2182 Alharthi
Asian J. Chem.
O
A comparative study of FT-IR for calcined (HPW-Cal)
and non-calcined (HPW) sample is depicted in Fig. 2. From
the IR spectra, it is evident that Kegging structure unaltered
upon heat treatment [16]. A clear defined peak at 1075.48 and
963.93 cm-1 was observed for P-O and W=O stretching vibra-
tions. On the other hand, a peak at 883.07 cm-1 signified for
W-O-W modes of vibration.
Ar
O
O
HPW
ArCHO
room temp.
O
1
3a-f
2
Scheme-I: Synthesis of benzylidene derivatives (3a-f) from a aromatic
aldehydes (1) and dimedone (2)
1584 (C=C); 1H NMR (DMSO, δ ppm): 7.89, (s, 1H, CH=),
6.76-7.07 (4H, m, Ar-H); 13C NMR (DMSO, δ ppm): 196.58,
163.14, 158.00, 136.88, 129.45, 115.06, 113.68, 55.37, 50.51,
32.32, 30.74, 29.14, 26.93.
HPW
HPW-Cal
200
5,5-Dimethyl-2-(2,4,6-trimethoxybenzylidene)cyclo-
hexane-1,3-dione (3e): White, m.p.: 207 ºC, m.f. C18H22O5.
FT-IR (ATR, νmax, cm-1): 2955 (C=H), 1665, 1625 (2C=O),
100
1
1591 (C=C); H NMR (DMSO, δ ppm): 7.26 (s, 1H, CH=),
6.41-6.61 (2H, m, Ar-H); 13C NMR (DMSO, δ ppm): 196.69,
163.53, 152.80, 140.36, 136.38, 114.71, 105.84, 60.37, 56.23,
50.50, 32.33, 31.63, 29.16, 26.81.
1075.48
1614.33
0
2-(Indoline-3ylmethylene)-5,5-dimethylcyclohexane-
1,3-dione (3f): Light pink, m.p.: 112 ºC, m.f. C17H19NO2. FT-
IR (ATR, νmax, cm-1): 2930 (C=H), 1631, 1611 (2C=O), 1575
746.81
963.93
3000
2500
2000
1500
1000
500
1
Wavenumber (cm–1)
(C=C); H NMR (DMSO, δ ppm): 8.29 (s, 1H, CH=), 7.20-
8.10 (4H, m,Ar-H); 13C NMR (DMSO, δppm): 185.45, 138.94,
137.50, 123.93, 122.59, 121.28, 112.88, 102.88, 32.59, 28.41.
Fig. 2. FT-IR spectra analysis for non-calcined (HPW) and calcined
tungstophosphoric acid (HPW-Cal)
RESULTS AND DISCUSSION
The TGA profile for tungstophosphoric acid catalyst
(HPW) is shown in Fig. 3. It can be seen that there are three
weight loss regions at about 50, 175 and 450 ºC, respectively.
The first weight loss, around 5 % can be attributed to the removal
of physisorbed water, whereas the second weight loss, roughly
3 %, can be ascribed to the bonded water to acidic protons in
H3PW12O40. The weight loss beyond 450 ºC was due to the
loss of the remaining water molecules that corresponds to the
loss of all acidic protons and the beginning of decomposition
of the Keggin structure. This result is consistent with previous
studies [17]. This indicates that calcination of HPW at 300 ºC
does not effect the structure of HPW, in good agreement with
FT-IR spectrum, and increases the acidity of HPW by removal
of water molecules.
Characterization of the catalyst was performed using
different techniques such as XRD, SEM and FT-IR analysis
before and after calcination. The powder XRD patterns of non-
calcined and calcined tungstophosphoric acid samples are
illustrated in Fig. 1. From the pattern of non-calcined tungsto-
phosphoric acid (HPW), it is obvious that there is a sharp
crystalline peak at 2θ = 5º which matches with the position of
tungsten metal. On the other hand, it was absent in calcined
tungstophosphoric acid (HPW-Cal), which can be attributed
to the evaporation of water molecules adhered before calci-
nation. Generally, tungstophosphoric acid appeared to be more
crystalline after calcination and eventually due course bronsted
acid capacity increased [14].
SEM images for non-calcined (HPW) and calcined tungsto-
phosphoric acid (HPW-Cal) are shown in Fig. 4. From the
HPW
HPW-Cal
102
100
98
0.4
0.2
200
100
0
0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
96
94
92
90
10
20
30
40
50
60
70
80
150
300
450
Temperature (°C)
Fig. 3. TGA analysis of tungstophosphoric acid
600
750
900
2θ (°)
Fig. 1. Powder X-ray diffraction patterns for non-calcined (HPW) and
calcined tungstophosphoric acid (HPW-Cal)