The introduction of two new imidazole-based bis-dicationic Br?nsted acidic ionic liquids and comparison of their catalytic activity in the synthesis of barbituric acid derivatives

Article abstract of DOI:10.1039/c8nj01179f

In this article, the preparation of bis-imidazolium hydrogen sulfate and bis-imidazolium perchlorate as two new bis-dicationic Br?nsted acidic ionic liquids based on imidazole is reported. After characterization by FT-IR, mass and NMR spectroscopy and pH titration, the applicability of these reagents is studied in the promotion of the synthesis of 5-arylidene barbituric acids and pyrano[2,3-d] pyrimidinone derivatives. These methods possess some advantages such as ease of preparation of the catalyst, simple work-up procedure, short reaction times, excellent yields, and use of nonorganic solvents during all steps of the reactions and good reusability of the catalysts.

Full text of DOI:10.1039/c8nj01179f

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The introduction of two new imidazole-based
bis-dicationic Bronsted acidic ionic liquids and
comparison of their catalytic activity in the
¨
Cite this:DOI: 10.1039/c8nj01179f
synthesis of barbituric acid derivatives†
Nader Daneshvar,a Mitra Nasiri,b Maryam Shirzad,b
ab
Mohaddeseh Safarpoor Nikoo Langarudi,b Farhad Shirini
*
and Hassan Tajikab
In this article, the preparation of bis-imidazolium hydrogen sulfate and bis-imidazolium perchlorate as two
new bis-dicationic Bronsted acidic ionic liquids based on imidazole is reported. After characterization by
¨
FT-IR, mass and NMR spectroscopy and pH titration, the applicability of these reagents is studied in the
promotion of the synthesis of 5-arylidene barbituric acids and pyrano[2,3-d] pyrimidinone derivatives.
These methods possess some advantages such as ease of preparation of the catalyst, simple work-up
procedure, short reaction times, excellent yields, and use of nonorganic solvents during all steps of the
reactions and good reusability of the catalysts.
Received 10th March 2018,
Accepted 7th May 2018
DOI: 10.1039/c8nj01179f
rsc.li/njc
prepared to use in many organic reactions.4 In this regard,
Introduction
¨
imidazole-based Bronsted acidic ionic liquids have a special
Ionic liquids (ILs) are considered as powerful alternatives to position among BAILs and show effective catalytic ability under
conventional molecular organic solvents and catalysts and have mild conditions.5
various applications in the field of chemical synthesis. This is due to
In recent years, attention has been focused on dicationic ionic
their particular properties such as negligible vapor pressure, ability liquids which have different and customizable properties. These
to dissolve many organic and inorganic substances, recyclability, compounds as the catalysts have higher thermal stability and
good thermal stability, tunable viscosity, and miscibility with water selectivity while their toxicity is quite a bit lower than that of their
and organic solvents. The other advantage of these compounds is mono-cationic homologs.6 The length of the chain in these com-
their good ability for extracting metal ions, which mainly pounds can affect the lipophilicity, conductivity and morphology of
depends on their special structures. Also, ILs have received the compound.7 Since these compounds have two cations and two
considerable attention as environmentally friendly and green anions, more efficient applications can be considered for them.8
reaction media in organic synthesis.1
Nowadays, dicationic ionic liquids have been used in the fields of
Ionic liquids consist of organic (mostly heterocyclic) cations and solar cells, catalysts, lubricants, fuel cells and batteries.9 One of the
organic/inorganic anions and most of them are non-metallic salts most important compounds of this category is the imidazole-based
which exhibit promising applications in many fields, especially in ionic liquids, which are used as lubricants, surfactants, nano-
2
catalysis. Among these types of compounds, Bronsted acidic ionic particle coatings and solvents.10 Recently, dicationic ionic liquids
¨
liquids (BAILs) are prepared to replace traditional mineral liquid based on imidazole and methylimidazole have been synthesized
acids such as sulfuric acid and hydrochloric acid using chemical and studies on their structure have been performed.11
methods.3
Barbituric acid is a cyclic amide that has been used as a
¨
An important unique feature of Bronsted acidic ionic liquids precursor of barbiturates. This substance is not hypnotic and
is their applicability in the field of catalysis. BAILs are more seductive on its own but its derivatives with alkyls and aryls
acidic than traditional ionic liquids and for this reason, are show these abilities.12 Among them, different derivatives of
5-benzylidene barbituric acids have been paid much attention
a Department of Chemistry, College of Science, University of Guilan,
as starting materials, dyes and nonlinear optical materials.13
Also, these compounds can be used as therapeutic agents and
some of them show considerable antimicrobial, antifungal,
antitumor and anticancer activities.14
University Campus 2, Iran. E-mail: ndxdaneshvar@gmail.com
b Department of Chemistry, College of Sciences, University of Guilan, 41335, Rasht,
Iran. E-mail: shirini@guilan.ac.ir; Fax: +98 131 3233262; Tel: +98 131 3233262
† Electronic supplementary information (ESI) available: FT-IR, 1H NMR, 13C
NMR, mass spectroscopy & pH titration and reusability curves of the catalysts
The Knoevenagel reaction is a traditional and classical
and FT-IR, 1H NMR & 13C NMR of the new products. See DOI: 10.1039/c8nj01179f method for the formation of a C–C bond in organic chemistry.15
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Many catalysts have been reported for the preparation of 5-benzyl-
idene barbituric acid derivatives via this reaction, of which
SBA-Pr-SO3H,16 BF3/nano g-Al2O3,17 CuO-Nps,18 L-tyrosine,19
CoFeO4,20 NH2SO3H,21 PVP-Ni-Nps,22 [bmim]BF4,23 EAN,24
CTMAB,25 CH3COONa,26 CMZO27 and Fly ash/NaOH28 are examples.
Pyran derivatives are common structural subunits in a variety
of important natural products such as carbohydrates, alkaloids,
polyether antibiotics, pheromones and iridoids.29 Pyrano[2,3-d]-
pyrimidines are six member unsaturated heterocycle rings. These
compounds consist of a mixture (fusion) of pyran and pyrimidine
rings which can include an oxygen atom at position number 8 and
two nitrogen atoms in position numbers 1 and 3.30 Pyrano[2,3-d]-
pyrimidine derivatives have received more attention from chemists
because of their biological activities such as, antiallergic, anti-
hypertensive, cardiotonic, antibronchitic, antitumor hepato-
protective, antifungal, antimalarial, analgesic, antiviral evaluation,
antibacterial, antileishmanial, vasodilator and herbicidal activities.31
Preparation of pyrano[2,3-d]pyrimidines is based on multi-
component reactions such as Knoevenagel condensation and
Michael addition followed by a cyclodehydration strategy and
hetrocyclization.32 Different methods have been reported for
the preparation of these heterocycles under various conditions
using microwave irradiation,33 ultrasonic irradiation,34 nano-
SBA-Pr-SO3H,35 Al-HMS-20,36 CaHPO4,37 choline chlorideꢀ
ZnCl2,38 Zn[L-proline]2,39 boric acid and nano-titania sulfuric
acid40 and ZnO@CuO41 as accelerators.
Scheme 1 Preparation of two imidazole-based bis-dicationic Bronsted
acidic ionic liquids.
¨
1H NMR and 13C NMR spectra were determined on a Bruker
AV-400 MHz or 500 MHz using TMS (0.00 ppm) as an internal
standard and DMSO-d6 as the solvent.
Preparation of 1,4-di(1H-imidazol-1-yl)butane [Bisim]
In a 50 mL round-bottomed flask, a mixture of imidazole (1.374 g,
20.0 mmol) and sodium hydroxide (0.800 g, 10.0 mmol) in DMSO
(8 mL) was stirred at 60 1C for 1 hour. Then 1,4-dichlorobutane
(1.271 g, 10.0 mmol) was added and stirred under the same
conditions for 2 hours. After that, the solution was cooled to
room temperature. Then crushed ice and a saturated solution
of sodium chloride (30 mL) were added to it while it was stirring.
The solution became turbid slowly and a white precipitate was
suddenly settled down. The mixture was filtrated and the filtrate
was washed several times with cold water. After drying a white puffy
solid is achieved. After recrystallization from ethanol, needle-like
crystals of 1,4-di(1H-imidazol-1-yl)butane were obtained in 88%
yield (Scheme 1). It should be mentioned that the synthesis of this
compound as a puffy solid is claimed in an analytical paper but
sufficient proof for the characterization was not presented and the
method of the separation was not clear and applicable.42
Experimental section
Materials
All of the aldehydes, malononitrile, and barbituric acid were
purchased from Merck Chemical Company (Munich) and were
used without further purification. The purity of the substrates was
monitored by thin layer chromatography (TLC). Perchloric acid (CAS:
7601-90-3, MW: 100.46.17 g molꢁ1, assay Z 70% w/w%) and sulfuric
acid (CAS: 7664-93-9, MW: 98.08 g molꢁ1, assay Z 99.99 v/v%) were
purchased from Sigma-Aldrich (Mumbai). Both assays were reported
by the company and were not examined more. All solvents were
prepared from Merck (Munich) and were kept sealed in airtight
bottles as well to minimize the absorption of atmosphere moisturize.
Moreover, they were distilled before being used.
Spectral data for 1,4-di(1H-imidazol-1-yl) butane: m.p. 82–84 1C;
FT-IR (KBr) 3407, 3181, 3122, 2932, 2866, 1672, 1507, 1465 cmꢁ1
;
1H NMR (400 MHz, DMSO-d6, 25 1C, TMS): d = 1.60–1.66 (m, 4H,
C–CH2–C), 3.94–3.99 (m, 4H, N–CH2–C), 6.89 (t, 3J(H,H) = 1.2 Hz, 2H,
Ar–CH), 7.15 (t, 3J(H,H) = 1.2 Hz, 2H, Ar–CH), 7.62 (t, 3J(H,H) =
1.2 Hz, 2H, N–CH–N) ppm; 13C NMR (100 MHz, DMSO-d6, 25 1C,
TMS): d = 28.1, 47.2, 119.7, 128.8, 137.6 ppm.
Characterization techniques
Products were characterized by their physical constants, com-
parison with authentic samples and IR and NMR spectroscopy.
The purity determination of the substrate and reaction monitoring
Preparation of 1,10-(butane-1,4-diyl)bis(1H-imidazol-3-ium)
hydrogen sulfate {[H2-Bisim][HSO4]2}
was accomplished by TLC on silica-gel polygram SILG/UV 254 In a 50 mL round-bottomed flask, to a stirring mixture of
plates. Melting points were measured by electrothermal IA9100 1,4-di(1H-imidazol-1-yl)butane (1.901 g, 10.0 mmol) in dry CH2Cl2
melting point apparatus in capillary tubes. The starting tempera- (20 mL) in an ice bath, anhydrous sulfuric acid (1.1 mL–20 mmol)
ture of the approximate melting range was input via the keyboard was added dropwise and stirred for an additional 4 hours. After that,
and the melting point range was spotted visually. FT-IR spectra the solvent was decanted and the residue was washed with diethyl
were recorded on a Perkin-Elmer Spectrum BX series and KBr ether (3 ꢂ 20 mL). Finally, the solvent was evaporated using a rotary
pellets were used for solid samples. Mass spectra were obtained system under vacuum. During this process, a transparent viscous
on an Agilent Technologies 5975C spectrometer via mass selective ionic liquid of [H2-Bisim][HSO4]2 was achieved in 94% yield
detector (MSD) operating at an ionization potential of 70 eV. (Scheme 1).
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Spectral data of 1,10-(butane-1,4-diyl)bis(1H-imidazol-3-ium) separated by filtration. The separated product was washed several
hydrogen sulfate: MS (70 eV, EI): m/z (%): 386 (M+); FT-IR (KBr) times with water. After drying, the pure product was obtained and
3417, 3180, 2924,1638, 1500, 1417, 1383, 1156, 1083,1017, 851, there was no need for a further purification process using organic
763, 630 cmꢁ1 1H NMR (500 MHz, DMSO-d6, 25 1C, TMS): solvents. In continuation, water was evaporated from the filtrated
;
d = 1.74 (s, 4H, C–CH2–C), 4.22 (s, 4H, N–CH2–C), 7.07 (s, 2H, solution to obtain the ionic liquid catalysts.
HSO4ꢁ), 7,58 (s, 2H, Ar–H), 7.70 (s, 2H, Ar–H), 9.02 (s, 2H,
N–CH–N), 14.29 (brs, 2H) ppm; 13C NMR (125 MHz, DMSO-d6,
The spectral data of the new compounds
25 1C, TMS): d = 26.7, 48.2, 120.5, 122.5, 135.6 ppm.
5-((1-Methyl-1H-pyrrol-2-yl)methylene)pyrimidine-2,4,6-
(1H,3H,5H)-trione (Table 3, entry 20). Yellow powder; m.p.
280 1C (Dec.); FT-IR (KBr) 3416, 3178, 3097, 3027, 2828, 1735,
Preparation of 1,10-(butane-1,4-diyl)bis(1H-imidazol-3-ium)
perchlorate {[H2-Bisim][ClO4]2}
1689, 1654, 1559, 1497, 1451, 1290,1208, 1148, 1063 cmꢁ1
;
1H NMR (400 MHz, DMSO-d6, 25 1C, TMS) d: 3.94 (s, 3H), 6.49
In a 50 mL round-bottomed flask, to a stirring mixture of
1,4-di(1H-imidazol-1-yl)butane (1.901 g, 10.0 mmol) in a dry CH2Cl2
(20 mL) in an ice bath, perchloric acid (1.3 mL–20 mmol) was added
dropwise and stirred for 4 hours. After that, the solvent was decanted
and the residue was washed with diethyl ether (3 ꢂ 20 mL). Finally,
the solvent was evaporated using a rotary system under vacuum.
During this process, a white amorphous solid of [H2-Bim][ClO4]2 was
achieved in 95% yield (Scheme 1).
2
2
3
(dd, J1(H,H) = 4.4 Hz, J2(H,H) = 2.4 Hz, 1H), 7.69 (t, J(H,H) =
2.0, 1H), 8.28 (s, 1H), 8.49 (dd, 2J1(H,H) = 4.4 Hz, 2J2(H,H) =
1.6 Hz, 1H), 11.03 (s, 1H), 11.19 (s, 1H) ppm; 13C NMR (100 MHz,
DMSO-d6, 25 1C, TMS) d: 34.3, 106.6, 111.7, 126.9, 128.9, 136.5,
137.6, 150.2, 150.3, 162.4, 164.5 ppm.
7-Amino-5-(3-bromophenyl)-2,4-dioxo-1,3,4,5-tetrahydro-2H-
pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 4, entry 18). White
powder, m.p. 236–238 1C; FT-IR (KBr) 3415, 3318, 3216, 3196,
3010, 2942, 2852, 2852, 2789, 2192, 1715, 1661, 1568, 1471, 1399,
134, 1277, 1208, 1174, 1070, 983, 798 cmꢁ1; 1H NMR (400 MHz,
DMSO-d6, 25 1C, TMS) d: 4.30 (s, 1H), 7.24 (s, 2H), 726–7.34
(m, 2H), 7.45–7.48 (m, 2H), 11.14 (s, 1H), 12.15 (s, 1H) ppm; 13C NMR
(100 MHz, DMSO-d6, 25 1C, TMS) d: 35.3, 58.0, 87.6, 119.0, 121.5,
126.5, 129.6, 130.0, 130.4, 146.8, 149.4, 152.4, 157.6, 162.4 ppm.
Spectral data of 1,10-(butane-1,4-diyl)bis(1H-imidazol-3-ium)
perchlorate: m.p. 180 1C; MS (70 eV, EI): m/z (%): 390 (M+);
FT-IR (KBr, cmꢁ1) nmax: 3424, 3143, 2862, 1636, 1578, 1548,
1454, 1289, 1145, 1085, 831, 758, 628. 1H NMR (400 MHz,
DMSO-d6, 25 1C, TMS) d: 1.76–1.85 (m, 4H), 4.21–4.26
3
3
(m, 4H), 7.70 (t, 2H, J(H,H) = 1.6 Hz, Ar–H), 7.75 (t, 2H, J(H,H) =
1.6 Hz, Ar–H), 9.07 (t, 2H, 3J(H,H) = 1.6 Hz, N–CH–N) ppm,
14.25 (brs, 2H); 13C NMR (100 MHz, DMSO-d6, 25 1C, TMS) d:
26.6, 48.3, 120.4, 122.3, 135.6 ppm.
Results and discussion
General procedure for the synthesis of 5-arylidene barbituric
acid derivatives
In recent years, preparation, characterization and use of ionic liquid
In a 25 mL round-bottomed flask a mixture of aldehyde (1.0 mmol), catalysts in organic transformations became an important part of
barbituric acid (1.0 mmol) and the requested acidic ionic liquid our ongoing research program.43–50 Herein and in continuation of
{0.024 g (6.2 mol%) in the case of [H2-Bisim][HSO4]2 or 0.030 g these studies we wish to introduce two new members of this family
(7.6 mol%) in the case of [H2-Bisim][ClO4]2} in water (3 mL) was which can act as efficient promoters in multi-component reactions
heated at 80 1C for the appropriate time. After the completion of leading to important biologically active compounds. These new
¨
the reaction which was monitored by TLC (n-hexane: EtOAc; 3 : 1), imidazole-based bis-dicationic Bronsted acidic ionic liquids can be
10 mL of water was added and stirred for 2 minutes. During this formulated as [H2-Bisim][HSO4]2 and [H2-Bisim][ClO4]2 (Scheme 1).
time the product was precipitated and separated by filtration. The The preparation and structure of these compounds are proved using
1
separated product was washed several times with water. After different types of techniques including FT-IR, HNMR, 13C NMR,
drying, the pure product was obtained while there was no need mass spectroscopy and pH titration methods. Below are some
to further purification using the addition of organic solvents. In elucidations in detail.
continuation, water was evaporated from the filtrated solution to
obtain the ionic liquid catalysts.
It should be mentioned that since the functional groups of
imidazole and its bis form are nearly the same, there is no
meaningful difference between the FT-IR spectra of these
compounds. However, a small decrease in the number and
intensity of the peaks in the FT-IR spectra of the bis form can be
General procedure for the synthesis of pyrano[2,3-d]-
pyrimidinones
In a 25 mL round-bottomed flask a mixture of aldehyde (1.0 mmol), observed which may be due to limited movement of the
barbituric acid (1.0 mmol), malononitrile, (1.1 mmol) and the relatively locked structure in this form resulting in a decrease
requested acidic ionic liquid {0.024 g (6.2 mol%)} in the case of in the observed vibrations.
{[H2-Bisim][HSO4]2} or 0.030 g (7.6 mol%) in the case of {[H2-Bisim]-
FT-IR spectra [H2-Bisim][HSO4]2 can be explained as: N–H
[ClO4]2} in water (3 mL) was heated at reflux temperature for the stretching at 3417 cmꢁ1 which is overlapped with the broad-
appropriate time. After the completion of the reaction which was band related to the acidic OH stretching (2700–3400 cmꢁ1).
monitored by TLC [n-hexane: EtOAc; 3 : 1(for the first run) and Aliphatic C–H stretching vibrations appear at 2924 cmꢁ1 while
EtOAc (for the second run)], 10 mL of water was added and stirred N–H bending occurs at 1638 cmꢁ1. In this spectrum, the bands
for 2 minutes. During this time the product was precipitated and at 1450 cmꢁ1 and 1417 cmꢁ1 are attributed to C–C stretching
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and stretching vibration of C–N appears at 1383 cmꢁ1. Also, cations and anions in the liquid crystal arrangement. However,
ꢁ
SQO symmetric and asymmetric stretching peaks of HSO4
for this substance as a symmetric compound, the observed peaks
appeared at 1383 cmꢁ1 and 1156 cmꢁ1 and S–O bending peaks are two singlet peaks of the aliphatic chain at 1.74 ppm (Ha) and
appeared at 851 cmꢁ1 and 580 cmꢁ1
4.22 ppm (Hb). Three aromatic peaks of imidazole appeared as a
.
In the case of [H2-Bisim][ClO4]2 the FT-IR can be explained as: singlet at 7.57 ppm (Hc), 7.70 ppm (Hd) and 9.02 ppm (He). Also,
broadening in the 2700–3300 cmꢁ1 area occurred due to acidic the peaks of HSO4 and NH+ appeared as a singlet at 7.07 ppm
ꢁ
hydrogen bonds. N–H broad stretching is at 3423 cmꢁ1 and C–H (Hf) and a broad singlet at 14.29 ppm (Hg), respectively. In the
stretching of the aromatic and aliphatic bonds appears at 3140 cmꢁ1 13C NMR spectrum of this compound, since no carbon is added
and 2862 cmꢁ1, respectively. N–H bending appeared at 1634 cmꢁ1 to 1,4-di(1H-imidazol-1-yl)butane, again five types of peaks are
while CQC bending occurred at 1578 cmꢁ1 and 1548 cmꢁ1
.
.
observable with little shifts caused by changes in the polarity of
the bonds and the entire structure while having ionic peripheral
C–C stretching peaks occurred at 1454 cmꢁ1 and 1405 cmꢁ1
The peak at 1289 cmꢁ1 is attributed to the C–N stretching bond. interactions.
Peaks at 1145 cmꢁ1 and 1085 cmꢁ1 are related to symmetric
In the 1HNMR spectra of [H2-Bisim][HClO4]2, six expected
and asymmetric ClO4ꢁ stretching while peaks at 831 cmꢁ1 and peaks were observed due to six different types of hydrogens in
623 cmꢁ1 are related to its bending vibrations.
its structure: a multiplet at 1.76–1.85 ppm (Ha) and a multiplet
In the mass spectrum of [H2-Bisim][HSO4]2 and [H2-Bisim]- at 4.21–4.26 ppm (Hb) for the aliphatic hydrogen atoms and
[ClO4]2, the molecular ion peak (M+) appeared at m/z = 386 and three triplets for Hc, Hd and He atoms at 7.70 ppm, 7.75 ppm
390, respectively, which corresponds to the molecular weight of and 9.07 ppm, respectively, for the imidazole ring. A broad
the catalysts. Also, other peaks related to the other fragmenta- singlet peak at 14.25 ppm is related to NH+. Without adding any
tions can be seen in these spectra.
carbon to this compound, the same five peaks are observed in
In the H NMR spectrum of 1,4-di(1H-imidazol-1-yl)butane the 13C NMR spectra of [H2-Bisim][HClO4]2. In this spectrum,
as a symmetric compound, five peaks related to five types of the peaks at 26.6 ppm and 48.3 ppm are related to C1 and C2 of
hydrogen are observed. A multiplet peak at 1.60–1.66 ppm for the methylenes of the aliphatic chain. Three aromatic C3, C4
Ha, a multiplet peak at 3.94–3.99 ppm for Hb, two triplet peaks
1
at 6.89 ppm and 7.15 ppm for Hc and Hd and a triplet peak at
7.62 ppm for He, respectively. 13C NMR also shows five peaks
Table 2 Optimization of the reaction conditions for the preparation of
pyrano[2,3-d]pyrimidinone derivatives of 4-chlorobenzaldehyde
related to five different carbons, two peaks at 28.1 ppm (related
to C1) and 47.2 ppm (related to C2) in the aliphatic area and
three peaks at 119.7 ppm, 128.8 ppm and 137.6 ppm (related to
C3, C4 and C5) of the imidazole ring in the aromatic area.
After the addition of H2SO4 to 1,4-di(1H-imidazol-1-yl)butane,
seven expected peaks related to seven types of hydrogen
Catalyst
(mol%)
Time
(min)
Yield (%)
(isolated)
Entry
A
B
Solvent
Temp. (1C)
A
B
A
B
1
2
3
4
5
6
7
8
No cat.
15
15
15
15
15
15
15
15
—
—
100
100
120
120
120
120
120
120
120
120
120
120
Tracea
Tracea
Tracea
Tracea
Tracea
Tracea
Tracea
35a Mix.a
Tracea
79 78
1
n-Hexane
CH2Cl2
CHCl3
CH3CN
EtOH
EtOH
H2O
Reflux
Reflux
Reflux
Reflux
R.T.
Reflux
R.T.
50
80
80
Reflux
Reflux
appeared in the H NMR spectra. It should be mentioned that
in these spectra the multiplicity of all the peaks was not observed
and all of the peaks tended to be a singlet. This may be caused by
severing of the ionic peripheral and surrounding lattice of the
9
10
11
12
13
14
15
15
15
H2O
H2O
Table 1 Optimization of the reaction conditions for the preparation of
5-arylidene barbituric acid derivatives of 4-chlorobenzaldehyde
30 40 86 83
6.2 7.6 H2O
6.2 7.6 H2O
3.0 3.8 H2O
25 35 94 92
12 15 90 89
50 60 78 79
35 40 85 81
Catalyst
(mol%)
Time
(min)
Yield (%)
(isolated)
6.2 7.6 EtOH/H2O (1 : 1) Reflux
a
Entry
A
B
Solvent
Temp. (1C)
A
B
A
B
A: [H2-Bisim][HSO4]2. B:[H2-Bisim][ClO4]2 Reaction was not completed.
1
2
3
4
5
6
7
8
No cat.
15
15
15
15
15
15
15
15
—
—
100
100
120
120
120
120
120
120
120
120
120
120
9
Tracea
Tracea
Tracea
Tracea
Tracea
Tracea
Tracea
n-Hexane
CH2Cl2
CHCl3
CH3CN
EtOH
EtOH
H2O
Reflux
Reflux
Reflux
Relux
R.T.
Reflux
R.T.
50
80
80
Reflux
Reflux
35a 25a
9
Tracea
65
13 83
10
11
12
13
14
15
15
15
H2O
H2O
60
88
93
89
81
85
6.2 7.6 H2O
6.2 7.6 H2O
3.0 3.8 H2O
3
2
3
3
91
90
30 45 76
20 27 82
Scheme 2 Synthesis of 5-arylidene barbituric acid and pyrano[2,3-d]-
pyrimidinone derivatives using [H2-Bisim][HSO4]2 and [H2-Bisim][ClO4]2
under optimized conditions.
6.2 7.6 EtOH/H2O (1 : 1) Reflux
a
A: [H2-Bisim][HSO4]2. B: [H2-Bisim][ClO4]2 Reaction was not completed.
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Table 3 Synthesis of different derivatives of 5-arylidene barbituric acids
Time (min)
Yielda (%)
M.P. (1C)
Obs.
[H2-Bisim] [H2-Bisim] [H2-Bisim ] [H2-Bisim]
Entry Product
[HSO4]2
[ClO4]2
[HSO4]2
[ClO4]2
[H2-Bisim][HSO4]2 [H2-Bisim][ClO4]2 Lit.ref.
1
4
5
84
82
249–252
249–251
270–272
270–271
249–251
276–277
224–225
233–234
298–300
293–294
4300
253–255
252–254
271–273
268–270
250–252
275–277
226–228
230–232
298–300
292–294
4300
255–25648
250–25218
274–27648
268–26951
249–25048
272–27428
228–23052
227–23017
298–30052
291–29248
430026
2
3
8
3
10
25
10
6
91
93
79
72
93
89
86
91
90
93
85
89
93
93
82
70
91
87
83
93
94
90
85
92
3
4
15
15
5
5
6
7
30
20
3
35
20
3
8
9
10
11
12
13
12
3
15
4
40
15
45
20
259–560
293–294
259–260
294–297
268–27048
297–30048
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Table 3 (continued)
Time (min)
Yielda (%)
M.P. (1C)
Obs.
[H2-Bisim] [H2-Bisim] [H2-Bisim ] [H2-Bisim]
Entry Product
14
[HSO4]2
45
[ClO4]2
50
[HSO4]2
86
[ClO4]2
87
[H2-Bisim][HSO4]2 [H2-Bisim][ClO4]2 Lit.ref.
275–276
277–280
275–27748
15
16
5
4
5
5
92
95
87
90
4300
4300
430048
4300
4300
430048
17
18
19
20
7
10
12
8
10
12
15
10
92
88
89
94
91
94
85
92
260–262
260–261
277–278
280 Dec
261–263
267–268
278–280
280 Dec
262–26318
26853
278–27948
New product
a
Isolated yields.
and C5 of the imidazole also appeared at 120.4 ppm, 122.3 ppm
and 135.6 ppm, respectively.
V2 = 37.5 mL (required NaOH solution against 1 mmol H+
for [H2-Bisim][ClO4]2)
pH titration curves of 0.100 M solutions of [H2-Bisim][HSO4]2
and [H2-Bisim][ClO4]2 were obtained with a standard solution of The above-mentioned structural studies confirm that the pre-
NaOH (0.035 M) in the case of [H2-Bisim][HSO4]2 and 0.040 M in pared ionic liquids are acidic reagents which may be able to
the case of [H2-Bisim][ClO4]2. According to calculations (eqn (1)), catalyze the reactions needing an acidic catalyst to speed them
it can be concluded that 37.5 mL of NaOH is needed for the up. So, in order to investigate this ability, we were interested in
neutralization of each mmol H+. This information showed that investigating their effectiveness in the promotion of the synthesis
[H2-Bisim][HSO4]2 and [H2-Bisim][ClO4]2 contain four and two of 5-benzylidene barbituric acid and pyrano[2,3-d]pyrimidinone
mmol H+, respectively.
derivatives.
At first, for the optimization of the reaction conditions, the
M1V1 = M2V2
(1)
effect of different factors including catalyst loading, tempera-
ture, and solvent in the preparation of 4-chlorobenzaldehyde
derivatives was studied for both reactions and the obtained
results are tabulated in Tables 1 and 2. These results confirm
that the best conditions for the synthesis of the requested
products are as shown in Scheme 2.
(0.100 M) (15 mL) = (0.035) V2
(0.100 M) (15 mL) = (0.040) V2
V2 = 42.8 mL (required NaOH solution against 1 mmol H+
for [H2-Bisim][HSO4]2)
After the optimization step, different types of aldehydes
containing both electron-donating and electron-withdrawing
groups and also heterocyclic aldehydes were used in both
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Paper
Table 4 Synthesis of different derivatives of pyrano[2,3,d] pyrimidinone(thione)
Time (min)
Yielda (%)
M.P. (1C)
Obs.
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
Entry
1
Product
[H2-Bisim][HSO4]2
[H2-Bisim][ClO4]2
224–226
Lit.ref.
25
20
15
25
45
10
30
20
20
20
45
25
70
96
93
91
52
94
65
93
90
84
58
91
220–222
207–209
254–255
233–235
168–170
245–246
224–22548
2
3
4
5
6
208–209
255–257
239–241
160–163
241–243
211–21252
254–25652
23051
160–16252
240–24152
7
8
55
50
45
35
89
79
92
88
260–261
229–231
262–264
234–236
262–26348
233–23553
9
12
15
94
92
232–234
232–234
232–23454
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Table 4 (continued)
Time (min)
Yielda (%)
M.P. (1C)
Obs.
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
Entry
10
Product
[H2-Bisim][HSO4]2
[H2-Bisim][ClO4]2
228–230
Lit.ref.
10
20
10
50
30
40
45
95
90
92
81
92
88
92
96
91
86
90
85
228–229
266–269
236–238
279–281
222–224
4300
229–23148
11
12
13
14
15
5
268–270
239–240
280–284
223–225
4300
268–27040
236–23748
280–28139
225–22852
430036
55
20
40
50
16
15
20
90
90
4300
4300
430048
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Paper
Table 4 (continued)
Time (min)
Yielda (%)
M.P. (1C)
Obs.
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
[H2-Bisim]
[HSO4]2
[H2-Bisim]
[ClO4]2
Entry
17
Product
[H2-Bisim][HSO4]2
[H2-Bisim][ClO4]2
279–280
Lit.ref.
15
20
88
82
283–285
281–28340
18
19
15
20
94
95
254–256
254–256
New product
Mixture of
products
Mixure of
products
120
120
120
120
—
—
—
—
231–23352
Mixture of
products
Mixture of
products
20
—
a
Isolated yields.
reactions. All of them (except entries 19 and 20 in Table 4, in the presence of these ionic liquids were compared with the
because of the formation of unidentified by-products under results obtained for the same reactions using other catalysts. In all
acidic conditions) were successfully converted to their corres- cases, in comparison to classic catalysts and other types of ionic
ponding products in high yields during acceptable reaction liquids, our introduced ionic liquids in this work have better
times. No meaningful differences between electron-donating catalytic performance. Our ionic liquids had one or more advan-
and electron-withdrawing groups of the aldehydes in the time tages from the viewpoint of time, yield, amount of catalyst, and
and yield of the reactions were observed (Tables 3 and 4).
reaction conditions (Tables 5 and 6). As it is shown in Tables 5
In order to prove the ability of these ionic liquids as the and 6, in some cases the amounts of the reported catalysts for the
catalysts in the studied reactions, some of the obtained results mentioned reactions are near or even in an equimolar ratio with a
Table 5 Comparison between the efficiency of some of the previously reported catalysts and our newly introduced ionic liquids in the synthesis of
5-(4-chlorobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione
Entry
Catalystref.
Amount of catalyst
Condition
Time (min)
Yield (%)
17
1
2
3
4
5
6
7
8
BF3/nano-g-Al2O3
NH2SO3H21
60 mg
100 mol%
100 mg
0.2 mL
2 mL
50 mol%
100 mol%
200 mg
Ethanol, R.T.
Grinding-laying
Ethylene glycol, 50 1C
Grinding-laying
R.T.
H2O, R.T.
Grinding
EtOH, 60–70 1C
H2O, 70–80 1C
H2O, R.T.
H2O, R.T.
H2O, 80 1C
30
180
10–15
120
180
30
10
60
35
30
84
93
93
78
83
82
91
85
86
85
96
93
91
PVP-Ni Nps22
23
[bmim]BF4
EAN24
CTMAB25
CH3COONa26
CMZO27
9
Fly-ash/NaOH28
NH4Cl56
4 wt%
10
11
12
13
150 mol%
5 mol%
6.2 mol%
7.6 mol%
SiO2ꢀ12WO3ꢀ24H2O57
40
3
3
a
H2-Bsim[ClO4]2a
H2-Bim[HSO4]2
H2O, 80 1C
a
Current work.
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Table 6 Comparison between the efficiency of some of the previously reported catalysts and our newly introduced ionic liquids in the synthesis of
7-amino-5-(4-chlorophenyl)-2,4-dioxo-1,3,4,5-tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile
Entry
Catalystref.
Amount of catalyst
Condition
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
Al-HMS-2036
30 mg
30 mg
EtOH, R.T.
90 1C, S.F.
H2O/EtOH (4 : 1), 80 1C
EtOH, 75 1C
THF/H2O (4 : 1), reflux
EtOH/H2O (19 : 1), reflux
EtOH, reflux
H2O, reflux
EtOH/H2O (1 : 1), R.T.
H2O, 80 1C
H2O, reflux
H2O, reflux
720
180
120
120
110
60
50
12
120
40
15
92
92
92
94
85
89
90
91
89
93
92
94
[BMIm]BF455
37
CaHPO4
10 mol%
50 mol%
10 mol%
20 mg
17 mol%
30 mg
10 mol%
10 mol%
7.6 mol%
6.2 mol%
38
Choline chlorideꢀZnCl2
Boric acid40
Nano-titania sulfuric acid40
39
Zn[L-proline]2
ZnO@CuO41
DABCO58
Alum59
9
10
11
12
a
H2-Bim[ClO4]2
H2-Bim[HSO4]2
a
12
a
Current work.
limiting reagent. This can indicate the efficiency of the introduced followed by elimination of a molecule of water in a Knovenagel
synthetic ionic liquids as the catalyst for these reactions. condensation to produce 5-benzylidene barbituric acid deriva-
The proposed mechanisms of these reactions are shown in tives (Table 3). In the other way, these products can be attacked
Scheme 3. This scheme shows that both types of the prepared by activated malononitrile in a Micheal type reaction followed by
BAILs can activate the carbonyl group and also can accelerate cyclization to generate the intermediate (I) which in an imine–
the enolization of barbituric acid. The enolized barbituric acid enamine tautomerization resulted in pyrano[2,3-d]pyrimidinone
moiety attacks the carbonyl group of the aldehyde and this is derivatives (Table 4).
Scheme 3 The plausible mechanisms of the studied reactions in the presence of the mentioned ionic liquids.
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Also, the reusability of the catalysts was investigated by repeating
the same typical reactions (Table 3, entry 9 and Table 4, entry 9) in
the filtrated solution of the previous reactions. It was observed that
both ionic liquids had acceptable reusability for five rounds of
recycling in both of the reactions.
From the comparative point of view in the field of the
catalytic performance in the reactions, it should be said that
[H2-Bisim][HSO4]2 has relatively better performance in comparison
to [H2-Bisim][ClO4]2 since it has four acidic moieties in its structure.
Reasonably, this is why the amount of used catalyst in the case of
[H2-Bisim][HSO4]2 is less than [H2-Bisim][ClO4]2 in mol% scale. On
the other hand, [H2-Bisim][ClO4]2 has its own advantages because
of being a solid that is relatively more stable and non-hygroscopic
regarding liquid [H2-Bisim][HSO4]2 that has more tendency of
hygroscopy. In the same way, [H2-Bisim][ClO4]2 has an easier
weighing procedure for the reactions while having simpler
handling and storage.
Paper
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Conclusions
¨
In this study, two new imidazole-based bis-dicationic Bronsted
acidic ionic liquids were easily prepared and characterized
using various techniques. These reagents show excellent activity in
the promotion of the synthesis of 5-benzylidene barbituric acid and
pyrano[2,3-d]pyrimidinone derivatives. The use of these reagents has
some important advantages, of which high purity of the products,
short reaction times, reusability of the catalyst, low amounts of the
catalyst, preformation of the reaction in a green medium and very
easy work-up procedure needing no special separation methods and
organic solvents are the most important ones.
¨
¨
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We are thankful to the Research Council of the University of
Guilan for the partial support of this research.
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