Selective utilization of methoxy groups in lignin for: N -methylation reaction of anilines

Article abstract of DOI:10.1039/c8sc03006e

The utilization of lignin as a feedstock to produce valuable chemicals is of great importance. However, it is a great challenge to produce pure chemicals because of the complex structure of lignin. The selective utilization of specific groups on lignin molecules offers the possibility of preparing chemicals with high selectivity, but this strategy has not attracted attention. In this work, we propose a protocol to produce methyl-substituted amines by the selective reaction of the methoxy groups of lignin and aniline compounds. It was found that LiI in the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate could catalyze the reaction efficiently and the selectivity to the N-methylation product could be as high as 98%. Moreover, the lignin was not depolymerized in the reaction. As it was rich in hydroxyl groups, the residual material left over after the reaction was used as an efficient co-catalyst for the cycloaddition of epoxy propane with CO₂, using KI as the catalyst.

Full text of DOI:10.1039/c8sc03006e

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Selective utilization of methoxy groups in lignin for
N-methylation reaction of anilines†
Cite this: DOI: 10.1039/c8sc03006e
a
ab
Huizhen Liu, *ab Hangyu Liu, Junfeng Xianga
ab
All publication charges for this article Qingqing Mei,
Xiaojun Shen,
*
have been paid for by the Royal Society
ab
and Buxing Han
of Chemistry
The utilization of lignin as a feedstock to produce valuable chemicals is of great importance. However, it is
a great challenge to produce pure chemicals because of the complex structure of lignin. The selective
utilization of specific groups on lignin molecules offers the possibility of preparing chemicals with high
selectivity, but this strategy has not attracted attention. In this work, we propose a protocol to produce
methyl-substituted amines by the selective reaction of the methoxy groups of lignin and aniline
compounds. It was found that LiI in the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate
could catalyze the reaction efficiently and the selectivity to the N-methylation product could be as high
as 98%. Moreover, the lignin was not depolymerized in the reaction. As it was rich in hydroxyl groups,
the residual material left over after the reaction was used as an efficient co-catalyst for the cycloaddition
Received 6th July 2018
Accepted 31st October 2018
DOI: 10.1039/c8sc03006e
rsc.li/chemical-science
2
of epoxy propane with CO , using KI as the catalyst.
achieve high selectivity to a desired product, and much effort is
yet to be made for lignin as a feedstock. The lignin-rst
Introduction
30
Biomass is considered to be a renewable and sustainable alter- approach is a very promising route to improving the selec-
1,2
native to fossil resources. The utilization of biomass as a raw tivity and yield of aromatic monomers. This approach trans-
material to produce useful chemical compounds is of great forms the native lignin released from lignocellulose in situ and
3
–8
31,32
importance for the sustainable development of our society. As leaves other components as a solid residue.
As one of the few
9
the second most abundant form of biomass, lignin is drawing notable examples, Abu-Omar and co-workers developed
increasing attention.
Lignin is a byproduct in the pulp and a bimetallic Zn/Pd/C catalyst for the selective conversion of
paper industry, and it is usually burnt as low-grade fuel, which is intact woody biomass from a diverse selection of species.
10,11
33,34
12,13
recognized as a waste of its potential.
effort has been devoted to converting lignin into alternative fuels, 4-propylguaiacol and 4-propylsyringol, with small amounts of
platform compounds, value-added chemicals, and functional unidentied impurities. genetically-modied poplar
General approaches to transform lignin into valu- enhanced in syringyl monomer content yielded 4-propylguaia-
In recent years, much The diethylether extract liquor of the product contained mainly
A
1
4–16
materials.
able chemicals involve the depolymerization of lignin
1
7–20
and col as the single product, determined by gas chromatography,
Such approaches with a yield of 19 wt%. In contrast to yet unmodied native
21–25
further conversion into valuable products.
are very promising, although the depolymerized products are lignin, which contains a higher fraction of cleavable b-O-4
almost always mixtures, leading to serious separation and puri- linkages, the case for technical lignin is more challenging.

cation problems. Thus, it is of signicant importance to The structures of Kra, Sulte, Alkaline and Klason lignins that
improve the selectivity and obtain only a limited number of are readily available in the pulping industry are heavily modi-
1
6
16
dened products instead of complex mixtures.
Although great progress has been achieved for the selective cleavable b-O-4 and a-O-4 linkages are cleaved to varying
transformation of model compounds,
ed under relatively harsh processing conditions. The easily
26–29
it is challenging to degrees, and the random repolymerization forms highly recal-
11
citrant C–C bonds. As a result, it is extremely difficult to
selectively convert technical lignin into a limited number of
a
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid
and Interface and Thermodynamics, CAS Research/Education Center for Excellence
in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
desired products. On the other hand, the –OCH groups remain
3
16
mostly untouched during the technical fraction process. It is
known that the methoxy group is the most abundant group in
1
00190, P. R. China. E-mail: liuhz@iccas.ac.cn; hanbx@iccas.ac.cn; Fax: +86 10
2562821; Tel: +86 10 62562821
2
lignin. Thus, lignin, whether native or technical, can be
6
b
School of Chemistry and Chemical Engineering, University of Chinese Academy of regarded as an abundant renewable methoxyl source. Selective
Sciences, Beijing 100049, P. R. China
utilization of methoxy groups in lignin, while leaving the other
groups as a solid residue, provides a new approach to the
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8sc03006e
1
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selective transformation of lignin. We believe that using the selectively cleave the C–O bond of methoxy groups in lignin and
methoxyl-rst strategy to selectively produce valuable catalyze the N-methylation reaction of N-methylanilines using
compounds is a very interesting protocol for the valorization of lignin as a methylating agent to produce N,N-dimethylanilines.
35
lignin.
When Kra lignin was employed, the selectivity of N,N-dime-
Methyl-substituted amines are important intermediates for thylanilines reached as high as 98%. Furthermore, the leover
the synthesis of dyes and can also be used as solvents, stabi- material aer the N-methylation reaction can be used as an
lizers and analytical reagents. Traditional methods to produce efficient co-catalyst for the CO
methyl-substituted amines are through the N-methylation
2
/epoxide coupling reaction.
reaction using methyl iodide, methanol or dimethyl sulfate as
the methylating agent. These are highly toxic chemicals.
Results
Recently, CO combined with a reductant (hydrogen or hydro- Screen of catalytic systems
2
silane) has been developed as a greener starting material for the
We rst screened the catalytic system by testing the methylation
of N-methylaniline, using anisole as the methylation reagent.
The results are given in Table 1. In conventional organic
36–39
N-methylation reaction.
However, lignin, which is abundant
in methyl groups, has never been recognized as a cheap and
renewable methyl source.
solvents, such as CH
3
CN and toluene, the reaction did not occur
The cycloaddition of epoxides with CO
2
to produce cyclic
(Table 1, entries 1 and 2). The C–O bond of anisole remained
carbonates is one of the most promising and extensively studied
untouched under these reaction conditions. However, ionic
4
0
approaches for CO utilization. Numerous metal complexes,
ꢀ
2
liquids (ILs) containing BF
4
were efficient solvents for this
41
metal–organic hybrid materials
and metal-free organic
systems have been developed as efficient catalysts for this
reaction. Hydrogen-bond donor groups (–OH, –NH , –COOH,
etc.) have been found to induce synergistic effects to facilitate
reaction when LiI was used as the catalyst (Table 1, entries 3–4).
42
In particular, in HMimBF , the yield of N,N-dimethylaniline
4
2
could reach 72% (Table 1, entry 3). Other alkali halides, such as
NaI, KI, CsI, LiBr, and LiCl were inactive for this reaction (Table
43
CO
with hydroxyl groups could act as an efficient co-catalyst for
promoting the cycloaddition of epoxides with CO when using
2
/epoxide coupling. It has been reported that substances
1, entries 5–9). We also tested other ionic liquids with different
anions as the solvent, and the yields of N,N-dimethylaniline
2
were very low (Table 1, entries 10–14). The results indicate that
44
KI as the catalyst.
ꢀ
the BF
4
anion and iodates with strong Lewis acidity were
Herein, we made the rst attempt to utilize lignin as a methyl
source to produce methyl-substituted amines via an N-methyl-
ation reaction. It was demonstrated that lignin could be used as
a methylation agent for efficiently producing N,N-dimethylani-
lines from anilines. We found that a catalytic system
required, and LiI/HMimBF
catalytic systems studied.
4
was the most active among the
Optimization of reaction conditions
comprising LiI and an ionic liquid (IL, e.g. 1-hexyl-3- The effect of reaction parameters on the reaction was further
methylimidazolium tetrauoroborate, HMimBF
4
)
could studied using the LiI/HMimBF catalytic system, and the results
4
a
Table 1 Screening of the catalyst system of the reaction of anisole and N-methylaniline
Entry
Solvent
CH CN
Toluene
HMimBF
BMimBF
HMimBF
HMimBF
HMimBF
HMimBF
HMimBF
BMimAc
BMimN(CN)
BMimClO
BMimNO
BMimOTf
Catalyst
Conversion of N-methylaniline (%)
Yield of N,N-dimethylaniline (%)
Yield of phenol (%)
1
2
3
4
5
6
7
8
9
3
LiI
LiI
LiI
LiI
NaI
KI
CsI
LiBr
LiCl
LiI
LiI
LiI
LiI
LiI
0
0
77
74
0
0
0
0
0
0
1
20
6
33
0
0
72
68
Trace
Trace
Trace
Trace
Trace
0
0
0
95
90
0
0
0
0
0
1
2
9
3
4
4
4
4
4
4
4
1
1
1
1
1
0
1
2
3
4
2
1
10
2
25
4
3
25
a
ꢁ
Reaction conditions: N-methylaniline 1 mmol, anisole 1 mmol, metal halide 2 mmol, reaction temperature 120 C, reaction time 12 h, solvent 1
mL. The yield was calculated based on the NMR spectra using 1,3,5-trioxane as an internal standard.
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are given in Fig. 1. As expected, the conversion of N-methyl- amount of aniline in the experiment. This is another reason
aniline and the yield of N,N-dimethylaniline increased with that the conversion of N-methylaniline and yield of N,N-dime-
increasing amount of LiI, as shown in Fig. 1a. This may have thylaniline could not approach 100%. The conversion of
resulted from the increased acidity of the catalytic system. N-methylaniline and the yield of N,N-dimethylaniline increased
ꢁ
ꢁ
ꢁ
ꢁ
Fig. 1b demonstrates the effect of reaction time on the reaction. from 100 C to 120 C, and then decreased from 120 C to 130 C
The conversion and yield increased with time within 12 h, and (Fig. 1c). The standard enthalpy of the reaction was calculated to
ꢀ1
then became independent of time. The standard Gibbs free be ꢀ14.8 kJ mol , i.e., the reaction is exothermic. At lower
ꢀ
1
ꢁ
energy change of the reaction is ꢀ15.7 kJ mol at 120 C, as temperature, the reaction could not reach equilibrium within
45
calculated using the CBS-APNO method with the Gaussian 09 a reasonable reaction time. The reaction equilibrium was
46
ꢁ
package. The corresponding equilibrium constant of the reached at 120 C, and further increase of temperature resulted
reaction is 122.5 if the activity coefficients of the reactants and in the decrease of equilibrium conversion. Thus, a maximum
products are supposed to be unity, and the equilibrium conversion was observed in the conversion vs. temperature
4
conversion of anisole should be 91.7%. This can explain the fact curve (Fig. 1c). The amount of HMimBF (IL) also affected the
that the conversion and yield could not approach 100%. The conversion of N-methylaniline and the yield of N,N-dimethyla-
discrepancy between the experimental and theoretical equilib- niline. The reaction did not occur without the IL (Fig. 1d).
rium conversion values stems mainly from the fact that the However, the conversion and yield decreased with increasing
activity coefficients may not be unity. Moreover, the dispro- amount of IL. This may be ascribed to the dilution of the
portionation reaction of N-methylaniline (Scheme 1) may also reaction system and especially the decrease of the acidity, which
take place under the reaction conditions because the calculated resulted in slower reaction kinetics. Indeed, extending the
standard Gibbs free energy change of this process is reaction time slowly increased the conversion and yield.
ꢀ
1
ꢀ
1.9 kJ mol . The reactant, N-methylaniline, could be trans-
formed into aniline and N,N-dimethylaniline in the absence of
Lignin as the methylation agent
a methylation agent, and we detected the formation of a small
Then the performance of the LiI/HMimBF4 catalytic system
using Kra lignin as the methylation agent was investigated,
and the results are shown in Fig. 2. The methoxyl content of the
ꢀ1
used lignin was 3.5 mmol g , as determined using the iodine
35
stoichiometry titration method. The reaction could not
proceed without LiI. In the conversion of N-methylaniline, the
yield and selectivity of N,N-dimethylaniline increased with
increasing amount of LiI. When the amount of LiI was 3 mmol,
the selectivity of the desired product was 97% (Fig. 2a), and
a trace amount of quaternary ammonium salt was detected. The
conversion and yield increased with increasing amount of IL at
the beginning, and then decreased (Fig. 2b) due to the dilution
effect. The dependence of the conversion and yield on temper-
ature was similar to that of the reaction of anisole and
N-methylaniline, and the conversion of N-methylaniline and the
ꢁ
yield of the product could reach 70% at 120 C (Fig. 2c). Fig. 2d
illustrates that the conversion and yield increased with time and
reached equilibrium aer about 13 h. The effect of the amount
of lignin on the conversion of N-methylaniline and the yield of
the desired product was also checked (Fig. 2e). The conversion
and yield increased with increasing amount of lignin, while the
gap between the conversion and yield diminished, indicating
that the selectivity to the desired product N,N-dimethylaniline
increased. When the amount of Kra lignin was 0.2 g, the
selectivity could reach 97% under the reaction conditions. This
suggested that an adequate amount of lignin could inhibit the
disproportionation reaction of N-methylaniline. The by-product
was a small amount of quaternary ammonium salt.
Fig. 1 Conversion of N-methylaniline and the yield of N,N-dimethy-
laniline (1 mmol N-methylaniline, 1 mmol anisole). (a) Effect of LiI
ꢁ
amount with reaction time of 12 h at 120 C in 0.5 g HMimBF
(
(
4
solvent;
ꢁ
b) effect of reaction time at 120 C using 2 mmol LiI in 0.5 g HMimBF
c) effect of temperature with reaction time of 12 h at 120 C using
4
;
ꢁ
2
mmol LiI in 0.5 g HMimBF
4
; (d) effect of HMimBF
4
amount with
ꢁ
reaction time of 12 h at 120 C using 2 mmol LiI. The yield is based on
aniline compounds.
Substrate scope
We also studied the N-methylation reaction of different aniline
compounds to produce the corresponding N,N-dimethylani-
lines using Kra lignin as the methylation agent, and the results
are given in Table 2. Obviously, lignin could also be used as
Scheme 1 The disproportionation reaction of N-methylaniline in the
absence of lignin or anisole.
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Table 2 The N-methylation reactions of aniline compounds using
a
lignin as a methylating agent
Entry Substrates
1
Products
Conv. (%) Yield (%) Sel. (%)
72
68
70
65
97
96
2
3
4
69
57
67
56
97
98
5
55
54
98
a
Reaction conditions: N-methylaniline: 0.5 mmol, LiI: 3 mmol, reaction
as the solvent. The
conversion and yield were calculated based on the NMR spectra using
,3,5-trioxane as an internal standard. “Conv.” and “Sel.” are the
conversion of the substrate and the selectivity to the product,
time: 12 h, lignin: 0.2 g, 3 g ionic liquid HMimBF
4
1
respectively. The by-product was
a
trace amount of quaternary
Fig. 2 The conversion of N-methylaniline and the yield of N,N- ammonium salt.
dimethylaniline (N-methylaniline: 0.5 mmol). (a) Effect of the amount
ꢁ
of LiI in 3 g IL HMimBF
4
at 120 C with reaction time of 13 h and 0.2 g
ꢁ
Kraft lignin; (b) effect of HMimBF
4
amount at 120 C with reaction time
51
the molecular structure and the experimental conditions.
of 13 h using 3 mmol LiI and 0.2 g Kraft lignin; (c) effect of reaction
temperature using 3 mmol LiI in 3 g HMimBF
1
4
with reaction time of Fig. 3 shows that, aer the reaction, the diffusion coefficient
3 h and 0.2 g Kraft lignin; (d) effect of reaction time at 120 C using increased, indicating that the molecular weight decreased aer
ꢁ
3
1
mmol LiI in 3 g HMimBF
4
; (e) effect of the amount of Kraft lignin at
. The
the reaction. However, in the low molecular weight region (log D
z ꢀ9), there is no aromatic ring signal (d 6–8), demonstrating
that the lignin is not depolymerized into small molecules or low
ꢁ
20 C with reaction time of 13 h using 3 mmol LiI in 3 g HMimBF
4
yield is based on aniline compounds.
molecular weight fragments. The signal of –OCH is at 3.7 ppm,
3
and it becomes much weaker aer the reaction. Meanwhile,
new signals appear at lower eld (d 7.2–7.4), which suggests the
formation of catechol groups. These can also be gured out
from 2D-HSQC NMR spectra, as shown in Fig. S1 and S2.† The
efficient methylation reagent for producing other N,N-dime-
thylanilines. The selectivity to the desired products is more than
96%. No other byproducts were detected except for a small
amount of quaternary ammonium salt.
Discussions
We characterized the lignin before and aer the reaction using
47
Diffusion-Ordered NMR Spectroscopy (DOSY)
and two-
dimensional heteronuclear single quantum coherence
48
(
2D-HSQC) NMR Spectroscopy. DOSY is a powerful method for
size and molecular weight measurements for different classes of
49
macromolecules and complex mixtures. It has been demon-
strated to be applicable for constructive determination of lignin
50,51
structure and molar mass.
The measured diffusion coeffi-
cient (D) can be correlated to the molecular weight (MW) of the
analyzed molecule using the Mark–Houwink equation, i.e., D ¼
Fig. 3 The DOSY spectra of lignin before (red) and after (blue)
K MW , where the scaling parameters (K and a, K < 0) depend on reaction.
a
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2
Scheme 3 Cycloaddition of epoxy propane with CO using the left-
over material and original lignin as a catalyst under solvent-free
conditions.
Fig. 4 HPLC trace of the liquid mixture after the reaction.
conducted a cycloaddition reaction of epoxy propane with CO
2
using the residual lignin as the co-catalyst under solvent-free
ꢁ
conditions (Scheme 3). At 60 C under 2 MPa CO
2
atmo-
methoxy group signal (56.4/3.70 ppm, colored yellow) becomes
dramatically weaker aer the reaction. Meanwhile, a new signal
for catechyl units (colored brown) appears in the aromatic
region. We also characterized the liquid phase aer the reaction
using HPLC (Fig. 4). The trace clearly shows that N,N-dimethy-
laniline is almost the sole product, and no signal for depoly-
merized fragments of lignin was observed. This further
demonstrates the selective utilization of lignin.
sphere, the yield of 1,2-propylene cyclic carbonate reached 93%
at 8 h, while the original lignin only gave a yield of 49% under
the same reaction conditions. Without lignin, the reaction did
not take place. This result is consistent with the results reported
44
in the literature.
Conclusions
Reaction mechanism
In summary, a route to produce N,N-dimethylanilines using the
methoxy groups in lignin as the methylation reagent was
developed. N,N-dimethylanilines can be produced with a selec-
tivity of more than 96% using Kra lignin and aniline
compounds as the starting materials. This work reveals the
possibility of using lignin as a methylation agent, which may
benet the production processes of some bulk chemicals that
involve a methylation step. There are some obvious advantages
to using lignin as methylation agent, such as its low cost,
abundance and ease of separation. Moreover, the residual
lignin, which is abundant in hydroxyl groups, is more favorable
for use in certain applications than original lignin, such as the
synthesis of functional materials. We believe that this strategy,
which selectively transforms a class of functional groups in
lignin into a product with high purity, will trigger much more
research in the future.
The possible reaction pathway is schematically shown in
Scheme 2. In the reaction, LiI rst cleaves the ether bond of the
methoxy groups of lignin to form CH
the synergy of tetrauoroborate. The mechanism of the BF
3
I and intermediate A with
ꢀ
4
-
aided cleavage of the Ar-OCH ether bond is reported in our
3
52
previous work. Then CH I reacts with N-methylaniline to form
3
N,N-dimethylaniline and HI, which immediately react with
intermediate A to produce the leover material B and regen-
erated LiI.
Application of the leover material
Because only the methoxy groups are selectively converted, the
bulk structure is le as a solid residue. As suggested by the NMR
analysis, the leover material is rich in hydroxyl groups, which
endows it with more applications than original lignin, such as
in catalysis and the production of phenolic resin. Herein, we
Experimental
Chemicals
Kra lignin was provided by Beijing InnoChem Science & Tech-
nology Co., Ltd. Anisole (99%), toluene (99%), acetonitrile (99%),
N-methylaniline (99%), 4-(N-methylamino)benzonitrile (98%), N-
methyl-4-nitroaniline (97%), N-methyl-p-toluidine (98%), 2-u-
oro-N-methylaniline (98%), 1,3,5-trioxane (99%), epoxy propane
(98%), LiI (99%), LiBr (99%), LiCl (99%), NaI (99%), KI (99%) and
CsI (99%) were purchased from J&K scientic Ltd. HMimBF
4
(
(
(
1-hexyl-3-methylimidazolium tetrauoroborate, >98%), HMimCl
1-hexyl-3-methylimidazolium chloride, >98%), HMimOAc
1-hexyl-3-methylimidazoliumacetate, >98%), BMimCl (1-butyl-3-
methylimidazolium chloride, >98%) and BMimBF4 (1-butyl-3-
methylimidazoliumacetate, >98%) were provided by Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences. All
chemicals were used as received.
Scheme 2 The possible reaction pathway of the N-methylation
reaction using lignin as a methylating agent.
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Reaction procedures for N-methylation reaction
was used for HPLC analysis. The mobile phase was methanol
aqueous solution (MeOH : H O volume ratio of 55 : 45) with
2
The reaction was carried out in a Teon-lined stainless-steel
reactor of 15 mL in capacity with an inner diameter of 16
mm, using a magnetic stirrer. In the experiment, desired
amounts of catalyst, amines, Kra lignin or anisole and solvent
ꢀ
1
a ow rate of 0.8 mL min , and the temperature was kept at
ꢁ
5
0 C. The trace was collected for 80 min.
were loaded into the reactor. The reactor was purged with N to Computational details
2
remove the air. The reaction mixture was stirred at the required
temperature for the required time. The temperature was
controlled by a PID temperature controller (model SX/A-1, Bei-
jing Tianchen Electronic Company). Aer the reaction, the
reactor was placed in ice water to cool down. About 0.02 g 1,3,5-
trioxane as the internal standard was added to the liquid
mixture and stirred for 5 min. The mixture was centrifuged,
resulting in a liquid phase and a solid phase. The liquid phase
The free energy of each compound was calculated using the
45
CBS-APNO method. This approach is a compound method for
calculating highly accurate values for thermochemical param-
eters, which involves a series of calculations on a particular
geometry and a complete basis set model chemistry. All the
q
Gibbs free energies (G ) calculated in this paper are for a stan-
dard state of 393.15 K and 1 atm. The equilibrium constant (K)
q
DG
ꢀ
q
is based on the equation, K ¼ e RT , where the DG , R and T are
the standard free energy change of the reaction, the ideal gas
constant and the temperature, respectively.
3
(0.1 mL) was dissolved in MeCN-d (0.5 mL). The mixture was
centrifuged and the supernatant liquid was collected for
1
quantitative analysis using H NMR (Bruker Avance III 400 HD).
The residue solid phase was washed with MeCN (5 ꢂ 3 mL),
dilute HCl (pH ¼ 2, 2 ꢂ 3 mL) and deionized water (2 ꢂ 3 mL) in
Conflicts of interest
ꢁ
sequence. Finally, it is dried under vacuum at 60 C for 48 h over
The authors declare no conict of interest.
a P
HSQC and DOSY analysis as well as used as the co-catalyst for
the cycloaddition reaction of epoxy propane with CO
2 5
O desiccant. The obtained solid was characterized by 2D-
2
.
Acknowledgements
This work was supported by National Key Research and Devel-
opment Program of China (2017YFA0403103), the National
Natural Science Foundation of China (21603235), and Chinese
Academy of Sciences (QYZDY-SSW-SLH013), the Recruitment
Program of Global Youth Experts of China.
Reaction procedures for cycloaddition of epoxides with CO2
The reaction of CO and epoxide was also conducted in the
2
same reactor. In a typical experiment, the desired amount of
lignin or leover material, KI and PO were added into the
reactor. The reaction mixture was cooled down using liquid N
and then the reactor was sealed and purged with CO to remove
the air. Aer the temperature restored to room temperature,
2
,
2
Notes and references
2
CO was charged into the reactor until a pressure of 2.0 MPa was
1
M.
Saidi,
F.
Samimi,
D.
Karimipourfard,
reached. The pressure was determined by a pressure transducer
T. Nimmanwudipong, B. C. Gates and M. R. Rahimpour,
Energy Environ. Sci., 2014, 7, 103–129.
(
FOXBORO/ICT, Model 93), which could be accurate to
ꢁ
ꢃ0.025 MPa. Then the reactor was placed in an air bath at 60 C
for 8 h. Aer the reaction, the reactor was placed in ice water
and the gas was released. The yield of the product was deter-
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