Synthesis and comparison of different Ce:Mn ratios
Low surface area and leaching of metal ions from the surface of LDH composites reduce the efficiency of the catalyst process. As a result, in this work, to improve the surface area and increase the catalytic performance, different molar ratios of Ce to Mn (1:1, 1:2, 1:3, and 1:4) were synthesized and characterized with ICP-OES, XPS, BET, and UV-Vis.
Characterization of D by ICP
D was synthesized in four molar ratios of 1:1 (sample one), 1:2 (sample two), 1:3 (sample 3) and 1:4 (sample four) of Ce to Mn and were used separately as catalysts in the model reaction (1 mmol isatin, 1 mmol of aniline and 1 mmol of dimedone). Then, the content of copper was determined in D using ICP analysis, before (fresh) and after (used) its use. The results obtained from ICP show that the leaching of copper from the surface of the used D with a molar ratio of 1:4 is lower than the other three ratios, and as a result, this catalyst has a better efficiency (Table 1). These results are also consistent with UV-Vis and BET analysis.
Table 1. The Cu% in D before and after the reactions in the synthesis of 1(a-n).
Entry
|
The ratio of Ce: Mn
|
Cu% in D
|
Yield (%)
|
before the reaction (fresh)
|
after the reaction (used)
|
1
|
1:1 (sample one)
|
64
|
37
|
88
|
2
|
1:2 (sample two)
|
69.1
|
43.72
|
93
|
3
|
1:3 (sample three)
|
65.1
|
63.3
|
94
|
4
|
1:4 (sample four)
|
73.1
|
68.6
|
96
|
Characterization of D by UV/Vis
Fig. 3 shows the UV spectra of: 1) The copper acetate solution (blue), and 2) The remained copper acetate filtrate from the product of the reaction between copper acetate solution and four different molar ratios of 1:1, 1:2, 1:3, and 1:4 of D (green).
D was synthesized with different molar ratios of 1:1, 1:2, 1:3 and 1:4 of cerium to manganese. Then, to determine the amount of the loaded copper on it, the amount of copper in the copper acetate solution was measured before adding to the ligand and after that, using the UV/Vis spectrum. The UV absorption spectrum of copper acetate in D with the1:4 ratio showed that all copper acetate was relatively consumed indicating a strong interaction between copper ions and the ligand (Ce-Mn-LDH@CPTMS@NAP) to form a more stable copper complex (D) compared to the other three samples.
Characterization of D by BET
The textural properties of the LDH composite with four molar ratios (1:1, 1:2, 1:3, and 1:4) of Ce to Mn were investigated by nitrogen absorption-desorption analysis, and the obtained results (the surface area values, pore volumes, and pore diameters) were listed as below (Table 2).
Table 2. The N2 absorption-desorption parameters for different ratios of D.
LDH
|
SBET (m2/g)
|
Vt (cm3/g)
|
DBJH (nm)
|
Ce-Mn-LDH 1:1
|
34.740
|
0.1598
|
19.173
|
Ce-Mn-LDH 1:2
|
29.922
|
0.1656
|
21.362
|
Ce-Mn-LDH 1:3
|
14.781
|
0.0975
|
26.412
|
Ce-Mn-LDH 1:4
|
20.787
|
0.1316
|
25.325
|
According to Table 2, with increasing the mass ratio of Mn to Ce, the specific surface area (20.787 m2/g) and the pore volume (0.1316 cm3/g) decreases and the pore diameter (25.325 nm, in 1:4 molar ratio) increases. This observation is consistent with the findings of Huang et al., who reported that the specific surface area is inversely related to the pore size40.
As a result, with increasing the pore diameter, the specific surface area decreases. The larger pores at the ratio of 1:4 confirm the presence of a porous and macroporous structure in D, which is significant for potential applications such as adsorbents and catalysts (Fig. 4).
Characterization of D by XPS
The XPS analyses was performed to investigate the capacity of elements on the D surface with different molar ratios of Ce to Mn (1:1, 1:2, 1:3, and 1:4). The XPS spectra show the presence of carbon, oxygen, nitrogen, silicon, cerium, and manganese elements in D (Fig. 5-8).
Also, the corresponding Table 3 shows shifts of XPS peaks and binding energies of all elements in four prepared LDHs which are consistent with previous reports41-46.
Table 3. Measured values of XPS analyses in 1:1, 1:2, 1:3, and 1:4 molar ratios
Entry
|
The
Ce: Mn
|
Si2p
|
C1s
|
N1s
|
O1s
|
Mn2p
|
Ce3d
|
Cu2p
|
1
|
1:1
(sample one)
|
88.69
96.58
99.94
110.01
|
284.46
285.74
290.00
|
330.28
|
531.81
533.17
|
643.66
652.36
|
884.13
887.83
906.51
902.26
|
935.81
941.65
945.28
|
2
|
1:2
(sample two)
|
95.65
99.19
103 .77
107.04
|
281.63
286.16
290.64
|
330.0
|
532.92
532.27
|
643.02
654.70
|
875.54
886.41
901.65
906.62
|
935.87
947.24
955.17
|
3
|
1:3
(sample three)
|
95.16
99.89
104 .15
107.54
|
282.35
285.81
290.40
|
330.13
|
530.79
532.49
|
643.58
654.40
|
875.92
886.31
903.69
918. 02
|
935.77
947.58
954.95
|
4
|
1:4
(sample four)
|
96.04
101.3
104.3
108.95
|
284.58
286.87
290.80
|
330.25
|
532.30
533.52
|
642.94
655.72
|
876.05
886.38
904.01
918.17
|
935.99
947.94
955.51
|
The XPS analyses of 1:1, 1:2, 1:3 and 1:4 molar ratios for Cu2p, Ce3d, Mn2p, O1s, C1s, Si2p and N1s elements were investigated and compared which reveal the oxidation states of Cu2p through three distinct peaks across four samples.
The peaks with binding energies of 935.81, 935.87, 935.77, and 935.99 eV for Cu2p3/2, and 945.28, 955.17, 954.95, and 955.51 eV for Cu2p1/2 are clear indications for the presence of Cu and Cu+ ion, respectively. In addition, the peak found within the range of 941.65, 947.24, 947.58, and 947.94 eV is attributed to the Cu2+ ion located on the LDH composite structure’s surface.
Table 3 represents data suggesting that an increase in the Mn to Ce mass ratio is associated with an increase in both the peak intensity and the Cu2p bond energy. This trend indicates a strengthening of the Cu-N bond and, consequently, increasing the stability of the copper complex. These observations are also confirmed by the results obtained from ICP and UV/Vis analyses.
The Ce3d spectrum is characterized by high-resolution peaks in the range of 875-918 eV, representing the Ce3d5/2 and Ce3d3/2 states. Specifically, the Ce3d3/2 state is represented by peaks at (902.26, 906.51), (901.65, 906.62), (903.69, 918.02), and (904.01, 918.17) eV. Meanwhile, the Ce3d5/2 state is denoted by peaks at (887.83, 884.13), (875.54, 886.41), (875.92, 886.31), and (876.05, 886.38) eV. These peaks confirm the presence of Ce3+ oxidation state in the structure of Ce-Mn-LDH in all four investigated ratios.
In the broad Mn2p spectrum, two distinct peaks are observed. The Mn2p3/2 peaks are located at 642.94, 643.02, 643.66, 643.58 eV, and the Mn2p1/2 peaks are found at 652.36, 654.40, 654.70, 655.72 eV. These peaks are indicative of the presence of Mn2+ and Mn3+ ions within the material.
The O1s spectrum shows a set of peaks in the range of (531.81, 533.17), (532.92, 532.27), (530.79, 532.49), and (532.30, 533.52) eV. These peaks are related to metal-oxygen bonds (M-O), (C=O) and water molecules adsorbed on the surface, respectively.
The C1s spectrum covers a wide range with peaks at 290.00, 290.64, 290.40 and 290.80 eV corresponding to the carboxylate group (O-C=O). In addition, the peaks representing to C=C and carbonate ions (CO32-) are in the range of (284.46, 285.74), (281.63, 286.16), (282.35, 285.81), and (284.58, 286).
The Si2p spectrum reveals peaks at (88.69, 96.58, 99.94), (95.65, 99.19, 103.77), (95.16, 99.89, 104.15), and (96.04, 101.3, 104.3) eV, which are indicative of (Si), (Si-C), and (Si-O) bonds. Additionally, peaks at 110.01, 107.04, 107.54, and 108.95 eV are attributed to SiO2.
The analysis of binding energy results shows that increasing the molar ratio of manganese to cerium leads to an increase in peak intensity and binding energies. As a result, by increasing the binding energy, the electric charge density and interlayer anions increase, and by creating a strong electrostatic attraction, a strong network of Ce-Mn-LDH composite with high surface properties is formed for modification. This modification leads to the formation of a stable copper complex that improves the catalytic properties.
In addition, the obtained results from the BET, UV-Vis, XPS and ICP analyses showed that D with the 1:4 molar ratio of Ce to Mn is the best ratio to be used as a potent catalyst for the synthesis of spiro compounds 1(a-n).
Characterization of D (1:4 ratio)
The structure and morphology of D were determined by Fourier-Transform Infrared spectroscopy (FT-IR), X-ray Diffraction analysis (XRD), Energy Dispersive X-ray analysis (EDX), EDX-Mapping, Scanning Electron Microscopy (SEM), Transmission Electron Micros-copy (TEM), Thermo-Gravimetric-Differential Thermal Analysis (TGA-DTA), Ultraviolet-visible (UV-Vis) spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray Photoelectron Spectroscopy (XPS), and Brunauer–Emmett–Teller (BET).
Characterization of D
Fig. 9 shows the FT-IR spectra of A, B, C, and D. In curve A, the bands at 534-862 cm−1 are due to the LDH lattice vibrations (Mn-O, Ce-O, Ce-O-Mn)47-48. The broad peak around 3445 cm−1 is related to the stretching of -OH groups attached to metal ions. The bending vibration of interlayer water is found at 1636 cm−1 and absorption bands at 1740 and 1383 cm-1 indicate the stretching vibration of C=O and C-O. The band in 1449 cm-1 is due to the asymmetric band of in the CO2−.
Curve B shows the absorption peaks at 1037 and 1135 cm-1 which are attributed to the Si-O-M and Si-O-Si bonds confirming the modification of the surface of the LDH.
In curve C, a band at 3435 cm−1 is related to the NH bond, and the peaks at 2842 and 2958 cm−1 belong to the aliphatic CH group. Also, the weak bands at 1145, and 1309 cm−1 are attributed to the C-O and C-N vibration bands, respectively. In addition, the two peaks at 1418, and 1640 cm−1 belong to the C-N and N-H bonds.
In curve D, the peak at about 497 cm−1 is related to the Cu stretching modes.
Characterization of D (1:4) by XRD
The XRD structural information of A and D is shown in Fig. 10. The sharp and symmetrical peaks indicate the structure specifications of hydrotalcite. There are diffraction peaks at 2θ = 15.85°, 24.1°, 26.45°, 31.3°, 44.95°, 51.55°, 60°, 62.9° which are corresponded to the crystal planes of A. The diffraction peaks at 2θ = 23.65°, and 26.15° can be related to a metal oxide containing Ce and Mn. The XRD pattern of D is broad with low intensity due to the large ionic radius of Ce in the layers47-49. The appearance of peaks corresponding to copper metal at 2θ = 6° indicates the successful formation of D50.
Characterization of D (1:4) by EDX
To evaluate the catalyst content, the EDX analysis was used to confirm the presence of elements, namely C, O, N, Mn, Ce, Si, and Cu (Fig. 11).
Characterization of D (1:4) by SEM-mapping
Fig. 12 shows the qualitative elemental mapping, indicating the nice distribution of the expected chemical elements in D, namely Ce, Mn, C, O, N, Si, Cu, and all elements.
Characterization of D (1:4) by the SEM images
The surface and size of the particle catalyst were confirmed by the SEM images (Fig. 13). According to these SEM images, the spherical shape and the average particle size are estimated to be in the nanometer range (30-70 nm).
Characterization of D (1:4) by the TEM images
The crystalline structure and morphology of D were studied by the TEM images (Fig. 14). According to the basis of the TEM images, the core-shell structure and nature of the layered structure of the LDH phases suggest a strong interaction between the LDH sheets.
Characterization of D (1:4) by TGA-DTA
The thermal behavior of D was determined by the TGA-DTA curves in the temperature range of 25 to 1000 °C. At about 68.29 °C, organic solvents were lost. The weight loss at about 369.89 °C is probably related to the removal of water and CPTMS and NAP. The weight decreases at about 399.45 °C is related to the loss of carbonate ions (with the CO2 evolution) and the dehydroxylation of the LDH to show that the layered structure of D is stable up to 400 °C. The weight loss at about 450 °C is probably related to the decomposition of LDH. As the temperature increases, mass loss increases up to 1000 °C (Fig. 15).
Optimization of D (1:4)
To optimize the synthesis of 1(a-n), the one-pot three component condensation reaction of isatin, aniline, and 1,3-diketone were carried out in various temperature, catalyst amount, and solvent in the presence of D. The best optimal condition (a model reaction) was found to be the 1:1:1 mole of isatin, aniline, and diketone with 20 mg of D at 60 °C in ethanol (Table 4).
Table 4. Optimization of the reaction conditions for preparation of 1(a-n) by D.
Entry
|
Amount of catalyst
|
Solvent
|
Temp (°C)
|
Time (min)
|
Yield (%)
|
1
|
20 mg
|
H2O
|
r.t
|
90
|
45
|
2
|
20 mg
|
EtOH
|
r.t
|
50
|
75
|
3
|
20 mg
|
CH3CN
|
r.t
|
95
|
30
|
4
|
20 mg
|
no solvent
|
r.t
|
75
|
48
|
5
|
20 mg
|
H2O
|
reflux
|
60
|
68
|
6
|
20 mg
|
EtOH
|
reflux
|
50
|
80
|
7
|
20 mg
|
CH3CN
|
reflux
|
50
|
42
|
8
|
20 mg
|
EtOH
|
80
|
40
|
85
|
9
|
20 mg
|
EtOH
|
70
|
45
|
88
|
10
|
20 mg
|
EtOH
|
60
|
20
|
96
|
11
|
20 mg
|
EtOH
|
50
|
60
|
68
|
12
|
10 mg
|
EtOH
|
60
|
35
|
60
|
13
|
30 mg
|
EtOH
|
60
|
25
|
78
|
14
|
20 mg
|
no solvent
|
60
|
40
|
87
|
15
|
no catalyst
|
EtOH
|
60
|
120
|
65
|
Synthesis of 1(a-n) by D (1:4)
Based on the optimized results of the model reaction, spiro[acridine-9,3'-indole]triones 1(a-n) were synthesized in the similar conditions with high yields and short reaction times (Table 5). Since all prepared compounds were known, so they were characterized with comparison of their spectroscopic data and melting points with authentic samples.
According to Table 5, electron-withdrawing groups on aniline relatively increase the yield (entries 2-4), while the electron-releasing groups decrease it (entries 5, 6, 9, 10, 13, and 14).
Spectral data of 1(a-n)55-56
3,3,6’,6’-Tetramethyl-1’-phenyl-3,4,6’,7’-tetrahydro-1H-spiro[acridine-9,3’-indole]-1,2’,4’-(1’ H,2H,5’H,10H)-trione (1a)
Yield: 93%, m.p. 251-254 °C; IR: ʋ = 3329, 2960, 1724, 1694, 1647, 1599, 1475, 1377, 1348, 1229, 1129, 1199 and 905 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 0.95 (d, J = 7.0 Hz, 12H, CH3), 1.79-2.12 (m, 4H, CH2), 2.27-2.51 (m, 4H), 6.67 (d, J = 7.6 Hz, 1H, H-Ar), 6.72 – 6.85 (m, 2H, H-Ar), 6.90 (s, 1H, H-Ar), 6.93 (s, 1H, H-Ar), 7.04 (s, 1H, H-Ar), 7.09 (d, J = 7.6 Hz, 1H, H-Ar), 7.40 (s, 1H, H-Ar ), 8.85 (s, 1H, H-Ar ), 10.98 (s, 1H, N-H) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 203.9, 194.6, 182.3, 168.6, 144.7, 133.5, 131.7, 129.7, 128, 126.9, 121.9, 121.6, 120.3, 113, 111.7, 109.8, 108.5, 101.4, 100.6, 59.0, 54.2, 50.6, 46.8, 33.6, 32.8, 31.5, 29.1, 27.3 and 26.4 ppm.
1’-(2-Chloro-4-nitrophenyl)-3,3,6’,6’-tetramethyl-3,4,6’,7’-tetrahydro-1H-spiro[acridine-9,3’-indole]-1,2’,4’(1’H,2H,5’H,10H)-trione (1b)
Yield: 98%, m.p. 270-272 °C; IR: ʋ = 3430, 3057, 2962.97, 1733, 1711, 1667, 1617, 1470, 1346, 1315, 1223, 1168, 1031, 902, 747 and 675 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 0.96 (s, 12H, CH3), 1.86-2.25 (m, 4H, CH2), 2.42-2.70 (m, 4H, CH2), 6.75 (dd, 3H, J = 4.2 Hz, H-Ar), 7.05 (d, J = 7.5 Hz, 1H, H-Ar), 10.28 (s, 1H, N-H). 13C NMR (75 MHz, DMSO-d6) δC = 195.5, 178.7, 163.9, 144.3, 134.5, 128.2, 122.6, 121.1, 113.4, 108.9, 51, 32.1, 28.4 and 27.0 ppm.
7'-(2-Chloro-4-nitrophenyl)-1H-spiro[pyrimido[4,5-b]quinoline-5,5'-pyrrolo[2,3-d]pyrimidine]- 2,2',4,4',6'(1'H,3H,3'H,7'H,10H)-pentaone (1c)
Yield: 95%, m.p. 266-270 °C; IR: ʋ = 3366, 3263, 3096, 2845, 1770, 1712, 1619, 1482, 1470, 1409, 1348, 1229, 1184, 1120, 1028, 980, 769, 676 and 550 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 5.07 (s, 2H, N-H), 6.71 (d, J = 7.6 Hz, 1H, H-Ar), 6.92 (t, 1H, H-Ar), 7.12-7.22 (m, 2H, H-Ar), 10.60 (s, 1H, N-H), 11.16 (s, 1H, N-H), 11.23 (s, 1H, N-H) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 176.2, 168.1, 150.8, 143.6, 129.3, 128.6, 124.8, 110 and 54 ppm.
1-(2-Chloro-4-nitrophenyl)-1H-spiro[chromeno[2,3-b]pyrrole-3,11'-chromeno[2,3-b]quinoline]-2,4,12'(6'H)-trione (1d)
Yield: 91%, m.p. 200-203 °C; IR: ʋ = 3156, 3095, 3037, 2905, 2846, 1732, 1671, 1621, 1576, 1476, 1429, 1315, 1178, 1025, 976, 932, 757, 685 and 630 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 0.95 (d, J = 7.0 Hz, 12H, CH3), 1.79-2.12 (m, 4H, CH2), 2.19-2.54 (m, 4H, CH2), 6.67 (d, J = 7.6 Hz, 1H, H-Ar ), 6.72-6.85 (m, 2H, H-Ar ), 6.90 (s, 1H, H-Ar ), 6.93 (s, 1H, H-Ar ), 7.04 (s, 1H, H-Ar), 7.09 (d, J = 7.6 Hz, 1H, H-Ar), 7.40 (s, 1H, H-Ar), 8.85 (s, 1H, H-Ar ), 10.98 (s, 1H, N-H) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 176, 165.3, 160, 152.7, 143.5, 138.8, 133.4, 131.2, 130.4, 125.2, 124.9, 124.4, 123.6, 123.2, 122.2, 116.9, 116.7, 116.1, 112.7, 110.3, 101.3, 78.8 and 40.5 ppm.
1-(2,4-Dimethoxyphenyl)-1H-spiro[chromeno[2,3-b]pyrrole-3,11'-chromeno[2,3-b]quinoline]-2,4,12'(6'H)-trione (1e)
Yield: 88%, m.p. 281-285 °C; IR: ʋ = 3353, 3239, 3070, 2928, 1720, 1682, 1643, 1547, 1486, 1346, 1214 and 778 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 6.87 (d, J = 3.7 Hz, 2H, H-Ar), 7.21-7.30 (m, 2H, H-Ar), 7.36 (dd, 2H, H-Ar), 7.45-7.51 (m, 2H, H-Ar), 7.55 (td, J = 3.7 Hz, 3H, H-Ar), 7.81 (ddd, J = 3.7 Hz, 2H, H-Ar), 8.47 (dd, J = 16.1, 2H, H-Ar), 10.91 (s, 1H, N-H) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 181.1, 162.2, 150.5, 146.3, 139.9, 137.9, 135.1, 134.4, 131.5, 130.8, 129.9, 128.4, 127.5, 127.2, 123.7, 123, 121.8, 118.5, 116.9, 84.4 and 51.5 ppm.
3,3,6',6'-Tetramethyl-1'-phenyl-3,4,6',7'-tetrahydro-1H-spiro[acridine-9,3'-indole]-1,2',4'(1'H, 2H, 5'H,10H)-trione (1f)
Yield: 86%, m.p. 245-248 °C; IR: ʋ = 330, 3101, 2960, 2900, 1724, 1693, 1646, 1599, 1515, 1487, 1378, 1348, 1239, 1129, 1199, 1032, 905, 756, 608 and 558 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 0.92-1.08 (m, 12H, CH3), 1.83-2.12 (m, 4H, CH2), 2.17-2.42 (m, 4H, CH2), 6.52-6.89 (m, 4H, H-Ar), 6.90-7.26 (m, 3H, H-Ar), 7.41 (d, J = 7.8 Hz, 1H, H-Ar ), 8.85 (s, 1H, H-Ar), 10.99 (s, 1H, N-H) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 203.9, 194.7, 182.3, 168.7, 144.7, 133.5, 128, 126.8, 122, 121.6, 120.3, 109.8, 101.4, 59.1, 54.2, 50.6, 47.3, 46.9, 33.7, 32.8, 31.5, 29.1, 27.3 and 26.4 ppm.
1-Phenyl-1H-spiro[chromeno[2,3-b]pyrrole-3,11'-chromeno[2,3-b]quinoline]-2,4,12'-(6'H)trione (1g)
Yield: 83%, m.p. 279-284 °C; IR: ʋ = 3417, 3318, 3224, 2930, 2856, 1725, 1687, 1617, 1565, 1486, 1384, 1346, 1193, 1067, 894, 762, 680 and 559 cm−1; 1H NMR (300 MHz, DMSO-d6) δH = 5.57 (s, 1H, N-H), 6.60-6.87 (m, 3H, H-Ar), 6.96-7.39 (m, 6H, H-Ar), 7.49-8.14 (m, 5H, H-Ar) ppm. 13C NMR (75 MHz, DMSO-d6) δC = 199.5, 163.8, 152.4, 138.8, 134.4, 133.2, 132, 127.4, 125.6, 125.1, 124.4, 124, 123.7, 123.2, 121.6, 116.8, 116.1, 115.3, 112.6, 109.4 and 91.4 ppm.
1’-(4-Chlorophenyl)-3,3,6’,6’-tetramethyl-3,4,6’,7’-tetrahydro-1H-spiro[acridine-9,3’-indole]-1,2’,4’(1’H,2H,5’H,10H)-trione (1h)
Yield: 95%, m.p. 254-258 °C; IR: ʋ = 3331, 2960.07, 1724, 1693, 1647, 16, 1473, 1374, 1348, 1229, 1200, 1129, 905, 754 and 558 cm−1.
1’-(4-Bromophenyl)-3,3,6’,6’-tetramethyl-3,4,6’,7’-tetrahydro-1H-spiro[acridine-9,3’-indole]1, 2’,4’(1’H,2H,5’H,10H)-trione (1i)
Yield: 94%, m.p. 222-228 °C; IR: ʋ = 3330, 3238, 3157, 3099, 2897, 1724, 1694, 1647, 1572, 1599, 1488, 1378, 1348, 1278, 1129, 1020, 905, 753, 608 and 558 cm−1.
3,3,6',6'-Tetramethyl-1'-(p-tolyl)-3,4,6',7'-tetrahydro-1H-spiro[acridine-9,3'-indole]-1,2',4'(1'H, 2H,5'H,10H)-trione (1j)
Yield: 88%, m.p. 258-260 °C; IR: ʋ = 3330, 3109, 2961, 2890, 1724, 1694, 1600, 1647, 1474, 1378, 1349, 1229, 1200, 1129, 905, 756 and 558 cm−1.
1'-(4-Methoxyphenyl)-3,3,6',6'-tetramethyl-3,4,6',7'-tetrahydro-1H-spiro[acridine-9,3'-indole]-1, 2',4'(1'H,2H,5'H,10H)-trione (1k)
Yield: 87%, m.p. 260-262 °C; IR: ʋ = 3329, 3101, 2962, 2884, 1724, 1694, 1647, 1599, 1488, 1378, 1349, 1129, 1199, 1114, 905, 756, 608 and 558 cm−1.
7'-(4-Methoxyphenyl)-1H-spiro[pyrimido[4,5-b]quinoline-5,5'-pyrrolo[2,3-d]pyrimidine]2,2',4, 4',6'(1'H,3H,3'H,7'H,10H)-pentaone (1l)
Yield: 89%, m.p. >350°C; IR: ʋ = 3460, 3118, 3076, 2795, 1721, 1611, 1563, 1502, 1469, 1245, 1032, 937, 812 and 668 cm−1.
7'-(4-Nitrophenyl)-1H-spiro[pyrimido[4,5-b]quinoline-5,5'-pyrrolo[2,3-d]pyrimidine]-2,2',4,4', 6'(1'H,3H,3'H,7'H,10H)-pentaone (1m)
Yield: 86%, m.p. 233-238 °C; IR: ʋ = 3304, 3366, 3263, 3099, 2958, 2928, 2845, 1765, 1716, 1685, 1619, 1482, 1428, 1409, 1365, 1337, 1252, 1184, 1120, 1028, 796, 790, 691 and 509 cm−1.
7'-(p-Tolyl)-1H-spiro[pyrimido[4,5-b]quinoline-5,5'-pyrrolo[2,3-d]pyrimidine]-2,2',4,4',6'(1'H, 3H,3'H,7'H,10H)-pentaone (1n)
Yield: 87%, m.p.>350 °C; IR: ʋ = 3186, 3081, 2956, 1733, 1706, 1612, 1558, 1469, 1389, 1352, 1253, 814 and 668 cm−1.
Comparison of the catalyst activities
Table 6 shows the comparison of the previous methods (entries 1-10) used for the synthesis of 1(a-n) with our proposed method (entry 11). As can be seen, in our proposed method, the reaction will take place in a shorter reaction time (20 min) and higher yield (98%).
Table 6. Comparison of D with other catalysts for the synthesis of 1(a-n).
Entry
|
Catalyst
|
Conditions
|
Time (min)
|
Yield (%)
|
Ref.
|
1
|
MSrGO
|
Solvent-free, 70 °C
|
60
|
95
|
51
|
2
|
ChCl:ZnCl2 1:2
|
80 °C
|
30
|
94
|
52
|
3
|
AcOH
|
EtOH, reflux
|
120
|
91
|
53
|
4
|
L-proline
|
EtOH, 60 °C
|
360
|
90
|
54
|
5
|
β-CD
|
H2O, 80 °C
|
30
|
95
|
55
|
6
|
β-CD
|
H2O, 80 °C
|
30
|
92
|
56
|
7
|
Sulfonated MNPs
|
EtOH/H2O, 80 °C
|
180
|
93
|
57
|
9
|
L-proline
|
EtOH, 80 °C
|
300
|
90
|
58
|
10
|
(MWCNTs)COOH/La2O3
|
EtOH, reflux
|
120
|
94
|
59
|
11
|
Our catalyst
|
EtOH, 60 °C
|
20
|
98
|
This work
|
Proposed mechanism
Fig. 16 shows the possible mechanism for the synthesis of 1(a-n) by D. The nucleophilic addition of the amino group of aniline to the activated carbonyl group by D will form intermediate I, which by deletion of water from I, intermediate II will be formed. The nucleophilic addition of intermediate II to the activated carbonyl group of isatin will form intermediate III which is its tautomerization and internal cyclization will form the intermediates IV, and V, respectively. De-cyclization of V will form VI and its nucleophilic attack to the activated dimedone will form the intermediate VII. Consecutive removal of two water molecules and tautomerization will form the intermediates VIII, IX, and X (product).
Recyclability of D
An investigation of the catalytic recyclability and stability was conducted using a model reaction. After completion of the reaction (TLC), ethanol was added, the catalyst was removed, washed with ethanol and water, and dried at 80 °C. As a result, no significant decrease in catalyst activity was observed after four consecutive runs (Fig. 17).
The FT-IR spectrum of D before and after consecutive runs of recovery showed a very nice similarity (Fig. 18).