Characterization of catalyst
FT-IR spectra for the catalyst preparation steps are reported in Fig. 1. For FT-IR spectrum of GO, the peak at 3398 cm-1 is attributed to the O-H group stretching vibrations. The band at 1730 cm-1 describes carbonyl stretch for carboxylic acid. The peaks at 1383 and 1060 cm-1 assigned to the C–O stretching vibrations and epoxy groups, respectively. The FT-IR spectrum of SiO2 exhibits the adsorption peaks at 798, 1089 cm-1 corresponding to asymmetric vibrations of the Si–O–Si bonds. The band at 3370 cm-1 describes hydroxyl group vibrations. In SiO2@Cl and SiO2@Ethylenediamine spectra, the bands at around 950 cm-1 is related to ethoxy moieties vibrations. Functionalized graphene oxide shows the characteristic peak in 1102 cm-1 which reveals that functionalized SiO2 was successfully grafted on the graphene oxide.
XRD patterns of the catalyst in different steps are depicted in Fig. 2. GO sheets show a characteristic peak around 12o which proves the synthesis of graphene oxide. In comparison graphene oxide and functionalized graphene oxide, the new broad peak at 2θ = 25o is related to amorphous SiO2 which shows surface functionalization of graphene oxide. The small peak at 2θ = 44o correspond to cobalt in XRD pattern of final catalyst confirm successful modification of the GO surface.
The SEM images of GO(a) and GO@f-SiO2@Co (b) has been represented in Fig. 3. The SEM image of graphene oxide clearly shows the layer sheet structure of graphene oxide and GO@f-SiO2@Co exhibits the surface modification of graphene oxide with functionalized silica nanoparticles.
The presence of Si, Co, C, N in EDS spectrum of the catalyst (Fig. 4) confirm decoration of graphene oxide surface with functionalized SiO2.
The Raman spectra for GO and GO@f-SiO2 are shown in Fig. 5. The characteristic peaks for Go at 1362 and 1595 cm-1 are attributed to D and G bands, respectively. Also, the spectrum of GO@f-SiO2 also shows these peaks which confirm the presence of graphene oxide in the structure. In addition, after functionalization of GO slight increase in the ratio of ID/IG, indicating more transition from sp2 to sp3 from grafting of f-SiO2 on the graphene oxide.
According to the differential thermal analysis (DTA)/Thermogravimetric analysis (TGA) for the final catalyst (Fig. 6), the primary stage of decomposition occurred at 220 oC and continued to 800 oC with 18% weight loss in endothermic condition according to the curve of DTA. which is attributed to decomposition of the organic functional groups on the graphene oxide surface.
Catalyst reusability
The important point for a proper catalyst is recovery and recycling. The reusability of f-SiO2@GO@Co was investigated in the model reaction between phenylhydrazine, ninhydrin, and 2-nitrobenzaldhyde. For checking the reusability, after the completion of the reaction, the catalyst was recovered using filtration, and washed with ethanol to remove impurities and then dried. The recovery of the catalyst was excellent with an average yield (96%) after five times subsequent use. As shown in Fig. 7 the catalyst activity without considerable loss was approximately same for five cycles.
Proposed mechanism
In the first step, reaction of phenylhydrazine (1) with benzaldehyde (2) using f-SiO2@GO@Co as catalyst to form 1-benzylidene-2-phenylhydrazone (5) intermediate. Next, the intermediate (5) attacks to ninhydrin that was activated by the catalyst to generate zwitterionic (6). Further, its tautomer (7) by intermolecular H-atom transfer an nucleophile addition to a carbonyl group forms indeno[1,2-c]pyrazol- 4(1H)-one derivatives (4a-k) (Scheme 2).
Analysis and characterization of synthesized compound
In order to optimize the reaction conditions, different parameters such as temperature, solvent and catalyst loading were assessed on the model reaction between phenylhydrazine, ninhydrin, and 2-nitrobenzaldehyde. Firstly, the reaction was conducted in MeCN without catalyst in r.t. and, no product was formed after 24 h. When the reaction was carried out in the presence of f-SiO2@GO@Co in MeCN at 60oC, no significant yield was formed after 24 h (50%). Also, the reaction was carried out in the presence of f-SiO2@GO in ethanol and the product was obtained in 75% after 24 h (Table 1, entry4). Then it was tested in ethanol in different temperatures in the presence of f-SiO2@GO@Co as a catalyst (Table 1). The results revealed the yield of product increase at 60 oC (Table 1, entry7). According to results shown in Table 1, the best performance of the catalyst was in the presence of ethanol as a solvent. Furthermore, we investigated the effect of catalyst loading (Table 2) and the yield improvement was found with increasing the catalyst from 3 to 15 wt%. It should be mentioned, increasing the more amount of catalyst did not affect on the yield. The performance of the 15 wt% f-SiO2@GO@Co in the reaction rate in the presence of ethanol as efficient solvent and various aldehydes are given in Table 3.
To confirm the accuracy of desired products (4a–k), we used FT-IR, 1H NMR, and 13CNMR. The IR spectrum of the compound 4i exhibits the peak at 3461 cm-1 that is attributed to the stretching vibrations of hydroxyl groups. The strong peak at around 1710 cm-1 indicates the presence of carbonyl group. It shows singlet peaks at δ = 7.93 ppm and δ = 7.31 ppm due to hydroxyl groups. The protons on the aromatic rings appear between δ = 8.37 to 7 ppm. In addition, the peak for carbonyl group in 13CNMR appears at 196 ppm. The (C-O) carbons observe in 96.06 and 89.12 ppm.
Table 1
Investigation different temperature and solvents on the reaction a
Entry
|
Solvent
|
Catalyst
|
Temperature(oC)
|
Time
|
Yield b (%)
|
1
|
MeCN
|
-
|
r.t.
|
24 h
|
-
|
2
|
MeCN
|
f-SiO2@GO@Co
|
60
|
24 h
|
50
|
3
|
Ethanol
|
-
|
60
|
24 h
|
20
|
4
|
Ethanol
|
f-SiO2@GO
|
60
|
24 h
|
75
|
5
|
Ethanol
|
f-SiO2@GO@Co
|
25
|
45
|
60
|
6
|
Ethanol
|
f-SiO2@GO@Co
|
40
|
30
|
85
|
7
|
Ethanol
|
f-SiO2@GO@Co
|
60
|
20
|
96
|
8
|
Ethanol/H2O
|
f-SiO2@GO@Co
|
60
|
50
|
89
|
9
|
CHCl3
|
f-SiO2@GO@Co
|
60
|
50
|
40
|
a Reaction conditions: phenylhydrazine (1 mmol), 2-nitro benzaldehyde (1 mmol), and ninhydrin (1 mmol) in the presence of f-SiO2@GO@Co as catalyst. |
bIsolated yield |
Table 2
Investigation of the amounts of f-SiO2@GO@Co on the reaction a
Entry
|
Catalyst
|
Time(min)
|
Yieldb (%)
|
1
|
3
|
140
|
58
|
2
|
5
|
140
|
75
|
3
|
10
|
50
|
85
|
4
|
15
|
20
|
96
|
a Reaction conditions: ethanol (5 ml), phenylhydrazine (1 mmol), 2-nitro benzaldehyde (1 mmol), and ninhydrin (1 mmol) in the presence of SiO2@GO@Co as catalyst. b Isolated yield. |
Spectral Data
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(4-Nitrophenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one(4a): Yellow solid; m.p. 235–237 oC; IR (KBr): ʋ = 3410, 1725, 1594,1528, 1493 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 8.34–8.30 (d, J = 8.8 Hz, 2H), 8.28–8.24(d, J = 8.8 Hz, 2H), 8.07 (s, OH), 7.82–7.78 (d, J = 8.1 Hz, 2H), 7.76–7.72 (m, 2H), 7.68 (d, J = 8.0 Hz, 1H), 7.58 (t, J = 7.6 Hz, 1H), 7.43–7.38 (t, J = 8.0 Hz, 2H), 7.29 (s, OH), 7.09 (t, J = 7.6 Hz, 1H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(4-Chlorophenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one (4b): Yellow solid, m.p. 229–232 oC; IR (KBr): ʋ= 3273, 1701, 1595, 1489 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 8.10–8.07 (d, J = 8.3 Hz, 2H), 7.84 (s, OH), 7.76–7.69 (m, 4H), 7.65 (d, J = 8 Hz, 1H), 7.54 (t, J = 7.2 Hz, 1H), 7.48–7.44 (d, J = 8.3 Hz, 2H), 7.39–7.34 (t, J = 8 Hz, 2H), 7.14 (s, OH), 7.03(t, J = 7.5 Hz, 1H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(4-Bromophenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one (4c): Yellow solid; m.p. 222–225 oC; IR (KBr): ʋ= 3307, 3073, 1701, 1595, 1489 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 8.10–8.07 (d, J = 8.3 Hz, 2H), 7.97 (s, OH), 7.76–7.69 (m, 4H), 7.67–7.64 (d, J = 8 Hz, 1H), 7.55 (t, J = 7.2 Hz, 1H), 7.48–7.44 (d, J = 8.3 Hz, 2H), 7.33–7.25 (t, J = 8 Hz, 2H), 7.14 (s, OH), 7.02 (t, J = 7.5 Hz, 1H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(3-Nitrophenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one(4d): Yellow solid; m.p. 242–244 oC ; IR (KBr): ʋ= 3474, 1725, 1596, 1494 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 8.94 (s, 1H), 8.47 (d, J = 8.0 Hz, 1H), 8.17 (d, J = 8 Hz, 1H), 8.01 (s, OH), 7.81–7.72 (m, 4H), 7.69–7.65 (t, J = 6.1 Hz, 2H), 7.58 (t, J = 7.4 Hz, 1H), 7.42–7.36 (t, J = 7.8 Hz, 2H), 7.29 (s, OH), 7.08 (t, J = 7.4 Hz, 1H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(4-methylphenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one(4e): Yellow solid; m.p. 253–255 oC; IR (KBr): ʋ= 3439, 3267, 1707, 1595, 1491 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 7.99–7.96 (d, J = 7.9 Hz, 2H), 7.75–7.67 (m, 5H), 7.63(d, J = 7.9 Hz, 1H), 7.54 (t, J = 7.5 Hz, 1H), 7.39–7.33 (t, J = 7.2 Hz, 2H), 7.22–7.16 (d, J = 7.5 Hz, 2H), 7.03 (s, OH), 6.99 (d, J = 6.7 Hz, 1H), 2.31 (s, 3H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(4-methoxyphenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one (4f): Orange solid; m.p. 210–213 oC ;IR (KBr): ʋ= 3426, 1708, 1596, 1492 cm-1;1H NMR (400 MHz, DMSO): δ = 8.05–8.01 (d, J = 8.4 Hz, 2H), 7.73–7.68 (m, 5H), 7.63 (m, 1H), 7.54 (t, J = 6.2 Hz, 1H), 7.37–7.32 (t, J = 7.1 Hz, 2H), 7.04–6.94 (m, 4H), 3.78 (s, 3H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(2-hydroxyphenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one(4 g): Yellow solid; m.p. 190–193 oC; IR (KBr): ʋ=3392, 1724, 1595, 1491 cm-1; 1H NMR (400 MHz, DMSO): δ = 10.4 (s, OH), 8.29 (d, J = 8 Hz, CH), 7.90 (s, OH), 7.75-–7.69 (m, 2CH), 7.58– 7.55 (m, 3CH), 7.51 (d, J = 7.9 Hz, 1H), 7.44–7.39 (t, J = 8 Hz, 2CH), 7.34 (s, OH), 7.24 (t, J = 8 Hz, 1H), 7.11 (t, J = 7.2 Hz, 1H), 6.96 (t, J = 7.2 Hz, 1H), 6.89 (d, J = 8.1 Hz, 1H).
cis-3a,8b-Dihydro-3a,8b-dihydroxy-1,3-diphenylindeno[1,2-c]pyrazol-4(1H)-one(4 h): Yellow solid; m.p. 219–222 oC; IR (KBr): ʋ=3430, 1706, 1594,1491 cm-1; 1H NMR (400 MHz, DMSO-d6): δ = 8.12–8.07 (d, J = 8 Hz, 2H), 7.77–7.72 (d, J = 8.0 Hz, 2H), 7.69–7.62 (m, 3H), 7.52–7.48 (t, J = 7.2 Hz, 2H), 7.38–7.26 (m, 6H), 6.97(t, J = 7.2 Hz, 1H).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(2-Nitrophenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one(4i): Yellow solid; m.p. 165–168 oC; IR (KBr): ʋ=3461, 1710, 1597, 1530 cm-1; 1H NMR (400 MHz, DMSO-d6)= δ = 8.38 (d, J = 8 Hz, 1H), 7.93(s, OH), 7.78–7.69 (m, 4H), 7.61–7.50 (m, 5H), 7.40–7.34 (t, J = 8 Hz, 2H), 7.31 (s, OH), 7.06 (t, J = 7.2 Hz, 1H); 13C NMR (DMSO): δ = 196.63 (C = O), 148.54 (C), 147.60 (C), 141.732 (C), 137.56 (C), 137.24 (C), 136.78 (C), 134.34 (CH), 130.99 (CH), 130.76 (CH), 129.93 (CH), 129.04 (2CH), 125.35 (CH), 123.88 (CH), 123.28 (CH), 123.24 (CH), 122.74 (CH), 117.49 (2CH), 96.06 (C), 89.12 (C).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(2,3-dihydroxyphenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one (4j): Yellow solid; m.p. 222–224 oC; IR (KBr): 3473, 3365,1726, 1598, 1494 cm-1; 1H NMR (400 MHz, DMSO): δ = 10.45 (s, OH), 8.91 (s, OH), 7.89 (s, OH), 7.78– 7.66 (m, 3H), 7.6– 7.54 (m, 3H), 7.50 (d, J = 6.9 Hz, 1H), 7.45–7.39 (dd, J = 6.8, 2H), 7.32 (s, 1H), 7.18–7.07 (m, 1H), 6.81–6.71 (m, 2H). 13C NMR (DMSO-d6): δ = 197.00 (C), 156.40 (C), 147.51 (C), 145.34 (C), 141.28 (C), 136.84 (C), 134.19 (C), 130.77 (C), 129.98 (CH), 129.34 (2CH), 129.25 (CH), 125.39 (CH), 123.42 (CH), 122.91 (CH), 118.89 (CH), 117.73 (2CH), 116.06 (CH), 115.08(CH), 94.71 (C), 89.66 (C).
Cis-3a,8b-Dihydro-3a,8b-dihydroxy-3-(2-hydroxy-5-Bromo-phenyl)-1-phenyl-indeno[1,2-c]pyrazol-4(1H)-one (4 k): Yellow solid, m.p. 226–228 oC; IR (KBr): 3324, 3192, 1735, 1597, 1488 cm-1; 1H NMR (400 MHz, DMSO): δ = 10.47 (s, OH), 8.43 (s, 1H), 8.03 (s, 1H), 7.77 (d, J = 7.6 Hz, 1H), 7.72 (d, J = 7.6 Hz, 1H), 7.62–7.56 (t, J = 6.9 Hz, 3H), 7.53 (d, J = 8 Hz, 1H), 7.45–7.36 (m, 4H), 7.12 (t, J = 7.2 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H).
13C NMR (DMSO-d6): δ = 196.83 (C = O), 155.50 (C), 147.53 (C), 143.57 (C), 141.00(C), 137.00 (C),134.13(C), 132.19 (C), 131.14 (CH), 130.85 (CH), 129.28 (2CH), 125.40 (CH), 123.58 (CH), 123.22 (CH), 118.33 (CH), 117.93 (2CH), 117.10 (CH), 110.15 (CH), 94.80 (C), 89.27 (C).