Friedel-crafts alkylation of arenes catalyzed by ion-exchange resin nanoparticles: An expedient synthesis of triarylmethanes

Article abstract of DOI:10.1166/jnn.2015.10671

Friedel-Crafts alkylation of electron-rich arenes with aldehydes has been achieved in the presence of an active and selective Amberlyst-15 catalyst at the reaction temperature of 60 ° C in solvent-free conditions. The catalyst exhibitsby a very high activity and offers the corresponding triarylmethanes in excellent yields with a high selectivity. The use of highly reactive and selective Amberlyist-15 makes this procedure simple, convenient, cost-effective, practical and environmentally friendly. This method provides an easy access to triarylmethanes in a single step using a readily available acidic ionic resin, which is a stable and easy to separate from the reaction mixture by a simple filtration technique.

Full text of DOI:10.1166/jnn.2015.10671

Article
Journal of
Nanoscience and Nanotechnology
Vol. 15, 6826–6832, 2015
Copyright © 2015 American Scientific Publishers
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Printed in the United States of America
Friedel-Crafts Alkylation of Arenes Catalyzed by
Ion-Exchange Resin Nanoparticles: An Expedient
Synthesis of Triarylmethanes
B. V. Subba Reddy1ꢀ4ꢀ∗, A. Venkateswarlu4, B. Sridevi4,
Salem S. Aldeyab3, and Ajayan Vinu1ꢀ2ꢀ∗
1International Center for Materials Nanoarchtectonics, National Institute for Materials Science,
1-1, Namiki, Tsukuba, 305-0044, Japan
2Australian Institute for Bioengineering and Nanotechnology, The University of Queensland,
Brisbane 4072, QLD, Australia
3Department of Chemistry, Petrochemicals Research Chair, Faculty of Science, King Saud University,
P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia
4Natural Product Chemistry, Indian Institute of Chemical Technology, Hyderabad 500007, India
Friedel-Crafts alkylation of electron-rich arenes with aldehydes has been achieved in the presence
of an active and selective Amberlyst-15® catalyst at the reaction temperature of 60 ꢀC in solvent-free
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conditions. The catalyst exhibits a very high activity and offers the corresponding triarylmethanes
®
IP: 117.253.104.110 On: Thu, 10 Dec 2015 07:53:50
in excellent yields with a high selectivity. The use of highly reactive and selective Amberlyist-15
Copyright: American Scientific Publishers
makes this procedure simple, convenient, cost-effective, practical and environmentally friendly. This
method provides an easy access to triarylmethanes in a single step using a readily available acidic
ionic resin, which is a stable and easy to separate from the reaction mixture by a simple filtration
technique.
Keywords: Ion-Exchange Resin, Nanoparticles, Triarylmethanes, Alkylation.
1. INTRODUCTION
recently because of the formation of many side products
such as diarylmethanes, triarylmethanes and anthracene
derivatives.7 For example, diarylmethanes are formed
selectively in the reaction of arenes with formaldehyde in
the presence of acid catalysts such as CaCl2,8 Sc(OTf)3,9
and InCl3/TMSCl.10 Subsequently, the preparation of tri-
arylmethanes have been reported using various catalytic
systems such as AuCl3/AgOTf,11 Ir(COD)Cl2/SnCl4,12
Yb(OTf)3,13 and SbCl3.14 The silica supported ZnBr2/AcBr
has also been used for the synthesis of triarylmethanes.15
However, the use of acetyl halides as activators, high tem-
peratures, extended reaction times and harsh conditions
and the necessity of several reaction steps in many cases
limit their practical utility in large scale synthesis. There-
fore, the development of a simple, convenient and efficient
method for the preparation of triarylmethanes would cer-
tainly expand the scope of the Friedel-Crafts alkylation.
Recently, the use of solid acidic catalysts such as sul-
fated zirconia, heteropoly acids, acidic polymers, clays
and zeolites has enhanced the replacement of liquid acid
Multi-component reactions (MCRs) are highly important
because of their wide range of applications in pharma-
ceutical chemistry for production of highly diversified
structural scaffolds and combinatorial libraries for drug
discovery.1 MCRs are extremely convergent, producing a
remarkably high molecular complexity in a single step.
Triarylmethanes have attracted much attention in syn-
thetic, medicinal, and industrial chemistry.2 They are also
used as photochromic materials3 and dyes.4 In particu-
lar, hydroxy substituted triarylmethanes are attractive as
antioxidants and antitumor agents especially in medicinal
chemistry.5 The acid-catalyzed condensation of veratrole
with formaldehyde leads to cyclotriveratralene which is an
important building block in supramolecular chemistry to
construct more complex cage-like cryptophane.6
The mostpopular AlCl3-catalyzed alkylation of arenes
with aldehydes has not received much attention until
∗Authors to whom correspondence should be addressed.
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1533-4880/2015/15/6826/007
doi:10.1166/jnn.2015.10671

Reddy et al.
Friedel-Crafts Alkylation of Arenes Catalyzed by Ion-Exchange Resin Nanoparticles
catalysts for organic transformations.16 Due to their oper-
ational simplicity, environmental compatibility, non-toxic,
reusability, low cost, and ease of isolation. In particu-
lar, ion exchange resins are the most widely used het-
erogeneous catalysts due to their advantages such as high
activity and selectivity, reusability, non-hazardous nature
and ease of removal from the reaction mixture via sim-
ple filtration.17 However, there are no reports on the use
of acidic ion-exchange resins for the direct alkylation of
electron-rich arenes with aldehydes.
(d, J = 8ꢁ7 Hz, 4 H), 5.41 (s, 1 H), 3.78 (s, 6 H); 13C NMR
(75 MHz, CDCl3): ꢀ 158.3, 143.3, 136.0, 132.1, 130.8,
130.3, 128.5, 113.9, 55.3, 54.7; IR (KBr): ꢃmax 3419, 2980,
2910, 2840, 1560, 1511, 1240, 1120, 1023, 810, 740 cm−1
;
ESI-MS: m/z 361 (M+Na)+.
2.4. 1,2-Dimethoxy-4-((3,4-Dimethoxyphenyl)
(4-Methoxyphenyl)Methyl)Benzene (3c)
Red color semisolid; 1H NMR (500 MHz, CDCl3ꢂ: ꢀ 6.96
(d, J = 7ꢁ55 Hz, 2 H), 6.76 (d, J = 7ꢁ55 Hz, 2 H), 6.71
(d, J = 8ꢁ30 Hz, 2 H), 6.59 (s 2 H), 6.51 (d, J = 8ꢁ30 Hz,
2 H), 5.32 (s, 1 H), 3.82 (s, 6 H), 3.76 (s, 1 H), 3.74 (s,
1 H); 13C NMR (75 MHz, CDCl3): ꢀ 149.4, 148.7, 174.6,
145.3, 133.2, 128.7, 123.2, 120.0, 111.6, 110.8, 56.2, 55.4,
55.3, IR (KBr): ꢃmax 3345, 2944, 2832, 1655, 1413, 1111,
1205, 752, 599 cm−1; ESI-MS: m/z 412(M+NH4ꢂ+.
2. EXPERIMENTAL SECTION
IR spectra were recorded on FT-IR spectrometer and
1
reported in reciprocal centimeters (cm−1). H NMR spec-
tra were recorded at 300 MHz and 13C NMR at 75 MHz.
1
For H NMR, tetramethylsilane (TMS) was used as inter-
nal standard (ꢀ = 0) and the values are reported as
follows: chemical shift, integration, multiplicity (s = sin-
glet, d = doublet, t = triplet, q = quartet, m = multiplet,
br = broad), and the coupling constants in Hz. For
13C NMR, CDCl3 (ꢀ = 77ꢁ27) was used as internal stan-
dard and spectra were obtained with complete proton
decoupling. Low-resolution MS and HRMS data were
obtained using APCI ionization. Melting points were mea-
sured on micro melting point apparatus.
2.5. 1(Bis(3,4Dimethoxyphenyl)Methyl)
2,4-Dichlorobenzene (3d)
White solid m.p. 110–112 ꢀC; 1H NMR (500 MHz,
CDCl3ꢂ: ꢀ 6.87 (d, J = 8ꢁ78 Hz, 1 H), 6.72 (d, J =
8ꢁ78 Hz, 2 H), 6.55 (s 2 H), 6.44 (d, J = 8ꢁ78 Hz,
2 H), 5.70 (s, 1 H), 3.85 (s 6 H), 3.76 (s 6 H); 13CNMR
(75 MHz, CDCl3ꢂ: ꢀ 148.8, 147.6, 140.6, 137.6, 131.6,
129.3, 126.7, 121.2, 112.5, 110.7, 55.9, 55.7, 52.0; IR
(KBr): ꢃmax 3419, 300, 2931, 2834, 1590, 1515, 1258,
1138, 1023, 812, 750 cm−1; ESI-MS: m/z 455 (M+Na)+;
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2.1. General Procedure
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HRMS Calculated for C23H22O4Cl2Na 455.0792, Found:
A mixture of aromatic aldehyde (1 mmol), aromatic ether
(2 mmol) and Amberlyst-15 (100 mg) was stirred at 60 ꢀC
under solvent free condition. Upon completion as indi-
cated by TLC, the catalyst was recovered by simple filtra-
tion with ethyl acetate. After evaporation of the solvent,
the crude product was purified by silica gel column chro-
matography (100–200 mesh) using n-hexane-EtOAc (8:2)
to afford the pure triarylmethane derivative. Spectral data
for the selected products.
Copyright: American Scientific Publishers
455.0782.
2.6. 2-(Bis(3,4-Dimethoxyphenyl)Methyl)-
1,3-Dimethoxy Benzene (3e)
White solid, m.p. 131–134 ꢀC; 1H NMR (300 MHz,
CDCl3): ꢀ 6.76–6.63(m, 3 H), 6.54 (s, 2 H), 6.49 (d, J =
8ꢁ3 Hz, 2 H), 6.38 (d, J = 2ꢁ8 Hz, 1 H), 5.69 (s, 1 H),
3.84 (s, 6 H), 3.76 (s, 6 H), 3.66 (s, 3 H), 3.64 (s, 3 H);
13C NMR (75 MHz, CDCl3ꢂ: ꢀ 153.3, 151.4, 148.5, 147.2,
136.2, 134.4, 121.1, 117.1, 112.6, 111.0, 110.8, 110.6,
56.3, 55.7, 55.5, 48.8; IR (KBr): ꢃmax 3430, 2944, 1593,
1511, 1461, 1269, 1213, 1024, 815, 757 cm−1; ESI-MS:
m/z: 447 (M + Na); HRMS Calculated for C25H28O6Na
447.1783, Found: 447.1804.
2.2. 4,4-(Phenyl Ethylene)Bis(1,2-Dimethoxy-
benzene) (3a)
White solid, m.p. 120–122 ꢀC; 1H NMR (300 MHz,
CDCl3): ꢀ 7.19–7.27 (m, 3 H), 7.09 (d, J = 1ꢁ5 Hz, 1 H),
7.05 (d, J = 1ꢁ5 Hz, 1 H), 6.74 (s, 1 H), 6.71 (s, 1 H),
6.60 (d, J = 1ꢁ9 Hz, 2 H), 6.54 (d, J = 1ꢁ9 Hz, 1 H),
6.52 (d, J = 2ꢁ3 Hz, 1 H), 5.39 (s, 1 H), 3.84 (s, 6 H),
3.75 (s, 6 H);13C NMR (75 MHz, CDCl3ꢂ: ꢀ 148.7, 147.4,
144.3, 136.7, 129.2, 128.2, 121.4, 112.7, 110.7, 58.79,
55.85; IR (KBr): ꢃmax 3448, 1591, 1460, 1262, 1228, 1026,
743 cm−1; ESI-MS: m/z 387 (M+Na); HRMS Calculated
for C23H24O4Na, 387.1572, Found: 387.1584.
2.7. 2-(Bis(3-Bromo-4-Methoxyphenyl)Methyl)
Naphthalene (3f)
White solid, m.p. 145–146 ꢀC; 1H NMR (500 MHz,
CDCl3ꢂ: ꢀ 7.82–7.72 (m, 4 H), 7.61 (s, 1 H), 7.53
(d, J = 1ꢁ95 Hz, 2 H), 7.44 (t, J = 2ꢁ93 Hz, 2 H), 7.35
(d, J = 8ꢁ80, Hz 1 H), 7.10 (d, J = 8ꢁ80 Hz, 2 H), 6.78
(d, J = 8ꢁ8 Hz, 2 H), 5.87 (s, 1 H), 3.88 (s, 6 H);
13C NMR (75 MHz, CDCl3): ꢀ 155.0, 143.4, 140.0, 132.6,
128.4, 128.1, 128.0, 127.4, 126.4, 126.3, 125.7, 111.7,
111.4, 111.1, 57, 56.2; IR (KBr): ꢃmax 3450, 2922, 2851,
1599, 1493, 1257, 1054, 1020, 786, 679, 1257, 1054, 786,
679 cm−1; ESI-MS: m/z 512 (M)+.
2.3. Bis(4-Methoxyphenyl)(4-Chlorophenyl)
Methane (3b)
1
white solid, m.p. 69–70 ꢀC; H NMR (300 MHz, CDCl3):
ꢀ 7.23 (d, J = 8ꢁ4 Hz, 2 H), 7.05–6.95 (m, 6 H), 6.82
J. Nanosci. Nanotechnol. 15, 6826–6832, 2015
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Friedel-Crafts Alkylation of Arenes Catalyzed by Ion-Exchange Resin Nanoparticles
Reddy et al.
2.8. 1,2-Dimethoxy-4-((3,4-Dimethoxyphenyl)
(4-Nitrophenyl)Methyl) Benzene (3g)
Light yellow color solid m.p. 151–154 ꢀC; 1H NMR
CHO
2
MeO
MeO
Amberlyst-15
60 ºC
OMe
OMe
OMe
OMe
MeO
MeO
(300 MHz, CDCl3): ꢀ 8.12 (d, J = 9ꢁ06 Hz, 2 H), 7.25 (d,
J = 9ꢁ06 Hz, 2 H), 6.75 (d, J = 8ꢁ30 Hz, 2 H), 6.57 (d,
J = 2ꢁ26 Hz, 2 H), 6.50 (d, J = 2ꢁ26 Hz, 2 H), 6.48 (d,
J = 8ꢁ30 Hz, 1 H), 5.47 (s, 1 H), 3.85 (s, 1 H), 3.76 (s,
6 H); 13C NMR (75 MHz, CDCl3ꢂ: ꢀ 151.9, 148.7, 147.6,
146.1, 134.8, 129.8, 123.2, 121.0, 112.2, 110.8, 55.6, 55.4,
IR (KBr): ꢃmax 3405, 2945, 2257, 1592, 1540, 1455, 1268,
998, 698 cm−1; ESI-MS: m/z 412 (M+NH4ꢂ+.
+
1
1
3a
Scheme 1. Preparation of triarylmethane 3a.
5.53 (s, 1 H), 3.79 (s, 6 H); 13C NMR (75 MHz, CDCl3):
ꢀ 158.5, 152.5, 146.5, 134.9, 130.3,130.2, 123.6, 114.1,
55.4, 55.2; IR (KBr): ꢃmax 3399, 2945, 2257, 1540, 1455,
1268, 998, 598 cm−1; ESI-MS: m/z 350 (M+H)+.
2.9. Bis(4-Methoxy-1-Naphthyl)Phenylmethane (3h)
1
White solid, m.p. 97–99 ꢀC; H NMR (300 MHz, CDCl3):
3. RESULTS AND DISCUSSION
ꢀ 8.32 (d, J = 8ꢁ1 Hz, 2 H), 7.89 (d, J = 8ꢁ1 Hz, 2 H),
7.50–7.10 (m, 8 H), 6.79 (d, J = 8ꢁ1 Hz, 2 H), 6.73 (s,
1 H), 6.63 (d, J = 8ꢁ1 Hz, 2 H), 3.95 (s, 6 H); 13C NMR
(75 MHz, CDCl3ꢂ: ꢀ 154.6, 144.2, 132.8, 132.2, 130.0,
128.5, 127.9, 126.8, 126.4, 126.2, 124.9, 124.2, 122.6,
103.2, 55.5, 48.9; IR (KBr): ꢃmax 3399, 2925, 2257, 1650,
1455, 998, 760 cm−1; ESI-MS: m/z 423 (M+Na)+.
In continuation of our efforts to explore the synthetic util-
ity of Amberlyst-15®18, we herein report for the first time,
a metal free approach for the synthesis of triarylmethanes
via the Friedel–Crafts alkylation of electron-rich olefins
with aromatic aldehydes using Amberlyst-15® as a novel
solid acid catalyst. Accordingly, we first attempted the
alkylation of 1,2-dimethoxybenzene (2 mmol, 1) with ben-
zaldehyde (1 mmol, 2) in the presence of Amberlyst-15®
(100 mg). Though the reaction proceeds at room temper-
ature, the desired triarylmethane 3a was obtained only in
20% yield after a long reaction time (6 h). Interestingly,
the yield of 3a was increased from 20 to 90% and the
reaction time was drastically reduced from 6 h to 30 min
2.10. Bis(4-Methoxyphenyl)(p-Tolyl)Methane (3i)
White solid, m.p. 55–56 ꢀC; 1H NMR (300 MHz, CDCl3ꢂ:
ꢀ 7.11–6.97 (m, 8 H), 6.82 (d, J = 8ꢁ4 Hz, 4 H), 5.42
(s, 1 H), 3.78 (s, 6 H), 2.32 (s, 3 H); 13C NMR (75 MHz,
CDCl ): ꢀ 158.0, 141.8, 136.8, 130.4, 129.3, 129.1, 113.7,
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3
55.3, 54.9, 21.1; IR (KBr): ꢃmax 3362, 2929, 1599, 1451,
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ꢀ
when the reaction was performed at 60 C (Scheme 1).
Next, we compared the catalytic efficiency of the
1024, 693, 524 cm−1; ESI-MS: m/z 419 (M+H) .
+
Copyright: American Scientific Publishers
Amberlyst-15® with other solid acids such as KSF clay
and heteropoly acids including unsupported PMA and sil-
ica supported PMA and the results are presented in Table I.
Among the catalysts studied, Amberlyst-15® was found to
give the best results in terms of yields and selectivity.
After optimizing the reaction conditions, various
aldehydes bearing both electron-donating and electron-
withdrawing groups were investigated for the present pro-
tocol. It was found that the reactions proceeded well in
2.11. Bis(4-Methoxyphenyl)Phenylmethane (3j)
White solid, m.p. 99–101 ꢀC; 1H NMR (300 MHz,
CDCl3): ꢀ 7.31–7.14 (m, 3 H), 7.09 (d, J = 7ꢁ2 Hz, 2 H),
7.01 (d, J = 8ꢁ7 Hz, 4 H), 6.81 (d, J = 8ꢁ7 Hz, 4 H),
5.44 (s, 1 H), 3.77 (s, 6 H); 13C NMR (75 MHz, CDCl3ꢂ:
ꢀ 158.1, 144.7, 136.6, 130.4, 129.4, 128.4, 126.3, 113.8,
55.3; IR (KBr): ꢃmax 3448, 1551, 1440, 1252, 1228, 1150,
1026, 743 cm−1; ESI-MS: m/z 315 (M+H)+.
ꢀ
both cases at 60 C, affording the corresponding products
2.12. 6,6((4-Bromophenyl)Methylene)Bis
in good yields (Table II). Notably, a sterically hindered
2-naphthaldehyde also gave the desired product in fairly
good yield (entry f, Table II). Among the solvents such
as benzene, toluene, THF and 1,4-dioxane studied for this
transformation, solvent free condition gave the best results.
Therefore, we decided to utilize solvent free condition
(2,3-Dihydrobenzo[b][1,4]Dioxane) (3k)
Liquid, 1H NMR (300 MHz, CDCl3): ꢀ 7.35 (d, J =
8ꢁ5 Hz, 2 H), 6.95 (d, J = 8ꢁ3 Hz, 2 H), 6.72 (s, 1 H), 6.69
(s, 3 H), 6.52–6.48 (m, 4 H), 5.22 (s, 1 H), 4.20 (s, 8 H);
13C NMR (75 MHz, CDCl3): ꢀ 143.2, 142.0, 136.7, 131.7,
130.9, 122.1, 117.9, 117.0, 64.3, 54.7. IR (KBr): ꢃmax
2923, 1588, 1502, 1286, 1066, 882, 779 cm−1; ESI-
MS: m/z 439 (M+). HRMS calculated for C23H19BrO4
439.3152, Found: 439.3157.
Table I. Efficiency of various acid catalysts in the synthesis of 3a.
Entry
Catalyst
Catalyst Wt (mg) Time (min) Yield (%)a
a
b
c
d
KSF clay
PMA
5% PMA/SiO2
Amberlyst-15
100
100
100
100
20
20
20
20
60
40
58
90
2.13. Bis(4-Methoxyphenyl)(4-Nitrophenyl)
Methane (3l)
White solid, m.p. 45–46 ꢀC; 1H NMR (300 MHz, CDCl3ꢂ:
ꢀ 8.13 (d, J = 8ꢁ7 Hz, 2 H), 7.27 (d, J = 8ꢁ4 Hz, 2 H),
6.98 (d, J = 8ꢁ4 Hz, 4 H), 6.83 (d, J = 8ꢁ7 Hz, 4 H),
Note: aThe reaction was carried out at 60 ꢀC with 1 mmol of benzaldehyde and
2 mmol of 1,2-dimetoxybenzene.
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Reddy et al.
Friedel-Crafts Alkylation of Arenes Catalyzed by Ion-Exchange Resin Nanoparticles
Table II. Amberlsyt-15 promoted synthesis of triarylmethanes via the Friedel-Crafts alkylation.
Entry
a
Aldehyde
Arene
Product
Time (min)
30
Yield (%)
90
CHO
OMe
OMe
OMe
OMe
MeO
MeO
b
40
82
Cl
CHO
OMe
Cl
MeO
OMe
c
25
85
OMe
CHO
OMe
OMe
MeO
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OMe
OMe
OMe
MeO
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Copyright: American Scientific Publishers
d
35
86
Cl
CHO
Cl
Cl
OMe
OMe
MeO
MeO
OMe
OMe
Cl
e
25
80
MeO
OMe
CHO
OMe
OMe
OMe
OMe
MeO
MeO
MeO
OMe
f
35
70
OMe
Br
Br
Br
CHO
OMe
MeO
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Friedel-Crafts Alkylation of Arenes Catalyzed by Ion-Exchange Resin Nanoparticles
Reddy et al.
Table II. Continued.
Entry
g
Aldehyde
Arene
Producta
Time (min)
30
Yield (%)
83
NO2
CHO
OMe
OMe
MeO
MeO
OMe
OMe
O2N
h
40
45
75
85
OMe
MeO
CHO
OMe
i
Me
CHO
Me
OMe
OMe
MeO
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Copyright: American Scientific Publishers
j
35
80
CHO
OMe
OMe
MeO
k
40
85
Br
CHO
O
O
O
O
O
O
Br
l
55
78
NO2
CHO
OMe
NO2
OMe
MeO
Notes. aAll products were characterized by 1 H NMR, 1R and mass spectroscopy. bYield refers to pure products after chromatography.
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Reddy et al.
Friedel-Crafts Alkylation of Arenes Catalyzed by Ion-Exchange Resin Nanoparticles
H
O
..
O
OMe
H
H
H
–H2O
OMe
+
OMe
OMe
OMe
OMe
OMe
OMe
+
..
OMe
H
OMe
OMe
OMe
OMe
OMe
Scheme 2. A plausible reaction pathway.
to perform the Friedel–Crafts reaction of aldehydes with
other aromatic ethers. Among various aromatic ethers, dis-
ubstituted benzene derivatives such as 1,4-benzodioxane,
and 1,2-dimethoxybenzene are much more active than
mono-substituted aromatic ethers (Table II).
Acknowledgments: AVR thanks CSIR, New Delhi
for the award of a fellowship. One of the authors
A. Venkateswarlu thanks Australian Research Council for
the Future Fellowship. The project was also financially
supported by King Saud University, Vice Deanship of Sci-
entific Research Chair.
As seen in Table II, the condensation of aromatic alde-
hydes with electron-rich arenes allows the preparation of
a wide range of triarylmethane derivatives in a single
step process. All the products were characterized and con-
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Copyright: American Scientific Publishers
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repeated cycles using the recovered catalyst, the reaction
of 1,2-dimethoxybenzene with benzaldehyde gave 90, 87
and 85% yields respectively. These results reveal that the
catalyst Amberlyst-15® can be recycled several times with-
out losing much activity. In addition, the catalyst is highly
active, selective, easy to handle, eco-friendly, thermally
robust, non-volatile, and non-explosive for this conversion.
The above results confirm that Amberlyst-15® works effi-
ciently for this transformation. The scope and generality of
this process is illustrated with respect to various aromatic
ethers and aryl aldehydes and the results are presented in
Table II.19
Mechanistically, we assume that arene initially attacks
on activated aldehyde by acidic resin followed by dehydra-
tion to give the quinone intermediate, which subsequently
reacts with another equivalent of arene to give the desired
triarylmethane derivative (Scheme 2).
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4. CONCLUSION
In summary, Amberlyst-15® has proved to be an effi-
cient and reusable solid acid catalyst for the synthesis of
triarylmethanes in high yields with high selectivity. This
method offers significant advantages such as operational
simplicity, low cost and reusability of the catalyst which
make this procedure an attractive strategy for the synthesis
of triarylmethanes.
J. Nanosci. Nanotechnol. 15, 6826–6832, 2015
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Received: 11 August 2014. Accepted: 30 October 2014.
Delivered by Publishing Technology to: Rice University
IP: 117.253.104.110 On: Thu, 10 Dec 2015 07:53:50
Copyright: American Scientific Publishers
6832
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