Design and Characterization of l-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst and Its Catalytic Application in the Synthesis of Pyrazol-Derivates

Article abstract of DOI:10.1007/s10562-015-1668-3

The [Amb]l-prolinate obtained from the immobilization of l-prolinate anion onto amberlite IRA900OH, was used as a new organocatalyst for the efficient synthesis of 4,4′-(arylmethylene)-bis-(1H-pyrazol-5-ol) derivatives. The prepared heterogeneous organoca

Full text of DOI:10.1007/s10562-015-1668-3

Catal Lett
DOI 10.1007/s10562-015-1668-3
Design and Characterization of L-Prolinate-Amberlite as a Novel
Heterogeneous Organocatalyst and Its Catalytic Application
in the Synthesis of Pyrazol-Derivates
Mosadegh Keshavarz1 Masoumeh Vafaei-Nezhad2
•
Received: 28 September 2015 / Accepted: 26 November 2015
Ó Springer Science+Business Media New York 2015
Abstract The [Amb]L-prolinate obtained from the immo-
bilization of L-prolinate anion onto amberlite IRA900OH, was
used as a new organocatalyst for the efficient synthesis of 4,40-
(arylmethylene)-bis-(1H-pyrazol-5-ol) derivatives. The pre-
pared heterogeneous organocatalyst was well characterized by
using of FTIR, TGA, DTG, XRD and elemental analysis
techniques. Short reaction times (5–18 min), excellent yields
(82–98 %) and simple experimental procedure with an easy
work-up are some of the advantages of the procedure.
Graphical Abstract
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3C
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Keywords L-Proline Á Anion-exchange resin Á
Organocatalyst Á Heterogeneous catalyst Á 4,40-
(Arylmethylene)-bis-(1H-pyrazol-5-ol)s
& Mosadegh Keshavarz
Chem.mosadegh@gmail.com
1 Introduction
1
2
Department of Gas and Petroleum, Yasouj University,
Gachsaran, Iran
Over the last few decades, green chemistry has been rec-
ognized as a culture and methodology for achieving sus-
tainable development [1]. Catalysis (including enzyme
Department of Chemistry, Arak Branch, Islamic Azad
University, Arak, Iran
123

M. Keshavarz, M. Vafaei-Nezhad
catalysis, heterogeneous catalysis, and organocatalysis, in
particular) is identified to be at the heart of greening of
chemistry [2] because this branch of science is found to
reduce the environmental impact of chemical processes [3].
The absence of metal in organocatalyst brings an undeni-
able advantage considering both the principles of ‘‘green
chemistry’’ and the economic point of view [4]. At the
same time immobilization and recycling of organocatalysts
have experienced a very good growth [5–9]. From both
industrial and environmental viewpoints, Immobilization is
an effective methodology for heterogenizing an organic
molecule onto inorganic material. The two principal
mechanisms used to prepare the heterogeneous
organocatalysts are of both covalent and noncovalent nat-
ure which lead to (i) the formation of covalent adduct
between catalyst and substrate, and (ii) the processes that
rely on noncovalent interactions such as hydrogen bonding
or within the catalytic cycle is the formation of ions pairs
[10].
propyltriethylenetetramine [29], nano n-propylsulfonated
c-Fe2O3 [30], Poly(4-vinylpyridine)-supported dual acidic
ionic liquid [31], 1-sulfopyridinium chloride [32], phos-
phomolybdic acid [33], 3-amminopropylated silica gel
[34], poly(ethylene glycol)-bound sulfonic acid [35], xan-
than sulfuric acid [36], LiOHÁH2O [37], 1,3-disulfonic
acid imidazolium tetrachloroaluminate [38], sulfuric acid
([3-(3-silicapropyl) sulfanyl]propyl)ester [39], poly(ethylene
glycol)-400 [40] and silica-bonded S-sulfonic acid [41].
Some of these methods suffer from limitations such as long
reaction times, unsatisfactory yield, harsh reaction condi-
tions, complex and expensive catalysts and tedious workup
procedures.
Considering the above mentioned reasons and in con-
tinuation of our previous studies on the applications of ion-
exchange resins for click synthesis of 1,4-disubstituted-1H-
1,2,3-triazoles [42, 43], we have prepared and character-
ized ion-exchange resin Amberlite IRA900OH (AmbIR-
A900OH) as a cationic polymer support for the ion-pair
immobilization of L-proline anion via ionic interaction
between carboxylate group of L-prolinate and quaternary
ammonium cation of the cationic Amb support. The
heterogeneous catalyst was utilized as an efficient and
reusable organocatalyst for the one-pot pseudo three-
component synthesis of 4,40-(arylmethylene)-bis-(1H-
pyrazol-5-ol)s in ethanol.
The proline catalyzed Robinson annulation was one of
the earliest examples of an enantioselective reaction using
an organic catalyst [11]. In recent years, prolines, espe-
cially L-proline, have been used to catalyze essential
transformations in the fine chemical and pharmaceutical
industries, such as Multicomponent reactions [12–14].
These amino acids contain both a nucleophilic secondary
amino group and a carboxylic acid moiety functioning as a
Brønsted acid [4]. Although the L-proline is commercially
available at low cost, however the reaction catalysis by
using of L-proline requires high catalyst loading. In gen-
eral, organocatalytic methods often require catalyst load-
ings as high as 30 mol% for the achievement of high
conversions in reasonable reaction times [15]. This is the
main reason for the need of an efficient immobilization and
recycling procedure. Therefore, attempts to improve or
modify the catalytic activity of L-proline, taking advantages
of specific properties of the support, would justify the
immobilization in many instances [16].
2 Experimental
2.1 General
All chemicals were purchased from Merck or Fluka Chemical
Companies. The chemicals were used in this study with their
purity
included:
3-methyl-1-phenyl-2-pyrazolin-5-one
(C98 %), benzaldehyde (C99 %), 4-nitrobenzaldehyde
(C98 %), 4-chlorobenzaldehyde (C98 %), 2,4-dichloroben-
zaldehyde (C98 %) 3-chlorobenzaldehyde (C98 %),
4-hydroxybenzaldehyde (C98 %), 3-hydroxybenzaldehyde
(C99 %), 3,4-isopropylbenzaldehyde (C99 %), 3,4-dimeth-
oxybenzaldehyde (C99 %), 4-methylbenzaldehyde (C99 %),
3-bromobenzaldehyde(C98 %), 2-bromobenzaldehyde(C98
%), ethanol (C99.5 %), 4-methoxybenzaldehyde (C98 %),
4-fluorobenzaldehyde (C98 %), phenylglyoxal monohydrate
(C97 %), 4-methylbenzaldehyde (C97 %), 4-cyanoben-
zaldehyde. Amberlite IRA 900 (OH-form) was purchased
from Sigma-Aldrich Company and was used in its original
form. 1H NMR spectra of samples were recorded at a Bruker
Advanced DPX 400-MHz spectrometer. X-ray diffraction
(XRD) patterns were recorded on a Philips X’PERT-Pro-
Presently, pyrazolone derivatives are paid much atten-
tion for their different biological activities, such as selec-
tive COX-2 inhibitory [17] and antitumor [18]. Among
them, compounds that contain two pyrazolone rings can be
used as gastric secretion stimulatory [19], antidepressant
[20] and antibacterial [21, 22]. In addition, the analogous
4,40-(arylmethylene)bis(1H-pyrazol-5-ol)s are used as
insecticides [23], pesticides [24], fungicides [25] and
chelating as well as extracting reagents for different metal
ions [26]. The most common method for the preparation of
this type of compounds involves one-pot pseudo three-
component condensation of aldehydes with 3-methyl-1-
phenyl-2-pyrazolin-5-one. Therefore, a variety of catalysts
and reagents have been used for this reaction, including
H3PW12O40 [27], Nano-SiO2/HClO4 [28], silica-bonded N-
˚
MPD diffractometer using Cu Ka radiation (k = 1.542 A). A
continuous scan mode was used to collect 2 h from 5 to 40.
Fourier transform infrared (FT-IR) spectra were obtained as
123

Design and Characterization of L-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst…
potassium bromide pellets in the range 400–4000 cm-1 using
an AVATAR 370 Thermo Nicolet spectrophotometer. Ele-
mental analyses (C, H, and N) were performed with a Heraeus
CHN-O-Rapid analyzer. The thermogravimetric and differ-
ential thermogravimetric (TG–DTG) analysis was performed
on Netsch STA449c. The sample weight was ca. 10 mg and
was heated from room temperature up to 600 °C with 10 °C/
min using alumina sample holders.
126.38 (CH), 127.67 (CH), 128.61(C), 129.40 (CH),
142.68 (C), 146.81(C) ppm.
2.3.1.2 4,40-[(4-Methylphenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3b) White powder, recrys-
tallized from ethanol, yield: 0.38 g (85 %), m.p.
203–205 °C (203 °C [27]). IR (KBr): m = 3450 (OH),
3025 (CH arom), 2850 (CH aliph), 1598 (C=C), 1499
(C=C), 1410 (C=C), 1290 (C=N), 1022, 800, 745, 690.1H
NMR: d = 2.26 (3H, s, CH3), 2.33 (6H, s, 2 CH3), 4.93
(1H, s, CH), 7.08 (2H, d, J = 8.0 Hz, 2CH), 7.15 (2H, d,
J = 8.0 Hz, 2 CH), 7.25 (2H, t, J = 7.6 Hz, 2 CH), 7.45
(4H, t, J = 7.6 Hz, 4 CH), 7.72 (4H, d, J = 7.6 Hz, 4 CH),
13.93 (2H, br.s, 2 OH). 13C NMR: d = 12.10 (CH3),
21.01(CH3), 33.23 (CH), 120.95 (C), 126.02 (CH), 127.56
(CH), 129.17 (C), 129.40 (CH), 135.31(CH), 139.55 (C),
146.78 (C) ppm.
2.2 Preparation of the [Amb]L-Prolinate catalyst
Amberlite IRA-900OH (mesh 16–50, 1 g) was suspended
in 10 mL of a 1 M solution of L-proline in MeOH:H2O
(1:1). The system was heated at 60 °C for 6 h. The filtra-
tion of the reaction mixture followed by washing with
MeOH:H2O (1:1) (2 9 10 mL) and H2O (2 9 10 mL)
afforded [Amb]L-Prolinate catalyst. The prepared catalyst
was collected and dried under vacuum.
2.3.1.3 4,40-[(4-Chlorophenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3c) White powder, recrys-
tallized from ethanol, yield: 0.43 g (92 %), m.p.
211–213 °C (210 °C [27]). IR (KBr): m = 3400 (OH),
3050 (CH arom), 2900 (CH aliph), 1600 (C=C), 1590
(C=C), 1578 (C=C), 1498 (C=C), 1415 (C=C), 1280
2.3 General Procedure for the [Amb]L-Prolinate
Catalyzed Synthesis of 3,30-Diaryloxindol
Derivatives
A
mixture of 3-methyl-1-phenyl-2-pyrazoline-5-one
1
(2 mmol), aromatic aldehyde (1 mmol), were placed
together in a round-bottom flask containing 5 mL of EtOH.
[Amb]L-prolinate catalyst (0.08 g, 10 mol%), was added to
the mixture. The suspension was magnetically stirred at
reflux condition for appropriate time according to Table 2.
After completion of the reaction as followed by TLC (n-
hexane: ethyl acetate; 3:1), the catalyst was filtered and
washed with hot ethanol (2 9 5 mL). The recovered cat-
alyst was washed with acetone, dried and stored for other
similar consecutive runs. The filtrate mixture was recrys-
tallized to provide the pure crystals of 4,40-(aryl-
(C=N), 808, 742, 685 cm-1. H NMR: d = 2.34 (6H, s, 2
CH3), 4.99 (1H, s, CH), 7.24-7.29 (4H, m, 4 CH), 7.35 (2H,
d, J = 8.4 Hz, 2 CH), 7.46 (4H, t, J = 7.6 Hz, 4 CH), 7.72
(4H, d, J = 8 Hz, 4 CH), 13.89 (2H, br.s, 2 OH) ppm. 13C
NMR: d = 12.07 (CH3), 33.02 (CH), 121.01(C), 126.11
(CH), 128.50 (C), 129.41(CH), 129.63 (CH), 131.06 (CH),
141.58 (C), 149.76 (C) ppm.
2.3.1.4 4,40-[(2-Chlorophenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3d) White powder, recrys-
tallized from ethanol, yield: 0.38 g (80 %), m.p.
233–235 °C (236–237 °C [27]). IR (KBr): m = 3450 (OH),
3060 (CH arom), 2905 (CH aliph), 1615 (C=C), 1595
(C=C), 1555 (C=C), 1496 (C=C), 1400 (C=C), 1350, 1295
methylene)-bis-(1H-pyrazol-5-ol)
derivatives.
The
products are known compounds and are characterized by
IR and NMR spectroscopy data for new compounds. Their
melting points are compared with reported values [27–41].
1
(C=N), 836, 750, 690 cm-1. H NMR: d = 2.30 (6H, s, 2
CH3), 5.17 (1H, s, CH), 7.22–7.34 (4H, m, 4 CH), 7.40
(1H, d, J = 7.82 Hz, CH), 7.44 (4H, t, J = 8.0 Hz, 4 CH),
7.71 (4H, d, J = 8.0 Hz, 4 CH), 7.81 (1H, d, J = 7.2 Hz,
CH), 13.92 (2H, br.s, 2 OH) ppm. 13C NMR: d = 12.33
(CH3), 32.14 (CH), 121.07 (C), 126.13 (CH), 127.4 (CH),
128.55 (C), 129.41(CH), 129.95(CH), 130.71(CH), 132.4
(CH), 137.63 (CH), 139.89 (C), 146.54(C) ppm.
2.3.1 Selected Spectroscopic Data
2.3.1.1 4,40-(Phenylmethylene)-Bis-(3-Methyl-1-Phenyl-1H-
Pyrazol-5-ol) (3a) White powder, recrystallized from
ethanol, yield: 0.36 g (82 %), m.p. 169–171 °C
(171–172 °C [27]). IR (KBr): m = 3400 (OH), 3050 (CH
arom), 2900 (CH aliph), 1598 (C=C), 1496 (C=C), 1403
(C=C), 1270 (C=N), 1020, 730, 690 cm-1
.
1H NMR:
2.3.1.5 4,40-[(2,4-Dichlorophenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3e) White powder, recrys-
tallized from ethanol, yield: 0.42 g (84 %), m.p.
229–231 °C (228–230 °C [27]). IR (KBr): m = 3480 (OH),
3050 (CH arom), 2900 (CH aliph), 1620 (C=C), 1590
d = 2.34 (6H, s, 2 CH3), 4.99 (1H, s, CH), 7.16–7.32 (7H,
m, 7 CH), 7.45 (4H, t, J = 7.6 Hz, 4 CH), 7.73 (4H, d,
J = 8.0 Hz, 4 CH), 13.98 (2H, br.s, 2 OH) ppm. 13C NMR:
d = 12.12 (CH3), 33.60 (CH), 121.0 (C), 126.04 (CH),
123

M. Keshavarz, M. Vafaei-Nezhad
(C=C), 1550 (C=C), 1499 (C=C), 1420 (C=C), 1380, 1290
1
OH) ppm. 13C NMR: d = 12.50 (CH3), 33.25 (CH), 115.73
(CH), 121.37 (C), 126.38 (CH), 128.96 (C), 129.77 (CH),
133.18 (CH), 147.04 (C), 156.37 (C) ppm.
(C=N), 850, 760, 680 cm-1. H NMR: d = 2.33 (6H, s, 2
CH3), 5.22 (1H, s, CH), 7.11 (1H, d, J = 7.8 Hz, CH), 7.25
(1H, d, J = 7.83 Hz, CH), 7.45 (2H, t, J = 7.72 Hz, 2
CH), 7.58 (4H, t, J = 7.76 Hz, 4 CH), 7.62 (4H, d,
J = 7.75 Hz, 4 CH),7.68 (1H, s, CH), 13.88 (2H, br.s, 2
OH) ppm. 13C NMR: d = 12.46 (CH3), 33.54 (CH), 122.3
(C), 122.8 (CH), 126.54 (CH), 126.8 (CH), 128.76 (C),
129.85 (CH), 130.3 (CH), 131.8 (CH), 132.7 (C), 135.7
(C), 136.2 (C), 137.5 (C), 145.2 (C) ppm.
2.3.1.9 4,40-[(3-Hydroxyphenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3i) Yellow powder, recrystal-
lized from ethanol, yield: 0.40 g (88 %), m.p. 169–170 °C
(165–168 °C [27]). IR (KBr): m = 3460 (OH), 3050 (CH
arom), 2950 (CH aliph), 1599 (C=C), 1580 (C=C), 1455
1
(C=C), 1369, 1250 (C=N), 790, 680, 600, 590 cm-1. H
NMR: d = 2.36 (6H, s, 2 CH3), 4.91 (1H, s, CH), 6.76 (1H,
d, J = 8.21 Hz, CH), 6.91 (1H, d, J = 8.26 Hz, CH), 6.97
(1H, s, CH), 7.16 (1H, t, J = 8.0 Hz, CH), 7.48 (2H, t,
J = 7.46 Hz, 2 CH), 7.56 (4H, t, J = 7.67 Hz, 4 CH), 7.62
(2H, d, J = 7.31 Hz, 2 CH), 9.43 (1H, s, OH), 12.5 (1H,
br.s, OH), 13.88 (1H, br.s, OH) ppm. 13C NMR: d = 13.3
(CH3), 32.9 (CH), 112.9 (CH), 114.7 (CH), 121.3 (C),
121.6 (CH), 122.5 (CH), 126.2 (CH), 128.8 (C), 129.3
(CH), 130.0 (CH), 137.5 (C), 139.2 (C), 147.1(C), 156.7
(C) ppm.
2.3.1.6 4,40-[(4-Nitrophenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3f) Yellow powder, recrystal-
lized from ethanol, yield: 0.46 g (96 %), m.p. 225–227 °C
(224–226 °C [27]). IR (KBr): m = 3420 (OH), 3060 (CH
arom), 2800 (CH aliph), 1598 (C=C), 1510 (C=C), 1490
(C=C), 1419 (C=C), 1400 (C=C), 1290 (C=N), 1342, 750,
690 cm-1. 1H NMR: d = 2.37 (6H, s, 2 CH3), 5.15 (1H, s,
CH), 7.26 (2H, t, J = 7.6 Hz, 2 CH), 7.46 (4H, t,
J = 8.0 Hz, 4 CH), 7.53 (2H, d, J = 8.4 Hz, 2 CH), 7.72
(4H, d, J = 8.0 Hz, 4 CH), 8.18 (2H, d, J = 8.8 Hz, 2
CH), 13.88 (2H, br.s, 2 OH) ppm. 13C NMR: d = 12.06
(CH3), 33.65 (CH), 121.07 (C), 123.82 (CH), 126.2 (CH),
129.1 (C), 129.42 (CH), 137.64 (C), 146.4 (C), 146.79 (C),
151.79 (C) ppm.
2.3.1.10 4,40-[(3,4-Dimethoxyphenyl)Methylene)]-Bis-
(3-Methyl-1-Phenyl-1H-Pyrazol-5-ol) (3j) White cream
powder, recrystallized from ethanol, yield: 0.40 g (81 %),
m.p. 194–196 °C (19–197 °C [27]). IR (KBr): m = 3420
(OH), 3150 (CH arom), 3090 (CH arom), 2920 (CH aliph),
1590 (C=C), 1500 (C=C), 1420 (C=C), 1270 (C=N), 1120
(C–O), 745, 690 cm-1. 1H NMR: d = 2.29 (6H, s, 2 CH3),
3.63 (3H, s, OCH3), 3.67 (3H, s, OCH3), 4.86 (1H, s, CH),
6.78–6.83 (2H, m, 2 CH), 6.87 (1H, s, CH), 7.20 (2H, t,
J = 6.8 Hz, 2 CH), 7.40 (4H, t, J = 7.4 Hz, 4 CH), 7.68
(4H, d, J = 7.8 Hz, 4 CH), 13.99 (1H, s, OH) ppm. 13C
NMR: d = 12.53 (CH3), 33.82 (CH), 56.39 (OCH3), 56.43
(OCH3), 112.56 (CH), 112.68 (CH), 120.20 (C), 121.46
(CH), 126.44 (CH), 129.78 (C), 135.85 (CH), 138.19 (C),
147.07(C), 148.15 (C), 149.32 (C) ppm.
2.3.1.7 4,40-[(3-Nitrophenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3g) Pale yellow powder,
recrystallized from ethanol, yield: 0.41 g (86 %), m.p.
152–154 °C (149–150 °C [27]). IR (KBr): m = 3400 (OH),
3050 (CH arom), 2915 (CH aliph), 1610 (C=C), 1590
(C=C), 1510 (C=C), 1498 (C=C), 1420 (C=C), 1345
(C=N), 760, 725, 690, 598 cm-1. 1H NMR: d = 2.37 (6H,
s, 2 CH3), 5.17 (1H, s, CH), 7.27 (2H, t, J = 7.2 Hz, 2
CH), 7.46 (4H, t, J = 8.0 Hz, 4 CH), 7.62 (1H, t,
J = 8.4 Hz, CH), 7.71-7.76 (5H, m, 5 CH), 8.09 (2H, d,
J = 6.8 Hz, 2 CH), 13.89 (2H, br.s, 2 OH) ppm. 13C NMR:
d = 12.09 (CH3), 33.31(CH), 121.10 (C), 121.69 (CH),
122.23 (CH), 126.23(CH), 129.45 (C), 130.18 (CH),
134.83 (CH), 145.06 (C), 146.82 (C), 148.24 (C) ppm.
2.3.1.11 4,40-[(4-Methylthiophenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3k) Yellow powder, recrystal-
lized from ethanol, yield: 0.41 g (86 %), m.p. 205–207 °C
(201–203 °C [27]). IR (KBr): m = 3440 (OH), 3055 (CH
arom), 2900 (CH aliph), 1590 (C=C), 1500 (C=C),
2.3.1.8 4,40-[(4-Hydroxyphenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3h) Yellow powder, recrys-
tallized from ethanol, yield: 0.38 g (84 %), m.p.
153–155 °C (152–153 °C [27]). IR (KBr): m = 3480 (OH),
3050 (CH arom), 2900 (CH aliph), 1595 (C=C), 1585
(C=C), 1450 (C=C), 1360, 1280 (C=N), 750, 690, 600,
595 cm-1. 1H NMR: d = 2.31 (6H, s, 2 CH3), 4.86 (1H, s,
CH), 6.67 (2H, d, J = 8.7 Hz, 2 CH), 7.06 (2H, d,
J = 8.5 Hz, 2 CH), 7.25 (2H, t, J = 7.33 Hz, 2 CH), 7.45
(4H, t, J = 7.83 Hz, 4 CH), 7.72 (4H, d, J = 7.98 Hz, 4
CH), 9.16 (1H, s, OH), 12.2 (1H, br.s, OH), 13.96 (1H, br.s,
1
1450(C=C), 1300 (C=N), 1040, 790, 750, 680 cm-1. H
NMR: d = 2.52 (6H, s, 2 CH3), 2.53 (3H, s, CH3), 4.81
(1H, s, CH), 7.22 (2H, d, J = 7.92 Hz, 2 CH), 7.31 (2H, d,
J = 7.81 Hz, 2 CH), 7.38 (2H, t, J = 7.1 Hz, 2 CH), 7.48
(4H, t, J = 7.5 Hz, 4 CH), 7.79 (4H, d, J = 7.72 Hz, 4
CH), 13.91 (2H, br.s, OH) ppm. 13C NMR: d = 12.62
(CH3), 21.54 (CH3), 34.24 (CH), 121.30 (C), 122.84 (CH),
122.09 (CH), 127.68 (CH), 128.98 (C), 129.33 (CH),
129.89 (CH), 134.39 (C), 134.85 (C), 137.54 (C), 138.65
(C), 145.84 (C) ppm.
123

Design and Characterization of L-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst…
2.3.1.12 4,40-[(4-Cyanophenyl)Methylene)]-Bis-(3-Methyl-1-
2.83 (1H, sep, J = 6.8 Hz, CH), 4.93 (1H, s, CH), 7.15
Phenyl-1H-Pyrazol-5-ol) (3l) Yellow powder, recrystal-
lized from ethanol, yield: 0.43 g (93 %), m.p. 206–208 °C
(210–212 °C [27]). IR (KBr): m = 3400 (OH), 3050 (CH
arom), 2900 (CH aliph), 2210 (CN), 1595 (C=C), 1500
(C=C), 1458 (C=C), 1410, 1280 (C=N), 808, 748,
682 cm-1. 1H NMR: d = 2.36 (6H, s, 2 CH3), 5.09 (1H, s,
CH), 7.26 (2H, t, J = 7.2 Hz, 2 CH), 7.43–7.49 (6H, m, 6
CH), 7.73–7.79 (6H, m, 6 CH), 14.01 (1H, br.s, OH) ppm.
13C NMR: d = 12.10 (CH3), 33.81(CH), 109.28 (C),
119.51 (C), 120.69 (C), 121.06 (CH), 125.35 (CH), 126.12
(CH), 128.88 (C), 129.4 (CH), 132.58 (CH), 137.74 (C),
146.79 (C), 148.71(C) ppm.
(2H, d, J = 8.0 Hz, 2 CH), 7.19-7.27 (4H, m, 4 CH), 7.45
(4H, t, J = 7.6 Hz, 4 CH), 7.74 (4H, d, J = 8.0 Hz, 4 CH),
14.11 (1H, br.s, OH) ppm. 13C NMR: d = 12.14 (CH3),
24.40 (CH3), 33.32 (CH), 33.47 (CH), 118.81 (C), 120.96
(CH), 125.98 (CH), 126.54 (CH), 127.55 (C), 129.38 (CH),
137.92 (C), 140.21 (C), 146.33 (C), 146.77 (C) ppm.
2.3.1.16 4,40-[(4-Methoxyphenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3p) White cream powder,
recrystallized from ethanol, yield: 0.41 g (89 %), m.p.
174–176 °C. IR (KBr): m = 3450 (OH), 3050 (CH arom),
2800 (CH aliph), 1605 (C=C), 1598 (C=C), 1577 (C=C),
1505 (C=C), 1490 (C=C), 1385, 1245 (C=N), 1180, 1110,
1
1038, 870, 812, 785, 750, 690 cm-1. H NMR: d = 2.33
2.3.1.13 4,40-[(2-Hydroxyphenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3m) Yellow powder, recrys-
tallized from ethanol, yield: 0.36 g (80 %), m.p.
228–230 °C (230–231 °C [28]). IR (KBr): m = 3400 (OH),
3050 (CH arom), 2900 (CH aliph), 1596 (C=C), 1570
(C=C), 1498 (C=C), 1450 (C=C), 1366, 1280 (C=N), 750,
687 cm-1. 1H NMR: d = 2.32 (6H, s, 2 CH3), 5.21 (1H, s,
CH), 6.72–6.79 (2H, m, 2 CH), 6.99 (1H, t, J = 7.6 Hz,
CH), 7.25 (2H, t, J = 7.2 Hz, 2 CH), 7.45 (4H, t,
J = 7.6 Hz, 4 CH), 7.59 (1H, d, J = 7.6 Hz, CH), 7.72
(4H, d, J = 8.0 Hz, 4 CH), 9.58 (1H, br.s, OH), 12.33 (1H,
br.s, OH), 14.39 (1H, br.s, OH) ppm. 13C NMR: d = 12.24
(CH3), 27.77 (CH), 115.29 (CH), 119.08 (C), 121.08 (CH),
125.97 (C), 127.39 (CH), 129.27 (C), 129.38 (CH), 129.69
(CH), 146.81(C), 154.35 (C) ppm.
(6H, s, 2 CH3), 3.71 (3H, s, OCH3), 4.92 (1H, s, CH), 6.85
(2H, d, J = 8.8 Hz, 2 CH), 7.19 (2H, d, J = 8.4 Hz, 2
CH), 7.25 (2H, t, J = 7.2 Hz, 2 CH), 7.45 (4H, t,
J = 7.6 Hz, 4 CH), 7.73 (4H, d, J = 8.0 Hz, 4 CH), 14.03
(1H, br.s, OH) ppm. 13C NMR: d = 12.13 (CH3), 32.87
(CH), 55.46 (OCH3), 113.98 (CH), 120.94 (C), 125.97 (C),
128.65 (C), 129.38 (CH), 134.61(CH), 137.91(CH), 146.68
(C), 157.99 (C) ppm. Anal. Calcd for C27H26N4O3: C,
72.09; H, 5.62; N, 12.01 (%). Found: C, 72.03; H, 5.45; N,
12.14(%).
2.3.1.17 4,40-[(2-Bromophenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3q) White cream powder,
recrystallized from ethanol, yield: 0.44 g (86 %), m.p.
201–204 °C (198–200 °C [28]). IR (KBr): m = 3450 (OH),
3050 (CH arom), 2900 (CH aliph), 1618 (C=C), 1596
(C=C), 1565 (C=C), 1550 (C=C), 1495 (C=C), 1395, 1365,
2.3.1.14 4,40-[(4-Fluorophenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3n) White powder, recrystal-
lized from ethanol, yield: 0.43 g (94 %), m.p. 180–182 °C
(182 °C [28]). IR (KBr): m = 3480 (OH), 3050 (CH arom),
2800 (CH aliph), 1600 (C=C), 1585 (C=C), 1498 (C=C),
1400 (C=C), 1370, 1318, 1219 (C=N), 1150 (C–F), 1020,
1310 (C=N), 1020, 900, 838, 790, 750, 690 cm-1 1H
.
NMR: d = 2.31 (6H, s, 2 CH3), 5.12 (1H, s, CH), 7.15 (1H,
t, J = 7.2 Hz, CH), 7.6 (2H, t, J = 7.2 Hz, 2 CH), 7.35
(1H, t, J = 7.6 Hz, CH), 7.45 (4H, t, J = 7.6 Hz, 4 CH),
7.55 (1H, d, J = 8.0 Hz, CH), 7.71 (4H, d, J = 8.0 Hz, 4
CH), 7.83 (1H, m, CH), 12.58 (1H, br.s, OH), 13.76 (1H, s,
OH) ppm. 13C NMR: d = 12.55 (CH3), 34.82 (CH), 121.03
(CH), 123.30 (CH), 126.06 (C), 127.92 (CH), 128.84 (C),
129.41 (CH), 131.01(CH), 133.30 (CH), 141.48 (C),
146.53 (C) ppm.
1
800, 790, 745, 680 cm-1. H NMR: d = 2.34 (6H, s, 2
CH3), 4.99(1H, s, CH), 7.12 (2H, t, J = 8.8 Hz, 2 CH),
7.24-7.32 (4H, m, 4 CH), 7.45 (4H, t, J = 8.0 Hz, 4 CH),
7.73 (4H, d, J = 8.0 Hz, 4 CH), 13.95 (1H, br.s, OH) ppm.
13C NMR: d = 12.09 (CH3), 32.92 (CH), 115.11(CH),
115.32 (CH), 121.02 (CH), 126.08 (CH), 129.4 (C), 129.47
(CH), 129.55 (C), 138.65 (C), 146.71 (C), 159.95–162.36
1
2.3.1.18 4,40-[(3-Bromophenyl)Methylene)]-Bis-(3-Methyl-1-
Phenyl-1H-Pyrazol-5-ol) (3r) White cream powder,
recrystallized from ethanol, yield: 0.45 g (88 %), m.p.
164–166 °C. IR (KBr): m = 3400 (OH), 3050 (CH arom),
2950–2800 (CH aliph), 1610 (C=C), 1595 (C=C), 1578
(C=C), 1563 (C=C), 1490, 1450,1398, 1362, 1318, 1299
(C–F, JCF = 241 Hz) ppm.
2.3.1.15 4,40-[(4-Isopropylphenyl)Methylene)]-Bis-(3-Methyl-
1-Phenyl-1H-Pyrazol-5-ol) (3o) White cream powder,
recrystallized from ethanol, yield: 0.39 g (82 %), m.p.
132–134 °C (132–134 °C [28]). IR (KBr): m = 3400 (OH),
3090 (CH arom), 2950–2850 (CH aliph), 1610 (C=C), 1598
(C=C), 1578 (C=C), 1495 (C=C), 1419, 1410, 1370, 1358,
(C=N),1000, 862, 790,768, 755, 684 cm-1 1H NMR:
;
d = 2.35 (6H, s, 2 CH3), 5.02 (1H, s, CH), 7.24–7.32 (4H,
m, 4 CH), 7.39–7.48 (6H, m, 6 CH), 7.73 (4H, d,
J = 8.4 Hz, 4CH), 14.01 (1H, br.s, OH) ppm. 13C NMR:
1280 (C=N), 1020, 780, 745, 682 cm-1
.
1H NMR:
d = 1.17 (6H, d, J = 6.8 Hz, 2 CH3), 2.36 (6H, s, 2 CH3),
123

M. Keshavarz, M. Vafaei-Nezhad
d = 12.10 (CH3), 33.37 (CH), 121.06 (C), 122.08 (CH),
126.13 (C), 126.96 (CH), 129.42 (C), 130.37 (CH),
130.81(CH), 137.75 (CH), 145.67 (CH), 146.76 (C),
157.66 (C) ppm. Anal. Calcd for C27H23BrN4O2: C, 62.92;
H, 4.50; N, 10.87 (%). Found: C, 62.64; H, 4.59; N, 10.78
(%)0.3
3 Results and Discussion
3.1 Catalyst Preparation
The procedure followed to obtain the ion-pair immobi-
lization of L-prolinate anion on the cationic polymer resin
is outlined in Scheme 1. The strategy consists of building
up suitable heterogeneous macroporous polymer-supported
L-prolinate catalyst on the surface of commercially avail-
able amberlite IRA-900OH (mesh 16–50). Preparation of
the heterogeneous polymer-supported L-prolinate catalyst
by this procedure is facile and straightforward. In a typi-
cally procedure AmbIRA900OH was treated with a solu-
tion of 0.01 M L-proline at 60 °C to achieve [Amb]
L-prolinate hybrid.
Fig. 1 FT-IR spectrum of [Amb]OH (a), [Amb]L-prolinate (b) and
pristine L-proline (c)
3056 cm-1in FT-IR spectrum of [Amb]L-prolinate. All the
results from the comparison of FT-IR spectra encourage us
to anticipate that the L-prolinate anion successfully loaded
onto the polymer surface through ionic interaction using
ion-pair binding between carboxylate group of L-prolinate
and quaternary ammonium cation of the cationic Amb
support.
3.2 Characterization of the Catalyst
3.2.2 TGA and DTG Analysis
3.2.1 IR Spectra
Thermogravimetric analysis (TGA) and differential ther-
mal analysis (DTG) associated with the decomposition
profiles of the AmbIRA900OH, pristine L-proline and
[Amb]L-prolinate hybrid under a nitrogen atmosphere
provide further evidence for the immobilization of L-pro-
linate anion onto the polymer surface(Figs. 2, 3). The
100 % weight loss of pristine L-proline appears at
215–250 °C on the base of its TGA and DTG curves and
The ion-pair immobilization of L-prolinate anion on the
polymer resin can be confirmed by characterizing the pure
AmbIRA900OH, pristine L-proline and [Amb]L-prolinate
hybrid using FT-IR spectroscopy, as shown in Fig. 1. The
FT-IR spectrum of pristine L-proline shows characteristic
stretching frequencies include: N–H asymmetric stretching
at 3056 cm-1 and carboxylate (COO-) asymmetric and
symmetric stretching at 1622 and 1380 cm-1, respectively
(Fig. 1a). These bands are observed as new peaks in the
FT-IR spectrum of [Amb]L-prolinate hybrid when com-
pared with the FT-IR spectrum of pure AmbIRA900OH
(Fig. 1b vs. a). The carboxylate (COO-) asymmetric and
symmetric stretching are presented in [Amb]L-prolinate
and found to shift to lower positions at 1615 and
1375 cm-1 respectively (Fig. 1b). In addition, the band at
3056 cm-1 corresponding to the asymmetric stretching
vibration of the N–H group in L-proline is also found at
O
0.01 M L-proline in
MeOH-H2O (1:1)
O
C
P
S
N
H
O
PS
N
°
60 C, 6 h
HN
[Amb]L-Prolinate
[Amb]OH
Fig. 2 TGA curve of [Amb]L-prolinate (a), [Amb]OH (b) and
pristine L-proline (c)
Scheme 1 Preparation of [Amb]L-prolinate hybrid
123

Design and Characterization of L-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst…
through the ion-pair exchanges between hydroxyl and
L-prolinate anions on the surface of ion-exchange resin and
is an indirect proof for the presence of ion-pair interaction
between L-prolinate anions and quaternary ammonium
cations on the surface of cationic support (Fig. 3a vs.
c).The high loading of L-prolinate on the surface of Amb
(15 wt%), together with the unique ion-pair binding
behaviors between L-prolinate and Amb-cation, makes the
[Amb]L-prolinate hybrid efficient and stable in the reaction
system.
3.2.3 XRD
Fig. 3 DTG curve of [Amb]L-prolinate (a), [Amb]OH (b) and
pristine L-proline (c)
The crystalline nature of [Amb]L-prolinate hybrid confirms
that L-prolinate is non-conveniently supported on cationic
polymer support via ion-pair immobilization. The main
intense diffraction peaks of pristine L-proline based on the
standard spectrum (Fig. 4a) are observed in the XRD pat-
tern of [Amb]L-prolinate hybrid due to the presence of the
L-prolinate on the Amb support thanks to a favourable ion-
pair binding with quaternary ammonium cations of the ion-
exchange resin (Fig. 4b vs. a). This technique gives
robustness to the catalytic system and on the other hand lets
the L-prolinate organocatalyst to be flexible, mobile and
free on the surface of the polymer at the same time.
Moreover, the thermal stability of organocatalyst has been
improved by this way. These mentioned advantages are
characteristic properties of homogeneous and heteroge-
neous catalysts which have been included in [Amb]L-pro-
linate hybrid.
assigned to the successive cleavage of the L-proline at this
interval (Figs. 2c, 3c).The TGA curve of pure AmbIR-
A900OH shows three weight loss step intervals at 65–100,
150–250 and 370–470 °C. The first weight loss interval at
65–100 °C is most probably due to a loss of adsorbed water
(weight loss = ca. 11 wt%). The second weight loss
interval at 150–250 °C presumably assigned to the loss of
some functional groups(weight loss = ca. 19 wt%) and
finally the third weight loss interval at 370–470 °C (weight
loss = ca. 34 wt%) could presumably assigned to partial
polymer decomposition (Fig. 2b). Figure 3b displays the
DTG curve of AmbIRA900OH and is in accordance with
the weight loss steps from its TGA curve. The TGA curve
of [Amb]L-prolinate hybrid displays four weight loss steps
include: 60–100, 150–250, 250–370, and 370–470 °C
intervals (Fig. 2a). These four weight loss peaks are well
distinguished in the corresponding DTG curve (Fig. 3a).
Obviously, in comparison with AmbIRA900OH, a new
decomposition interval is observed in TGA and DTGcurves
of [Amb]L-prolinate hybrid (weight loss = ca. 15 wt%).
This weight loss is assigned to the successive cleavage of
L-prolinate anion loaded on the surface of the polymer and
also referred to the content of L-prolinate moiety on the
Amb-cationic support. The calculation from TG curve was
indicated that 1.3 mmol of L-prolinate organocatalyst is
loaded per 1 g of the [Amb]L-prolinate hybrid. It is
noticeable that the decomposition temperature of L-proli-
nate anion in [Amb]L-prolinate hybrid has been increased
to 250–370 °C in comparison with the decomposition
temperature of pristine L-proline (215–250 °C). These
observations mean that the thermal stability of the L-pro-
linate has been increased in comparison with the pristine L-
proline and also explain the carboxylate asymmetric and
symmetric stretching shifts to lower positions in FT-IR
spectrum of [Amb]L-prolinate hybrid (Fig. 1b).
3.3 Optimization of the Reaction Conditions
After preparation and characterization of [Amb]L-prolinate
catalyst, its catalytic activity was investigated in a one-pot
The increased decomposition temperature of the L-pro-
linate suggests that the guest/host interaction was done
Fig. 4 XRD pattern of pristine L-proline (a) and [Amb]L-prolinate (b)
123

M. Keshavarz, M. Vafaei-Nezhad
pseudo three-component reaction for the synthesis of 4,40-
(arylmethylene)-bis-(1H-pyrazol-5-ol)s. To search for the
optimal conditions, the reaction of benzaldehyde and two
equivalents of 3-methyl-1-phenyl-2-pyrazolin-5-one was
selected as the model reaction to examine the effect of
[Amb]L-prolinate catalyst (2–15 mol%) under a variety of
conditions (Table 1).
wide range of aromatic aldehydes bearing both electron-
donating and electron-withdrawing substituents (3a–r).
We proposed a plausible mechanism for the formation
of 3a–r from aromatic aldehydes (1) and 3-methyl-l-phe-
nyl-2-pyrazolin-5-one (2) using [Amb]L-prolinate as cata-
lyst. Initially, 1 reacts with L-prolinate anion of catalyst to
form an iminium carboxylate (I). Then L-prolinate anion
abstracts a proton from the 3-methyl-l-phenyl-2-pyrazolin-
5-one (2) to form the enolate intermediate (II). In the next
step, Michael addition of enolate (II) to the iminium car-
boxylate (I) furnishes intermediate III. Finally the second
molecule of 2 is added to intermediate III by the Michael
addition fashion to give final product 3 (Scheme 3).
The present optimization studies revealed that the best
result was achieved by caring out the reaction in the
presence of 10 mol% of [Amb]L-prolinate under reflux
condition in ethanol (Table 1, entry 9). The yield smoothly
increased with the catalyst load up to 10 mol% and use of
larger amounts of the catalyst (15 mol%) did not improve
the yield while decreasing the amount of the catalyst led to
decreased yield.
The recovery of a catalyst is highly preferable for a
greener process. For this purpose, the reusability of
[Amb]L-prolinate was examined for eight consecutive
cycles (fresh ? seven cycles) for the synthesis of 4,40-
(phenylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-
ol) (3a). From Fig. 5, It can be seen that [Amb]L-prolinate
can be reused up to 8 runs without need to reload and the
Using these optimized reaction conditions, the effi-
ciency of this approach was explored for the synthesis of a
wide variety of 4,40-(arylmethylene)-bis-(1H-pyrazol-5-
ol)s (Scheme 2; Table 2). All the reactions (Table 2)
delivered excellent product yields and accommodated a
Table 1 Investigation of catalytic activity of [Amb]L-prolinate for the synthesis of 4,40-(phenylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-
5-ol) (3a) under various conditions
O
P
h
H
3C
H
C
O
3
H
3C
P
S
N
C
O
HN
+
2
N
N
N
O
P
h
H
N
Condition
N
N
P
h
H
O
H
O
P
h
P
h
Entry
Conditions
Temperature (°C)
[Amb]L-prolinate (mol%)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
a
Neat
100
2
2
45
50
40
45
35
30
25
20
11
16
65
60
65
50
58
75
85
92
97
98
CH2Cl2
CH3CN
THF
Reflux
Reflux
65
2
2
DMF
100
2
H2O/DMF
H2O
100
5
Reflux
Reflux
Reflux
Reflux
5
CH3CH2OH
CH3CH2OH
CH3CH2OH
5
10
15
Yield refer to isolated and pure product
Scheme 2 Synthesis of 4,40-
(arylmethylene)-bis-(1H-
pyrazol-5-ol) derivatives
Ar
H
3C
H
C
H
3
3C
EtOH, reflux
5-18 min
O
catalyzed by [Amb]L-prolinate
2
+
N
N
N
O
Ar
H
O
N
N
N
O
PS
N
C
Ph
HO
HO
Ph
Ph
HN
1
2
a-r
3
123

Design and Characterization of L-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst…
Table 2 Synthesis of 4,40-(arylmethylene)-bis-(1H-pyrazol-5-ol)s (3a–r) catalyzed by [Amb]L-prolinate
Entry
Ar
Product
Time (min)
Yielda (%)
m.p. (°C)
Found
Reported
1
C6H5–
3a
3b
3c
3d
3e
3f
11
12
10
10
15
8
97
95
92
90
94
96
88
90
88
91
86
93
87
98
82
89
96
88
170–172
203–205
213–215
233–235
227–229
225–227
152–154
153–155
169–170
194–196
205–207
210–212
232–234
180–182
132–134
173–175
198–200
170–173
171–172
202–204
213–215
236–237
227–229
224–226
149–150
152–153
165–168
195–197
201–203
210–212
230–231
180–182
132–134
172–174
198–200
173–175
2
4-Me–C6H4–
4-Cl–C6H4–
2-Cl–C6H4–
2,4-(Cl)2–C6H3–
4-NO2–C6H4–
3-NO2–C6H4–
4-OH–C6H4–
3-OH–C6H4–
3,4-(MeO)2–C6H3–
4-MeS–C6H4–
4-CN–C6H4–
2-OH–C6H4–
4-F–C6H4–
3
4
5
6
7
3g
3h
3i
8
8
15
14
7
9
10
11
12
13
14
15
16
17
18
a
3j
3k
3l
15
16
18
14
10
8
3m
3n
3o
3p
3q
3r
4-iPr–C6H4–
4-MeO–C6H4–
2-Br–C6H4–
3-Br–C6H4–
5
6
Isolated yield
O
O
O
O
e
M
O
O
H
H
+
+
C
+
C
C
N
H
N
H
O
N
N
O
N
r
A
e
M
H
r
A
H
P
h
2
I
1
N
O
N
II
P
h
r
A
e
M
e
M
e
M
H
O
O
H
N
+
N
C
N
H
N
N
N
O
N
P
h
H
HO
O
P
h
P
h
O
O
r
A
r
A
e
e
M
M
H
e
M
3
+
C
e
M
N
H
N
N
N
N
N
N
N
O
N
H
O
O
O
P
h
P
h
P
h
P
h
III
Scheme 3 Plausible mechanism for the formation of 4,40-(arylmethylene)-bis-(1H-pyrazol-5-ol)s
yield difference between the first and 8th runs is only 5 %
which indicated that the catalyst efficiency is almost
completely maintained during 8 consecutive runs. The
nitrogen content of the fresh and reused catalyst was
measured by using of elemental analysis and the
comparison of the nitrogen contents indicated that the
catalyst lost only 3 % of its nitrogen content after 8 runs.
This is a good proof for very low leaching account of
L-proline organocatalyst from [Amb]L-prolinate catalyst
into the reaction mixture during 8 runs and also confirms
123

M. Keshavarz, M. Vafaei-Nezhad
Fig. 5 Recycling of [Amb]L-
prolinate for the synthesis of
4,40-(phenylmethylene)-bis-(3-
methyl-1-phenyl-1H-pyrazol-5-
ol) (3a)
Ph
H3C
CH3
N
H3C
O
EtOH, reflux
2
N
N
+
N
O
Ph
H
N
O
N
O
N
PS
C
Ph
HO
HO
Ph
Ph
8 runs
HN
97
96
100
80
60
40
20
0
96
95
94
93
93
92
Yield(%)
Time(min)
11
15
11
15
20
25
15
20
1
2
3
4
5
6
7
8
No. of Runs
Table 3 Comparison of the catalytic efficiency of [Amb]L-prolinate with various catalysts reported for the synthesis of 3a
Entry
Catalyst
Condition
Time (min)
Yield (%)
References
1
[Amb]L-prolinate (10 mol%)
H3PW12O40 (10 mol%)
Nano-SiO2/HClO4
EtOH/reflux
EtOH/reflux
H2O/reflux
11
15
20
30
3
97
91
94
90
93
95
89
96
98
92
95
80
86
90
80
This work
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
2
3
4
SBNPTT
EtOH/reflux
H2O/r.t
5
NPS-c-Fe2O3
6
[P4VPy-BuSO3H]HSO4
[Pyridine–SO3H]Cl (1 mol%)
Phosphomolybdic acid
AP-SiO2(30 mol%)
PEG-SO3H (1.5 mol%)
Xanthan sulfuric acid
LiOHÁH2O (10 mol%)
[Dsim]AlCl4 (1 mol%)
SASPSPE (0.1 g)
EtOH/reflux
Solvent-free/50 °C
EtOH/r.t
42
11
240
10
30
15
75
60
18
120
7
8
9
CH3CN/r.t
10
11
12
13
14
15
H2O/reflux
[35]
[36]
[37]
EtOH/reflux
H2O/90 °C
Solvent-free/50 °C
EtOH/reflux
EtOH/reflux
[38]
[39]
[41]
SBSSA (18 mol%)
that the catalytic ability of [Amb]L-prolinate almost com-
pletely has been remained stable after 8 runs in agreement
with the recyclability study.
in Table 3. It is clear from the data that our method has short
reaction times and provides higher yields of the products.
In addition, to show the efficiency of this method in
comparison with other reported procedures, we selected the
reaction of benzaldehyde and two equivalents of 3-methyl-
1-phenyl-2-pyrazolin-5-one for the synthesis of 4,40-
(phenylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ol)
(3a) as a representative model. This comparison is shown
4 Conclusions
In summary, we have reported the one-pot pseudo three-
component synthesis of 4,40-(arylmethylene)-bis-(1H-
pyrazol-5-ol) derivatives using ion-pair immobilization of
123

Design and Characterization of L-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst…
17. El-Sayed MA, Abdel-Aziz NI, Abdel-Aziz AA, El-Azab AS, El-
Tahir KE (2012) Bioorg Med Chem 20:3306–3316
L-proline on the surface of amberlite hydroxide as a new,
heterogeneous and reusable organocatalyst. This method-
ology made the organocatalyst to be mobile and flexible
which not only helped the supported catalyst to be as
powerful as its non-supported form, but also made it to be
easily recoverable with simple filtration. Some attractive
features of this protocol are simple procedure, excellent
yields, short reaction times, easy work-up, high catalytic
activity and recyclability, and reusability of the catalyst.
The catalyst can be used at least eight times without sub-
stantial reduction in its catalytic activity.
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