A reactive and environmentally friendly protocol for expeditious synthesis of various resorcinarenes using zinc hydrogen sulfate

Article abstract of DOI:10.1080/10610278.2019.1598557

In this work, for the first time, metal hydrogen phosphates and sulfates have been studied as effective solid acid catalysts for the condensation of resorcinol with aromatic and aliphatic aldehydes to give tetrameric cyclic products, resorcinarenes, which

Full text of DOI:10.1080/10610278.2019.1598557

Supramolecular Chemistry
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A reactive and environmentally friendly
protocol for expeditious synthesis of various
resorcinarenes using zinc hydrogen sulfate
Arash Mouradzadegun, Mohammad Reza Ganjali, Neda Kheirandish &
Fatemeh Abadast
To cite this article: Arash Mouradzadegun, Mohammad Reza Ganjali, Neda Kheirandish
& Fatemeh Abadast (2019): A reactive and environmentally friendly protocol for expeditious
synthesis of various resorcinarenes using zinc hydrogen sulfate, Supramolecular Chemistry, DOI:
10.1080/10610278.2019.1598557
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SUPRAMOLECULAR CHEMISTRY
https://doi.org/10.1080/10610278.2019.1598557
ARTICLE
A reactive and environmentally friendly protocol for expeditious synthesis of
various resorcinarenes using zinc hydrogen sulfate
Arash Mouradzadeguna,b, Mohammad Reza Ganjalib,c, Neda Kheirandisha and Fatemeh Abadasta
b
aDepartment of Chemistry, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran; Center of Excellence in Electrochemistry,
c
University of Tehran, Tehran, Iran; Biosensor Research Center, Endocrinology & Metabolism Molecular-Cellular Sciences Institute, Tehran
University of Medical Sciences, Tehran, Iran
ABSTRACT
ARTICLE HISTORY
Received 17 July 2017
Accepted 14 March 2019
In this work, for the first time, metal hydrogen phosphates and sulfates have been studied as
effective solid acid catalysts for the condensation of resorcinol with aromatic and aliphatic
aldehydes to give tetrameric cyclic products, resorcinarenes, which have major roles in biological
and industrial activities. This catalyst has several advantages, it is non-toxic, thermally and
mechanically stable, inexpensive and highly resistant against organic solvents. It increases the
reaction rate about six fold and makes this method an attractive alternative to the existing
methods for resorcinarene formation. Interestingly, the present catalyst exhibited a high turnover
number (TON) and turnover frequency (TOF) which were even comparable with that of HCl.
KEYWORDS
Resorcinarene; metal
hydrogen sulfates and
phosphates; solid acid; zinc
hydrogen sulfate;
stereoisomer
HO
OH
H
HO
OH
R
OH
OH
R
H
HO
HO
Zn(HSO4)2
R = Alkyl or Aryl
O
H
R
R
H
R
H
HO
OH
1. Introduction
associated with several shortcomings such as the use
of toxic, expensive and unrecyclable catalysts such as
Yb(OTf)3, Bi(CF3SO3)3 · 4H2O and p-TsOH, multiple
steps, long reaction times (2–4 days), low product
yields, difficult workup procedures and the use of
large quantities of concentrated HCl. Therefore, it is
still a great challenge to find simple and fast ways to
synthesise these compounds according to principles of
green chemistry using mild reaction conditions in
short reaction times.
Solid inorganic acidic salts play a prominent role in
organic synthesis under heterogeneous conditions. In
view of green chemistry, the substitution of harmful
liquid acids by reusable solid acids as catalysts in organic
synthesis is the most promising approach (16–18). These
factors, coupled with the normal advantages of solid
acids (e.g. low toxicity, high stability towards humidity,
recyclability and air stability) make the compounds
attractive materials to organic and industrial chemists.
Calixarenes are a class of macrocycles formed by con-
densation of phenols with various aldehydes. Calix[4]
resorcinarene macrocycles are one of the calixarene
compounds comprising four phenolic moieties joined
in cyclic array at the meta-positions by methylene
bridges (1). The possibility of modifying these com-
pounds either via nucleophilic aromatic substitutions
on the aromatic ring or the phenol hydroxyl groups or
the lower rim increases their potential for forming mul-
tifunctional compounds. These macrocycles are the
subject for increasing interest in the field of host-
guest chemistry, liquid crystals, sensors, surfactants,
catalyst, etc (2–9). Hence, a practical method for the
preparation of such compounds is of great interest in
synthetic organic chemistry.
Although a variety of strategies have been reported
in this area (10–15), most of these methods suffer from
the absence of green chemistry, and have been
CONTACT Arash Mouradzadegun
arash_m@scu.ac.ir
Department of Chemistry, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran
Provide short biographical notes on all contributors here if the journal requires them.
Supplemental data for this article can be accessed here.
© 2019 Informa UK Limited, trading as Taylor & Francis Group

2
A. MOURADZADEGUN ET AL.
In continuation of our new interest in the application
a period of 30 min. After the addition was completed,
the reaction was cooled about 15 min. Then, the reac-
tion was reflux for 65 min. After TLC indicated that the
reaction had gone to completion, the catalyst was
separated by vacuum filtration. Fifty-millilitre water
was added to filtrate to precipitate resorcinarene
A and recrystallised from ethanol/water (50:50) to give
pure product (82.7% yield).
of calix[4]resorcinarene and its 3D-network porous poly-
mer for the preparation of biologically important mole-
cules (19–24) in this work, for the first time, we report
the application of new inexpensive solid acids as an
eco-efficient and environmentally friendly catalyst for
the synthesis of resorcinarene derivatives.
2. Experimental
2.4. Typical procedure for the condensation of
aromatic aldehydes with resorcinol catalysed by
Zn(HSO4)2
2.1. General
Chemicals were purchased from Fluka, Merck, and
Aldrich chemical companies. Monitoring of the reac-
tions was accomplished by TLC. IR spectra were
obtained on a Bomen MB:102 FT-IR spectrophotometer.
1H NMR and 13C NMR spectra were recorded on
a Bruker spectrometer at 400 and 100 MHz, respec-
tively, in DMSO. MS spectra were measured on
a Finnigan MAT TSQ 70 mass spectrometer.
To a solution of 1.1 g (10−2 mol) of resorcinol and 10−2
mol of substituted benzaldehyde in 30 ml of 95%
ethanol was added 10 mol% of Zn(HSO4)2 . The result-
ing heterogeneous mixture was heated at 80°C under
nitrogen. The reaction was monitored by TLC using
a 20:80 mixture of ether: n-hexane as an eluent, after
completion of the reaction, catalyst and precipitated
C4v isomer was separated by vacuum filtration. The
solid residue was triturated with water (50 ml) at
ambient temperature to remove the catalyst from C4v
isomer (25–40% yields). Then, water was added to the
filtrate to precipitate the C2h isomer. The C2h isomer
was filtered and washed several times with water
(30 ml) and recrystallised from hot ethanol (5–10 ml)
and then cooled slowly to ambient temperature
(30–60% yields).
2.2. Synthesis of metal hydrogen phosphates and
sulfates
All metal hydrogen phosphates and sulfates were
synthesised from the corresponding anhydrous metal
chlorides and the appropriate amount of concentrated
sulfuric acid or phosphoric acid by the method pre-
viously described (25).
This general procedure is exemplified by the synth-
esis of resorcinarene D: 1.1 g resorcinol was dissolved in
30 ml ethanol and 0.1 g Zn(HSO4)2 was added under
nitrogen. Then, 2.05 g benzaldehyde was added over
a period of 30 min. The reaction was reflux for 20 min.
After TLC indicated that the reaction had gone to com-
pletion, the catalyst and precipitated C4v isomer was
separated by vacuum filtration. The residue triturated
with 50 ml water at ambient temperature to remove
the catalyst from C4v isomer.Then, water (20 ml) was
added to the filtrate to precipitate the C2h isomer. The
C2h isomer was filtered and washed several times with
30 ml water and recrystallised from 5 ml hot ethanol
and then cooled slowly to ambient temperature (57.6%
for both C4v and C2h isomer).
2.3. Typical procedure for the condensation of
aliphatic aldehydes with resorcinol catalysed by
Zn(HSO4)2
To a solution of 1.10 g (10−2 mol) of resorcinol in 20 ml
of 95% ethanol, 10 mol% Zn(HSO4)2 was added under
nitrogen at room temperature. To this stirred mixture,
10−2 mol of the relevant aldehyde was added drop-
wise over a period of 30 min. After the addition was
complete, the reaction was cooled in a water bath to
control the exotherm (15 min.). Then, the reaction
mixture was heated at reflux (80°C). The reaction was
monitored by TLC using a 20:80 mixture of ether:
n-hexane as an eluent, after completion of the reac-
tion, the catalyst was then separated by vacuum filtra-
tion. The water (50 ml) was added to the filtrate to
precipitate the product, which was then recrystallised
from ethanol/water (50:50) to give the pure product
(82–98% yields).
3. Results and discussion
Resorcinarene derivatives are prepared by the acid-
catalysed cyclocondensation of resorcinol with various
aliphatic or aromatic aldehydes (Scheme 1).
Preliminary tests were carried out to survey the
requisite reaction conditions and establish the modifi-
cations required for this methodology. The reaction of
This general procedure is exemplified by the synth-
esis of resorcinarene A: 1.1 g resorcinol was dissolved in
20 ml ethanol and 0.1 g Zn(HSO4)2 was added under
nitrogen. Then, 0.44 g acetaldehyde was added over

SUPRAMOLECULAR CHEMISTRY
3
HO
OH
H
R
OH
R
H
HO
HO
Acidic Catalyst
HO
OH
O
R
H
OH
H
R
R
H
R = Alkyl or Aryl
HO
OH
Scheme 1. Synthesis of resorcinarene derivatives from resorcinol by acidic catalyst.
acetaldehyde and resorcinol for the synthesis of calix[4]
resorcinarene was chosen as the model reaction to
identify and optimise the reaction conditions.
Metal hydrogen sulfates and phosphates were easily
prepared from the corresponding anhydrous metal
chlorides and sulfuric or phosphoric acid, respectively
(25). The reactions are very clean and did not require
a work-up procedure because HCl evolves as a by-
product from the reaction vessel immediately.
dihydrogen phosphates including Al(H2PO4)3, Mg(H2
PO4)2, Zn(H2PO4)2 (Table 1).
As shown in Table 1, the corresponding calix[4]resor-
cinarene was synthesised successfully in the presence
of Zn(HSO4)2 with high yield at 65 min, while this reac-
tion was done in the presence of HCl as the common
catalyst in a 4 days period (26).
Mg(HSO4)2 also catalysed this condensation but with
longer reaction times. In the presence of other catalysts
unidentified products were observed.
Therefore, we have tabulated the model reaction in
the presence of a catalytic amount of solid acids such as
metal hydrogen sulfates including Al(HSO4)3,
The structure of product was settled from their phy-
sical and spectroscopic (IR, 1H NMR, 13C NMR and Mass)
data (see ESI).
Mg(HSO4)2, Zn(HSO4)2, Fe(HSO4)3, and
metal
Encouraged by this observation, further experiments
were designed to optimise this reaction in the presence
of Zn(HSO4)2. The best results were obtained when 10
mol% of catalyst in ethanol as solvent were used.
To further examine the efficacy of this synthetic
opportunity, the process is illustrated with various ali-
phatic aldehydes in the presence of Zn(HSO4)2 as cata-
lyst (Table 2). In these reactions, only the C4v isomers
(thermodynamically isomer) were isolated with high
selectivity.
Table 1. Synthesis of C-methyl calix[4]resorcinarene catalysed by
various solid acids.
Entry
Solid acid
Time
15 h
15 h
80 min
140 min
65 min
15 h
1
2
3
4
5
6
7
Al(HSO4)3
Al(H2PO4)3
Mg(HSO4)2
Mg(H2PO4)2
Zn(HSO4)2
Zn(H2PO4)2
Fe(HSO4)3
120 min
Table 2. The reaction of resorcinol with various aliphatic aldehydes using Zn(HSO4)2 under optimised conditions.
H
O
O
H
H
O
O
O
O
H
HO
OH
+
R
R
O
Zn(HSO4)2
R
H
R
R
H
H
H
R = Aliphaticgroup
O
O
H
Entry
R
Time (min)
Yield (%)
m.p. °C
1
3
4
CH3
CH3(CH2)3
CH3(CH2)4
65
50
40
82.7
87.6
98
> 360
345
330

4
A. MOURADZADEGUN ET AL.
H
O
HO
O
OH
H
H
O
O
O
O
H
HO
HO
OH
OH
R
R
R
R
HO
OH
+
O
Zn(HSO4)2
+
R
H
R
R
R
R
H
H
H
O
O
HO
OH
H
B (rctt, C2h)
A (rccc, C4v)
Scheme 2. The diastereomers A (rccc, C4v) and B (rctt, C2h).
Table 4. The comparison of the catalytic performance of
Zn(HSO4)2 with commercially available HCl as a catalyst.
As can be observed in Table 2, the reaction of other
aliphatic aldehydes with resorcinol was successful too
in short reaction times and high yields compared with
conventional methods.
Time
Time
Yield (%)
Yield (%)
in HCl
Entry
R
in Zn(HSO4)2 in HCl in Zn(HSO4)2
1
2
3
4
5
6
7
CH3
65 min
50 min
40 min
20 min
35 min
60 min
155 min
4 days
6 days
6 days
4 days
5 days
5 days
6 days
82.7
87.6
98
57.6٭
97.7٭
92.5٭
98٭
60
89
77
64٭
84٭
88٭
93٭
CH3(CH2)3
CH3(CH2)4
C6H5
4-BrC6H4
4-ClC6H4
4-CH3OC6H4
In order to further expand the scope of this catalytic
system, resorcinol was treated with aromatic aldehydes.
In the presence of aromatic aldehydes a mixture of
diastereomers A (rccc) and B (rctt) was observed
which is in agreement with the authentic samples
(Scheme 2). Due to the different solubility of two
stereoisomers (C4v, C2h) in ethanol and water, separa-
tion of the two stereoisomers was accomplished by
simple crystallisation. Since the relative ratio of the A/
B dependent on the reaction times, we reported the
total yields of reactions (Table 3).
Pleasingly, in all cases the desired products obtained
in good yields. Since the vibration of rccc and rctt
isomers was different, their behaviour in IR spectra
was different too. Due to hydrogen bonds between
phenolic groups, the OH peak is wider in the rccc
isomer than in rctt isomer (ESM section). All products
identified by comparing their physical and spectral data
with those of authentic samples (10–15).
It is noteworthy that the formation of various resor-
cinarenes by the present method are of considerable
interest, since this is the first attempt at the synthesis of
these privileged compounds in the presence of
Zn(HSO4)2 as an effective solid acid catalyst.
In order to show the merit of the catalyst, Table 4
compares the results obtained from commercially avail-
able HCl with the results in the presence of Zn(HSO4)2
as a catalyst under optimised conditions (Table 4).
٭ Total yields including C4v and C2h isomers.
The results in Table 4 show a greater superiority of
Zn(HSO4)2 to HCl. It can be seen that the Zn(HSO4)2
exhibited a significantly higher turnover (TON) number
and turnover frequency (TOF) than those reported for
HCl systems. Based on these results, we believe that
Zn(HSO4)2 is a suitable catalyst for synthesis of valuable
resorcinarenes in laboratory and industrial applications.
4. Conclusions
In summary, the superiority of using Zn(HSO4)2 over
other methods includes a very rapid reaction with effec-
tive and readily available catalyst. Further, our method
can be applied to a wide range of substrates and results
in good yield and short reaction times. Overall, the
present protocol offers more efficient and particularly
economically advantageous process towards the synth-
esis of valuable resorcinarenes, which serves a useful
synthetic alternative for large-scale conversions.
Disclosure statement
No potential conflict of interest was reported by the authors.
Table 3. The reaction of resorcinol with various aromatic alde-
hydes using Zn(HSO4)2 under optimised conditions.
Entry
R
Time (min)
Yield (%): A/B
m.p. °C
Funding
1
2
3
4
C6H5
20
35
60
57.6: 40.2/17.4
97.7: 52/45.7
92.5: 52.5/40
98: 56.3/41.7
285–330
> 360
> 360
4-BrC6H4
4-ClC6H4
4-CH3OC6H4
This work was supported by the Research Council at the
University of Shahid Chamran.
155
> 360

SUPRAMOLECULAR CHEMISTRY
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