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Original article
10 (
2_suppl
); S2902-S2907
doi:
10.1016/j.arabjc.2013.11.021

A green protocol for the synthesis of quinoxaline derivatives catalyzed by polymer supported sulphanilic acid

, ,
 Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat, India

⁎Corresponding author. Tel.: +91 02692 226856x211; fax: +91 02692 236475. dipanalka@yahoo.com (Dipak K. Raval) dk_raval@spuvvn.edu (Dipak K. Raval)

Received: , Accepted: ,
© The Author(s) 2013
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Polymer supported sulphanilic acid was found to be an effective heterogeneous catalyst for one pot synthesis of various quinoxaline derivatives from the condensation reaction between 1,2-diamines and 1,2-dicarbonyl compounds in ethanol. Synthesis was attempted under reflux as well as at room temperature using ethanol as the solvent to afford excellent yields. Heterogeneity of the catalyst allowed its recycling for five times with almost retention in catalytic activity. Prepared quinoxaline derivatives were also tested for their antioxidant activity by the FRAP assay method.

Keywords

Quinoxaline
Antioxidant activity
Heterogeneous catalyst
Phenylenediamine
1,2-Diarylketone
1

1 Introduction

Quinoxaline derivatives are of significant interest as they are noteworthy intermediates for the manufacturing of pharmaceuticals and advanced materials (Sato, 1996; Matsuoka et al., 1992). A number of nitrogen-containing heterocycles show antimicrobial activity and have been synthesized for medical use. Among various classes of heterocyclic units, quinoxaline ring has frequently been used as a component of various antibiotic molecules. The most striking examples are levomycin and hinomycin which inhibit the growth of Gram-positive bacteria and are active against various transplantable tumors (Dell et al., 1975; Bailly et al., 1999).

Quinoxalines are very important compounds due to their wide spectrum of biological activities such as anticancer (Lindsley et al., 2005), antibacterial (Seitz et al., 2002), and activity as kinase inhibitors (He et al., 2003). They are well known for their application in rigid subunits in macrocyclic receptors (Mizuno et al., 2002), electroluminescent materials (Justin Thomas et al., 2005), organic semiconductors (O’Brien et al., 1996) and DNA cleaving agents (Hegedus et al., 2003). Considering the significant applications in the fields of medicinal, industrial and synthetic organic chemistry, there has been tremendous interest in developing efficient methods for the synthesis of quinoxalines.

Improved methods have been reported by using different catalysts such as Pd(OAc)2 (Robinson and Taylor, 2005), MnO2 (Raw et al., 2003), ceric ammonium nitrate (More et al., 2006), manganese octahedral molecular sieves (Sithambaram et al., 2008), task-specific ionic liquid (Dong et al., 2008) and bismuth(III) (Yadav et al., 2008). A number of synthetic strategies have been developed for the preparation of substituted quinoxalines. Although great success has been obtained, many of these methodologies suffer one or more drawbacks such as drastic reaction conditions, low yields, tedious work-up, use of toxic metal salts as catalyst, long reaction times and relatively expensive reagents (More et al., 2006; Zhao et al., 2004; Bhosale et al., 2005; Heravi et al., 2007; Raw et al., 2004; Antoniotti and Duñach, 2002; Woo et al., 2002; Mizuno et al., 2002; Crossley and Johnston, 2002). The most common methods involve condensation of an aryl-1,2-diamine with a 1,2-dicarbonyl compound in refluxing ethanol or acetic acid for 2–12 h typically giving yields of 34–70%.

The search for a better alternative catalytic method is being actively pursued in our laboratory (Avalani et al., 2012, 2013; Dadhania et al., 2011, 2012a,b; Patel et al., 2013a,b; Satasia et al., 2013; Tarpada et al., 2012). In the present article, we have successfully attempted one-pot synthesis of quinoxaline derivatives using polymer supported sulphanilic acid from o-phenylenediamines and 1,2-diaryl ketones under mild conditions. The novel green protocol also tolerated a wide range of functional groups in the building blocks (See Scheme 1).

General synthetic pathway for the synthesis of quinoxaline derivatives.
Scheme 1 General synthetic pathway for the synthesis of quinoxaline derivatives.

2

2 Experimental

2.1

2.1 Chemicals and reagents

All chemicals used were of laboratory reagent grade and used without further purification. Phenol, formaldehyde and Epichlorohydrin, TPTZ(2,4,6-tripyridyl-s-triazine), Ferric chloride and ascorbic acid were obtained from S.D. Fine Chem. Pvt. Ltd., Mumbai, India. o-Phenylenediamines, sodium hydroxide and sulphanilic acid were obtained from Samir Tech Chem. Pvt. Ltd., Vadodara, India. Various 1,2-diketones were used as received from Merck, Mumbai, India. All the solvents were purchased from Sisco Chem. Pvt. Ltd., Mumbai, India.

2.2

2.2 Analytical methods

Melting points were determined by the open capillary method and are uncorrected. 1H NMR and 13C NMR spectra were recorded as solutions in DMSO-d6 on a Bruker Avance 400 spectrometer operating at 400 MHz for 1H NMR, and 100 MHz for 13C NMR. Chemical shifts (δ) are expressed in parts per million (ppm) and referenced to the residual protic solvent. FT-IR spectra were recorded on ABB Bomem Inc. FT-IR 3000 spectrophotometer and are expressed in wave numbers (cm−1). The mass spectra (ESI–MS) were recorded on Shimadzu LCMS-2010 spectrometer. Carbon, Hydrogen and Nitrogen were estimated on a PerkinElmer 2400 Series II CHNS/O Elemental Analyzer. Optical density values were recorded on Shimadzu UV–VIS spectrophotometer 160A. All the reactions were monitored by TLC using an aluminum sheet precoated with silica gel 60 F254 (Merck).

2.3

2.3 General procedure for the modification of Epoxy novolac phenolformaldehyde using sulphanilic acid (ENPFSA)

ENPFSA was prepared by modification of Epoxy novolac phenol formaldehyde resin by sulphanilic acid as reported earlier (Tarpada et al., 2012).

2.4

2.4 General procedure for the synthesis of quinoxaline 3a

To a mixture of o-phenylenediamine (1 mmol) and benzil (1 mmol) in ethanol (5 mL), 5% w/w ENPFSA with respect to benzil was added. The mixture was stirred at room temperature. The progress of the reaction was monitored by TLC using an aluminum sheet precoated with silica gel 60 F254 (Merck). After completion of the reaction, ethyl acetate was added to the solidified mixture and the insoluble catalyst was separated by filtration. The filtrate was dried over anhydrous Na2SO4. The solvent was evaporated with care and the pure product was obtained. The product was characterized by FT-IR, 1H NMR, 13C NMR and GC–MS analysis. The recovered catalyst was washed with ethanol, chloroform, diethyl ether and subsequently dried at 80 °C to recycle in the subsequent model reaction. A variety of substituted 1,2-phenylenediamines were condensed with 1,2-diaryl ketones to prepare variously substituted quinoxalines (Table 2).

2.5

2.5 Procedure for antioxidant activity

FRAP assay was employed to measure total antioxidant capacity of the compounds. It measures reduction power of the compounds, converting ferric tripyridyl triazine (Fe(III)–TPTZ) complex into a blue colored ferrous tripyridyl triazine (Fe(II)–TPTZ) complex at low pH, measurable at 593 nm (Benzie and Strain, 1996).

Fe(II)–TPTZ(2,4,6-tripyridyl-s-triazine) reagent was prepared by mixing a 10.0 mL TPTZ solution, 10 mL FeCl36H2O solution and 100 mL acetate buffer at pH 3.6. A mixture of 400.0 μL sample solution and 3 mL of Fe(II)TPTZ reagent was incubated at 37 °C for 15 min. The absorbance of the colored complex Fe(II)TPTZ was measured at 593 nm using ascorbic acid as the standard. The results were expressed as ascorbic equivalent (mmol/100 g compound). Ascorbic acid taken = 3.99 × 10 - 4 mm,Sample taken = 0.04 mg Ascorbic acid concentration ( mmol / 100 g of sample ) = OD at 593 nm of test sample OD at 593 nm of standard × standard ( mm ) sample ( mg ) × 100

2.6

2.6 Characterization of selected compounds

2.6.1

2.6.1 2,3-Di (furan-2-yl)-6-nitroquinoxaline 3n

IR (KBr): 1566,1520, 1474, 1342, 1011, 910, 887 cm−1; 1H NMR (DMSO-d6, δ ppm): 8.77 (d, 1H, J = 2.4 Hz, Ar–H), 8.464 (dd, 1H, J = 2.8 Hz, J = 9.2 Hz, Ar–H), 8.23 (d, 1H, J = 9.2 Hz, Ar–H), 7.97 (dd, 2H, J = 0.8 Hz, J = 6.4 Hz, Ar–H), 6.89–6.75 (m, 4H, Ar–H); 13C NMR (DMSO-d6, δ ppm):150.17, 150.07, 148.01, 146.78, 146.24, 146.00, 144.54, 144.00, 142.84, 138.91, 130.89, 130.76, 124.93, 124.22, 113.04, 112.82; ESI-MS: m/z 308.10 (M + H)+; Anal. Calcd.% for C16H9N3O4: C, 62.54; H, 2.95; N, 13.68, O, 20.83; % Found: C, 62.63; H, 2.35; N, 20.94.

2.6.2

2.6.2 6-Chloro-2, 3-dip-tolylquinoxaline 3q

IR (KBr): 1605,1466, 1335, 1242, 1180, 1065, 980, 818, 725, 602 cm−1; 1H NMR (DMSO-d6, δ ppm): 8.19–8.13 (m, 2H, Ar–H), 7.86 (dd, 1H, J = 2.4 Hz, J = 8.8 Hz, Ar–H), 7.37 (d, 4H, J = 8 Hz, Ar–H), 7.177 (d, 4H, J = 7.6 Hz, Ar–H), 2.329 (s, 6H); 13C NMR (DMSO-d6, δ ppm): 154.42, 153.84, 141.17, 139.51, 139.13, 139.03, 136.18, 136.12, 134.85, 131.27, 131.12, 130.10, 129.65, 129.42, 129.23, 129.15, 128.92, 127.96, 127.80; ESI-MS: m/z 345.2 (M + H)+; Anal. Calcd.% for C22H17ClN2: C, 76.63; H, 4.97; N, 8.12; % Found: C, 76.93; H, 5.31; N, 8.25.

3

3 Result and discussion

3.1

3.1 Optimization of reaction conditions

The condensation reaction of benzene-1,2-diamine with benzil using ethanol as the solvent was employed as the model reaction to screen the suitable reaction conditions (Table 1). Among different catalysts and ENPFSA (Table 1, entries 1–12), 5% w/w ENPFSA was found to be the best suited for the reaction. The reaction was studied at the reflux temperature as well as at room temperature. Increasing the reaction temperature to reflux had only a marginal effect on % yield (Table 1). Reaction was also optimized by varying the amount of ENPFSA (Table 1, entries 8–13). It was observed that 5% w/w amount of catalyst was enough to complete the reaction in a moderate time with high yields. Higher amounts of the catalyst did not increase the yield noticeably. Thus, it was concluded that the condensation reaction carried out in the presence of 5% w/w ENPFSA at room temperature showed the highest conversion. This was chosen as the optimized condition for performing other reactions.

Table 1 Effect of different catalysts on the condensation of benzil and benzene-1,2-diamine in ethanol as the solvent at room temperature and at reflux.
Entry Catalyst At room temperature Reflux
Timea (min) Yieldsb (%) Timea (min) Yieldsb (%)
1 1 mmol% HCl 100 75 85 80
2 1 mmol% CH3COOH 100 75 85 80
3 1 mmol% H2SO4 100 75 85 80
4 1 mmol% ZnCl2 110 75 90 80
5 1 mmol% CoCl2 110 75 90 80
6 1 mmol% NiCl2 110 75 90 80
7 1 mmol% PEG-600 85 80 80 85
8 1% ENPFSA 45 65 40 70
9 2% ENPFSA 45 70 40 72
10 3% ENPFSA 45 73 40 75
11 4% ENPFSA 45 75 40 80
12 5% ENPFSA 40 88 35 90
13 6% ENPFSA 50 83 40 85
a Reaction was monitored by TLC.
b Isolated yields.

3.2

3.2 Effect of different catalysts

Model reaction was carried out by using different catalysts such as HCl, CH3COOH, H2SO4, ZnCl2, CoCl2, NiCl2 and PEG-600. It was found that by using HCl, CH3COOH and H2SO4 as the catalyst, reaction was completed in 85 min with 80% yield under reflux and in 100 min with 75% yield at room temperature (Table 1, entries 1–3).

By using ZnCl2, CoCl2, NiCl2 as the catalyst, reaction got completed in 90 min with 80% yield under reflux and in 110 min with 75% yield at room temperature (Table 1, entry 4–6). The reaction was completed in a shorter time with high yields by using acid catalyst as compared to metal chloride as catalysts. Using PEG-600 as the catalyst, reaction was completed in 80 min with 85% yield under reflux and in 85 min with 80% yields at room temperature (Table 1, entry 7). The model reaction was performed by using 5% polymer supported sulphanilic acid (ENPFSA) as the catalyst. Reaction was completed in 35 min with 90% yield under reflux and in 40 min with 88% yield at room temperature (Table 1, entry 12).

By using this optimized conditions, various quinoxaline derivatives 3b–t were synthesized in a shorter time as well as in high yields. It was observed that diketone having the phenyl ring as the substituents underwent the conversion smoothly in a short time as compared to diketone having furyl and thenyl ring as the substituents. The diamine component carrying the electron withdrawing group (Table 2, entries 11–15) underwent the reaction in a shorter time with high yields as compared to diamines carrying the electron donating group (Table 2, entries 6–10 and 16–20).

Table 2 Synthesis of quinoxaline 3a–t by using ENPFSA as heterogeneous catalyst in ethanol at room temperature.
Entry Product R R1 Time (min.)a Yieldb (%) Melting point (°C)
Observed Reported
1 3a H C6H5 40 88 126 126–127 More et al. (2006)
2 3b H p-CH3C6H4 45 85 147 147–148 Guo et al. (2009)
3 3c H Phenanthrene-9,10-dionec 45 85 225 224.8–225.7 Kaupp and Naimi-Jamal (2002)
4 3d H 2-Furyl 50 80 132 131 More et al. (2005)
5 3e H 2-Thenyl 50 82 140 –
6 3f CH3 C6H5 45 84 116 116–117 Kaupp and Naimi-Jamal (2002)
7 3g CH3 p-CH3C6H4 48 80 137 137 Kaupp and Naimi-Jamal (2002)
8 3h CH3 Phenanthrene-9,10-dionec 48 84 209 208–210 Kaupp and Naimi-Jamal (2002)
9 3i CH3 2-Furyl 52 80 118 117–119 Akkilagunta et al. (2010)
10 3j CH3 2-thenyl 52 80 110 –
11 3k NO2 C6H5 38 88 192 192–193 Kaupp and Naimi-Jamal (2002)
12 3l NO2 p-CH3C6H4 41 86 168 168–169 Guo et al. (2009)
13 3m NO2 Phenanthrene-9,10-dionec 41 86 245 –
14 3n NO2 2-Furyl 45 85 165 164–166 Guo et al. (2009)
15 3o NO2 2-Thenyl 45 85 220 –
16 3p Cl C6H5 42 84 115 115–116 Kaupp and Naimi-Jamal (2002)
17 3q Cl p-CH3C6H4 45 84 170 169–171 Akkilagunta et al. (2010)
18 3r Cl Phenanthrene-9,10-dionec 45 85 225 –
19 3s Cl 2-Furyl 48 82 133 133–135 Akkilagunta et al. (2010)
20 3t Cl 2-Thenyl 48 82 190 –
a Reaction were monitored by TLC.
b Isolated yields.
c Name of diketone employed for the synthesis.

3.3

3.3 Mechanism for the formation of quinoxaline

The formation of quinoxaline derivatives is outlined in Scheme 2. 1,2-diketone stabilized in the interlayer of ENPFSA via interaction with H+ by the partial polarization of carbonyl group reacts readily with o-phenylenediamine. The resultant amino-1,2-diol undergoes dehydration to give quinoxaline as the end product.

Plausible mechanism for the formation of quinoxaline.
Scheme 2 Plausible mechanism for the formation of quinoxaline.

3.4

3.4 Recyclability of catalyst

Recyclability of the catalyst was studied by using the ENPFSA recovered from the previous batch in the model reaction. The reaction proceeded smoothly yielding 85–88% of the product at room temperature for five successive runs (Table 3). The result indicates that activity of the catalyst was not much affected upon recycling at least for five times.

Table 3 Recyclability of catalyst.
No. of cycles Reaction timea Yieldb (%)
1 40 88
2 40 88
3 40 86
4 40 86
5 40 85
a Reaction was monitored by TLC.
b Isolated yields.

3.5

3.5 Antioxidant activity of quinoxalines

Capacity to transfer a single electron i.e., the antioxidant power of all compounds was determined by a FRAP assay. The FRAP values are expressed as an equivalent of standard antioxidant ascorbic acid (mmol/100 g of dried compound). FRAP values indicate that all the compounds have a ferric reducing antioxidant power. The compounds 3k, 3m, 3p, 3r, 3s and 3t (Table 4, entries 11, 13, 16, 18, 19 and 20) showed relatively high antioxidant activity whereas compound 3f (Table 4, entry 6) showed poor antioxidant power. The high antioxidant activity may be due to the presence of the electron withdrawing substituent in compounds or the presence of the furyl or thiophene ring.

Table 4 Antioxidant activity of synthesized compounds by FRAP assay method.
Entry Compound OD (593 nm) FRAP value (mmol/100 g)
1 3a 1.200 242.05
2 3b 0.548 110.53
3 3c 0.531 107.11
4 3d 1.023 206.34
5 3e 0.967 195.05
6 3f 0.482 97.22
7 3g 0.542 109.32
8 3h 1.024 206.55
9 3i 1.202 242.45
10 3j 0.987 199.09
11 3k 1.520 306.59
12 3l 0.543 109.53
13 3m 1.890 381.23
14 3n 0.545 109.93
15 3o 1.072 216.23
16 3p 1.680 338.87
17 3q 0.502 101.26
18 3r 2.203 444.37
19 3s 1.892 381.63
20 3t 1.558 314.26

4

4 Conclusion

We have reported a green and efficient protocol for one-pot synthesis of quinoxaline derivatives from readily available o-phenylenediamines and 1,2-diarylketones using a polymer supported catalyst. The conditions are mild and a wide range of functional groups can be tolerated in the building blocks for the synthesized quinoxalines. ENPFSA as catalyst offered advantages including simplicity of operation, easy workup, time savvy and recyclability to give excellent purity and high yields of products. Synthesized compounds showed good to moderate antioxidant activity by FRAP assay method.

Acknowledgements

Authors thank the Head, Department of Chemistry, Sardar Patel University for providing research facilities. DKR gratefully acknowledges Sardar Patel University for allocation of partial research funding in terms of seed grant-2011. UPT is grateful to UGC, New Delhi for providing senior research fellowship in science for meritorious students for the academic years 2012–2015.

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Appendix A

Supplementary data

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.arabjc.2013.11.021.

Appendix A

Supplementary data

Supplementary data 1

Supplementary data 1 Supplementary material.


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