Light-assisted: O -methylation of phenol with dimethyl carbonate over a layered double oxide catalyst

Article abstract of DOI:10.1039/c8cy02579g

Layered double oxides (LDOs) exhibit high catalytic activity in the O-methylation of phenol under light irradiation, owing to the synergy of the light absorption of phenol molecules to achieve excited states and the facilitated adsorption of reactant molecules by the acid-base pairs of Mg₃Al-LDO, both of which can promote phenol deprotonation.

Full text of DOI:10.1039/c8cy02579g

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DOI: 10.1039/C8CY02579G
Catalysis Science & Technology
COMMUNICATION
Light-assisted O-methylation of Phenol with Dimethyl Carbonate
over Layered Double Oxide Catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Xiaoyu Wang,a,b Ruiyi Wang,* Xianmo Gu, Jianfeng Jia and Zhanfeng Zheng*
a
a
c
a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
Layered double oxide (LDO) exhibit high catalytic activity in O- catalyst for the O-methylation of phenol with DMC, in which reduce
1
2
methylation of phenol under light irradiation, owing to the the reaction temperature to 443 K by using microwave method.
synergism of the light absorption of phenol molecules to achieve Layered double oxides (LDO) originated from thermal
excited states as well as the facilitated adsorption of reactant decomposition of Layered double hydroxides (LDHs). LDO have the
molecules by acid-base pairs of Mg
promote phenol deprotonation.
3
Al-LDO, which can both advantages of high surface area and thermal stability, along with
the tunable acidity and basicity, which are characterized by the
13-15
presence of acid-base pairs.
These acid-base pairs could
facilitate the adsorption of reactants molecules. According to
The O-methylation of phenols is of crucial importance in synthesis
products for used as stabilizers for plastics and antioxidants for oils
and grease as well as intermediates in the field of dyes, agricultural
1
6
Chizallet et al., the contact between a protic reactant molecule
and an oxide surface can provoke its deprotonation. Jyothi and co-
workers demonstrated that LDO catalysts can efficiently drive the
1
chemicals, and fragrances. Traditional synthesis methods generally
17
O-methylation of catechol with DMC, at 573 K. Till now, the O-
methylation of phenols at a milder condition is rarely reported.
involved the use of toxic alkylating agents (methyl halide, phosgene
2-5
or dimethyl sulfate), high reaction temperature
and generating
large quantity of waste. Dimethyl carbonate (DMC) is found to be
an efficient methylating agent, the by-product methanol can be
Herein we describe a light-assisted green process for O-
methylation of phenol with dimethyl carbonate to synthesize
anisole on LDO catalysts with high conversion and product
selectivity. The catalytic performance of various LDO catalysts:
6
recycled for the production of DMC. The O-methylation of phenol
7
,8
with DMC has been reported over potassium carbonate and 1-n-
9
butyl-3-methylimidazolium chloride. To avoid the limitations of
Mg
phenol were evaluated in presence and absence of light (high-
pressure mercury lamp), respectively. As shown in Fig. 1a, Mg Al-
3 3 3
Al-LDO, Ni Al-LDO, and Zn Al-LDO in the O-methylation of
homogeneous catalytic process with the difficulty of catalyst
recovery and product separation, the development of an
environmentally benign heterogeneous catalyst for the O-
methylation of phenol continues to attract significant interest.
3
LDO exhibits the highest activity with the DMC conversion at 82.5%
and selectivity to anisole at 95.6% under high-pressure mercury
lamp irradiation at 160 °C for 6 h, which is much higher than Ni
3
Al-
A variety of catalysts have been investigated for the O-
methylation of phenol reaction. Bal and co-workers found that
alkali loaded silica catalyst can efficiently drive the selective O-
LDO (Conv.=56.3%, Sel.=88.4%) and Zn Al-LDO (Conv.=47.2%,
3
Sel.=69.7%). It is noted that all the catalyst exhibit much higher
activity under light irradiation than in the dark. Normally, the
difference between the activation energies of the light irradiated
system and the system in the dark indicates the contribution of
1
0
alkylation of phenol at 673 K. Fu et al. reported that X-zeolites can
1
1
be used for the O-methylation of phenol with DMC at 553K. Both
of the above reactions need to be completed in the gas phase and
high temperature conditions. Recently, Gadge and co-workers
demonstrated that magnesium oxide was used as heterogeneous
18
irradiation towards reducing the apparent activation energy. The
activation energies of light-driven and thermal-driven reaction were
calculated according to the Arrhenius equation shown in Fig. 1b
(
calculation details shown in the ESI), being 97.55 and 106.58
a.
kJ/mol, respectively. This means that light energy can facilitate the
reaction.18 The catalyst activity remained stable (Fig. S4a) and the
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese
Academy of Sciences, Taiyuan, Shanxi 030001, PR China. Email:
wangruiyi@sxicc.ac.cn, zfzheng@sxicc.ac.cn
Center of Materials Science and Optoelectronics Engineering, University of
Chinese Academy of Sciences, Beijing 100049, PR China
structure of Mg
reused for five cycles. Thus we choose catalyst Mg
investigate the activation of reactants.
3
Al-LDO had no obvious change (Fig. S4b) after
b.
c.
3
Al-LDO to
The School of Chemical and Material Science, Shanxi Normal University, Linfen,
Shanxi 041004, PR China
†
Electronic Supplementary Information (ESI) available: More experimental details,
catalyst characterization and reaction test results. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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sites of LDO, while DMC is adsorbed on the acidic sites of LDO via its
View Article Online
DOI: 10.1039/C8CY02579G
2
1
carbonyl oxygen, as the pre-literature.
The surface acidic and basic sites were determined by CO
TPD and NH -TPD technique as shown in Table S2, Fig. 2c and Fig.
d. For the CO -TPD profiles (Fig. 2c), broad CO desorption peak in
2
-
3
2
2
2
the range 100-700 °C can be deconvoluted into two peaks with
desorption peaks with maximal temperatures at 300 °C and 500 °C,
which can be assigned to the medium and strong basic sites,
respectively. The weak, medium and strong basic sites are derived
-
2+ 2-
3+ 2-
from OH , metal-oxygen pair (Mg -O , Al -O ) and low-
2
-
22
coordination oxygen anion (O ), respectively. In the NH
profiles (Fig. 2d), a broad peak from NH desorption between 100-
00 °C can be deconvoluted into three contributions with a maximal
temperature in the region 120-220 °C, 250-450 °C and 450-700 °C,
which can be identified as the weak (Mg ), medium and strong
acidic site (Al ), respectively. Notably, it is observed that the
catalyst Mg Al-LDO gives the largest amount of both medium basic
3
-TPD
3
8
2
+
3
+
23
3
site with 1.50 mmol/g and medium and strong acidic site with 0.71
mmol/g and 0.29 mmol/g, respectively (Table S2). It indicates that
2
+
2-
the medium strength Lewis basic sites (mostly Mg -O ) serve as
active center to activate phenol to produce phenoxyl species, while
3
+
medium and strong acidic site (Al ) act as active site toward
associated to carbonyl oxygen of DMC.
Fig. 1 (a) Catalytic performance: conversion rate under irradiation and dark,
selectivities of DMC using varied catalysts under irradiation. (b) Plot of (1−Xb)-1
versus reaction time at different temperatures on the Mg3Al-LDO catalyst: the
reaction was conducted in light (solid line) or in the dark (dotted line), and the
activation energy scheme (upper left corner). Reaction conditions: catalyst, 0.28
2
g; phenol, 135 mmol; DMC, 67.5 mmol; Ar, 1 atm; light intensity, 66 mW/cm ;
reaction temperature, 160 °C; reaction time, 6 h. MgO-Al2O3: MgO and Al2O3
were mechanically mixed in a mortar according to n(Mg): n(Al)=3:1.
In-situ FT-IR spectra after coadsorption of phenol and DMC
on Mg Al-LDO was conducted (Fig. 2a and Fig. 2b) to understand
3
the activation process of the reactants (detailed explanation shown
in the ESI). The diminished in intensity of O-H stretching vibrations
-
1
-1
band of phenol at 3662 cm and 3639 cm indicating the hydroxyl
19
of phenol has been deprotonated. Low frequency shift of the C-H
stretching vibrations bands of the aromatic ring of phenol at 3064
cm and 3036 cm indicating the phenol H-bonded (of hydroxyl) to
base sites of LDO. Low frequency shift of the vibration band of DMC
carbonyl oxygen group at 1683 cm indicating the carbonyl oxygen
atoms of DMC associated with the acidic sites of LDO. The
asymmetric variable angle vibration band of anisole methyl group at
Fig. 2 (a) In-situ FT-IR spectra of Mg3Al-LDO after co-adsorption of phenol and
-1
-1
-1
-1
DMC: from 4000 cm to 2000 cm and (b) from 2000 cm to 600 cm .
(downward arrow: band intensity decreases with the increase of time; upward
arrow: band gradually appears with the increase of time); (c) TPD profiles of CO2-
TPD and (d) NH3-TPD of Mg3Al-LDO, Ni3Al-LDO, and Zn3Al-LDO.
-
1
-1
-1
2
0
To further prove the role of acidic and basic sites, control
-
1
1
446 cm appeared from nothing and increased in intensity experiments with a series of catalysts with different amount of
indicating the anisole production. It is revealed that both reactants acidic and basic sites (Mg
3
Al-LDHs, MgO, Al , MgO-Al ) were
2
O
3
2 3
O
are adsorbed on the catalyst surface during the O-methylation conducted (Fig. 1a). The physical properties of catalysts are shown
reaction. Phenol is activated by H-bonding (of hydroxyl) to the basic in Table S1. Obviously, the surface area is not the decisive factor on
the performance, as the optimal catalyst has a relatively small
2
| J. Name., 2012, 00, 1-3
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specific surface area. Basic sites on the catalysts surface alone key factors to promote the reaction. In addition, thVeieiwnAflruticelencOenlinoef
cannot simply be the dominate factor enhancing the catalyst light intensity on the reactivity was conducDteOdI:(1F0i.g1.03S97/)C. 8ItCiYs0f2o5u79nGd
performance, since MgO and Mg
but both exhibit low activity under irradiation and in the dark, light intensity, which indicates that the reaction is driven by light in
respectively. Acidic sites on the catalysts alone also cannot be the the presence of Mg Al-LDO.
dominating factor, since Al have acid surface sites but exhibit
low activity either. Physically mixed MgO and Al catalyst also
3
Al-LDHs have basic surface sites that the conversion rate of DMC decreases with the decrease of
3
2 3
O
To further investigate the role of light in our reaction system, the
UV-Vis spectra of DMC and phenol were conducted shown in Fig. 3a.
Although DMC display an absorption band in 201 nm ascribed to π-
2 3
O
exhibit lower activity than layered double oxide, which due to that
LDO containing the acid-base pairs. It should be noted that
excellent catalytic results have been obtained with catalysts
2
6
π* transition, the energy of light source used (high-pressure
mercury lamp, 240-740nm) was not enough to stimulate it. While
phenol display strong absorption in 205 nm and 270 nm ascribed to
π-π* transition, indicating that phenol molecules can absorb light to
2
4,25
containing acid-base pairs.
In this case, a cooperative role of
acid-base sites has been found that allow substituting strong bases
by very simple catalysts with mild acid-base pairs. The superior
behavior of LDO could be due to a combined acid-base catalyzed O-
methylation of phenol, the acidic sites of LDO associated to
carbonyl oxygen of DMC and the basic sites of LDO associated to
hydrogen of phenolic hydroxyl which can activate the hydroxyl
group of phenol adsorbed on the surface of catalyst.
MgAl-LDO with varied Mg/Al ratios were synthesized (Mg
Mg Al-LDO, Mg Al-LDO) and the catalytic performance also agree
with the above results (Fig. 1a). Mg Al-LDO, which has the
maximum amount of basic sites and acidic sites among the varied
Mg/Al ratio of MgAl-LDO, exhibited the best catalytic performance.
3 3
Catalyst Zn Al-LDO with the conversion of 47.2% and Ni Al-LDO with
the conversion of 56.3% exhibit slightly better performance under
high-pressure mercury lamp irradiation than in the dark with the
conversion of 35.9% and 45.0%, respectively. Mg Al-LDO exhibited
3
the best performance under irradiation could be attributed to the
better ability to adsorbed reactant molecule and the fact that
irradiation can enhance the catalytic performance. Besides,
according to the UV-Vis spectra of Mg
Zn Al-LDO shown in Fig. S6a, Mg Al-LDO shows no light absorption
in the high-pressure mercury lamp output spectrum range.
Although Ni Al-LDO and Zn Al-LDO both exhibit bandgap absorption
2
6
achieve the excited states. Using the long-range corrected cam-
B3LYP method of density functional theory (DFT) with 6-311++g
(
d,p) basis set, we have investigated the structure of phenol-DMC
aggregate both in the ground state and in the first excited state. The
calculation of the excited state was performed with time-dependent
DFT method. As shown in Fig. 3b, in the ground state, the phenol
interacts with DMC through a hydrogen bond. The calculated O-H
hydrogen bond length is 1.825 Å. The C=O bond length of the
carbonyl in DMC is 1.212 Å, which obviously longer than the C=O
bond length (1.203 Å) in free DMC. The calculated irradiation
wavelength for the first excited state is 240 nm. The transition
density of this excitation is shown in Fig. 3b, it is mainly a n-π*
transition on the phenol. It is obviously that the hydrogen bond
between phenol and DMC were enhanced in the excited state. As
shown in Fig. 3b, the calculated hydrogen bond length is 1.740 Å in
the excited state. The enhanced hydrogen bond further activates
the carbonyl of DMC. The C=O bond length slightly elongates to
1
7,21
Besides,
1
Al-LDO,
2
3
3
1.214 Å in the excited state. The above results demonstrate that
3 3
Al-LDO, Ni Al-LDO, and
phenol molecules absorbed light to achieve the first excited states,
then hydrogen bond between phenol and DMC were enhanced,
resulting in deprotonation occurs more readily in the excited state.
This is consistent with the literature report that the lone pair of
electrons on the phenolic hydroxyl groups tend to become more
conjugated to the aromatic ring system in the excited state,
3
3
3
3
at ca. 370 nm in the UV-Vis spectra and can generate electron-hole
pairs under high-pressure mercury lamp irradiation, but their
catalytic activities are much lower than that of Mg
full-spectrum Xe lamp (350-880 nm) is used, both of Ni
Zn Al-LDO exhibit activity similar to that under dark condition (Fig.
S6b). Moreover, the catalytic activity of O-methylation of phenol
over TiO -P25 catalyst under high-pressure mercury lamp
irradiation was conducted and the activities under irradiation and in
the dark are similar (Fig. S6b). Therefore, it can be concluded that
2
photogenerated electrons and holes in LDOs and TiO are not the
3
Al-LDO. When a
2
7
resulting in the hydroxyl group more acidic.
3
Al-LDO and
3
On the basis of above analysis, a tentative mechanism for the
O-methylation of phenol is proposed (Scheme 1). Firstly, phenol and
DMC are adsorbed on the surface of LDO, the acidic sites of LDO
2
3
+
(
(
Al ) associated to carbonyl oxygen of DMC and basic sites of LDO
2
+
2-
Mg -O ) associated to hydrogen of phenolic hydroxyl (I).
Fig. 3 (a) UV-Vis spectra of DMC and phenol. (b) DFT calculation results of ground and excited states of phenol-DMC aggregate.
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Secondly, when phenol molecules absorb light to achieve the
excited states, the deprotonation of phenolic hydroxyl group occurs
more readily because the electrons on the phenolic hydroxyl groups
are shifted into the phenol ring in the excited state, making this
hydroxyl group more acidic (II). Meanwhile, the basic sites of
catalyst can bind the hydrogen atom of the phenol molecule and
also facilitate the O-H cleavage on the surface. Thirdly, the
formation of anisole proceeds presumably via nucleophilic attack at
the methyl carbon of DMC by the phenol oxygen (III and IV). Finally,
the catalyst surface regenerates for another reaction cycle by
Acknowledgements
View Article Online
DOI: 10.1039/C8CY02579G
This work was supported by the National Natural Science
Foundation of China (Nos. 21773284, 21703276), the Shanxi
Science and Technology Department (Nos. 201801D221093,
201601D021032) and the Hundred Talents Programs of the
22
Chinese Academy of Sciences and Shanxi Province.
Notes and references
desorption of methanol and CO
residual methyl hydrogen carbonate (V). It noted that the amounts
of methanol and CO generated during reaction are in good
2
which are decomposed from the
1
2
3
4
E. Fuhrmann and J. Talbiersky, Org. Process Res. Dev., 2005,
9, 206-211.
2
S. Oae and R. Kiritani, Bull. Chem. Soc. Jpn., 1966, 39, 611-
614.
stoichiometric relation and the carbon balance of the reaction is
satisfied within experimental error (Table S3).
S. C. Lee, S. W. Lee, K. S. Kim, T. Jin. Lee, D. H. Kim and J. C.
Kim, Catal. Today, 1998, 44, 253-258.
M. C. Samolada, E. Grigoriadou, Z. Kiparissides and I. A.
Vasalos, J. Catal., 1995, 152, 52-62.
5
6
P. Tundo and M. Selva, Acc. Chem. Res., 2002, 35, 706-716.
D. Delledonne, F. Rivetti and U. Romano, J. Organomet.
Chem., 1995, 488, 15-19.
S. Ouk, S. Thiebaud, E. Borredon, P. Legarsb and L. Lecomte,
Tetrahedron Lett., 2002, 43, 2661-2663.
A. Bomben, M. Selva, and P. Tundo, Ind. Eng. Chem. Res.,
7
8
9
1
1
999, 38, 2075-2079.
Z. L. Shen, X. Z. Jiang, W. M. Mo, B. X. Hua and N. Sun, Green
Chem., 2005, 7, 97-99.
0 R. Bal and S. Sivasanker, Appl. Catal. A: Gen., 2003, 246, 373-
382.
1
1 Z. H. Fu and Y. Ono, Catal. Lett., 1993, 21, 43-47.
2 S. T. Gadge, A. Mishra, A. L. Gajengi, N. V. Shahi and B. M.
Bhanage, RSC Adv., 2014, 4, 50271-50276.
1
1
1
1
1
3 D. G. Costa, A. B. Rocha, W. F. Souza, S. S. X. Chiaro, and A. A.
Leitao, J. Phys. Chem. C., 2012, 116, 13679-13687.
4 V. R. L. Constantino and T. J. Pinnavaia, Inorg. Chem., 1995,
34, 883-892.
5 D. P. Debecker, E. M. Gaigeaux and G. Busca, Chem. Eur. J.,
009, 15, 3920-3935.
6 C. Chizallet, M. L. Bailly, G. Costentin, H. L. Pernot, J. M.
Krafft, P. Bazin, J. Saussey, M. Che, Catal. Today, 2006, 116,
196-205.
2
Conclusions
17 T.M. Jyothi, T. Raja, M. B. Talawar, B. S. Rao, Appl. Catal., A:
Gen., 2001, 211, 41-46.
Scheme 1 Schematic diagram of the proposed reaction mechanism.
18 S. Sarina, E. R. Waclawik and H. Zhu, Green Chem., 2013, 15,
1814-1833.
1
9 T. Ebata, T. Watanabe and N. Mikami, J. Phys. Chem., 1995,
99, 5761-5764.
3
In summary, Mg Al-LDO prepared by the facile calcination of
20 J. S. Byrne, P. F. Jackson and K. J. Morgan, Perkin Trans.,
hydrotalcite is found to be an efficient catalyst for O-methylation of
phenol using dimethyl carbonate as alkylating agent under light
irradiation. The excellent catalytic performance can attribute to the
synergistic effects of two factors: (1) The phenol molecules can
1975, 2, 1800-1802.
2
1 T. Beutel, J. Chem. Soc., Faraday Trans. 1998, 94, 985-993
2 B. N. Zope, D. D. Hibbitts, M. Neurock, R. J. Davis, Science,
2010, 330, 74-78.
2
absorb light to achieve the excited states, which promote its 23 D. Tichit and F. Fajula, Stud. Surf. Sci. Catal., 1999, 125, 329-
3
40.
deprotonation occurs more readily; (2) The acid-base pairs of
Mg Al-LDO can facilitate the adsorption of reactants molecules and
provoke deprotonation. This simple, cost-effective, and
2
2
4 B. M. Bhat, Orient. J. Chem., 2012, 28, 1751-1760.
5 A. H. Padmasri, A. Venugopal, V. D. Kumari, K. S. Rama Rao,
P. K. Rao, J. Mol. Catal. A: Chem., 2002, 188, 255-265.
3
environmentally benign catalytic process exhibits great potential in 26 DMS Documentation of Molecular Spectroscopy: UV Atlas of
the alkylation of phenols.
organic compounds, London, 1960–1971.
2
7 J. R. Lakowicz, Springer Science+Business Media, New York,
1999.
Conflicts of interest
There are no conflicts of interest to declare.
4
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DOI: 10.1039/C8CY02579G
Table of Content：
Light-assisted O-methylation of Phenol with Dimethyl
Carbonate over Layered Double Oxide Catalyst
a,b
a
a
c
a,b
Xiaoyu Wang, Ruiyi Wang,* Xianmo Gu, Jianfeng Jia and Zhanfeng Zheng*
a
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese
Academy of Sciences, Taiyuan, Shanxi 030001, China
b
Center of Materials Science and Optoelectronics Engineering, University of Chinese
Academy of Sciences, Beijing 100049, PR China
c
The School of Chemical and Material Science, Shanxi Normal University, Linfen,
Shanxi 041004, PR China
Phenol molecules can adsorb light to achieve the excited states, which promote its
deprotonation occurs more readily.