Selective catalytic transformation of lignin with guaiacol as the only liquid product

Article abstract of DOI:10.1039/c9sc05892c

Guaiacol is an important feedstock for producing various high-value chemicals. However, the current production route of guaiacol relies heavily on fossil resources. Using lignin as a cheap and renewable feedstock to selectively produce guaiacol has great potential, but it is a challenge because of its heterogeneity and inert reactivity. Herein, we discovered that La(OTf)₃ could catalyze the transformation of lignin with guaiacol as the only liquid product. In the reaction, La(OTf)₃ catalyzed the hydrolysis of lignin ether linkages to form alkyl-syringol and alkyl-guaiacol, which further underwent decarbonization and demethoxylation to produce guaiacol with a yield of up to 25.5 wt%, and the remaining residue was solid. In the scale-up experiment, the isolated yield of guaiacol reached up to 21.2 wt%. To our knowledge, this is the first work to produce pure guaiacol selectively from lignin. The bio-guaiacol may be considered as a platform to promote lignin utilization.

Full text of DOI:10.1039/c9sc05892c

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Selective catalytic transformation of lignin with
guaiacol as the only liquid product†
Cite this: DOI: 10.1039/c9sc05892c
ab
*
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
Xiaojun Shen,
Jinliang Song,
Qinglei Meng, a Qingqing Mei, a Huizhen Liu, abc Jiang Yan,ab
a
a
Dongxing Tan,ab Bingfeng Chen,
Zhanrong Zhang,a
Guanying Yanga and Buxing Han
abcd
*
Guaiacol is an important feedstock for producing various high-value chemicals. However, the current
production route of guaiacol relies heavily on fossil resources. Using lignin as a cheap and renewable
feedstock to selectively produce guaiacol has great potential, but it is a challenge because of its
heterogeneity and inert reactivity. Herein, we discovered that La(OTf)3 could catalyze the transformation
of lignin with guaiacol as the only liquid product. In the reaction, La(OTf)3 catalyzed the hydrolysis of
lignin ether linkages to form alkyl-syringol and alkyl-guaiacol, which further underwent decarbonization
and demethoxylation to produce guaiacol with a yield of up to 25.5 wt%, and the remaining residue was
solid. In the scale-up experiment, the isolated yield of guaiacol reached up to 21.2 wt%. To our
knowledge, this is the first work to produce pure guaiacol selectively from lignin. The bio-guaiacol may
be considered as a platform to promote lignin utilization.
Received 20th November 2019
Accepted 15th December 2019
DOI: 10.1039/c9sc05892c
rsc.li/chemical-science
whether in the woody or herbaceous plants.14–16 Hence, using
lignin as a cheap and renewable feedstock to produce guaiacol
Introduction
has considerable potential, and can decrease the dependence on
fossil resources for producing this important chemical.15,17,18
Moreover, guaiacol would be used to produce more chemicals,
both in category and quantity, if we could obtain cheap and
renewable guaiacol from lignin.
However, lignin has high heterogeneity and low reactivity,
because it is predominately bonded by a series of inert C–O and
C–C linkages (accounting for approximately 70% and 30%,
respectively).16 Although some technologies, such as hydrogena-
tion,19–21 oxidation,22 hydrolysis,12,23,24 and multiple strategies,25
have been developed to depolymerize lignin into low-molecular-
weight lignin monomers, the primary products from these
processes are mixtures of compounds (phenols, arenes, aromatic
In the chemical industry, guaiacol is considered as an important
raw material for the syntheses of many value-added chemicals,
such as spices (vanillin, veratraldehyde and eugenol),1,2 pesti-
cides,3 drugs (eugenol, potassium guaiacolsulfonate, guaifene-
sin, berberine, and isoprenaline),4–8 a plant growth regulator (2-
methoxy-5-nitrophenol sodium salt) and so on. Based on a global
market survey, the demand for the above high-value chemicals
increases year by year. Typically, annual demand for guaifenesin,
vanillin, and eugenol is 37 000, 16 000, and 7300 t per year,
respectively,5,9–12 all of which may be synthesized from guaiacol.
Therefore, the demand for guaiacol is large. However, current
production of guaiacol is mainly based on the methylation of
catechol which is an expensive downstream chemical from fossil
resources, using additional methylation reagents, for example,
methanol and methyl chloride (Fig. 1A).13 Lignin is an aromatic
abundant renewable source that is rich in guaiacyl (G) units,
aBeijing National Laboratory for Molecular Science, CAS Key Laboratory of Colloid and
Interface and Thermodynamics, CAS Research/Education Centre for Excellence in
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
100190, China. E-mail: mengqinglei@iccas.ac.cn; hanbx@iccas.ac.cn
bSchool of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China
cPhysical Science Laboratory, Huairou National Comprehensive Science Centre, Beijing
101407, P. R. China
dShanghai Key Laboratory of Green Chemistry and Chemical Processes, School of
Chemistry and Molecular Engineering, East China Normal University, Shanghai
200062, China
Fig. 1 Production route to guaiacol: (A) traditional route, (B) new route
in this work.
† Electronic supplementary information (ESI) available: Scheme S1, Table S1 and
Fig. S1–S7. See DOI: 10.1039/c9sc05892c
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acids, and so on) due to the complex structure of lignin,14,26 and lignin from Eucalyptus. Initially, lignin transformation was
guaiacol can be generated in low yield as one of the monomer studied with various catalysts in methanol (Table 1, entries 1–8).
products in the mixtures.27–30 The liquid mixtures usually make It was found that no guaiacol was generated without catalyst
product separation and purication processes very complicated. (Table 1, entry 1). As we know, ether linkages can be efficiently
It is therefore attractive to selectively transform lignin into cleaved with Lewis acid catalysts.12,32–37 However, guaiacol could
a single value-added chemical, such as guaiacol, but this is not be effectively obtained from lignin using weak Lewis acid
particularly challenging to achieve efficiently.31
catalysts, such as La(NO3)3, Al(OTf)3 and LaCl3 (Table 1, entries
Herein, we discovered that Lewis acid La(OTf)3 could effi- 2–4). Unlike the above acids, the triate salts with stronger
ciently catalyze the selective transformation of lignin into Lewis acidity could effectively catalyze the production of
guaiacol (Fig. 1B). As a catalytic system, La(OTf)3 efficiently guaiacol from lignin with various yields (Table 1, entries 5–8
catalyzed the hydrolysis of ether linkages in lignin to form alkyl- and Fig. S1A†). Methane was the only gaseous product
syringol and alkyl-guaiacol products. Alkyl-guaiacol products (Fig. S1B†). We also analysed the reaction mixtures by HPLC,
further underwent decarbonization to produce guaiacol, while and the spectra clearly indicated that guaiacol was essentially
alkyl-syringol was transformed into guaiacol via decarbon- the sole product (Fig. S1C†), establishing this transformation of
ization and demethoxylation. The unique feature of this meth- lignin, delivering guaiacol as the only liquid product. The
odology is that guaiacol can be directly produced from the results above reveal that catalytic activity of La(OTf)3 was the
transformation of lignin with high yield, and the methylation highest among these catalysts, and the yield of guaiacol could
process is not required in this route.
reach 14.9%. As is well known, a larger water exchange rate
constant (WERC) value is benecial to the fast hydrolysis of the
ether linkages.38 Among the metal cations, the La3+ ion has one
of the largest WERC values.33,37,39 Furthermore, the higher
temperature and stronger acidity cooperatively promoted the
decarbonization of the side chain to form guaiacol.21 Therefore,
Results and discussion
In this work, we rstly screened catalytic systems and optimized
the reaction conditions for the transformation of organosolv
Table 1 Transformation of lignin under different reaction conditionsa
Catalytic system
Solvent/water
Entry
Catalyst
(mL/mL)
Temperature (ꢀC)
Catalyst (mg)
Guaiacol yield (wt%) b
1c
2
3
4
5
6
7
8
9
10
11
12
13
14
15d
16e
17f
18g
19h
—
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.00
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
4.0/0.01
270
270
270
270
270
270
270
270
270
250
255
260
265
275
270
270
270
270
270
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
0.0
0.0
0.6
1.2
6.6
La(NO3)3
Al(OTf)3
LaCl3
HOTf
Fe(OTf)3
Yb(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
La(OTf)3
7.0
7.8
14.9
22.5
8.6
11.4
18.9
21.7
22.5
1.2
0
0
25.5
12.6
a
b
Reaction conditions: 50 mg lignin, 20 mg catalyst, 4 mL methanol, 0.01 mL water if needed, 24 h, 0.1 MPa Ar, and 500 rpm. Guaiacol yield is
calculated based on the weight of lignin. c Without catalyst. d Ethanol/water instead of methanol/water. e Cyclohexane/water instead of methanol/
water. f Toluene/water instead of methanol/water. g Substrate is conifer wood enzymatic mild acidolysis lignin from pine (EMAL-p). h Substrate is
grass enzymatic mild acidolysis lignin from bamboo (EMAL-b).
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La(OTf)3 could effectively hydrolyze the ether linkages and examined using 2D-HSQC NMR.14,44,45 As shown in Fig. 2, Aa (dC/
cleave the side chains in lignin. dH 71.4/4.87, purple), Ab (dC/dH for G units: 84.1/4.32, purple; dC/
It is known that hydrolysis of ether linkage is much easier dH for S units: 87.1/4.11, purple) and Ag (dC/dH 59.9/3.81, purple)
than alcoholysis.26,31 We found that water could improve the corresponding to the side chain of b-O-4 were almost dis-
guaiacol yield (Table S1†), and a 22.5 wt% yield of guaiacol could appeared. Other units (b–b and b-5) were no longer observed
be obtained (Table 1, entry 9). However, too much water in the aer the catalytic reaction. These results conrmed that the
catalytic system limited the production of guaiacol (Table S1,† lignin was dissociated in the reactions, and perhaps beyond just
entries 1–5), presumably due to the poor solubility of organosolv the b-ethers. The cross signals correlating with the syringyl (S)
lignin in water.40 According to previous studies, metal triates (dC/dH 104.0/6.72, red) and oxidized syringyl (S0) (dC/dH 106.3/
exhibit excellent stability at high temperature.33,37,39 In this 7.30, red) units were no longer present in the HSQC spectrum
strategy, the reaction temperature had a signicant effect on the aer the reaction, and only guaiacyl (G) units (dC/dH 111/6.8,
yield of guaiacol. As shown in Table 1, the yield of guaiacol 115/6.7, 119/6.6, green) were observed, suggesting that deme-
increased from 8.6 to 22.5 wt% with the temperature increasing thoxylation of syringyl units had occurred to form guaiacyl
from 250 to 270 C, and then became independent of tempera- units.14 This is consistent with the aforementioned analysis of
ꢀ
ture (Table 1, entries 9–14). In addition, the solvents also inu- the liquid products. To further conrm the uniqueness of
ence the yield of guaiacol (Table 1, entries 9 and 15–17). Guaiacol guaiacol in the liquid product, we used deuterated methanol
was hardly obtained in ethanol, cyclohexane, or toluene. This is (methanol-d4) as the solvent in the lignin transformation. The
understandable because methanol is generally an effective 2D-HSQC NMR spectra of the obtained liquid product revealed
hydrogen donor.41 With methanol steam reforming, methanol that only guaiacol could be detected (Figs. S1D and 1E†).
could release hydrogen for catalytic transfer hydrogenation of the
To further study the catalytic mechanism, the conversion of
lignin intermediate products (for details see Table 2 and lignin model compound a was performed, and the results are
Fig. S7†), whereas ethanol, cyclohexane, and toluene are not good shown in Table 2, Fig. 3 and S2.† As shown in Table 2, La(OTf)3
hydrogen donors. Furthermore, lignin has very low solubility in could efficiently catalyze the conversion of a into guaiacol. The
cyclohexane and toluene and is therefore not favorable for the results illustrated that the b-O-4 linkage was broken to generate
transformation of lignin.42,43 Therefore, methanol/water was the 4-ethylguaiacol at 220 ꢀC. Moreover, as the reaction temperature
optimum solvent. In addition, the yield of guaiacol from lignin
increased gradually from 3 to 22.5 wt% with the increase of
La(OTf)3 dosage (Table 1, entry 9 and Table S1† entries 6–9).
Under the determined optimal conditions, we also investigated
the transformation of other lignin samples from conifer wood
(EMAL-p) and grass (EMAL-b) lignin using La(OTf)3 as the cata-
lyst, and the yields of guaiacol were 25.5 and 12.6 wt%, respec-
tively (Table 1, entries 18 and 19), further indicating the excellent
catalytic performance of La(OTf)3.
To gain further information on the transformation of the
lignin, lignin structures before and aer the reaction were
Table 2 Results showing the effect of reaction temperature on the
conversion of the lignin model compoundsa
Yield (%)
Temperature
(ꢀC)
Conversion
(%)
Entry
1
2
3
4
1
2
3
4
5
6
220
230
240
250
260
270
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
79
95
86
71
49
31
—
4
12
17
18
11
—
—
—
11
31
49
Fig. 2 The 2D-HSQC NMR spectra of the organosolv lignin from
Eucalyptus (top) and reaction residue (bottom) transformation (reac-
tion conditions: Table 1, entry 9).
a
Reaction conditions: 50 mg lignin model compound a, 20 mg
La(OTf)3, 0.1 MPa Ar, 500 rpm. 24 h, and methanol/water (4/0.01, v/v).
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Fig. 4 Scale-up production of guaiacol from lignin. Reaction condi-
tions: 1.50 g organosolv lignin, 0.6 g La(OTf)3, 120 mL methanol,
0.3 mL water, 270 ꢀC, 0.1 MPa Ar, and 24 h.
Fig. 3 (A) The time-course of the product distributions for the C–C
bond cleavage of the ethyl group in 4-ethyl guaiacol with the La(OTf)3
catalyst. Reaction conditions: 4-ethyl guaiacol (50 mg), La(OTf)3 (20
mg), methanol 4 mL, 10 mL water, 270 ꢀC, 0.1 MPa Ar, and stirring at
800 rpm. (B) Reaction pathway for C–C bond cleavage of the ethyl
group in 4-ethyl guaiacol.
and S6†). The yield of alkyl-syringol was almost negligible,
whereas guaiacol was generated in high yield. The results of
these experiments using model compounds are therefore
consistent with the lignin transformation results in revealing
that even syringyl units really do produce guaiacol (via deme-
thoxylation) under these conditions.
Under optimal conditions, we also performed a scale-up
experiment using a larger amount of organosolv lignin. Aer
the separation and purication, a 21.2 wt% yield of isolated
guaiacol (0.32 g) could be obtained from 1.50 g lignin (Fig. 4 and
S7†), indicating that pure guaiacol with appreciable yield could
be produced from real lignin via this strategy.
increased, the C–C bond in the ethyl group of 4-ethylguaiacol
was gradually cleaved to form 4-methylguaiacol and then
further transformed into guaiacol,21,25,46 which was futher
established by the decarbonization of 4-ethylguaiacol (Fig. 3). As
shown in Fig. 3A, 4-methylguaiacol was initially the major liquid
product due to the cleavage of the C–C bond between Ca and Cb
in the side chain of 4-ethylguaiacol. With an extension of the
reaction time, the remaining methyl chain in 4-methylguaiacol
was cleaved, and then guaiacol was formed.21,47 Correspond-
ingly, methane was generated as the main gaseous product
(Fig. 3), which conrmed that guaiacol was indeed formed by
successive cleavage of the C–C bond in the side chain, as
depicted in Fig. 3B. This is different from various reported
studies.12,33,34,36 Although Lewis acids have been used as cata-
lysts12,36 or one of the active components of the catalytic
system33,34 for transformation of lignin into aromatic chemicals,
only a trace of guaiacol was usually generated together with
various other compounds, mainly because the reaction was
conducted at much lower reaction temperatures in the reported
work. In addition, we also used ethanol as a solvent to study the
reaction (Fig. S4†). The product distribution was different from
that in methanol. 4-Vinylguaiacol was the major product in
ethanol for the side-chain elimination reaction, which revealed
again that methanol was an excellent organic solvent.40,48,49
Although the amount of S units is higher than that of G units
in the organosolv lignin, guaiacol was the only monomeric
product observed and the corresponding residual solid con-
tained only G units, as determined by NMR. Therefore, the
reactions of S units in lignin model compound b (see ESI†) and
2, 6-dimethoxy-4-methylphenol were also investigated (Fig. S5
Conclusions
In summary, guaiacol can be selectively produced from lignin
using Lewis acid La(OTf)3 as a catalyst in methanol/water
solvent. The yield of guaiacol reached up to 25.5 wt%, and the
remaining residue is solid. As a catalytic system, La(OTf)3 effi-
ciently catalyzed the hydrolysis of ether linkages in lignin to
form alkyl-syringol and alkyl-guaiacol products. Alkyl-guaiacol
products further underwent decarbonization to produce
guaiacol, while alkyl-syringol was transformed into guaiacol via
decarbonization and demethoxylation. In the scale-up experi-
ment, 0.32 g of guaiacol can be obtained from 1.50 g lignin, and
the residue is solid. This work opens the way to produce pure
guaiacol from lignin selectively and bridges plant-based lignin
and fossil-based products, affording a green and sustainable
strategy that is of great importance for the valorization of lignin.
Experimental
Catalytic performance
The reaction was carried out in a Teon-lined stainless-steel
reactor of 20 mL with a magnetic stirrer. In a typical experi-
ment, desired amounts of reactant, catalyst (e.g. La(OTf)3),
solvent (e.g. methanol) and H2O (if used) were loaded into the
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reactor. The reactor was sealed and purged with Ar to remove lignin. Aer centrifugation, the organosolv lignin was collected,
the air at room temperature. Then the reactor was placed in and washed with dilute HCl solution several times. Finally,
a furnace at desired temperature controlled by a PID tempera- puried organosolv lignin was obtained by freeze-drying.
ture controller (model SX/A-1, Beijing Tianchen Electronic
Company), and the stirrer was started. Aer the reaction, the
reactor was placed in ice water and the gas released was
Preparation of enzymatic mild acidolysis lignins (EMALs)
from sowood and grass
collected in a gas bag. The gas sample was analyzed by using
The method was similar to that reported in the literature.50,51 The
a GC (Agilent 4890D) equipped with a TCD detector and
raw sawdust (pine and bamboo) was milled for 1 h at 450 rpm in
a packed column (carbon molecular sieve TDX-01, 1 m in length
a planetary ball mill (Fritsch GMBH, Idar-Oberstein, Germany).
and 3 mm in diameter) using argon as the carrier gas. A known
The ball-milled wood (5.0 g) was then suspended in acetate buffer
amount of n-dodecane as the internal standard was added into
the reactor. Aer that, the liquid reaction mixture was centri-
(0.05 mol Lꢂ1, 100 mL, pH 4.8), with the loading of 100 FPU
cellulase (Celluclast 1.5 L) and 100 FPU b-glucosidase (Novozyme
fuged, and the supernatant liquid was collected for qualitative
188). The reaction mixture was incubated at 50 ꢀC in a rotary
analysis using a GC-MS (Agilent 5977A, HP-5MS capillary
shaker (150 rpm) for 48 h. Aer enzymatic hydrolysis, the residue
column (30 m ꢁ 0.25 mm ꢁ 0.25 mm)) and quantitative analysis
was collected by centrifugation and washed with acidied water
using a GC (Agilent 7890) equipped with a ame ionization
(pH 2) followed by freeze-drying. The residues were then treated
with 0.05 M HCl in acidic dioxane–water (85 : 15, v/v) at 86 C
under a nitrogen atmosphere for 2 h. The resulting mixture was
ltered and the ltrate containing lignin was collected. The solid
detector (FID) and a HP-5MS capillary column. The yield of
guaiacol was calculated from the GC data. The HPLC analysis of
the supernatant liquid was conducted on an Agilent LC-20AT
liquid chromatograph with a C18 chromatographic column
ꢀ
residue was washed with fresh dioxane–water (85 : 15, v/v) until
and a UV-Vis detector (275 nm). The mobile phase was aceto-
the ltrate became clear. The ltrate and washings were
nitrile with a ow rate of 0.8 mL minꢂ1, and the temperature
combined and then neutralized with solid sodium bicarbonate.
The neutralized solution was concentrated and nally precipi-
tated in a large quantity of acidied water (10 volumes, pH 2). The
precipitated lignin was collected by centrifugation and freeze-
dried under high vacuum. To remove the carbohydrate remain-
ing in the lignin, the lignin was dissolved in 90% acetic acid (20
mL), and then the lignin solution was dropped into 10 volumes of
acidic water (pH 2) producing a lignin precipitate. The precipi-
tated lignin was washed with acidied water several times and
then freeze-dried. EMAL-p and EMAL-b stand for the lignin from
pine (conifer wood lignin) and bamboo (grass), respectively.
ꢀ
was kept at 50 C. The chromatography was run for 60 min. In
the case with lignin as the reactant, the residual solid was
ꢀ
washed with deionized water, then dried in a vacuum at 60 C
for 48 h over the P2O5 desiccant and characterized by 2D-HSQC
NMR in DMSO-d6 (Bruker Advance III 600) according to the
reported procedure.14,44 When deuterated methanol (methanol-
d4) was used as the solvent, the procedure was the same as that
described for the above reaction in methanol. Aer that, the
liquid mixture was centrifuged and the methanol-d4 phase was
directly characterized using a 2D-HSQC NMR (Bruker Advance
III 400) without adding additional deuterated solvent.
The scale-up reaction was performed in a batch reactor of
Hastelloy C-276 (500 mL internal volume, Sen Long Instruments
Company, Beijing, China). In the reaction, 1.50 g organosolv
lignin, 0.6 g La(OTf)3, 120 mL methanol, and 0.3 mL water were
added into the reactor. The reactor was sealed and purged with
Ar to remove the air at room temperature. Then the reactor was
heated to 270 ꢀC under stirring at 800 rpm, and the reaction was
maintained for 24 h at 270 ꢀC. Aer the reaction, the reactor was
immediately cooled to room temperature and a gas was released
and collected in a gas bag. The liquid product was concentrated
in vacuo. The product was puried on a silica-gel column with
ethyl acetate–hexane as the solvent (1 : 9, v/v).
Conflicts of interest
The authors declare no competing nancial interests.
Acknowledgements
This work was supported nancially by National Key Research
and Development Program of China (2017YFA0403103),
National Natural Science Foundation of China (21703258,
21733011, 21890761, and 21533011), Beijing Municipal Science
& Technology Commission (Z181100004218004), and Chinese
Academy of Sciences (QYZDY-SSW-SLH013).
Preparation of organosolv lignin from hardwood
References
Preparation of organosolv lignin was conducted according to
a literature method.27 In the experiment, Eucalyptus powder (50
g) was added to 70% isopropanol/water solution (500 mL). The
batch reactor was heated to 220 ꢀC under stirring at 1000 rpm,
and the reaction was maintained for 1 h at 220 ꢀC. Aer the
reaction, the batch reactor was immediately cooled to room
temperature in the ice water. The reaction mixture was ltered
via a Buchner funnel. The ltrate was poured into ten volumes
dilute HCl solution with a pH of 2.0 to precipitate the dissolved
1 K. Li and J. W. Frost, J. Am. Chem. Soc., 1998, 120, 10545–
10546.
2 L. J. Esposito, K. Formanek, G. Kientz, F. Mauger,
V. Maureaux, G. Robert and F. Truchet, in Van Nostrand's
Encyclopedia of Chemistry, ed. G.D. Considine, John Wiley &
Sons, Ltd., 2005, p. 1.
3 L. Yang, W. Zhou, K. Seshan and Y. Li, J. Mol. Catal. A: Chem.,
2013, 368–369, 61–65.
This journal is © The Royal Society of Chemistry 2019
Chem. Sci.

View Article Online
Chemical Science
Edge Article
´
¨
4 N. Mahe, B. Nicolaı, M. Barrio, M.-A. Perrin, B. Do, 25 M. Wang, M. Liu, H. Li, Z. Zhao, X. Zhang and F. Wang, ACS
´
J.-L. Tamarit, R. Ceolin and I. B. Rietveld, Cryst. Growth
Catal., 2018, 8, 6837–6843.
Des., 2013, 13, 3028–3035.
5 A. A. Khalil, U. u. Rahman, M. R. Khan, A. Sahar,
26 H. Zeng, D. Cao, Z. Qiu and C.-J. Li, Angew. Chem., Int. Ed.,
2018, 57, 3752–3757.
T. Mehmood and M. Khan, RSC Adv., 2017, 7, 32669–32681. 27 X.-J. Shen, P.-L. Huang, J.-L. Wen and R.-C. Sun, Fuel Process.
6 S. L. Bhanawase and G. D. Yadav, Catal. Today, 2017, 291,
213–222.
7 D. Liu and W. Zhang, in Pharmaceutical Process Chemistry,
Technol., 2017, 167, 491–501.
28 J. Gong, A. Imbault and R. Farnood, Appl. Catal., B, 2017,
204, 296–303.
´
´
ed. T. Shioiri, K. Izawa and T. Konoike, Wiley-VCH Verlag 29 H. Pinkowska, P. Wolak and A. Złocinska, Chem. Eng. J.,
GmbH & Co. KGaA, 2010, p. 273. 2012, 187, 410–414.
8 C. S. P. Sastry, K. E. Rao and U. V. Prasad, Talanta, 1982, 29, 30 A. Toledano, L. Serrano and J. Labidi, J. Chem. Technol.
917–920. Biotechnol., 2012, 87, 1593–1599.
9 P. C. Rodrigues Pinto, E. A. Borges da Silva and 31 Q. Mei, H. Liu, X. Shen, Q. Meng, H. Liu, J. Xiang and B. Han,
A. E. Rodrigues, in Biomass Conversion: The Interface of Angew. Chem., Int. Ed., 2017, 56, 14868–14872.
Biotechnology, Chemistry and Materials Science, ed. C. 32 A. C. Atesin, N. A. Ray, P. C. Stair and T. J. Marks, J. Am.
Baskar, S. Baskar and R. S. Dhillon, Springer Berlin
Heidelberg, Berlin, Heidelberg, 2012, p. 381.
10 Eugenol Market Forecast, Trend Analysis & Competition
Tracking – Global Market insights 2017 to 2026, 2018,
Chem. Soc., 2012, 134, 14682–14685.
33 R. Jastrzebski, S. Constant, C. S. Lanceeld, N. J. Westwood,
B. M. Weckhuysen and P. C. A. Bruijnincx, ChemSusChem,
2016, 9, 2074–2079.
´
available electronically at https://www.factmr.com/report/ 34 X. Huang, J. Zhu, T. I. Koranyi, M. D. Boot and
513/eugenol-market. E. J. M. Hensen, ChemSusChem, 2016, 9, 3262–3267.
11 Global Guaifenesin (API)Sales Market Report 2018, 2018, 35 P. J. Deuss, C. W. Lahive, C. S. Lanceeld, N. J. Westwood,
available
electronically
at
https://
P. C. J. Kamer, K. Barta and J. G. de Vries, ChemSusChem,
2016, 9, 2974–2981.
36 P. J. Deuss, C. S. Lanceeld, A. Narani, J. G. de Vries,
N. J. Westwood and K. Barta, Green Chem., 2017, 19, 2774–2782.
37 H. Wang, H. Wang, E. Kuhn, M. P. Tucker and B. Yang,
ChemSusChem, 2018, 11, 285–291.
38 S. Kobayashi and K. Manabe, Acc. Chem. Res., 2002, 35, 209–
217.
39 H.-J. Song, J. Deng, M.-S. Cui, X.-L. Li, X.-X. Liu, R. Zhu,
W.-P. Wu and Y. Fu, ChemSusChem, 2015, 8, 4250–4255.
www.marketresearchhub.com/report/global-guaifenesin-
api-sales-market-report-2018-report. html.
12 P. J. Deuss, M. Scott, F. Tran, N. J. Westwood, J. G. de Vries
and K. Barta, J. Am. Chem. Soc., 2015, 137, 7456–7467.
13 R. Bal, M. Tada, T. Sasaki and Y. Iwasawa, Angew. Chem., Int.
Ed., 2006, 45, 448–452.
14 S. D. Manseld, H. Kim, F. Lu and J. Ralph, Nat. Protoc.,
2012, 7, 1579.
15 A. J. Ragauskas, G. T. Beckham, M. J. Biddy, R. Chandra,
F. Chen, M. F. Davis, B. H. Davison, R. A. Dixon, P. Gilna 40 T. Renders, S. Van den Bosch, T. Vangeel, T. Ennaert,
and M. Keller, Science, 2014, 344, 1246843.
16 R. Rinaldi, R. Jastrzebski, M. T. Clough, J. Ralph,
M. Kennema, P. C. Bruijnincx and B. M. Weckhuysen,
Angew. Chem., Int. Ed., 2016, 55, 8164–8215.
17 B. M. Upton and A. M. Kasko, Chem. Rev., 2016, 116, 2275–
2306.
S.-F. Koelewijn, G. Van den Bossche, C. M. Courtin,
W. Schutyser and B. F. Sels, ACS Sustainable Chem. Eng.,
2016, 4, 6894–6904.
41 K. Barta, T. D. Matson, M. L. Fettig, S. L. Scott, A. V. Iretskii
and P. C. Ford, Green Chem., 2010, 12, 1640–1647.
42 C. Li, X. Zhao, A. Wang, G. W. Huber and T. Zhang, Chem.
Rev., 2015, 115, 11559–11624.
43 W. Schutyser, T. Renders, S. Van den Bosch, S. F. Koelewijn,
G. T. Beckham and B. F. Sels, Chem. Soc. Rev., 2018, 47, 852–908.
18 Z. Sun, B. Fridrich, A. de Santi, S. Elangovan and K. Barta,
Chem. Rev., 2018, 118, 614–678.
´
19 L. Shuai, M. T. Amiri, Y. M. Questell-Santiago, F. Heroguel,
Y. Li, H. Kim, R. Meilan, C. Chapple, J. Ralph and 44 H. Kim and J. Ralph, Org. Biomol. Chem., 2010, 8, 576–591.
J. S. Luterbacher, Science, 2016, 354, 329–333.
45 H. Kim, J. Ralph and T. Akiyama, BioEnergy Res., 2008, 1, 56–
20 Y. Li, L. Shuai, H. Kim, A. H. Motagamwala, J. K. Mobley,
66.
¨
F. Yue, Y. Tobimatsu, D. Havkin-Frenkel, F. Chen, 46 S. Song, J. Zhang, G. Gozaydın and N. Yan, Angew. Chem., Int.
R. A. Dixon, J. S. Luterbacher, J. A. Dumesic and J. Ralph,
Ed., 2019, 58, 4934.
Sci. Adv. Mater., 2018, 4, eaau2968.
21 L. Dong, L. Lin, X. Han, X. Si, X. Liu, Y. Guo, F. Lu, S. Rudic,
47 Y. Shao, Q. Xia, L. Dong, X. Liu, X. Han, S. F. Parker,
Y. Cheng, L. L. Daemen, A. J. Ramirez-Cuesta, S. Yang and
Y. Wang, Nat. Commun., 2017, 8, 16104.
´
S. F. Parker, S. Yang and Y. Wang, Chem, 2019, 5, 1521–1536.
22 W. Lan, J. Behaghel de Bueren and J. Luterbacher, Angew. 48 X. Ouyang, X. Huang, J. Zhu, M. D. Boot and E. J. M. Hensen,
Chem., Int. Ed., 2019, 131, 2675. ACS Sustainable Chem. Eng., 2019, 7, 13764–13773.
23 A. Rahimi, A. Azarpira, H. Kim, J. Ralph and S. S. Stahl, J. Am. 49 L.-P. Xiao, S. Wang, H. Li, Z. Li, Z.-J. Shi, L. Xiao, R.-C. Sun,
Chem. Soc., 2013, 135, 6415–6418. Y. Fang and G. Song, ACS Catal., 2017, 7, 7535–7542.
24 A. Rahimi, A. Ulbrich, J. J. Coon and S. S. Stahl, Nature, 2014, 50 J.-L. Wen, S.-N. Sun, T.-Q. Yuan, F. Xu and R.-C. Sun,
515, 249.
Bioresour. Technol., 2013, 150, 278–286.
51 H. Li and G. Song, ACS Catal., 2019, 9, 4054.
Chem. Sci.
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