A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH2 Metal–Organic Framework for Synthesis of Oximes

Article abstract of DOI:10.1007/s10562-020-03203-1

An efficient supported ionic liquid catalyst is designed for condensation reaction of aldehydes and ketones. The Zr-based metal–organic framework (MOF), UiO-66-NH_2, was initially functionalized with N,N′-dibutyl imidazolium ionic liquid (UiO-66-NH₂-ILBr^–), and then urea was attached to the ionic liquid (IL) to form a task-specific IL. Bromide was exchanged with tetrafluoroborate and the catalyst exhibits excellent performance for the synthesis of oximes. The ionic liquid/urea coupling showed a synergistic effect on the efficiency of the reaction. The supported catalyst system was recycled simply by filtration and reused for five times without significant decrease in its activity. The catalyst was characterized with PXRD, FTIR, TGA, XPS, BET, FE-SEM, EDS, elemental mapping and elemental analysis (CHN). Graphic Abstract: MOF/IL/urea catalytic system was used for the synthesis of oximes[Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-020-03203-1

Catalysis Letters
https://doi.org/10.1007/s10562-020-03203-1
A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported
on UiO‑66‑NH Metal–Organic Framework for Synthesis of Oximes
2
1
1
2
2
Saeed Askari · Mohammad Jafarzadeh · David Benjamin Christensen · Søren Kegnæs
Received: 11 February 2020 / Accepted: 27 March 2020
©
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
An efcient supported ionic liquid catalyst is designed ꢀor condensation reaction oꢀ aldehydes and ketones. The Zr-based
metal–organic ꢀramework (MOF), UiO-66-NH was initially ꢀunctionalized with N,N′-dibutyl imidazolium ionic liquid (UiO-
2
,
–
6
6-NH -ILBr ), and then urea was attached to the ionic liquid (IL) to ꢀorm a task-speciꢁc IL. Bromide was exchanged with
2
tetraꢂuoroborate and the catalyst exhibits excellent perꢀormance ꢀor the synthesis oꢀ oximes. The ionic liquid/urea coupling
showed a synergistic eꢃect on the efciency oꢀ the reaction. The supported catalyst system was recycled simply by ꢁltration
and reused ꢀor ꢁve times without signiꢁcant decrease in its activity. The catalyst was characterized with PXRD, FTIR, TGA,
XPS, BET, FE-SEM, EDS, elemental mapping and elemental analysis (CHN).
Graphic Abstract
MOF/IL/urea catalytic system was used ꢀor the synthesis oꢀ oximes
Keywords Supported ionic-liquid phase · Metal–organic ꢀrameworks · UiO-66-NH · Oxime synthesis
2
1
Introduction
Electronic supplementary material The online version oꢀ this
article (https://doi.org/10.1007/s10562-020-03203-1) contains
supplementary material, which is available to authorized users.
Supported ionic liquids (SILs) and supported ionic liquid
phase (SILPs) have attracted some interests due to their
unique properties and activities compared to conventional
ionic liquids (ILs) [1, 2]. A SILP material is deꢁned as a
thin and multilayer ꢁlm (a ꢀew nanometer thick) oꢀ the ionic
*
Mohammad Jaꢀarzadeh
m.jaꢀar@razi.ac.ir
Extended author inꢀormation available on the last page oꢀ the article
Vol.:(0
1
123456789)
3

S. Askari et al.
liquid physisorbed on the surꢀace oꢀ porous materials [3],
while in SILs a monolayer oꢀ an ionic liquid is covalently
immobilized on the surꢀace (sometimes called as supported
ionic liquid-like phase; SILLP) [1]. These concepts diminish
the typical issue oꢀ the ILs such as high cost, large volume
usage, high viscosity (cause difculty in mass transꢀer and
reactant diꢃusion) [4], and the need ꢀor liquid–liquid extrac-
tion ꢀor their recovery. Heterogenization oꢀ ILs on support
materials (e.g. silica, alumina, titania, activated carbon,
polymer) [5–7] not only reduce the amount oꢀ ionic liquid,
provide short diꢃusion distance (due to a nanometer thick-
ness) [4], makes ꢀor easier handling, recycling and long-term
stability oꢀ ionic liquids [6], and reduce potential risk to the
environment due their poor biodegradability [1], but also
promotes the perꢀormance oꢀ the hybrid materials in their
applications [6].
oꢀ a nitrogen source) [45], oxidation oꢀ primary amines
[46], ammoximation oꢀ diꢃerent ketones and aldehydes
using polyoxometalates [47, 48], and transoximation [49],
but the conventional method is still considered due to the
simplicity oꢀ the procedure. Oximes are generally synthe-
sized via a condensation reaction oꢀ carbonyl compounds
(aldehydes and ketones) with hydroxylamine in acidic or
basic conditions [50]. Since hydroxylamine is dangerous to
handle and use [51], hydroxylamine hydrochloride is gen-
erally employed to generate in-situ hydroxylamine in the
reaction medium, with only water and HCl as by-products
[50]. Besides conventional conditions ꢀor the synthesis oꢀ
oximes, microwave-assisted [52], ultrasonic [42], and mech-
anochemical [53] methods have been also developed. ILs
have ꢀound much interest as an alternative reaction media
ꢀor the synthesis oꢀ oximes [54–56]. It is expected that the
application oꢀ SILs in the synthesis oꢀ oximes can ꢁnd some
beneꢁts in an aspect oꢀ economic and environment.
Although, SILPs have some advantages such as easy
preparation and simple operation particularly in ꢁxed-bed
reactors ꢀor gas phase reactions, but they suꢃer ꢀrom pore
blocking and instability in the reaction medium especially
in liquid phase. The IL can be removed ꢀrom the surꢀace
In the present work, zirconium-based MOF, UiO-66-NH ,
2
is modiꢁed by a post-synthesis with imidazolium bromide
−
(ILBr ) ꢀor the preparation oꢀ supported ionic liquid on the
(
leaching) by ꢀorce oꢀ mechanical stirring and/or dissolving
surꢀace oꢀ the MOF. The SIL was ꢀurther ꢀunctionalized with
urea to prepare a TSIL. Urea oꢃers basic sites and hydrogen
bond donors [57] ꢀor catalyzing organic synthesis oꢀ oximes,
similar to the glycine-catalyzed synthesis in the previous
report [58]. However, the urea-ꢀunctionalized SIL serves as
a catalyst and medium in this work. It is expected that the
ꢀunctionalized MOF exhibits heterogeneous characteristics
ꢀor the IL and the base.
in reaction media [1, 8, 9]. In contrast, by covalent graꢀting
oꢀ ILs to the ꢀunctional groups on the surꢀace oꢀ the sup-
port, the stability and durability oꢀ SILs in organic syntheses
may improve signiꢁcantly. SILs have been used as hosts ꢀor
organocatalysts [10], metal-complexes [8], and metal nano-
particles [6, 11] and generated task-speciꢁc ionic liquids
(
TSILs) [12–15] and speciꢁcally the concept oꢀ supported
ionic liquid catalysts (SILC) [9, 16–18]. Metal–organic
rameworks (MOFs), as class oꢀ promising porous materials,
ꢀ
have been employed as suitable supports ꢀor immobilizing
ILs [19, 20] and catalysts [21, 22] due to their high surꢀace
area, large pore volume, and available/accessible pores [23].
A synergic eꢃect arising ꢀrom their hybridization have pre-
viously been shown to enhance the efciency oꢀ the cata-
lytic reactions [19, 20]. MOF/TSIL hybrid materials have
been used ꢀor various organic reactions such as acetalization
oꢀ benzaldehydes with glycol [24], selective oxidation oꢀ
cyclohexenes [25] and benzyl alcohols [26, 27], adsorptive
desulꢀurization [28, 29], Knoevenagel condensation [30],
2 Experimental
2.1 Synthesis
of 1,3‑Bis‑(4‑bromo‑butyl)‑3H‑imidazol‑1‑ium
−
Bromide (ILBr )
The preparation oꢀ the ionic liquid was adopted ꢀrom a previ-
ously reported method [59]. Imidazole (290 mg, 4.3 mmol)
was dissolved in THF (4 mL), and then a solution oꢀ sodium
hydride (135 mg, 5 mmol) in THF (3 mL) was slowly added
at 0 °C. Aꢀter 45 min oꢀ stirring at room temperature,
1,4-dibromobutane (0.51 mL, 4.3 mmol) was added slowly
to the above solution and stirred ꢀor 2 days. The product
was extracted ꢀrom the reaction mixture using ethyl acetate.
In the second step, the product was dissolved in THF and
stirred ꢀor 45 min. 1,4-dibromobutane (0.55 mL, 4.6 mmol)
was then added into the mixture and reꢂuxed ꢀor 2 days. The
ꢁnal product was isolated by extraction using ethyl acetate.
cycloaddition oꢀ CO with epoxides [31–33] and synthesis
2
oꢀ biodiesels [34].
Oximes are important intermediates ꢀor synthesis oꢀ
nitriles [35], amides (Beckmann rearrangement) [36–38],
nitrones, hydroximinoyl chlorides, and chiral α-sulꢁnyl oxi-
mes [39]. They are also used ꢀor preparation oꢀ carbonyl
compounds [40] and metal complexes [41], protecting car-
bonyl compounds, inhibiting enzymes [42] and manuꢀac-
turing oꢀ pharmaceutical products and insecticides [43].
Although various methods have been developed recently
1
13
The products were identiꢁed by H and C NMR and the
spectra were compared with data ꢀor a similar structure [60]
(reꢀer to Supporting Inꢀormation ꢀor details).
ꢀ
or the synthesis oꢀ oximes such as decomposition oꢀ tosyl-
hydrazones [44], oxidation oꢀ methylarenes (in the presence
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
−
2
.2 Preparation of UiO‑66‑NH ‑ILBF ‑Urea
2.4.2 Entry 2 (2‑Hydroxylbenzaldehyde Oxime)
2
4
1
UiO-66-NH was prepared according the method reported
H NMR (400 MHz, d -DMSO): δ (ppm) 8.33 (s, 1H),
2
6
in the literature [61, 62]. The prepared UiO-66-NH
7.49–7.47 (dd, 1H), 7.25–7.21 (dd, 1H), 6.90–6.86 (m,
2
1
3
(
0.1 g) was dispersed in 10 mL DMF in a round-bottomed
2H); C NMR (100 MHz, d -DMSO): δ (ppm) 156.42,
6
ꢂask using sonication ꢀor 5 min. Next, (0.03 mmol, 10 mg)
147.96, 130.93, 128.30, 119.80, 118.72, 116.46.
1
,3-bis-(4-bromo-butyl)-3H-imidazol-1-ium bromide
was added to the mixture, and the solution was stirred
under reꢂux ꢀor 24 h. Next, (0.06 mmol, 3.6 mg) urea was
added to the mixture to ꢀorm Task Speciꢁc Ionic Liquid
2
.4.3 Entry 3 (2‑Methylbenzaldehyde Oxime)
1
H NMR (400 MHz, d -DMSO): δ (ppm) 8.29 (s, 1H),
6
(
TSIL). Aꢀter 24 h stirring under reꢂux, the precipitate
7
.67–7.64 (dd, 1H), 7.50–7.35 (td, 1H), 7.08–7.06 (d,
1
3
was isolated by centriꢀugation. The product (UiO-66-
1
H), 6.98–6.94 (t, 1H), 3.41 (s, 3H); C NMR (100 MHz,
–
NH -ILBr -urea) was washed with DMF, water and etha-
2
d -DMSO): δ (ppm) 157.26, 143.86, 131.23, 125.88,
6
nol. The supported ionic liquid phase was dried at 80 °C
1
21.38, 121.07, 112.19, 56.10. (Figure S10, Supporting
in an oven ꢀor 24 h. In the next step, an anion exchange
Inꢀormation).
was carried out by addition oꢀ sodium tetraꢂuoroborate
–
(
0.175 g, 1.5 mmol) to the solution oꢀ UiO-66-NH -ILBr -
2
2
.4.4 Entry 4 (3,4,5‑Trimethoxybenzaldehyde Oxime)
urea (0.1 g) in acetone (2 mL) ꢀollowed by stirred at room
temperature ꢀor 24 h. The exchanged IL was then ꢁltered
and washed with H O (3 × 10 mL), EtOH (3 mL), Et O
1
H NMR (400 MHz, CDCl ): δ (ppm) 8.08 (s, 1H), 6.84 (s,
3
13
2
2
2
H), 3.90 (s, 9H); C NMR (100 MHz, CDCl ): δ (ppm)
3
(
2.5 mL), and acetone (2.5 mL). The resulting UiO-66-
1
53.48, 150.21, 139.71, 127.40, 104.12, 60.95, 56.18.
–
NH -ILBF -urea was dried at 50 °C in an oven overnight
2
4
(
Figure S11, Supporting Inꢀormation).
to give the ꢁnal product.
2
.4.5 Entry 5 (Cinnamaldehyde Oxime)
2
.3 General Procedure for the Synthesis of Oximes
1
H NMR (400 MHz, d -DMSO): δ (ppm) 7.58–7.56 (d,
6
1
H), 7.42–7.39 (dd, 2H), 7.38–7.36 (t, 1H), 7.33–7.32 (dd,
–
0
.05 g oꢀ UiO-66-NH -ILBF -urea dispersed in 1 mL
2
4
13
2
H), 7.29 (d, 1H), 6.98–6.95 (d, 1H); C NMR (100 MHz,
ethanol was added to a mixture oꢀ benzaldehyde (1 mmol,
d -DMSO): δ (ppm) 147.68, 138.35, 136.36, 129.50,
6
0
0
.11 mL) and hydroxylamine hydrochloride (1.5 mmol,
.1 g). Stirring at 25 °C (room temperature) was continued
1
29.36, 127.67, 116.59.
until the benzaldehyde was consumed, as monitored by
thin layer chromatography (TLC). Aꢀter completion oꢀ the
reaction, the reaction mixture was added to 10 mL water
and extracted with ether (3 × 10 mL). Further puriꢁca-
tion was accomplished by washing it with ethyl acetate
and n-hexane. The organic products were identiꢁed by
2
.4.6 Entry 6 (4‑Nitrobenzaldehyde Oxime)
1
H NMR (400 MHz, d -DMSO): δ (ppm) 8.31 (s, 1H),
6
1
3
8
.27–8.24 (dd, 2H), 7.88–7.84 (dd, 2H); C NMR
(
100 MHz, d -DMSO): δ (ppm) 147.97, 147.29, 139.96,
6
1
13
127.80, 124.45.
H and C Nuclear Magnetic Resonance (NMR, Bruker
4
00 MHz) spectroscopy, by comparing with data in the
literature [63]. The catalyst was washed with water and
ethanol, and dried at 60 °C in an oven overnight. The cata-
lyst was reused ꢀor several times under the same reaction
conditions.
2.4.7 Entry 7 (3‑Nitrobenzaldehyde Oxime)
1
H-NMR (400 MHz, d -DMSO): δ (ppm) 8.42–8.41 (t,
6
1H), 8.32 (s, 1H), 8.23–8.20 (dd, 1H), 8.06–8.03 (dd,
1
3
1
H), 7.72–7.68 (t, 1H); C NMR (100 MHz, d -DMSO):
6
δ (ppm) 148.57, 147.04, 135.39, 132.77, 130.79, 124.11,
121.26.
2.4 Spectral Data
2.4.1 Entry 1 (Benzaldehyde Oxime)
2
.4.8 Entry 8 (2‑Chlorobenzaldehyde Oxime)
1
1
H NMR (400 MHz, d -DMSO): δ (ppm) 8.14 (s, 1H),
6
H NMR (400 MHz, d -DMSO): δ (ppm) 8.37 (s, 1H),
6
7
.77–7.75 (d, 2H), 7.40–7.38 (m, 1H), 7.03–7.0 (dd, 2H);
7
.83–7.81 (dd, 1H), 7.52–7.50 (dd, 1H), 7.45–7.42
1
3
1
3
C NMR (100 MHz, d -DMSO): δ (ppm) 167.52, 151.64,
6
(dd, 1H), 7.40–7.38 (dd, 1 H); C NMR (100 MHz,
1
31.88, 129.71, 126.84, 118.02, 115.06.
1
3

S. Askari et al.
d -DMSO): δ (ppm) 144.99, 132.64, 131.40, 130.74,
using KBr pellets. The chemical composition oꢀ the modiꢁed
MOF was examined by a CHN elemental analyzer (Euro
6
1
30.29, 128.01, 127.26.
EA—HEKAtech GmbH) under N gas ꢀlow and X-ray
2
2.4.9 Entry 9 (4‑Methoxybenzaldehyde Oxime)
photoelectron spectroscopy (XPS) on a Kratos Axis Ultra-
DLS spectrometer (Al K source). The data was analyzed
α
1
H NMR (400 MHz, d -DMSO): δ (ppm) 8.06 (s, 1H),
using the CasaXPS soꢀtware. The thermal stability and
organic species loading were studied by thermogravimetric
analysis (TGA; Perkin Elmer STA 6000) at a heating rate
6
7
.96–7.93 (d, 1H), 7.53–7.51 (d, 1H), 7.31 (d, 1H),
1
3
6
.99–6.95 (t, 1H), 3.79 (s, 3H); C NMR (100 MHz,
−
1
d -DMSO): δ (ppm) 160.25, 148.07, 144.71, 132.76,
oꢀ 10 °C min under nitrogen ꢂow. The morphology and
elemental analysis were carried out by a ꢁeld emission scan-
ning electron microscope (FE-SEM; FEI NOVA NanoSEM
6
1
28.28, 114.64, 114.13, 55.66. (Figure S12, Supporting
Inꢀormation).
4
50) equipped with energy dispersive X-ray spectroscopy
2.4.10 Entry 10 (Acetophenone Oxime)
(EDX). Platinum spurring was carried out on the samples
beꢀore analysis to avoid undesirable electron charging. The
BET (Brunauer–Emmett–Teller) speciꢁc surꢀace area and
adsorption BJH (Barrett–Joyner–Halenda) pore size/volume
oꢀ the samples were measured by an automatic porosimeter
(Micromeritics, Tristar II 3020). The samples were degassed
under vacuum overnight beꢀore analysis. TEM images was
acquired on a FEI Tecnai T20 G2 instrument at 200 kV ꢀrom
Thermo Fisher Scientiꢁc. Powdered samples were placed on
holey carbon grids with no prior treatment.
1
H NMR (400 MHz, d -DMSO): δ (ppm) 7.32–7.27 (dd,
6
1
3
2
H), 7.21–7.19 (dd, 2H), 7.18 (t, 1H), 1.64 (s, 3H);
C
NMR (100 MHz, d -DMSO): δ (ppm) 155.05, 138.11,
6
1
28.90, 126.60, 13.50.
2.4.11 Entry 11 (Cyclohexanone Oxime)
1
H NMR (400 MHz, d -DMSO): δ (ppm) 2.40–2.37 (t, 2H),
6
13
2
.17–2.14 (m, 2H), 1.58–1.52 (m, 6H); C NMR (100 MHz,
d -DMSO): δ (ppm) 159.35, 31.80, 27.03, 25.72, 24.53.
6
3
Results and Discussion
2.5 Characterization Techniques
3
.1 Preparation and Characterization
−
Powder X-ray diꢃraction (PXRD) was used to study the
of UiO‑66‑NH ‑ILBF ‑Urea Catalyst
2
4
crystalline nature oꢀ the MOF (UiO-66-NH ) beꢀore and
2
aꢀter modiꢁcation (ꢀresh and reused catalyst) by a Rigaku
D-Max C III diꢃractometer (Cu Kα, λ=1.5418 Å). Inꢀrared
spectra were recorded by a Fourier transꢀorm inꢀrared spec-
troscopy (FT-IR), ꢀrom a Bruker vector 22 spectrometer,
Aꢀter synthesizing the ionic liquid, 1,3-bis-(4-bromo-butyl)-
−
3H-imidazol-1-ium bromide (ILBr ), the UiO-66-NH was
2
−
ꢀunctionalized by ILBr and ꢀollowed by urea. The reac-
−
tion pathway to prepare UiO-66-NH -ILBr -urea is given
2
–
Scheme 1 Preparation oꢀ ILBr
1,4-dibromobutane
NaH, THF
1,4-dibromobutane
(
CH2)2
(CH
)
2 2
–
N
NH
N
N
(CH2)2
(CH )
and UiO-66-NH -ILBr -urea
Br
N+
2
Br
N
Br
(CH2)2
(CH
2
)
2
THF
Br-
2 2
ILBr
(
2 4
CH )
(CH
2
)
4
N
N
+
Br
NH
2
N
Br-
H
Urea
(CH
2
)
4
NH
(CH
2
)
4
N+
N
N
H
Br-
O
2
H N
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
−
−1
in Scheme 1. In addition, UiO-66-NH -ILBF -urea was
observed [64]. A stretching vibration at 503 cm was
2
4
−
−
−
prepared via an anion exchange, Br replaced by BF . The
attributed to CH –Br aꢀter attachment oꢀ ILBr to the
4
2
−
preparation steps were monitored by applying diꢃerent char-
ligand oꢀ the MOF. For UiO-66-NH -ILBF -urea, the
2
4
−
1
acterization techniques.
bands at 3370 and 3215 cm were related to the stretching
−
1
XRD was used to study the crystalline structure oꢀ the
vibration oꢀ N–H in amines, while the band at 1630 cm is
−
−1
UiO-66-NH aꢀter ꢀunctionalization by ILBr and graꢀt-
attributed to the amide group in urea. Bands at 1590 cm
2
−
1
ing by urea (Fig. 1a). The characteristic diꢃraction oꢀ the
and 1460 cm were assigned to the C=N and imidazolium
ring, respectively.
UiO-66-NH was observed at angles oꢀ 14.7°, 17.4°, 22.2°,
2
2
5
5.7°, 30.6°, 31.1°, 35.9°, 37.7°, 40.1°, 43.6°, 50.5°, and
Figure 1c, d demonstrated the N adsorption–desorption
2
6.8° corresponding to the (222), (400), (511), (600), (711),
isotherm and pore size distribution oꢀ the MOF. The iso-
therm showed a type IV hysteresis that is a characteristic
pattern ꢀor mesoporous materials, while a ꢀast adsorption
at low pressure is consistence with microporous materials.
Figure 1d showed a uniꢀorm distribution oꢀ the pore size in
the ꢀramework. The surꢀace area and porosity oꢀ the UiO-66-
(
731), (820), (751), (664), (933), (955), and (12 42) planes,
−
respectively [64]. The UiO-66-NH -ILBF -urea showed
2
4
isostructural and similar pattern to that oꢀ the pristine MOF,
indicating that the post-synthesis maintained the crystal-
line structure oꢀ the ꢀrameworks. Additional diꢃractions at
−
1
7.95°, 28.7°, 29.25°, and 47.9° were observed and could
NH -ILBF -urea were determined (Table 1). As expected,
2
4
be attributed to IL-Urea.
the surꢀace area and pore size/volume were reduced aꢀter
The ꢀunctionalization oꢀ the MOF was investigated
by FT-IR (Fig. 1b). The characteristic peaks related
modiꢁcation oꢀ UiO-66-NH . The BET surꢀace area, total
2
pore volume, and average pore size were obtained to be 600
−
1
2
−1
3
−1
to the N–H stretch oꢀ primary amines (3457 cm and
m g , 0.39 cm g , and 0.9 nm, respectively. The pore size
oꢀ 0.9 nm belongs to the microporous materials according to
the IUPAC classiꢁcation oꢀ porous materials [65].
−
1
−1
3
351 cm ), carbonyl stretch (1661 cm ), C–N stretch
1
(
1259 cm− ), and Zr–O stretch (600–800 cm−1) were
(
a)
(c)
2
2
1
1
50
00
50
00
5
0
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Relaꢀve pressure (p/p°)
(
b)
(d)5
4
3
2
1
0
4
000
3600
3200
2800
2400
2000
1600
1200
800
400
Wavenumber (cm-1
0
5
10
15
20
25
30
35
40
)
Pore width (Å)
–
Fig. 1 a PXRD patterns oꢀ UiO-66-NH -ILBF -urea in ꢀresh and
N adsorption–desorption isotherm and d pore size distribution oꢀ the
2
4
2
reused (aꢀter ꢁve times recycling), and b FT-IR spectra oꢀ UiO-
ꢀresh (blue) and reused (red), aꢀter ꢁve times recycling, UiO-66-NH -
2
−
−
6
6-NH (black), UiO-66-NH -ILBr (red), ꢀresh UiO-66-NH -
ILBF -urea. The solid spheres are reꢀerred to adsorption and the
2
2
2
4
−
−
ILBF -urea (blue) and reused UiO-66-NH -ILBF -urea (green). c
gray ones are ꢀor desorption
4
2
4
1
3

S. Askari et al.
Table 1 Surꢀace area and
UiO-66-NH -ILBF −-
UiO-66-NH2
UiO-66-NH -
2
−
2
4
porosity oꢀ the UiO-66-NH -
2
urea (ꢀresh)
ILBF -urea
4
−
ILBF -urea in ꢀresh and
4
(
recycled)
recycled ꢀorms
BET surꢀace area (m g−1)
Total pore volume (cm g−1)
Average pore size (nm)
2
1280
0.60
1.89
601
0.39
0.93
427
0.34
1.0
3
Table 2 Elemental
MOFs
CHN (At%)
XPS (At%)
compositions oꢀ the UiO-
–
6
6-NH , UiO-66-NH -ILBr
C
N
Zr
O
C
N
Br
2
2
−
and UiO-66-NH -ILBr -urea
2
UiO-66-NH2
UiO-66-NH -ILBr
UiO-66-NH -ILBr -urea
21.28
24.28
18.39
4.49
5.65
3.48
2.88
2.41
7.61
31.47
23.32
30.12
60.72
64.07
37.46
4.84
2.60
0.9
–
7.60
23.90
–
2
–
2
CHN analysis was used to determine the amount oꢀ
organic species loading on the surꢀace oꢀ the MOFs
(in the linker and the imidazolium rings) [68]. The peak at
290 eV was also ꢀound to be correlated to the C=O in the
linker and the urea [69].
(
Table 2). The results showed that the content oꢀ carbon and
nitrogen increased aꢀter modiꢁcation oꢀ the UiO-66-NH
The thermal stability and mass loading oꢀ ionic-liquid and
2
with ionic-liquid. The atomic percentage oꢀ carbon and
nitrogen decreased aꢀter graꢀting urea to the ionic liquid,
which can be related to the presence oꢀ heavy elements (i.e.
Br) in the structure. XPS was also employed ꢀor detection
the elements and their quantities (Table 2). The presence oꢀ
relevant elements (Zr, O, C, N, Br) in the structure oꢀ the
MOF and the ionic liquid on the surꢀace was veriꢁed. There
is a diꢃerence in the elemental compositions obtained ꢀrom
CHN and XPS techniques due to their diꢃerent operations
applied ꢀor the analysis. In CHN, the content oꢀ selected
elements (e.g. C, N, H) in the entire bulk oꢀ the samples is
measured, while in XPS, almost all elements (except H) in
the selected points oꢀ the samples in the surꢀace and sub-
layer with thickness < 10 nm is analyzed. Figures S7–S9
urea into the ꢀramework were studied by TGA. In Fig. 3, The
–
–
UiO-66-NH -ILBF and UiO-66-NH -ILBF -urea showed
2
4
2
4
almost similar thermal stability with the UiO-66-NH . An
2
initial weight loss oꢀ ~ 5% and ~ 10% was ꢀound ꢀor UiO-
–
–
66-NH -ILBF and UiO-66-NH -ILBF -urea, respectively
2
4
2
4
at below ~ 100 °C, while ~ 20% weight loss observed ꢀor
the pristine MOF. The initial weight loss is related to the
removal oꢀ the residual solvent (e.g. water and/or ethanol)
ꢀrom the pores. Moreover, an additional weight loss was
observed at ~ 180–250 °C ꢀor the modiꢁed MOFs, relating
to the escape oꢀ DMF coordinated to the nodes. Such event
was not observed ꢀor the UiO-66-NH because the MOF
2
activation via a solvent extraction was efcient in removal
oꢀ DMF. At temperature above 250 °C, slight reduction in
the weight might be attributed to the thermal decomposi-
tion oꢀ the IL [70] and also urea groups in the modiꢁed
MOFs, and removal oꢀ residual coordinated DMF inside the
(
Supporting Inꢀormation) display the XPS surveys oꢀ UiO-
−
−
6
6-NH , UiO-66-NH -ILBr and UiO-66-NH -ILBr -urea,
2 2 2
respectively. For UiO-66-NH (Figure S5), the N 1s peak at
2
3
97 eV was attributed to NH groups on the organic linkers.
micropore oꢀ the UiO-66-NH and partial degradation oꢀ the
2
2
For the supported ILs, the O 1s peaks at 531 and 530.5 eV
were assigned to the C=O groups in the linker and the urea,
respectively (Figure S6 and S7), while the peak at 182 eV
corresponded to the Br 3p in the C–Br bond (Figure S8).
High-resolution XPS and the relevant deconvolution, in
Fig. 2a, exhibited two components ꢀor the N peak. The peaks
at~401 and~399.5 eV were assigned to the cationic N and
MOF structures ~ 400 °C. A ꢀurther weight loss at ~ 500 °C
was observed ꢀor the modiꢁed and pristine MOFs due to the
ꢀramework degradation to ZrO [64].
2
The TEM and SEM images (Fig. 4a, b) showed irregular
–
round-shaped particles ꢀor UiO-66-NH -ILBF -urea with
2
4
sizes ranging ꢀrom 50 to 100 nm. The EDS conꢁrms the
existence oꢀ the elements incorporated in the MOF (Fig. 4c).
Zr (5.5%), O (17.3%), C (35.6%), N (7.6%), B (9.8%), and
the neutral N (–NH ), respectively [66]. The peak at 401 eV
2
conꢁrms the presence oꢀ the imidazolium ring in the IL-
F (24.0%) were ꢀound. The result conꢁrms the presence
–
supported UiO-66-NH [67]. High-resolution XPS oꢀ the
oꢀ B and F (corresponding to BF ) along with other ele-
2
4
C 1s peak consists oꢀ three ꢁtted peaks at binding energies
oꢀ 283 and 284 and 290 eV (Fig. 2b). The peak at 283 eV
was attributed to the C–C aliphatic (alkyl groups oꢀ the IL),
while the peak at 284 eV was ꢀor C–N, C=C, and C=N
ments in the structure. The trace amount oꢀ Br inꢀerred an
–
–
almost complete replacement oꢀ Br with BF within anion
4
exchange. The elemental mapping demonstrated a homoge-
neous distribution oꢀ elements in the ꢀrameworks (Fig. 4d).
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
Fig. 2 High resolution XPS oꢀ
−
a N 1 s ꢀor UiO-66-NH -ILBr
2
and b C 1s ꢀor UiO-66-NH -
2
−
ILBr -urea
3
.2 Synthesis of Oximes Using
−
UiO‑66‑NH ‑ILBF ‑Urea Heterogeneous
2
4
Catalyst
A zirconium MOF with incorporated IL and urea (UiO-
–
6
6-NH -ILBF -urea) was used as a platꢀorm ꢀor catalyz-
2
4
ing organic reactions. In the current work, the synthesis oꢀ
oximes was selected due to the simplicity oꢀ the procedure
(
highly crystalline compound [39]), an efcient condensa-
tion reaction, and an interesting intermediate with broad
applications. Oxime is basically an imine with a general
ꢀ
ormula: RR′C=NOH, where R is an alkyl and R′ could be
hydrogen (to ꢀorm aldoxime) and/or alkyl (to ꢀorm ketox-
ime). The condensation reaction between benzaldehyde and
hydroxylammonium chloride was chosen as a model reaction
Fig. 3 Thermograms oꢀ (A) UiO-66-NH -ILBF −, (B) UiO-66-NH2-
2
4
−
ILBF4 -urea, and (C )UiO-66-NH
2
1
3

S. Askari et al.
(
a)
(b)
cps/eV
(
c)
8
7
6
5
4
3
2
1
0
B
N
O
C
Zr
F
Br Zr
Br
Zr
2
4
6
8
10
keV
12
14
16
18
20
(
d)
Fig. 4 TEM (a) and SEM (b) images, EDS spectrum (c), and elemental mapping in selected area (d) oꢀ the UiO-66-NH -ILBF −-urea
2
4
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
−
to examine the catalytic activity oꢀ UiO-66-NH -ILBF -
constant. It was observed that 0.05 g oꢀ catalyst was suf-
2
4
urea as a heterogeneous catalyst. Urea acts as a basic site
cient ꢀor completion oꢀ the reaction. It was observed that by
using a higher amount oꢀ catalyst, the yield oꢀ the reaction
was not enhanced. The optimum condition was ꢀound to be
0.05 g oꢀ the catalyst, ethanol as a solvent, temperature at
25 °C with a reaction time oꢀ 15 min.
ꢀ
or catalyzing the reaction and also adjust the pH oꢀ the
medium to neutral as HCl is generated ꢀrom hydroxylamine
hydrochloride [42]. With regards to the mechanism, the
amine group oꢀ urea initially activates the oxygen oꢀ the
carbonyl group (oꢀ benzaldehyde) via a hydrogen bonding
and ꢀacilitates the nucleophilic addition oꢀ hydroxylamine
to the carbon oꢀ the carbonyl [42]. Two hydrogen bonding
donors have been proposed ꢀor urea on the carbonyl activa-
tion [57]. Oxime is ꢁnally ꢀormed by a dehydration reaction.
To optimize the reaction conditions, the eꢃect oꢀ vari-
ous reaction parameters such as type oꢀ solvent, tempera-
ture, and amount oꢀ catalyst were studied in the ꢁrst stage
To extent the current approach, a variety oꢀ substrates
were used ꢀor the synthesis oꢀ diꢃerent oximes. As shown
in Table 4 various types oꢀ aromatic aldehydes with elec-
tron donating and withdrawing groups were successꢀully
reacted with hydroxylamine hydrochloride and aꢃorded
the corresponding oximes in good to excellent yields. The
nature oꢀ the substituents did not show a signiꢁcant eꢃect
on the reaction efciency, which is in good agreement with
the results reported in the literature [71]. According to the
results, hydroxy as an electron-donating group improved
the reaction yield (Table 4, entry 2), while the alkyl and
halide groups in the ortho position made a steric hindrance
ꢀor the reaction and reduce the yield (Table 4, entries 3 and
8). Moreover, cinnamaldehyde as a non-aromatic showed a
reasonable yield in the reaction (Table 4, entry 5). The nitro
group in the para position (Table 4, entry 6) exhibited more
deactivating eꢃect in the condensation reaction compared to
that in the meta position (Table 4, entry 7) due to an eꢃec-
tive electron delocalization oꢀ the carbonyl group towards
the nitro group in the para position. Methoxy groups in the
para and meta positions showed unexpected results, com-
pared to electron-donating and -withdrawing groups, ꢀor
unknown reasons (Table 4, entries 4 and 9). On the other
hand, aromatic ketones are generally less reactive in the con-
densation reaction compared to aromatic aldehydes due to
their steric hindrance [50]. Acetophenone (Table 4, entry 10)
exhibited a good yield (75% in 25 min) in comparison with
the reported result with (55% yield in 10 min) using nano-
structured pyrophosphate catalyst [71]. An aliphatic cyclic
ketone, cyclohexanone (Table 4, entry 1 l), showed better
results compared to aromatic ketones and comparable result
with aromatic aldehydes.
(
Table 3). The eꢃect oꢀ common solvents such as ethanol,
acetonitrile, mixture oꢀ water and ethanol, and toluene were
investigated on the reaction (Table 3, entry 1–3 and 6). The
results revealed that a solvent with medium polarity oꢀ is
indispensable ꢀor the reaction to proceed. Ethanol was ꢀound
to be the best choice ꢀor this reaction. The eꢃect oꢀ various
temperatures such as (25, 60 and 90 °C) were studied ꢀor
the model reaction (Table 3, entry 4–6). In contrast to the
reported results, the lower temperature (25 °C) showed a
better result compared to the higher temperatures. When the
temperature was increased ꢀrom 25 to 90 °C, the yield was
decreased ꢀrom 86 to 51% (Table 3, entry 4). It is proposed
that the local motions oꢀ the linear and long alkyl group
(
attached to urea) increase by increasing the temperature
leading to unꢀavorable interaction between urea and the imi-
dazolium ring (synergic eꢃect, discuss later). Hence, the
urea (in cooperation with the IL) is not able to activate the
carbonyl group oꢀ aldehydes and ketones ꢀor nucleophilic
addition reaction. The eꢃect oꢀ the catalyst amount on the
reaction was also studied by varying it ꢀrom 0.05–0.1 g
(
Table 3, entry 6–9), while keeping the other parameters
Table 3 Optimization oꢀ the reaction conditions ꢀor the synthesis oꢀ
−
oximes using UiO-66-NH -ILBF -urea as the catalyst
2
4
−
−
The eꢃect oꢀ anion incorporated on the IL (BF vs. Br )
Yield (%)a
4
Entry
Solvents
Catalyst
Tempera-
ture (°C)
was also studied by keeping the other parameters such as
amount (g)
amount oꢀ catalyst, solvent type and temperature (Table 5).
1
2
3
4
5
6
7
8
9
Toluene
Acetonitrile
Ethanol+H O
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
0.05
0.05
0.05
0.05
0.05
0.05
0.04
0.03
0.1
25
25
25
90
60
25
25
25
25
43
50
68
51
70
86
80
70
86
−
−
By replacing Br with BF , the reaction time is reduced,
4
and the reaction efciency enhanced, which was consist-
2
ent with the reported results; the IL oꢀ bmiBF has showed
4
−
higher yields compared to bmiCl [54]. Moreover, Br has a
hydrophilic nature and is miscible in highly polar solvents,
thus the ion solvation restricts the activity oꢀ the supported
−
IL, in contrast BF exhibit hydrophobicity and immisci-
4
bility in aqueous media [73]. The eꢃect oꢀ the substrate
(
i.e. UiO-66-NH ) was examined and the result showed a
2
medium activity probably due to high surꢀace area and avail-
able basic sites on the MOF. In addition, the activity oꢀ the
Reaction conditions: benzaldehyde (1 mmol), hydroxylammonium
chloride (1.5 mmol), solvent (1 mL), catalyst, reaction time (15 min)
a
−
−
Isolated yield
ionic liquid (e.g. ILBr , IL-BF ) and urea in homogenous
4
1
3

S. Askari et al.
Table 4 Synthesis oꢀ oximes via reaction oꢀ aldehydes and/or ketones with hydroxylammonium chloride
O
NOH
R2
Cat
NH OH.HCl
2
R1
R2
R1
Ethanol, rt
Entry
1
Substrate
Time (min)
15
Yield (%)a
Melting point (°C) [Reꢀ.]
31–33 (33–35) [56]
86
O
H
2
25
92
55–58 (57–59) [56]
O
H
OH
3
4
25
30
82
67
57–59 (51–53) [72]
178–182
O
H
CH3
O
H CO
3
H
H CO
3
OCH3
5
6
25
30
78
77
132–136 (136–138) [56]
126–128 (128–130) [56]
O
H
O
H
O N
2
7
8
30
30
83
61
116–118 (116–118) [42]
63–65 (68–72) [42]
O
H
NO2
O
H
Cl
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
Table 4 (continued)
Entry
9
Substrate
Time (min)
35
Yield (%)a
65
Melting point (°C) [Reꢀ.]
131–133 (131–133) [56]
O
H
H CO
3
1
1
0
1
25
20
75
83
56–57 (56–59) [42]
80–85 (84–85) [42]
O
CH3
O
Reaction conditions: aldehyde or ketone (1 mmol), hydroxylammonium chloride (1.5 mmol), ethanol (1 mL), UiO-66-NH -ILBF −-urea (0.05 g)
2
4
at 25 °C in 15–35 min
Isolated yield
a
1
00
Table 5 The catalytic activity oꢀ the catalyst, the support and the IL
in homogeneous phase
86
85
8
3
8
0
7
7
8
0
Catalyst
Time (min)
Yield (%)a
UiO-66-NH -ILBF −-urea
15
20
30
35
35
35
86
70
43
33
20
Trace
60
2
4
−
UiO-66-NH -ILBr -urea
2
4
0
UiO-66-NH2
−
ILBF4
ILBr–
20
0
Urea
1
2
3
4
5
Reaction conditions: benzaldehyde (1 mmol), hydroxylammonium
Number of runs
chloride (1.5 mmol), ethanol (1 mL), temperature (25 °C), and cata-
lyst or UiO-66-NH or IL (0.05 g)
2
Fig. 5 Reusability oꢀ the catalyst ꢀor the synthesis oꢀ oxime
a
Isolated yield
phase were investigated. ILs exhibited a limited eꢃect on
the activation oꢀ the carbonyl groups and deprotonation oꢀ
(Fig. 5). Aꢀter each cycle, the catalyst was reactivated by
centriꢀugation, washing with water and ethanol (to remove
the residual starting materials on the catalyst surꢀace and
pores), and drying at 60 °C in an oven overnight. The cata-
lyst was successꢀully recycled and reused 5 times without
signiꢁcant loss oꢀ the perꢀormance. The slight reduction in
catalyst activity might be related to the partial blocking oꢀ
the pores by trapped starting materials or product [75, 76].
The BET surꢀace area and total pore volume oꢀ the reused
catalyst were reduced (cf. the ꢀresh catalyst) and ꢀound to be
−
−
hydroxyl amine by Br and BF . Urea as a base was not
4
eꢃective in the homogeneous phase, while by graꢀting to
the IL and the MOF, their synergic eꢃects may promote
the hydrogen-bonding donation oꢀ the urea in heterogene-
ous phase. A similar synergic activation has been ꢀound ꢀor
(
2-hydroxyethyl)trimethylammonium in choline chloride/
urea system supported on molecular sieves ꢀor the CO cycli-
2
zation with epoxides [74].
2
−1
3
−1
4
27 m g and 0.34 cm g , respectively, although a slight
3.2.1 Catalyst Recycling and Stability
increase in pore size (1.0 nm) was observed (Table 1). The
N adsorption–desorption isotherm and pore size distribu-
2
The recyclability and reusability oꢀ the catalyst were stud-
ied ꢀor the condensation reaction using a model reaction
between benzaldehyde with hydroxylammonium chloride
tion oꢀ the reused catalyst can be ꢀound in Fig. 1c, d.
The catalyst stability was investigated by XRD, FTIR,
electron microscopy, and elemental analysis. XRD pattern
1
3

S. Askari et al.
–
and the FT-IR spectrum oꢀ the reused UiO-66-NH -ILBF -
composition ꢀor the recycled catalyst in comparison with
those ꢀor the ꢀresh catalyst. An atomic percentage ꢀor the
corresponding elements in the recycled catalyst was ꢀound
to be Zr (4.4%), O (18.6%), C (39.1%), N (5.2%), B (9.3%),
2
4
urea show similar patterns (Fig. 1a, b) to those in ꢀresh
catalyst, indicating that the catalyst is almost stable under
reaction conditions aꢀter ꢁve times oꢀ recycling and reusing.
Furthermore, the morphology and the chemical composition
and F (23.3%). A slight reduction in the content oꢀ B and F
–
–
oꢀ the UiO-66-NH -ILBF -urea (aꢀter ꢁve times oꢀ reusing)
(corresponding to BF ) caused negligible leaching ꢀor the
2
4
4
were studied by FE-SEM (Fig. 6) and elemental analysis/
mapping (Figure S8 and S9, Supporting Inꢀormation). The
results showed a slight change in the morphology and similar
reused catalyst aꢀter ꢁve successive recycling. Furthermore,
the activity oꢀ the extracted catalyst aꢀter hot ꢁltration (70 °C
in EtOH ꢀor 2 h) was reduced to a yield oꢀ 80%, which could
−
be related to leaching oꢀ BF at an elevated temperature.
4
Consequently, the catalyst can be easily recycled and reused
several times with a reasonable stability.
Diꢃerent types oꢀ acidic (Brønsted, Lewis, and solid
acids, entries 1–11, Table 6) and basic (metal hydroxide and
organic bases, entries 12–15) conditions were used ꢀor the
synthesis oꢀ oximes. Organic and polar solvents and also
solventless conditions were suitable media ꢀor the syntheses.
Microwave (MW) and ultrasonic (US) irradiations, reꢂux,
and grinding were applied to accelerate the reactions. Ionic
liquids were also employed as a catalyst or reaction medium.
Major environmental and economic concerns on the reported
catalytic systems are catalyst recoverability and reusability,
thereꢀore, integration oꢀ catalysts to solid porous supports is
encouraging. The current catalytic system, a heterogeneous
basic catalyst, showed comparable results in terms oꢀ yield
and reaction conditions (e.g. temperature and time), and
Fig. 6 FE-SEM image oꢀ the catalyst aꢀter ꢁve times reuse
Table 6 Synthesis oꢀ oximes via reaction oꢀ benzaldehydes with hydroxylammonium chloride (NH OH.HCl) using diꢃerent catalytic systems
2
Entry
Catalytic systems
Reaction conditions
Time (min)
Yield (%)
Reꢀ
−
1
2
3
4
5
6
7
8
9
TiO /SO42 (0.05 g)
130 °C, solventless
US (25–35 °C), EtOH
1
5
100
88
[50]
[42]
[77]
[43]
[43]
[39]
[52]
[52]
[71]
[71]
[51]
[53]
[56]
[56]
[58]
[55]
[54]
This work
2
Na SO (0.1 mmol)
HCl (2 drops), K CO (10%), pH 10
BF ·Et O (10 mol%)
BF ·Et O (10 mol%)
Silica gel 60, 230–400 mesh (1 g)
Wet basic Al O (1.5 equiv.)
Molecular sieves 4 Å (2.5 g)
2
4
US, H O
Immediately
3.5 (h)
6
3
5
30
4
10
6 (h)
2
70 (s)
90
5 (h)
5
30
15
91
2
3
2
a
Reꢂux, CH OH
87
3
2
3
a
MW, CH OH
95
3
2
3
MW (800 W, 80–90 °C), solventless
MW, solventless
Grinding
MW (400 W, 80 °C), solventless
80 °C, solventless
100
79
60
82
83
95
2
3
Na CaP O nanostructure (0.1 g)
2
2
7
10
11
12
13
14
15
16
17
18
Na CaP O nanostructure (0.1 g)
2
2
7
Na [WZn (H O) (ZnW O ) ] (0.01 mmol)
H O (27%), NH (25%), H O, rt
12
3
2
2
9
34 2
2
2
3
2
b
NaOH (1.2 mol)
DABCO (1 mmol)
(PhCH ) N (1 mmol)
Glycine (0.5 mmol)
[bmIm]OH (2 mmol)
Grinding, CH OH (2–4 drops), rt
71
3
c
Grinding and MW (900 W), solventless
Grinding and MW (900 W), solventless
DMF, rt
US, EtOH, rt
rt
98
98
96
2
3
d
91
95
d
bmiBF (2 mmol)
4
UiO-66-NH -ILBF −-urea (0.05 g)
EtOH, rt
86
2
4
a
CH CONHOH was used instead oꢀ NH OH·HCl
3
2
b
c
d
2
-Hydroxybenzaldehyde as a precursor
1
,4-Diazabicyclo[2.2.2]octane
Cyclohexane as a precursor
1
3

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH Metal–…
2
superior recyclability, reusability, and robustness compared
to the reported systems.
8. Riisager A, Fehrmann R, Haumann M, Wasserscheid P (2006)
Supported ionic liquid phase (SILP) catalysis: An innovative con-
cept ꢀor homogeneous catalysis in continuous ꢁxed-bed reactors.
Eur J Inorg Chem 2006:695–706
9
.
Zhang Q, Zhang S, Deng Y (2011) Recent advances in ionic liquid
catalysis. Green Chem 13:2619–2637
4
Conclusion
1
0. Hagiwara H, Sekiꢀuji M, Hoshi T, Qiao K, Yokoyama C (2007)
Synthesis oꢀ bis(indolyl)methanes catalyzed by acidic ionic liquid
immobilized on silica (ILIS). Synlett 2007:1320–1322
A robust supported ionic liquid system is introduced ꢀor
the organic synthesis oꢀ oximes. In the design strategy, the
basic heterogeneous catalyst was successꢀully prepared by
employing a chemical/thermal stable Zr-based MOF, UiO-
1
1
1. Gu Y, Li G (2009) Ionic liquids-based catalysis with solids: state
oꢀ the art. Adv Synth Catal 351:817–847
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aldehydes and ketones with hydroxylammonium chloride in
good yields. Ethanol was the best candidate as a solvent in
the current method. The catalyst was successꢀully recycled
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they can be extensively employed in various catalytic reac-
tions with efcient perꢀormance. Moreover, a large number
oꢀ available pores in MOFs can be a suitable host ꢀor ionic
liquids to produce a large variety oꢀ heterogeneous catalysts.
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3
Acknowledgements M. Jaꢀarzadeh is thankꢀul to Razi University ꢀor
the partial ꢁnancial supports, and Proꢀ. Kim Daasbjerg and Monica
Rohde Madsen (Aarhus University, Denmark) ꢀor XPS analysis.
2
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Aꢀliations
1
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Saeed Askari · Mohammad Jafarzadeh · David Benjamin Christensen · Søren Kegnæs
1
2
Faculty oꢀ Chemistry, Razi University,
7144-14971 Kermanshah, Iran
Department oꢀ Chemistry, Technical University oꢀ Denmark,
2800 Kgs. Lyngby, Denmark
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