Melamine trisulfonic acid: A new efficient catalyst for the synthesis of aryldithienylmethanes

Article abstract of DOI:10.1080/10426507.2011.559496

An efficient method has been developed for the synthesis of dithienylmethanes via bisarylation of aldehydes with thiophene in the presence of melamine trisulfonic acid as a catalyst under solvent-free conditions.

Full text of DOI:10.1080/10426507.2011.559496

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Melamine Trisulfonic Acid: A New
Efficient Catalyst for the Synthesis of
Aryldithienylmethanes
Liqiang Wu a , Yunhui Yan b & Fulin Yan a
a School of Pharmacy, Xinxiang Medical University, Xinxiang, Henan,
China
b School of Basic Medicine, Xinxiang Medical University, Xinxiang,
Henan, China
Published online: 05 Jan 2012.
To cite this article: Liqiang Wu , Yunhui Yan & Fulin Yan (2012) Melamine Trisulfonic Acid: A New
Efficient Catalyst for the Synthesis of Aryldithienylmethanes, Phosphorus, Sulfur, and Silicon and the
Related Elements, 187:2, 149-154, DOI: 10.1080/10426507.2011.559496
To link to this article: http://dx.doi.org/10.1080/10426507.2011.559496
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Phosphorus, Sulfur, and Silicon, 187:149–154, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.559496
MELAMINE TRISULFONIC ACID: A NEW EFFICIENT
CATALYST FOR THE SYNTHESIS OF
ARYLDITHIENYLMETHANES
Liqiang Wu,1 Yunhui Yan,2 and Fulin Yan1
1School of Pharmacy, Xinxiang Medical University, Xinxiang, Henan, China
2School of Basic Medicine, Xinxiang Medical University, Xinxiang, Henan, China
GRAPHICAL ABSTRACT
Abstract An efficient method has been developed for the synthesis of dithienylmethanes via
bisarylation of aldehydes with thiophene in the presence of melamine trisulfonic acid as a
catalyst under solvent-free conditions.
Keywords Dithienylmethanes; melamine trisulfonic acid; solvent-free; thiophene
INTRODUCTION
Dithienylmethanes are widely used as important building blocks for the synthesis
of a variety of functionational porphyrins and porphyrin analogs,1 which can be of wide
interest in materials science.2 Usually, the preparations of dithienylmethanes were carried
out by the reaction of aldehydes with thiophene under catalysis of reagents such as tri-
fluoroacetic acid,1a BF3·Et2O,1a TiCl4,1b and NaHSO4-SiO2.3 However, these approaches
are often hindered by the formation of by-products, high catalyst loading, long reaction
time, and environmental unfriendliness. Thus, a mild, efficient, and green method using an
economical, recoverable catalyst is worth exploring.
Recently, melamine trisulfonic acid (MTSA, Figure 1) has emerged as a promising
solid acid catalyst for acid-catalyzed reactions, such as acetylation of alcohols, phenols,
and amines,4 oxathioacetalyzation of aldehydes,5 methoxymethylation of alcohols,6 and
synthesis of thiocyanohydrins.7 This catalyst is safe, easy tohandle, environmentallybenign,
Received 10 September 2010; accepted 27 January 2011.
We are pleased to acknowledge the financial support from Xinxiang Medical University.
Address correspondence to Liqiang Wu, School of Pharmacy, Xinxiang Medical University, Xinxiang,
Henan 453003, China. E-mail: wliq1974@sohu.com
149

150
L. WU ET AL.
Figure 1
and presents fewer disposal problems than other catalysts. Melamine trisulfonic acid as a
solid acid catalyst was prepared from the reaction of melamine with neat chlorosulfonic
acid at room temperature.4–7
We herein report a simple and environmentally benign methodology for the synthesis
of dithienylmethanes under solvent-free conditions using MTSA as the catalyst (Scheme 1).
Scheme 1
RESULTS AND DISCUSSION
In order to optimize the reaction conditions, we first examined the amount of catalyst
and the reaction temperature. The reaction of benzaldehyde with thiophene to the corre-
sponding 2,2ꢁ-(phenylmethylene)dithiophene was studied under solvent-free conditions in
the presence of MTSA at different temperatures. The results are summarized in Table 1. As
Table 1 The amount of catalyst and the reaction temperature optimization for the synthesis of 2,2ꢁ-
(phenylmethylene)dithiophenea
Entry
MSTA/mol%
Temp./◦C
Time/min
Yield/%b
1
2
3
4
5
6
7
8
9
10
11
12
13
0
5
5
84
r.t.
84
r.t.
30
40
50
60
70
84
70
84
84
90
90
40
90
90
60
60
60
40
40
40
40
40
0
41
71
50
53
62
69
74
80
84
79
83
83
10
10
10
10
10
10
10
15
15
20
aReaction conditions: benzaldehyde (1 mmol); thiophene (10 mmol); neat.
bIsolated yield.

MELAMINE TRISULFONIC ACID
151
Table 2 Synthesis of dithienylmethanes catalyzed by MTSAa
Entry
R
Time/min
Productsb
Yield/%c
mp (L)/◦C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
C6H5
40
30
30
30
30
30
50
60
60
60
90
90
60
60
60
60
90
90
90
90
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
84 (82,80,76)d
70–72 (73–74)3
53–54
4-Cl-C6H4
4-Br-C6H4
4-F-C6H4
86
84
86
85
82
78
75
70
72
65
63
68
70
72
76
60
63
62
59
64–65 (62–64)3
oil
4-NO2-C6H4
3-NO2-C6H4
4-MeO-C6H4
4-Me-C6H4
3-OH-C6H4
4-OH-C6H4
3- MeO-4-OH-C6H3
4- MeO-3-OH-C6H3
3,4-(OCH2O)-C6H3
2-Thienyl
2-furanyl
4-pyridyl
H
CH3
(CH3)2CH
(CH3)3C
85–86 (87–89)3
70–73 (72–74)3
89–91 (88–90)3
102–103
oil (oil)3
oil
61–62 (59–61)3
67–69 (66–68)3
92–94 (94–96)3
48–49 (50–51)3
56–57
101–103
46–473
52–53
oil
3t
oil
aReaction conditions: aldehyde (1 mmol); thiophene (10 mmol); MTSA (0.1 mmol); neat; 84 ◦C.
bAll products except 3b, 3d, 3j, 3p, 3r, 3o, 3s, 3t were identified by comparing their physical and spectral data
with those of the authentic samples (see ref. 3).
cIsolated yield.
dYields after three times of catalyst recovery.
shown in Table 1, the reaction using 10% mmol MTSA at 84 ◦C temperature proceeded to
highest yield.
Encouraged by the results, we investigated a number of other aldehydes to probe their
behavior under the current catalytic conditions. Thus, a range of dithienylmethanes were
synthesized by heating a mixture of the aldehyde, thiophene in the presence of 10 mol%
MTSA at reflux temperature for 30–60 min under solvent-free conditions in 68%–86%
yields. It was demonstrated that the reaction of the aldehydes with electron-withdrawing
groups such as 4-chlorobenzaldehyde, 4-bromobenzaldehyde, 4-nitrobenzaldehyde, and 3-
nitrobenzaldehyde went to completion in 30 min to afford the expected dithienylmethanes in
good yields (entries 2–5). However, the reaction of those aldehydes with electron-donating
groups such as 3-hydroxy-benzaldehyde, piperonal led to lower reaction yields and required
longer time as well (entries 7–8). The results are summarized in Table 2.
The reusability of the catalyst was tested in the synthesis of 2,2ꢁ-(phenylmethylene)
dithiophene. The catalyst was recovered after each run, washed with CH2Cl2, dried in an
oven at 100 ◦C for 30 min prior to use, and tested for its activity in the subsequent run and
fresh catalyst was not added. The catalyst was tested for three runs and the recovery rate of
catalyst was 90% in each run. It was seen that the catalyst displayed very good reusability
(Table 2, entry 1). Under the same conditions, using the fresh catalyst NaHSO4-SiO2, the
yield of the product 2,2ꢁ-(phenylmethylene)dithiophene was 82%, while with the recovered
catalyst, the three subsequent yields were 79%, 76%, and 72%.

152
L. WU ET AL.
Table 3 MTSA-catalyzed synthesis of 2,2ꢁ-(phenylmethylene)dithiophene in comparison with other literature
methods
Entry
Reaction conditions
Time/min Yield/% Reference
1
2
3
4
benzaldehyde: thiophene: MTSA = 1:10:0.1, 84 ◦C, neat
benzaldehyde: thiophene: BF3·Et2O = 1:37:1, r.t., neat
benzaldehyde: thiophene: CF3COOH = 1:37:10, r.t., neat
benzaldehyde: thiophene: NaHSO4-SiO2 = 1:37:0.5, 84 ◦C, neat
40
30
22
84
62
60
82
This work
1a
1a
3
150
In order to assess the capability of the present method with respect to the reported
methods for the preparation of dithienylmethanes from aldehydes and thiophene, the syn-
thesis of compound 3a was compared with the reported methods. It is clear from Table 3
that the present method has high yields, moderate reaction times, simple procedure, and
uses inexpensive and environmentally benign catalysts.
CONCLUSION
In summary, we have established for the first time, a novel, eco-friendly, and simple
protocol for the synthesis of dithienylmethanes using inexpensive MTSA. The short reaction
procedure and reusability of the catalyst make this method one of the most efficient methods
for the synthesis of this class of compounds.
EXPERIMENTAL
NMR spectra were determined on Bruker AV-400 spectrometer at room temperature
using TMS as internal standard, coupling constants (J) were measured in Hz; elemental
analysis was performed by a Vario-III elemental analyzer; mass spectra were taken on
a Macro mass spectrometer (Waters) by electro-spray method (ES); melting points were
determined on a XT-4 binocular microscope and were uncorrected; MTSA was prepared
according to ref. 4; Commercially available reagents were used throughout without further
purification unless otherwise stated.
General Procedure for the Synthesis of Dithienylmethanes
A mixture of aldehyde (1 mmol), thiophene (10 mmol), and MTSA (0.1 mmol)
was heated at reflux for an appropriate time (TLC). After the completion of the reaction,
excess thiophene was evaporated, and CH2Cl2 (10 mL) was added. The mixture was
filtered, CH2Cl2 was evaporated, and the crude product was purified by silica gel column
chromatography using ethyl acetate and hexane (1:10) as eluent to afford the pure product.
The spectroscopic data for the new products are given below.
2,2ꢀ-((4-Chlorophenyl)Methylene)Dithiophene (3b)
1H NMR (400 MHz, CDCl3): δ 7.40–7.18 (m, 6H), 6.97–6.60 (m, 4H), 5.79 (s, 1H)
ppm; 13C NMR (100 MHz, CDCl3): δ 145.2, 141.9, 132.2, 130.5, 125.9, 125.2, 123.6,
120.6, 44.1 ppm; MS (ESI): m/z 292 [M+H]+; Anal. calcd for C15H11ClS2: C 61.95, H
3.81, S 22.05%; found: C 62.06, H 3.75, S 21.98%.

MELAMINE TRISULFONIC ACID
153
2,2ꢀ-((4-Fluorophenyl)Methylene)Dithiophene (3d)
1H NMR (400 MHz, CDCl3): δ 7.48–7.20 (m, 6H), 6.95 (dd, 2H, J = 3.2, 4.8 Hz),
6.90 (d, 2H, J = 3.2 Hz), 5.84 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3): δ 146.9, 142.8,
132.6, 131.0, 126.2, 125.9, 124.9, 121.0, 42.8 ppm; MS (ESI): m/z 275 [M+H]+; Anal.
calcd for C15H11FS2: C 65.66, H 4.04, S 23.07%; found: C 65.80, H 4.09, S 23.10%.
4-(Di(Thiophen-2-yl)Methyl)Phenol (3j)
1H NMR (400 MHz, CDCl3): δ 7.26 (d, 2H, J = 4.8 Hz), 7.12 (d, 2H, J = 8.0 Hz),
6.92 (dd, 2H, J = 3.2, 5.2 Hz), 6.88 (d, 2H, J = 3.2 Hz), 6.70 (d, 2H, J = 8.0 Hz), 5.76 (s,
1H), 5.52 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3): δ 152.9, 141.5, 131.2, 130.8, 128.2,
127.9, 126.8, 125.6, 52.6 ppm; MS (ESI): m/z 273 [M+H]+; Anal. calcd for C15H12OS2:
C 66.14, H 4.44, S 23.54%; found: C 66.02, H 4.48, S 23.48%.
2-(Di(Thiophen-2-yl)Methyl)Furan (3o)
1H NMR (400 MHz, CDCl3): δ 7.36 (dd, 1H, J = 2.0, 5.2 Hz), 7.26 (dd, 2H, J = 1.6
Hz, J = 4.8 Hz), 7.01–6.97 (m, 4H), 6.45–6.18 (m, 2H), 5.78 (s, 1H), 5.52 (s, 1H) ppm;
13C NMR (100 MHz, CDCl3): δ 152.2, 143.2, 138.5, 127.9, 127.0, 125.8, 110.8, 107.1,
50.2 ppm; MS (ESI): m/z 247 [M+H]+; Anal. calcd for C13H10OS2: C 63.38, H 4.09, S
26.03%; found: C 63.42, H 4.15, S 26.10%.
4-(Di(Thiophen-2-yl)Methyl)Pyridine (3p)
1H NMR (400 MHz, CDCl3): δ 8.22 (d, 2H, J = 8.4 Hz),7.50 (d, 2H, J = 8.8 Hz),
7.26 (d, 2H, J = 4.2 Hz), 6.96 (dd, 2H, J = 3.2, 4.8 Hz), 6.88 (d, 2H, J = 3.2 Hz), 5.87 (s,
1H) ppm; 13C NMR (100 MHz, CDCl3): δ 150.1, 145.9, 140.2, 126.9, 126.5, 125.2, 123.8,
49.9 ppm; MS (ESI): m/z 258 [M+H]+; Anal. calcd for C14H11NS2: C 65.33, H 4.31, N
5.44, S 24.92%; found: C 65.28, H 4.40, N 5.44, S 25.04%.
2,2ꢀ-(Ethane-1,1-diyl)Dithiophene (3r)
1H NMR (400 MHz, CDCl3): δ 7.22 (d, 2H, J = 5.2 Hz), 6.96 (dd, 2H, J = 3.6, 5.2
Hz), 6.89 (d, 2H, J = 3.6 Hz), 4.48 (d, 1H, J = 6.8 Hz), 1.42 (d, 3H, J = 6.8 Hz) ppm; 13C
NMR (100 MHz, CDCl3): δ 144.2, 126.9, 125.2, 123.7, 46.9, 32.9 ppm; MS (ESI): m/z 195
[M+H]+; Anal. calcd for C10H10S2: C 61.81, H 5.19, S 33.00%; found: C 61.82, H 5.25,
S 33.12%.
2,2ꢀ-(2-Methylpropane-1,1-diyl)Dithiophene (3s)
1H NMR (400 MHz, CDCl3): δ 7.20 (d, 2H, J = 5.2 Hz), 6.97 (dd, 2H, J = 3.6, 4.8
Hz), 6.92 (d, 2H, J = 4.0 Hz), 4.45 (m, 1H), 2.63 (d, 1H, J = 7.2 Hz), 1.01 (d, 6H, J =
7.2 Hz) ppm; 13C NMR (100 MHz, CDCl3): δ 143.5, 126.4, 125.6, 122.9, 48.2, 35.5, 21.8
ppm; MS (ESI): m/z 223 [M+H]+; Anal. calcd for C12H14S2: C 64.81, H 6.35, S 28.84%;
found: C 64.92, H 6.30, S 28.65%,

154
L. WU ET AL.
2,2ꢀ-(2,2-Dimethylpropane-1,1-diyl)Dithiophene (3t)
1H NMR (400 MHz, CDCl3): δ 7.24 (d, 2H, J = 4.8 Hz), 6.96 (dd, 2H, J = 3.2,
4.8 Hz), 6.90 (d, 2H, J = 3.6 Hz), 4.39 (s, 1H), 0.99 (s, 9H) ppm; 13C NMR (100 MHz,
CDCl3): δ 143.8, 126.0, 125.2, 123.4, 52.6, 35.6, 28.8 ppm; MS (ESI): m/z 237 [M+H]+;
Anal. calcd for C13H16S2: C 66.05, H 6.82, S 27.13%; found: C 66.20, H 6.70, S 27.10%.
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