Vanadium dodecylamino phosphate: A novel efficient catalyst for synthesis of polyhydroquinolines

Article abstract of DOI:10.2478/s11696-013-0441-6

A novel vanadium dodecylamino phosphate was synthesised by an instant reaction between phosphoric acid and vanadyl acetylacetonoate using dodecylamine as the structure-directing agent at ambient temperature. The physicochemical characteristics of the mate

Full text of DOI:10.2478/s11696-013-0441-6

Chemical Papers
DOI: 10.2478/s11696-013-0441-6
ORIGINAL PAPER
Vanadium dodecylamino phosphate: A novel efficient catalyst
for synthesis of polyhydroquinolines
Anumula Rajini, Muralasetti Nookaraju, Ingala Ajit Kumar Reddy,
Venkatathri Narayanan*
Department of Chemistry, National Institute of Technology Warangal, Warangal-506 004, Andhra Pradesh, India
Received 31 January 2013; Revised 3 May 2013; Accepted 13 May 2013
A novel vanadium dodecylamino phosphate was synthesised by an instant reaction between phos-
phoric acid and vanadyl acetylacetonoate using dodecylamine as the structure-directing agent at
ambient temperature. The physicochemical characteristics of the material were investigated by a
variety of analytical techniques. XRD studies revealed the presence of vanadium phosphate and
hydrated vanadium phosphate phases in the framework of the material. The catalytic application
of this material toward in the synthesis of polyhydroquinolines via Hantzsch condensation was in-
vestigated at ambient temperature. This method affords high yields within short reaction times.
The influence of various reaction parameters such as different solvents, catalyst dosage, effect of
aldehydes, and reusability was studied and a plausible mechanism proposed.
ꢀ
c 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: vanadium, dodecylamine, Hantzsch condensation, polyhydroquinolines
Introduction
in the treatment of Alzheimer’s disease (Kumar et al.,
008). In view of the overall biological importance of
2
Quinolines, having a 1,4-dihydropyridine nucleus
1,4-DHPs), are important bioactive compounds, well-
1,4-DHPs as a valuable drug in pharmacological appli-
cations, several methods have been reported for their
synthesis.
(
2+
known Ca channel-blockers and analogues of NADH
coenzymes. 1,4-DHPs exhibit a variety of phar-
macological properties such as anti-malarial, anti-
inflammatory, anti-asthmatic, and antibacterial ac-
tivities, as well as being tyrosine kinase- inhibiting
agents (Chen et al., 2001). The heterocyclic rings of
Standard methods such as refluxing in acetic
acid or in alcohol have been reported for the syn-
thesis of these derivatives. However, these methods
suffer from drawbacks such as long reaction times,
harsh refluxing conditions, use of large quantities
of organic solvents, and low product yields. A sur-
vey of the literature reveals a number of homoge-
neous and heterogeneous catalytic systems in use for
the synthesis of polyhydroquinoline derivatives, in-
cluding the use of microwaves, autoclave, TMSCl-
NaI (Sabitha et al., 2003a), ionic liquids (Ji et
al., 2004), InCl3, Cs-Norit carbons (Perozo-Rondon
et al., 2006), molecular iodine (Ko et al., 2005),
metal triflates (Wang et al., 2005), organocatalyst,
tris(pentafluorophenyl)borane (Chandrasekhar et al.,
2008), ceric ammonium nitrate, HClO –SiO , silica
1
,4-DHP function biologically as vasodilators, bron-
chodilators, anti-atherosclerotic, anti-tumour, gero-
protective, hepatoprotective, and anti-diabetic agents
and for the treatment of cardiovascular diseases (Shan
et al., 2004). Dihydropyridyl-based cardiovascular
agents which are effective in the treatment of hy-
pertension include nifedipine, nicardipine, amlodip-
ine, and other related derivatives (Heydari et al.,
2
009). Studies reveal that 1,4-DHPs present a num-
ber of medicinal applications, e.g., as a neuroprotec-
tant, platelet anti-aggregatory agent, chemo sensitiser
in tumour therapy, and cerebral anti-ischemic agent
4
2
sulphuric acid (Kolvari et al., 2011), L-proline and
*Corresponding author, e-mail: venkatathrin@yahoo.com

ii
A. Rajini et al./Chemical Papers
derivatives, potassium dodecatungstocobaltate trihy-
drate (Nagarapu et al., 2008), HY zeolite (Das et
al., 2006), montmorillonite K-10 (Song et al., 2005),
heteropoly acid, molybdenum(VI) complex, tetra-
butylammonium hydrogen sulphate, fluoroboric acid
ones (Sabitha et al., 2003b), and coumarins (Sunil Ku-
mar et al., 2006).
The present study details a highly efficient route
for the synthesis of polyhydroquinolines using an in-
expensive novel open-framework vanadium dodecy-
lamino phosphate. The material was readily prepared
by simple mixing of its precursors and characterised
by various physicochemical techniques such as powder
XRD, SEM-EDAX, FT-IR, Raman spectroscopy, UV-
VIS DRS, 31P and C MAS NMR. The catalytic ac-
tivity of the vanadium dodecylamino phosphate in the
Hantzsch condensation synthesis of polyhydroquino-
lines at ambient temperature is described. The effect
of various parameters such as solvent nature, catalyst
dosage, and catalyst reusability was determined.
(Chen et al., 2007), boronic acids, nickel nanopar-
ticle, PTSA-SDS, BINOL-phosphoric acid deriva-
tives (Evans & Gestwicki, 2009), and hafnium(IV)
bis(perfluorooctanesulphonyl)imide complex (Hong et
al., 2010). However, some of the above methods have
their limitations in terms of yields, elevated temper-
atures, extended reaction times, difficult procedures,
and the use of expensive reagents. In some cases, the
catalysts in use are acidic or basic and are harmful to
the environment.
13
Hence, it was desirable to develop a new and con-
venient method for the synthesis of polyhydroquino-
lines. All of the above disadvantages reflect the need
for further improvements to the synthesis of new eco-
nomically viable catalysts.
Experimental
Materials and methods
Phosphates are effective in several industrial acid-
based reactions (Samantaray et al., 2000). The phos-
phates appear to enhance the catalytic properties, sta-
bilise the surface area and crystal phase, improve the
surface acidity, and render the material porous. Metal
phosphates also attract interest for their practical ap-
plications in areas such as catalysis, ion exchange, in-
tercalation chemistry, proton conduction, optical and
electromagnetic functional materials (Das & Parida,
Vanadyl acetylacetonoate (Sigma–Aldrich, Ban-
galore, India, 98 %), dodecylamine (Sigma–Aldrich,
Bangalore, India, 98 %) and orthophosphoric acid
(Merck, Mumbai, India, 85 %) were used. Aldehydes
were purchased from Sisco Research Laboratories, In-
dia and dimedone from Oakwood Chemical Labora-
tories, USA. All chemicals were of analytical reagent
grade and used without further purification.
The synthesis of vanadium dodecylamino phos-
phate (VDDAP) was performed under ambient tem-
perature conditions as reported elsewhere (Venkata-
thri et al., 2008). In a typical synthesis, a pre-
determined quantity of orthophosphoric acid (1 M)
was added to vanadyl acetylacetonoate (0.01 M) and
stirred until all the vanadyl acetylacetonoate was dis-
solved. Dodecylamine (4 M) was added to this well-
stirred mixture and stirred well to obtain a solid
product. The product thus obtained was thoroughly
2
008). Among the various metal phosphates, vana-
dium phosphates (VPO) are of interest due to their
exceptional structures, interesting host–guest chem-
istry, and potential applications in catalysis. VPOs
are layered compounds and have found many ap-
plications in materials science and as heterogeneous
catalysts in various oxidation reactions (Solsona et
al., 2003). Vanadium-containing microporous molec-
ular sieves were found to be active in a number of
oxidation reactions (Whittington & Anderson, 1993).
They are extremely important in heterogeneous catal-
ysis for the selective oxidation of o-xylene to phthalic
anhydride (Dias et al., 1997), methane and methanol
to formaldehyde, benzyl alcohol to benzaldehyde, es-
terification of oleic acid, ammoximation of aromatics
and alkyl aromatics (Cavani et al., 1987), butane to
maleic anhydride (Bergman & Frisch, 1966), propane
to acrylic acid (Gribot-Perrin et al., 1996), oxidative
dehydrogenation of ethane and propane (Kondratenko
et al., 2006), and epoxidation of allylic alcohols. How-
ever, the activity of VPO catalysts in liquid phase re-
actions is very limited. To the best of our knowledge,
the application of vanadium-based catalyst in the syn-
thesis of polyhydroquinolines has not been reported,
although there have been reports on the application
of vanadium-based catalysts in organic synthesis such
as tetrahydropyranylation of alcohols, thiols, and phe-
nols (Choudary et al., 2001), acylation of alcohols and
phenols (Oskooie et al., 2008), dihydropyrimidin-(2H)-
◦
ground, washed with ether and dried at 50 C for ap-
proximately 30 min.
Qualitative phase analysis of VDDAP was per-
formed using a AXS D8 Advance diffractometer
(Bruker, USA) at ambient temperature with CuK
α
˚
X-ray source of wavelength of 1.5406 A using a Si
(Li) PSD detector. The morphology of the synthe-
sised material was investigated using a JSM-6390LV
scanning electron microscope (JEOL, Japan) and the
surface elemental composition (EDAX) was exam-
ined using a JED-2300 model (JEOL, Japan). Fourier
transform infrared (FT-IR) spectra were recorded on
an Avatar 370 spectrophotometer (Thermo Nicolet,
UK) equipped with a pyroelectric detector (DTGS
−
1
type); a resolution of 4 cm was adopted, provided
with a KBr beam-splitter. Dispersive Raman spec-
troscopy was performed on a Bruker Senterra at a
wavelength of 532 nm using laser radiation as the
source (Bruker, USA). The coordination and the ox-
idation state of vanadium in VDDAP were exam-

A. Rajini et al./Chemical Papers
iii
ined by diffuse reflectance UV-VIS spectrophotometry
measured with regard to 85 % H3PO4 as the exter-
nal reference. The solid state 13C magic angle spin-
ning (MAS) nuclear magnetic resonance (NMR) spec-
tra were recorded on a DSX-300 Avance-III 400(L)
NMR spectrometer (Bruker, USA). The 13C MAS
NMR spectrum was recorded at 75.47 MHz in the
frequency range of 10–12 kHz equipped with using
a 5 mm dual probe head of pulse duration 4.25 µs.
The 31P and C solid state MAS NMR spectra were
(
8
UV-VIS DRS) on a Cary 5000 in the range of 175–
00 nm (Varian, USA). Solid state P magic angle
31
spinning (MAS) nuclear magnetic resonance (NMR)
spectra were recorded on a DRX-500 AV-III 500(S)
31
spectrometer (Bruker, USA). The P MAS NMR
spectrum was recorded at 121.49 MHz in the fre-
quency range of 10–12 kHz using a 5 mm dual probe
head of pulse duration 5 µs. The chemical shift was
13
Table 1. Physical and spectral data of 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl es-
ter (I), 2,7,7-trimethyl-5-oxo-4-(4-methylphenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester (II), 2,7,7-
trimethyl-5-oxo-4-(4-methoxyphenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester (III), 2,7,7-trimethyl-
5
-oxo-4-(4-hydroxyphenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester (IV ), 2,7,7-trimethyl-5-oxo-4-(4-
chlorophenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester (V ), 2,7,7-trimethyl-5-oxo-4-(4-bromophenyl)-
,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester (VI), 2,7,7-trimethyl-5-oxo-4-(4-nitrophenyl)-1,4,5,6,7,8-
1
hexahydroquinoline-3-carboxylic acid ethyl ester (VII), and 2,7,7-trimethyl-5-oxo-4-(3-nitrophenyl)-1,4,5,6,7,8-hexa-
hydroquinoline-3-carboxylic acid ethyl ester (VIII)
Compound
Characterisation data
◦
white solid, mp/ C: 202–204
I
IR (KBr), ν˜ /cm 1: 3287, 3077, 2964, 1696, 1610
−
1
H NMR (CDCl3, 300 MHz), δ: 0.93 (s, 3H), 1.07 (s, 3H), 1.19 (t, J = 7.1 Hz, 3H), 2.13–2.32 (m, 4H), 2.37 (s, 3H),
4
.05 (q, J = 7.2 Hz, 2H), 5.05 (s, 1H), 6.21 (s, 1H), 7.06–7.31 (m, 5H)
+
MS (EI), m/z: 339 (M
)
◦
II
white solid, mp/ C: 260–262
IR (KBr), ν˜ /cm 1: 3275, 3080, 2960, 1700, 1650
−
1
H NMR (CDCl3, 300 MHz), δ: 0.94 (s, 3H), 1.08 (s, 3H), 1.21 (t, J = 7.1 Hz, 3H), 2.10–2.24 (m, 4H), 2.26 (s, 3H),
2
.37 (s, 3H), 4.06 (q, J = 7.1 Hz, 2H), 5.03 (s, 1H), 5.96 (s, 1H), 7.02 (d, J = 8.0 Hz, 2H), 7.19 (d, J = 8.0 Hz, 2H)
+
MS (EI), m/z: 353 (M
)
◦
III
IV
yellow solid, mp/ C: 255–257
IR (KBr), ν˜ /cm 1: 3275, 2957, 1705, 1647, 1605, 1497, 1382, 1217, 1032, 766
−
1
H NMR (CDCl3, 300 MHz), δ: 0.94 (s, 3H), 1.07 (s, 3H), 1.21 (t, J = 7.2 Hz, 3H), 2.13–2.27 (m, 3H), 2.31–2.37
m, 4H), 3.74 (s, 3H), 4.06 (q, J = 7.2 Hz, 2H), 5.00 (s, 1H), 6.01 (s, 1H), 6.72–6.75 (m, 2H), 7.20–7.26 (m, 2H)
MS (EI), m/z: 369 (M
(
+
)
◦
white solid, mp/ C: 232–234
IR (KBr), ν˜ /cm 1: 3390, 2955, 1700, 1645, 1590, 1480, 1385, 1220, 782
−
1
H NMR (CDCl3, 300 MHz), δ: 0.93 (s, 3H), 1.07 (s, 3H), 1.19 (t, J = 7.2 Hz, 3H), 2.09–2.19 (m, 3H), 2.20–2.34
(m, 4H), 4.06 (q, J = 7.6 Hz, 2H), 4.98 (s, 1H), 5.61 (s, 1H), 6.10 (s, 1H), 6.65 (d, J = 8.9 Hz, 2H), 7.17 (d, J =
8
.4 Hz, 2H)
MS (EI), m/z: 356 (M+)
◦
V
off-white solid, mp/ C: 244–246
IR (KBr), ν˜ /cm 1: 3275, 3075, 2965, 1705, 1650, 1605
H NMR (CDCl3, 300 MHz), δ: 0.93 (s, 3H), 1.07 (s, 3H), 1.19 (t, J = 7.2 Hz, 3H), 2.12–2.35 (m, 4H), 2.37 (m,
−
1
3
H), 4.06 (q, J = 7.2 Hz, 2H), 5.02 (s, 1H), 6.13 (s, 1H), 7.15 (d, J = 8.0 Hz, 2H), 7.31 (d, J = 8.0 Hz, 2H)
+
MS (EI), m/z: 374 (M
)
◦
VI
white solid, mp/ C: 253–255
IR (KBr), ν˜ /cm 1: 3290, 2962, 1700, 1606, 1510, 1380, 1230, 1020, 764
−
1
H NMR (CDCl3, 300 MHz), δ: 0.93 (s, 3H), 1.07 (s, 3H), 1.19 (t, J = 7.2 Hz, 3H), 2.19–2.27 (m, 3H), 2.34–2.41
(
m, 4H), 4.05 (q, J = 7.2 Hz, 2H), 5.03 (s, 1H), 5.78 (s, 1H), 7.19 (d, J = 8.0 Hz, 2H), 7.34 (d, J = 8.0 Hz, 2H)
+
MS (EI), m/z: 417 (M
)
◦
VII
VIII
yellow solid, mp/ C: 244–246
IR (KBr), ν˜ /cm 1: 3288, 3077, 2964, 1705, 1605, 1530
−
1
H NMR (CDCl3, 300 MHz), δ: 0.93 (s, 3H), 1.07 (s, 3H), 1.22 (t, J = 7.1 Hz, 3H), 2.12–2.41 (m, 4H), 2.12–2.32
m, 3H), 3.99 (q, J = 7.1 Hz, 2H), 5.15 (s, 1H), 6.86 (s, 1H), 7.35 (t, J = 7.9 Hz, 1H), 7.72 (d, J = 7.9 Hz, 1H)
MS (EI), m/z: 384 (M
(
+
)
◦
yellow solid, mp/ C: 176–179
IR (KBr), ν˜ /cm 1: 3303, 2954, 1683, 1610, 1167, 759
−
1
H NMR (CDCl3, 300 MHz), δ: 0.96 (s, 3H), 1.04 (s, 3H), 1.22 (t, J = 7.3 Hz, 3H), 2.10–2.34 (m, 4H), 2.38 (s, 3H),
4
.01 (q, J = 7.3 Hz, 2H), 4.96 (s, 1H), 6.32 (s, 1H), 6.74–7.38 (m, 4H)
+
MS (EI), m/z: 385 (M
)

iv
A. Rajini et al./Chemical Papers
recorded at ambient temperature. The melting points
of the polyhydroquinoline derivatives were determined
using a DS-50 thermal analyser (Shimadzu, Japan).
1
The H NMR spectra were recorded on a AM 300
(300 MHz) (Bruker, USA) in CDCl3 using TMS as
internal standard. The FT-IR spectra were obtained
in KBr discs on a Shimadzu spectrometer (Shimadzu,
Japan). The mass spectra were determined on a Sat-
urn 2000GC/MS instrument (Varian, USA).
General procedure for synthesis of polyhydro-
quinoline derivatives
A mixture of aromatic aldehyde (1.0 mmol), 5,5-
dimethylcyclohexane-1,3-dione (1.0 mmol), ethyl ace-
toacetate (1.0 mmol), ammonium acetate (1.0 mmol),
and VDDAP (0.1 g) in a methanol : water mixture
Fig. 1. PowderX-ray diffraction pattern of VDDAP.
(ϕr = 1 : 1) was stirred magnetically in a round-
bottom flask at ambient temperature. The progress
of the reaction was monitored by TLC using a chloro-
form : ethyl acetate mixture (ϕr = 7 : 3) as a solvent.
The reaction mixture was treated with ethyl acetate
(15 mL) and water (5 mL) was added to the flask.
The ethyl acetate layer was separated and washed with
cold water (10 mL). The organic layer was then dried
over anhydrous sodium sulphate, filtered, and the sol-
vent distilled under vacuum to afford the crude prod-
uct. The crude product was further recrystallised from
absolute alcohol to afford the pure product. The struc-
tures of the products were confirmed by physical and
1
spectroscopic data (IR, H NMR, and MS spectra) as
compared with the data in the literature. The spectral
data of some polyhydroquinoline derivatives are given
in Table 1.
Results and discussion
Catalyst characterisation
Fig. 2. Scanning electron micrograph of VDDAP (inset shows
high resolution image of VDDAP).
The powder X-ray diffraction pattern (Fig. 1) of
◦
◦
◦
◦
VDDAP shows peaks at 2θ of 5.5 , 8.1 , 10.8 , 13.5 ,
◦
◦
2
1
1.2 , 22.2 and the corresponding d-spacings are
The scanning electron micrograph (Fig. 2) shows
that the particles have a fibrous morphology (Macha-
do et al., 2004). The energy dispersive X-ray analysis
(Fig. 3) shows the distribution of the constituent el-
ements O, P, N, and V in the synthesised material
(Table 2).
˚
˚
◦
˚
◦
˚
˚
˚
5.9 A, 10.8 A, 8.1 A, 6.5 A, 4.1 A, 3.9 A. The peaks
◦
at 2θ of 21.2 , 13.5 , and 22.2 indicate the presence
of vanadium ions (Xue et al., 2010) of VOPO4 phases
(
Rownaghi et al., 2009), and hydrated VOPO4 phases
4+
(
VOHPO4 · H2O) predominantly in the V state with
5+
a small amount of V species in VDDAP (Guan et
al., 2008). The crystallite size of the VDDAP was cal-
culated by employing Scherer’s equation
The Fourier transform infrared spectrum (Fig. 4)
−
1
of VDDAP shows a peak at 540 cm associated with
the V—O—V rotational vibrations. The small edge
−
1
−1
at 2920 cm and the peak at 1475 cm correspond
to the asymmetric stretching and bending vibrations
of methylene groups (–CH2) of amine. The peak at
0
.9λ
D =
(1)
β cos θ
−
1
where D represents the mean grain size, λ is the wave-
length of X-ray radiation, β is the full width at half
the maximum height of the peak, and θ represents
the diffraction angle. The average crystallite size of
VDDAP was found to be 2.09 nm.
approximately 1220–1080 cm
C—N stretching vibration. The peaks at 1085 cm
and 1171 cm
corresponds to the
−
1
−
1
are due to the asymmetric stretch-
ing and anti-symmetric stretching of the P—O bond,
respectively (Borah & Datta, 2010). The band at

A. Rajini et al./Chemical Papers
v
Table 2. Elemental analysis of VDDAP
Content
Error
%
Element
Atomic number
Series
mass %
at. %
O
P
N
C
V
8
15
7
6
23
K-series
K-series
K-series
K-series
K-series
56.54
19.07
14.02
10.21
0.16
58.86
10.25
16.67
14.16
0.05
32.2
0.8
5.8
4.2
0.0
–
Total
100.00
100.00
Fig. 3. Energy dispersive X-ray analysis spectrum of VDDAP.
Fig. 6. Dispersive Raman spectrum of VDDAP.
al., 2008). The peaks in the range of 850–980 cm 1 are
−
attributed to the stretching frequency of the –V—O
bond in VDDAP (Nguyen-Phan et al., 2011). The
−
1
peak at 889 cm
may correspond to the presence
of condensed P—N units in VDDAP. The absence of
−
1
−1
bands at 1580 cm and 1540 cm , which are char-
+
acteristic of the N—H bending vibrations of the NH3
group, indicates that the incorporated amine is not in
the protonated form (Datta et al., 2005). Absorption
band corresponding to the VOPO4 lattice vibration
−
1
Fig. 4. Fourier transform infrared spectrum of VDDAP.
at 962 cm
was retained after the synthesis, sug-
gesting the lamellar nature of the compound involv-
ing a V—P—O framework with the organic molecules.
The structure of VDDAP was found to possess vana-
dium phosphate layers in which the amine molecules
interact with the vanadium and phosphate to form
an open-framework sandwiched polymeric material
(Fig. 5).
The dispersive Raman spectrum (Fig. 6) of VDDAP
−
1
shows a small peak at 880 cm
corresponding to
the presence of VOHPO4 ·H2O (Guliants et al., 1996)
−
1
while the band at 1050 cm is assigned to the strong
V—O—P band of the VOPO4 phase in VDDAP (Wu
Fig. 5. Structure proposed for VDDAP.
−
1
et al., 2010). The band near to 945 cm corresponds
to the symmetric stretching vibration of the phosphate
tetrahedron of the VOPO4 phase in VDDAP (Beneš
et al., 2006).
−
1
1
240 cm can be ascribed to the asymmetric stretch-
ing vibration mode of the P—O bond (Nagaraju et

vi
A. Rajini et al./Chemical Papers
Fig. 7. UV-VIS diffuse reflectance spectrum of VDDAP.
Fig. 9. 13C MAS NMR spectrum of VDDAP.
3
2–34 is due to the alkyl chains of interior methylene
carbons in trans conformation (Dasgupta et al., 2002).
The peak at δ = 14 is due to the interaction of the
terminal methyl group of dodecylamine with the VPO
matrix. The peaks at δ = 42.8 and δ = 39.4 correspond
to the carbon (C1) adjacent to the amine head group
and the carbon (C2) next to it, respectively, indicat-
ing the strong interaction of the amine head group
with the vanadium phosphate matrix (Dasgupta et
al., 2004).
Catalytic studies
The applicability of a novel VDDAP in the syn-
thesis of polyhydroquinolines is reported for the first
time.To explore the efficacy of the catalyst and the
optimum conditions required for the reaction, the four
component condensation of benzaldehyde (1.0 mmol),
5,5-dimethylcyclohexane-1,3-dione (1.0 mmol), ethyl
acetoacetate (1.0 mmol), and ammonium acetate
(1.0 mmol) in a solvent-free media and without any
catalyst were investigated at ambient temperature. It
was found that under these conditions a very low yield
was obtained. The same reaction was performed in the
presence of VDDAP under solvent-free conditions and
the time required for the reaction to achieve a slight
yield was 240 min.
Since the solvent properties play a crucial role in
organic reactions, the effect of various solvents differ-
ing in polarity was studied on the synthesis. Solvents
such as ethanol, acetonitrile, chloroform, methanol,
aqueous methanol solution, water, and tetrahydro-
furan were screened using the model reaction. Ace-
tonitrile, chloroform, water, tetrahydrofuran, and the
solvent-free system did not favour formation of prod-
uct. Ultimately, the methanol or methanol : water
(ϕr = 1 : 1) mixture was found to be a solvent sys-
Fig. 8. 31P MAS NMR spectrum of VDDAP.
The UV-VIS diffuse reflectance spectrum (Fig. 7)
of VDDAP shows a band at 250 nm due to the VO2
species present in the tetrahedral coordination. The
band at 300–320 nm favours high dispersion of V5
ions in the tetrahedral environment (Wang et al.,
+
+
2
011). The UV-VIS diffuse reflectance spectrum in-
4+
5+
dicates that V and V ions are coexistent in the
catalyst. The presence of a broad peak at 410–460 nm
is due to the charge transfer transitions of the V5
species (V—O) in square pyramidal geometry.
The solid state P MAS NMR spectrum (Fig. 8)
of VDDAP shows a sharp signal centred at δ = 2.034.
The signal corresponds to the phosphorous atoms of
the phosphate linkage. The P MAS NMR signals in
the δ range from –22 to 4 correspond to the phos-
phorous atoms of the VOPO4 phases. That only one
resonance peak present is a clear indicator that all the
phosphorous atoms are equal in VDDAP.
+
31
31
13
The C MAS NMR spectrum (Fig. 9) of VDDAP
shows that the 13C chemical shift in the δ range of

A. Rajini et al./Chemical Papers
vii
Table 3. Reaction of benzaldehyde, ethylacetoacetate, dimedone, and ammonium acetate in the presence of 0.1 g of catalyst
VDDAP at ambient temperature: effect of solvents
a
Entry
Solvent (5 mL)
Time/min
Yield /%
1
2
3
4
5
6
7
8
Methanol
Ethanol
140
180
NR
NR
NR
120
NR
240
75
65
–
–
–
83
–
63
Acetonitrile
Chloroform
Tetrahydrofuran
Methanol : water (1 : 1)
Water
Solvent-free
a) Isolated yield; NR – no reaction.
Fig. 10. VDDAP catalyst-mediated synthesis of polyhydroquinolines.
Table 4. Reaction of benzaldehyde, ethylacetoacetate, dime-
the increase in the amount of catalyst. The reaction
yield was found to be 85 % for 0.1 g of catalyst whereas
it was 68 % for 0.05 g of the catalyst. The results in-
dicate that an increase in the amount of VDDAP sig-
nificantly improved the reaction; this may be due to
presence of vanadium ions. The optimum amount of
catalyst was found to be 0.1 g with regard to product
yield. The role of the catalyst is to activate the alde-
hyde by binding the oxygen atom of the aldehyde with
the vacant orbital of vanadium in VDDAP (Fig. 11).
Fig. 11 shows a tentatively proposed mechanism
for the synthesis of polyhydroquinolines. The synthe-
sis of polyhydroquinolines follows the Knoevenagel re-
action between ethyl acetoacetate, benzaldehyde, and
ammonia to afford their condensation and ester enam-
ine intermediates, respectively. Further, dimedone un-
dergoes Knoevenagel condensation with ammonia and
benzaldehyde to give ester enamine and cyclic ben-
zaldehyde derivatives of dimedone. The intermediates
thus formed further undergo condensation to yield
polyhydroquinolines.
Subsequent to the above results, the protocol was
extended to a variety of aromatic aldehydes using
VDDAP (0.1 g) in the methanol : water (ϕr = 1 : 1)
mixture at ambient temperature. The effect of aro-
matic aldehydes carrying either electron-donating or
electron-withdrawing substituents in the ortho, meta,
and para positions exhibits equal facility in product
formation with good to high yields. But the para-
substituted aldehydes afforded better results than the
ortho substituent due to the steric hindrance asso-
done, and ammonium acetate in methanol : water
(1 : 1) mixture at ambient temperature: effect of VD-
DAP catalyst dosage
a
Amount of catalyst/g
Time/min
Yield /%
0
.03
290
220
180
120
59
68
74
85
0.05
0
0
.07
.10
a) Isolated yield.
tem permitting the reaction to proceed smoothly but
yielding a moderate amount of the product (65 %).
When VDDAP was used in the presence of the
methanol : water (ϕr = 1 : 1) mixture at ambient tem-
perature the reaction was completed smoothly within
2
h and afforded the product with an 83 % yield (Ta-
ble 3, entry 6). The results indicate that polar sol-
vents, methanol, and water, solubilise the reactants,
bring the reactants onto the surface of the catalyst and
enhance the yield. Studies show that VDDAP in the
presence of the methanol : water mixture was found
to be an effective catalyst towards the reaction in re-
spect of reaction time as well as of the product yield
at ambient temperature (Fig. 10).
To study the optimisation of the catalyst, the reac-
tion was investigated using different amounts of cat-
alyst ranging from 0.03 g to 0.1 g (Table 4). It was
found that the reaction product yield increased with

viii
A. Rajini et al./Chemical Papers
Fig. 11. Proposed reaction mechanism for formation of polyhydroquinolines.
Table 5. VDDAP catalysed (0.1 g) synthesis of polyhydro-
quinoline derivatives in methanol : water (1 : 1) mix-
ture at ambient temperature: effect of substituents
withdrawing groups facilitated the reaction rapidly
and afforded higher yields in shorter reaction times.
The catalyst reusability was examined by treating
benzaldehyde (1.0 mmol) 5,5-dimethylcyclohexane-
a
Entry
Ar
Time/min
Yield /%
1
,3-dione (1.0 mmol), ethylacetoacetate (1.0 mmol),
1
2
3
4
5
6
7
8
9
C6H5
p-ClC6H5
120
135
140
160
120
90
120
110
90
83
70
68
69
78
73
76
79
82
80
and ammonium acetate (1.0 mmol) in the presence
of VDDAP (0.1 g). At the end of the reaction, the
catalyst was removed by filtration, washed with di-
ethyl ether, dried at ambient temperature, and re-
used in the succeeding cycles. The reaction proceeded
smoothly with an increase in reaction time and af-
forded moderate to good yields in successive runs.
The results show that the catalyst could be re-used
for three successive runs without appreciable loss of
catalytic activity. The product yields achieved in the
subsequent cycles were found to be 83 %, 79 %, 75 %,
and 74 % (Table 6).
p-MeC6H5
p-OMeC6H5
m-NO2C6H5
p-OHC6H5
p-FC6H5
o-NO2C6H5
p-NO2C6H5
p-BrC6H5
10
90
a) Isolated yield.
Table 6. Reusability of VDDAP catalyst for synthesis of poly-
hydroquinolines using methanol : water (1 : 1) mix-
ture
Conclusions
In summary, a novel VDDAP was synthesised at
ambient temperature employing a vanadium precur-
sor in the presence of phosphate using organic amine
as the template. The powder XRD data suggest the
presence of VOPO4 and hydrated VOPO4 phases in
the framework of the material. The presence of –V—O
Entry
Run
Time/min
Yield/%
1
2
3
4
Fresh catalyst
120
180
200
230
83
79
75
74
1
2
3
and V—O—P bonds in the framework was confirmed
by the presence of the corresponding vibrational bands
of the infrared and Raman spectra. The coexistence of
4
+
5+
V
and V in the framework was suggested from the
31
ciated with the ortho substituent. The correspond-
ing products and yields are presented in Table 5. It
was also observed that aldehydes bearing electron-
UV-VIS DRS studies. The P MAS NMR spectrum
revealed the phosphorous atoms to be of the VOPO4
phases. 13C suggests the interaction of an amino group

A. Rajini et al./Chemical Papers
ix
with the vanadium phosphate matrix. The catalytic
application of this material in the synthesis of polyhy-
droquinolines demonstrated the efficiency of the ma-
terial. The use of this inexpensive and reusable cata-
lyst renders the protocol attractive from an economic
perspective. The catalyst can be recycled and reused
without any loss of catalytic activity in subsequent
cycles of the reaction. These characteristics render
the procedure an attractive alternative to the exist-
ing methods for the synthesis of polyhydroquinolines
at ambient temperature in a one-pot synthesis.
Dasgupta, S., Agarwal, M., & Datta, A. (2004). Surfactant as-
sisted organization of an exfoliated vanadyl ortho phosphate
to a mesostructured lamellar vanadium phosphate phase.
Microporous and Mesoporous Materials, 67, 229–234. DOI:
10.1016/j.micromeso.2003.11.006.
Datta, A., Dasgupta, S., Agarwal, M., & Ray, S. S. (2005).
Mesolamellar VPO phases obtained by incorporating long
chain alkyl amine surfactants into the layered vanadium
phosphate dihydrate phase. Microporous and Mesoporous
Materials, 83, 114–124. DOI: 10.1016/j.micromeso.2005.03.
019.
Dias, C. R., Portela, M. F., Galán-Fereres, M., Ba n˜ ares, M.
A., López Granados, M., Pe n˜ a, M. A., & Fierro, J. L. G.
(1997). Selective oxidation of o-xylene to phthalic anhydride
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Evans, C. G., & Gestwicki, J. E. (2009). Enantioselective
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Acknowledgements. The authors A. R., and M. N. are
grateful to the Director, the National Institute of Technology
Warangal and MHRD, the Government of India for providing
their fellowships.
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