A rapid tandem knoevenagel/michael reaction using mohr's salt as a highly efficient catalyst: Green synthesis of bis(pyrazolyl)methanes

Article abstract of DOI:10.2174/1570178612666141204224826

A convenient access to some new and known bis(pyrazolyl)methanes synthesis has been successfully achieved via an alternative Knoevenagel/Michael reaction of aromatic aldehydes and pyrazole-5-one in the presence of Mohr's salt as a green catalyst. This nov

Full text of DOI:10.2174/1570178612666141204224826

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38
Letters in Organic Chemistry, 2015, 12, 38-43
A Rapid Tandem Knoevenagel/Michael Reaction Using Mohr’s Salt as a
Highly Efficient Catalyst: Green Synthesis of Bis(pyrazolyl)methanes
Khalil Eskandari*a, Bahador Karamia, Saeed Khodabakhshib and Mahnaz Farahia
b
aDepartment of Chemistry, P. O. Box 353, Yasouj University, Yasouj, 75918-74831, Iran; Nanotechnology Research
Center, Research Institute of Petroleum Industry, Tehran, Iran
Received March 29, 2014: Revised April 25, 2014: Accepted December 04, 2014
Abstract: A convenient access to some new and known bis(pyrazolyl)methanes synthesis has been successfully achieved
via an alternative Knoevenagel/Michael reaction of aromatic aldehydes and pyrazole-5-one in the presence of Mohr’s salt
as a green catalyst. This novel procedure has some advantages such as high efficiency, simplicity, high rate and environ-
mental safety.
Keywords: Green synthesis, Knoevenagel condensation, Michael addition, aqueous media, bis(pyrazolyl)methane, Mohr’s salt.
INTRODUCTION
cient catalyst for the green synthesis of some novel and
Pyrazole derivatives have shown important pharmacol-
known bis(pyrazolyl)methanes.
ogical activity and chemical activity in medicinal and or-
ganic chemistry [1-3]. Pharmaceutically, they exhibit con-
siderable antitubercular [4], antifungal [5], antibacterial [6],
anti-inflammatory [7], and antitumor activities [8]. Syntheti-
cally, some pyrazole derivatives such as pyrazole-2-ones act
as methylene active compounds for synthesis of various het-
erocycles [9-14]. Recently, some synthetic routes to
bis(pyrazolyl)methanes under various conditions have been
reported in the literature. The general method is tandem
Knoevenagel and Michael addition reaction between alde-
hydes and pyrazolones in the presence of several catalytic
systems including silica-bonded s-sulfonic acid [15], sulfuric
acid ([3-(3-silicapropyl)sulfanyl]propyl)ester [16], cellulose
sulfuric acid [17], 2-hydroxyethylammonium acetate [18],
nano n-propylsulphonated-ꢀ-Fe2O3 [19], poly(ethylene gly-
col)-400 (PEG-400) [20], 1,3-disulfonic acid imidazolium
tetrachloroaluminate [21], electrolysis [22], sodium dodecyl
sulfate [23], ceric ammonium nitrate [24], PEG-SO3H [25],
lithium hydroxide [26], and sonication [27]. Despite the ad-
vantages of reported methods, some of them suffer from dis-
advantages such as toxicity, environmental pollution, low
product yield, long reaction times, and use of extra tools and
expensive catalysts.
RESULTS AND DISCUSSION
In continuation of our studies on the development of new
strategies for the synthesis of organic compounds [30-35],
herein, we wish to report a new access high efficient conden-
sation between aromatic aldehydes 1, and 3-methyl-1-
phenyl-5-pyrazolone 2 to bis(pyrazolyl)methanes 3 synthesis
in the presence of Mohr’s salt as a green catalyst in aqueous
media (Scheme 1).
At first, in order to optimize reaction conditions, the reac-
tion of benzaldehyde with 3-methyl-1-phenyl-5-pyrazolone
was chosen as a model (compound 3a).
We firstly evaluated required amount of the catalyst for
this transformation. In the absence of catalyst, the reaction
did not considerably proceed even for 90 min. By adding 1
mol% of the catalyst, the reaction showed an appreciable
progress and completed in about 30 min. When 2 mol% of
catalyst was used, the reaction efficiently proceeded and
completed in less reaction time (20 min). By further increas-
ing catalyst amount no appreciable improvement in the
product yield and reaction time was observed.
In analytical chemistry, ferrous ammonium sulfate
known as Mohr's salt is a common laboratory reagent pre-
ferred over other salts of iron for titration purposes as it is
much less prone to oxidation by air to iron (III) [28]. Re-
cently, Mohr’s salt was reported as a new and powerful cata-
lyst in organic synthesis by our research group [29]. Herein,
we report a new application of Mohr’s salt as a highly effi-
Next, the model reaction was established at room tem-
perature in the presence of Mohr's salt (2 mol%) as catalyst,
but the reaction rate decreased and did not complete after
120 min.
A number of solvents such as EtOH, MeOH, CH2Cl2,
H2O, and THF were also tried with catalytic amount of
Mohr's salt (2 mol%) and it was found that the use of protic
solvents such as EtOH and MeOH dramatically reduces the
reaction time with improved product yield at room tempera-
ture (Table 1).
*Address correspondence to this author at the Department of Chemistry, P.
O. Box 353, Yasouj University, Yasouj, 75918-74831, Iran
Tel: +98 7412223048; Fax: +98 7412242167;
E-mail: kh.eskandari@mail.yu.ac.ir
1875-6255/15 $58.00+.00
© 2015 Bentham Science Publishers

Green Synthesis of Bis(pyrazolyl)methanes Using Mohr’s Salt
Letters in Organic Chemistry, 2015, Vol. 12, No. 1 39
Ar
H3C
CH3
N
O
N
N
Fe(SO4)2.(NH4)2.6(H2O)
2 mol%
O
N
OH
N
HO
2
Ar
H
EtOH/H2O, reflux
N
CH3
3
1
2
Scheme 1. Synthesis of bis(pyrazolyl)methanes using Mohr's salt.
Table 1. Solvent effect in the synthesis of model compound 3a.
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
CH2Cl2
THF
120
60
25
40
80
90
70
90
MeOH
30
EtOH
20
H2O
120
20
EtOH/H2O (1:1)
Table 2. Synthesis of bispyrazoles 3 using Mohr's salt (2 mol%).
Entry
Aldehyde
Product
Time (min)
Yielda (%) [Lit.]
1
2
C6H5CHO
2,4-(MeO)2C6H3CHO
3-(EtO)-4-(HO)C6H3CHO
1-NaphthylCHO
4-(C6H5)C6H4CHO
3-IndolylCHO
3a
3b
3c
3d
3e
3f
20
25
30
30
20
30
20
20
20
30
20
20
25
90 [20]
85
3
87
4
88
5
90
6
88
7
2,4-Cl2C6H3CHO
3-O2NC6H4CHO
4-O2NC6H4CHO
4-MeC6H4CHO
3g
3h
3i
85 [15]
90 [20]
92 [20]
85 [20]
90 [20]
85 [26]
87 [20]
8
9
10
11
12
3j
2-ClC6H4CHO
3k
3l
4-MeOC6H4CHO
3-BrC6H4CHO
13
3m
a Isolated yields.
fication of products 3a-3m, a simple filtration and recrystal-
lization from boiling EtOH is needed.
From the economic and environmental point of view, an
equal mixture of H2O/EtOH was selected as medium for all
further reactions. Therefore, the best reaction conditions
were obtained by using 2 mol% of Mohr's salt as the catalyst
under reflux in H2O/EtOH (1:1).
Reactions of aromatic aldehydes bearing electron-
withdrawing/donating group with 2 gave the expected prod-
ucts in excellent yields under the same reaction conditions.
Compounds 3a-m are stable solids which their structures
By loading the reaction in achieved optimal conditions, a
variety of novel and known bis(pyrazolyl)methanes 3 were
successfully synthesized and results of this new procedure
were shown in Table 2. It is worthwhile to note that for puri-
1
were confirmed by C H N analyses, IR, H, and 13C NMR
spectroscopy. It should be also mentioned that our efforts on
the use of aliphatic aldehydes instead of aromatic ones were

40 Letters in Organic Chemistry, 2015, Vol. 12, No. 1
Eskandari et al.
Table 3. Comparison of present work with other methods reported in the literature for synthesis of 3a.
Entry
Conditions
Time (min)
Yielda (%) [Lit.]
1
2
Mohr’s salt (2 mol%), H2O/EtOH, Reflux
SBSSAc (0.1 g), EtOH, Reflux
20
120
180
120
15
90b
80 [15]
90 [16]
74 [17]
90 [18]
93 [19]
92 [20]
86 [21]
82 [22]
87 [23]
3
SASPSPEd (0.1 g), EtOH, Reflux
Cellulose sulfuric acid (0.2 g), H2O/EtOH, Reflux
2-HEAAe (5 mol%), EtOH, r.t.
4
5
6
NPS-ꢁ-Fe2O3f (2 mol%), H2O, r.t.
PEG-400g, 110 °C
180
120
60
7
8
[Dsim]AlCl4h (1 mol%), 50 °C
9
Electrolysis, EtOH, NaBr (0.1 g), 20 °C
Sodium dodecyl sulfate (5 mol%), H2O, Reflux
33
10
60
a
b
c
d
e
f
Isolated yields. Present work. Silica-bonded S-sulfonic acid. Sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl) ester. 2-hydroxyethylammonium acetate. Nano n-
propylsulphonated-ꢁ-Fe2O3. g Poly(ethylene glycol)-400. h 1,3-disulfonic acid imidazolium tetrachloroaluminate.
unsuccessful. We believe that it is a consequence of the eno-
lization of aliphatic aldehydes and the lower electrophilicity
of their carbonyl group.
ter to separate the catalyst. The pure product 3 was obtained
after recrystallization from boiling EtOH and no further puri-
fication was needed.
In order to show the efficiency of the present work, Table
3 shows the results of some previously reported methods in
the literature. According to the summarized data, the Mohr’s
salt catalyzed synthesis of 3 can be considered as an effi-
cient, green and economical method due to the generation of
desired product in high yield, short reaction time and envi-
ronmentally safe conditions using a little amount of inexpen-
sive catalyst in comparison with previous ones.
Representative Spectral Data
4,4'-(Phenylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (3a)
Light yellow crystals; mp 167-169 °C (lit.20 168-170 °C);
FT-IR (KBr) (ꢀmax, cm-1): 3424, 3062, 2917, 1598, 1498,
1
1415, 1284, 1186, 1027, 755, 692; H NMR (400.13 MHz,
DMSO-d6) ꢀ (ppm): 13.96 (s, 1H, OH), 12.39 (s, 1H, OH),
7.71 (d, J = 8.4 Hz, 4H, aromatic CH), 7.45 (t, J = 7.2 Hz,
4H, aromatic CH), 7.31-7.24 (m, 6H, aromatic CH), 7.20-
7.17 (m, 1H, aromatic CH), 5.00 (s, 1H, CH), 2.33 (s, 6H,
2CH3); 13C NMR (100.62 MHz, DMSO-d6) ꢀ (ppm): 157.6,
146.4, 140.7, 136.9, 128.8, 128.3, 127.1, 126.4, 126.2, 121.3,
105.7, 33.6, 11.5.
EXPERIMENTAL
General
Chemicals were purchased from Merck and Aldrich
chemical companies. Melting points were measured on an
electro thermal KSB1N apparatus. IR spectra were recorded
in the matrix of KBr with a JASCO FT-IR-680 plus spec-
trometer. 1H NMR and 13C NMR spectra were recorded on a
FT-NMR Bruker Avance Ultra Shield Spectrometer at
400.13 MHz (300 and 250 MHz for some products) and
100.62 MHz (76.5 and 62.5 MHz for some products) in
DMSO-d6 as solvent in the presence of tetra methyl silane as
internal standard. Elemental analyses were performed on a
Heraeus CHN-O-Rapid analyzer. TLC was performed on
TLC-Grade silica gel-G/UV 254 nm plates. All products
4,4'-((2,4-Dimethoxyphenyl)methylene)bis(3-methyl-1-
phenyl-1H-pyrazol-5-ol) (3b)
Yellow crystals; mp 190-192 °C; FT-IR (KBr) (ꢀmax
,
cm-1): 3428, 2996, 2958, 2839, 1613, 1503, 1460, 1406,
1
1294, 1209, 1122, 1041, 839, 757, 580; H NMR (300.13
MHz, DMSO-d6) ꢀ (ppm): 14.35 (s, 1H, OH), 12.38 (s, 1H,
OH), 7.69 (d, J = 7.8 Hz, 4H, aromatic CH), 7.39-7.50 (m,
5H, aromatic CH), 7.22 (t, J = 6.9 Hz, 2H, aromatic CH),
6.46 (t, J = 9.6 Hz, 2H, aromatic CH), 5.09 (s, 1H, CH), 3.79
(s, 3H, OCH3), 3.69 (s, 3H, OCH3), 2.26 (s, 6H, 2CH3); 13C
NMR (76.46 MHz, DMSO-d6) ꢀ (ppm): 158.8, 156.7, 146.1,
137.6, 137.4, 137.3, 137.1, 136.7, 133.6, 131.9, 128.8, 125.4,
122.9, 120.5, 104.1, 98.2, 55.4, 55.0, 26.9, 11.6. Anal. calcd
for C29H28N4O4: C, 70.15; H, 5.68; N, 11.28; Found: C,
70.22; H, 5.62; N, 11.25%.
1
were isolated, purified and deduced from IR, H NMR, and
13C NMR spectral data.
General Procedure to the Synthesis of Novel and Known
Bispyrazols Using Mohr’s Salt
A solution of the aromatic aldehyde 1 (1 mmol), the
pyrazolone 2 (2 mmol) and Mohr’s salt (2 mol%) in
EtOH/H2O (1:1, 10 mL) was stirred under reflux for a stipu-
lated time. The progress of the reaction was monitored by
TLC. After completion, the reaction mixture was cooled at
room temperature and solvent was evaporated under reduced
pressure. The precipitate was washed with cool distilled wa-
4,4'-((3-Ethoxy-4-hydroxyphenyl)methylene)bis(3-methyl-
1-phenyl-1H-pyrazol-5-ol) (3c)
Chocolate crystals; mp 212-213 °C; FT-IR (KBr) (ꢀmax
,
cm-1): 3420, 3219, 2985, 2927, 1596, 1498, 1400, 1275,

Green Synthesis of Bis(pyrazolyl)methanes Using Mohr’s Salt
Letters in Organic Chemistry, 2015, Vol. 12, No. 1 41
1
1214, 1126, 1043, 811, 753, 691. H NMR (300.13 MHz,
4,4'-((2,4-Dichlorophenyl)methylene)bis(3-methyl-1-
phenyl-1H-pyrazol-5-ol) (3g)
DMSO-d6) ꢀ (ppm): 13.97 (s, 1H, OH), 12.36 (s, 1H, OH),
8.67 (s, 1H, OH), 7.69 (d, J = 8.1 Hz, 4H, aromatic CH),
7.42 (t, J = 7.8 Hz, 4H, aromatic CH), 7.22 (t, J = 7.2 Hz,
2H, aromatic CH), 6.82 (s, 1H, CH), 6.66 (s, 2H, CH) 4.82
(s, 1H, CH), 3.90 (q, J = 6.9 Hz, 2H, CH2), 2.29 (s, 6H,
2CH3), 1.25 (t, J = 6.9 Hz, 3H, CH3). 13C NMR (76.46 MHz,
DMSO-d6) ꢀ (ppm): 146.1, 145.1, 142.6, 137.3, 137.0, 133.1,
131.6, 128.9, 125.5, 120.5, 119.7, 115.2, 113.4, 63.9, 32.7,
14.7, 11.6. Anal. calcd for C29H28N4O4: C, 70.15; H, 5.68; N,
11.28; Found: C, 70.19; H, 5.57; N, 11.26%.
Bisque crystals, mp 228-230 °C (lit.15 227–229 °C); FT-
IR (KBr) (ꢀmax, cm-1): 3420, 3057, 2920, 1597, 1572, 1500,
1470, 1380, 1298, 1189, 845, 792, 752, 690; 1H NMR
(250.13 MHz, DMSO-d6) ꢀ (ppm): 13.95 (s, 1H, OH), 12.67
(s, 1H, OH), 7.65-7.74 (m, 5H, aromatic CH), 7.53 (d, J =
2.0 Hz, 1H, aromatic CH), 7.36-7.44 (m, 5H, aromatic CH),
7.22 (t, J = 7.2 Hz, 2H, aromatic CH), 5.05 (s, 1H, CH), 2.26
(s, 6H, 2CH3); 13C NMR (62.89 MHz, DMSO-d6) ꢀ (ppm):
148.3, 147.1, 146.0, 137.3, 134.9, 128.8, 125.4, 120.5, 119.2,
111.6, 111.5, 104.9, 104.6, 31.7, 11.6.
4,4'-(Naphthalen-1-ylmethylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol) (3d)
4,4'-((3-Nitrophenyl)methylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol) (3h)
Navajo white crystals; mp 228-230 °C; FT-IR (KBr)
(ꢀmax, cm-1): 3419, 3062, 2922, 1608, 1542, 1497, 1402,
Yellow crystals, mp 152-154 °C (lit.20,16 151-153 °C);
1
FT-IR (KBr) (ꢀmax, cm-1): 3420, 3068, 2920, 1598, 1579,
1370, 1132, 829, 783, 756, 689. H NMR (300.13 MHz,
1
DMSO-d6) ꢀ (ppm): 13.15 (s, 1H, OH), 12.19 (s, 1H, OH),
8.10-8.00 (m, 1H, aromatic CH), 7.92 (d, J = 6.6 Hz, 1H,
aromatic CH), 7.80 (d, J = 7.2 Hz, 1H, aromatic CH), 7.62-
7.75 (m, 5H, aromatic CH), 7.34-7.57 (m, 7H, aromatic CH),
7.15-7.25 (m, 2H, aromatic CH), 5.61 (s, 1H, CH), 2.25 (s,
6H, 2CH3). 13C NMR (76.46 MHz, DMSO-d6) ꢀ (ppm):
146.0, 144.1, 140.6, 137.3, 136.7, 133.6, 130.7, 128.8, 128.7,
127.0, 125.9, 125.7, 125.3, 125.2, 123.5, 119.9, 105.6, 30.9,
11.9, 11.8. Anal. calcd for C31H26N4O2: C, 76.52; H, 5.39; N,
11.51; Found: C, 76.57; H, 5.33; N, 11.48%.
1524, 1500, 1415, 1348, 785, 753, 691. H NMR (400.13
MHz, DMSO-d6) ꢀ (ppm): 13.91 (s, 2H, OH), 8.06-8.10 (m,
2H, aromatic CH), 7.68-7.74 (m, 5H, aromatic CH), 7.60 (t,
J = 8.3 Hz, 1H, aromatic CH), 7.45 (t, J = 7.6 Hz, 4H, aro-
matic CH), 7.26 (t, J = 7.3 Hz, 2H, aromatic CH), 5.14 (s,
1H, CH), 2.35 (s, 6H, 2CH3). 13C NMR (100.62 MHz, DM-
SO-d6) ꢀ (ppm): 147.7, 146.3, 144.5, 137.3, 134.3, 129.7,
128.9, 125.8, 125.7, 121.7, 121.2, 120.6, 32.8, 11.5.
4,4'-((4-Nitrophenyl)methylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol) (3i)
4,4'-([1,1'-Biphenyl]-4-ylmethylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ol) (3e)
Yellow crystals, mp 228-230 °C (lit.20 229-231 °C); FT-
IR (KBr) (ꢀmax, cm-1): 3068, 2920, 1598, 1579, 1524, 1500,
1
Navajo white crystals; mp 218-220 °C; FT-IR (KBr)
1415, 1348, 785, 753, 691. H NMR (400.13 MHz, DMSO-
(ꢀmax, cm-1): 3444, 3026, 2922, 1599, 1580, 1499, 1405,
d6) ꢀ (ppm): 13.90 (s, 1H, OH), 12.49 (s, 1H, OH), 8.18 (d, J
= 8.8 Hz, 2H, aromatic CH), 7.73 (d, J = 8.0 Hz, 4H, aro-
matic CH), 7.54 (d, J = 8.8 Hz, 2H, aromatic CH), 7.45 (t, J
= 8.0 Hz, 4H, aromatic CH), 7.25 (t, J = 8.0 Hz, 2H, aro-
matic CH), 5.14 (s, 1H, CH), 2.37 (s, 6H, 2CH3); 13C NMR
(100.62 MHz, DMSO-d6) ꢀ (ppm): 150.3, 146.2, 145.8,
137.1, 129.1, 128.9, 128.5, 125.6, 123.3, 120.5, 104.0, 33.1,
11.5.
1
1294, 818, 751, 692; H NMR (300.13 MHz, DMSO-d6) ꢀ
(ppm): 14.05 (s, 1H, OH), 12.48 (s, 1H, OH), 7.74 (d, J = 7.8
Hz, 4H, aromatic CH), 7.55-7.62 (m, 4H, aromatic CH),
7.46-7.34 (m, 9H, aromatic CH), 7.23 (t, J = 7.2 Hz, 2H,
aromatic CH), 5.01 (s, 1H, CH), 2.35 (s, 6H, 2CH3); 13C
NMR (76.46 MHz, DMSO-d6) ꢀ (ppm): 146.3, 141.5, 140.0,
137.9, 137.4, 137.3, 128.9, 128.8, 127.8, 127.1, 126.5, 125.5,
120.5, 104.9, 104.6, 32.8, 11.6. Anal. calcd for C33H28N4O2:
C, 77.32; H, 5.51; N, 10.93; Found: C, 77.38; H, 5.43; N,
10.84%.
4,4'-((4-Methylphenyl)methylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ol) (3j)
White crystals, mp 203-205 °C (lit.20 201-203 °C); FT-IR
(KBr) (ꢀmax, cm-1): 3437, 2923, 1600, 1499, 1407, 1295,
4,4'-((1H-Indol-3-yl)methylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol) (3f)
1
1024, 803, 749, 690. H NMR (400.13 MHz, DMSO-d6) ꢀ
(ppm): 13.92 (s, 1H, OH), 12.40 (s, 1H, OH), 7.08–7.71 (m,
14H, aromatic CH), 4.91 (s, 1H, CH), 2.31 (s, 6H, 2CH3),
2.24 (s, 3H, CH3). 13C NMR (100.62 MHz, DMSO-d6) ꢀ
(ppm): 147.1, 140.0, 135.7, 129.8, 129.6, 127.9, 126.4,
121.4, 40.9, 33.6, 21.4, 12.5.
Yellow crystals; mp 242-244 °C; FT-IR (KBr) (ꢀmax
,
cm-1): 3470, 3042, 2920, 1618, 1540, 1488, 1405, 1370,
1136, 830, 786, 755, 689; 1H NMR (400.13 MHz,
DMSO-d6) ꢀ (ppm): 12.65 (s, 2H, OH), 9.85 (s, 1H, NH),
8.13-8.11 (m, 2H, aromatic CH), 8.06 (s, 1H, aromatic CH),
8.05-8.01 (m, 2H, aromatic CH), 7.60-7.58 (m, 1H, aromatic
CH), 7.44-7.40 (m, 4H, aromatic CH), 7.32-7.29 (m, 4H,
aromatic CH), 7.17-7.13 (m, 1H, aromatic CH), 7.15-7.25
(m, 2H, aromatic CH), 3.49 (s, 1H, CH), 2.39 (s, 6H, 2CH3);
13C NMR (100.62 MHz, DMSO-d6) ꢀ (ppm): 162.7, 150.8,
138.9, 138.2, 136.9, 136.4, 128.6, 128.1, 123.8, 123.4, 122.0,
118.5, 118.0, 112.8, 112.2, 18.5, 12.9. Anal. calcd for
C29H25N5O2: C, 73.25; H, 5.30; N, 14.73; Found: C, 73.31;
H, 5.23; N, 14.66%.
4,4'-((2-Chlorophenyl)methylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ol) (3k)
White crystals, mp 238-240 °C (lit.20,16 236-237 °C); FT-
IR (KBr) (ꢀmax, cm-1): 3433, 3062, 2921, 1613, 1560, 1499,
1401, 747, 690. 1H NMR (400.13 MHz, DMSO-d6) ꢁ (ppm):
13.92 (br, 2H, 2OH), 7.75-7.77 (m, 4H, aromatic CH), 7.41-
7.43 (m, 8H, aromatic CH), 7.27-7.29 (m, 2H, aromatic CH),
5.08 (s, 1H, CH), 2.26 (s, 6H, 2CH3). 13C NMR (100.62

42 Letters in Organic Chemistry, 2015, Vol. 12, No. 1
Eskandari et al.
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MHz, DMSO-d6) ꢀ (ppm): 141.1, 140.6, 137.3, 135.9, 130.3,
129.4, 128.9, 128.0, 126.9, 123.6, 120.6, 32.4, 11.6.
4,4'-((4-Methoxyphenyl)methylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ol) (3l)
White crystals, mp 163-165 °C (lit.26 162-163 °C); FT-IR
(KBr) (ꢀmax, cm-1): 3433, 2924, 1601, 1507, 1406, 1245,
1
1030, 753, 692. H NMR (500 MHz, DMSO-d6) ꢁ (ppm):
13.85 (br, 2H, 2OH), 7.64 (d, J = 8.0 Hz, 4H, aromatic CH),
7.39 (d, J = 7.4 Hz, 4H, aromatic CH), 7.20 (t, J = 7.45 Hz,
2H, aromatic CH), 7.12 (d, J = 8.6 Hz, 2H, aromatic CH),
7.8 (d, J = 8.5 Hz, 2H, aromatic CH), 4.84 (s, 1H, CH), 3.85
(s, 3H, OCH3), 2.46 (s, 6H, 2CH3). 13C NMR (125 MHz,
DMSO-d6) ꢀ (ppm): 157.5, 146.1, 137.9, 134.6, 129.2, 128.9,
128.1, 125.4, 120.4, 113.5, 105.0, 54.9, 32.4, 11.6.
[5]
[6]
4,4'-((3-Bromophenyl)methylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ol) (3m)
[7]
White crystals, mp 173-176 °C (lit.20 172-175 °C); FT-IR
(KBr) (ꢀmax, cm-1): 3066, 2973, 2918, 1595, 1500, 1416,
1297, 880, 754, 691. 1H NMR (500 MHz, DMSO-d6) ꢁ
(ppm): 13.92 (s, 1H, OH), 12.40 (s, 1H, OH), 6.82-7.71 (m,
14H, aromatic CH), 4.89 (s, 1H, CH), 2.30 (s, 6H, 2CH3).
13C NMR (125 MHz, DMSO-d6) ꢀ (ppm): 154.4, 145.9,
140.4, 133.6, 132.4, 129.7, 128.7, 128.3, 127.7, 127.2, 125.4,
123.6, 117.9, 14.3, 10.0.
[8]
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CONCLUSION
In summary, the present work discloses a rapid and ex-
pedient novel strategy for the condensation of aromatic alde-
hydes 1 and pyrazolone 2 in the presence of Mohr’s salt as a
green, available and powerful catalyst in H2O/EtOH to afford
new and known bis(pyrazolyl)methanes. The operational
simplicity, short reaction times, excellent yields, and little
environmental impact are notable advantages of this proce-
dure.
[13]
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Niknam, K.; Saberi, D.; Sadegheyan, M.; Deris, A. Silica-bonded
S-sulfonic acid: an efficient and recyclable solid acid catalyst for
the synthesis of 4,4ꢂ-(arylmethylene)bis(1H-pyrazol-5-ols). Tetra-
hedron Lett., 2010, 51, 692-694.
Tayebi, S.; Baghernejad, M.; Saberi, D.; Niknam, K. Sulfuric acid
([3-(3-silicapropyl)sulfanyl]propyl) ester as a recyclable catalyst
for the synthesis of 4,4ꢂ-(arylmethylene)bis(1H-pyrazol-5-ols).
Chin. J. Catal., 2011, 32, 1477-1483.
Mosaddegh, E.; Hassankhani, A.; Baghizadeh, A. Cellulose sulfu-
ric acid as a new, biodegradable and environmentally friendly bio-
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Sobhani, S.; Nasseri, R.; Honarmand, M. 2-Hydroxyethyl-
ammonium acetate as a reusable and cost-effective ionic liquid for
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Sobhani, S.; Pakdin-Parizi, Z.; Nasseri, R. Nano n-propyl-
sulphonated ꢂ-Fe2O3: A novel magnetically recyclable heterogene-
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CONFLICT OF INTEREST
The authors confirm that this article content has no con-
flict of interest.
ACKNOWLEDGEMENTS
We are grateful to the Yasouj University Research Coun-
cil for financial helps.
SUPPLEMENTARY MATERIAL
Supplementary material is available on the publisher’s
web site along with the published article.
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