Phosphomolybdic acid: An efficient and recyclable solid acid catalyst for the synthesis of 4,4′-(arylmethylene)bis(1hpyrazol-5-ols)

Article abstract of DOI:10.1080/00397911.2010.539759

An efficient and environmentally friendly method has been developed for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) by condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone in the presence of phosphomolybdic acid as a

Full text of DOI:10.1080/00397911.2010.539759

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Phosphomolybdic Acid: An Efficient and
Recyclable Solid Acid Catalyst for the
Synthesis of 4,4′-(Arylmethylene)bis(1H-
pyrazol-5-ols)
Kiran R. Phatangare a , Vikas S. Padalkar a , Vinod D. Gupta a , Vikas
S. Patil a , Prashant G. Umape a & N. Sekar a
a Institute of Chemical Technology, Mumbai, India
Accepted author version posted online: 21 Oct 2011.Published
online: 11 Jan 2012.
To cite this article: Kiran R. Phatangare , Vikas S. Padalkar , Vinod D. Gupta , Vikas S. Patil , Prashant
G. Umape & N. Sekar (2012) Phosphomolybdic Acid: An Efficient and Recyclable Solid Acid Catalyst
for the Synthesis of 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols), Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 42:9, 1349-1358, DOI:
10.1080/00397911.2010.539759
To link to this article: http://dx.doi.org/10.1080/00397911.2010.539759
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Synthetic Communications1, 42: 1349–1358, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.539759
PHOSPHOMOLYBDIC ACID: AN EFFICIENT AND
RECYCLABLE SOLID ACID CATALYST FOR THE
SYNTHESIS OF 4,4’-(ARYLMETHYLENE)BIS(1H-
PYRAZOL-5-OLS)
Kiran R. Phatangare, Vikas S. Padalkar, Vinod D. Gupta,
Vikas S. Patil, Prashant G. Umape, and N. Sekar
Institute of Chemical Technology, Mumbai, India
GRAPHICAL ABSTRACT
Abstract An efficient and environmentally friendly method has been developed for synthesis
of 4,40-(arylmethylene)bis(1H-pyrazol-5-ols) by condensation reaction of aromatic alde-
hydes with 3-methyl-l-phenyl-5-pyrazolone in the presence of phosphomolybdic acid as a
recyclable catalyst in ethanol at ambient temperature in excellent yields.
Keywords Aromatic aldehydes; bispyrazole; catalysis; 3-methyl-l-phenyl-5-pyrazolone;
phosphomolybdic acid
INTRODUCTION
Heterocyclic compounds occur very widely in nature and are essential to life.
Nitrogen-containing heterocyclic molecules constitute the largest portion of chemical
entities, which are part of many natural products, fine chemicals, and biologically
active pharmaceuticals vital for enhancing the quality of life.[1,2] Among a large var-
iety of nitrogen-containing heterocyclic compounds, heterocycles containing pyra-
zoles and their derivatives are an important class of biologically active drug
targets in the pharmaceutical industry, as they are the core structures of numerous
biologically active compounds[3,4] and have therapeutic importance. Compounds
containing this ring system are known to display diverse pharmacological activities
Received August 16, 2010.
Address correspondence to N. Sekar, Institute of Chemical Technology, N. P. Marg, Matunga,
Mumbai 400 019, India. E-mail: n.sekar@ictmumbai.edu.in; nethi.sekar@gmail.com
1349

1350
K. R. PHATANGARE ET AL.
such as antidepressant,[5] antibacterial,[6] anti-inflammatory,[7] and antipyretic[8]
activities.
Appropriately functionalized pyrazoles have emerged as HIV-1 reverse transcrip-
tase inhibitors[9] and sodium channel blockers.[10] They also are corresponding
4,4’(arylmethylene)bis(1H-pyrazol-5-ols) and chelating and extracting reagents for dif-
ferent metal ions.[11–13] In pesticide chemistry, the significance of fully substituted pyr-
azoles, particularly 4,40-(arylmethylene)bis(1H-pyrazol-5-ol), has been well
recognized.[14] They are also used as fungicides,[15] insecticides,[16] and dyestuffs.[11–13]
Furthermore, pyrazoles are not only of interest as intermediates in chemical synthesis
but also as efficient analytical regents in the complexation of transition-metal ions.[17]
The general approach to 4,40-(arylmethylene)bis(3-methyl-1-phenyl-pyrazol-5-
ol) involves the one-pot tandem Knoevenagel–Michael reaction of arylaldehydes
with 2 equivalents of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one performed
under different reaction conditions,[18,19] such as catalysis of the components with
piperidine in alcoholic solution[20,21] or the uncatalyzed tandem Knoevenagel–
Michael reaction under neutral conditions in either ethanol or benzene solution.[22]
Even though it affords the corresponding 4,40-(arylmethylene)bis(1H-pyrazol 5-ols)
in 70–90% yields, the reaction requires 3–12 h of initial reflux with a further 24 h
under ambient temperature for completion. Wang et al.[23] reported this synthesis
in water using sodium dodecyl sulfate as the surfactant catalyst over a 1-h period,
but the reaction does require a temperature up to 100 ꢀC. Elinson et al. utilized
electrocatalytic tandem Knoevenagel–Michael procedure for its synthesis.[24]
Sujatha and coworkers reported the synthesis and antiviral activity of
4,40-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ols) using ceric ammonium
nitrate (CAN) as a catalyst.[25] Recently Nikam et al. reported this synthesis by using
silica-bonded S-sulfonic acid.[26] However, most of the methods suffer from different
limitations such as moderate yields, longer reaction times, harsh reaction conditions,
and tedious workup procedures.
In recent decades, the use of phosphomolybdic acid as a heteropolyacid (HPA)
catalyst has become important in industries with fine chemicals.[27] HPAs are more
active catalyst than conventional mineral and organic acids for various organic
transformations.[28,29] Solid HPAs have gained importance because of easy workup
procedures and minimization of waste generation. They are noncorrosive and
environmentally benign, as they can be reused and recycled.[30]
Thus, considering these reports, advantages, and applications of phospho-
molybdic acid, we attempted the convenient and practical synthesis of
4,40-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ols) by condensation reac-
tion between aromatic aldehydes and 3-methyl-l-phenyl-5-pyrazolone in the presence
of a catalytic amount of phosphomolybdic acid in ethanol as a solvent at room
temperature (Scheme 1).
The suitable reaction conditions for the transformations were established by
the reaction of benzaldehyde and 3-methyl-l-phenyl-5-pyrazolone in various
solvents, and results are summarized in Table 1.
The results mentioned in Table 1 demonstrate the effective use of ethanol as a
solvent for preparation of 4,40-(phenylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol in the presence of a catalytic amount of phosphomolybdic acid as a solid acid
catalyst.

NOVEL BISPYRAZOLE SYNTHESIS
1351
Scheme 1. Synthesis of 4,40-(arylmethylene)bis(1H-pyrazol-5-ols) from 3-methyl-l-phenyl-5-pyrazolone.
We observed that catalyst concentration also plays a detrimental role in cata-
lyzing the condensation reaction for the synthesis of 4,40-(phenylmethylene)bis(3-
methyl-1-phenyl-1H-pyrazol-5-ol). The condensation of benzaldehyde with
3-methyl-1phenyl-5-pyrazolone was performed as a model reaction, varying the con-
centration of phosphomolybdic acid, and it was found that the optimum reaction
rate and yield could be achieved at 10 mol% catalyst concentration Table 2. On
further increasing the amount of catalyst, the yield of the corresponding product
decreased, ascribable to increased acidity.
Thus, we used phosphomolybdic acid as a catalyst in the present work. To
elucidate the role of the phosphomolybdic acid as catalyst, a controlled reaction
was conducted using benzaldehyde and 3-methyl-1-phenyl-5-pyrazolone in ethanol
in the absence of catalyst. This resulted in the formation of a trace amount of fused
product after 45 h at room temperature. However, reaction with the same substrate
using 10 mol% of phosphomolybdic acid at room temperature in ethanol afforded
the products in quantitative yield in 4 h. Thus, in the absence of phosphomolybdic
acid, the reaction was slow and required drastic conditions with unsatisfactory
yields. This could be overcome with the use of phosphomolybdic acid at room tem-
perature. It is postulated that the phosphomolybdic acid plays a vital role in accel-
erating the coupling reaction and thus promotes the formation of products. The
Table 1. Effect of solvents for preparation of 4,40-(phenylmethylene)bis(3-methyl-1-
phenyl-1H-pyrazol-5-ol)a
Entry
Solvent
Time (h)
Yield (%)b
1
2
3
4
5
6
Ethanol
Methanol
DMF
4
96
93
89
87
80
90
5
6
Acetonitrile
Acetone
Water
5.5
6
12
aReaction conditions: Benzaldehyde (0.01 mol), 3-methyl-l-phenyl-5-pyrazolone
(0.02 mol), phosphomolybdic acid (10 mol%), and solvent (5 vol).
bYield: isolated.

1352
K. R. PHATANGARE ET AL.
Table 2. Optimization of the amount of phosphomolybdic acid for the synthesis of
4,40-(phenylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)a
Entry
Amount of catalyst (mol%)
Time (h)
Yield (%)b
1
2
3
4
5
—
5
45
4
13
73
96
89
85
10
15
20
4
4
4
aReaction conditions: benzaldehyde (0.01 mol), 3-methyl-l-phenyl-5-pyrazolone
(0.02 mol), phosphomolybdic acid (mol%), and solvent (5 vol).
bYield: isolated.
mechanistic role of phosphomolybdic acid chemistry for the formation of product is
proposed in Scheme 2.
To investigate the feasibility of this synthetic methodology for
4,40-(arylmethylene)bis(1H-pyrazol-5-ols) derivatives, we have extended the reaction
of different aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone under similar
conditions, furnishing the respective 4,40-(arylmethylene)bis(1H-pyrazol-5-ols) in
good yields. The optimized results are summarized in Table 3.
1
Products were characterized by infrared (IR), H NMR, 13CNMR, and physi-
cal constant. All new compounds were also characterized by mass spectrometry.
Scheme 2. Proposed mechanism for synthesis of 4,40-(arylmethylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol).

NOVEL BISPYRAZOLE SYNTHESIS
1353
Table 3. Synthesis of 4,40-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)a
Entry
Ar (2)
Product (3)
Time (h)
Yield (%)b
Mp(ꢀC)
Lit. mp(ꢀC)
1
2
C6H5-
3a
3b
3c
3d
3e
3f
4
4
96
95
96
94
93
93
91
93
92
92
95
94
170–172
152–154
224–226
224–226
152–154
218–220
176–178
188–190
212–214
180–182
198–200
182–184
170–172[18]
151–153[19]
225–227[19]
224–226[16]
153–154[16]
218–219[17]
176–177[17]
189–190[18]
213–214[18]
3-NO2-C6H5-
4-NO2-C6H5-
2-NO2-C6H5-
3-Cl-C6H5-
3
3.5
3.5
4
4
5
6
2-OH-C6H5-
4-OMe-C6H5-
Furfuraldehyde
(CH3)2-CH-
3-OMe-C6H5-
3-Ph-C6H5-
4
7
3g
3h
3i
4.5
4
8
9
5.5
4
10
11
12
3j
3k
3l
4
4-F-C6H5-
4
aReaction condition: aldehyde (0.01 mol), 3-methyl-1-phenyl-5-pyrazolone (0.02 mol), phosphomolyb-
dic acid (10 mol%), and ethanol (5 vol) at rt.
bYield: isolated.
From Table 3, we conclude that the results were excellent in terms of yields and
product purity using aromatic aldehydes carrying electron-donating or electron-
withdrawing substituents in the presence of phosphomolybdic acid, while in the case
of aliphatic aldehydes the rate of reaction is very slow.
Recovery and reusability of the catalyst is demanded for an ecofriendly cata-
lytic process. In this protocol, we used phosphomolybdic acid as recyclable catalyst.
Progress of the reaction was monitored by thin-layer chromatography (TLC). After
completion of the reaction, as indicated by the TLC, the reaction mixture was con-
centrated to dryness, the solid product was washed with water, the product was
recrystallized from isopropyl alcohol, and the aqueous layer was concentrated to
recover phosphomoybdic acid, which was reused for three more processes (Fig. 1).
Figure 1. Recyclability of the system of phosphomolybdic acid for preparation of 4,40-
(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol). (Figure is provided in color online.)

1354
K. R. PHATANGARE ET AL.
CONCLUSION
In conclusion, we have demonstrated a new, efficient, and environmentally
friendly procedure for the synthesis of 4,40-(arylmethylene)bis(3-methyl-1-phenyl-
1H-pyrazol-5-ols) by condensing aromatic aldehydes with 3-methyl-1-phenyl-5-
pyrazolone catalyzed by phosphomolybdic acid in ethanol as a solvent. The advan-
tages of our protocol are easy workup, faster reaction rates, mild reaction con-
ditions, and good yields, which make the method an attractive and useful
contribution to the present methodologies.
EXPERIMENTAL
All commercial reagents were used as received without purification, and all sol-
vents were reagent grade. The reaction was monitored by TLC using on 0.25-mm
E-Merck silica-gel 60 F254 precoated plates, which were visualized with ultraviolet
light. Melting points were measured on a standard melting-point apparatus from
Sunder Industrial Product Mumbai and are uncorrected. The infrared (IR) spectra
1
were recorded on a Perkin-Elmer 257 spectrometer using KBr discs. H NMR spec-
tra were recorded on a VXR 300-MHz instrument and 13C spectra on a VXR 75-
MHz instrument.
General Experimental Procedure
A mixture of aldehyde (0.01 mol), 3-methyl-1-phenyl-5-pyrazolone (0.02 mol),
and phosphomolybdic acid (10 mol%) in ethanol (5 vol) was stirred at room tem-
perature for an appropriate time as mentioned in Table 3. Progress of the reaction
was monitored by TLC. After completion of the reaction, as indicated by TLC,
the reaction mixture was concentrated to dryness; the solid product was washed with
water. The aqueous layer was concentrated to recover phosphomolybdic acid, which
was reused three times. The crude product was crystallized by using isopropyl
alcohol to afford the pure product.
Representative Spectral Data
4,4’-[(Phenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) (Table
3, Entry 1) (3a). IR (KBr): 3408, 3085, 2910, 1600, 1510, 1405, 1280, 1015, 734,
1
695 cmꢁ1. H NMR (300 MHz, CDCl3): 2.39 (s, 6H), 5.12 (s, 1H), 7.13–7.16 (t,
2H), 7.17 (m, 1H), 7.24–7.26 (m, 2H), 7.36 (m, 1H), 7.38–7.43 (m, 2H), 7.62–7.64
(d, 2H), 14.05 (bs, 2H)d (ppm). 13C NMR (75 MHz, CDCl3): 14.1, 31.1, 100.8,
121.5, 125.5, 126.6, 128.0, 128.3, 129.5, 140.2, 143.9, 146.1, 146.4 d (ppm). Mp:
170–172 ꢀC.
4,4’-[(3-Nitrophenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 2) (3b). IR (KBr): 3422, 3086, 2915, 1598, 1485, 1360, 755, 730,
1
696, 592 cmꢁ1. H NMR (300 MHz, CDCl3): 2.38 (s, 6H), 5.20 (s, 1H), 7.32 (t,
2H), 7.50 (t, 4H), 7.65 (t, 1H), 7.70–7.76 (m, 5H), 8.10–8.15 (m, 2H), 14.10 (bs,
2H)d (ppm). 13C NMR (75 MHz, CDCl3): 14.1, 31.4, 100.9, 121.6, 121.8, 127.7,
128.0, 129.5, 129.6, 133.0, 140.3, 143.4, 145.3, 146.1, 146.4. d (ppm). Mp: 152–154 ꢀC.

NOVEL BISPYRAZOLE SYNTHESIS
1355
4,4’-[(4-Nitrophenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 3) (3c). IR (KBr): 3422, 3056, 2972, 2920, 1604, 1580, 1504, 1348,
1
1108, 756, 740 cmꢁ1. H NMR (300 MHz, CDCl3): 2.35 (s, 6 H), 5.46 (s, 1 H),
7.20–7.40 (m, 4H), 7.38 (d, 2H). 7.73–7.78 (dd, 2H), 8.38–8.42 (dd, 2H), 13.52 (bs,
2H) d (ppm). 13C NMR (75 MHz, CDCl3): 14.2, 30.9, 100.9, 121.6, 122.1, 128.0,
129.6, 130.1, 140.3, 146.2, 146.4, 148.8, 150.3 d (ppm). Mp: 224–226 ꢀC.
4,4’-[(2-Nitrophenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 4) (3d). IR (KBr): 3450, 3070, 2910, 1610, 1555, 1495, 1360, 1300,
.
835, 740, 690 cmꢁ1 1H NMR (300 MHz, CDCl3): 2.29 (s, 6H), 5.19 (s, 1H),
7.35–7.40 (m, 4H), 7.45 (d, 1H), 7.48 (t, 4H), 7.73 (d, 4H), 7.83 (d, 1H), 13.52 (bs,
2H) d (ppm). 13C NMR (75 MHz, CDCl3): 14.2, 30.4, 101.3, 121.6, 122.1, 128.0,
129.6, 129.7, 130.1, 130.4, 135.2, 140.2, 146.0, 146.4, 148.9 d (ppm). Mp: 224–226 ꢀC.
4,4’-[(3-Chlorophenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (Table 3, Entry 5) (3e). IR (KBr): 3420, 3110, 2980, 1605, 1470, 1415, 1356,
1
1290, 1110, 1065, 875, 750 cmꢁ1. H NMR (300 MHz, CDCl3): 2.33 (s, 6H), 4.99 (s,
1H), 7.10–7.22 (m, 6H), 7.38–7.42 (d, 6H), 7.48–7.51 (m, 2H), 13.80 (bs, 2H) d
(ppm). 13C NMR (75 MHz, CDCl3): 14.5, 32.4, 100.3, 121.8, 125.6, 126.9, 128.0,
128.2, 129.6, 129.8, 132.4, 140.4, 144.3, 146.2, 146.5 d (ppm). Mp: 152–154 ꢀC.
4,4’-[(2-Hydroxyphenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (Table 3, Entry 6) (3f). IR (KBr): 3455, 3075, 2920, 1616, 1550, 1498, 1388,
1
1356, 1305, 838, 746, 695 cmꢁ1. H NMR (300 MHz, CDCl3): 2.15 (s, 6H), 5.05 (s,
1H), 7.20–7.28 (m, 4H), 7.35 (d, 1H), 7.40 (t, 4H), 7.66 (d, 4H), 7.78 (d, 1H), 9.21
(s, 1H), 13.80 (bs, 2H) d (ppm). 13C NMR (75 MHz, CDCl3): 14.2, 25.1, 101.6,
115.8, 118.3, 121.6, 126.2, 129.9, 127.8, 128.3, 129.7, 140.3, 146.3, 146.8, 155.1 d
(ppm). Mp: 218–220 ꢀC.
4,4’-[(4-Methoxylphenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (Table 3, Entry 7) (3g). IR (KBr): 3436, 3088, 2921, 1584, 1514, 1434, 1137,
1029, 807, 658 cmꢁ1. 1H NMR (300 MHz, CDCl3): 2.38 (s, 6H), 3.42 (s, 3H), 5.09 (s,
1H), 7.11–7.16 (d, 4H), 7.34–7.37 (dd, 4H), 7.38–7.42 (m, 4H), 7.54–7.57 (dd, 2H),
13.89 (bs, 2H) d (ppm). 13C NMR (75 MHz, CDCl3): 14.1, 30.9, 55.1, 100.6,
110.6, 121.3, 127.8, 128.0, 129.5, 139.5, 140.1, 146.0, 146.6, 159.8 d (ppm). Mp:
176–178 ꢀC.
4,4’-[(Furan-2-yl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 8) (3h). IR (KBr): 3425, 2920, 1610, 1500, 1300, 1287, 764 cmꢁ1. 1H
NMR (300 MHz, CDCl3): 2.33 (s, 6H), 5.01 (s, 1H), 6.23 (dd, 1H), 6.55 (dd, 1H),
7.14–7.16 (d, 4H), 7.35–7.43 (m, 7H), 13.24 (bs, 2H) d (ppm). 13C NMR (75 MHz,
CDCl3): 13.6, 27.7, 98.7, 107.5, 121.5, 128.1, 128.3, 129.4, 140.2, 141.8, 144.3,
147.1, 155.2 d (ppm). Mp: 188–190 ꢀC.
4,4’-[(2-Propyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) (Table
3, Entry 9) (3i). IR: 3428, 3061, 2959, 2733, 1585, 1499, 1291, 1182, 1122, 1027,
1
901, 791, 750, 638 cmꢁ1. H NMR (300 MHz, CDCl3): 0.96 (d, 6H), 2.38 (s, 6H),
2.43 (m, 1H), 4.87 (s, 1H), 7.16–7.18 (d, 4H), 7.36 (m, 2H), 7.39–7.41 (m, 4H),
14.4 (bs, 2H) d (ppm). 13C NMR (75 MHz, CDCl3): 14.8, 21.9, 31.9, 40.4, 99.7,
121.7, 128.0, 129.6, 139.7, 145.3, 146.6 d (ppm). Mp: 212–214 ꢀC.

1356
K. R. PHATANGARE ET AL.
4,4’-[(3-Methoxylphenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (Table 3, Entry 10) (3j). IR (KBr): 3428, 3085, 2920, 1580, 1508, 1410, 1133,
1
1025, 804, 685 cmꢁ1. H NMR (300 MHz, CDCl3): 2.42 (s, 6H), 3.51(s, 3H) 4.71 (s,
1H), 6.55 (dd, 1H), 6.66–6.72 (m, 2H), 7.89 (t, 1H), 7.32 (t, 2H), 7.45 (t, 4H), 7.73 (d,
4H), 13.25 (bs, 2H) d (ppm). 13C NMR (75 MHz, CDCl3): 13.9, 32.1, 53.4, 99.8,
114.6, 118.3, 119.8, 121.3, 120.9, 127.5, 129.3, 139.8, 144.2, 145.3, 145.8, 157.5 d
(ppm). MS: m=z (%) ¼ 466 (0.2, Mþ), 292 (100), 291 (21), 185 (34), 174 (41), 115
(17), 105 (22), 91 (30), 77 (81), 51 (59). Mp: 180–182 ꢀC.
4,4’-[(Biphenyl-3-yl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 11) (3k). IR (KBr): 3410, 3150, 3080, 2920, 1592, 1495, 1270, 1168,
1042, 750, 690 cmꢁ1. 1H NMR (300 MHz, CDCl3): 2.25 (s, 6H), 5.35 (s, 1H), 7.19 (m,
1H), 7.33 (m, 1H), 7.39 (dd, 1H), 7.41 (d, 1H), 7.45 (d, 2H), 7.51 (m, 2H), 7.52 (d,
2H), 7.58 (d, 4H), 7.62 (m, 4H), 7.79 (dd, 1H), 13.34 (bs, 2H) d (ppm). 13C NMR
(75 MHz, CDCl3): 14.2, 32.4, 100.8, 121.1, 122.5, 127.0, 128.0, 128.5, 129.0, 129.4,
129.9, 130.5, 131.1, 137.7, 140.2, 143.9, 146.1, 148.5, 157.6 d (ppm). MS:
m=z (%) ¼ 512 (0.1, Mþ), 338 (33), 185 (87), 174 (85), 128 (25), 105 (52), 91 (75),
77 (100), 51 (30). Mp: 198–200 ꢀC.
4,4’-[(4-Fluorophenyl)methylene]bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(Table 3, Entry 12) (3l). IR (KBr): 3425, 3085, 2925, 1595, 1495, 1415, 1295, 810,
1
742, 688 cmꢁ1. H NMR (300 MHz, CDCl3): 2.34 (s, 6H), 4.94 (s, 1H) 7.26–7.32
(m, 4H), 7.33 (d, 2H), 7.48 (t, 4H), 7.75 (d, 4H), 13.70 (bs, 2H) d (ppm). 13C
NMR (75 MHz, CDCl3): 14.0, 30.3, 100.2, 113.2, 121.6, 128.0, 128.6, 129.6, 139.4,
140.5, 144.9, 146.8, 160.2 d (ppm). MS: m=z (%) ¼ 454 (0.2, Mþ), 280 (29), 185
(91), 174 (76), 128 (31), 105 (39), 91 (89), 77 (100), 51 (42). Mp: 182–184 ꢀC.
ACKNOWLEDGMENTS
The author is thankful to SAIF, Indian Institute of Technology, Mumbai, for
providing the spectral facility and the University Grants Commission for providing a
research fellowship.
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