A synthesis of copper based metal-organic framework for O-acetylation of alcohols

Article abstract of DOI:10.1016/j.catcom.2013.10.016

A novel metal-organic framework, Cu-BDC was synthesized by static hydrothermal method using innocuous solvents and characterized by several techniques such as powder XRD, ESR, TG-DTA, elemental analysis, ICP-AES, SEM, EDXS, FT-IR, BET surface area, pore volume and pore size. The catalytic performance of Cu-BDC was explored for O-acetylation of alcohols under solvent-free conditions at room temperature. The catalyst exhibited remarkable activity and reusability affording the desired products in excellent yields.

Full text of DOI:10.1016/j.catcom.2013.10.016

Catalysis Communications 44 (2014) 24–28
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
A synthesis of copper based metal-organic framework for O-acetylation
of alcohols
Savita J. Singh a,1, Sandip R. Kale a,1, Manoj B. Gawande b,2,3, A. Velhinho , Radha V. Jayaram ⁎
c
a, ,1
a
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400019, India
b
REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
CENIMAT/I3N, Departmento de Ciências dos Materiais, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 May 2013
Received in revised form 26 September 2013
Accepted 14 October 2013
Available online 26 October 2013
A novel metal-organic framework, Cu–BDC was synthesized by static hydrothermal method using innocuous
solvents and characterized by several techniques such as powder XRD, ESR, TG–DTA, elemental analysis, ICP-
AES, SEM, EDXS, FT-IR, BET surface area, pore volume and pore size. The catalytic performance of Cu–BDC was
explored for O-acetylation of alcohols under solvent-free conditions at room temperature. The catalyst exhibited
remarkable activity and reusability affording the desired products in excellent yields.
©
2013 Elsevier B.V. All rights reserved.
Keywords:
Metal-organic framework
Cu–BDC
Hydrothermal synthesis
O-acetylation
Heterogeneous catalyst
1
. Introduction
temperatures starting at room temperature and up to solvothermal
conditions at 200 °C.
Catalysis plays a dynamic role in achieving chemical conversions
Although the applications [6–10] of this new and emerging class of
material have been significant in storage, separation and sensing; their
catalytic properties have not been fully explored. The high metal con-
tent in MOFs, their insolubility in water and common organic solvents
offer immense scope for their exploration as new heterogeneous cata-
lysts. Also the possibility of incorporating various metal ions in variable
valence states makes them excellent model systems for unraveling the
electronic and matrix effects in catalysis. There are very few reports
demonstrating the catalytic activity of MOFs [11–17]. Most of the
work has been focused on the synthesis and characterization of MOFs
providing catalysis as a supplementary study in short with the reactions
unexplored with respect to the substrates. Thus, a detailed investigation
on MOF as catalyst for organic transformation has been the subject of
recent focus.
Acetylation of alcohols is a fundamental step in many organic
syntheses. Hydroxyl groups are present in a number of compounds of
biological and synthetic interest. Among the protecting groups for alco-
hols, the esters are the most important with acetate being the easiest of
all. A wide range of homogeneous and some heterogeneous catalysts
have been reported for this transformation [18–21]. A number of copper
salts [18,22,23] have also been used in homogeneous catalyst for O-
acetylation of alcohols but they suffer from the drawbacks of difficulty
in catalyst/product separation and result in permanent deactivation of
the catalyst which adds directly to the waste stream. Therefore, intro-
duction of new methods and greener and better catalysts for the prepa-
ration of esters is still in demand.
in an economically and commercially viable manner and is the
foundational pillar of green chemistry as it offers a clear opportuni-
ty to provide realistic solutions to many environmental issues. In
the present era, when pollution is a major problem, the focus is
also on placing precincts to the use of conventional, corrosive and
non-recoverable homogeneous catalysts and identifying robust,
easy to handle, and recoverable heterogeneous catalysts. Metal-
organic frameworks (MOFs) [1–4] belong to the class of materials
that can fulfill the requirements for an environmentally viable het-
erogeneous catalyst and have potential to replace the traditional
ones in the future. They have received a momentous attention in
the area of inorganic–organic hybrid materials [5]. MOFs are porous
polymeric are porous polymeric materials consisting of metal ions
linked together by organic bridging ligands. After combination of
solutions of these inorganic and organic components under stirring,
the metal-organic structures are formed by self-assembly at
⁎
Corresponding author at: Department of Chemistry, Institute of Chemical Technology,
N. Parekh Marg, Matunga, Mumbai 400019, India.
E-mail addresses: manoj.gawande@upol.cz (M.B. Gawande),
rv.jayaram@ictmumbai.edu.in (R.V. Jayaram).
1
Fax: +91 22 2269 2102.
Tel.: +351 21 2948300; fax: +351 21 2948550.
Present Address: Regional Centre of Advanced Technologies and Materials, Faculty of
2
3
Science, Phys. Chemistry Department, Palacky University, Olomouc, 17. Listopadu 12, 771
6 Olomouc, Czech Republic.
4
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.10.016

S.J. Singh et al. / Catalysis Communications 44 (2014) 24–28
25
O
C
O
C
(
D) from X-ray line broadening was calculated using the Scherrer
Cu-BDC
Eq. (1),
ROH
+
ROCOCH3
Solvent-free, R.T
H C
O
CH3
0:9λ
R = alkyl
3
D ¼ β
1=2cosθ
;
ð1Þ
Scheme 1. O-acetylation of alcohol using acetic anhydride.
where, λ is the wavelength of the X-ray beam, β1/2 is the angular
width at the half maximum intensity and θ is the Bragg's angle. The
crystallite size of the material was found to be of the order of magni-
tude of 0.1–0.2 μm, at the extreme limit of applicability of the equa-
tion. Apart from crystallite size, results computed through Eq. (1) are
sensitive to other peak broadening contributions, e.g. from the
material's microstrained state. Indeed, considering that the MOF is
prepared via a hydrothermal method, subject to high pressure and
elevated temperature inside an autoclave, it may be expected that
its crystallites are in a highly strained state. As a consequence, the
calculated values for D should be regarded simply as a lower bound
for crystallite size.
The powder XRD data of Cu–BDC could be indexed into a monoclinic
3
cell as a =3.099 Å, b = 18.520 Å, c = 11.750 Å, V =571.555Å and β =
122.047°.
The appearance of the signal (g=2.18) in ESR indicates the presence
+
+
of copper in 2 oxidation state as the copper in 1 state is not EPR active
because they lack unpaired electrons (Fig. 2).
Fig. 1. X-ray powder diffraction pattern of Cu–BDC.
The thermal gravimetric and differential thermal analyses were
carried out from 30 °C to 800 °C at a heating rate of 5 °C per minute.
It was observed that the MOF is thermally stable up to nearly
210 °C. The sample undergoes almost one half weight loss between
213 °C–434 °C. The onset of decomposition of the sample was found
to be at 294°C, which is confirmed, by both TG as well as DTA curves.
The weight of the residue left at 434 °C is 48% and remains the same
up to 800 °C.
In continuation of our research activities in nanocatalysis, greener syn-
thesis and application of heterogeneous catalysts for various organic
transformations [24–30] herein, we report the catalytic activity of copper
based metal-organic framework material (Cu–BDC) for O-acetylation of
alcohols under solvent-free condition at room temperature (Scheme 1).
The MOF is prepared by simple static hydrothermal method employing
non-hazardous solvents in an autoclave and using inexpensive precursors
Cu(NO
3
)
2
·3H
2
O and BDC (1,4-benzenedicarboxylic acid). Excellent yield
Particle size and shape of Cu–BDC were observed using SEM. The im-
ages show a rod like shape of the particles with approximately 2.5 ±
1μm in length and 0.4± 0.1μm in width. Coupled with the above men-
tioned crystallite size, this is a clear indication of the polycrystalline na-
ture of the particles. The different magnification images are as shown in
Fig. 3(a), (b) and (c).
of desired products was obtained and the catalyst was successively
recycled for several runs with no significant loss in activity.
2
. Results and discussion
2
.1. Catalyst characterization
The EDXS data of Cu–BDC is summarized in Table 1, which is consis-
tent with the ICP-AES and elemental analysis data.
The powder XRD pattern of the Cu–BDC is depicted in Fig. 1, and
the material appears to be crystalline. The average crystallite size
FT-IR spectrum confirms the formation of Cu–BDC (Fig. 4). The
−
1
bands observed at 471, 499, 563 and 628 cm
are probably due to
Fig. 2. ESR spectrum of Cu–BDC.

26
S.J. Singh et al. / Catalysis Communications 44 (2014) 24–28
Table 1
EDXS data of Cu–BDC.
a) SEM of Cu-BDC at 10 µm
Element
Mass %
At %
44.17
41.70
14.13
K-ratio
C K
O K
Cu K
Total
25.31
31.83
42.85
9.6845
78.9263
53.1718
100.00
100.00
spectrum. However, when the compound is diluted, the extent of hy-
drogen bonding decreases or in any situation, where hydrogen bonding
is not possible due to structural reasons, similar to the case of Cu–BDC,
only free –OH group exists and the absorption is due to free –OH
group which gives a sharp peak nearly in the region 3550–3450 cm−
1
.
In the case of Cu–BDC which is a solid co-ordination polymer, the –OH
group is present in a rigid structure where hydrogen bonding is not pos-
sible and the absorption is due to free –OH group which gives a sharp
−
1
absorption at 3611cm as seen in the IR spectrum of Cu–BDC.
2
Surface area of the material was found to be 58.8 m /g with a pore
3
volume of 0.016 cm /g and pore diameter of 14.66 Å. The low surface
b) SEM of Cu-BDC at 2 µm
area can be attributed to very small pore size of the material. The
small pore size could also be the reason for the inability of the nitrogen
molecules to access the pores of the particles resulting in a less surface
area [33]. The nitrogen uptake by this class of material is also highly de-
pendent on the activation procedure [6,34].
2.2. Reaction studies
The scope of MOF catalyzed O-acetylation of alcohols was explored
by using 20wt.% of Cu–BDC at room temperature under solvent-free con-
dition (Table 2, entries 1–8). Various primary and secondary aliphatic
alcohols underwent smooth acetylation with acetic anhydride provid-
ing high yield of desired products. The standard reaction of benzyl alco-
hol with acetic anhydride gave 87% yield of benzyl acetate (entry 1).
Benzyl alcohol having electron donating and electron withdrawing
groups reacted efficiently with acetic anhydride providing the desired
product in excellent yields. The protocol was also applicable for acetyla-
tion of long chain aliphatic alcohols providing the desired products in
good yields. Thus, the MOF showed excellent catalytic activity and was
applicable for a wide variety of substrates.
c) SEM of Cu-BDC at 1 µm.
The effect of temperature on O-acetylation of benzyl alcohol using
acetic anhydride as acetylating agent was studied under solvent-free
conditions (Table 3, entries 1–4). Notably, the yield of corresponding
products was increased with an increase in temperature up to 80 °C.
Further increase in temperature to 100 °C did not have much effect on
the reaction yield. However, further studies were performed at room
temperature.
The concentration–time study of the reaction was monitored using a
gas chromatograph (Table 3, entries 5–8). Initially, the reaction pro-
ceeds comparatively fast and becomes slow at the later period. The
probable reason may be that the ester competes with the reactant for
similar surface sites of the catalyst thereby inhibiting its adsorption on
the catalyst surface. Thus, an increase in product concentration de-
creases the reaction rate as few sites are available for the reactant to
get activated.
Catalyst reusability was examined for the standard reaction of O-
acetylation of benzyl alcohol at room temperature. The recycled catalyst
after each run was separated by filtration, washed with diethyl ether
and dried in air for 24 h. The catalyst was activated at 120 °C in air for
Fig. 3. (a) SEM of Cu–BDC at 10μm. (b) SEM of Cu–BDC at 2μm. (c) SEM of Cu–BDC at 1μm.
2
h prior to the next run and was reused up to three times with no sig-
nificant loss in activity.
Cu(II)\O vibrations in agreement with the literature reports [31,32]. In
any compound containing –OH group, the molecules are connected by
inter-molecular hydrogen bonding due to which a strong broad band
of –OH in the region 3400–3200 cm−1 is usually obtained in the IR
A probable mechanism for the reaction can be explained as follows
[18]. The free metallic sites in the framework of Cu–BDC interact with
the –CO– group of acetic anhydride thereby activating the acetyl
group of the anhydride and enhancing the leaving ability of the acetate

S.J. Singh et al. / Catalysis Communications 44 (2014) 24–28
27
1
05.5
00
1
9
9
8
8
7
7
6
5
0
5
0
5
0
5
6
47.52
1
152.30
1102.15
628.31
4
4
99.38
71.07
1
015.13
2335.16
2973.68
1939.47
%
R
60
875.22
8
30.89
5
5
4
4
3
3
2
2
5
0
5
0
5
0
5
0
563.45
3611.47
1
319.90
1501.28
735.28
926.83
1
570.70
1
406.23
1
4.2
000.0
4
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
450.0
cm-1
Fig. 4. FT-IR spectrum of Cu–BDC.
counterpart. The activated acetic anhydride on the catalyst surface fur-
ther reacts with the alcohol to give ester as the product.
with conventional powder diffractometer (Philips 1050) using
graphite monochromatized Cu Kα radiation operating in Bragg–
Brentano (θ/2θ) geometry. Thermal gravimetric and differential
thermal analyses were performed with a Diamond TG/DTA analyzer
3
. Experimental
(
PerkinElmer). Elemental analysis was done on a model FLASH EA
3
.1. General
1112 series (Thermo Finnigan). Percentage of copper was obtained
by inductively coupled plasma-atomic emission spectroscopy (ICP-
AES) on JY Ultima-2 (Jobin Yvon) instrument. Scanning electron mi-
croscopic (SEM) images were obtained on JEOL (JSM 6380-LA) and
All the chemicals purchased were of analytical grade and used
without further purification. The powder XRD pattern was obtained
Table 2
a
Liquid phase O-acetylation of alcohols catalyzed by Cu–BDC .
Entry
1
Alcohol
Product
Yieldb (%)
c
87, 87, 85, 82
2
3
4
5
6
93
85
72
86
70
3 2 3 2 5 2
CH (CH ) CH(C H )CH OH
3 2 3 2 5 2 3
CH (CH ) CH(C H )CH OCOCH
7
8
(CH
CH (CH
3
3
)
2
CHCH
2
2
CH OH
(CH
CH (CH
3
3
)
2
CHCH
2
CH
2
OCOCH
3
88
90
2 7
) OH
2 7
) OCOCH
3
a
Reaction conditions: alcohol = 2 mmol; acetic anhydride = 4 mmol; catalyst = 20 wt.% (w.r.t. alcohol); time = 24 h under neat condition at room temperature.
GC yield.
Yield after fourth cycle.
b
c

28
S.J. Singh et al. / Catalysis Communications 44 (2014) 24–28
Table 3
4. Conclusion
a
Effect of temperature and time on O-acetylation of benzyl alcohol .
Entry
Temperature (°C)
Time (h)
Yieldb (%)
In summary, a novel metal organic framework (Cu–BDC) has been
hydrothermally synthesized using innocuous solvents and its catalytic
activity is successfully demonstrated for the O-acetylation of alcohols
at ambient conditions. The catalyst, heterogeneous by nature, showed
excellent activity and reusability affording high yields of desired prod-
ucts under solvent-free condition. The ease of preparation of catalyst,
high metal content and insolubility in common organic solvents make
it an attractive alternative to the present range of conventional Lewis
acid mediated reactions. Further work is in progress to extrapolate the
catalytic activity of Cu–BDC for other organic transformations.
Effect of temperature
1
2
3
4
40
60
80
100
2
2
2
2
58
75
95
98
Effect of time
5
6
7
8
r.t.
r.t.
r.t.
r.t.
2
8
15
24
35
64
75
87
a
Reaction conditions: alcohol = 2 mmol; acetic anhydride = 4 mmol; catalyst =
0 wt.% (w.r.t. alcohol) under neat condition.
GC yield.
Acknowledgments
2
b
Savita Singh and Sandip Kale would like to thank the Council of Sci-
entific and Industrial Research (New Delhi, India) for the award of a Se-
nior Research Fellowship. A. Velhinho would like to acknowledge FCT/
MCTES for funding granted to CENIMAT/I3N under project PEst-
C/CTM/LA0025/2013-14 (Strategic Project-LA25-2013-2014).
energy-dispersive X-ray spectroscopy (EDXS) data was collected
from the model JED-2300 series (EX-2300BU). FT-IR spectrum was
recorded on PerkinElmer model. BET surface area was determined
using NOVA 1200 Quantachrome by nitrogen adsorption. The yield
of the products for O-acetylation reaction was based on the analysis
using capillary column equipped gas chromatograph (Chemito
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2013.10.016.
1
000). The products of the O-acetylation reaction were identified
by GC/MS (Shimadzu, GCMS-QP 2010).
References
[
1] O.M. Yaghi, M. O'Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423
2003) 705.
(
3
.2. Catalyst preparation
Cu(NO ·3H O (19.5 g) and 1,4-benzenedicarboxylic acid (1.8 g)
[
[
[
2] J.L.C. Rowsell, O.M. Yaghi, Microporous Mesoporous Mater. 73 (2004) 3.
3] M.J. Rosseinsky, Microporous Mesoporous Mater. 73 (2004) 15.
4] N.W. Ockwig, O. Delgado-Friedrichs, M. O'Keeffe, O.M. Yaghi, Acc. Chem. Res. 38
)
3 2
2
(2005) 176.
were dissolved in water (75 mL) and ethanol (75 mL) respectively.
The two solutions were mixed and stirred for 20 to 30min on a magnetic
stirrer. The mixture was then transferred in an autoclave and allowed to
react at 90 °C without stirring. After 18h, the autoclave was allowed to
cool at ambient temperature. A light blue colored material was collected
by filtration and washed several times with water and hot boiling etha-
nol and dried in air overnight at 110–115 °C in an oven. The as synthe-
sized material was found to be insoluble in water and common
organic solvents such as acetone, ethanol, acetonitrile, pet ether, chloro-
form, ethyl acetate, dichloromethane, dimethylformamide (DMF), n-
hexane, and diethyl ether. Elemental analysis revealed carbon and
hydrogen content as 24.67% and 1.61% respectively. Copper content
was analyzed by ICP-AES and was found to be 39.96%.
[
5] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 43 (2004) 2334.
[6] J.L.C. Rowsell, A.R. Millward, K.S. Park, O.M. Yaghi, J. Am. Chem. Soc. 126 (2004) 5666.
[
[
[
7] T. Duren, L. Sarkisov, O.M. Yaghi, R.Q. Snurr, Langmuir 20 (2004) 2683.
8] Y. Li, R.T. Yang, J. Am. Chem. Soc. 128 (2006) 726.
9] A.G. Wong-Foy, A.J. Matzger, O.M. Yaghi, J. Am. Chem. Soc. 128 (2006) 3494.
[10] Q.M. Wang, D. Shen, M. Bulow, M.L. Lau, S. Deng, F.R. Fitch, N.O. Lemcoff, J.
Semanscin, Microporous Mesoporous Mater. 55 (2002) 217.
11] K. Tanaka, S. Oda, M. Shiro, Chem. Commun. (2008) 820.
12] D. Jiang, T. Mallat, F. Krumeich, A. Baiker, J. Catal. 257 (2008) 390.
[13] F.X.L. Xamena, O. Casanova, R.G. Tailleur, H. Garcia, A. Corma, J. Catal. 255 (2008)
220.
14] S. Cho, B. Ma, S.T. Nguyen, J.T. Hupp, T.E. Albrecht-Schmitt, Chem. Commun. (2006)
563.
15] K. Schlichte, T. Kratzke, S. Kaskel, Microporous Mesoporous Mater. 73 (2004) 81.
[16] J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim, Nature 404 (2000) 982.
17] S.D. Rosa, G. Giordano, T. Granato, A. Katovic, A. Siciliano, F. Tripicchio, J. Agric. Food
Chem. 53 (2005) 8306.
[
[
[
2
[
[
[
[
18] K. Jeyakumar, D.K. Chand, J. Mol. Catal. A Chem. 255 (2006) 275.
19] A.R. Gholap, K. Venkatesan, T. Daniel, R.J. Lahoti, K.V. Srinivasan, Green Chem. 5
(
2003) 693.
3
.3. Typical procedure for O-acetylation of alcohols
[
[
20] J.R. Satam, M.B. Gawande, S.S. Deshpande, R.V. Jayaram, Synth. Commun. 37 (2007) 3011.
21] T.S. Reddy, M. Narasimhulu, N. Suryakiran, K.C. Mahesh, K. Ashalatha, Y.
Venkateswarlu, Tetrahedron Lett. 47 (2006) 6825.
22] K.L. Chandra, P. Saravanan, R.K. Singh, V.K. Singh, Tetrahedron 58 (2002) 1369.
23] R.K. Khunger, Synlett (2006) 327.
Alcohol (2 mmol) and Cu–BDC (20 wt.% w.r.t. alcohol and
[
[
[
preactivated at 120°C for 1.5h) were added to a 10mL round bottom
flask equipped with a magnetic stirrer. To this, acetic anhydride
24] S.J. Singh, R.V. Jayaram, Tetrahedron Lett. 49 (2008) 4249.
[25] S.J. Singh, R.V. Jayaram, Catal. Commun. 10 (2009) 2004.
(
4 mmol) was added. The reaction mixture was stirred for 24 h at
[
[
26] S.J. Singh, S.R. Kale, R.V. Jayaram, Curr. Catal. 2 (2013) 130.
27] M.B. Gawande, D.B. Bonifacio Vasco, R. Luque, P.S. Branco, R.S. Varma, Chem. Soc.
Rev. 42 (2013) 5522.
[28] M.B. Gawande, P.S. Branco, R.S. Varma, Chem. Soc. Rev. 42 (2013) 3371.
[29] M.B. Gawande, P.S. Branco, I.D. Nogueira, C.A.A. Ghumman, N. Bundaleski, A. Santos,
O.M.N.D. Teodoro, R. Luque, Green Chem. 15 (2013) 682.
room temperature. After completion, the reaction mixture was dilut-
ed with diethyl ether (10 mL) and centrifuged. The supernatant liq-
uid was decanted and diethyl ether (5 mL) was again added to the
solid mass and centrifuged. The decanted aliquots were combined
and washed with 10% sodium bicarbonate solution and then with
water. The organic layer was dried using anhydrous sodium sulfate
and concentrated to afford the crude product. The yields reported
were based on GC analysis in comparison with an authentic sample.
All compounds are known compounds and were characterized using
GC–MS (Shimadzu QP2010).
[
30] M.B. Gawande, A. Rathi, I.D. Nogueira, R.S. Varma, P.S. Branco, Green Chem. 15
2013) 1895–1899.
[31] G. Cordoba, R. Arroyo, J.L.G. Fierro, M. Viniegra, J. Solid State Chem. 123 (1996) 93.
(
[
[
32] E.M. Fixman, M.C. Abello, O.F. Gorriz, L.A. Arrua, Appl. Catal. A 319 (2007) 111.
33] A.B.M. Danna, S.E. Iyuke, A. Fakhrul-Razi, T.G. Chuah, M.A. Atieh, M.F. Al-Khatib,
Environ. Info. Arch. 1 (2003) 597.
[34] H. Li, M. Eddaoudi, M. O'Keeffe, O.M. Yaghi, Nature 402 (1999) 276.