Synthesis and luminescence-structure relationship of 2,4,5-triarylimidazoles

Article abstract of DOI:10.14233/ajchem.2014.16368

2,4,5-Triarylimidazoles were efficiently synthesized with excellent yields (90-96%) via the one-pot concentration of benzil, aromatic aldehyde and ammonium acetate in ionic liquid [BMIM][BF₄] in the present of acetic acid. The luminescence-structure relationship of products was investigated.

Full text of DOI:10.14233/ajchem.2014.16368

Asian Journal of Chemistry; Vol. 26, No. 19 (2014), 6328-6330
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16368
Synthesis and Luminescence-Structure Relationship of 2,4,5-Triarylimidazoles
1
2
1
1
1
1
SHU-NING YUE , YU WAN , LING YE , WEN-LI ZHANG , HAO CUI , LI-ZHUO ZHANG ,
1
1
1
1
2
1,2,*
QIU-JU ZHOU , HUAN ZOU , ZHEN-TAO LIU , LING-LING ZHAO , SHENG-LIANG ZHOU and HUI WU
1School of Chemistry and Chemical Engineering, Jiangsu Normal University, Jiangsu Key Laboratory of Green Synthesis of Functional
Material, Xuzhou 221116, P.R. China
2Jiangsu Key Laboratory of Biotechnology on Medical Plant, Xuzhou 221116, P.R. China
*Corresponding author: Fax: +86 516 83500164; Tel: +86 516 83403163; E-mail: wuhui72@126.com
Received: 13 September 2013;
Accepted: 15 February 2014;
Published online: 16 September 2014;
AJC-15911
2,4,5-Triarylimidazoles were efficiently synthesized with excellent yields (90-96 %) via the one-pot concentration of benzil, aromatic
aldehyde and ammonium acetate in ionic liquid [BMIM][BF4] in the present of acetic acid. The luminescence-structure relationship of
products was investigated.
Keywords: Synthesis, Luminescence-structure relationship, 2,4,5-Triarylimidazoles.
temperatures created by microwave irradiation at 180-200 °C.
Therefore, the development of a mild and efficient way for
synthesis of this valuable heterocycle to overcome previous
shortcomings is still a serious challenge.
INTRODUCTION
The imidazole core is a fertile source of biologically
important molecules. Compounds containing imidazole moiety
have many pharmacological properties and play important
roles in biochemical processes. They act as potent and selective
inhibitors of p38 MAP kinase1, B-Raf kinase2, cyclooxygenase-
2 (COX-2)3 and biosynthesis of interleukin-1 (IL-1)4. Many
of the substituted imidazoles are known as antibacterial5,
antitumor agents6 and also as pesticides7. In addition, 2,4,5-
triaryl substituted imidazoles possess non-coplanar structure,
which is beneficial to retard aggregation8. So the arylated
imidazoles not only show the above-mentioned traits but also
act as an emitting chromophore in a molecular design which
will be beneficial for favorable properties such as emission
color purity, photoluminescence quantum yield and thermal
stability9.
Recently, ionic liquids (ILs) have attracted much attention
as promising alternative 'green' solvents to hazardous traditional
organic solvents, due to their properties such as non-flammability,
negligible vapour pressure, high thermal stability, solvating
ability and easy recyclability15. We now report a simple, environ-
ment-friendly and efficient method one-pot synthesis of 2,4,5-
triarylimidazoles in excellent yields in ionic liquid [BMIM][BF4]
in the present of acetic acid. The luminescence-structure relation-
ship of products was investigated in detail via ultraviolet absor-
ption and fluorescence spectra.
EXPERIMENTAL
All melting points are uncorrected and were measured on
XT5 melting point apparatus. The NMR spectra were run on a
Bruker Avance DMX 400 spectrometer in DMSO-d6 using
TMS as internal standard. Fluorescence spectrum was reported
on F-4500 Fluorescence Spectrophotometer (Hitachi, Japan).
The IR spectra were obtained in potassium bromide pellets
with a Bruker 27FTIR-Tensor using KBr optics. The ultraviolet
absorption spectrum was measured with a Tu-1201 ultraviolet
spectrophotometer (Shimadzu). All reagents were obtained
from commercial suppliers and used without further purifi-
cation.
Therefore, numerous methods have been flourished for
the preparation of 2,4,5-trisubstituted imidazoles such as the
hetero-cope rearrangement10, four-component condensation of
arylglyoxals, primary amines, carboxylic acids and isocyanides
on Wang resin11. Recently, the synthesis of 2,4,5-trisubstituted
imidazoles has been catalyzed by ZrCl412, ionic liquid13, silica
gel or Zeolite HY14 and also by microwave irradiation using
acetic acid as promotor. However, most of these methods
suffered from one or more drawbacks, such as complex work-
up and purification, significant amounts of waste materials,
occurrence of side reactions, low yields and the use of expen-
sive reagents. Additionally, many of them required elevated
Synthesis of 2,4,5-triarylimidazoles (Scheme-I): The
mixture of aromatic aldehyde 1 (1 mmol), benzil 2 (1 mmol),

Vol. 26, No. 19 (2014)
Synthesis and Luminescence-Structure Relationship of 2,4,5-Triarylimidazoles 6329
O
O
N
CHO
AcOH, [BMIM][BF4 ]
+
NH OAc
4
R
+
N
H
R
10 0°C, 3-4 h
1
3
4
2
Scheme-I: Synthesis of 2,4,5-triarylimidazoles
ammonium acetate (NH4OAc) 3 (5 mmol), acetic acid (3 mL)
and ionic liquid [BMIM][BF4] (1 mL) was stirred at 100 °C
for 3-4 h.At the end of reaction (monitored by TLC), the mixture
was diluted with water (15-20 mL). The crude solid was filtered
and washed with water and then recrystallized with 95 % EtOH
to provide the pure products 4 (Table-1).
NMR (400 MHz, DMSO-d6) (δ, ppm): 7.21-7.49 (14H, m,
Ar-H), 13.26 (1H, s, N-H).
4-(4,5-Diphenyl-1H-imidazol-2-yl)benzonitrile (4c):
m.p. 264-266 ºC; IR (KBr, νmax, cm-1): 3295, 2245, 1650, 1600;
1H NMR (400 MHz, DMSO-d6) (δ, ppm): 7.16-7.75 (14H, m,
Ar-H), 12.81 (1H, s, N-H).
2-(2-Bromophenyl)-4,5-diphenyl-1H-imidazole (4d):
m.p. 196-198 ºC; IR (KBr, νmax, cm-1): 3395, 1630, 1615; 1H
NMR (400 MHz, DMSO-d6) (δ, ppm): 7.06-7.58 (14H, m,
Ar-H), 12.91 (1H, s, N-H).
TABLE-1
SYNTHESIS OF 2,4,5-TRIARYLIMIDAZOLES 4a
Comp.
4a
R
2-NO2-3-Cl
4-Cl
Time (h) Yield (%)
m.p. ( oC)
3
94
275-277
2-(2-Methoxyphenyl)-4,5-diphenyl-1H-imidazole (4e):
m.p. 203-205 ºC; IR (KBr, νmax, cm-1): 3300, 1650, 1600, 1250;
1H NMR (400 MHz, DMSO-d6) (δ, ppm): 6.16-7.65 (14H, m,
Ar-H), 3.62 (3H, s, OCH3), 12.88 (1H, s, N-H).
3.5
3.5
3.5
3
96(9516)
95(8416)
96(7117)
92(9318)
90(9819)
94(8518)
92(9320)
260-261(262-26316)
264-266(259-26116)
196-198(201-20217)
203-205(208-21018)
231-232(233-23419)
290-292(292-29418)
204-206(20520)
4b
4-CN
4c
2-Br
4d
2-OCH3
2,4-(OCH3)2
3-Br
4e
2-(2,4-Dimethoxyphenyl)-4,5-diphenyl-1H-imidazole
(4f): m.p. 231-232 ºC; IR (KBr, νmax, cm-1): 3340, 1625, 1210;
1H NMR (400 MHz, DMSO-d6) (δ, ppm): 6.68-7.48 (13H, m,
Ar-H), 3.75 (6H, s, OCH3), 12.69 (1H, s, N-H).
3.5
3.5
4
4f
4g
2-OH
4h
aReaction condition: aromatic aldehyde (1 mmol), benzil (1 mmol),
ammonium acetate (5 mmol) and acetic acid (3 mL) in [BMIM][BF4]
(1 mL) at 100 oC
2-(3-Bromophenyl)-4,5-diphenyl-1H-imidazole (4g):
m.p. 290-292 ºC; IR (KBr, νmax, cm-1): 3345, 1640, 1590; 1H
NMR (400 MHz, DMSO-d6) (δ, ppm): 7.21-7.65 (14H, m,
Ar-H), 13.11 (1H, s, N-H).
General process of luminescence determination: The
CHCl3 solution of product 4a-4h (1 × 10-6 mol/L) were
measured on ultraviolet and fluorescence spectrophotometer
to give their absorption and emission spectra, respectively
(Table-2).
2-(4,5-Diphenyl-1H-imidazol-2-yl)phenol (4h): m.p.
204-206 ºC; IR (KBr, νmax, cm-1): 3610, 3465, 1690, 1600; 1H
NMR (400 MHz, DMSO-d6) (δ, ppm): 6.68-7.54 (14H, m,
Ar-H), 8.21 (1H, s, O-H), 12.91 (1H, s, N-H).
TABLE-2
LUMINESCENCE OF PRODUCTS
RESULTS AND DISCUSSION
In this paper, it was found that the electronic nature and
steric effect of substituted group in aromatic aldehyde have
slight effect on this reaction. The luminescence properties of
products were shown in Table-2. From Table-2, we can clearly
see that: (1) Compared with the fluorescence emission of
quinine sulfate (in 0.05 mol/L of sulfate acid aqueous solution)
at 385 nm, the emission of 4a and 4c moved to 403 and 444
nm, respectively, the blue-shifted λmax (ex) of them means that
they can emit stronger fluorescence than quinine sulfate. (2)
The electro and steric effect of substituted group on aromatic
aldehydes have large influence on the fluorescence properties.
It seems that electron-donoring group in any position is not
the favourable group which give poor fluorescence quantum
yield (4e, 4f, 4h). The possible reason is that the two phenyls
in 4- and 5- position are strong electron-donoring group, if
another electron-donoring one is introduced into the imidazole
ring, the molecule can not act as a classic D-π-A molecule to
display strong fluorescence. (3) Besides 4b, other products
with electron-withdrawing group (4a, 4c, 4d, 4g) exhibited
stronger fluorescence with more than half fluorescence
λex
(nm)
256
333
345
308
312
λem
(nm)
Φsa
Product
R
Stokes (nm) RFI
2-NO2-3-Cl
4-Cl
403
379
444
387
380
393
379
302
147
46
99
79
68
82
67
23
8
0.32
4a
4b
4c
4d
4e
4f
2316 0.03
565 0.45
396 0.30
308 0.21
376 0.11
1518 0.35
102 0.20
4-CN
2-Br
2-OCH3
2,4-(OCH3)2 311
3-Br
312
4g
2-OH
279
4h
aThe fluorescence quantum yields (Φ) were measured in CHCl3 using
quinine sulfate in 0.05 mol/L of sulfate acid aqueous solution (Φ =
0.55) as standard, Φs = (Φr × Fs × As)/(Fr × Ar)
Spectral data for compounds
2-(3-Chloro-2-nitrophenyl)-4,5-diphenyl-1H-
imidazole (4a): m.p. 275-277 ºC; IR (KBr, νmax, cm-1): 3330,
1575, 1680, 1600; 1H NMR (400 MHz, DMSO-d6) (δ, ppm):
7.12-8.19 (13H, m, Ar-H), 12.95 (1H, s, N-H).
2-(4-Chlorophenyl)-4,5-diphenyl-1H-imidazole (4b):
m.p. 260-261 ºC; IR (KBr, νmax, cm-1): 3315, 1650, 1610; 1H

6330 Yue et al.
Asian J. Chem.
3. J.H.M. Lange, H.H. van Stuivenberg, H.K.A.C. Coolen, T.J.P. Adolfs,
A.C. McCreary, H.G. Keizer, H.C. Wals, W. Veerman, A.J.M. Borst,
W. de Looff, P.C. Verveer and C.G. Kruse, J. Med. Chem., 48, 1823
(2005).
quantum yield of quinine sulfate (Φr = 0.55, CHCl3), which
showed their potential application as new fluorescent probe
or luminescence material.
4. T.F. Gallagher, S.M. Fier-Thompson, R.S. Garigipati, M.E. Sorenson,
J.M. Smietana, D. Lee, P.E. Bender, J.C. Lee, J.T. Laydon, D.E.
Griswold, M.C. Chabot-Fletcher, J.J. Breton and J.L. Adams, Bioorg.
Med. Chem. Lett., 5, 1171 (1995).
Conclusion
In summary, this new protocol provides an environmen-
tally benign route along with the associated advantages of
simplicity of operation and higher atomic efficiency. So, we
hope our efforts can provide some supports for the synthesis
of substituted imidazoles and give some supplements for the
applied range of ionic liquid [BMIM][BF4]. The investigation
of products' luminescence-structure relationship indicated that
if we wish to develop 2-aryl-4,5-diphenylimidazoles as lumine-
scence material, introduce electron-donoring group in 4'-
position of 2-aryl in imidazole ring is the reasonable choice.
5. M.Antolini, A. Bozzoli, C. Ghiron, G. Kennedy, T. Rossi andA. Ursini,
Bioorg. Med. Chem. Lett., 9, 1023 (1999).
6. L. Wang, K.W. Woods, Q. Li, K.J. Barr, R.W. McCroskey, S.M.
Hannick, L. Gherke, R.B. Credo, Y.-H. Hui, K. Marsh, R. Warner, J.Y.
Lee, N. Zielinski-Mozng, D. Frost, S.H. Rosenberg and H.L. Sham, J.
Med. Chem., 45, 1697 (2002).
7. T. Maier, R. Schmierer, K. Bauer, H. Bieringer, H. Buerstell and B.
Sachse, US Patent 4820335 (1989).
8. W.L. Pan, H.B. Tan, Y. Chen, D.H. Mu, H.B. Liu, Y.Q. Wan and H.C.
Song, Dyes Pigments, 76, 17 (2008).
9. (a) L. Zhao, S.B. Li, G.A. Wen, B. Peng and W. Huang, Mater. Chem.
Phys., 100, 460 (2006); (b) Q. Peng, G. Fu and D. Su, Synth. Met.,
160, 1672 (2010).
ACKNOWLEDGEMENTS
10. I. Lantos, W.Y. Zhang, X. Shui and D.S. Eggleston, J. Org. Chem., 58,
7092 (1993).
The authors are grateful to the foundation of the National
Natural Sciences Foundation of China (No. 31300067), Major
Project of Natural Science Research of University in Jiangsu
(No. 14KJA430003), Natural Sciences Foundation of Jiangsu
Normal University (No. 13XLA01, 13XLA03, CXLX13_972,
2013YYB121, 2014YYB023, 2014YYB024, 2014YYB028)
for financial support.
11. C. Zhang, E.J. Moran, T.F. Woiwode, K.M. Short and A.M.M. Mjalli,
Tetrahedron Lett., 37, 751 (1996).
12. G.V. Sharma, Y. Jyothi and P.S. Lakshmi, Synth. Commun., 36, 2991
(2006).
13. S.A. Siddiqui, U.C. Narkhede, S.S. Palimkar, T. Daniel, R.J. Lahoti
and K.V. Srinivasan, Tetrahedron, 61, 3539 (2005).
14. S. Balalaie and A. Arabanian, Green Chem., 2, 274 (2000).
15. (a) T. Welton, Chem. Rev., 99, 2071 (1999); (b) P. Wasserscheid and W.
Keim, Angew. Chem. Int. Ed. Engl., 39, 3772 (2000).
16. B. Das, J. Kashanna, R.A. Kumar and P. Jangili, Monatsh. Chem., 144,
223 (2013).
REFERENCES
1. J.C. Lee, J.T. Laydon, P.C. McDonnell, T.F. Gallagher, S. Kumar, D.
Green, D. McNulty, M.J. Blumenthal, J.R. Keys, S.W. Land vatter,
J.E. Strickler, M.M. McLaughlin, I.R. Siemens, S.M. Fisher, G.P. Livi,
J.R. White, J.L. Adams and P.R. Young, Nature, 372, 739 (1994).
2. A.K. Takle, M.J.B. Brown, S. Davies, D.K. Dean, G. Francis, A. Gaiba,
A.W. Hird, F.D. King, P.J. Lovell,A. Naylor, A.D. Reith, J.G. Steadman
and D.M. Wilson, Bioorg. Med. Chem. Lett., 16, 378 (2006).
17. H. Zang, Q.H. Su,Y. Mo, B.-W. Cheng and S. Jun, Ultrason. Sonochem.,
17, 749 (2010).
18. S.F. Hojati, S.A. Nezhadhoseiny and Z. Beykzadeh, Monatsh. Chem.,
144, 387 (2013).
19. D. Nagargoje, P. Mandhane, S. Shingote, P. Badadhe and C. Gill,
Ultrason. Sonochem., 19, 94 (2012).
20. P.A. Clarke, M. Grist, M. Ebden, C. Wilson and A.J. Blake, Tetrahedron,
61, 353 (2005).