Microwave-assisted fast conversion of lignin model compounds and organosolv lignin over methyltrioxorhenium in ionic liquids

Article abstract of DOI:10.1039/c5ra18738a

Conversion of a series of lignin β-O-4 model compounds 2-aryloxy-1-arylethanols and organosolv lignin to aromatic chemicals over methyltrioxorhenium (MTO) in ionic liquids without any oxidant and reducing agent under mild conditions was developed. Microwave irradiation accelerates the cleavage of aryl ether bonds and shortens the reaction time to 2 min.

Full text of DOI:10.1039/c5ra18738a

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: B. Zhang, C. li, T.
Dai, G. Huber, A. Wang and T. Zhang, RSC Adv., 2015, DOI: 10.1039/C5RA18738A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 6
View Article Online
DOI: 10.1039/C5RA18738A
Journal Name
COMMUNICATION
Microwave-assisted fast conversion of lignin model compounds and
organosolv lignin over methyltrioxorhenium in ionic liquids
Bo Zhang,a† Changzhi Li,a† Tao Dai,a,b George W. Huber,a,c Aiqin Wang,a and Tao Zhang*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Catalytic conversion of a series of lignin β-O-4 model compounds molecular oxygen as additional oxidant agent with broad products
2-aryloxy-1-arylethanols and organosolv lignin to aromatic distributions. The development of efficient and mild condition
chemicals over methyltrioxorhenium (MTO) in ionic liquid without strategy for lignin depolymerization without additional source
any oxidant and reducing agent under mild conditions were including hydrogen or oxidant agent remains an important
developed. Microwave irradiation accelerates the cleavage of aryl challenge in catalysis due to the amorphous carbon-based inactive
ether bonds and shortens the reaction time to 2 min.
property and highly heterogeneous nature of lignin.18-19
Methyltrioxorhenium (MTO) has been used as a very efficient
and versatile catalyst for several reactions particularly
deoxydehydration reactions of biomass-derived polyols20- 23 and
lignin oxidation reaction.24 Kühn and co-workers recently made an
obvious progress for the application of MTO in lignin conversion.
They reported for the first time that methyldioxorhenium (MDO),
which in situ generated by reduction of MTO, can effectively
catalyze C-O bond cleavage of variety of lignin β-O-4 model
compounds in p-xylene without oxidant.25 Whereas in this system
lignin feedstock conversion still faces challenge due to the poor
dissolubility of lignin in p-xylene, and the relatively low reaction
rate (typical 12 h was needed for model compounds conversion).
One possible strategy to overcome the heterogeneous nature of
lignin is to use ionic liquid (IL) solvents, since some of them readily
dissolve lignin, which would make the catalyst more accessible to
the substrates.26-27 More importantly, it is reported that ILs have
excellent dielectric properties for transformation of microwave into
heat, 28 the combination of microwave irradiation and ILs is
expected to enhance the catalytic activity and improve the reaction
rate. However, as compared with molecular organic solvent such as
p-xylene, ionic liquid might lead to different reaction pathway due
to the strong ion environment of ionic liquid.29-30 Based on above
points, we present a strategy for selective cleavage of the C-O
bonds of β-O-4 hydroxy aryl ether and organosolv lignin
depolymerisation using MTO as catalyst without additional source
in ionic liquids under mild conditions.
With the gradual diminishing fossil fuel reserves and growing
demand for energy, much more attention is focused on
lignocellulosic biomass, which is a renewable resource that has the
potential to serve as a feedstock for the production of chemicals
and fuels.1-2 Lignin accounts for 10-35% by weight, up to 40% by
energy in lignocellulosic biomass, 3 and is the most abundant
renewable source of aromatic units in nature. In comparison with
the other two components (cellulose and hemicellulose) in
lignocellulose, lignin has
a more complicated structure that
possesses a wide variety of linkages in it. An ideal chemical process
would be able to depolymerize lignin into mono cyclic aromatic
chemicals.4 Over the past few years there have been a number of
studies that have been focused on lignin depolymerization.5 One
approach is to thermally treat lignin with a hydrogen source using
various supported metal such as Ru,6 Pd7, Pt,8 Rh,9 Ni,10-11 Cu12 and
Mo13 as catalysts to produce mono cyclic aromatics. It is one of the
most popular and efficient strategies applying in deconstruction of
lignin into components such as low depolymerized lignin, phenols,
and other valuable chemicals. However, high hydrogen pressures (>
o
4 MPa) as well as high temperatures (> 200 C) are required in the
reaction. Accordingly, oxidation reaction catalyzed by V,14 Co,15
Mn16 and Re17 can also produce aromatic chemicals from lignin
including vanillin, syringaldehyde, and vanillic acid. This reaction
usually occurs under the condition employing hydrogen peroxide or
2-(2-Methoxyphenoxy)-1-phenyl ethanol (1), a common lignin β-
O-4 dimeric model compounds, was first investigated for
depolymerization reaction, with various catalyst concentrations and
in different ILs (Table 1). The products were identified by GC-MS
(see ESI E2). The catalyst activity and selectivity depends on the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 6
View Article Online
DOI: 10.1039/C5RA18738A
Journal Name
COMMUNICATION
Table 1. C-O bond cleavage of lignin model compound 1 in different reaction conditions.
Entry
Cat. Conc.
Solvent
Conversion [%]a
Yield 1a [%]a
Yield 1b [%]a
Yield 1c [%]a
[mol %]
Cb
49
15
19
55
98
38
10
Mc
79
72
86
75
98
79
14
Cb
Mc
--
Cb
Mc
Cb
Mc
1
2
3
4
5
6
7
5
5
5
5
5
3
1
[Bmim]Cl
[Bmim]BF4
[Bmim]PF6
[Bdmim]Cl
[Bmim]NTf2
[Bmim]NTf2
[Bmim]NTf2
--
3
4
2
8
4
--
9
28
25
2
2
8
--
13
--
3
3
3
--
4
5
15
--
60
25
2
64
46
9
67
31
6
69
46
9
--
--
--
--
--
a Conversion and yield were determined by HPLC with external standard technology.
Reaction conditions: 0.2mmol compound 1, different amount of MTO in 1.0 g ionic liquid at 180 oC, t = 14 h; “C” is the abbreviation of
b
conventional heating.
c Reaction conditions: 0.2mmol compound 1, different amount of MTO in 1.0 g ionic liquid under 240 W microwave irradiation, T = 180 oC, t
= 2 min; “M” is the abbreviation of microwave heating.
ionic liquid solvent used (Table 1). A higher yields of the products
were obtained in [Bmim]NTf2 (Entry 5) as compared to other ILs reaction mixture was heated up rapidly, volumetrically and
such as [Bmim]Cl (Entry 1), [Bmim]BF4 (BF4 = Tetrafluoroborate) simultaneously by the “specific microwave effects”,34-35 and some
(Entry 2), [Bmim]PF6 (PF6 = hexafluorophosphate) (Entry 3) and known problems such as partly overheating under conventional
[Bdmim]Cl ([Bdmim] = 1-butyl-2,3-dimethylimidazolium) (Entry 4) conditions were avoided. A blank experiment without catalyst
under both conventional (CON) or microwave (MW) heating. under the same conditions shows no conversion either under CON
Kiefer31 and co-workers have shown that the hydrogen atom on C-2 heating or MW irradiation. It is interesting to note that besides
position of the positively charged ring in 1,3-dialkylimidazolium- phenylacetaldehyde and guaiacol, catechol (1c) was detected when
based IL is very active, which suggest that this functionality may be other ILs were employed, except for [Bmim]NTf2, which
involved in the reactions for lignin depolymerization. To exclude the
possibility of involvement of the hydrogen on C-2 position in this
reaction, [Bmim]Cl and [Bdmim]Cl were used as solvents (Table 1
entries 1 and 4). Similar results were obtained with these two
solvents, indicating that the C-2 proton of 1,3-disubstituted
imidazolium cations has no clear effect on the conversion of
compound 1. Lower catalyst concentrations of 3 mol% and 1 mol%
led to decreased conversions even though the reaction time is
prolonged to 24 h under CON heating, and the selectivity of 1b is
lower under MW than under CON heating due that the olefin-
intermediate is not completely converted to final product 1b in
such a short time with lower catalyst amount (Entry 6). A catalyst
loading of 5 mol% was necessary to obtain complete conversion of
lignin model compound 1 under both CON and MW heating. The
catalyst activity is higher for MW heating compared to CON heating Figure 1. Time course of guaiacol conversion catalyzed by MTO in
in all case in Table 1 except entry 5. The enhancement of catalytic [Bmim]Cl under microwave irradiation of 80 W (50 oC) and 240 W
activity might derive from the fact that ILs have excellent dielectric (180 oC). Typical reaction procedure: after 2 mmol guaiacol and 5
o
properties for transformation of microwave into heat.32 It has been mol% MTO were dissolved in 1.0 g [Bmim]Cl at 80 C, the reaction
reported that the higher the concentration of ions, the stronger the mixtures was immediately subjected to microwave irradiation for a
heat effect.33 The pure ionic circumstance of ILs ensures that the certain time.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 6
View Article Online
DOI: 10.1039/C5RA18738A
Journal Name
COMMUNICATION
did not produce any catechol (Table 1). Catechol might be Table 2. C-O bond cleavage of various 2-Aryloxy-1-aryethanols.
generated from C-O bond cleavage of guaiacol. In order to verify
this hypothesis, we monitored the time course of guaiacol
conversion using [Bmim]Cl as reaction solvent under MW heating.
The different microwave power of 80 W and 240 W stand for the
Subs
R1
R2
R3
Conv.
[%]a
Yield a
[%] a
Yield b
[%] a
different reaction temperature. The results indicate that within 20
min a 10% conversion of guaiacol and 5% yield of catechol were
Cb Mc Cb Mc Cb Mc
98 98 60 64 67 69
96 97 46 65 52 66
detected under microwave power 80
W (Figure 1). Further
increasing the irradiation power to 240 W increased the catechol
yield to 70% and guaiacol conversion to 86% within 5 min reaction
time. This indicates that the depolymerization of lignin model
compound guaiacol increases with increasing microwave irradiation
power. The relative high acidity of [Bmim]Cl and the strong
hydrogen bond may play important roles in the conversion of
guaiacol to catechol.36-37 It has been reported that depolymerization
of guaiacol is intractable due to the stable structures.38-39 For
example, Savage’s group reported that 75% conversion of guaiacol
and 65% yield of catechol was obtained at 250 oC when using In
(OTf)3 as catalyst, 40 and Wahyudiono et al. hydrolysed guaiacol in
1
2
3
4
5
6
H
OCH3
H
H
H
H
H
OCH3
H
OCH3 92 98 48 61 47 57
OCH3
OCH3
OCH3
H
H
94 98 21 41 30 50
95 98 19 37 28 46
OCH3
OCH3
OCH3 94 97 25 29 28 41
a Conversion and yield were determined by HPLC with external
standard technology.
b Reaction conditions: 0.2mmol compound 1, 5 mol% MTO in 1.0 g
[Bmim]NTf2 ionic liquid at 180 oC, t = 14 h; “C” is the abbreviation of
conventional heating.
o
water at 250 C for 2 h and obtained 6% conversion.41 While in our
c
Reaction conditions: 0.2mmol compound 1, 5 mol% MTO in 1.0 g
ionic liquid under 240 W microwave irradiation, T = 180 oC, t = 2
min; “M” is the abbreviation of microwave heating.
systems 86% conversion of guaiacol and 70% yield of catechol was
achieved in short time 5 min, which could be promising route for
depolymerizing guaiacol.
is important to point out that the high selectivity in cleavage of aryl
C-O bonds is in contrast to the hydrogenation of aryl ethers with
heterogeneous catalysts. In the latter case, the products are
typically a mixture of arenes, cycloalkanes and phenols.6, 44 The
conversions of all substrates are higher than 90% in our reaction
system, while the aromatics yields varied (Table 2). The lignin model
compounds with the methoxyl substitution in the R1 position result
in distinctly lower yields than those without methoxyl group (the
substrates 1-3 vs 4-6). The methoxyl groups in R2 and R3 positions
also have little influence on the yield of the depolymerization
products. Under MW heating, the yields of both a and b were in the
following order: 4 > 5 > 6, implying that the methoxyl groups in R2
and R3 positions have negative effect on the yields of the target
products, which might arise from the stereochemical effect because
LC-MS was performed to analyze the unknown species in
[Bmim]Cl system (Table 1, Entry 1) and to try to explain why higher
activity with [Bmim]NTf2 was observed. The unknown products we
detected were 2-aryloxy-1-arylethanols dimers (see ESI E3), such as
2-phenoxy-1-phenylethanol ([m-H]-/z of 213 at retention time 7.78
mins), and 2-(2-hydroxy-2-phenylethoxy)phenol ([m-H]-/z of 229 at
retention time 10.35 mins). The former product was generated
from elimination of methoxyl group of model compound 1, while
the latter product was produced from C-O bond cleavage of
methoxyl group of the substrate. These results are in agreement
with the results in Table 1 (Entry 1) and Figure 1 that show that
[Bmim]Cl prefers to cleave C-O bond of methoxyl group.
Additionally, isomeric olefins (E)- and (Z)-2(styryloxy) phenol with
[m-H]-/z of 211 were detected at the retention time 13.87 and
14.24 min in the LC-MS spectra. These products were formed from
dehydration of the substrate. Four additional peaks at retention
time at 15.00, 15.67, 16.02 and 16.34 mins with the same [m-H]-/z
of 277 were also detected. These peaks were probably chlorine
substitution products of the substrate on different positions of
aromatic ring. The above by-products are most likely responsible for
the lower yields of the target products 1a and 1b when using
[Bmim]Cl as the reaction solvent.
of
a relatively large metal compound of MTO catalyst. The
substrates with two methoxyl groups in R2 and R3 positions of the
aryl group have been reported to be too cumbersome to cleave.45-46
It is interesting to note that the substrates 5 and 6 display moderate
yields under MW heating. Similar conversion of all substrates was
obtained with both microwave and conventional heating. However,
the product yields were higher with MW heating. This further
confirms that the combination of IL and MW heating exhibits great
benefits for selective depolymerization of various lignin model
compounds.
A series of 2-aryloxy-1-arylethanols with different substitution
groups in R1-R3 positions were employed as the substrates (Table 2)
under the same conditions as Entry 5 in Table 1. The substrates in
Table 2 have the same chemical groups as found in natural lignin.3
For example, 2-(2-methoxyphenoxy)-1-phenylethanol (Substrate 1
in Table 2), is a major β-O-4 moiety in hard wood such as birch.42 2-
Phenoxy-1-phenylethanol (Substrate 2) without methoxy
substitution on phenyl ring is one component in grass lignin.43 After
reaction, it was found that the aldehyde and phenol (compound a
and b in Table 2) are dominant products in all cases, suggesting that
in the [Bmim]NTf2/MTO system the aryl C-O bonds of the substrates
were selectively cleaved with the aryl rings intact in the products. It
All investigated lignin model compounds 1-6 produced
phenylacetaldehyde which is generated from 1,2-shift of the O
atom and phenol, rather than 1-phenyl ethanol or methyl phenyl
ketone. Model compound 1 was used as the probe substrate with
CON heating at 180 oC to provide insight into the reaction pathway,
which is monitored by GC-MS and 1H-NMR technologies (see ESI E2
1
and E4). According to the H-NMR results, during the conversion of
the substrate 1 to 1a and 1b, an isomeric mixture of olefins –
1
intermediates (see ESI E4, H-NMR resonance shows signals at 5.48
ppm) formed via dehydration of compound 1 within 2 h. After 4 h
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 6
View Article Online
DOI: 10.1039/C5RA18738A
COMMUNICATION
Journal Name
of Kühn et al, in which MTO was reduced by the hydroxyl of the
substrate to MDO that is responsible for the C-O bond activation. 20-
25
This finding matches well with the GC-MS results (see ESI E2) in
which the trace amounts of ketone was produced via reduction of
MTO by the hydroxyl.
The excellent results obtained from model compounds
motivated us to investigate the conversion of organolsolv lignin, a
more realistic lignin feedstock. Organolsolve lignin has been
reported to have a structure close to natural lignin.48 Organosolv
lignin breaks down to a low molecular weight (LMW) oil with a yield
of 34.2 wt % in [Bmim]NTf2 within 2 min under MW heating. It is
worthy to note that further increase the reaction time will lead to
repolymerization of the products and other side reactions. 2min
was found to be the optimum reaction time. The main components
of the LMW oil are simple aromatic monomers shown in Table 3
(See ESI E5). Most aromatic products in the oil are generated from
the cleavage reactions between lignin interunits, and are valuable
chemicals and intermediates used in many industries. For example,
syringaldehyde (7) is largely employed as a pharmaceutical
precursor and dye agent,49 and syringol (1) a composed of guaiacyl
and syringyl units.50 Compound 2 belongs to aguaiacyl origin, and
compounds 1, 7-10 could be associated with syringyl units. The
structure 4 did not possess methoxyl group but tertiary butyl,
probably due to radical reactions in the depolymerization process.
Scheme 1. Possible reaction pathway of C-O bond cleavage in lignin
model compound β-O-4 (1); MDO formed from interaction between
the substrate and MTO (2).
Table 3. Detected compounds by GC-MS in the degraded
organosolv lignin products under MW irradiation within 2 min.
No.
Compund Relative
No.
Compund Relative
Structure
formula
area
(%)a
Structure
area
(%)a
formula
O
O
OH
O
O
1
2.7
2.8
6
11.8
11.1
2.0
Figure 2. IR spectra of Re=O stretching range 850-1100 cm-1 of pure
MTO (1a, 1b), and MTO in the reaction (2a, 2b). 1b (solid line) and
2b (dashed line) is the 4th derivative of the spectra.
O
OH
OH
O
O
O
product 1a (see ESI E4, 1H-NMR shows signals at 9.68 ppm) was
observed. The substrate was first converted into olefins-
intermediates, and then converted to the final products from the
intermediates (Scheme 1). This result is in agreement with the work
of Kühn et al,25 suggesting that the substrate follows a same
reaction pathway in ionic liquid compared to the reaction in organic
solvent p-xylene. Trace amount of ketone was detected by GC-MS
as well, which could be generated from the interaction between the
substrate and MTO to form methyldioxorhenium (MDO). 20-25
2
7
O
O
OH
O
O
3
12.8
10.5
3.4
8
O
The experimentally observed vibrational fundamentals of pure
CH3ReO3 and CH3ReO3 in the reaction are presented in Figure 2. The
concentration ratio of the catalyst and substrate 1 is 1:1 in
[Bmim]NTf2 (100 mg) under 240 W within 30 second, which is
examined by IR. The Re=O stretching mode of the MTO in the
reaction is shifted to ~997 cm-1, ~966 cm-1, and ~937 cm-1 in B
spectra, which is in accord with what has been reported on MDO-
Re(V) symmetry vibration modes.47 The fourth derivatives (1b and
2b) of the original spectra 1a and 2a are shown in Figure 2C. The
clear wavenumber shift can be ascribed to a further distortion of
the ReO local symmetry. These results are consistent with the work
OH
OH
OH
O
O
O
O
4
9
2.0
O
O
O
O
O
5
10
6.3
a
The relative percentages were calculated with peak area
normalization method in GC-MS.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 6
View Article Online
DOI: 10.1039/C5RA18738A
Journal Name
COMMUNICATION
The carbonyl groups (ketone or aldehyde) in the α position of was then diluted by 15 mL acetonitrile. This mixture was then
compounds 2, 5-7, and 9-10 might have been formed during ether- separated by centrifugation at 9000 rpm for 15 min. The organic
linkage cleavage between aliphatic carbon and the oxygen.51 The phase was concentrated under vacuum and 34.2 mg of organic
relatively high concentrations of syringyl and guaiacyl derivatives soluble fraction products after subtracting mass of IL and catalyst
observed in this work are in agreement with our previous work of were obtained (after subtracting 1.0 g ionic liquid and 10 mg MTO).
depolymerization of birch wood catalyzed by Ni-W2C catalyst.52 All The ILs phase was extracted with diethyl ether (5 × 10 mL). After
of above results suggest that breakage of the β-O-4 linkages are the vacuum distilling diethyl ether, the sample was injected into a GC-
main reaction route in this reaction. In contrast to other solvents, MS for identification of depolymerization products.
the high solubility of organosolv lignin in ionic liquid probably plays Typical procedure for the extraction of organosolv lignin: Birch
an important role in helping to depolymerize lignin.53-54 This mild wood organosolv lignin was prepared as previously described. 56
system without additional reductant has several advantages over The treatment for lignin extraction consisted of the digestion of
the heterogeneous catalytic systems that use a high hydrogen or birch wood powder in a mixture of ethanol–water (70 wt %) at 200
oxygen pressure.55
oC for 90 min in a stainless-steel autoclave (Parr, 100 mL) with
In summary, an efficient method was developed for conversion constant stirring at 700 rpm. The solid (10 g)-to-liquid (60 g) ratio
of lignin model compounds and organosolv lignin with a MTO was 1 : 6 (w/w). After the high-temperature extraction, the mixture
catalyst in ionic liquid under mild conditions. A series of lignin β–O- was cooled to room temperature and was filtered; two volumes of
4 model compounds were investigated that were able to be acidified water (pH = 2) were added to the liquid fraction in order to
converted to their corresponding phenols as the primary products precipitate the lignin. The precipitated lignin was then separated by
with high yields up to 69 %. The IL is not only able to dissolve lignin, centrifugation (4000 rpm, 20 min) and dried at 80 oC overnight
but also has excellent dielectric properties for transformation of before use.
microwave energy into heat. The combination of IL with microwave
irradiation accelerated the degradation rate and increased the
Acknowledgements
reaction activity. Depolymerization of
a birch wood derived
organosolv lignin under microwave irradiation produced 34.2 wt %
yield of the main phenolic monomers- syringyl and guaiacyl
derivatives within 2 min. MDO was generated by reduction of MTO
via IR spectroscopic studies. NMR and GC-MS were used to track
the formation of the intermediate products. This work
demonstrates a strategy for the controllable production of value-
added aromatic chemicals from lignin, which offers the advantages
of fast reaction rate, high selectivity, mild conditions and no need of
any oxidant and reducing agent.
B. Zhang thanks China Postdoctoral Science Foundation funded
Project (2015M571341). C. Z. Li thanks the National Science
Foundation of China (21473187). The Project-sponsored by SRF for
ROCS, SEM.
References
1 G. W. Huber, S. Iborra, A. Corma, Chem. Rev. 2006, 106, 4044.
2 A. Corma, S. Iborra, A. Velty, Chem. Rev. 2007, 107, 2411.
3 X. Zhang, M. B. Tu, M. G. Paice, Bioenerg. Res. 2011, 4, 246.
4 J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius, B. M. Weckhuysen,
Chem. Rev. 2010, 110, 3552.
Experimental Section
Typical procedure for C-O cleavage of lignin model compounds in
oil bath: A 25 mL heavy wall glass tube with [Bmim]NTf2 ionic liquid
(1.0 g), the lignin model compound (0.2 mmol) and MTO (2.5 mg, 5
mol %) was heated for 14 h at 180 oC. After cooling to room
temperature, the reaction mixture was diluted to 25 mL volumetric
flask with CH3CN/H2O (6 : 4 by volume). The product samples were
analyzed by HPLC using an external standard calibration curve
method (R2 > 0.999).
5 C. A. Gasser, G. Hommes, A. Schäffer, P. F. X. Corvini, Appl.
Microbiol. Biotechnol. 2012, 95, 1115.
6 W. Zhang, J. Z. Chen, R. L. Liu, S. P. Wang, L. M. Chen, K. G. Li, ACS
Sustain. Chem. Eng. 2014, 2, 683.
7 Zhao, C.; Kou, Y.; Lemonidou, A. A.; Li, X. B.; Lercher, J. A. Angew.
Chem., Int. Ed. 2009, 48, 3987.
Typical procedure for depolymerization of lignin model
compounds under microwave irradiation condition: Lignin model
compounds (0.2 mmol) and MTO (2.5 mg, 5 mol %) were dissolved
in ionic liquid (1.0 g) at 80 oC, the reaction mixture was then
immediately subjected to microwave irradiation of 240 W at 180 oC
for 2 min. The products in the reactor were rinsed to a 25 mL
volumetric flask with CH3CN/H2O(6 : 4 by volume) for HPLC, using
an external standard calibration curve method (R2 > 0.999).
Catalytic produces for depolymerization of organosolv lignin:
Organosolv lignin (100 mg) and MTO (10 mg) were dissolved in
8 Y. X. Wang, T. He, K. T. Liu, J. H. Wu, Y. M. Fang, Bioresour.
Technol. 2012, 108, 280.
9 N. Yan, C. Zhao, D. J. Dyson, C. Wang, L. Liu, Y, Kou,
ChemSusChem. 2008, 1, 626.
10 J. He, C. Zhao, J. A. Lercher, J. Am. Chem. Soc. 2012, 134, 20768.
11 A. G. Sergeev, J. F. Hartwig, Science, 2011, 332, 439.
12 K. Barta, G. R. Warner, E. S. Beach, P. T. Anastas, Green Chem.
2014, 16, 191.
13 V. M. L. Whiffen, K. J. Smith, Energy Fuels 2010, 24, 4728.
14 S. K. Hanson, R. Wu, L. A. P. Silks, Angew. Chem. Int. Ed, 2012, 51,
3410.
o
[Bmim]NTf2 (1.0 g) at 80 C. The reaction mixture was immediately
subjected to microwave irradiation of 240 W at 180 oC for 2 min.
15 D. Cedeno, J. J.Bozell, Tetrahedron Lett. 2012, 53, 2380.
The reaction mixture was cooled down to room temperature and
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 6
View Article Online
DOI: 10.1039/C5RA18738A
COMMUNICATION
Journal Name
16 S. Riano, D. Fernandez, L. Fadini, Catal. Commun. 2008, 9, 1282.
17 C. Crestini, P. Pro, V. Neri, R. Saladino, Bioorg. Med. Chem. 2005,
13, 2569.
50 M. Lewin, I. S. Goldstein, Wood Structure and Composition; CRC
Press: Boca Raton, 1991; p 183.
51 A. Toledano, L. Serrano, A. M. Balu, R. Luque, A. Pineda, J. Labidi,
ChemSusChem. 2013, 6, 529.
18 R. Ma, W. Hao, X. Ma, Y. Tian, Y. Li, Angew. Chem. Int. Ed. 2014,
53, 7310.
52 C. Li, M. Zheng, A. Wang, T. Zhang, Energy Environ. Sci. 2012, 5,
6383.
19 A. Rahimi, A. Ulbrich, J. J. Coon, S. S. Stahl, Nature, 2014, 515,
249.
53 W. E. S. Hart, J. B. Harper, L. Aldous, Green Chem. 2015, 17, 214.
54 M. M. Hossain, L. Aldous, Aust. J. Chem. 2012, 65, 1465.
20 M. Shirzmizu, F. D. Toste, Angew. Chem. Int. Ed. 2012, 51, 8082.
21 J. E. Ziegler, M. J. Zdilla, A. J. Evans, M. M. Abu-Omar, Inorg. 55 H. Konnerth, J. Zhang, D. Ma, M. H. G. Prechtl, N. Yan, Chem.
Chem. 2009, 48, 9998.
Eng. Sci. 2015, 123, 155.
56 A. Toledano, L. Serrano, J. Labidi, Ind. Eng. Chem. Res. 2011, 50,
22 A. L. Denning, H. Dang, Z. Liu, K. M. Nicholas, F. C. Jentoft,
ChemCatChem 2013, 5, 3567.
6573.
23 X. Li, D. Wu, T. Lu, G. Yin, H. Su, Y. Zhang, Angew. Chem. Int. Ed.
2014, 53, 4200.
24 H. Lange, S. Decina, C. Crestini, Eur. Polym. J. 2013, 49, 1151.
25 R. G. Harms, I. I. E. Markovits, M. Drees, W. A. Herrmann, M.
Cokoja, F. E. Kühn, ChemSusChem 2014, 7, 429.
26 S. Jia, B. J. Cox, X. Guo, Z. C. Zhang, J. G. Ekerdt, ChemSusChem
2010, 3, 1078.
Graphical Abstract:
27 A. George, D. Tran, T. Y. Morgan, P. I. Benke, C. Berueco, E.
Lorernte, B. C. Wu, Y. D. Keasling, B. A. Simmons, B. M. Holmes,
Green. Chem. 2011, 13, 3375.
28 C. O. Kappe, Chem. Soc. Rev. 2008, 37, 1127.
29 C. D. Hubbard, P. Illner, R. V. Eldik, Chem. Soc. Rev. 2011, 40, 272.
30 M. Schmeisser, R. V. Eldik, Dalton. Trans. 2014, 43, 15675.
31 K. Noack, P. S. Schulz. N. Paape, J. Kiefer, P. Wasserscheid, A.
Leipertz, Phys. Chem. Chem. Phys. 2010, 12, 14153.
32 C. O. Kappe, Chem. Soc. Rev. 2008, 37, 1127.
33 C. Li, Z. K. Zhao, H. Cai, A. Wang, T. Zhang, Biomass. Bioenerg.
2011, 35, 2013.
34 R. M. palou, Mol. Diversity 2010, 14, 3.
35 C. O. Kappe, Chem. Soc. Rev. 2008, 37, 1127.
36 B. J. Cox, S. Jia, Z. C. Zhang, J. G. Ekerdt, Polym. Degrad. Stab.
2011, 96, 426.
37 A. Oehlke, K. Hofmann, S. Spange, New. J. Chem. 2006, 30, 533.
38 L. Yang, W. Zhou, K. Seshan, Y. Li, J. Mol. Catal. A: Chem. 2013,
368-369, 61.
39 M. A. Gonzalez-Borja, D. E. Resasco. Energy Fuels 2011, 25, 4155.
40 L. Yang, Y. Li, P. E. Savage, Ind. Eng. Chem. Res. 2014, 53, 2633.
41 Wahyudiono, M. Sasaki, M. Goto, J. Mater. Cycles Waste
Manage. 2011, 13, 68.
42 K. Gabov, R. J. A. Gosselink, A. I. Smeds, P. Fardim, J. Agric. Food.
Chem. 2014, 62, 10759.
43 H. Nadji, Y. Bedard, A. Benaboura, D. Rodrigue, T. Stevanovic, B.
Riedl, J. Apple. Polym. Sci, 2010, 115, 1546.
44 J. He, C. Zhao, D. Mei, J. A. Lercher, J. Catal. 2014, 309, 280.
45 J. M. Nichols, L. M. Bishop, R. G. Bergman, J. A. Ellman, J. Am.
Chem. Soc. 2010, 132, 12554.
46 S. Son, F. D. Toste, Angew. Chem. Int. Ed. 2010, 49, 3791.
47 W. A. Herrmann, P. W. Roesky, M. Wang, W. Scherer,
Organometallics 1994, 13, 4531.
48 V. M. Roberts, V. Stein, T. Reiner, A. Lemonidow, X. Li, J. A.
Lercher, Chem. Eur. J. 2011, 17, 5939.
49 C. Eckert, C. Liotta, A. Ragauskas, J. Hallett, C. Kitchens, E. Hill, L.
Draucker, Green. Chem. 2007, 9, 545.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins