TiO2 nanopowder catalyzed microwave-induced one-pot synthesis of novel quinoline/benzo[h]quinoline3-carbonitrile under solvent free conditions

Article abstract of DOI:10.1080/10426500802424048

A rapid and efficient method for the synthesis of various carbonitrile quinoline/benzo[h]quinolines has been developed through the Knoevenagel condensation, Michael addition of aromatic aldehyde/amine with carbonyl compounds in the presence of a nanostruc

Full text of DOI:10.1080/10426500802424048

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Phosphorus, Sulfur, and Silicon
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TiO2 Nanopowder Catalyzed
Microwave-Induced One-
Pot Synthesis of Novel
Quinoline/Benzo[h]quinoline3-
carbonitrile Under Solvent
Free Conditions
H. R. Prakash Naik a , H. S. Bhojya Naik a , T. R.
Ravikumar Naik a , T. Aravinda a & D. S. Lamani a
a Department of Studies and Research in Industrial
Chemistry, School of Chemical Sciences, Kuvempu
University, Shankaraghatta, India
Version of record first published: 22 Jul 2009.
To cite this article: H. R. Prakash Naik , H. S. Bhojya Naik , T. R. Ravikumar Naik ,
T. Aravinda & D. S. Lamani (2009): TiO2 Nanopowder Catalyzed Microwave-Induced
One-Pot Synthesis of Novel Quinoline/Benzo[h]quinoline3-carbonitrile Under Solvent
Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 184:8,
2109-2114
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Phosphorus, Sulfur, and Silicon, 184:2109–2114, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802424048
TiO2 Nanopowder Catalyzed Microwave-Induced One-Pot
Synthesis of Novel Quinoline/Benzo[h]quinoline-
3-carbonitrile Under Solvent Free Conditions
H. R. Prakash Naik, H. S. Bhojya Naik, T. R. Ravikumar
Naik, T. Aravinda, and D. S. Lamani
Department of Studies and Research in Industrial Chemistry, School of
Chemical Sciences, Kuvempu University, Shankaraghatta, India
A rapid and efficient method for the synthesis of various carbonitrile quino-
line/benzo[h]quinolines has been developed through the Knoevenagel condensa-
tion, Michael addition of aromatic aldehyde/amine with carbonyl compounds in
the presence of a nanostructured TiO2 photocatalyst by microwave irradiation un-
der solvent-free conditions.
Keywords Microwave-solvent free; nanostructured TiO2; quinoline; rapid-efficient
INTRODUCTION
In recent years, metal oxide semiconductor photocatalysis using partic-
ulate TiO2 has proven to be a promising technology for use in photocat-
alytic reactions, in the cleanup of water contaminated with hazardous
industrial byproducts,1–6 or as a photoactive material in nanocrys-
talline solar cells.7–13 Titanium dioxide is a photocatalyst of consider-
able interest because of its photocatalytic properties, and it is a choice
for a large variety of applications because it is cheap, nontoxic, and has
redox properties that are favorable both for oxidation of many organics
and for reduction of a number of metal ions or organics in aqueous
solution.
Quinolines and their derivatives are a very important class of com-
pounds because of their wide occurrence in natural products14 and
Received 16 July 2008; accepted 21 August 2008.
One of the authors (H. R. Prakash Naik) is thankful to the Indian Institute of Science,
Bangalore, for the spectral data; University of Mysore for elemental analysis facility and
SC/ST cell; and Kuvempu University for awarding Junior Research Fellowship (JRF).
Address correspondence to H. S. Bhojya Naik, Department of Studies and Re-
search in Industrial Chemistry, School of Chemical Sciences, Kuvempu University,
Shankaraghatta-577 451, India. E-mail: hsb naik@rediffmail.com
2109

2110
H. R. P. Naik et al.
biologically active compounds.15 Furthermore, poly-substituted quino-
lines have been found to undergo hierarchical self-assembly into a va-
riety of nano- and mesostructures with enhanced electronic and pho-
tonic functions.16 In view of these points, a great deal of effort has been
committed to develop new and efficient synthetic routes to quinoline
derivatives in both synthetic organic and medicinal chemistry.
The use of scientific microwave apparatus in the development of
efficient and selective greener methods has become a major focus
of researchers worldwide, and selection of appropriate alternate eco-
friendly reaction media has become an integral part of this paradigm
shift.17 Microwave (MW) irradiation as an alternative energy source in
conjunction with water as reaction medium has proven to be a success-
ful “greener” chemical approach.
Our approach is to develop a rapid and efficient scientifically
based framework for greener preparation of these carbonitrile quino-
line/benzoquinolines in a manner that renders the materials less mobile
in the environment and reduces or eliminates the use and generation
of hazardous substances. The following areas of opportunity are be-
ing exploited to engage green chemistry: (i) choice of solvent and (ii)
the catalytic agent employed. We found microwave (MW) irradiation to
be an efficient and selective mode of activation in rapid and efficient
synthesis of 2-hydroxy-4-phenyl/benzo[h]quinoline -3-carbonitrile.
RESULTS AND DISCUSSION
The required colloidal TiO2 was prepared according to a reported pro-
cedure by a dropwise addition of titanium(IV) tetrachloride to wa-
ter cooled to 4◦C. The temperature and component mixing of reac-
tants were controlled by an apparatus developed for automatic colloid
preparation.18 Herein we utilized the photocatalytic activity of TiO2
to synthesize biological molecules via microwave irradiation. The main
drawback for using TiO2 itself for catalytic action is that it absorbs light
energy in the UV part of the spectrum. It has been found that surface
atoms of TiO2 are coordinated19 with the organic molecules and provide
an opportunity for alternating the effective band gap of nanoparticles.
From the above results, it can be seen that the generality of this
facile condensation was established in the presence of titanium dioxide
nanosurface under solvent-free conditions to furnish the correspond-
ing quinolines. By comparison, substrates 4a–c and d demonstrate
a superior reaction activity to the conventional method of approach,
which consumed 39–50 min for completion of the reaction, in which
the employed microwave output is only 150 W. Because the foregoing

Novel Quinoline/Benzo[h]quinoline-3-carbonitrile
2111
SCHEME 1 Synthetic route for quinoline-3-carbonitriles (where R1 = H, CH3,
and OCH3).
optimization work has demonstrated that this kind of reaction can also
be efficiently promoted by conventional heating under neat conditions,
we tried to obtain all the above products under solvent-free conditions
(Schemes 1 and 2).
CONCLUSION
In conclusion, we have described the efficient synthesis of novel
quinoline/benzo[h]quinoline -3-carbonitriles by using TiO2 nano cat-
alyst. The structures of 4a–c, d were confirmed by elemental analysis,
IR, NMR, and mass spectroscopic data. Finally, the obtained molecular
ion peaks matching to their exact molecular weights for all the com-
pounds (4, 4a, 4b, and d) provides additional strong evidence for the
expected structure. This also provided proof that further aromatization
took place successfully. A plausible mechanism for formation of target
molecules (4, 4a, 4b, and d) is outlined in Scheme 3. We tried to gain the
intermediates by carrying out the same reactions under dry nitrogen,
but the same products were obtained.
EXPERIMENTAL
A dry, 50 mL flask was charged with arylaldehyde (5 mmol), cyano ac-
etate (5 mmol), aniline (5 mmol), and titanium dioxide (TiO2) nanopow-
SCHEME 2 Synthetic route for benzo[h]quinoline-3-carbonitrile.

2112
H. R. P. Naik et al.
SCHEME 3 A suggested mechanism for both 2-hydroxy-4-phenyl/
benzo[h]quinoline -3-carbonitrile.
der (500 mg). The mixture was well mixed, and then irradiated in
a SANYOEM-350S microwave oven at 300W or 150W for a desig-
nated time (60 sec) as required for completing the reaction (determined
by TLC); see Table I. Then, after being cooled to room temperature,
under these conditions, the reaction mass was poured on crushed ice,
the solid material was filtered off, and the crude product was purified
by recrystallization from DMF. The similar reaction procedure has been
followed for other derivatives.
TABLE I Reaction Time Data of Both Conventional
and MW Methods
Compound
Time (min)—Conventional heating
Time (Sec)—MW
4a
4b
4c
4d
45
48
39
50
60
65
60
70

Novel Quinoline/Benzo[h]quinoline-3-carbonitrile
2113
2-Hydroxy-4-phenylquinoline-3-carbonitrile (4a)
Pale red solid, Yield 85%, mp 132◦C ; IR (ν) (KBr) cm−1; 3019 ( C-H,
Ar-H ); 2224 (C N); 3278 (OH); 1H NMR (DMSO d6), δ 7.65 (d, 1H, Ar-
H, J = 8.03 Hz), 7.58 (d, 1H, Ar-H, J = 7.63 Hz), 7.36 (d, 1H, Ar-H, J =
7.45 Hz), 7.94 (d, 1H, Ar-H, J = 8.77 Hz), 7.24 (d, 1H, Ar-H, J = 7.13
Hz), 7.27 (d, 1H, Ar-H, J = 7.35 Hz), 7.47 (d, 1H, Ar-H, J = 7.37 Hz),
7.45 (d, 1H, Ar-H, J = 7.37 Hz), 7.34 (d, 1H, Ar-H, J = 7.47 Hz), 11.2
(s, 1H, O-H, J = 11.03 Hz); m/z (%) [M]+ :[246]+; Elemental anlysis,
Found: C, 78.04; H, 4.08; N, 11.37. Calculated for C16H10N2O: C, 78.03;
H, 4.09; N, 11.38.
2-Hydroxy-6-methyl-4-phenylquinoline-3-carbonitrile (4b)
Brown solid, Yield 68%, mp 121◦C ; IR (ν) (KBr) cm−1; 3025 (C-H, Ar-H);
2231 (C N); 3298 (OH); 2950 (C-H of CH3); 1H NMR ( DMSO d6), δ 7.43
(d, 1H, Ar-H, J = 7.68 Hz), 7.45 (d, 1H, Ar-H, J = 7.61 Hz), 7.85 (d, 1H,
Ar-H, J = 8.05 Hz), 7.48 (d, 1H, Ar-H, J = 7.26 Hz), 7.32 (d, 1H, Ar-
H, J = 7.26 Hz), 7.22 (d, 1H, Ar-H, J = 7.26 Hz), 7.32 (d, 1H, Ar-H,
J = 7.26 Hz), 7.48 (d, 1H, Ar-H, J = 7.26 Hz), 7.34 (d, 1H, Ar-H, J =
7.47 Hz), 2.36 (d, 3H, CH3), 11.5 (s, 1H, O-H, J = 11.03 Hz); m/z (%)
[M]+ :[260]+; Elemental anlysis, Found: C, 78.43; H, 4.66; N, 10.77.
Calculated for C17H12N2O: C, 78.44; H, 4.65; N, 10.76.
2-Hydroxy-6-methoxy-4-phenylquinoline-3-carbonitrile (4c)
Brown solid, Yield 76%, mp 112◦C ; IR (ν) (KBr) cm−1; 3021 (C-H, Ar-H);
2236 (C N); 3284 (OH); 1250 (C-O-C of OCH3); 1H NMR (DMSO d6), δ
6.94 (d, 1H, Ar-H, J = 7.68 Hz), 7.31 (d, 1H, Ar-H, J = 7.61 Hz), 7.84
(d, 1H, Ar-H, J = 8.05 Hz), 7.50 (d, 1H, Ar-H, J = 7.26 Hz), 7.35 (d, 1H,
Ar-H, J = 7.26 Hz), 7.28 (d, 1H, Ar-H, J = 7.26 Hz), 7.28 (d, 1H, Ar- H,
J = 7.26 Hz), 7.54 (d, 1H, Ar-H, J = 7.26 Hz), 3.73 (d, 3H, OCH3), 11.2
(s, 1H, O-H, J = 11.03 Hz); m/z (%) [M]+ :[276]+; Elemental anlysis,
Found: C, 73.91; H, 4.39; N, 10.13. Calculated for C17H12N2O2: C, 73.90;
H, 4.38; N, 10.14.
2-Hydroxy-4-phenylbenzo[h]quinoline-3-carbonitrile (4d)
Dark violet solid, Yield 81%, mp 151◦C; IR (ν) (KBr) cm−1; 3015 (C-H,
1
Ar-H ); 2225 (C N); 3271 (OH); H NMR (DMSO d6), δ 7.64 (d, 1H,
Ar-H, J = 7.68 Hz), 7.35 (d, 1H, Ar-H, J = 7.43 Hz), 7.67 (d, 1H, Ar-H,
J = 7.67 Hz), 7.32 (d, 1H, Ar-H, J = 7.32 Hz), 7.34 (d, 1H, Ar-H, J =
7.32 Hz), 7.72 (d, 1H, Ar-H, J = 7.68 Hz), 7.48 (d, 1H, Ar-H, J = 7.26

2114
H. R. P. Naik et al.
Hz), 7.32 (d, 1H, Ar-H, J = 7.26 Hz), 7.22 (d, 1H, Ar-H, J = 7.26 Hz),
7.32 (d, 1H, Ar-H, J = 7.26 Hz), 7.48 (d, 1H, Ar-H, J = 7.26 Hz), 11.8
(s, 1H, O-H, J = 11.03 Hz); m/z (%) [M]+ :[296]+; Elemental anlysis,
Found: C, 81.08; H, 4.07; N, 9.46. Calculated for C20H12N2O: C, 81.07;
H, 4.08; N, 9.45.
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