Crosslinked sulfonated polyacrylamide (Cross-PAA-SO3H) attached to nano-Fe3O4 as a superior catalyst for the synthesis of oxindoles
Hossein Shahbazi-Alavi
1
(
Young Researchers and Elite Club, Kashan Branch, Islamic Azad University, Kashan, Iran, E-mail addresses: hossien_shahbazi@yahoo.com
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Iran
)
Javad Safaei-Ghomi
2
(
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Iran
)
Keywords: Isatin, Nanocatalyst, polyacrylamide, oxindoles, Nano-Fe3O4,
Abstract :
Crosslinked sulfonated polyacrylamide (Cross- PAA- SO3H) attached to nano - Fe3O4 as an efficient heterogeneous solid acid catalyst has been used for the preparation of spiro[ pyrazoloquinoline - oxindoles] and spiro[ chromenopyrazolo - oxindoles] through a four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2 - naphthol under reflux condition in ethanol.Spirooxindoles have appeared as a series of significant heterocycles due to their presence in a wide spectrum of natural and synthetic organic compounds. These activities make spirooxindoles attractive goals in organic synthesis. The modifying crosslinked polyacrylamides make them attractive objects in chemistry and polymer science. Sulfonated polyacrylamides have unique characteristics such as high strength, hydrophilicity, and proton conductivity. The statistic of results from SEM images clearly demonstrate that the average size of Cross-PAA-SO3H@nano-Fe3O4 is about 7-25 nanometers. The remarkable advantages of this methodology are easy work-up, short reaction times, high to excellent product yields, operational simplicity, low catalyst loading and reusability of the catalyst.
Journal of Nanoanalysis., Vol. xx, No. x, pp. xx-xx
Cross-linked sulfonated polyacrylamide (Cross-PAA-SO3H) attached to nano-Fe3O4 as a superior catalyst for the synthesis of oxindoles
Abstract
Cross-linked sulfonated polyacrylamide (Cross-PAA-SO3H) attached to nano-Fe3O4 as an efficient heterogeneous solid acid catalyst has been used for the preparation of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] through a four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2-naphthol under reflux conditions in ethanol. The remarkable advantages of this methodology are easy work-up, short reaction times, high to excellent product yields, operational simplicity, low catalyst loading and reusability of the catalyst.
Keywords: polyacrylamide; oxindoles; nanocatalyst; isatin; nano-Fe3O4.
1. INRODUCTION
Spirooxindoles have appeared as a series of significant heterocycles due to their presence in a wide spectrum of natural and synthetic organic compounds [1-3], with various biological characterizes including antimicrobial [4-6], antitumor [7-8], antidiabetic [9], and can also serve as synthetic intermediates for diverse kinds of pharmaceuticals or drug precursors [10]. These activities make spirooxindoles attractive goals in organic synthesis. The synthesis of spirooxindoles has been reported using pTSA [11,12], piperidine [13], alum (KAl(SO4)2. 12H2O) [14], SBA-Pr-NH2 [15], nanocrystalline MgO [16], and L-Proline [17]. However, some of the developed methods endure drawbacks such as long reaction times and harsh reaction conditions. To elude these restrictions,
discovery of an efficient, easily accessible catalyst with high catalytic activity for the preparation of spirooxindoles is still favored. The modifying cross-linked polyacrylamides make them attractive objects in chemistry and polymer science [18-20]. Sulfonated polyacrylamides have unique characteristics such as high strength, hydrophilicity, and proton conductivity [21-22]. Recently, magnetic nanoparticles (MNPs) have been successfully utilized to immobilize enzymes, polymers, transition metal catalysts and organocatalysts [23-24]. In the current study, we investigated an easy and rapid method for the synthesis of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] through a four-component reactions of
phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2-naphthol using cross-linked sulfonated polyacrylamide (Cross-PAA-SO3H), attached to nano-Fe3O4, as an efficient catalyst under reflux conditions in ethanol (Scheme 1).
2. Experimental section
Chemicals and apparatus
NMR spectra were obtained on a Bruker Avance 400 MHz spectrometer (1H NMR at 400 Hz, 13C NMR at 100 Hz) in DMSO-d6 using TMS as an internal standard. Powder X-ray diffraction (XRD) was carried out on a Philips diffractometer of X’pert Company with monochromatized Cu Kα radiation (λ = 1.5406 Å). Microscopic morphology of products was visualized by SEM (MIRA3). The thermogravimetric analysis (TGA) curves are recorded using a V5.1A DUPONT 2000. The magnetic measurement of samples were carried out in a vibrating sample magnetometer (VSM) (Meghnatis Daghigh Kavir Co.; Kashan Kavir; Iran) at room temperature in an applied magnetic field sweeping between ±10 k Oe.
Preparation of Crosslinked Sulfonated Polyacrylamide (Cross-PAA-SO3H):
In a round-bottom flask (200 mL) equipped with magnetic stirrer and condenser, 5 g of acrylamid (AAM) (70 mmol) and 5.17 g of 2-acryloylamino-2-methylpropane-1-sulfonic acid (25 mmol) (AAMPS), (approximately AAM/AAMPS (3/1)) and 0.77 gr of N,N-methylene-bis-acrylamid (NNMBA) (5 mmol) as crosslinking agent and benzoyl peroxide as initiator were added to 80 mL EtOH under reflux condition for 5 h. After completion of reaction, the white precipitate was formed, filtered, washed and dried in vacuum oven in 70 ºC for 12 h. The weight of polymer was 10.1 gr with the yield of 91.8 %. This catalyst was characterized with infrared spectroscopy and back titration acid-base to confirm sulfonation and determine accurate sulfonation levels. Acidic capacity of this catalyst was estimated 1.1 mmol/g.
Preparation of cross-linked solfonated polyacrylamide@nano-Fe3O4:
1g of cross-linked sulfonated polyacrylamide was poured in 100 mL round bottom flask under stirring at room temperature, and then 50 mL HCl (0.4 M) was added to flask. 0.43 g FeCl2.4H2O and 1.17 g FeCl3.6H2O were added to the mixture. The mixture was stirred until dissolved completely (flask 1). In another 500 mL round-bottom flask 2, 400 mL aqueous solution of NH3 (0.7M) was poured under argon gas. Then flask 1 was added to flask 2 immediately. Nanocatalyst was filtered and washed with water (2×25 mL) and dried in oven on 50 o C.
General procedure for the synthesis of spirooxindoles:
A mixture of isatin derivatives (1 mmol), phenylhydrazine or hydrazine hydrate (1 mmol), alkyl acetoacetate (1 mmol), naphthalene amine or 2-naphthol (1 mmol) and Cross-PAA-SO3H@nano-Fe3O4 (7 mg) in EtOH (15 mL) was refluxed for the appropriate times. The reaction was monitored by TLC (n-hexan/ethyl acetate 8:2). After completion of the reaction, the mixture was cooled to room temperature and the nanocatalyst was easily separated using an external magnet. The solvent was evaporated and the obtained solid was filtered and then washed with EtOH and water to get pure product.
5'-Chloro-10-methyl-8H-spiro [benzo-[5, 6]-chromeno-[2, 3-c]-pyrazole-11, 3'-indolin]-2'-one (5a): Yellow solid; M. p. 196-198 °C, – IR (KBr): ν = 3321, 3201, 3071, 1689, 1618, 1433 cm-1. – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 1.86 (s, 3H, CH3), 6.90-6.95 (m, 2H, ArH), 7.10-7.15 (m, 6 H, ArH), 7.70 (s, 1H, ArH), 10.24 (s, 1H, NH-CO), 11.25 (s, 1H, NH). – 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 10.13 (CH3), 48.80 (C), 108.70 (C), 111.09 (C), 117.51 (CH), 120.28 (2CH), 123.20 (CH) 124.51 (C), 125.90 (2CH), 125.99 (2C), 128.35 (C), 130.74 (CH), 133.93 (C-Cl), 133.98 (C), 136.70 (CH), 137.92 (C), 142.56 (CH-C-Cl), 156.70 (CH-C-O), 163.74 (C=O).– Analysis for C22H14ClN3O2: calcd. C 68.13, H 3.64, N 10.83; Found C 68.06; H 3.55, N, 10.70.
10-Methyl-8H-spiro [benzo-[5, 6]-chromeno-[2, 3-c]-pyrazole-11, 3'-indolin]-2'-one (5b): Yellow solid; M. p. 185-187 °C, – IR (KBr): ν = 3332, 3202, 3071, 1680, 1616, 1435 cm-1 . – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 1.92 (s, 3H, CH3), 6.45 (m, 2H, ArH), 6.75 (m, 2H, ArH), 6.86 (m, 2H, ArH), 6.96-7.21 (m, 4H, ArH), 10.18 (s, 1H, NH-CO), 11.20 (s, 1H, NH). – 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 10.10 (CH3), 49.07 (C), 106.72 (C), 111.07 (C), 112.09 (CH), 117.34 (2CH), 120.13 (CH), 123.20 (2CH), 124.37 (CH), 125.99 (CH), 126.90 (CH), 128.63 (C), 128.82 (CH), 130.66 (C), 133.92 (C) , 135.90 (C), 137.00 (C), 141.33 (C), 156.60 (CH-C-O), 165.07 (C=O).– Analysis for C22H15N3O2: calcd. C 74.78, H 4.28, N 11.89; Found C 74.65, H 4.22, N 11.74.
5'-Methyl-10-methyl-8H-spiro [benzo-[5, 6]-chromeno-[2, 3-c]-pyrazole-11, 3'-indolin]-2'-one (5c): Yellow solid; M. p. 171-173 °C, – IR (KBr): ν = 3330, 3209, 3075, 1682, 1613, 1433 cm-1. – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 1.90 (s, 3H, CH3), 2.30 (s, 3H, CH3), 6.50-6.80 (m, 4H, ArH), 6.82-6.87 (m, 2H, ArH), 7.16-7.35 (m, 3H, ArH), 10.18 (s, 1H, NH-CO), 11.20 (s, 1H, NH). – 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 10.19 (CH3), 23.45 (CH3), 49.10 (C), 107.75 (C), 112.04 (C), 112.18 (CH), 117.44 (2CH), 120.22 (CH), 123.25 (2 CH), 124.41 (C), 125.90 (C), 126.84 (CH), 128.74 (CH), 128.84 (C), 130.72 (CH), 133.94 (C), 135.96 (C), 137.21 (C), 141.43 (C), 156.64 (CH-C-O), 165.12 (C=O).– Analysis for C23H17N3O2: calcd. C 75.19, H 4.66, N 11.44; Found C 75.25, H 4.55, N 11.42.
5'-nitro-10-Methyl-8H-spiro [benzo-[5, 6]-chromeno-[2, 3-c]-pyrazole-11, 3'-indolin]-2'-one (5d): yellow solid; M. p. 190-192 °C, – IR (KBr): ν = 3335, 3223, 3087, 1692, 1627, 1430 cm-1, – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 1.88 (s, 3H, CH3), 6.92-6.98 (m, 2H,
ArH), 7.14-7.18 (m, 6H, ArH), 7.92 (s, 1H, ArH), 10.24 (s, 1H, NH-CO), 11.25 (s, 1H, NH).– 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 10.18 (CH3), 48.78 (C), 107.78 (C) , 111.29 (C), 117.63 (2CH), 120.38 (CH), 124.22 (2CH), 124.55 (CH), 125.93 (C), 126.80 (CH), 128.10 (CH), 128.25 (CH) , 130.87 (C), 133.76 (C), 134.57 (C), 137.88 (C), 139.62 (C), 143.42 (C-NO2), 156.62 (CH-C-O),, 163.95 (C=O).– Analysis for C22H14N4O4: calcd. C 66.33, H 3.54, N 14.06; Found C 66.22, H 3.41, N 14.10.
Table 1: Peak assignment of crosslinked Sulfonated Polyacrylamide (Cross-PAA-SO3H)
Peak position (cm-1 ) | Assignment |
3100-3500 | N-H stretching of NH2,OH stretching of (- SO3H) |
1658 | C=O stretching of CO in AAM and AAMPS |
1545 | Secondary amid band of AAMPS |
1042 | Sulfonic acid (- SO3H) group |
1175-1216 | Symmetric band of SO2 |
1453 | Stretching of the C-N band (amid) |
Characterization of the nanocatalyst
In this study, we synthesized the cross-linked sulfonated polyacrylamide (Cross-PAA-SO3H) with simultaneous radical co-polymerization in presence of initiator and crosslinking agent. The FT-IR absorbance spectra of the dried cross-linked sulfonated polyacrylamide (poly AAM-co-AAMPS), Fe3O4 and Cross-PAA-SO3H@nano-Fe3O4 are shown in Figure 1. The N–H stretching vibration of the amide groups in AAm and AAMPS and overlapping O–H stretching vibration of sulfonic acid group in AAMPS are observed in the region 3100–3500 cm−1. The strong absorption band in 1658 cm−1 can be attributed to the stretching vibrations of C=O groups in both AAm and AAMPS. Secondary amide band of AAMPS unit has a peak in 1545 cm−1. The sharp peak at 1042 cm −1 is related to sulfonic acid (–SO3H) group. The symmetric band of SO2 is observed in the 1178-1216 cm −1. The band at 1453 cm−1 is assigned to the stretching vibration of the C–N bond (amide) and the asymmetric bending of the C–H bond in methyl groups of AMPS. Table 1 gives the main characteristic peak assignment of the FT-IR spectra. Also a schematic illustration of the reaction is shown in the scheme 2. The absence of the olefinic band at 1620–1635 cm −1 confirms that, there is no residual monomer in the system. The results in Fig 1 (c) suggest the integration of Fe3O4 NPs and Cross-PAA-SO3H.
Fig 1. The FT-IR spectra of (a) Fe3O4 NPs, (b) Cross-PAA-SO3H and (c) Cross-PAA-SO3H@ nano-Fe3O4
Scheme 2. Preparation of cross-linked Sulfonated Polyacrylamide (Cross-PAA-SO3H)
The particle size and morphology of Cross-PAA-SO3H@nano-Fe3O4 was determined by Scanning Electronic Microscopy (SEM). The statistic of results from SEM images clearly demonstrate that the average size of Cross-PAA-SO3H@nano-Fe3O4 is about 7-25 nanometers (Figure 2).
Fig. 2. SEM image of Cross-PAA-SO3H@nano-Fe3O4
Figure 3 shows the powder X-ray diffraction (XRD) pattern. The pattern agrees well with the reported pattern for Fe3O4 (JCPDS No. 75-0449). The crystallite size of Cross-PAA-SO3H@nano-Fe3O4 calculated by the Debye–Scherer equation is about 20-25 nm, in good agreement with the result obtained by SEM.
Fig 3. The XRD pattern of Cross-PAA-SO3H@nano-Fe3O4
An EDS (energy dispersive X-ray) spectrum of Cross-PAA-SO3H@nano-Fe3O4 (Figure 4) shows that the elemental compositions are carbon, oxygen, sulfur, iron and nitrogen.
Fig. 4. EDS spectrum of Cross-PAA-SO3H@nano-Fe3O4
The magnetic properties of nano-Fe3O4 and Cross-PAA-SO3H@nano-Fe3O4 were determined with the help of a vibrating sample magnetometer (VSM) at room temperature in an applied magnetic field sweeping between ±10,000 Oe (Figure 5). The amount of saturation-magnetization for nano-Fe3O4 and Cross-PAA-SO3H@nano-Fe3O4 is 47.2 emu/g and 26.8 emu/g.
Fig. 5. The VSM curve of: (a) nano-Fe3O4 and (b) Cross-PAA-SO3H@nano-Fe3O4
Thermogravimetric analysis (TGA) evaluates the thermal stability of the Cross- PAA-SO3H@nano-Fe3O4. These nanoparticles show suitable thermal stability without a significant decrease in weight (Figure 6). The weight loss at temperatures below 200 ºC is due to the removal of physically adsorbed solvent and surface hydroxyl groups. The curve shows a weight loss about 20 % from 250 to 600 ºC, resulting from the decomposition of the organic spacer grafting to the nano-Fe3O4 surface.
Fig. 6. TGA curve of Cross-PAA-SO3H@nano-Fe3O4.
Catalytic behaviors of Cross-PAA-SO3H@nano-Fe3O4 for the synthesis of oxindoles
Initially, we had optimized various reaction parameters for the synthesis of spirooxindoles by the condensation reaction of 5-chloro-isatin, hydrazine hydrate, ethyl acetoacetate and 2-naphthol as a model reaction. The model reactions were performed by CAN, NaHSO4, Et3N, NiCl2, ZrOCl2, p-TSA and nano-Fe3O4 and Cross-PAA-SO3H@nano-Fe3O4. Several reactions were scrutinized using various solvents including EtOH, CH3CN, water or DMF. The best results were obtained in ethanol and we found that the reaction gave satisfying results by cross-PAA-SO3H@nano-Fe3O4 (7 mg) under reflux conditions (Tables 2). Scheme 2 shows a proposed mechanism for this reaction in the presence of Cross-PAA-SO3H@nano-Fe3O4 as catalyst. Initially hydrazine hydrate is reacted with 1,-3-dicarbonyl compound to form intermediate (I) via condensation reaction. Secondly, intermediate (I), in the presence of Cross-PAA-SO3H@nano-Fe3O4, is condensed with isatin derivatives to form intermediate (II) via Knoevenagel condensation reaction. In the next step, naphthylamine or 2-naphthol reacts with intermediate (II) through Michael addition. Lastly, the final product is formed by intra-molecular cyclization reactions.
We explored the feasibility of the reaction by choosing some representative substrates (Table 3). It has been considered that better yields are achieved with substrates having electron-withdrawing groups. To study the limitation of this catalytic process, hydrazine hydrate or phenylhydrazine, isatins, ketoesters and naphthylamine or 2-naphthol was chosen as substrates. Investigations of the reaction scope revealed that various isatins (bearing electron-withdrawing and electron-donating groups) can be utilized in this protocol (Table 3). The reusability of Cross-PAA-SO3H@nano-Fe3O4 was studied for the reaction of 5-chloro-isatin, hydrazine hydrate, ethyl acetoacetate and 2-naphthol and it was found that product yields decreased to a small extent on each reuse (run 1, 88%; run 2, 88%; run 3, 87%; run 4, 87%; run 5, 86%; run 6, 86%;). After completion of the reaction, the nanocatalyst was easily separated by an external magnet. The catalyst was washed four times with EtOH and dried at room temperature for 20 h.
4. Conclusions
In conclusion, we have reported an efficient way for the synthesis of spirooxindoles using Cross-PAA-SO3H@nano-Fe3O4 under reflux condition in ethanol. The method offers several advantages including high yields, shorter reaction times, reusability of the catalyst and low catalyst loading.
Scheme 2. Proposed reaction pathway for the synthesis of spirooxindoles
Table 2. Optimization of reaction conditions using different catalysts a
Entry | Solvent (reflux) | Catalyst | Time (min) | Yield (%) b |
1 | ------- | 200 | trace | |
2 | EtOH | CAN (5 mol %) | 120 | 17 |
3 | EtOH | NaHSO4 (10 mol %) | 120 | 32 |
4 | EtOH | Et3N (10 mol %) | 120 | 38 |
5 | Fe3O4 NP (50 mg) | 120 | 22 | |
6 | EtOH | TsOH (20 mol%) | 120 | 51 |
7 | H2O | Cross-PAA-SO3H@nano-Fe3O4 (10 mg) | 120 | 45 |
8 | DMF | Cross-PAA-SO3H@nano-Fe3O4 (10 mg) | 120 | 54 |
9 | CH3CN | Cross-PAA-SO3H@nano-Fe3O4 (10 mg) | 120 | 65 |
10 | EtOH | Cross-PAA-SO3H@nano-Fe3O4 (5 mg) | 120 | 84 |
11 | EtOH | Cross-PAA-SO3H@nano-Fe3O4 (7 mg) | 120 | 88 |
12 | EtOH | Cross-PAA-SO3H@nano-Fe3O4 (10 mg) | 120 | 88 |
13 | EtOH | NiCl2 (10 mg) | 150 | 42 |
14 | EtOH | ZrOCl2 (10 mg) | 150 | 58 |
a hydrazine hydrate (1 mmol), 5-chloro-isatin (1 mmol), ethyl acetoacetate (1 mmol), 2-naphthol (1 mmol). b Isolated yield
Table 3. Synthesis of spirooxindoles
Isatins R |
R΄ |
R˝ | 4a or 4b |
Product | Time (min) | Yield (%) a | M.p. (°C) Found | M.p. (°C) Literature [Ref.] |
Cl | H | Me | 4a | 5a | 120 | 88 | 196-198 | — |
H | H | Me | 4a | 5b | 150 | 86 | 185-187 | — |
Me | H | Me | 4a | 5c | 150 | 83 | 171-173 | — |
NO2 | H | Me | 4a | 5d | 120 | 88 | 190-192 | — |
H | Ar | Me | 4b | 6a | 150 | 82 | 255-258 [11] | |
Cl | Ar | Me | 4b | 6b | 150 | 84 | 264-267 [11] | |
H | Ar | 4b | 6c | 150 | 79 | 300-302 | 304-307 [11] | |
Cl | Ar | n-Pr | 4b | 6d | 150 | 82 | 295-297 | 298-301 [11] |
aIsolated yield
Acknowledgement
The authors are grateful to university of Kashan for supporting this work by Grant NO: 159196/XXII.
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