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An efficient and one-pot synthesis of benzimidazoles, benzoxazoles, benzothiazoles and quinoxalines catalyzed via nano-solid acid catalysts
Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
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Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata
An efficient and one-pot synthesis of benzimidazoles, benzoxazoles, benzothiazoles and quinoxalines catalyzed via nano-solid acid catalysts Abbas Teimouri a,∗ , Alireza Najafi Chermahini b , Hossien Salavati a , Leila Ghorbanian c a b c
Chemistry Department, Payame Noor University, Tehran 19395-4697, Iran Department of Chemistry, Isfahan University of Technology, Isfahan 841543111, Iran Materials Engineering Department, Isfahan University of Technology, Isfahan, Iran
a r t i c l e
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Article history: Received 9 December 2012 Received in revised form 6 February 2013 Accepted 23 February 2013 Available online 14 March 2013 Keywords: Benzimidazoles Benzoxazoles Nano-sulfated zirconia Nano-sized ZnO Nano-␥-alumina Nano-ZSM-5 zeolites
a b s t r a c t A simple highly versatile and efficient synthesis of benzimidazoles, benzoxazoles, benzothiazoles, and quinoxalinesis achieved from carbonyl compounds and o-substituted aminoaromatics using nanosulfated zirconia, nano-structured ZnO, nano-␥-alumina and nano-ZSM-5 zeolites, as the catalyst. The characteristic structural features of the materials were determined by techniques, such as XRD, FT-IR and SEM. The advantages of method are short reaction times and milder conditions and easy work-up. The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of efficiency. Published by Elsevier B.V.
1. Introduction The benzoxazoles, benzothiazoles, benzimidazoles and quinoxaline have attracted much interest in diverse areas of chemistry [1]. These heterocycles have shown different pharmacological activities such as antibacterial, antiulcers, antihypertensives, antivirals, antifungals, anticancers, and antihistaminics [2–7]. These compounds are also used as ligands for asymmetric transformations [8], exhibit nonlinear optical [9] and luminescent [10] /fluorescent [11]. Benzimidazole derivatives exhibit significant activity against several viruses such as HIV [12,13], herpes (HSV-1) [14], RNA [15], potential antitumor agents [16], antimicrobial agents [17] and influenza [18]. They also act as topoisomerase inhibitors [19], selective neuropeptide YY1 receptor antagonists [20], angiotensin II inhibitors [21], and smooth muscle cell proliferation inhibitors [22] and have much more importance in organic synthesis [23]. Quinoxaline and its derivatives are an important class of benzoheterocycles displaying a broad spectrum of biological activities which have made them privileged structures in pharmacologically active compounds [24–27] and catalytic systems [28,29]. They have
∗ Corresponding author at: Department of Chemistry, Payame Noor University (PNU), Isfahan P.O. Box 81395-671, Iran. Tel.: +98 311 3521804; fax: +98 311 3521802. E-mail addresses: a [email protected], [email protected], a [email protected], [email protected] (A. Teimouri). 1381-1169/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.molcata.2013.02.030
also been found applications as building blocks in the synthesis of organic semiconductors [30], rigid subunits in macrocyclic receptors or molecular recognition [31], and chemically controllable switches [32]. A number of methods have been reported for the synthesis of the benzimidazole [33], benzothiazole [34] and benzoxazole [35] by condensing benzene-1,2-diamine, 2-aminophenol and 2aminobenzenethiol with acyl chlorides or aldehydes. Recently, some other methods for the preparation of quinoxaline derivatives have been reported [36]. However, most of the traditional processes suffer from one or more of the following drawbacks such as strong acidic conditions, pollution, high cost, low yields of the products, requirements for long reaction time, and tedious work-up procedures, need to excess amounts of reagent and the use of toxic reagents, catalysts and/or solvents. Therefore, there is a strong demand for a highly efficient and environmentally benign method for the synthesis of these heterocycles. In the recent years, the use of nano-structured ZnO [37], nano-sulfated zirconia [38], nano-␥-alumina [39] and nano-ZSM-5 zeolite [40], catalysts has received considerable interest in organic synthesis. This extensive application of heterogeneous catalysts in synthetic organic chemistry can make the synthetic process more efficient from both environmental and economic point of view [41] and used-catalyst can be easily recycled. Very recently we have developed a convenient and efficient procedure for the synthesis of 2,4,5-trisubstituted imidazoles using
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
clays, zeolite, nano-crystalline sulfated zirconia (SZ) as catalyst [42]. In the present study, we report the synthesis of benzimidazoles, benzoxazoles, benzothiazoles, by the condensation of 1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes and the synthesis of quinoxalines derivatives by the condensation of 1,2-diaminobenzene and 1,2-dicarbonyl in ethanol using nano-structured ZnO, nano-sulfated zirconia, nano␥-alumina and nano-ZSM-5 zeolites, as the catalyst. 2. Experimental 2.1. Instruments and characterization Diethanolamine (DEA), zinc acetate dehydrate, aluminum nitrate, sodium carbonate, tetrapropyl ammonium hydroxide and tetra ethyl ortho silicate and other reagents were purchased from Merck and Aldrich and used without further purification. Products were characterized by spectroscopy data (FTIR, 1 H NMR and 13 C NMR spectra), elemental analysis (CHN) and melting points. A JASCO FT/IR-680 PLUS spectrometer was used to record IR spectra using KBr pellets. NMR spectra were recorded on a Bruker 400 Ultrasheild NMR and DMSO-d6 was used as solvent. Melting points reported were determined by open capillary method using a Galen Kamp melting point apparatus and are uncorrected. The total surface acidity of catalysts, was measured by a Micromeritics Pulse Chemisorb instrument by means of NH3 adsorption-desorption. Mass Spectra were recorded on a Shimadzu Gas Chromatograph Mass Spectrometer GCMS-QP5050A/Q P5000 apparatus. 2.2. Catalyst preparation 2.2.1. Synthesis of nano-crystalline sulfated zirconia Nano-crystalline sulfated zirconia has been prepared by one step sol–gel technique [43]. A typical synthesis involves the addition of concentrated sulfuric acid (1.02 ml) to zirconium npropoxide precursor (30 wt%) followed by the hydrolysis with water. After 3 h aging at room temperature, the resulting gel was dried at 110 ◦ C for 12 h followed by calcination at 600 ◦ C for 2 h. The bulk sulfur of the sulfated zirconia after calcination at 600 ◦ C was 3.2 wt% as measured by elemental analyzer. 2.2.2. Synthesis of nano-sized ZnO Nano-structure ZnO has been prepared by one step sol–gel technique [44]. In a typical procedure, mixtures of ethanol, diethanolamine (DEA) and zinc acetate dihydrate, were prepared. The concentration of zinc acetate dihydrate in solvent was 0.2 M. The molar ratios of zinc acetate dehydrate and diethanolamine was 1.0. Then the pH of the mixture was reached to about 9. When the zinc acetate crystals were dissolved completely, sodium hydroxide (NaOH) pellets were added to the solution to increase the pH of the mixture to about 11. Then, the washed precipitates were dried at 130 ◦ C and calcined at 600 ◦ C for 15 min in a oven to obtain white nano-sized ZnO particles. 2.2.3. Synthesis of nano--Al2 O3 catalyst The nano-␥-Al2 O3 was prepared by sol–gel method according to a procedure described [45]. In a typical experiment, Aluminum nitrate (15.614 g) was added to 400 ml of deionized water. Similarly solution of sodium carbonate is prepared by dissolving (7.95 g) in 400 ml of deionized water. 200 ml of deionized water is taken in a 2 L capacity round-bottom flask and stirred well using magnetic stirrer. Then sodium carbonate and aluminum nitrate solutions are added to 200 ml of deionized water (from separate burettes) drop wise. The temperature was maintained 70 ◦ C during experiment. The pH after precipitation was found to be in the range of 7.5–8.5. The
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mixture was stirred for 4 h. The digested precipitates were filtered and re-dispersed again in hot 2 l of deionized water, filtered and finally washed with ethanol first followed by acetone to avoid contamination of ‘Na’ ions; and air dried at room temperature. The dried precipitates were calcined in a furnace at 550 ◦ C for 5 h to produce nano-sized ␥-Al2 O3 powders. 2.2.4. Synthesis of nano-ZSM-5 For synthesis of nano-ZSM-5, tetrapropyl ammonium hydroxide and tetra ethyl ortho silicate were the sources of aluminum and silicon, respectively. nano-ZSM-5 Zeolite was synthesized according to the procedure described in advance. [39] The components were mixed with constant stirring. After adding all the ingredients the solution was left to hydrolyze at room temperature for 48 h. The gel thus obtained was heated at 80 ◦ C to evaporate water and ethanol formed during reaction. The obtained solution was charged into a Teflon-lined stainless-steel autoclave under pressure and static conditions at 170 ◦ C for of 48 h. The solid phase obtained was filtered, washed with distilled water several times, dried at 120 ◦ C and then calcined at 550 ◦ C for 12 h. 2.2.5. Characterization X-ray diffraction pattern were recorded on diffractometer ˚ Crystallite size (Philips X’pert) using CuK␣ radiation ( = 1.5405 A), of the crystalline phase was determined from the peak of maximum intensity by using Scherrer formula [46], with a shape factor (K) of 0.9, as below: Crystallite size = K·/W·cos , where, W = Wb − Ws and Wb is the broadened profile width of experimental sample and Ws is the standard profile width of reference silicon sample. FT-IR spectra of the catalysts were recorded by FT-IR spectrophotometer in the range of 400–4000 cm−1 with a resolution of 4 cm−1 by mixing the sample with KBr. Specific surface area, pore volume and pore size distribution of samples calcined at 600 ◦ C were determined from N2 adsorption–desorption isotherms at 77K (ASAP 2010 Micromeritics). Surface area was calculated by using BET equation; pore volume and pore size distribution were calculated by BJH method [47]. The samples were degassed under vacuum at 120 ◦ C for 4 h, prior to adsorption measurement to evacuate the physisorbed moisture. The detailed imaging information about the morphology and surface texture of the catalyst was provided by SEM (Philips XL30 ESEM TMP), a part of the spectra data has been published in our previous work [42]. The total surface acidity of catalysts was measured by a Micromeritics Pulse Chemisorb instrument by means of NH3 adsorption–desorption. The bulk sulfur (wt%) retained in sulfated zirconia samples before and after calcination at 600 ◦ C was analyzed by C H N S/O elemental analyzer. 2.3. General procedure for the synthesis of benzimidazoles derivatives In a 50 mL round bottom flask aldehyde (1 mmol) and 1,2diaminobenzene, 2-aminophenol, or 2-aminothiophenol (1 mmol) were thoroughly mixed in ethanol (10 mL) then catalyst (10 mol%) was added, and the solution was refluxed for appropriate time. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was cooled to room temperature and the resulting solid was collected by filtration and dissolved in 20 mL ethyl acetate. The catalyst was recovered by filtration. After evaporation of the solvent, the resulting solid product was recrystallized from ethanol to obtain pure product. Compound 1a: Mp 292–294 ◦ C. FTIR (KBr, cm−1 ): 3452, 1618, 1460 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.18–7.22 (m, 5H), 7.52–7.59 (m, 4H), 12.81 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı116.3 (2C), 123.5 (2C), 127.5 (2C), 128.6, 129.3 (2C), 130.6, 138.9
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(2C), 152.9; ESI MS (m/z): 194.08 (M+ ); Anal. Calcd. for C13 H10 N2 : C, 80.39; H, 5.19; N, 14.42. Found: C, 80.11; H, 4.89; N, 14.10. Compound 1b: Mp 290–292 ◦ C. FTIR (KBr, cm−1 ): 3446, 1628, 1477 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.28 (d, 2H), 7.30–7.34 (m, 2H), 7.38–7.42 (m, 1H), 7.62–7.66 (m, 1H), 8.56 (d, 2H), 12.13 (s, 1H); ESI MS (m/z): 228.05 (M+ ); Anal. Calcd for C13 H9 ClN2 : C, 68.28; H, 3.97; N, 15.50. Found: C, 67.86; H, 3.59; N, 15.16. Compound 1c: Mp 268–270 ◦ C. FTIR (KBr, cm−1 ): 3438, 1635, 1434 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.32 (d, 2H), 7.38–7.42 (m, 2H), 7.46–7.50 (m, 1H), 7.66–7.70 (m, 1H), 8.44 (d, 2H), 12.53 (s, 1H); ESI MS (m/z): 271.95 (M+ ); Anal. Calcd for C13 H9 BrN2 : C, 57.18; H, 3.32; N, 29.26. Found: C, 56.89; H, 3.09; N, 28.87. Compound 1d: Mp 318–320 ◦ C. FTIR (KBr, cm−1 ): 3448, 1626, 1587, 1529, 1356 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.26 (d, 2H), 7.34–7.38 (m, 2H), 7.42–7.48 (m, 1H), 7.58–7.63 (m, 1H), 8.62 (d, 2H), 12.28 (s, 1H); ESI MS (m/z): 239.08 (M+ ); Anal. Calcd for C13 H9 N3 O2 : C, 65.27; H, 3.79; N, 17.56. Found: C, 65.06; H, 3.39; N, 17.19. Compound 1e: Mp 288–290 ◦ C. FTIR (KBr, cm−1 ): 3561, 3434, 1621, 1463 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.23 (d, 2H), 7.29–7.33 (m, 2H), 7.38–7.42 (m, 1H), 7.64–7.68 (m, 1H), 8.44 (d, 2H), 9.58 (s, 1H), 12.32 (s, 1H); ESI MS (m/z): 210.07 (M+ ); Anal. Calcd for C13 H10 N2 O: C, 74.27; H, 4.79; N, 13.33. Found: C, 74.06; H, 4.38; N, 13.88. Compound 1f: Mp 260–262 ◦ C. FTIR (KBr, cm−1 ): 3432, 1622, 1456 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.35 (s, 3H), 7.16 (d, 2H), 7.32–7.38 (m, 2H), 7.43–7.49 (m, 1H), 7.61–7.64 (m, 1H), 8.09 (d, 2H), 12.80 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı 24.3, 115.3 (2C), 123.0 (2C), 127.4 (2C), 127.7, 129.6 (2C), 137.4, 138.7 (2C), 152.9; ESI MS (m/z): 208.01 (M+ ); Anal. Calcd for C14 H12 N2 : C, 80.74; H, 5.81; N, 13.45. Found: C, 80.21; H, 5.39; N, 13.08. Compound 1g: Mp 180–182 ◦ C. FTIR (KBr, cm−1 ): 3443, 1627, 1459 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 3H), 7.22 (d, 2H), 7.38–7.47 (m, 2H), 7.48–7.55 (m, 1H), 7.58–7.75 (m, 1H), 7.92 (d, 2H), 12.93 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı 55.6, 114.6 (2C), 115.3 (2C), 123.0 (2C), 123.2, 128.5 (2C), 138.7 (2C), 152.8, 160.7; MS (m/z): 224.08 (M+ ); Anal. Calcd for C14 H12 N2 O: C, 74.98; H, 5.39; N, 12.48. Found: C, 74.34; H, 5.06; N, 11.98. Compound 2a: Mp 100–102 ◦ C. FTIR (KBr, cm−1 ): 3456, 1638, 1454 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.23–7.27 (m, 5H), 7.51–7.58 (m, 4H); 13 C NMR (400 MHz, DMSO-d6): ı 121.6, 122.3, 123.5, 124.6 (2C), 125.4, 129.4 (2C), 132.3, 138.5, 150.6, 154.2, 162.2;MS (m/z): 195.07 (M+ ); Anal. Calcd for C13 H9 NO: C, 79.98; H, 4.65; N, 7.16. Found: C, 79.61; H, 3.28; N, 6.84. Compound 2b: Mp 146–148 ◦ C. FTIR (KBr, cm−1 ): 3451, 1632, 1458 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.28–7.39 (d, 2H), 7.52–7.60 (m, 1H), 7.65–7.74 (d, 2H), 7.35–7. 86 (m, 1H), 8.11–8.19 (m, 2H); MS (m/z): 229.03 (M+ ); Anal. Calcd for C13 H8 ClNO: C, 67.99; H, 3.51; N, 6.10. Found: C, 67.64; H, 3.18; N, 5.92. Compound 2c: Mp 142–144 ◦ C. FTIR (KBr, cm−1 ): 3456, 1642, 1463 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.32–7.43 (d, 2H), 7.54–7.62 (m, 1H), 7.63–7.72 (d, 2H), 7.30–7. 81 (m, 1H), 8.09–8.17 (m, 2H); ESI MS (m/z): 272.98 (M+ ); Anal. Calcd for C13 H8 BrNO: C, 56.97; H, 2.94; N, 5.11. Found: C, 56.46; H, 2.58; N, 4.78. Compound 2d: Mp 262–264 ◦ C. FTIR (KBr, cm−1 ): 3448, 1587, 1531, 1354 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.30–7.41 (d, 2H), 7.50–7.58 (m, 1H), 7.62–7.71 (d, 2H), 7.33–7. 84 (m, 1H), 8.10–8.18 (m, 2H); ESI MS (m/z): 240.05 (M+ ); Anal. Calcd for C13 H8 N2 O3 : C, 65.01; H, 3.36; N, 11.76. Found: C, 64.74; H, 3.08; N, 11.72. Compound 2e: Mp 282–284 ◦ C. FTIR (KBr, cm−1 ): 3541, 3448, 1647, 1454 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.27–7.38 (d, 2H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.41–7. 57(m, 1H), 8.16–8.32 (m, 2H)), 9.42 (s, 1H); MS (m/z): 211.05 (M+ ); Anal. Calcd for C13 H9 NO2 : C, 73.91; H, 4.59; N, 6.63. Found: C, 73.64; H, 3.96; N, 6.42.
Compound 2f: Mp 126–128 ◦ C. FTIR (KBr, cm−1 ): 3440, 1646, 1461 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.26–7.37 (d, 2H), 7.41–7.49 (m, 1H), 7.56–7.65 (d, 2H), 7.24–7. 74 (m, 1H), 8.06–8.22 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 21.3, 110.7, 119.6, 123.4, 124.8, 126.4, 127.4 (2C), 129.6 (2C), 138.4, 141.5, 150.4, 162.2; ESI MS (m/z): 209.08 (M+ ); Anal. Calcd for C14 H11 NO: C, 80.36; H, 5.30; N, 6.69. Found: C, 79.98; H, 5.02; N, 6.32. Compound 2g: Mp 96–98 ◦ C. FTIR (KBr, cm−1 ): 3448, 1651, 1462 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.64 (s, 3H), 7.28–7.39 (d, 2H), 7.44–7.52 (m, 1H), 7.54–7.63 (d, 2H), 7.33–7.53 (m, 1H), 8.11–8.27 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 54.3, 110.7, 116.4 (2C), 118.5, 121.3, 122.4, 124.7, 127.6 (2C), 142.2, 150.4, 161.4, 164.7;ESI MS (m/z): 225.08 (M+ ); Anal. Calcd for C14 H11 NO2 : C, 74.65; H, 4.92; N, 6.22. Found: C, 74.22; H, 4.62; N, 6.02. Compound 3a: Mp 110–112 ◦ C. FTIR (KBr, cm−1 ): 3426, 1658, 1448 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.38–7.42 (m, 5H), 7.66–7.73 (m, 4H); 13 C NMR (400 MHz, DMSO-d6): ı 121.8, 122.2, 123.5, 125.6 (2C), 126.6, 129.2 (2C), 132.3, 135.3, 151.1, 154.2, 166.3;ESI MS (m/z): 211.05 (M+ ); Anal. Calcd for C13 H9 NS: C, 73.90; H, 4.59; N, 6.63. Found: C, 73.56; H, 3.86; N, 6.44. Compound 3b: Mp 106–108 ◦ C. FTIR (KBr, cm−1 ): 3456, 1638, 1445 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.24–7.35 (d, 2H), 7.48–7.56 (m, 1H), 7.62–7.71 (d, 2H), 7.40–7. 81 (m, 1H), 8.31–8.48 (m, 2H); ESI MS (m/z): 245.01 (M+ ); Anal. Calcd for C13 H8 ClNS: C, 63.54; H, 3.28; N, 5.70. Found: C, 63.11; H, 2.94; N, 5.42. Compound 3c: Mp 102–104 ◦ C. FTIR (KBr, cm−1 ): 3450, 1644, 1432 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.31–7.42 (d, 2H), 7.50–7.58 (m, 1H), 7.64–7.73 (d, 2H), 7.48–7. 88 (m, 1H), 8.26–8.32 (m, 2H); ESI MS (m/z): 288.96 (M+ ); Anal. Calcd for C13 H8 BrNS: C, 58.93; H, 2.78; N, 4.83. Found: C, 58.46; H, 2.34; N, 4.56. Compound 3d: Mp 228–230 ◦ C. FTIR (KBr, cm−1 ): 3446, 1576, 1537, 1352 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.25–7.36 (d, 2H), 7.45–7.53 (m, 1H), 7.62–7.71 (d, 2H), 7.48–7.98 (m, 1H), 8.28–8.44 (m, 2H); ESI MS (m/z): 256.03 (M+ ); Anal. Calcd for C13 H8 N2 O2 S: C, 60.93; H, 3.15; N, 10.93. Found: C, 69.44; H, 2.91; N, 10.62. Compound 3e: Mp 224–226 ◦ C. FTIR (KBr, cm−1 ): 3536, 3441, 1652, 1448 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.10–7.21 (d, 2H), 7.32–7.40 (m, 1H), 7.51–7.60 (d, 2H), 7.46–7.96 (m, 1H), 8.19–8.35 (m, 2H) 11.3 (s, 1H); ESI MS (m/z): 227.04 (M+ ); Anal. Calcd for C13 H9 NOS: C, 68.70; H, 3.99; N, 6.16. Found: C, 68.36; H, 3.62; N, 5.86. Compound 3f: Mp 82–84 ◦ C. FTIR (KBr, cm−1 ): 3437, 1648, 1452 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.18–7.29 (d, 2H), 7.40–7.48 (m, 1H), 7.54–7.63 (d, 2H), 7.42–7.92 (m, 1H), 8.21–8.37 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 21.3, 121.7, 123.2, 125.2, 125.5 (2C), 126.4, 132.9, 133.5, 135.1, 138.9 (2C), 154.1, 168.7;ESI MS (m/z): 225.06 (M+ ); Anal. Calcd for C14 H11 NS: C, 74.63; H, 4.92; N, 6.22. Found: C, 69.34; H, 4.58; N, 5.82. Compound 3g: Mp 118–120 ◦ C. FTIR (KBr, cm−1 ): 3432, 1646, 1458 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.85 (s, 3H), 7.15–7.26 (d, 2H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.48–7.98 (m, 1H), 8.16–8.32 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 54.3, 121.8, 123.7, 125.8, 126.7, 127.4 (2C), 130.3 (2C), 135.4, 137.4, 144.4, 154.2, 166.4;ESI MS (m/z): 241.06 (M+ ); Anal. Calcd for C14 H11 NOS: C, 69.68; H, 4.59; N, 5.80. Found: C, 69.34; H, 4.18; N, 5.62.
2.4. General procedure for the synthesis of quinoxalines derivatives To a mixture of 1,2-diaminobenzene (1 mmol) and 1,2dicarbonyl compound (1 mmol) in ethanol (10 mL), catalyst (10 mol%) was added and the solution was refluxed for appropriate time. The progress of the reaction was monitored by TLC. After completion of the reaction, ethyl acetate was added to the
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
solidified mixture and the insoluble catalyst was separated by filtration. After evaporation of the solvent, the resulting solid product was recrystallized from ethanol to obtain pure product. Compound 4a: Mp 130–132 ◦ C. FTIR (KBr, cm−1 ): 3052, 1646, 1344 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.41 (m, 6H), 7.55 (m, 4H), 7.79 (d, 2H), 8.18 (d, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 128.30, 128.83, 129.05, 129.23, 129.87, 129.99, 134.90, 139.10, 141.24, 153.49;ESI MS (m/z): 282.12 (M+ ); Anal. Calcd for C20 H14 N2 : C, 85.08; H, 5.01; N, 9.92. Found: C, 84.84; H, 4.78; N, 9.62. Compound 4b: Mp 192–194 ◦ C. FTIR (KBr, cm−1 ): 3038, 1642, 1336 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 6.74 (d, 4H), 7.68 (d, 4H), 7.58 (d, 2H), 8.26 (d, 2H); ESI MS (m/z): 350.05 (M+ ); Anal. Calcd for C20 H12 Cl2 N2 : C, 68.39; H, 3.44; N, 7.98. Found: C, 68.08; H, 3.11; N, 7.58. Compound 4c:Mp 132–134 ◦ C. FTIR (KBr, cm−1 ): 3044, 1645, 1352 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 6.78 (d, 4H), 7.70 (d, 4H), 7.56 (d, 2H), 8.22 (d, 2H); ESI MS (m/z): 318.01 (M+ ); Anal. Calcd for C20 H12 F2 N2 : C, 75.46; H, 3.80; N, 8.80. Found: C, 75.13; H, 3.62; N, 8.48. Compound 4d: Mp 128–130 ◦ C. FTIR (KBr, cm−1 ): 3034, 1641, 1347 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.42 (s, 6H), 6.76 (d, 4H), 7.73 (d, 4H), 7.55 (d, 2H), 8.21 (d, 2H); ESI MS (m/z):310.15 (M+ ); Anal. Calcd for C22 H18 N2 : C, 85.13; H, 5.85; N, 9.03. Found: C, 84.91; H, 5.51; N, 8.68. Compound 4e: Mp 148–150 ◦ C. FTIR (KBr, cm−1 ): 3042, 1626, 1345 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 6H), 6.89 (d, 4H), 7.50 (d, 4H), 7.65 (d, 2H), 8.16 (d, 2H); ESI MS (m/z): 342.18 (M+ ); Anal. Calcd for C22 H18 N2 O2 : C, 77.17; H, 5.30; N, 8.18. Found: C, 76.87; H, 5.08; N, 7.72. 3. Results and discussion In the reaction between aldehydes and 1,2-diaminobenzene, 2aminophenol, or 2-aminothiophenol and 1,2-diaminobenzene and 1,2-dicarbonyl compounds effect of the catalyst amount was investigated. To minimize the formation of byproducts and to achieve good yield of the desired product, the reaction is optimized by varying the amount of catalyst,the percentage yield of the product with 5, 10 and 15 mg of nano-sulfated zirconia as a catalyst are 80%, 92% and 70%, respectively (Table 1, entries 2–4). The percentage yield of the product with 5, 10 and 15 mol% of nano-ZnO as a catalyst are 75%, 80% and 65%, respectively (Table 1, entries 5–7). For the nano-␥-alumina and nano-ZMS-5 as the catalyst, when the catalyst content was increased to 15 mg,the product yield decreased to 70% (Table 1, entry 10) and 65% (Table 1, entry 13) respectively. It is noteworthy to mention that in the absence of catalyst, no product was found even after 24 h. These results indicate that the catalyst exhibits a high catalytic activity in this transformation.
41
Table 2 Effect of various solvents on the reaction times and yields using nano SZ as the catalysts. Entry
Solventa
Time (min)b
Yield (%)c
1 2 3 4 5 6
H2 O EtOH MeOH CH3 CN 1,4-Dioxan THF
90 90 90 90 90 90
75 92 80 75 65 60
a Reaction was performed with benzaldehyde (2.0 mmol), benzene-1,2-diamine (2.0 mmol) in the presence of 10 mg nano SZ as the catalyst in various solvents. b Reaction time monitored by TLC. c Isolated yield.
In order to optimize the reaction conditions, including solvents and temperature, the reaction of benzaldehyde (2 mmol) and 1,2diaminobenzene (2 mmol) was optimized by time of the reaction and using various solvents such as H2 O, EtOH, MeOH, CH3 CN, 1,4Dioxan, and THF in the presence of nano SZ as the catalyst. (Table 2, entries 1–6). Reaction in 1,4-Dioxan, and THF solvent gave low product yields even after 120 min (Table 2, entries 5 and 6). The yields were moderate in case of methanol and acetonitrile under reflux condition. (Table 2, entries 3 and 4). The best results were obtained when the reaction was carried out in ethanol at reflux 90 min in the presence of catalyst (Table 2, entry 2). Therefore, ethanol was selected as a solvent for this reaction. The reaction of benzil with 1,2-diaminobenzene was chosen as a model reaction to study the effect of various solvents on the yield of quinoxaline. Among the solvents examined, ethanol was found to be the most effective solvent. Although water is a desirable solvent for chemical reactions for reasons of cost, safety and environmental concerns, we found that using water in this reaction gave moderate yields of products under reflux condition after long reaction times. Synthesis of benzimidazoles, benzoxazoles, benzothiazoles, by condensation of 1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes and the synthesis of quinoxalines derivatives by the condensation of 1,2diaminobenzene and 1,2-dicarbonyl in ethanol using (Tables 4–7) preferred values of catalysts achieved. In all reactions good to excellent yields was obtained. The isolated compounds were characterized using spectroscopic and physical methods and compared with those data in literature. The total acidity of catalysts was determined by temperatureprogrammed description of ammonia (TPD). The catalysts were treated under helium at 200 ◦ C for 1 h, and then treated with a NH3 flow for 5 min at 100 ◦ C. The excess physisorbed ammonia was flushed out with pure He gas flow at 120 ◦ C for 1 h and the temperature subsequently raised up to 600 ◦ C at 10◦ /min. The total
Table 1 Effect of type and amount of catalyst on the synthesis of benzimidazoles derivatives. Entry
Catalyst
Catalyst loading
Catalyst (mol%)
Time (h)
Yield (%)a
1 2 3 4 5 6 7 8 9 10 11 12 13
None Nano-SZ Nano-SZ Nano-SZ Nano-ZnO Nano-ZnO Nano-ZnO Nano-␥-alumina Nano-␥-alumina Nano-␥-alumina Nano-ZMS-5 Nano-ZMS-5 Nano-ZMS-5
– 5 (mg) 10 (mg) 15 (mg) 5 (mol%) 10 (mol%) 15 (mol%) 5 (mg) 10 (mg) 15 (mg) 5 (mg) 10 (mg) 15 (mg)
– 5 10 15 5 10 15 5 10 15 5 10 15
24 5 5 5 5 5 5 5 5 5 5 5 5
No reaction 80 92 70 75 80 65 75 85 70 73 75 65
a
Yields after isolation of product.
42
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 3 Summary of acidic measured by NH3 -TPD of synthesized catalysts. Catalyst
Acidic sites (mmol NH3 /g)
Nano-crystalline SZ Nano-␥-Al2 O3 Nano-ZMS-5 Nano size-ZnO
T1 (<200 ◦ C)
T2 (>500 ◦ C)
Total
0.223 0.197 0.186 0.173
0.199 0.175 0.172 0.142
0.402 0.372 0.358 0.315
evacuation of NH3 from the catalysts was measured. The results of the TPD measurements are summarized in Table 3. In view of the above results obtained, it has now become clear that all four catalysts have both Bronsted and Lewis acid sites. The total number of acid sites, nano-crystalline SZ was found to have 0.402 mmol/g whereas the nano ␥-Al2 O3 , nano-ZMS-5 and nano size-ZnO have 0.372, 0.358 and 0.315 mmol/g, respectively. Sulfated zirconia possesses stronger surface acidity due to the presence of sulfate group binding with zirconia surface. The highest catalytic activity for sulfated zirconia could be attributed to its stronger surface acidity compared to other studied catalysts. Therefore, nano-crystalline SZ had the largest acidity and nano size-ZnO had the smallest acidity as compared to the other catalysts. These results are in good agreement with previous works [48]. The FT-IR spectra of alumina samples calcined at 600 ◦ C (Fig. 1) showed an intense band centered around 3500 cm−1 and a broad band at 1650 cm−1 , these are assigned to stretching and bending modes of adsorbed water. The Al–O–Al bending stretching vibrations observed at around 1150 cm−1 are due to symmetric and asymmetric bending modes, respectively. The OH torsional mode observed at 800 cm−1 overlaps with Al–O stretching vibrations. The weak band at 2091 cm−1 is assigned to a combination band. The bands observed at 617 and 481 cm−1 are attributable to stretching and bending modes of AlO6 [49]. The XRD patterns of nano-sized ZnO powders obtained. All nano-ZnO samples exhibited a hexagonal structure. Characteristic peaks of ZnO appeared at 31.7, 34.5, 36.2 and 56.5. (Fig. 2) The morphology of the as prepared nano-size-␥-Al2 O3 and nano-sized ZnO powders analyzed by SEM is shown in Figs. 3 and 4. The SEM image demonstrates clearly the formation of spherical ZnO nanoparticles. The ␥-Al2 O3 powders indicated strong agglomeration of particles with varied spherical sizes. One of the most important advantages of heterogeneous catalysis over the homogeneous counterpart is the possibility of reusing the catalyst by simple filtration, without loss of activity. The recovery and reusability of the catalyst was investigated in the product formation. After completion of the reaction, the catalyst was separated by filtration, washed 3 times with 5 ml acetone, then with
Fig. 1. FT-IR spectra nano-␥-alumina catalyst.
Fig. 2. XRD pattern of nano-ZnO catalyst.
Fig. 3. SEM micrograph of nano-␥-alumina catalyst.
Fig. 4. SEM micrograph of nano-ZnO catalyst.
doubly distilled water several times and dried at 110 ◦ C. Then the recovered catalyst was used in the next run. The results of three consecutive runs showed that the catalyst could be reused several times without significant loss of its activity (see Fig. 5). To generalize the scope and versatility of this protocol, different substituted arylaldehydes are used for the synthesis of these products. Aldehyde compounds which have electron donating or electron withdrawing groups were used and as expected it gives good yield of products, it can be seen that electron donating and electron withdrawing groups does not show any difference on the reaction yields (Tables 4–7). This indicates that the present catalyst efficiently makes the condensation reaction much faster with increased yields (Fig. 6). The method described here for synthesis of quinoxalines derivatives can be compared with other catalysts that reported literature [59–61]. To account for the facile formation of benzimidazoles, benzoxazoles and benzothiazoles, by the condensation of
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
43
Table 4 Acid-catalyzed synthesis of benzimidazoles derivatives.a
H N
NH2
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
N
NH2 Ar
1 (1a) 2 (1b) 3 (1c) 4 (1d) 5 (1e) 6 (1f) 7 (1g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/yield (%)b
Entry/product
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/88 100/70 90/72 95/64 80/65 90/74 80/70
90/88 80/82 85/76 90/74 80/82 90/78 85/74
85/90 85/85 90/84 80/82 80/80 75/84 70/82
45/92 60/88 75/81 70/90 85/82 90/92 90/85
292–294 (290–293) [50] 290–292 (288–291) [51] 268–270 (261.5–263.5) [52] 318–320 (322–323) [50] 288–290 (265–267) [52] 260–262 (264–265) [50] 180–182 (223–226) [53]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
Table 5 Acid-catalyzed synthesis of benzoxazoles derivatives.a
NH2
N
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
OH
O Ar
1 (2a) 2 (2b) 3 (2c) 4 (2d) 5 (2e) 6 (2f) 7 (2g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b
Entry/product
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/86 100/70 95/76 90/70 85/75 90/76 85/75
90/88 80/80 80/77 95/78 80/78 95/78 80/80
80/90 85/80 80/82 80/82 90/80 70/80 75/84
45/86 60/86 60/85 75/84 80/85 85/87 90/87
100–102 (102–103) [50] 146–148 (149–150) [50] 142–144 262–264 (266–267) [50] 282–284 (287–289) [54] 126–128 (100–101) [54] 96–98 (100–101) [50]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
Table 6 Acid-catalyzed synthesis of benzothiazoles derivatives.a
N
NH2
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
S
SH Entry/product
Ar
1 (3a) 2 (3b) 3 (3c) 4 (3d) 5 (3e) 6 (3f) 7 (3g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/86 90/75 80/72 95/72 80/70 95/76 80/70
90/87 80/80 85/78 95/78 90/76 95/80 85/76
85/92 80/84 90/82 90/80 80/78 75/82 70/80
45/92 60/94 60/85 75/91 80/92 85/92 90/90
110–112(112–114) [55] 108–110 (103–104) [56] 102–104 228–230 (230–231) [57] 224–226 (227) [57] 82–84 (85) [57] 118–120 (120–121) [55]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes, the following mechanism (Fig. 7) is proposed. The reaction between an aldehyde and aromatic amine leads to the formation of Schiff base which is stabilized by catalyst. Then intramolecular attack by the second group on C N double bond to give the final product. This reaction is likely to follow the proposed mechanism of acid-catalyzed coordination of a 1,2-dicarbonyl onto
acid sites, followed by the nucleophilic attack on the diketone and then followed by dehydration to give a carbocation intermediate and elimination of a proton to give quinoxaline products as shown in Fig. 7. A similar mechanism has been proposed for this reaction [62]. In conclusion, a one-pot, multicomponent methodology has been developed for the synthesis of, benzimidazoles, benzoxazoles,
44
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 7 Acid-catalyzed synthesis of quinoxalines derivatives.a
Ar
O
H2N Catalyst
+ Ar
O
EtOH, reflux
Ar
H2N Ar
1 (4a) 2 (4b) 3 (4c) 4 (4d) 5 (4e)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5
a
N MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b
Entry/product
b
N
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
70/86 80/72 90/76 95/76 80/75
70/88 70/80 85/78 90/80 80/82
75/90 65/85 90/84 80/82 80/80
30/92 20/94 25/90 20/88 15/88
130–132 (128–129) [58] 192–194 (195–196) [58] 132–134 (135–137) [58] 128–130 148–150 (151–152.5) [58]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
benzothiazolesand quinoxalines derivatives catalyzed by nanosulfated zirconia, nano-structured ZnO, nano-␥-alumina and nano-ZSM-5 zeolites with the nano-sulfated zirconia exhibiting greater activity has also been demonstrated. Compared to previously reported methods, Moreover, the mild reaction conditions, easy work-up, clean reaction profiles, lower catalyst loading and cost efficiency render this approach as an interesting alternative to the existing methods. Acknowledgements
Fig. 5. The results obtained from catalyst reuse in the product formation.
Ar
Supports from the Payame Noor University in Isfahan research council and helps of Isfahan University of technology are gratefully acknowledged. Thanks are also due to Mrs. Shahraki and Mr. Narimani for recording the FT-IR spectra of the compound.
CHO O
H
Ar
References
H H
H H
H2N
-H2O
HX N
Ar
N Ar
H
H N
X
Ar H
X
H
HX
H
Fig. 6. Proposed mechanism for the synthesis of benzimidazoles, benzoxazoles and benzothiazoles derivatives.
H
Ar
O
Ar
O
H H
H
Ar
N
N
Ar
O
Ar H2N H2N
OH2
-2H2O H
Ar
O
N
Ar
H Ar
N OH2
Fig. 7. A plausible mechanism for the condensation reaction of 1,2-diamine with 1,2-dicarbonyl compounds by catalyst.
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Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata
An efficient and one-pot synthesis of benzimidazoles, benzoxazoles, benzothiazoles and quinoxalines catalyzed via nano-solid acid catalysts Abbas Teimouri a,∗ , Alireza Najafi Chermahini b , Hossien Salavati a , Leila Ghorbanian c a b c
Chemistry Department, Payame Noor University, Tehran 19395-4697, Iran Department of Chemistry, Isfahan University of Technology, Isfahan 841543111, Iran Materials Engineering Department, Isfahan University of Technology, Isfahan, Iran
a r t i c l e
i n f o
Article history: Received 9 December 2012 Received in revised form 6 February 2013 Accepted 23 February 2013 Available online 14 March 2013 Keywords: Benzimidazoles Benzoxazoles Nano-sulfated zirconia Nano-sized ZnO Nano-␥-alumina Nano-ZSM-5 zeolites
a b s t r a c t A simple highly versatile and efficient synthesis of benzimidazoles, benzoxazoles, benzothiazoles, and quinoxalinesis achieved from carbonyl compounds and o-substituted aminoaromatics using nanosulfated zirconia, nano-structured ZnO, nano-␥-alumina and nano-ZSM-5 zeolites, as the catalyst. The characteristic structural features of the materials were determined by techniques, such as XRD, FT-IR and SEM. The advantages of method are short reaction times and milder conditions and easy work-up. The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of efficiency. Published by Elsevier B.V.
1. Introduction The benzoxazoles, benzothiazoles, benzimidazoles and quinoxaline have attracted much interest in diverse areas of chemistry [1]. These heterocycles have shown different pharmacological activities such as antibacterial, antiulcers, antihypertensives, antivirals, antifungals, anticancers, and antihistaminics [2–7]. These compounds are also used as ligands for asymmetric transformations [8], exhibit nonlinear optical [9] and luminescent [10] /fluorescent [11]. Benzimidazole derivatives exhibit significant activity against several viruses such as HIV [12,13], herpes (HSV-1) [14], RNA [15], potential antitumor agents [16], antimicrobial agents [17] and influenza [18]. They also act as topoisomerase inhibitors [19], selective neuropeptide YY1 receptor antagonists [20], angiotensin II inhibitors [21], and smooth muscle cell proliferation inhibitors [22] and have much more importance in organic synthesis [23]. Quinoxaline and its derivatives are an important class of benzoheterocycles displaying a broad spectrum of biological activities which have made them privileged structures in pharmacologically active compounds [24–27] and catalytic systems [28,29]. They have
∗ Corresponding author at: Department of Chemistry, Payame Noor University (PNU), Isfahan P.O. Box 81395-671, Iran. Tel.: +98 311 3521804; fax: +98 311 3521802. E-mail addresses: a [email protected], [email protected], a [email protected], [email protected] (A. Teimouri). 1381-1169/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.molcata.2013.02.030
also been found applications as building blocks in the synthesis of organic semiconductors [30], rigid subunits in macrocyclic receptors or molecular recognition [31], and chemically controllable switches [32]. A number of methods have been reported for the synthesis of the benzimidazole [33], benzothiazole [34] and benzoxazole [35] by condensing benzene-1,2-diamine, 2-aminophenol and 2aminobenzenethiol with acyl chlorides or aldehydes. Recently, some other methods for the preparation of quinoxaline derivatives have been reported [36]. However, most of the traditional processes suffer from one or more of the following drawbacks such as strong acidic conditions, pollution, high cost, low yields of the products, requirements for long reaction time, and tedious work-up procedures, need to excess amounts of reagent and the use of toxic reagents, catalysts and/or solvents. Therefore, there is a strong demand for a highly efficient and environmentally benign method for the synthesis of these heterocycles. In the recent years, the use of nano-structured ZnO [37], nano-sulfated zirconia [38], nano-␥-alumina [39] and nano-ZSM-5 zeolite [40], catalysts has received considerable interest in organic synthesis. This extensive application of heterogeneous catalysts in synthetic organic chemistry can make the synthetic process more efficient from both environmental and economic point of view [41] and used-catalyst can be easily recycled. Very recently we have developed a convenient and efficient procedure for the synthesis of 2,4,5-trisubstituted imidazoles using
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clays, zeolite, nano-crystalline sulfated zirconia (SZ) as catalyst [42]. In the present study, we report the synthesis of benzimidazoles, benzoxazoles, benzothiazoles, by the condensation of 1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes and the synthesis of quinoxalines derivatives by the condensation of 1,2-diaminobenzene and 1,2-dicarbonyl in ethanol using nano-structured ZnO, nano-sulfated zirconia, nano␥-alumina and nano-ZSM-5 zeolites, as the catalyst. 2. Experimental 2.1. Instruments and characterization Diethanolamine (DEA), zinc acetate dehydrate, aluminum nitrate, sodium carbonate, tetrapropyl ammonium hydroxide and tetra ethyl ortho silicate and other reagents were purchased from Merck and Aldrich and used without further purification. Products were characterized by spectroscopy data (FTIR, 1 H NMR and 13 C NMR spectra), elemental analysis (CHN) and melting points. A JASCO FT/IR-680 PLUS spectrometer was used to record IR spectra using KBr pellets. NMR spectra were recorded on a Bruker 400 Ultrasheild NMR and DMSO-d6 was used as solvent. Melting points reported were determined by open capillary method using a Galen Kamp melting point apparatus and are uncorrected. The total surface acidity of catalysts, was measured by a Micromeritics Pulse Chemisorb instrument by means of NH3 adsorption-desorption. Mass Spectra were recorded on a Shimadzu Gas Chromatograph Mass Spectrometer GCMS-QP5050A/Q P5000 apparatus. 2.2. Catalyst preparation 2.2.1. Synthesis of nano-crystalline sulfated zirconia Nano-crystalline sulfated zirconia has been prepared by one step sol–gel technique [43]. A typical synthesis involves the addition of concentrated sulfuric acid (1.02 ml) to zirconium npropoxide precursor (30 wt%) followed by the hydrolysis with water. After 3 h aging at room temperature, the resulting gel was dried at 110 ◦ C for 12 h followed by calcination at 600 ◦ C for 2 h. The bulk sulfur of the sulfated zirconia after calcination at 600 ◦ C was 3.2 wt% as measured by elemental analyzer. 2.2.2. Synthesis of nano-sized ZnO Nano-structure ZnO has been prepared by one step sol–gel technique [44]. In a typical procedure, mixtures of ethanol, diethanolamine (DEA) and zinc acetate dihydrate, were prepared. The concentration of zinc acetate dihydrate in solvent was 0.2 M. The molar ratios of zinc acetate dehydrate and diethanolamine was 1.0. Then the pH of the mixture was reached to about 9. When the zinc acetate crystals were dissolved completely, sodium hydroxide (NaOH) pellets were added to the solution to increase the pH of the mixture to about 11. Then, the washed precipitates were dried at 130 ◦ C and calcined at 600 ◦ C for 15 min in a oven to obtain white nano-sized ZnO particles. 2.2.3. Synthesis of nano--Al2 O3 catalyst The nano-␥-Al2 O3 was prepared by sol–gel method according to a procedure described [45]. In a typical experiment, Aluminum nitrate (15.614 g) was added to 400 ml of deionized water. Similarly solution of sodium carbonate is prepared by dissolving (7.95 g) in 400 ml of deionized water. 200 ml of deionized water is taken in a 2 L capacity round-bottom flask and stirred well using magnetic stirrer. Then sodium carbonate and aluminum nitrate solutions are added to 200 ml of deionized water (from separate burettes) drop wise. The temperature was maintained 70 ◦ C during experiment. The pH after precipitation was found to be in the range of 7.5–8.5. The
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mixture was stirred for 4 h. The digested precipitates were filtered and re-dispersed again in hot 2 l of deionized water, filtered and finally washed with ethanol first followed by acetone to avoid contamination of ‘Na’ ions; and air dried at room temperature. The dried precipitates were calcined in a furnace at 550 ◦ C for 5 h to produce nano-sized ␥-Al2 O3 powders. 2.2.4. Synthesis of nano-ZSM-5 For synthesis of nano-ZSM-5, tetrapropyl ammonium hydroxide and tetra ethyl ortho silicate were the sources of aluminum and silicon, respectively. nano-ZSM-5 Zeolite was synthesized according to the procedure described in advance. [39] The components were mixed with constant stirring. After adding all the ingredients the solution was left to hydrolyze at room temperature for 48 h. The gel thus obtained was heated at 80 ◦ C to evaporate water and ethanol formed during reaction. The obtained solution was charged into a Teflon-lined stainless-steel autoclave under pressure and static conditions at 170 ◦ C for of 48 h. The solid phase obtained was filtered, washed with distilled water several times, dried at 120 ◦ C and then calcined at 550 ◦ C for 12 h. 2.2.5. Characterization X-ray diffraction pattern were recorded on diffractometer ˚ Crystallite size (Philips X’pert) using CuK␣ radiation ( = 1.5405 A), of the crystalline phase was determined from the peak of maximum intensity by using Scherrer formula [46], with a shape factor (K) of 0.9, as below: Crystallite size = K·/W·cos , where, W = Wb − Ws and Wb is the broadened profile width of experimental sample and Ws is the standard profile width of reference silicon sample. FT-IR spectra of the catalysts were recorded by FT-IR spectrophotometer in the range of 400–4000 cm−1 with a resolution of 4 cm−1 by mixing the sample with KBr. Specific surface area, pore volume and pore size distribution of samples calcined at 600 ◦ C were determined from N2 adsorption–desorption isotherms at 77K (ASAP 2010 Micromeritics). Surface area was calculated by using BET equation; pore volume and pore size distribution were calculated by BJH method [47]. The samples were degassed under vacuum at 120 ◦ C for 4 h, prior to adsorption measurement to evacuate the physisorbed moisture. The detailed imaging information about the morphology and surface texture of the catalyst was provided by SEM (Philips XL30 ESEM TMP), a part of the spectra data has been published in our previous work [42]. The total surface acidity of catalysts was measured by a Micromeritics Pulse Chemisorb instrument by means of NH3 adsorption–desorption. The bulk sulfur (wt%) retained in sulfated zirconia samples before and after calcination at 600 ◦ C was analyzed by C H N S/O elemental analyzer. 2.3. General procedure for the synthesis of benzimidazoles derivatives In a 50 mL round bottom flask aldehyde (1 mmol) and 1,2diaminobenzene, 2-aminophenol, or 2-aminothiophenol (1 mmol) were thoroughly mixed in ethanol (10 mL) then catalyst (10 mol%) was added, and the solution was refluxed for appropriate time. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was cooled to room temperature and the resulting solid was collected by filtration and dissolved in 20 mL ethyl acetate. The catalyst was recovered by filtration. After evaporation of the solvent, the resulting solid product was recrystallized from ethanol to obtain pure product. Compound 1a: Mp 292–294 ◦ C. FTIR (KBr, cm−1 ): 3452, 1618, 1460 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.18–7.22 (m, 5H), 7.52–7.59 (m, 4H), 12.81 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı116.3 (2C), 123.5 (2C), 127.5 (2C), 128.6, 129.3 (2C), 130.6, 138.9
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(2C), 152.9; ESI MS (m/z): 194.08 (M+ ); Anal. Calcd. for C13 H10 N2 : C, 80.39; H, 5.19; N, 14.42. Found: C, 80.11; H, 4.89; N, 14.10. Compound 1b: Mp 290–292 ◦ C. FTIR (KBr, cm−1 ): 3446, 1628, 1477 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.28 (d, 2H), 7.30–7.34 (m, 2H), 7.38–7.42 (m, 1H), 7.62–7.66 (m, 1H), 8.56 (d, 2H), 12.13 (s, 1H); ESI MS (m/z): 228.05 (M+ ); Anal. Calcd for C13 H9 ClN2 : C, 68.28; H, 3.97; N, 15.50. Found: C, 67.86; H, 3.59; N, 15.16. Compound 1c: Mp 268–270 ◦ C. FTIR (KBr, cm−1 ): 3438, 1635, 1434 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.32 (d, 2H), 7.38–7.42 (m, 2H), 7.46–7.50 (m, 1H), 7.66–7.70 (m, 1H), 8.44 (d, 2H), 12.53 (s, 1H); ESI MS (m/z): 271.95 (M+ ); Anal. Calcd for C13 H9 BrN2 : C, 57.18; H, 3.32; N, 29.26. Found: C, 56.89; H, 3.09; N, 28.87. Compound 1d: Mp 318–320 ◦ C. FTIR (KBr, cm−1 ): 3448, 1626, 1587, 1529, 1356 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.26 (d, 2H), 7.34–7.38 (m, 2H), 7.42–7.48 (m, 1H), 7.58–7.63 (m, 1H), 8.62 (d, 2H), 12.28 (s, 1H); ESI MS (m/z): 239.08 (M+ ); Anal. Calcd for C13 H9 N3 O2 : C, 65.27; H, 3.79; N, 17.56. Found: C, 65.06; H, 3.39; N, 17.19. Compound 1e: Mp 288–290 ◦ C. FTIR (KBr, cm−1 ): 3561, 3434, 1621, 1463 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.23 (d, 2H), 7.29–7.33 (m, 2H), 7.38–7.42 (m, 1H), 7.64–7.68 (m, 1H), 8.44 (d, 2H), 9.58 (s, 1H), 12.32 (s, 1H); ESI MS (m/z): 210.07 (M+ ); Anal. Calcd for C13 H10 N2 O: C, 74.27; H, 4.79; N, 13.33. Found: C, 74.06; H, 4.38; N, 13.88. Compound 1f: Mp 260–262 ◦ C. FTIR (KBr, cm−1 ): 3432, 1622, 1456 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.35 (s, 3H), 7.16 (d, 2H), 7.32–7.38 (m, 2H), 7.43–7.49 (m, 1H), 7.61–7.64 (m, 1H), 8.09 (d, 2H), 12.80 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı 24.3, 115.3 (2C), 123.0 (2C), 127.4 (2C), 127.7, 129.6 (2C), 137.4, 138.7 (2C), 152.9; ESI MS (m/z): 208.01 (M+ ); Anal. Calcd for C14 H12 N2 : C, 80.74; H, 5.81; N, 13.45. Found: C, 80.21; H, 5.39; N, 13.08. Compound 1g: Mp 180–182 ◦ C. FTIR (KBr, cm−1 ): 3443, 1627, 1459 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 3H), 7.22 (d, 2H), 7.38–7.47 (m, 2H), 7.48–7.55 (m, 1H), 7.58–7.75 (m, 1H), 7.92 (d, 2H), 12.93 (s, 1H); 13 C NMR (400 MHz, DMSO-d6): ı 55.6, 114.6 (2C), 115.3 (2C), 123.0 (2C), 123.2, 128.5 (2C), 138.7 (2C), 152.8, 160.7; MS (m/z): 224.08 (M+ ); Anal. Calcd for C14 H12 N2 O: C, 74.98; H, 5.39; N, 12.48. Found: C, 74.34; H, 5.06; N, 11.98. Compound 2a: Mp 100–102 ◦ C. FTIR (KBr, cm−1 ): 3456, 1638, 1454 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.23–7.27 (m, 5H), 7.51–7.58 (m, 4H); 13 C NMR (400 MHz, DMSO-d6): ı 121.6, 122.3, 123.5, 124.6 (2C), 125.4, 129.4 (2C), 132.3, 138.5, 150.6, 154.2, 162.2;MS (m/z): 195.07 (M+ ); Anal. Calcd for C13 H9 NO: C, 79.98; H, 4.65; N, 7.16. Found: C, 79.61; H, 3.28; N, 6.84. Compound 2b: Mp 146–148 ◦ C. FTIR (KBr, cm−1 ): 3451, 1632, 1458 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.28–7.39 (d, 2H), 7.52–7.60 (m, 1H), 7.65–7.74 (d, 2H), 7.35–7. 86 (m, 1H), 8.11–8.19 (m, 2H); MS (m/z): 229.03 (M+ ); Anal. Calcd for C13 H8 ClNO: C, 67.99; H, 3.51; N, 6.10. Found: C, 67.64; H, 3.18; N, 5.92. Compound 2c: Mp 142–144 ◦ C. FTIR (KBr, cm−1 ): 3456, 1642, 1463 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.32–7.43 (d, 2H), 7.54–7.62 (m, 1H), 7.63–7.72 (d, 2H), 7.30–7. 81 (m, 1H), 8.09–8.17 (m, 2H); ESI MS (m/z): 272.98 (M+ ); Anal. Calcd for C13 H8 BrNO: C, 56.97; H, 2.94; N, 5.11. Found: C, 56.46; H, 2.58; N, 4.78. Compound 2d: Mp 262–264 ◦ C. FTIR (KBr, cm−1 ): 3448, 1587, 1531, 1354 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.30–7.41 (d, 2H), 7.50–7.58 (m, 1H), 7.62–7.71 (d, 2H), 7.33–7. 84 (m, 1H), 8.10–8.18 (m, 2H); ESI MS (m/z): 240.05 (M+ ); Anal. Calcd for C13 H8 N2 O3 : C, 65.01; H, 3.36; N, 11.76. Found: C, 64.74; H, 3.08; N, 11.72. Compound 2e: Mp 282–284 ◦ C. FTIR (KBr, cm−1 ): 3541, 3448, 1647, 1454 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.27–7.38 (d, 2H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.41–7. 57(m, 1H), 8.16–8.32 (m, 2H)), 9.42 (s, 1H); MS (m/z): 211.05 (M+ ); Anal. Calcd for C13 H9 NO2 : C, 73.91; H, 4.59; N, 6.63. Found: C, 73.64; H, 3.96; N, 6.42.
Compound 2f: Mp 126–128 ◦ C. FTIR (KBr, cm−1 ): 3440, 1646, 1461 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.26–7.37 (d, 2H), 7.41–7.49 (m, 1H), 7.56–7.65 (d, 2H), 7.24–7. 74 (m, 1H), 8.06–8.22 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 21.3, 110.7, 119.6, 123.4, 124.8, 126.4, 127.4 (2C), 129.6 (2C), 138.4, 141.5, 150.4, 162.2; ESI MS (m/z): 209.08 (M+ ); Anal. Calcd for C14 H11 NO: C, 80.36; H, 5.30; N, 6.69. Found: C, 79.98; H, 5.02; N, 6.32. Compound 2g: Mp 96–98 ◦ C. FTIR (KBr, cm−1 ): 3448, 1651, 1462 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.64 (s, 3H), 7.28–7.39 (d, 2H), 7.44–7.52 (m, 1H), 7.54–7.63 (d, 2H), 7.33–7.53 (m, 1H), 8.11–8.27 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 54.3, 110.7, 116.4 (2C), 118.5, 121.3, 122.4, 124.7, 127.6 (2C), 142.2, 150.4, 161.4, 164.7;ESI MS (m/z): 225.08 (M+ ); Anal. Calcd for C14 H11 NO2 : C, 74.65; H, 4.92; N, 6.22. Found: C, 74.22; H, 4.62; N, 6.02. Compound 3a: Mp 110–112 ◦ C. FTIR (KBr, cm−1 ): 3426, 1658, 1448 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.38–7.42 (m, 5H), 7.66–7.73 (m, 4H); 13 C NMR (400 MHz, DMSO-d6): ı 121.8, 122.2, 123.5, 125.6 (2C), 126.6, 129.2 (2C), 132.3, 135.3, 151.1, 154.2, 166.3;ESI MS (m/z): 211.05 (M+ ); Anal. Calcd for C13 H9 NS: C, 73.90; H, 4.59; N, 6.63. Found: C, 73.56; H, 3.86; N, 6.44. Compound 3b: Mp 106–108 ◦ C. FTIR (KBr, cm−1 ): 3456, 1638, 1445 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.24–7.35 (d, 2H), 7.48–7.56 (m, 1H), 7.62–7.71 (d, 2H), 7.40–7. 81 (m, 1H), 8.31–8.48 (m, 2H); ESI MS (m/z): 245.01 (M+ ); Anal. Calcd for C13 H8 ClNS: C, 63.54; H, 3.28; N, 5.70. Found: C, 63.11; H, 2.94; N, 5.42. Compound 3c: Mp 102–104 ◦ C. FTIR (KBr, cm−1 ): 3450, 1644, 1432 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.31–7.42 (d, 2H), 7.50–7.58 (m, 1H), 7.64–7.73 (d, 2H), 7.48–7. 88 (m, 1H), 8.26–8.32 (m, 2H); ESI MS (m/z): 288.96 (M+ ); Anal. Calcd for C13 H8 BrNS: C, 58.93; H, 2.78; N, 4.83. Found: C, 58.46; H, 2.34; N, 4.56. Compound 3d: Mp 228–230 ◦ C. FTIR (KBr, cm−1 ): 3446, 1576, 1537, 1352 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.25–7.36 (d, 2H), 7.45–7.53 (m, 1H), 7.62–7.71 (d, 2H), 7.48–7.98 (m, 1H), 8.28–8.44 (m, 2H); ESI MS (m/z): 256.03 (M+ ); Anal. Calcd for C13 H8 N2 O2 S: C, 60.93; H, 3.15; N, 10.93. Found: C, 69.44; H, 2.91; N, 10.62. Compound 3e: Mp 224–226 ◦ C. FTIR (KBr, cm−1 ): 3536, 3441, 1652, 1448 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.10–7.21 (d, 2H), 7.32–7.40 (m, 1H), 7.51–7.60 (d, 2H), 7.46–7.96 (m, 1H), 8.19–8.35 (m, 2H) 11.3 (s, 1H); ESI MS (m/z): 227.04 (M+ ); Anal. Calcd for C13 H9 NOS: C, 68.70; H, 3.99; N, 6.16. Found: C, 68.36; H, 3.62; N, 5.86. Compound 3f: Mp 82–84 ◦ C. FTIR (KBr, cm−1 ): 3437, 1648, 1452 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.18–7.29 (d, 2H), 7.40–7.48 (m, 1H), 7.54–7.63 (d, 2H), 7.42–7.92 (m, 1H), 8.21–8.37 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 21.3, 121.7, 123.2, 125.2, 125.5 (2C), 126.4, 132.9, 133.5, 135.1, 138.9 (2C), 154.1, 168.7;ESI MS (m/z): 225.06 (M+ ); Anal. Calcd for C14 H11 NS: C, 74.63; H, 4.92; N, 6.22. Found: C, 69.34; H, 4.58; N, 5.82. Compound 3g: Mp 118–120 ◦ C. FTIR (KBr, cm−1 ): 3432, 1646, 1458 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.85 (s, 3H), 7.15–7.26 (d, 2H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.48–7.98 (m, 1H), 8.16–8.32 (m, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 54.3, 121.8, 123.7, 125.8, 126.7, 127.4 (2C), 130.3 (2C), 135.4, 137.4, 144.4, 154.2, 166.4;ESI MS (m/z): 241.06 (M+ ); Anal. Calcd for C14 H11 NOS: C, 69.68; H, 4.59; N, 5.80. Found: C, 69.34; H, 4.18; N, 5.62.
2.4. General procedure for the synthesis of quinoxalines derivatives To a mixture of 1,2-diaminobenzene (1 mmol) and 1,2dicarbonyl compound (1 mmol) in ethanol (10 mL), catalyst (10 mol%) was added and the solution was refluxed for appropriate time. The progress of the reaction was monitored by TLC. After completion of the reaction, ethyl acetate was added to the
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
solidified mixture and the insoluble catalyst was separated by filtration. After evaporation of the solvent, the resulting solid product was recrystallized from ethanol to obtain pure product. Compound 4a: Mp 130–132 ◦ C. FTIR (KBr, cm−1 ): 3052, 1646, 1344 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 7.41 (m, 6H), 7.55 (m, 4H), 7.79 (d, 2H), 8.18 (d, 2H); 13 C NMR (400 MHz, DMSO-d6): ı 128.30, 128.83, 129.05, 129.23, 129.87, 129.99, 134.90, 139.10, 141.24, 153.49;ESI MS (m/z): 282.12 (M+ ); Anal. Calcd for C20 H14 N2 : C, 85.08; H, 5.01; N, 9.92. Found: C, 84.84; H, 4.78; N, 9.62. Compound 4b: Mp 192–194 ◦ C. FTIR (KBr, cm−1 ): 3038, 1642, 1336 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 6.74 (d, 4H), 7.68 (d, 4H), 7.58 (d, 2H), 8.26 (d, 2H); ESI MS (m/z): 350.05 (M+ ); Anal. Calcd for C20 H12 Cl2 N2 : C, 68.39; H, 3.44; N, 7.98. Found: C, 68.08; H, 3.11; N, 7.58. Compound 4c:Mp 132–134 ◦ C. FTIR (KBr, cm−1 ): 3044, 1645, 1352 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 6.78 (d, 4H), 7.70 (d, 4H), 7.56 (d, 2H), 8.22 (d, 2H); ESI MS (m/z): 318.01 (M+ ); Anal. Calcd for C20 H12 F2 N2 : C, 75.46; H, 3.80; N, 8.80. Found: C, 75.13; H, 3.62; N, 8.48. Compound 4d: Mp 128–130 ◦ C. FTIR (KBr, cm−1 ): 3034, 1641, 1347 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 2.42 (s, 6H), 6.76 (d, 4H), 7.73 (d, 4H), 7.55 (d, 2H), 8.21 (d, 2H); ESI MS (m/z):310.15 (M+ ); Anal. Calcd for C22 H18 N2 : C, 85.13; H, 5.85; N, 9.03. Found: C, 84.91; H, 5.51; N, 8.68. Compound 4e: Mp 148–150 ◦ C. FTIR (KBr, cm−1 ): 3042, 1626, 1345 cm−1 ; 1 H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 6H), 6.89 (d, 4H), 7.50 (d, 4H), 7.65 (d, 2H), 8.16 (d, 2H); ESI MS (m/z): 342.18 (M+ ); Anal. Calcd for C22 H18 N2 O2 : C, 77.17; H, 5.30; N, 8.18. Found: C, 76.87; H, 5.08; N, 7.72. 3. Results and discussion In the reaction between aldehydes and 1,2-diaminobenzene, 2aminophenol, or 2-aminothiophenol and 1,2-diaminobenzene and 1,2-dicarbonyl compounds effect of the catalyst amount was investigated. To minimize the formation of byproducts and to achieve good yield of the desired product, the reaction is optimized by varying the amount of catalyst,the percentage yield of the product with 5, 10 and 15 mg of nano-sulfated zirconia as a catalyst are 80%, 92% and 70%, respectively (Table 1, entries 2–4). The percentage yield of the product with 5, 10 and 15 mol% of nano-ZnO as a catalyst are 75%, 80% and 65%, respectively (Table 1, entries 5–7). For the nano-␥-alumina and nano-ZMS-5 as the catalyst, when the catalyst content was increased to 15 mg,the product yield decreased to 70% (Table 1, entry 10) and 65% (Table 1, entry 13) respectively. It is noteworthy to mention that in the absence of catalyst, no product was found even after 24 h. These results indicate that the catalyst exhibits a high catalytic activity in this transformation.
41
Table 2 Effect of various solvents on the reaction times and yields using nano SZ as the catalysts. Entry
Solventa
Time (min)b
Yield (%)c
1 2 3 4 5 6
H2 O EtOH MeOH CH3 CN 1,4-Dioxan THF
90 90 90 90 90 90
75 92 80 75 65 60
a Reaction was performed with benzaldehyde (2.0 mmol), benzene-1,2-diamine (2.0 mmol) in the presence of 10 mg nano SZ as the catalyst in various solvents. b Reaction time monitored by TLC. c Isolated yield.
In order to optimize the reaction conditions, including solvents and temperature, the reaction of benzaldehyde (2 mmol) and 1,2diaminobenzene (2 mmol) was optimized by time of the reaction and using various solvents such as H2 O, EtOH, MeOH, CH3 CN, 1,4Dioxan, and THF in the presence of nano SZ as the catalyst. (Table 2, entries 1–6). Reaction in 1,4-Dioxan, and THF solvent gave low product yields even after 120 min (Table 2, entries 5 and 6). The yields were moderate in case of methanol and acetonitrile under reflux condition. (Table 2, entries 3 and 4). The best results were obtained when the reaction was carried out in ethanol at reflux 90 min in the presence of catalyst (Table 2, entry 2). Therefore, ethanol was selected as a solvent for this reaction. The reaction of benzil with 1,2-diaminobenzene was chosen as a model reaction to study the effect of various solvents on the yield of quinoxaline. Among the solvents examined, ethanol was found to be the most effective solvent. Although water is a desirable solvent for chemical reactions for reasons of cost, safety and environmental concerns, we found that using water in this reaction gave moderate yields of products under reflux condition after long reaction times. Synthesis of benzimidazoles, benzoxazoles, benzothiazoles, by condensation of 1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes and the synthesis of quinoxalines derivatives by the condensation of 1,2diaminobenzene and 1,2-dicarbonyl in ethanol using (Tables 4–7) preferred values of catalysts achieved. In all reactions good to excellent yields was obtained. The isolated compounds were characterized using spectroscopic and physical methods and compared with those data in literature. The total acidity of catalysts was determined by temperatureprogrammed description of ammonia (TPD). The catalysts were treated under helium at 200 ◦ C for 1 h, and then treated with a NH3 flow for 5 min at 100 ◦ C. The excess physisorbed ammonia was flushed out with pure He gas flow at 120 ◦ C for 1 h and the temperature subsequently raised up to 600 ◦ C at 10◦ /min. The total
Table 1 Effect of type and amount of catalyst on the synthesis of benzimidazoles derivatives. Entry
Catalyst
Catalyst loading
Catalyst (mol%)
Time (h)
Yield (%)a
1 2 3 4 5 6 7 8 9 10 11 12 13
None Nano-SZ Nano-SZ Nano-SZ Nano-ZnO Nano-ZnO Nano-ZnO Nano-␥-alumina Nano-␥-alumina Nano-␥-alumina Nano-ZMS-5 Nano-ZMS-5 Nano-ZMS-5
– 5 (mg) 10 (mg) 15 (mg) 5 (mol%) 10 (mol%) 15 (mol%) 5 (mg) 10 (mg) 15 (mg) 5 (mg) 10 (mg) 15 (mg)
– 5 10 15 5 10 15 5 10 15 5 10 15
24 5 5 5 5 5 5 5 5 5 5 5 5
No reaction 80 92 70 75 80 65 75 85 70 73 75 65
a
Yields after isolation of product.
42
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 3 Summary of acidic measured by NH3 -TPD of synthesized catalysts. Catalyst
Acidic sites (mmol NH3 /g)
Nano-crystalline SZ Nano-␥-Al2 O3 Nano-ZMS-5 Nano size-ZnO
T1 (<200 ◦ C)
T2 (>500 ◦ C)
Total
0.223 0.197 0.186 0.173
0.199 0.175 0.172 0.142
0.402 0.372 0.358 0.315
evacuation of NH3 from the catalysts was measured. The results of the TPD measurements are summarized in Table 3. In view of the above results obtained, it has now become clear that all four catalysts have both Bronsted and Lewis acid sites. The total number of acid sites, nano-crystalline SZ was found to have 0.402 mmol/g whereas the nano ␥-Al2 O3 , nano-ZMS-5 and nano size-ZnO have 0.372, 0.358 and 0.315 mmol/g, respectively. Sulfated zirconia possesses stronger surface acidity due to the presence of sulfate group binding with zirconia surface. The highest catalytic activity for sulfated zirconia could be attributed to its stronger surface acidity compared to other studied catalysts. Therefore, nano-crystalline SZ had the largest acidity and nano size-ZnO had the smallest acidity as compared to the other catalysts. These results are in good agreement with previous works [48]. The FT-IR spectra of alumina samples calcined at 600 ◦ C (Fig. 1) showed an intense band centered around 3500 cm−1 and a broad band at 1650 cm−1 , these are assigned to stretching and bending modes of adsorbed water. The Al–O–Al bending stretching vibrations observed at around 1150 cm−1 are due to symmetric and asymmetric bending modes, respectively. The OH torsional mode observed at 800 cm−1 overlaps with Al–O stretching vibrations. The weak band at 2091 cm−1 is assigned to a combination band. The bands observed at 617 and 481 cm−1 are attributable to stretching and bending modes of AlO6 [49]. The XRD patterns of nano-sized ZnO powders obtained. All nano-ZnO samples exhibited a hexagonal structure. Characteristic peaks of ZnO appeared at 31.7, 34.5, 36.2 and 56.5. (Fig. 2) The morphology of the as prepared nano-size-␥-Al2 O3 and nano-sized ZnO powders analyzed by SEM is shown in Figs. 3 and 4. The SEM image demonstrates clearly the formation of spherical ZnO nanoparticles. The ␥-Al2 O3 powders indicated strong agglomeration of particles with varied spherical sizes. One of the most important advantages of heterogeneous catalysis over the homogeneous counterpart is the possibility of reusing the catalyst by simple filtration, without loss of activity. The recovery and reusability of the catalyst was investigated in the product formation. After completion of the reaction, the catalyst was separated by filtration, washed 3 times with 5 ml acetone, then with
Fig. 1. FT-IR spectra nano-␥-alumina catalyst.
Fig. 2. XRD pattern of nano-ZnO catalyst.
Fig. 3. SEM micrograph of nano-␥-alumina catalyst.
Fig. 4. SEM micrograph of nano-ZnO catalyst.
doubly distilled water several times and dried at 110 ◦ C. Then the recovered catalyst was used in the next run. The results of three consecutive runs showed that the catalyst could be reused several times without significant loss of its activity (see Fig. 5). To generalize the scope and versatility of this protocol, different substituted arylaldehydes are used for the synthesis of these products. Aldehyde compounds which have electron donating or electron withdrawing groups were used and as expected it gives good yield of products, it can be seen that electron donating and electron withdrawing groups does not show any difference on the reaction yields (Tables 4–7). This indicates that the present catalyst efficiently makes the condensation reaction much faster with increased yields (Fig. 6). The method described here for synthesis of quinoxalines derivatives can be compared with other catalysts that reported literature [59–61]. To account for the facile formation of benzimidazoles, benzoxazoles and benzothiazoles, by the condensation of
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
43
Table 4 Acid-catalyzed synthesis of benzimidazoles derivatives.a
H N
NH2
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
N
NH2 Ar
1 (1a) 2 (1b) 3 (1c) 4 (1d) 5 (1e) 6 (1f) 7 (1g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/yield (%)b
Entry/product
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/88 100/70 90/72 95/64 80/65 90/74 80/70
90/88 80/82 85/76 90/74 80/82 90/78 85/74
85/90 85/85 90/84 80/82 80/80 75/84 70/82
45/92 60/88 75/81 70/90 85/82 90/92 90/85
292–294 (290–293) [50] 290–292 (288–291) [51] 268–270 (261.5–263.5) [52] 318–320 (322–323) [50] 288–290 (265–267) [52] 260–262 (264–265) [50] 180–182 (223–226) [53]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
Table 5 Acid-catalyzed synthesis of benzoxazoles derivatives.a
NH2
N
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
OH
O Ar
1 (2a) 2 (2b) 3 (2c) 4 (2d) 5 (2e) 6 (2f) 7 (2g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b
Entry/product
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/86 100/70 95/76 90/70 85/75 90/76 85/75
90/88 80/80 80/77 95/78 80/78 95/78 80/80
80/90 85/80 80/82 80/82 90/80 70/80 75/84
45/86 60/86 60/85 75/84 80/85 85/87 90/87
100–102 (102–103) [50] 146–148 (149–150) [50] 142–144 262–264 (266–267) [50] 282–284 (287–289) [54] 126–128 (100–101) [54] 96–98 (100–101) [50]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
Table 6 Acid-catalyzed synthesis of benzothiazoles derivatives.a
N
NH2
+
Ar
CHO
Catalyst
Ar
EtOH, reflux
S
SH Entry/product
Ar
1 (3a) 2 (3b) 3 (3c) 4 (3d) 5 (3e) 6 (3f) 7 (3g)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5 4-CH3 C6 H5 4-OCH3 C6 H5
a b
MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
100/86 90/75 80/72 95/72 80/70 95/76 80/70
90/87 80/80 85/78 95/78 90/76 95/80 85/76
85/92 80/84 90/82 90/80 80/78 75/82 70/80
45/92 60/94 60/85 75/91 80/92 85/92 90/90
110–112(112–114) [55] 108–110 (103–104) [56] 102–104 228–230 (230–231) [57] 224–226 (227) [57] 82–84 (85) [57] 118–120 (120–121) [55]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and substituted aldehydes, the following mechanism (Fig. 7) is proposed. The reaction between an aldehyde and aromatic amine leads to the formation of Schiff base which is stabilized by catalyst. Then intramolecular attack by the second group on C N double bond to give the final product. This reaction is likely to follow the proposed mechanism of acid-catalyzed coordination of a 1,2-dicarbonyl onto
acid sites, followed by the nucleophilic attack on the diketone and then followed by dehydration to give a carbocation intermediate and elimination of a proton to give quinoxaline products as shown in Fig. 7. A similar mechanism has been proposed for this reaction [62]. In conclusion, a one-pot, multicomponent methodology has been developed for the synthesis of, benzimidazoles, benzoxazoles,
44
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 7 Acid-catalyzed synthesis of quinoxalines derivatives.a
Ar
O
H2N Catalyst
+ Ar
O
EtOH, reflux
Ar
H2N Ar
1 (4a) 2 (4b) 3 (4c) 4 (4d) 5 (4e)
C6 H5 4-ClC6 H5 4-BrC6 H5 4-NO2 C6 H5 4-OHC6 H5
a
N MP ◦ C (lit.) [Ref.]
Time (min)/Yield (%)b
Entry/product
b
N
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
70/86 80/72 90/76 95/76 80/75
70/88 70/80 85/78 90/80 80/82
75/90 65/85 90/84 80/82 80/80
30/92 20/94 25/90 20/88 15/88
130–132 (128–129) [58] 192–194 (195–196) [58] 132–134 (135–137) [58] 128–130 148–150 (151–152.5) [58]
The products were characterized by IR, 1 H NMR, 13 C NMR and mass spectroscopy. Isolated yields.
benzothiazolesand quinoxalines derivatives catalyzed by nanosulfated zirconia, nano-structured ZnO, nano-␥-alumina and nano-ZSM-5 zeolites with the nano-sulfated zirconia exhibiting greater activity has also been demonstrated. Compared to previously reported methods, Moreover, the mild reaction conditions, easy work-up, clean reaction profiles, lower catalyst loading and cost efficiency render this approach as an interesting alternative to the existing methods. Acknowledgements
Fig. 5. The results obtained from catalyst reuse in the product formation.
Ar
Supports from the Payame Noor University in Isfahan research council and helps of Isfahan University of technology are gratefully acknowledged. Thanks are also due to Mrs. Shahraki and Mr. Narimani for recording the FT-IR spectra of the compound.
CHO O
H
Ar
References
H H
H H
H2N
-H2O
HX N
Ar
N Ar
H
H N
X
Ar H
X
H
HX
H
Fig. 6. Proposed mechanism for the synthesis of benzimidazoles, benzoxazoles and benzothiazoles derivatives.
H
Ar
O
Ar
O
H H
H
Ar
N
N
Ar
O
Ar H2N H2N
OH2
-2H2O H
Ar
O
N
Ar
H Ar
N OH2
Fig. 7. A plausible mechanism for the condensation reaction of 1,2-diamine with 1,2-dicarbonyl compounds by catalyst.
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