed.

Inactive
Ni catalyst
Cornella, J; Zarate, C.; Martin, R. J. Am. Chem. Soc.
2013. 135. 1997
Kelley, P.; Lin, S.; Edouard, G.; Day, M. W.; Agapie, T. J. Am. Chem. Soc. 2012, 134, 5480−5483

Mechanism of Ni-NHC Catalyzed Hydrogenolysis of Aryl Ethers 3

rate-determining oxidative addition of the C−O bond takes place to afford a new andstable [NiII(NHCpr)(Ot Bu) (Ph)(OPh)]− intermediate
Liping Xu†, Lung Wa Chung*‡, and Yun-Dong Wu. ACS Catal. 2016, 6, 483−493

Mechanism of Ni-NHC Catalyzed Hydrogenolysis of Aryl Ethers 2delocalize the more negative charge on
the oxygen atom and reduce electronic
repulsion between the filled Ni dorbital and the filled O lone pair.

Liping Xu†, Lung Wa Chung*‡, and Yun-Dong Wu. ACS Catal. 2016, 6, 483−493

Summary 1• In the field of cleavage of aryl ether, Ni is very promising.
• Hartwig achieved selective cleavage of aromatic C-O bonds using metal and thecheap, mild, and atom-economical reductant hydrogen .
• but the catalyst loading and temperature for the current reaction are too high forthe reaction to be applicable on a large scale2-2. alkyl C-O bond cleaverage of lignin→Stahl’s work

Strategy 245-62%

Ellman and Bergman Lignin C-O bond cleavage with Ru

RuH2(CO)(PPh3)3 is known to be competent for both Dehydrogenation and C-O activation
chemistry and was chosen as the starting point for catalyst development.

Jason M. Nichols, Lee M. Bishop, Robert G. Bergman,* and Jonathan A. Ellman*J. AM. CHEM.
SOC. 2010, 132, 12554–12555

Ellman and Bergman Lignin C-O bond cleavage with Ru 2

<Mechanism study>

Jason M. Nichols, Lee M. Bishop, Robert G. Bergman,* and Jonathan A. Ellman*J. AM. CHEM.
SOC. 2010, 132, 12554–12555

This method can not be applied to real β-O-4 linkage

Adam Wu, Brian O. Patrick, Enoch Chung and Brian R. James*, Dalton Trans., 2012, 41, 11093–11106

Adam Wu, Brian O. Patrick, Enoch Chung and Brian R. James*, Dalton Trans., 2012, 41, 11093–11106

Toste’s Lignin C-O bond cleavage with Vanadium

O2 is needed because underN2 condition, catalyst 11
precipitated to become 12

Sunghee Son and F. Dean Toste*. Angew. Chem. Int. Ed. 2010, 49, 3791 –3794

Toste’s Lignin C-O bond cleavage with Vanadium 2Almost SM

Sunghee Son and F. Dean Toste*. Angew. Chem. Int. Ed. 2010, 49, 3791 –3794

Toste’s Lignin C-O bond cleavage with Vanadium 3

Sunghee Son and F. Dean Toste*. Angew. Chem. Int. Ed. 2010, 49, 3791 –3794

Stahl’s Chemoselective aerobic alcohol oxidation in lignin

Alireza Rahimi,† Ali Azarpira,‡ Hoon Kim,‡ John Ralph,‡ and Shannon S. Stahl*
J. Am. Chem. Soc. 2013, 135, 6415

Joseph C. Qiu, Priya P. Pradhan, Nyle B. Blanck, James M. Bobbitt,* and William F. Bailey*.
ORGANIC LETTERS 2012 Vol. 14, No. 1 350–353

Stahl’s Chemoselective aerobic alcohol oxidation in lignin 2• Electron rich substrates
afforded higher yields.
• Phenol did not disturb thisreaction.
• this oxidation method also
exhibits good reactivity andsimilar chemoselectivity
with real lignin

Alireza Rahimi,† Ali Azarpira,‡ Hoon Kim,‡ John Ralph,‡ and Shannon S. Stahl*
J. Am. Chem. Soc. 2013, 135, 6415

Stephenson’s photoredox strategy for lignin degradation.

John D. Nguyen,‡ Bryan S. Matsuura,‡ and Corey R. J. Stephenson. J. Am. Chem. Soc. 2014,
136, 1218−1221

Stephenson’s photoredox strategy for lignin degradation 2

John D. Nguyen,‡ Bryan S. Matsuura,‡ and Corey R. J. Stephenson. J. Am. Chem. Soc. 2014, 136,1218−1221

Stahl’s Depolymerization of oxidized lignin (Redox-neutral cleavage)

23456

Absence of a reducing metal showed good result.
Even better yields with 3eq NaCO2H.
Alireza Rahimi1 , Arne Ulbrich1 , Joshua J. Coon1,2 & Shannon S. Stahl, Nature, 515 , 249 (2014)

Depolymerization of oxidized lignin (Redox-neutral cleavage) 2

Syringyl

Guaniacyl• Unoxidized lignin in the reaction resulted in only 7.2wt% yield.
Alireza Rahimi1 , Arne Ulbrich1 , Joshua J. Coon1,2 & Shannon S. Stahl, Nature, 515 , 249 (2014)

Depolymerization of oxidized lignin (Redox-neutral cleavage) 3• KH/KD = 9.3 ± 0.2• Oxidation may be attributed to E2 elimination reaction.
• This mechanism accounts for the effect of buffered reaction medium.
Alireza Rahimi1 , Arne Ulbrich1 , Joshua J. Coon1,2 & Shannon S. Stahl, Nature, 515 , 249 (2014)

Problem of lignin separation

problem during biomass pretreatment processes<interunit C-C bond>Interunit C-C bond formed through lignin extraction inhibit lignin depolymerization.

Formaldehyde inhibit interunit C-C bond .

L. Shuai, M. Talebi Amiri, Y. M. Questell-Santiago, F. H8roguel, Y. Li, H. Kim, R. Meilan, C. Chapple, JRalph, J. S. Luterbacher, Science 2016, 354, 329– 333

Formaldehyde inhibit interunit C-C bond 2 .

L. Shuai, M. Talebi Amiri, Y. M. Questell-Santiago, F. H8roguel, Y. Li, H. Kim, R. Meilan, C. Chapple, J.
Ralph, J. S. Luterbacher, Science 2016, 354, 329– 333

Summary• Lignin deporymerization method have developed rapidly for ten years.
• Hartwig developed reductive C(sp2)-O bond cleavage.
• Stahl method showed highest monomer yield from real lignin from• Main problem now is how to separate lignin from lignocelloce.