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GHAFURI ET AL.
in denitrogenating of fuel oils.[12] In theory, more than a
million ILs can be synthesized. It is possible to adjust the
properties of ILs by selecting assured components which
suited for a precise application.[13] According to their
applications, many kinds of ILs were synthesized till
now: acidic ILS, functionalized ILs, covalently and non‐
covalently supported ILs, ILs transported into metal–
organic frame‐works (MOFs), superionic liquids, and
magnetic ILs, which each of them have their unique
proper‐ties.[14]
catalyst IL with great catalytic activity in condensation
reactions (scheme 1). Three kind of heterocycles were
synthesized by this dual solvent‐catalyst including the
synthesis of benzylidenes, bis‐hydroxyenones and xan-
thenes and characterized by FT‐IR, 1HNMR and 13CNMR
spectroscopy. Also synthesized [Caff‐TEA]+[ZnBr3]− was
characterized by Fourier transform infrared spectroscopy
(FT‐IR), X‐ray diffraction (XRD) and Energy‐dispersive
X‐ray spectroscopy (EDX) analysis.
Imidazolium‐based ILs are the most usable ionic liq-
uids which most researches in this field are on the basis
of them. One problem of imidazolium based ILs is their
synthetic method that cause environmental pollution.
To reduce this, natural‐based imidazolium structure
can be used. Caffeine, a methylxanthine alkaloid, is a
natural‐based imidazolium compound which extracted
from coffee beans. Previously, caffeine was used to syn-
thesize organometallic compounds, used as liquid IL as
catalysis in organic compounds, and also used to synthe-
size solid IL.[15] So, it could be used instead of synthetic
imidazole to synthesized ionic liquid. To enhance the
activity of IL, several functional groups can be used. It
should be noted that presence of functional groups with
active sites, such as free nitrogen and oxygen, make it
possible to place various metals in the structure of IL,
which cause development in the application of IL. From
this kind of compounds, triethanolamine (TEA) with free
adjacent hydroxyl groups, can be effective component in
the structure of IL to immobilize metals on it.
2 | EXPERIMENTAL
2.1 | Materials
All chemicals and solvents were purchased from Merck
and Sigma companies and used without any further puri-
fication. The ultrasonic reactions were carried out in an
Elmasonic S 60 H (220–240 V) sonicator, the FT‐IR
spectra were recorded by Shimadzu 800 IR 100 FT‐IR
spectrometer in KBr, EDX spectra were recorded by
Numerix DXP‐X10P, the powder X‐ray diffraction
patterns were recorded by PANalytical X‐PERT‐PRO
MPD diffractometer with Cu Kα (λ = 1.5406 Å) irradia-
tion, and NMR spectra were recorded by Burker DRX‐
500 Avance spectrometer (500 MHz/1HNMR and
125 MHz/13CNMR).
2.2 | Typical procedure for the synthesis
of [Caff‐TEA]+[ZnBr3]− IL
Heterocyclic Building Blocks have key role in synthesiz-
ing complicated chemical and biological compounds and
serving wide range of applications in immense scientific
fields. Of these kind of heterocyclic building blocks, thia-
zoles, hydrazones, pyrrolidines and bis‐cyclohexenones
can be men‐tioned. Bis‐hydroxyenones, from bis‐
cyclohexenones family, and benzilidenemalono‐nitriles/
benzilidene cyclohexenones are of these group of heterocy-
clic building blocks. Benzilidenemalononitriles can be syn-
thesized from the reaction of one moiety of diketone with
one ben‐zaldehyde and bis‐hydroxyenones can be synthe-
sized from the reaction of two moiety of diketones with
one benzaldehyde and formed more complicated heterocy-
clic compounds such as pyridines, chromenes, acridines
and xanthanes.[16] Various method for the synthesis of
these compound have been reports such as using Al2O3,
A
mixture of caffeine (1.0 mmol) and 1,3‐
dibromopropane (1.0 mmol) was added to a 50 ml flask
in DMF and stirred for 48 hr at 90 °C under N2 atmo-
sphere. To this mixture, TEA was added and stirred for
24 hr at 80 °C. After completion the reaction, DMF was
separated by rotary and obtained product, [Caff‐TEA]
+[ZnBr3]−, washed with EtOAc and dried under air atmo-
sphere at r.t for 24 hr. Melting point of resulted IL was
176 °C. To this synthesized IL, ZnBr2 (2.0 mmol) was
added in H2O and stirred for 24 hr at r.t. Resulted IL
was separated and washed at r.t. for 24 hr. Melting point
of synthesized IL was surprisingly decreased to 76 °C.
2.3 | Typical procedure for benzylidene
synthesis
[bmim]OH, Taurine, L‐Histidine, SiO2‐Cu, CoFe2O4,
[17]
HClO4–SiO2 and ZrOCl2/NaNH2,
but still better
methods should be provide to synthesize it.
A
mixture
of
benzaldehyde
(1.0
mmol),
In this contribution, a facile procedure for the
synthesis of novel natural‐based IL using caffeine,
1,3‐dibromine, triethanolamine (TEA) and ZnBr2 [Caff‐
TEA]+[ZnBr3]− was used and lead to dual solvent‐
dimedone/cyclohexandione (1.0 mmol) and IL [Caff‐
TEA]+[ZnBr3]− (0.5 mL) was added to a 50 ml flask and
sonicated for 15 min h at 80 °C under air atmosphere.
After completion the reaction, which was followed by