Oxidized Lignin Depolymerization using Formate Ionic Liquid as Catalyst and Solvent

Article abstract of DOI:10.1002/cctc.201700632

Lignin has been widely studied as a sustainable source of renewable materials, particularly aromatic feedstock chemicals, which are in great and increasing need in the world. Lignin oxidation and depolymerization presents a promising approach to functionalized phenolic products. In this work, a novel oxidative degradation of lignin using a formate ionic liquid was investigated resulting in ethyl acetate soluble and also water-soluble depolymerized lignin products. The β-O-4 bonds in lignin were oxidized and then depolymerized by a recyclable ionic liquid, 2-hydroxy ethylammonium formate. 2-Hydroxy ethylammonium formate, which could dissolve lignin acting as a solvent, was found to also catalyze the depolymerization of the oxidized lignin. The lignin depolymerization products were characterized.

Full text of DOI:10.1002/cctc.201700632

Accepted Article
Title: Oxidized lignin depolymerisation using formate ionic liquid as
catalyst and solvent
Authors: Jinhuo Dai, Antonio Patti, Lionel Longé, Gil Garnier, and Kei
Saito
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201700632
Link to VoR: http://dx.doi.org/10.1002/cctc.201700632
A Journal of
www.chemcatchem.org

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
Oxidized lignin depolymerisation using formate ionic liquid as
catalyst and solvent
Jinhuo Dai,[a] Antonio F. Patti,* [a] Lionel Longé,[a] Gil Garnier,[b] and Kei Saito*[a]
[
3,9,10]
Abstract: Lignin has been widely studied as a sustainable source of
renewable materials, particularly aromatic feedstock chemicals, which
are in great and increasing need in the world. Lignin oxidation and
depolymerisation presents a promising approach to functionalized
phenolic products. In this work, a novel oxidative degradation of lignin
using a formate ionic liquid was investigated resulting in ethyl acetate
soluble and also water-soluble depolymerised lignin products. The β-
O-4 bonds in lignin were oxidized and then depolymerised by a
recyclable ionic liquid, 2-hydroxy ethylammonium formate. 2-Hydroxy
ethylammonium formate, which could dissolve lignin acting as a
solvent, was found to also catalyse the depolymerisation of the
oxidised lignin. The lignin depolymerisation products were
characterized.
depolymerisation.
Lignin oxidation, compared to other
methods, showed high selectivity and efficiency of lignin
depolymerisation to yield specific products. [6,11] The reported
products are mainly phenolic with low molecular weight, which
can be potentially used as a source for producing valuable fine
chemicals. [
2,8,12]
Various oxidation methods including enzyme-
based oxidation, biomimetic oxidation and metal complex-
catalyzed oxidation have been developed during the past
[
9,13,14]
decades.
Some of these methods have reported an
oxidation mechanism targeting the specific β-O-4 bonds, which
are the most abundant linkages in lignin. Stahl et al. [15] proposed
a mechanism involving the initial aerobic oxidation of alcohol
groups in lignin catalysed by TEMPO catalyst (Scheme 1). Further
depolymerisation requires other catalysts to react with the
oxidized lignin to produce low molecular weight molecules using
this oxidation method.
Introduction
Sustainable raw materials, such as biomass, are an important
feedstock source to produce green energy and fine chemicals.
Lignocellulose, which contains 25-35% lignin, 30-50% cellulose
and 20-35% hemicellulose, has been utilized for many
applications, such as production of fine chemicals, functional
paper, and fuel. [1,2,3] Compared to cellulose and hemicellulose,
lignin is different due to its high content of aromatic rings in the
structure, and hence provides the widest, cheapest and most
sustainable source of phenolics for fine chemicals. [3,4,5] However,
most of the lignin currently produced by the paper and pulp
industries is still simply used for energy production.
The utilization of lignin has been studied for decades and many
different approaches to lignin valorization have been explored.
However, selective depolymerisation of lignin to produce well-
defined chemicals remains very challenging due to the complex
structure of lignin. [3,6,7] Numerous studies focused on lignin
depolymerisation, have reported lignin catalytic cracking,
Scheme 1. Proposed catalytic cycle for TEMPO oxidation of alcohols. [15]
Stahl’s group showed that lignin could be depolymerised with
formic acid and sodium formate after TEMPO’ (4-acetamido-
[16]
TEMPO)/O
2
catalysed oxidation.
This reaction yielded about
hydrolysis,
reductive
depolymerisation,
and
oxidative
61% of low molecular weight products (ethyl acetate soluble
products), in which some monomeric and oligomeric aromatics
were detected by high performance liquid chromatography
(HPLC).
[
a]
b]
Mr. Jinhuo Dai, Mr. Lionel Longé, A/Prof. Antonio F. Patti, and Dr.
Kei Saito
School of Chemistry
Ionic liquids (ILs), known as “designer solvents”, have been
applied for lignin extraction and depolymerisation due to the high
solubility of some lignins and lignocellulose biomass in ILs. They
also offer other advantages such as recyclability and non-
flammability. [12,17,18] Some studies have demonstrated a change
of the lignin structure following the treatment in ionic liquids, which
made lignin fragments smaller and hence easier to depolymerise.
Monash University
Clayton VIC 3800, Australia
E-mail: kei.saito@moansh.edu, tony.patti@moansh.edu
Prof. Gil Garnier
Department of Chemical Engineering
Monash University
[
Clayton VIC 3800, Australia
Supporting information for this article is given via a link at the end of
the document.
[
3,8,17]
Our group has previously developed
a pathway to
depolymerise lignin in 1-ethyl-3-methylimidazolium
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
xylenesulfonate [emim][ABS] involing redistribution mechanism.
organosolv lignin, alkali soluble lignin and kraft lignin were
selected for screening the depolymerisation reaction. A methanol
separation method was presented in our previous work. [27]
[
19,20]
Additionally, oxidative lignin fragmentation in ionic liquids has
also been investigated. Our group has recently reviewed the
developments in lignin oxidation [ and depolymerisation utilising
ionic liquids such as 1-butyl-3-methylimidazolium chloride
12]
[
21,22]
(
(
[bmim][Cl])
[Et N][i-PrNHC
dialkylimidazolium-based ionic liquid ([C
im]Br). [24,25]
, amine-sulfonate functionalized ionic liquids
[
23]
4
3
SO
3
],[Et
4
N][Me
2
NC
4
3
SO ])
and
and
4 1 3
C im]MeSO
4 1
[C C
In this study, we have applied a formate ionic liquid to function as
a catalyst and also as a solvent for lignin depolymerisation. This
formate ionic liquid was previously reported and is easy to
synthesize. [26]
Here, we test the hypothesis that an ionic liquid involving formate
can effect the depolymerisation of lignin if combined with an
oxidant, analogous to the depolymerisation (Scheme 2) reported
by Stahl et al[15,16]
liquid is that it can be recovered by conventional distillation.
. Another advantageous feature of this ionic
[
23]
First, several oxidation methods such as TEMPO’ (4-acetamido-
TEMPO) mediated oxidation and Fe(TAML)Li catalysed oxidation
were investigated to oxidise the benzylic alcohol structural moiety
in the lignin. 1-Phenylethanol was used as a simple model
compound for the screening of these oxidation catalysts. Lignin
samples with different molecular weight were also then tested for
the oxidation using the most suitable oxidation catalyst. Finally,
an ionic liquid, (2-hydroxy ethylammonium formate) was used to
depolymerise the oxidised lignin to produce low molecular weight
organic solvent or water-soluble products. Well-defined water-
soluble lignin oligomers are of high value for industrial
applications, especially if based on a simple reaction scheme.
Results and Discussion
Scheme 2. Proposed intermediates during the β-O-4 bonds oxidation and
depolymerisation reaction
Many papers have reported catalytic methods to oxidize β-O-4
linkages in lignin, which made lignin more reactive for further
depolymerisation. [7,8,9]
[16]
Firstly, we applied the recently developed oxidative
depolymerisation conditions involving TEMPO’/O
2
oxidation
followed by depolymerisation with formic acid and sodium formate
[
16]
to several different lignin samples. Common lignins, such as
Table 1. Properties of the different lignin feedstocks
Organosolv lignin
Alkali lignin
Mia
Kraft lignin
Mik
Name[a]
Mio
Mso
Msa
Msk
M
w
29,000
12,000
12,000
5,400
9,000
5,300
g/mol
[
a] Mio: methanol-insoluble organosolv lignin; Mso: methanol-soluble
Figure 1. Screening depolymerisations with TEMPO’/O
Oxidation condition: TEMPO’, oxygen flow, 60 °C , 12 h; depolymerisation
condition: formic acid, sodium formate 24 h, 110 °C )
2
and formic acid
organosolv lignin; Mia: methanol-insoluble alkali soluble lignin; Msa:
methanol-soluble alkali soluble lignin; Mik: methanol-insoluble kraft lignin;
Msk: methanol-soluble kraft lignin.
(
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
All three lignins were firstly suspended in methanol to give a
methanol insoluble part and methanol soluble fraction, which
have a higher and a lower molecular weight respectively (See
Table 1). From the methanol treatment, we obtained methanol-
insoluble organosolv lignin (Mio), methanol-soluble organosolv
lignin (Mso), methanol-insoluble alkali lignin (Mia), methanol-
soluble alkali lignin (Msa), methanol-insoluble kraft lignin (Mik),
and methanol-soluble kraft lignin. (Msk). All these lignin samples
were analysed by gel permeation chromatography (GPC). The
initial molecular weights of these lignin samples are listed in Table
1. After reaction, the depolymerised lignin was extracted and
fractionated between ethyl acetate and water. The ethyl acetate
layer contains the low molecular weight fraction; its yield was
calculated and shown in Figure 1.
All the yields of ethyl acetate soluble products became higher
after depolymerisation (Figure 1). This indicates that all these
lignin samples were successfully depolymerised with this
oxidation and depolymerisation method yielding more low
molecular products. Additionally, methanol soluble parts, which
had lower molecular weight, had higher yield of ethyl acetate
soluble products than those from methanol insoluble parts. Msk
lignin showed the similar depolymerisation yield of 60% which
compares to the Stahl group’s result achieved using Aspen lignin
Figure 2. Yield of ethyl acetate soluble fraction with different oxidation catalysts
Secondly,
TEMPO’/Cu(OAc)
TEMPO’/NaNO
DAIB), [32] were chosen to oxidize model compounds and lignin
to investigate optimal oxidation catalyst.
several
oxidation
catalysts,
TEMPO’/Fe(NO
including
,[28] TEMPO’/NaClO,
[29]
,[30]
2
3 3
)
[
31]
2
,
and Fe(TAML)Li/(diacetoxyiodo)benzene
(
n
with the molecular weight ca. M = 10,000. Based on these results,
1-Phenylethanol was used as a simple lignin model compound for
Msa lignin and Msk lignin were selected for further study.
screening the oxidation ability of the selected catalysts. The
results are shown in Table 2. The conversion of 1-phenylethanol
1
was determined by H-NMR. The peak from methyl proton shifted
after oxidation, which appears as a doublet at 1.41 ppm for 1-
phenylethanol and as a singlet at 2.59 ppm for acetophenone.
The conversion of oxidation reaction was calculated according to
the intergradation of these peaks. Acetonitrile as well as other
reported solvents were used for these oxidation reactions,
respectively. As the results showed, different solvents yield
different conversion of 1-phenylethanol. This is due to the
Scheme 3. Oxidation reaction for 1-phenylethanol
solubility of the starting material. Additionally, TEMPO’/Fe(NO
and TEMPO’/Cu(OAc) showed better oxidation ability compared
Table 2. Sceening reactions of model compounds with different oxidation catalysts to other catalysts in oxidizing 1-phenylethanol with a higher
3 3
)
2
Entry[a]
conversion of 100% and 55%, respectively.
TEMPO’
TEMPO’
Cu(OAc)
TEMPO’
NaClO
TEMPO’
Fe(NO
TEMPO’
NaNO
TAML
DAIB
O2
2
3
)
3
2
The performance of the catalysts investigated for oxidation of Msk
lignin and Msa lignin samples followed by the depolymerisation
with formic acid and sodium formate is summarized in Figure 2.
The yield (weight percentage) of ethyl acetate soluble products
was used as an indicator of the efficiency of oxidation ability of the
different catalysts.
Solvent
1[d]
CH
3
CN
CH
Water
3
CN
CH
Water
3
CN
DCE[b]
DCM[c]
Acetone
Water
45%
45%
50%
17%
100%
100%
55%
8%
0%
2[e]
55%
17%
50%
From Figure 2, TEMPO’/Cu(OAc)
5 h, air; most efficient oxidation ability for the depolymerisation of Msk
2 2
and TEMPO’/O showed the
[
a] The reaction conditions for all these catalyst systems are as follows:
TEMPO’/O 60 °C , 12 h, flow; TEMPO’/Cu(OAc) R.T.,
TEMPO’/NaClO: R.T., h, air; TEMPO’/Fe(NO R.T. h,
TEMPO’/NaNO : R.T. 3 h, air; Fe(TAML)Li/DAIB: 25 °C , 5 h [b] Dic hloroethane [c]
2
:
O
2
2
:
2
3
) :
3
2
O
2
flow;
lignin, as more than 50% yield of ethyl acetate soluble products
were generated after the depolymerisation. Similarly, for Msa
2
Dichloromethane [d] All the reactions were carried out with the solvents listed
above. [e] All the reactions were carried out in acetonitrile.
lignin, all the depolymerisation products oxidized by TEMPO’/O
TEMPO’/Cu(OAc) TEMPO’/NaClO and TEMPO’/Fe(NO
contained more than 50% of ethyl acetate soluble products.
2
,
)
3 3
2
,
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
Msa and Msk lignin were firstly oxidized by TEMPO’/Cu(OAc)
2
catalyst which showed the highest yield of ethyl acetate soluble
products from the screening tests. 2D-NMR was used to analyse
the lignin samples before and after oxidation.
Scheme 4. Formation of formate ionic liquid
Figure 3. GPC chromatograms of depolymerised Msa lignin
Figure 5. GPC chromatograms of Msa lignin depolymerised with formate ionic
liquid.
Figure 4. GPC chromatograms of depolymerised Msk lignin
Among all these results, Msk and Msa lignin oxidized by
TEMPO’/Cu(OAc) both gave the highest yield of ethyl acetate
2
soluble products (75%, 225mg out of 300 mg); this is higher than
the results previously reported. [16] All these ethyl acetate soluble
products were analysed by GPC to determine the molecular
weight distribution, which are shown in Figure 3 and Figure 4. All
these lignins were partially depolymerised as the molecular
weight distributions show products with decreased values (Figure
3
and 4). However, while a shift in molecular weight distribution to
lower values was observed, the GPC curves suggest that only
partial alteration of the lignin molecular structure has occurred. As
a
result, a better depolymerisation catalyst is required to
depolymerize lignin further that can result in 100% soluble low
molecular weight product; therefore, a formate ionic liquid
(
Scheme 4) was synthesized to serve both catalyst and solvent
[
23]
Figure 6. GPC chromatograms of Msk lignin depolymerised with formate ionic
for depolymerising oxidised lignin.
recovered by distillation at 120 °C and 0.2 mbar fo r 4 hours.
This ionic liquid could be
liquid
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
As the 2D-NMR spectra (Supporting Information) showed, the β-
O-4 bonds signals around 4.7 ppm, 87 ppm disappeared after the
oxidation for both lignin samples. This confirmed the successful
oxidation. Formate ionic liquid (2-hydroxy ethylammonium
formate) was used to dissolve lignin and the depolymerisation
reaction was performed at a temperature of 110 °C f or 24 hours.
After the reaction, the ionic liquid was removed by distillation. The
water after reaction. This work will facilitate industrial use of lignin
as a source of polyphenol by providing new lignin oligomers easily
processable.
1
recovered ionic liquid was analysed by H-NMR to confirm the
structure. As the 1H-NMR spectra (Supporting Information)
showed, the structure of ionic liquid stayed the same after the
reaction. This proved the recyclability of formate ionic liquid.
Experimental Section
Material
Significantly, all depolymerized product was fully water-soluble
Organosolv lignin was purchased from Chemical Point. Kraft lignin was
isolated from black liquor supplied by Australian Paper with the method
mentioned in the following part. Alkali lignin, TEMPO’ (4-acetamido-
(100%). Next, the mixture was extracted between water and ethyl
acetate to compare with the other depolymerisations. The
molecular weight of both water layer and ethyl acetate layer was
determined by GPC, as shown in Figure 5 and Figure 6.
2 3 3 2 2 2 3 2 4
TEMPO), Cu(OAc) , NaClO, Fe(NO ) , NaNO , Na S O , Na SO ,
diphenyl ether, DAIB, dichloroethane, dichloromethane, and 1-
phenylethanol were purchased from Sigma-Aldrich. Fe(TAML)Li was
purchased form GreenOx Catalysts, Inc. Hydrochloric acid (32%) was
obtained from Ajax Finechem. High purity oxygen gas purchased from Air
Liquid Australia was used for the experiments that required oxygen gas.
As seen from Figure 5, Msa lignin (5,400 g/mol) was successfully
depolymerised in formate ionic liquid. The ethyl acetate soluble
products gave a molecular weight of 1,900 g/mol, while the ethyl
acetate-insoluble fraction (aqueous layer) had a molecular weight
of 1,600 g/mol. The changed molecular weight shown in Figure 6
demonstrated Msk lignin was also successfully depolymerised in
formate ionic liquid. The molecular weights of the ethyl acetate-
soluble and ethyl acetate-insoluble fractions decreased from
3
Ethyl acetate, dimethyl formamide (DMF), chloroform (CDCl ), dimethyl
sulfoxide (DMSO-d ), and methanol were purchased from Merck. All
6
reagents were used as purchased from the supplier without any further
purification.
Measurement
5
,300 g/mol to 1,100 g/mol and 600 g/mol, respectively. These
1H NMR spectra were recorded on a Bruker DRK-400 spectrometer
results showed that both Msk lignin and Msa lignin were
successfully depolymerized in formate ionic liquid without need
for any other additives.
operating at 400 MHz as solutions in CDCl
weight of isolated lignin and depolymerised samples were measured by
GPC performed on Tosoh EcosHLC-8320 Gel Permeation
Chromatograph equipped with both refractive index (RI) and ultraviolet
UV) detectors (UV detection, λ = 280 nm) using Tosoh alpha 4000 and
3
6
and DMSO-d . The molecular
a
Moreover, the yields of the ethyl acetate layer and the water layer
fractions for the Msa lignin depolymerisation were 42% (~84 mg)
and 72% (~144 mg), respectively. For Msk lignin
depolymerisation, the yields of ethyl acetate layer component and
the water layer component were 43% (~86 mg) and 73% (~146
mg), respectively. For both reactions, the mass recovery of
depolymerized lignin was higher than the mass of starting material
lignin. A possible reason for this is that after oxidation and
depolymerisation, carboxylic acid derivatives were generated,
which could react with the cation in ionic liquid to form salts.
However, all these products showed lower molecular weight than
the original lignin, which indicated successful depolymerisation
with this method. Additionally, after depolymerisation, all the lignin
became water-soluble.
(
2000 columns. DMF (with 10 mM LiBr) was used as solvent to dissolve all
the lignin samples as well as mobile phase with flow rate of 1.0mL/min.UV
detector in GPC chromatograms set at 280 nm was used to analyze all the
depolymerised samples and isolated lignin. Calibration curves were
obtained using polystyrene standards. HPLC was performed using a
Waters Symmetry C18 5 ꢀm column (3.9 × 150 mm W10891D 039) with
two mobile phase A and B. Mobile phase A consisted of water with 10%
methanol and mobile phase B consisted of 100% methanol. The gradient
program selected used a flow rate of 0.8 mL/min and ambient temperature.
The gradient for analysis was as follows: 10% B for 1 min, to 70% B over
19 min, and held there for 5 min before immediately returning to initial
conditions in 1 min.
Isolation of kraft lignin from black liquor
At the beginning, there was only 18% water with 82% of solid content in
the black liquor from Maryvale pulp mill. More water was added to dilute
the black liquor to have 12% of solid content in order to reduce the
viscosity. While stirring the solution, hydrochloric acid was added to bring
the pH to around 1. High CO bubbling will happen around pH 6. The
2
resulting solid was filtered out, washed/rinsed with deionised water then
dried overnight at 40°C under vacuum. The dried lig nin was further washed
Conclusions
In this work, selected oxidation catalysts were investigated to
oxidise 1-phenylethanol as a model compound as well as several
lignin feedstocks. TEMPO’/Cu(OAc) was selected to oxidize the
2
lignin. An ionic liquid, 2-hydroxyamonium formate, was reported
for the first time for use both as a solvent and as a catalyst to
depolymerise oxidized lignin. Lignin could be significantly
depolymerised by using this oxidation and depolymerisation
method. Additionally, the lignin products were totally soluble in
by dissolving into 3%w/w sodium hydroxide solution to a total
concentration of 12%w/w lignin. The solution was heated at 100 °C for an
hour to further remove remaining hemicellulose. After cooling down, the
solution was once again acidified, filtered, rinsed and dried overnight.
Elemental analysis of carbon, hydrogen, nitrogen and sulphur gave the
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
following result (average over three measurement): Carbon 65.30%,
Hydrogen 6.07%, Nitrogen <0.3% (detection limit), Sulphur 2.57%
The solvent was removed by evaporation. For oxidation of 1-
phenylethanol, the sample was then sent for H-NMR to determine the
1
conversion of the reaction. For oxidized lignin, the solvents were removed
under vacuum. Oxidized lignin was subjected to the depolymerisation
reaction without further purification.
2
TEMPO’/O catalysed oxidation reaction
A 25 mL thick wall flask with a stirrer bar was charged with 1 mmol of 1-
phenylethanol (or 300 mg lignin) and 5 mol % of 4-acetamido-TEMPO
2
NaNO /TEMPO’ catalysed oxidation reaction
(
0.05 mmol, 10.6 mg). The flask was sealed with a septum, evacuated and
connected with a passing through oxygen flow. Then, 9.4 ꢀL of nitric acid
67%) (0.1 mmol, 6.3 mg) in 1 mL acetonitrile and 9.9 ꢀL of hydrochloric
The oxidation of 1-phenylethanol was carried out in air at ambient
temperature in a 50 mL long-necked round-bottomed flask equipped with
a magnetic stirrer. Typically, 1-phenylethanol (5.0mmol) and TEMPO’
(0.15 mmol) were dissolved in dichloromethane (8 mL). Concentrated
hydrochloric acid (0.50 mmol) was added to the mixture, followed by
NaNO (0.25 mmol). The resulting mixture was stirred at room temperature
2
and atmospheric pressure. For the oxidation of 1-phenylethanol, when
reaction completed, the liquid in the flask was transferred to a separate
(
acid (37%) (0.1 mmol, 3.65 mg) in 1 mL of acetonitrile were injected
through the septum with a syringe. An additional 3 mL of acetonitrile and
5
6
0 ꢀL of water were injected. The reaction mixture was stirred for 12 h at
0 °C . The solvent was evaporated. The residue of ox idized 1-
1
phenylethanol was subjected to H-NMR to obtain the conversion to the
products. Oxidized lignin was subjected to the depolymerisation reaction
without further purification.
funnel. The organic phase was washed with 30 wt % aqueous Na
solution and saturated aqueous NaHCO
oxidant and TEMPO’. The organic layer was dried over anhydrous Na
2
S
2
O
3
3
solution to remove the residual
SO
4
2
Cu(OAc) /TEMPO’ catalysed oxidation reaction
2
and concentrated to afford the desired product. 1H-NMR spectra were
obtained on the products to determine the conversion. For oxidized lignin,
the solvents were removed under vacuum. Oxidized lignin was subjected
to the depolymerisation reaction without further purification.
A mixture of 1-phenylethanol (5.0 mmol)/lignin (300 mg), Cu(OAc)
2
(9.1
mg, 0.05 mmol) and TEMPO’ (10.6 mg, 0.05 mmol) in CH CN/H O (5/10
3
2
mL) was stirred at room temperature for over night. For the oxidation of 1-
phenylethanol, after completion of the reaction, dichloromethane (15 mL)
was added to the resulting mixture. The dichloromethane phase was
separated, and the aqueous phase was further extracted with
dichloromethane (10 mL × 2). The combined organic layers were dried
over anhydrous sodium sulfate and concentrated to give a residue, which
was then analysed by 1H-NMR to obtain the conversion to the products.
For oxidized lignin, the solvents were removed under vacuum. Oxidized
lignin was subject to the depolymerisation reaction without further
purification.
Fe(TAML)Li/DAIB catalysed oxidation reaction
A Radleys tube was charged with the substrate (300 mg lignin or 1mmol
1-phenylethanol), diphenyl ether (0.1–0.25 equiv.), Fe(TAML)Li (1mol%),
and acetone/water (1:1) or acetonitrile (5 mL). The solution was placed on
a Radleys carrousel and thermostated at 25 °C. Iodo benzene diacetate (2
mmol) was added. For oxidation of 1- phenylethanol, after the completion
of reaction, water (5 mL) was added to the mixture, and was then extracted
with ethyl acetate (3 × 5 mL). The obtained solution was dried over Na
2
SO
4
1
and analysed by H-NMR to determine the conversion
.
For oxidized lignin,
Fe(NO
3
)
3
ꢀ3H
2
O/TEMPO’ catalysed oxidation reaction
the solvents were removed under vacuum. Oxidized lignin was subjected
to the depolymerisation reaction without further purification.
Fe(NO
3
)
3
·9H
2
O (0.05 mmol), DCE (4 mL), TEMPO’ (0.10 mmol) and NaCl
(
0.10 mmol) were added to a 10-mL dried three-necked flask under an
General procedure for depolymerisation of oxidized lignin with
formic acid and sodium formate
atmosphere of oxygen. The resulting suspension was stirred at room tem
perature for 5min under oxygen. For the oxidation of 1-phenylethanol, a
solution of 1-phenylethanol (1.0 mmol) in DCE (1,2-dichloroethane, 1 mL)
was then added to the suspension and the resulting mixture was stirred at
room temperature with oxygen passing through until the reaction was
completed as monitored by TLC (eluent: petroleum ether/ethyl acetate =
A 25 mL round bottom flask with a stirrer bar was charged with oxidized
lignin (300 mg), sodium formate (25 mg) and 5 mL of aqueous formic acid
(85-90 wt%). The flask was sealed with a glass stopper and heated for 24
h at 110 °C. After the reaction, formic acid was ev aporated and the residue
was extracted with ethyl acetate (3 × 15 mL). The organic soluble fraction
was concentrated under vacuum and the yield of viscous oil was calculated.
The organic insoluble material was washed with diethyl ether and then
water to remove all sodium formate and dried under vacuum. The weights
of obtained two fractions were measured to give the yield of different
reactions. GPC was used to measure the molecular weight of both ethyl
acetate soluble part and water-soluble part.
1
0 :1). The resulting mixture was diluted with diethyl ether (30 mL), and
dried over anhydrous MgSO
. After evaporation, 1H-NMR was used to
determine the conversion to the products. For oxidation of lignin, lignin
300mg), Fe(NO ·9H O (0.05 mmol), acetonitrile (15 mL), TEMPO’ (0.10
4
(
3
)
3
2
mmol) and NaCl (0.10 mmol) were added into a 50 ml round bottom flask.
The mixture was stirred under oxygen flow at room temperature for 24
hours. After reaction, the solvents were removed under vacuum. Oxidized
lignin was subjected to the depolymerisation reaction without further
purification.
Synthesis of the ionic liquid (2-hydroxy ethylammonium formate)[23]
NaClO/TEMPO’ catalysed oxidation reaction
2
-Amino ethanol (119.8 g, 0.2 mol) was placed in a two-necked flask
The starting materials (1 g of lignin or 1-phenylethanol) were suspended
in water (100 mL) containing TEMPO’ (21.1 mg, 0.1 mmol) and sodium
bromide (100 mg, 1 mmol). The 12% NaClO solution was adjusted to pH
equipped with a reflux condenser and a dropping funnel was mounted in
an ice bath. Under vigorous stirring with a magnetic stirring bar, 76 ml (0.2
mol) formic acid was added dropwise to the flask for about 45 min. Stirring
was continued for 24 h at room temperature, to obtain a viscous clear liquid.
1H-NMR spectrum (measured on a Bruker 250 MHz spectrometer, using
1
0 by the addition of 0.1 M HCl. The TEMPO’-mediated oxidation was
started by adding the desired amount of the NaClO solution (1.3-5.0 mmol
NaClO per gram of starting material), and was continued at room
temperature by stirring at 500 rpm. The pH was maintained at 10 by adding
DMSO-d
COO-); 6.9–7.7 ppm (broad signal, 4H, –NH
N); 2.8 ppm (t, 2H, –O–CH –).
6
as solvent with TMS as internal standard) δ: 8.4 ppm (s, 1H, H–
3
+OH); 3.6 ppm; (t, 2H, –CH
2
–
0
.5 M NaOH using a pH stat until no NaOH consumption was observed.
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
Depolymerisation of oxidized lignin in ionic liquid
[10] L. Longe, G. Garnier, K. Saito in Production of Biofuels and Chemicals
from Lignin (Eds.: Z. Fang, Jr., R. L. Smith) Springer Singapore, 2016 pp.
1
47-179.
A 25 mL round bottom flask with a stirrer bar was charged with oxidized
lignin sample (200 mg), and 10 mL of 2-hydroxy ethylammonium formate
was added into the flask. The flask was sealed with a glass stopper and
heated for 24 h at 110 °C . After the reaction, the ionic liquid was removed
by distillation under 0.2 mbar at a temperature of 120 °C . The final mixture
was extracted between ethyl acetate and water. The ethyl acetate was
removed by evaporation under vacuum on a rotary evaporator. Water was
removed by freeze dryer. Both of these samples were then subjected to
GPC analysis to give the molecular weight of the obtained product.
[
11] M. I. F. Mota, P. C. Rodrigues Pinto, J. M. Loureiro, A. E. Rodrigues,
Sep. Purif. Rev. 2016, 45, 227-259.
[
[
[
[
12] J. Dai, A. F. Patti, K. Saito, Tetrahedron Lett. 2016, 57, 4945-4951.
13] J. H. Grabber, Crop Sci. 2005, 45, 820-831.
14] F. S. Chakar, A. J. Ragauskas, Ind. Crop Prod. 2004, 20, 131-141.
15] A. Rahimi, A. Azarpira, H. Kim, J. Ralph, S. S. Stahl, J. Am. Chem. Soc.
2
013, 135, 6415-6418.
[
[
[
[
16] A. Rahimi, A. Ulbrich, J. J. Coon, S. S. Stahl, Nature 2014, 515, 249-252.
17] G. Chatel, R. D. Rogers, ACS Sustainable Chem. Eng. 2013, 2, 322-339.
18] T. Welton, Chem. Rev. 1999, 99, 2071-2084.
19] S. Mohtar, T. T. M. Busu, A. M. Noor, N. Shaari, N. Yusoff, M. Bustam,
M. A. Mutalib, H. Mat, Bioresour. Technol. 2015, 192, 212-218.
Acknowledgements
[
20] S. Nanayakkara, A. F. Patti, K. Saito, Green Chem. 2014, 16, 1897-1903.
21] S. Nanayakkara, A. F. Patti, K. Saito, ACS Sustainable Chem. Eng.
[
The financial support of the ARC Industrial Transformation
Research Hub - Bioprocessing Advanced Manufacturing Initiative
2
014, 2, 2159-2164.
[
[
[
22] K. A. Underkofler, R. E. Teixeira, S. A. Pietsch, K. G. Knapp, R. T.
(BAMI), Monash University, PRESTO JST, JPMJPR1515, Japan
Raines, ACS Sustainable Chem. Eng. 2015, 3, 606-613.
and the China Scholarship Council (CSC) is gratefully
acknowledged.
23] P. Yan, Z. Xu, C. Zhang, X. Liu, W. Xu, Z. C. Zhang, Green Chem. 2015,
1
7, 4913-4920.
24] N. Sathitsuksanoh, K. M. Holtman, D. J. Yelle, T. Morgan, V. Stavila, J.
Pelton, H. Blanch, B. A. Simmons, A. George, Green Chem. 2014, 16,
Keywords: Lignin oxidation • TEMPO • β-O-4 bonds • formate
1
236-1247.
ionic liquid • lignin depolymerisation
[
25] Y. Wang, L. Wei, K. Li, Y. Ma, N. Ma, S. Ding, L. Wang, D. Zhao, B. Yan,
W. Wan, Bioresour. Technol. 2014, 170, 499-505.
[1]
J. Zakzeski, P. C. Bruijnincx, A. L. Jongerius, B. M. Weckhuysen, Chem.
Rev. 2010, 110, 3552-3557.
[
26] N. Bicak, J. Mol. Liq. 2005, 116, 15-18.
[
27] J. Dai, S. Nanayakkara, T. C. Lamb, A. J. Clark, S.-X. Guo, J. Zhang, A.
F. Patti, K. Saito, New J. Chem. 2016, 40, 3511-3519.
[
[
2]
3]
R. Ma, Y. Xu, X. Zhang, ChemSusChem 2015, 8, 24-51.
C. Xu, R. A. D. Arancon, J. Labidi, R. Luque, Chem. Soc. Rev. 2014,
[
[
[
[
28] J.-A. Jiang, J.-L. Du, Z.-G. Wang, Z.-N. Zhang, X. Xu, G.-L. Zheng, Y.-F.
4
3, 7485-7500.
Ji, Tetrahedron Lett. 2014, 55, 1677-1681.
[
[
4]
M. P. Pandey, C. S. Kim, Chem. Eng. & Technol. 2011, 34, 29-41.
P. Azadi, O. R. Inderwildi, R. Farnood, D. A. King, Renewable and
Sustainable Energy Rev. 2013, 21, 506-523.
29] T. Saito, S. Kimura, Y. Nishiyama, A. Isogai, Biomacromolecules 2007,
5]
8
, 2485-2491.
30] S. Ma, J. Liu, S. Li, B. Chen, J. Cheng, J. Kuang, Y. Liu, B. Wan, Y.
Wang, J. Ye, Adv. Synth. Catal. 2011, 353, 1005-1017.
[
6]
7]
H. Lange, S. Decina, C. Crestini, Eur. Polym. J. 2013, 49, 1151-1173.
C. Rutten, A. Ramírez, J. Posada Duque, J. Chem. Technol. Biot. 2016,
[
31] X. Wang, R. Liu, Y. Jin, X. Liang, Chem. Eur. J. 2008, 14, 2679-2685.
9
2, 257-270.
[
8]
9]
A. Mukherjee, T. Mandal, A. Ganguly, P. K. Chatterjee, ChemBioEng
Rev. 2016, 3, 86-96.
Z. Jiang, C. Hu, J. Energ. Chem. 2016, 25, 947-956.
[32] F. Napoly, L. Jean‐ Gérard, C. Goux‐ Henry, M. Draye, B. Andrioletti,
Eur. J. Org. Chem. 2014, 2014, 781-787.
[
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201700632
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
FULL PAPER
Jinhuo Dai, Antonio F. Patti, Lionel
Longé, Gil Garnier and Kei Saito*
Page No. – Page No.
Oxidized lignin depolymerisation
using formate ionic liquid as catalyst
and solvent
An ionic liquid, 2-hydroxyammonium formate, was reported for use both as a
solvent and as catalyst to depolymerise oxidized lignin.
This article is protected by copyright. All rights reserved.