Simple and convenient synthesis of 1,3,5-triarylbenzenes from ketones

Article abstract of DOI:10.3184/030823407X275946

A new and efficient synthesis of a series of 1,3,5-triarylbenzenes was accomplished in good yields via the triple condensation of aryl methyl ketones promoted by thionyl chloride in anhydrous ethanol. The method is simple and convenient.

Full text of DOI:10.3184/030823407X275946

720 RESEARCH PAPER
DECEMBER, 720–721
JOURNAL OF CHEMICAL RESEARCH 2007
Simple and convenient synthesis of 1,3,5-triarylbenzenes from ketones
Huanan Hua,b,c, Anjiang Zhanga,c,d*, Lisheng Dinga,b, Xinxiang Leia,c and Lixue Zhangc
aChengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China
bGraduate School of Chinese Academy of Sciences, Beijing 100049, China
cCollege of Chemistry and Material Engineering, Wenzhou University, Wenzhou 325027, China
dNingbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315211, China
A new and efficient synthesis of a series of 1,3,5-triarylbenzenes was accomplished in good yields via the triple
condensation of aryl methyl ketones promoted by thionyl chloride in anhydrous ethanol. The method is simple and
convenient.
Keywords: 1,3,5-triarylbenzene, thionyl chloride, aryl methyl ketone
The properties of molecules or molecular complexes with
a high degree of symmetry are of interest in a large number
of research areas.1 1,3,5-Triarylbenzenes are important C3-
symmetrical aromatic compounds and can be converted into a
series of triphenylbenzene-cored dendrimers,2,3 a conducting
polymer and polymers for nonlinear optical applications.4
A simple method yielding these compounds involves the
triple condensation of aryl methyl ketones (1), as shown in
Scheme 1. The reported methods of inducing condensation
involve mainly one of the following catalysts: strong acids,5
aniline and aniline hydrochloride,6 or Lewis acids, such
as lanthanide chlorides,7 tetrachlorosilane,8 aluminium
chloride,9 tin tetrachloride10 and so on. These methods are
both inconvenient and unsuitable for synthesis because they
are very difficult to manipulate, need elevated temperatures or
take a long time.
Ar
SOCl2
Ethanol
2
3 RCOCH3
Ar
Ar
1
Scheme 1 Ar = (a) C6H5; (b) 4-MeC6H4; (c) 4-MeOC6H4;
(d) 4-ClC6H4; (e) 3- ClC6H4; (f) 4-BrC6H4; (g) 3-BrC6H4;
(h) 4-CF3C6H4; (i) 4-NO2C6H4.
by the condensation of the intermediate chalcones with aryl
methyl ketones in moderate to good yields regardless of
whether ketones contained electron-withdrawing or electron-
donating groups. The results are summarised in Table 3.
However, 1,3,5-trinitrophenylbenzene (2i) was not obtained
because the chalcone formed from 4-nitroacetophenone was
insoluble in anhydrous ethanol, and on precipitating from
the reaction mixture, stopped the condensation before the
1,3,5-trinitrophenylbenzenes (2i) was formed.9 On the other
hand, the triple condensation of aryl methyl ketones needs a
reaction time of more than 10 days and gives moderate yields
(50–60%) only using hydrogen chloride as catalyst.9 It may be
concluded that the triple condensation using thionyl chloride
as catalyst is not catalysed by hydrogen chloride, but that
hydrogen chloride produced from thionyl chloride can speed
up the reaction. Further studies on the reaction mechanism
are in progress.
We therefore sought a more efficient and general method to
convert (1) into (2) and now report that the triple condensation
of aryl methyl ketones promoted by thionyl chloride in
anhydrous ethanol at reflux temperature for no more than one
hour afforded good yields of 1,3,5-triarylbenzenes.
Results and discussion
For the investigation of reaction conditions for the triple
condensation of aryl methyl ketones (1) using thionyl chloride
as catalyst in anhydrous ethanol, we chose the synthesis of
1,3,5-triphenylbenzene (2a) as a model reaction. In the
experiments, we first investigated the effect of molar ratios of
acetophenone, anhydrous ethanol and catalyst on the yields at
reflux temperature for 60 min, and found that we could obtain
the best yields under the conditions of n(1a):n(ethanol):
n(SOCl2) = 3:15:5. The results are shown in Table 1.
We also surveyed the effect of reflux time on the yields with
the best molar ratio of reaction reagents and found that we
could obtain the best yields at reflux temperature for 60 min.
The results are given in Table 2.
Experimental
All melting points were determined on an XT-4A apparatus and are
uncorrected. TLC was performed using precoated silica gel GF254
(0.25 mm) and column chromatography was performed using silica
gel (200-300 meshs). H and 13C NMR spectra were measured on a
1
Bruker Advance 300 spectrometer using TMS as internal standard.
1
J-values are given in Hz.For AA'XX' systems in H J* = J23 + J25
The IR spectra were taken on a Bruker Vector 55 spectrometer.
Elemental analyses were carried out with an EA 1112 elemental
analyser. All the reagents used were AR grade.
The reaction mechanism involves the triple condensation
of aryl methyl ketones: firstly, the intermediate chalcones
were synthesised by the double condensation of aryl methyl
ketones, and then 1,3,5-triarylbenzenes were synthesised
Synthesis of 1,3,5-trialkylbenzenes 2a–h: general procedure
Thionyl chloride (1.82 ml, 25 mmol) was added slowly by a syringe
to a stirred solution of (1) (15 mmol) in anhydrous ethanol (4.4 ml,
Table 1 Effect of molar ratio of reaction reagents to catalyst on the yields
n(1a):n(ethanol):n(SOCl2)
Yield/%
3:4:4
37
3:10:4
58
3:14:4
64
3:15:4
72
3:15:5
85
3:15:6
79
Table 2 Effect of reflux time on the yields
Time/min
Yield/%
10
55
30
61
45
79
60
85
90
81
120
75
* Correspondent. E-mail: anjiangzhang@gmail.com
PAPER: 07/4887

JOURNAL OF CHEMICAL RESEARCH 2007 721
TMS) d: 7.73 (s, 3H), 7.57–7.63 (m, 3H), 7.38–7.43 (m, 3H), 7.28–
7.32 (m, 6H). 13C NMR (75 MHz, CDCl3) d: 142.4 (3C), 139.5 (3C),
136.4 (3C), 130.6 (3C), 130.2 (3C), 128.6 (3C), 125.8 (3C), 125.2
(3C). IR (KBr) ν: 3032, 1598, 1564, 1510, 1480, 880, 750 cm-1. Anal.
Calcd. for C24H15Cl3 (409.7): C, 70.35; H, 3.69. Found: C, 70.4; H,
3.75%.
Table 3 Yields of 1, 3, 5-triarylbenzenes from ketones
Entry
Product
Mp/°C
Yield/%a
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
2g
2h
2i
172
179–180
143
85
84
78
1,3,5-Tri(4-bromophenyl)benzene (2f): Light yellowish solid. M.p.
246
82
1
262–263°C (lit.10 263°C). H NMR (300 MHz, CDCl3, 25°C, TMS)
170–171
262–263
167–168
158–159
153
76
d: 7.66 (s, 3H), 7.49 (m, J* = 8.4 Hz, 6H), 7.37 (m, J* = 8.4 Hz, 6H).
13C NMR (75 MHz, CDCl3) d: 137.6 (3C), 135.6 (3C), 132.3 (6C),
128.3 (6C), 125.2 (3C), 124.1 (3C). IR (KBr) ν: 3030, 1592, 1560,
1510, 1470, 860, 755 cm-1. Anal. Calcd. for C24H15Br3 (543.1): C,
53.08; H, 2.78. Found: C, 53.1; H, 2.9%.
81
75
69
Trace
aIsolated yields.
1,3,5-Tri(3-bromophenyl benzene (2g): Light yellowish solid. M.p.
167–168°C. 1H NMR (300 MHz, CDCl3, 25°C, TMS) d: 7.73 (s, 3H),
7.63–7.67 (m, 3H), 7.37–7.43 (m, 6H), 7.25–7.28 (m, 3H). 13C NMR
(75 MHz, CDCl3) d: 137.6 (3C), 135.6 (3C), 132.3 (3C), 130.1 (3C),
128.3 (3C), 127.6 (3C), 125.2 (3C), 124.1 (3C). IR (KBr) ν: 3033,
1589, 1561, 1506, 1465, 880, 750 cm-1. Anal. Calcd. for C24H15Br3
(543.1): C, 53.08; H, 2.78. Found: C, 53.3; H, 2.8%.
1,3,5-Tri(4-trifluoromethylphenyl)benzene (2h): Light yellowish
solid. M.p. 158–159°C. 1H NMR (300 MHz, CDCl3, 25°C, TMS)
d: 7.75–7.83 (m, 15H). 13C NMR (75 MHz, CDCl3) d: 143.9 (3C),
141.4 (3C), 129.8 (q, J = 32.6 Hz, 3C), 127.6 (6C), 126.0 (6C), 125.9
(3C), 124.3 (q, J = 270.6 Hz, 3C). IR (KBr) ν: 3035, 1590, 1566,
1512, 1460, 872, 760 cm-1. Anal. Calcd. for C27H15F9 (510.4): C,
63.54; H, 2.96. Found: C, 63.6; H, 2.9%.
75 mmol). The mixture was stirred for 1 h at reflux temperature and
then neutralised with a saturated sodium carbonate solution. The solid
obtained on cooling was filtered, washed with cold water, ether and
ethanol, and dried under reduced pressure to give the title compound
(2a–h).
1,3,5-Triphenylbenzene (2a): Light yellowish solid. M.p. 171–
172°C (lit.10 172°C). 1H NMR (300 MHz, CDCl3, 25°C, TMS)
d: 7.78 (s, 3H), 7.67–7.71 (m, 6H), 7.44–7.50 (m, 6H), 7.35–7.41 (m,
3H). 13C NMR (75 MHz, CDCl3) d: 142.4 (3C), 141.2 (3C), 128.8
(6C), 127.5 (6C), 127.4 (3C), 125.2 (3C). IR (KBr) ν: 3032, 1595,
1570, 1491, 1460, 1380, 750 cm-1. Anal. Calcd. for C24H18 (306.4):
C, 94.08; H, 5.92. Found: C, 94.12; H, 5.89%.
1,3,5-Tri(4-methylphenyl)benzene (2b): Light yellowish solid.
M.p. 179–180°C (lit.9 178°C). 1H NMR (300 MHz, CDCl3, 25°C,
TMS) d: 7.73 (s, 3H), 7.57–7.61 (m, 6H), 7.25–7.29 (m, 6H), 2.42
(s, 9H). 13C NMR (75 MHz, CDCl3) d: 142.2 (3C), 138.4 (3C), 137.2
(3C), 129.5 (6C), 127.2 (6C), 124.6 (3C), 21.1 (3C). IR (KBr) ν: 3036,
2916, 2862, 1596, 1514, 1466, 1392, 870, 750 cm-1. Anal. Calcd. for
C27H24 (348.5): C, 93.06; H, 6.09. Found: C, 94.1; H, 6.2%.
1,3,5-Tri(4-methoxyphenyl)benzene (2c): Light yellowish solid.
M.p. 143°C (lit.10 143°C). 1H NMR (300 MHz, CDCl3, 25°C, TMS) d:
7.62–7.67 (m, 9H), 7.02 (m, J* = 8.7 Hz, 6H), 3.88 (s, 9H). 13C NMR
(75 MHz, CDCl3) d: 160.9 (3C), 137.6 (3C), 128.9 (3C), 128.4 (6C),
125.2 (3C), 114.6 (6C), 56.0 (3C). IR (KBr) ν: 3035, 2923, 2872,
1596, 1572, 1516, 1465, 1240, 1180, 860, 760 cm-1. Anal. Calcd.for
C27H24O3 (396.5): C, 81.79; H, 6.10. Found: C, 81.8; H, 6.2%.
1,3,5-Tri(4-chlorophenyl)benzene (2d): Light yellowish solid.
Received 15 October 2007; accepted 29 December 2007
Paper 07/4887
doi: 10.3184/030823407X275946
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