Synthesis and fluorescence properties of 5,7-diphenylquinoline and 2,5,7-triphenylquinoline derived from m-terphenylamine

Article abstract of DOI:10.3390/12050988

Synthesis of 5,7-phenylquinoline from the Skraup reaction of m-terphenylamine and glycerol in the presence of acid is reported. Further reaction of 5,7-diphenylquinoline with phenyl lithium prepared in situ led to the formation of 2,5,7-triphenylquinoline

Full text of DOI:10.3390/12050988

Molecules 2007, 12, 988-996
molecules
ISSN 1420-3049
http://www.mdpi.org
Full Paper
Synthesis and Fluorescence Properties of 5,7-Diphenylquinoline
and 2,5,7-Triphenylquinoline Derived from m-Terphenylamine
Shujian Qi, Kehui Shi, Hongyin Gao, Qiancai Liu * and Hong Wang
Department of Chemistry and Institute of Medicinal Chemistry, East China Normal University, 3663
Zhongshan Rd (N), Shanghai 200062, P. R. China
* Author to whom correspondence should be addressed; E-mail: qcliu@chem.ecnu.edu.cn; Phone:
(+86)-21-62233490; Fax: (+86)-21-62232414
Received: 8 February 2007; in revised form: 10 May 2007 / Accepted: 10 May 2007 / Published: 12
May 2007
Abstract: Synthesis of 5,7-phenylquinoline from the Skraup reaction of m-terphenyl-
amine and glycerol in the presence of acid is reported. Further reaction of 5,7-diphenyl-
quinoline with phenyl lithium prepared in situ led to the formation of 2,5,7-triphenyl-
quinoline. All of the products and their intermediates were characterized and the UV-Vis
and photo-luminescence (PL) spectra of m-terphenylamine, 5,7-diphenylquinoline and
2,5,7-triphenylquinoline are also reported.
Keywords: Synthesis, m-terphenylamine, Skraup reaction, 5,7-diphenylquinoline, 2,5,7-
triphenylquinoline.
Introduction
The exploitation of functional heterocyclic molecules is worthwhile due to their unique biological
properties in drug evaluation and possible utilization in organic electroluminescent diodes (OLEDs)
when coordinated with transition metal centers to form the corresponding organometallic compounds.
As the research into and development of OLEDs has advanced, more and more international
companies, for example: Philips, Siemens, Pioneer, Toyota, NEC, Kodak, HP, IBM, DuPont, Dow
Chemical, Samsung, Sanyo and so on, have paid considerable attention to this topic. Luminescent
materials include small organic molecules, organometallic compounds and polymers. Most of them are

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heterocyclic compounds and polymers containing heterocycles. 8-Hydroxyquinoline aluminum (Alq3)
[1] and poly-p-phenylacelylene (PPV) [2] are universal OLED materials. Quinoline, isoquinoline and
their derivatives are among the most important heterocyclic precursors [3]. For example Almq3 [tris(4-
methyl-8-quinolinolato)aluminum(III)] [4] and Zn(BTZ)2 [bis(2-(2-hydroxyphenyl)benzothiazole)-
zinc(II)] [5] are both excellent luminescent materials and good electron transmission materials formed
from quinoline derivatives coordinated with the metals Al and Zn, respectively. The synthesis of
quinolines and their derivatives has been of considerable interest to organic and medicinal chemists for
many years as a large number of natural products [6] and drugs [7] contain this heterocyclic nucleus,
e.g. 6-aminochrysene, discovered simultaneously in 1890 by Abegg [8] and Bamberger and Burgdorf
[9], which has recently acquired importance as a chemical inhibitor of the growth of spontaneous
adenocarcinoma of the breast. Acetylcholinesterase is the target of drugs that inhibit the hydrolysis of
acetylcholine and alleviate the cholinergic deficit associated with Alzheimer’s disease [10]. The
classical methods for quinoline synthesis involve Skraup’s procedure and the Doebner-Von Miller
synthesis. The mechanism of these procedures and the synthesis of numerous quinoline derivatives
have been studied in many papers [11]. In order to explore their synthetic utility and application, we
considered exploiting the functionality of m-terphenylamine as a precursor for the synthesis of
functional quinoline derivatives for further utilization, both in medicinal applications and optical-
electric devices, and we report herein the synthesis and properties of m-terphenylamine, 5,7-diphenyl-
quinoline and 2,5,7-triphenylquinoline.
Results and Discussion
Current research has focused on new synthetic routes to quinoline derivatives by multiple synthetic
methods starting from simple starting materials such as acetophenone and benzaldehyde. To prepare
the target molecule, m-terphenylamine was synthesized following a literature report [12]. Further
reaction of 5,7-diphenylquinoline with phenyl lithium prepared in situ, adopting a literature method
used for the synthesis of 2-substituted derivatives of 8-hydroxyquinoline compounds, led to the
formation of 2,5,7-triphenylquinoline [13] (Scheme 1).
Scheme 1.
O
O
O
O
COOEt
heat
O
O
OEt
Ph
aq. NaOH
Ph
PhCHO
+
EtONa
2
3
4
1
HO
NH2
N
AcCl/Ac2O
Py
Glycerol
PhNO2
PhLi
H2NOH.HCl
N
N
5
8
6
7

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990
Padmavathi et al. reported synthesis of diphenylquinoline or diphenyltetrahydroquinoline
derivatives from the o-allyl ethers of diarylcyclohexenone and diarylcyclohexanone by sigmatropic
rearrangement and cyclization [14], while Dufour et al. reported preparation of a series of
carcinogenic nitrogen compounds such as 2,7-, 4,7-disubstituted or 2,4,7-trisubstitued quinoline
derivatives by the Bayer-Combes reactions or the Doebner reaction of 3-aminobiphenyl [15]. The key
intermediates 6-carbethoxy-3,5-diphenylcyclohex-2-en-1-one (3) and 3,5-diphenylcyclohex-2-en-1-
one (4) were used as effective synthons by Padmavathi et al. for synthesis of a range of heterocyclic
derivatives [14b].
The intermediate 2 can also be prepared by using another method [16]. As for intermediate 4, it
was found that this product could be prepared in fairly good yield under either acidic or basic
conditions. When compound 3 was added to an aqueous solution of sodium hydroxide and the mixture
was subsequently refluxed for 3 hours to ensure completion of the reaction (as monitored by TLC) 4
could be obtained in 90% yield after workup and recrystallization from ethanol [17]. Alternative
attempts were initially conducted under basic reaction conditions (e.g. in aqueous alcoholic KOH
solution), and the resulting solution was refluxed overnight, then acidified by addition of 33 % sulfuric
acid to pH = 7 and refluxed for a further 90 minutes. After workup and recrystallization, product 4 was
obtained in 78% yield [18].
The Skraup reaction from 6 to 7 is usually vigorous and sometimes violent, as described by Clarke
and Davis in Organic Syntheses: “In the Skraup synthesis of quinoline, the principal difficulty has
always been the violence with which the reaction generally takes place; it occasionally proceeds
relatively smoothly, but in the majority of cases gets beyond control” [19a]. Experiments proved that
the violence of the ordinary Skraup reaction is due to the sudden liberation of acrolein, resulting from
the action of sulfuric acid upon the glycerol. In our case, we have succeeded in avoiding this problem
by the addition of acetic acid to dilute the reaction mixture [19b]. The acetic acid was introduced in an
effort to form a glycerol mono- or di-acetate and thereby remove a large proportion of the glycerol
from the reaction sphere. Additionally, it is surprising to find that not many side products were formed
when nitrobenzene was used as solvent and oxidant for preparation of quinolines from different
terphenylamines while the corresponding nitroarenes should be used as solvents and oxidants in
general. The decreased reaction yield might be due to product losses during decolorization in ethanol
over activated charcoal. Expected pure crystalline 5,7-diphenylquinoline was obtained in each run in
better than 35% yield. The violent reaction could be avoided and the toxicity of acrolein could also be
avoided. Efforts were also made to synthesize the title compounds using the Doebner-Miller synthesis
in a two-phase solvent system [20]. Good yields are obtained by this method (the isolated yield was
more than 50%) and the isolation is also easier, but in view of the toxicity and problems of acrolein
and from a scale-up point of view, the Skraup reaction was preferred and studied in detail. Certainly,
many other novel methods have been reported in synthesizing quinolines and their derivatives in good
yield. For instance, Bose and others reported preparations of quinoline and dihydroquinoline
derivatives under solvent-free conditions promoted with microwaves [21] or in the presence of metal
halides [11b].
The preparation of the final product 2,5,7-triphenylquinoline was initially conducted in ethyl ether
by adopting literature method as described for substituted 8-hydroxyquinolines [13]. Poor yields
resulted in several attempts, which might be due to the poor solubility of 5,7-diphenylquinoline in

Molecules 2007, 12
991
ethyl ether. Better results could be obtained when a mixture of solvents was used (phenyl lithium was
prepared in Et2O while the 5,7-diphenylquinoline was dissolved in THF), although there were still
some by-products and yield was still low. Further attempts give better results (ca. 35% yield) when
THF was used as the only solvent.
In order to study the properties of m-terphenylamine, 5,7-diphenylquinoline and 2,5,7-triphenyl
quinoline, a preliminary investigation of their UV-Vis and photoluminescence (PL) spectra recorded
for solutions of these compounds in CH2Cl2 (concentration: 2.5×10-5 mol/L) was undertaken. The
results are shown in Figures 1-4. The UV-Vis spectra of 5,7-diphenylquinoline showed three
absorptions at 210, 255 and 335 nm; whereas that of 2,5,7-triphenylquinoline showed three bands at
210, 275 and 350 nm, which are comparable to those of m-terphenylamine at 210, 250 and 320 nm,
respectively. One can see that the absorptions shift from 255 nm to 275 nm as the result of red shift
resulting from the increased conjugation.
Figure 1. The UV-Vis spectra of m-terphenylamine.
5
4
3
2
m-terphenylamine
1
0
300
400
500
Wavelength(nm)
Figure 2. The UV-Vis spectra of 5,7-diphenylquinoline and 2,5,7-triphenylquinoline.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
5,7-diphenylquinoline
2,5,7-triphenylquinoline
300
400
500
Wavelength(nm)

Molecules 2007, 12
992
As for the photoluminescence (PL) spectra, the PL spectrum of 2,5,7-triphenylquinoline shows an
absorption at 393.6 nm, while 5,7-diphenylquinoline shows one at 382.4 nm, that is, the absorption
shifts ca.11 nm, which is comparable to that of m-terphenylamine at 400.4 nm (Figure 3). This might
be the result of the replacement of the benzene ring of 2,5,7-triphenylquinoline causing a decrease in
the HOMO-LUMO orbital energy gap. The energy needed for the transition state electrons is
decreased, and the photoluminescent absorption of the molecules’ spectra shifts to longer
wavenumbers. It was obvious that 2,5,7-triphenylquinoline had better fluorescence intensity compared
to that of 5,7-diphenylquinoline (see Figure 4), so we expect that 2,5,7-triphenylquinoline might be a
promising precursor to develop new OLED materials, used either as single component or as a ligand
for further synthesis of metal complexes (e.g. with iridium, palladium and platinum, etc.).
Figure 3. The PL spectra of m-terphenylamine.
3000
2500
2000
1500
m-terphenylamine
1000
500
0
300
350
400
450
500
550
Wavelength(nm)
Figure 4. The PL spectra of 5, 7-diphenylquinoline and 2, 5, 7-triphenylquinoline.
2200
2000
1800
1600
1400
1200
5,7-diphenylquinoline
2,5,7-triphenylquinoline
1000
800
600
400
200
0
300
350
400
450
500
550
Wavelength(nm)

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Experimental
General
All of reactions were conducted under an inert atmosphere. Melting points were measured in open
glass capillaries on a Temperature Apparatus and are uncorrected. The purification of compounds was
accomplished by chromatography (Silica Gel HFG 254) with petroleum ether and ethyl acetate as
1
eluents. The H- and 13C-NMR spectra were recorded in CDCl3 on a Bruker AMX-500MHz
spectrometer with TMS as internal standard (chemical shift in ppm), UV-Vis and photoluminescence
(PL) spectra were measured by the Micro-analytical Chemistry Division, Department of Chemistry,
East China Normal University, Shanghai 200062, P.R. China.
1,3-Diphenyl-2-propen-1-one (2): M.p.: 57 °C; 1H-NMR δ = 8.03 (d, 2H, H-2, H-6), 7.84 (d, 1H, J= 16
Hz, -C = CH-Ph), 7.42-7.67 (m, 9H).
1
6-Carbethoxy-3,5-diphenylcyclohex-2-en-1-one (3): M.p.: 111 - 113 °C; H-NMR δ = 7.26-7.56 (m,
10H, Ph-H), 6.57 (d, 1H, J = 4Hz, H-2), 4.03 (q, 2H, J = 7Hz, -CH2CH3), 3.81 (m, 2H, H-5, H-6), 3.13
(m, 2H, H-4), 1.05 (t, 3H, J = 7 Hz, -CH2CH3).
3,5-Diphenylcyclohex-2-en-1-one (4): M.p.: 81 - 83°C; 1H-NMR δ = 7.26 - 7.57 (m, 10H, Ph-H), 6.52
(d, 1H, J = 3Hz, H-2), 3.36 (m, 1H, H-5), 3.08 (m, 2H, H-6), 2.78 (m, 2H, H-4).
1
3,5-Diphenylcyclohex-2-en -1-one oxime (5): M.p.: 162 - 165 °C; H-NMR δ = 7.26 - 7.58 (m, 10H,
Ph-H), 6.65 (s, 1H, H-2), 3.40 (m, 1H, H-5), 3.15 (m, 2H, H-4), 2.45 (m, 2H, H-6), 1.63 (br, 1H, -OH).
m-Terphenylamine (6): M.p.:107 - 109 °C; 1H-NMR δ = 7.62 (m, 4H, H-2´6´, H-2´´6´´), 7.43 (m, 6H,
H-3´4´5´, H-3´´4´´5´´), 7.20 (s, 1H, H-4), 6.89 (s, 2H, H-2, H-6), 4.0 (br, 2H, -NH2).
Preparation of 5,7-diphenylquinoline (7) [22].
A round bottle was charged FeSO4 (2.72 g, 11 mmol), m-terphenylamine (0.560 g, 3.7 mmol),
glycerol (5.55 g, 60 mmol), conc. H2SO4 (3 mL) and nitrobenzene (2.78 mL), then glacial acetic acid
(3.33 mL) was added and the mixture was heated to 145 °C for 4 h, then water (5 mL) was added.
After steam distillation, the dark viscous oil was extracted with CH2Cl2, the combined organic phase
was washed twice with water and brine and dried over MgSO4. After filtration, the filtrate was
evaporated to dryness. The residue was chromatographed (silica gel, eluent petroleum ether-EtOAc =
8:1) to give pale-yellow rhomboidal crystals of the title compound (1.02 g, yield: 33%); M.p.: 116 °C;
1H-NMR δ = 8.94 (d, 1H, J = 1Hz, H-2), 8.36 (s, 1H, H-8), 8.23 (d, 1H, J = 8Hz, H-4), 7.80 (s, 1H,
H-6), 7.43-7.80 (m, 10H, Ph-H), 7.41 (t, 1H, J = 7Hz, H-3); 13C-NMR δ = 150.7 (C-2), 149 (C-9),
141.6 (C-7), 140.1 (C-5), 140.19 (C-1´´), 139.41 (C-1´), 134.18 (C-4), 130.03 (C-3´5´), 128.99 (C-

Molecules 2007, 12
994
3´´5´´), 128.52 (C-2´6´), 127.96 (C-4´),127.78 (C-4´´), 127.52 (C-2´´6´´), 126.97 (C-6), 126.52 (C-10),
125.92 (C-3), 120.95 (C-8).
Preparation of 2,5,7-triphenylquinoline (8)
Freshly distilled bromobenzene (1.8 mmol) was added dropwise via syringe to a stirring
suspension of lithium metal (28 mg, 4 mmol) in THF (4 mL) under an inert atmosphere. The reaction
mixture was slowly warmed to ensure the formation of phenyl lithium during which the color changed
to dark red and the stirring was continued at ambient temperature for further 40 minutes. Then to the
mixture was added carefully a solution of 5,7-diphenylquinoline (200 mg, 0.6 mmol) in THF (4 mL)
and the resulting mixture was refluxed for 4 hours. After cooling, air was bubbled into the mixture to
remove all volatiles, then water (4 mL) and dichloromethane (4 mL) were added and the suspension
was neutralized with conc. HCl. After workup the residue was chromatographed (silica gel, petroleum
ether-EtOAc = 20:1) to give the title compound as a white solid (85 mg, yield 34.8 %); M.p.: 130 - 132
°C; 1H-NMR δ = 8.43 (s, 1H, H-8), 8.30 (d, 1H, J = 9Hz, H-4), 8.18 (d, 2H, J = 8Hz, H-2´´´6´´´), 7.78
13
(s, 1H, H-4), 7.39-7.56 (m, 14H); C-NMR δ = 157.6 (C-2), 149.2 (C-9), 141.7 (C-7), 140.7 (C-5),
140.3 (C-1´´), 139.6 (C-1´), 134.9 (C1), 130(C-1´´´), 129.4 (C-3´5´3´´5´´3´´´5´´´), 127.9 (C-2´6´2´´6´´),
127.6(C-2´´´6´´´), 128.5 (C-4´4´´4´´´), 124.8 (C-6) ,118.9 (C-3,10), 112.0 (C-8).
Acknowledgements
Q. L. is thankful for funds from the Scientific Research Foundation for Returned Overseas Chinese
Scholars, State Education Ministry of China (2004-527), The Scientific Innovation Foundation for the
Youth, East China Normal University (51103121). We appreciate Ms. Hongliu Ding and Ms. Ting
Zhao for their help in measuring the UV-Vis and PL spectra.
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Sample Availability: Samples of the compounds m-terphenylamine, 5,7-diphenylquinoline and 2,5,7-
triphenylquinoline are available from the authors.
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