Magnetic CoFe2O4 nanoparticle immobilized N-propyl diethylenetriamine sulfamic acid as an efficient and recyclable catalyst for the synthesis of amides via the Ritter reaction

Applied Catalysis A: General 482 (2014) 258–265

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Magnetic CoFe2 O4 nanoparticle immobilized N-propyl diethylenetriamine sulfamic acid as an efficient and recyclable catalyst for the synthesis of amides via the Ritter reaction Xiao-Na Zhao, Hai-Chuan Hu, Fu-Jun Zhang, Zhan-Hui Zhang ∗ College of Chemistry and Material Science, Hebei Normal University, Nanerhuan East Road, Shijiazhuang 050024, Hebei, China

a r t i c l e

i n f o

Article history: Received 9 March 2014 Received in revised form 29 May 2014 Accepted 4 June 2014 Available online 12 June 2014

a b s t r a c t A magnetic CoFe2 O4 nanoparticle immobilized diamine-N-sulfamic acid (CoFe2 O4 @SiO2 –DASA) was synthesized and used as efficient heterogeneous catalyst for the synthesis of amides via the Ritter reaction under solvent-free conditions. The magnetic nanocatalyst could be readily recovered by applying an external magnet and recycled several times without considerable loss of its catalytic activity. © 2014 Elsevier B.V. All rights reserved.

Keywords: Magnetic nanoparticle Sulfamic acid functionalized CoFe2 O4 Ritter reaction Amides

1. Introduction From the standpoint of environmentally benign organic synthesis, the design of novel, highly active and reusable immobilized catalysts has become a major area of research. Though various materials such as inorganic solids, polymers, ionic liquids have been explored as supports. Increasing attention has recently been paid to the use of nanoparticles (NPs) as supports due to their remarkable advantages such as small size, large specific surface area, high dispersion property, good catalytic activity and selectivity, and easy modifiable surface by chemical methods [1]. In this sense, magnetic nanoparticles (MNPs) are arguably the most extensively investigated and emerged as appealing catalyst supports [2–15]. Their magnetic character makes them be effective and easily separated from the reaction system by applying an external magnetic field, which eliminates the necessity of tedious filtration, centrifugation or membrane separation steps. Among the various MNPs as the core magnetic supports, cobalt ferrite is one of the most versatile magnetic materials as they have moderate saturation magnetization, inexpensiveness, high chemical stability and mechanical strength [16–18]. On the other hand, sulfonic acid catalysts have been widely used in various industries; however, it is often difficult to separate

∗ Corresponding author. Tel.: +86 31180787431; fax: +86 31180787431. E-mail address: [email protected] (Z.-H. Zhang). http://dx.doi.org/10.1016/j.apcata.2014.06.006 0926-860X/© 2014 Elsevier B.V. All rights reserved.

the final product after the reaction is complete. Although there are many reports on the preparation and applications of immobilization of sulfonic acid [19–26], to the best of our knowledge, no reports were devoted to the grafting of sulfuric acid on cobalt ferrite. The Ritter reaction is a very efficient and widely used method for the formation of amides. It is applied to a wide range of substrates and has become one of the most influential methods for the synthesis of natural products and pharmaceuticals [27–29]. Although there are many catalytic systems reported for this reaction [30–37], only a few heterogeneous catalysts have been described, including sulfated tungstate [38], silica-bonded N-propyl sulphamic acid (SBNPSA) [39], silica boron–sulfuric acid nanoparticles (SBSANs) [40], HClO4 –functionalized silicacoated magnetic nanoparticles [␥-Fe2 O3 @SiO2 –HClO4 ] [41], silica sulfuric acid [42], alumina–methanesulfonic acid (AMA) [43], and magnetite-supported sulfonic acid (nanocat-Fe–OSO3 H) [44]. Therefore, the research on the development of novel, more efficient, cheaper, and more easily recovered catalysts for the Ritter reaction is a particularly hot issue. These results in combination with our recent work on the designing magnetic nanocatalysts and their application in organic synthesis [45–52], let us to present a new type of magnetic CoFe2 O4 nanoparticle immobilized diamine-N-sulfamic acid (CoFe2 O4 @SiO2 –DASA) as a powerful catalyst for the green and efficient synthesis of amides via the Ritter reaction (Scheme 1).

X.-N. Zhao et al. / Applied Catalysis A: General 482 (2014) 258–265

Scheme 1. Synthesis of amides via the Ritter reaction.

2. Experimental

259

acid (2 mL) in dichloromethane (15 mL). The chlorosulfonic acid solution was added drop-wise over a period of 30 min at 0 ◦ C. After the addition was complete, the mixture was shaken for 1 h until all HCl was removed from reaction vessel. Then, the product was separated by magnetic decantation and washed thrice with EtOH to remove unattached substrates. Finally, the obtained sulphamic acid-functionalized magnetic CoFe2 O4 nanoparticles (CoFe2 O4 @SiO2 –DASA) were dried under vacuum at 60 ◦ C for 24 h. 2.3. General procedure for synthesis of amides

2.1. General X-ray power diffraction (XRD) analysis was carried out on a PANalytical X’Pert Pro X-ray diffractometer. Surface morphology and particle size were studied using a Hitachi S-4800 SEM instrument. Transmission electron microscope (TEM) images was obtained using Hitachi H-7650 microscope at 80 kV. Elemental compositions were determined with a Hitachi S-4800 scanning electron microscope equipped with an INCA 350 energy dispersive spectrometer (SEM–EDS) presenting a 133 eV resolution at 5.9 keV. The ICP-MS analyses were carried out with an X series 2 spectrometer. Melting points were determined using an X-4 apparatus and are uncorrected. FT-IR spectra were obtained with potassium bromide pellets or as liquid films on potassium bromide pellets in the range 400–4000 cm−1 with a Bruker-TENSOR 27 spectrometer. 1 H NMR (500 MHz) and 13 C NMR (125 MHz) spectra were recorded on a Bruker DRX-500 spectrometer using CDCl3 as the solvent with TMS as internal standard. Elemental analyses were performed by using a Vario EL III CHNOS elemental analyzer. 2.2. Preparation of magnetic CoFe2 O4 nanoparticle immobilized N-propyl diethylenetriamine sulfamic acid (CoFe2 O4 @SiO2 –PDTSA)

A mixture of alcohol (1 mmol), nitrile (1 mmol), CoFe2 O4 @SiO2 –DASA (0.1 g) was heated at 80 ◦ C under solventfree conditions. The reaction process was monitored by thin layer chromatography (TLC). After completion of the reaction, the reaction mixture was cooled to room temperature and ethyl acetate (5 mL) was added. The catalyst was removed by using a magnet and washed with ethyl acetate. The combined organic layers were dried over anhydrous MgSO4 , and the solvent was evaporated under reduced pressure. The pure product was obtained by column chromatography on silica gel using hexane/ethyl acetate as eluent. 3. Some selected spectral data of the products 3.1. N-benzyl-acetamide (3a) White solid, mp: 41–42 ◦ C; IR (KBr): 3293, 1643, 1555, 750, 694 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.03 (s, 3H), 4.44 (d, J = 5.5 Hz, 2H), 5.72 (s, 1H), 7.28–7.29 (m, 3H), 7.33 (d, J = 7.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 23.3, 30.9, 43.8, 127.6, 127.9, 128.7, 138.2 ppm. Anal. Calcd for C9 H11 NO: C, 72.46; H, 7.43; N, 9.39. Found: C, 72.39; H, 7.40; N, 9.40; ESI–MS: m/z = 150 (M+1)+ . 3.2. N-(2-methylbenzyl)-acetamide (3b)

CoFe2 O4 nanoparticles were synthesized according to a previously reported procedure [43]. 2.70 g of FeCl3 ·6H2 O and 1.19 g of CoCl2 ·6H2 O were dissolved in 50 mL deionized water. 25 mL of NaOH (3 mol/L) solution was added under vigorous stirring. The reaction mixture was then continually stirred under refluxing condition for 1 h. The reaction mixture was cooled to room temperature. The solid product was separated by an external magnet and washed with ethanol, then dried under vacuum at 50 ◦ C for 24 h. Coating of a layer of silica on the surface of the CoFe2 O4 NPs was achieved by adding distilled water (80 mL) to purified CoFe2 O4 NPs (1 g) which were then heated for 1 h at 40 ◦ C. Then concentrated ammonia solution (1.5 mL) was added and the resulting mixture was stirred at 40 ◦ C for 30 min. Subsequently, tetraethyl orthosilicate (TEOS, 1.0 mL) was charged to the reaction vessel and the mixture was continuously stirred for 24 h. After cooling the solution to room temperature, the silica-coated NPs were collected using a permanent magnet and washed three times with ethanol, diethyl ether, then dried at 100 ◦ C in a vacuum for 24 h. For the preparation of diamino-functionalized NPs, the obtained CoFe2 O4 @SiO2 (1 g) was added to the solution of N-(2-aminoethyl)-(3-aminopropyl)triethoxysilane (AEAPTS, 2 mmol) in dry toluene (20 mL) and the mixture was refluxed for 20 h. The diaminated-CoFe2 O4 @SiO2 were separated by a permanent magnet, washed with double-distilled water and anhydrous ethanol, and dried at 100 ◦ C for 5 h to give diamino-functionalized NPs (CoFe2 O4 @SiO2 –DA). N-propyl-ethylene-diamine sulfamic acid on CoFe2 O4 (CoFe2 O4 @SiO2 –DASA) was prepared by the reaction of CoFe2 O4 @SiO2 –DA and chlorosulfonic acid. Typically, a mixture of CoFe2 O4 @SiO2 –DA (0.5 g) was suspended in dichloromethane (5 mL) in a 100 mL round bottom flask equipped with a gas outlet tube and a dropping funnel containing a solution of chlorosulfonic

White solid, mp: 72–73 ◦ C; IR (KBr): 3295, 1640, 1549, 743 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.02 (s, 3H), 2.33 (s, 3H), 4.44 (d, J = 5.0 Hz, 2H), 5.54 (s, 1H), 7.18–7.23 (m, 4H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 19.0, 23.2, 41.9, 126.2, 127.8, 128.6, 130.6, 135.8, 136.5, 169.8 ppm. Anal. Calcd for C10 H13 NO: C, 73.59; H, 8.03; N, 8.58. Found: C, 73.49; H, 8.09; N, 8.66; ESI–MS: m/z = 164 (M+1)+ . 3.3. N-(4-methylbenzyl)-acetamide (3c) White solid, mp: 108–109 ◦ C; IR (KBr): 3289, 1647, 1555, 804 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.02 (s, 3H), 2.34 (s, 3H), 4.39 (d, J = 6.0 Hz, 2H), 5.67 (s, 1H), 7.15 (d, J = 8.0 Hz, 2H), 7.18 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 23.3, 43.5, 127.9, 129.4, 135.2, 137.3, 169.8 ppm. Anal. Calcd for C10 H13 NO: C, 73.59; H, 8.03; N, 8.58. Found: C, 73.48; H, 8.15; N, 8.71; ESI–MS: m/z = 164 (M+1)+ . 3.4. N-benzhydryl-acetamide (3d) White solid, mp: 151–152 ◦ C; IR (KBr): 3257, 3049, 1647, 1545 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.07 (s, 3H), 6.07 (s, 1H), 6.25 (d, J = 8.0 Hz, 1H), 7.22–7.35 (m, 10H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 23.3, 57.0, 127.5, 128.7, 141.6, 169.2 ppm. Anal. Calcd for C15 H15 NO: C, 79.97; H, 6.71; N, 6.22. Found: C, 79.83; H, 6.69; N, 6.17; ESI–MS: m/z = 226 (M+1)+ . 3.5. N-(1,1-dimethyl-2-phenyl-ethyl)-acetamide (3e) White solid, mp: 82–83 ◦ C; IR (KBr): 3330, 3025, 1673 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 1.33 (s, 6H), 1.91 (s, 3H), 3.05 (s, 2H), 5.03 (s, 1H), 7.13–7.30 (m, 5H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 24.6,

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27.4, 44.5, 54.0, 126.3, 128.0, 130.5, 138.1, 169.8 ppm. Anal. Calcd for C12 H17 NO: C, 75.35; H, 8.96; N, 7.32. Found: C, 75.41; H, 8.87; N, 7.23; ESI–MS: m/z = 192 (M+1)+ . 3.6. N-trityl-acetamide (3f) White solid, mp: 219–221 ◦ C; IR (KBr): 3242, 3023, 1655, 1526 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.09 (s, 3H), 6.58 (s, 1H), 7.20–7.31 (m, 15H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 24.7, 70.6, 127.1, 128.0, 128.7, 144.7, 169.1 ppm. Anal. Calcd for C21 H19 NO: C, 83.69; H, 6.35; N, 4.65. Found: C, 83.78; H, 6.38; N, 4.78; ESI–MS: m/z = 302 (M+1)+ . 3.7. N-(3-phenyl-allyl)-acetamide (3g) White solid, mp: 71–72 ◦ C; IR (KBr): 3283, 3092, 1728, 1643, 964 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.03 (s, 3H), 4.04 (t, J = 6.0 Hz, 2H), 5.60 (s, 1H), 6.19 (dt, J = 16.0, 6.0 Hz, 1H), 6.53 (d, J = 16.0 Hz, 1H), 7.23 (d, J = 7.5 Hz, 1H), 7.31 (t, J = 7.5 Hz, 2H), 7.35 (d, J = 7.5 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 23.3, 41.7, 125.5, 126.4, 127.8, 128.6, 132.3, 136.5, 169.9 ppm. Anal. Calcd for C11 H13 NO: C, 75.40; H, 7.48; N, 7.99. Found: C, 75.41; H, 7.40; N, 8.00; ESI–MS: m/z = 176 (M+1)+ .

3.12. N-benzhydryl-2,2-diphenyl-acetamide (3l) White solid, mp: 202–204 ◦ C; IR (KBr): 3254, 3055, 1649, 1543, 696 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 4.99 (s, 1H), 6.19 (d, J = 8.5 Hz, 1H), 6.31 (d, J = 8.0 Hz, 1H), 7.10 (d, J = 7.0 Hz, 4H), 7.24–7.25 (m, 6H), 7.26–7.33 (m, 10H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 57.1, 59.1, 127.3, 127.4, 127.5, 128.6, 128.8, 128.9, 139.3, 141.4, 170.9 ppm. Anal. Calcd for C27 H23 NO: C, 85.91; H, 6.14; N, 3.71. Found: C, 85.79; H, 6.25; N, 3.63; ESI–MS: m/z = 378 (M+1)+ . 3.13. N-benzhydryl-1-naphthamide (3m) White solid, mp: 161–163 ◦ C; IR (KBr): 3295, 1636, 1528, 1495, 772, 694 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 6.57–6.61 (m, 2H), 7.30–7.33 (m, 2H), 7.35–7.40 (m, 8H), 7.47 (t, J = 7.5 Hz, 1H), 7.53–7.54 (m, 2H), 7.67 (d, J = 7.0 Hz, 1H), 7.86–7.88 (m, 1H), 7.93 (d, J = 8.0 Hz, 1H), 8.30–8.31 (m, 1H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 57.4, 124.7, 124.9, 125.5, 126.5, 127.2, 127.5, 127.6, 128.3, 128.8, 130.3, 130.8, 133.7, 134.2, 141.5, 168.6 ppm. Anal. Calcd for C15 H14 FNO: C, 85.43; H, 5.68; N, 4.15. Found: C, 85.56; H, 5.71; N, 4.27; ESI–MS: m/z = 338 (M+1)+ . 3.14. N-benzyl-2-(4-chloro-phenyl)-acetamide (3o)

3.8. N-benzhydryl-4-fluoro-benzamide (3h) White solid, mp: 217–218 ◦ C; IR (KBr): 3295, 1641, 1503, 696 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 6.44 (d, J = 7.5 Hz, 1H), 6.62 (d, J = 7.5 Hz, 1H), 7.12 (t, J = 8.5 Hz, 2H), 7.29–7.31 (m, 6H), 7.35 (t, J = 7.0 Hz, 4H), 7.82–7.85 (m, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 30.9, 115.7 (d, 2 JCF = 21.8 Hz), 127.5, 127.7, 128.8, 129.4 (d, 3 J = 8.9 Hz), 130.4 (d, 4 J = 3.4 Hz), 141.3, 164.7 (d, 1 J = 197.4 Hz), CF CF CF 165.9 ppm. Anal. Calcd for C20 H16 FNO: C, 78.67; H, 5.28; N, 4.59. Found: C, 78.55; H, 5.30; N, 5.50; ESI–MS: m/z = 306 (M+1)+ . 3.9. N-benzhydryl-2-(4-chloro-phenyl)-acetamide (3i) White solid, mp: 175–177 ◦ C; IR (KBr): 3325, 3026, 1632, 1530, 698 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 3.61 (s, 2H), 5.97 (d, J = 8.0 Hz, 1H), 6.24 (d, J = 8.0 Hz, 1H), 7.11 (d, J = 7.5 Hz, 4H), 7.22 (d, J = 8.5 Hz, 2H), 7.25–7.33 (m, 8H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 43.1, 57.0, 127.3, 127.6, 128.7, 129.1, 130.7, 133.2, 133.4, 141.2, 169.4 ppm. Anal. Calcd for C21 H18 ClNO: C, 75.11; H, 5.40; N, 4.17. Found: C, 75.09; H, 5.41; N, 4.13; ESI–MS: m/z = 337 (M+1)+ . 3.10. N-benzhydryl-4-bromo-benzamide (3j) White solid, mp: 211–212 ◦ C; IR (KBr): 3360, 3318, 3177, 1643, 1526, 845 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 6.43 (d, J = 7.5 Hz, 1H), 6.67 (d, J = 7.5 Hz, 1H), 7.28–7.35 (m, 8H), 7.56–7.60 (m, 3H), 7.68–7.70 (m, 3H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 57.6, 127.5, 127.7, 128.7, 128.8, 129.0, 131.9, 133.0, 141.2, 165.7 ppm. Anal. Calcd for C20 H16 BrNO: C, 65.59; H, 4.40; N, 3.82. Found: C, 65.41; H, 4.47; N, 3.89; ESI–MS: m/z = 367 (M+1)+ .

White solid, mp: 148–150 ◦ C; IR (KBr): 3281, 1643, 1541, 1493, 1086, 743, 692 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 3.58 (s, 2H), 4.42 (d, J = 5.5 Hz, 2H), 5.66 (s, 1H), 7.21 (t, J = 6.5 Hz, 4H), 7.28 (s, 1H), 7.31 (d, J = 5.5 Hz, 2H), 7.32 (d, J = 6.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 43.1, 43.7, 127.5, 127.6, 128.7, 129.2, 130.7, 133.2, 133.4, 138.0, 170.2 ppm. Anal. Calcd for C15 H14 ClNO: C, 69.36; H, 5.43; N, 5.39. Found: C, 69.33; H, 5.39; N, 5.40; ESI–MS: m/z = 261 (M+1)+ . 3.15. 2-(4-Chlorophenyl)-N-(2-methylbenzyl)acetamide (3p) White solid, mp: 135–138 ◦ C; IR (KBr): 3306, 1643, 1557, 1491, 1256, 1015, 804, 750 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.25 (s, 3H), 3.57 (s, 2H), 4.42 (d, J = 5.5 Hz, 2H), 5.49 (s, 1H), 7.12 (t, J = 7.0 Hz, 1H), 7.16 (d, J = 6.0 Hz, 2H), 7.19 (d, J = 7.0 Hz, 1H), 7.22 (d, J = 8.0 Hz, 2H), 7.32 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 19.0, 42.0, 43.1, 126.2, 127.9, 128.3, 129.2, 130.6, 130.7, 133.2, 133.4, 135.5, 136.4, 170.0 ppm. Anal. Calcd for C16 H16 ClNO: C, 70.20; H, 5.89; N, 5.12. Found: C, 70.19; H, 5.77; N, 5.10; ESI–MS: m/z = 275 (M+1)+ . 3.16. 2-(4-Chlorophenyl)-N-(4-methylbenzyl)acetamide (3q) White solid, mp: 177–179 ◦ C; IR (KBr): 3287, 1640, 1535, 802 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.33 (s, 3H), 3.57 (s, 2H), 4.37 (d, J = 5.5 Hz, 2H), 5.61 (s, 1H), 7.09 (d, J = 8.0 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.5 Hz, 2H), 7.31 (d, J = 8.5 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 43.1, 43.5, 127.7, 129.1, 129.4, 130.7, 133.2, 133.3, 134.9, 137.3, 170.2 ppm. Anal. Calcd for C16 H16 ClNO: C, 70.20; H, 5.89; N, 5.12. Found: C, 70.09; H, 5.79; N, 5.15; ESI–MS: m/z = 275 (M+1)+ .

3.11. N-benzhydryl-4-chloromethyl-benzamide (3k) 3.17. 2-(4-Chlorophenyl)-N-tritylacetamide (3r) White solid, mp: 210–212 ◦ C; IR (KBr): 3266, 1630, 1533, 1505, 698 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 4.61 (s, 2H), 6.45 (d, J = 8.0 Hz, 1H), 6.66 (d, J = 7.5 Hz, 1H), 7.29–7.31 (m, 6H), 7.34–7.37 (m, 4H), 7.46 (d, J = 8.5 Hz, 2H), 7.82 (d, J = 8.5 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 45.4, 57.5, 127.4, 127.5, 127.7, 127.9, 128.8, 134.2, 141.1, 141.3, 165.9 ppm. Anal. Calcd for C21 H18 ClNO: C, 75.11; H, 5.40; N, 4.17. Found: C, 75.10; H, 5.39; N, 4.15; ESI–MS: m/z = 337 (M+1)+ .

White solid, mp: 106–107 ◦ C; IR (KBr): 3252, 1647, 1533, 1491, 1089, 696 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 3.59 (s, 2H), 6.52 (s, 1H), 7.08–7.10 (m, 6H), 7.20–7.26 (m, 11H), 7.32 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 44.4, 70.5, 127.1, 128.0, 128.5, 129.2, 130.6, 133.3, 133.5, 144.4, 169.1 ppm. Anal. Calcd for C27 H22 ClNO: C, 78.73; H, 5.38; N, 3.40. Found: C, 78.70; H, 5.40; N, 4.37; ESI–MS: m/z = 413 (M+1)+ .

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3.18. N-benzyl-4-chloromethyl-benzamide (3s) White solid, mp: 142–145 ◦ C; IR (KBr): 3316, 1641, 1551, 1452, 727, 687 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 4.61 (s, 2H), 4.66 (d, J = 6.0 Hz, 2H), 6.36 (s, 1H), 7.29–7.33 (m, 1H), 7.34–7.39 (m, 4H), 7.46 (d, J = 8.0 Hz, 2H), 7.79 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 44.2, 45.4, 127.4, 127.7, 128.0, 128.8, 128.9, 134.4, 138.0, 140.9, 166.7 ppm. Anal. Calcd for C15 H14 ClNO: C, 69.36; H, 5.43; N, 5.39. Found: C, 69.46; H, 5.40; N, 5.37; ESI–MS: m/z = 413 (M+1)+ . 3.19. 4-Chloromethyl-N-(2-methyl-benzyl)-benzamide (3t) White solid, mp: 127–130 ◦ C; IR (KBr): 3291, 1628, 1541, 1285, 760, 677 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.38 (s, 3H), 4.61 (s, 2H), 4.65 (d, J = 5.5 Hz, 2H), 6.19 (s, 1H), 7.21–7.24 (m, 3H), 4.65 (d, J = 5.5 Hz, 2H), 7.30 (d, J = 7.0 Hz, 1H), 7.78 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl , 125 MHz) ı 19.1, 42.4, 45.4, 126.3, 127.4, 128.0, 3 128.8, 130.7, 134.3, 135.6, 136.7, 140.9, 166.6 ppm. Anal. Calcd for C16 H16 ClNO: C, 70.20; H, 5.89; N, 5.12. Found: C, 70.25; H, 5.79; N, 5.16; ESI–MS: m/z = 275 (M+1)+ .

6.22; N, 5.09. Found: C, 82.70; H, 6.10; N, 5.17; ESI–MS: m/z = 276 (M+1)+ .

3.20. 4-Chloromethyl-N-(4-methyl-benzyl)-benzamide (3u)

3.24. N-bornyl-2-phenylacetamide (3z)

White solid, mp: 155–156 ◦ C; IR (KBr): 3337, 1641, 1541, 685 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.35 (s, 3H), 4.60 (s, 2H), 4.61 (s, 2H), 6.35 (s, 1H), 7.17 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 8.0 Hz, 2H), 7.78 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 44.0, 45.4, 127.4, 128.0, 128.7, 129.5, 134.4, 135.0, 137.5, 140.9, 166.7 ppm. Anal. Calcd for C16 H16 ClNO: C, 70.20; H, 5.89; N, 5.12. Found: C, 70.11; H, 5.88; N, 5.18; ESI–MS: m/z = 275 (M+1)+ .

White solid, mp: 141–142 ◦ C; IR (KBr): 3335, 2957, 1630, 1528, 1287, 718 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 0.88 (s, 3H), 0.92 (s, 3H), 1.01 (s, 3H), 1.19–1.24 (m, 1H), 1.35–1.40 (m, 1H), 1.59–1.81 (m, 4H), 1.95–1.99 (m, 1H), 4.09–4.14 (m, 1H), 6.05 (br s, 1H), 7.42–7.45 (m, 2H), 7.48–7.51 (m, 1H), 7.03–7.72 (m, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 11.8, 20.3, 20.4, 27.1, 30.9, 35.9, 39.3, 45.0, 47.2, 48.8, 57.2, 126.7, 128.6, 131.3, 135.2, 166.7 ppm. Anal. Calcd for C17 H23 NO: C, 79.33; H, 9.01; N, 5.44. Found: C, 79.35; H, 9.00; N, 5.45; ESI–MS: m/z = 258 (M+1)+ .

Scheme 2. Synthesis of CoFe2 O4 @SiO2 –DASA.

3.21. 4-Fluoro-N-(4-methyl-benzyl)-benzamide (3v) White solid, mp: 135–137 ◦ C; IR (KBr): 3296, 2924, 1638, 1505, 1290, 1234, 850 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.35 (s, 3H), 4.59 (d, J = 5.5 Hz, 2H), 6.31 (s, 1H), 7.10 (d, J = 8.5 Hz, 2H), 7.17 (d, J = 8.0 Hz, 2H), 7.24 (d, J = 8.0 Hz, 2H), 7.77–7.80 (m, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 44.0, 115.6 (d, 2 JCF = 21.8 Hz), 128.0, 129.3 (d, 3 JCF = 8.9 Hz), 130.8 (d, 4 JCF = 27.1 Hz), 135.0, 137.4, 164.7 (d, 1 JCF = 250.6 Hz), 166.3 ppm. Anal. Calcd for C15 H14 FNO: C, 74.06; H, 5.80; N, 5.76. Found: C, 74.00; H, 5.91; N, 5.77; ESI–MS: m/z = 244 (M+1)+ .

3.25. 4-(Chloromethyl)-N-(1,7,7-trimethylbicyclo[2.2.1]heptan2-yl)benzamide (3aa) Oil; IR (KBr): 3327, 2953, 2359, 1653, 1271, 714 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 0.90 (s, 3H), 0.93 (s, 3H), 1.03 (s, 3H), 1.21–1.26 (m, 1H), 1.36–1.41 (m, 1H), 1.61–1.84 (m, 4H), 1.96–2.00 (m, 1H), 4.10–4.15 (m, 1H), 4.63 (s, 2H), 6.08 (d, J = 8.0 Hz, 1H), 7.47 (d, J = 8.0 Hz, 2H), 7.72 (d, J = 8.0 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 11.8, 20.3, 20.4, 27.0, 29.7, 35.9, 39.2, 45.0, 45.4, 47.2, 48.9, 57.2, 127.2, 128.8, 135.2, 140.6, 166.2 ppm. Anal. Calcd for

3.22. 4-Bromo-N-(4-methyl-benzyl)-benzamide (3w) White solid, mp: 168–170 ◦ C; IR (KBr): 3323, 1640, 1549, 847, 660 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.38 (s, 3H), 4.62 (d, J = 5.5 Hz, 2H), 6.32 (s, 1H), 7.20 (d, J = 8.0 Hz, 2H), 7.27 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 8.5 Hz, 2H), 7.67 (d, J = 8.5 Hz, 2H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 44.1, 126.2, 128.0, 128.6, 129.2, 129.5, 131.8, 134.9, 137.6, 166.3 ppm. Anal. Calcd for C15 H14 FNO: C, 59.23; H, 4.64; N, 4.60. Found: C, 59.22; H, 4.69; N, 4.67; ESI–MS: m/z = 305 (M+1)+ . 3.23. Naphthalene-1-carboxylic acid 4-methyl-benzylamide (3x) White solid, mp: 156–157 ◦ C; IR (KBr): 3269, 1634, 1533, 1516, 1294, 775 cm−1 ; 1 H NMR (CDCl3 , 500 MHz) ı 2.38 (s, 3H), 4.73 (d, J = 5.5 Hz, 2H), 6.25 (s, 1H), 7.21 (d, J = 8.0 Hz, 2H), 7.33 (d, J = 8.0 Hz, 2H), 7.47 (t, J = 7.0 Hz, 1H), 7.54–7.60 (m, 2H), 7.65 (d, J = 7.0 Hz, 1H), 7.89 (d, J = 7.5 Hz, 1H), 7.94 (d, J = 8.5 Hz, 1H), 8.38 (d, J = 8.0 Hz, 1H) ppm; 13 C NMR (CDCl3 , 125 MHz) ı 21.1, 43.9, 124.7, 124.9, 125.5, 126.5, 127.2, 127.9, 128.3, 129.2, 129.5, 130.2, 130.7, 133.7, 135.1, 137.4, 169.3 ppm. Anal. Calcd for C15 H14 FNO: C, 82.88; H,

Fig. 1. XRD pattern of CoFe2 O4 @SiO2 –DASA.

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Fig. 2. SEM images of CoFe2 O4 @SiO2 –DASA: (left) “fresh” and (right) “recovered”.

C18 H24 ClNO: C, 70.69; H, 7.91; N, 4.58. Found: C, 70.70; H, 7.90; N, 4.60; ESI–MS: m/z = 306 (M+1)+ . 4. Results and discussion 4.1. Synthesis and characterization of CoFe2 O4 @SiO2 –DASA The details of the supported catalyst preparation procedure are presented in Scheme 2. The magnetic core CoFe2 O4 has been synthesized by a chemical co-precipitation technique using FeCl3 ·6H2 O and CoCl2 ·6H2 O as precursors according to a previously reported procedure [43]. After being coated by a layer of silica through a sol–gel process, particle surfaces were further functionalized with commercially available (N-(2-aminoethyl)3-aminopropyl)tris-(2-ethoxy)silane (DTPS) through the siloxane linkage. Finally, the reaction of amino groups with chlorosulfonic acid led to sulphamic acid-functionalized magnetic CoFe2 O4 nanoparticles (CoFe2 O4 @SiO2 –DASA). The content of sulfonic acid was determined by acid–base titration as 3.98 mmol/g. Also, the pH of this solid sulfamic acid (10%, w/v) was measured using pH meter. At first 0.5 g solid sulfamic acid was dispersed in 5 mL distilled water by ultrasonic bath for 1 h, then measured and found to be approximately about 0.44. 4.1.1. XRD analysis The XRD pattern of the sample is shown in Fig. 1. As seen in Fig. 1, CoFe2 O4 @SiO2 –DASA displays seven characteristic peaks at the 2 values of 18.6, 30.6, 36.0, 43.8, 54.2, 57.9 and 63.5, which could be attributed for the (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) reflections, respectively. The positions and relative intensities of all diffraction peaks matched well with those from the cubic reverse spinel phase of CoFe2 O4 (JCPDS 221086) [16], suggesting that the surface modification of MNPs did not significantly affect the phase composition of CoFe2 O4 . A weak broad band (2 = 21–23◦ ) appeared in functionalized magnetic pattern which be assigned to the amorphous silane formed around the magnetic cores.

Fig. 3. TEM images of CoFe2 O4 @SiO2 –DASA.

The Fe O stretching vibration near 581 cm−1 , O H stretching vibration near 3434 cm−1 and O H deformed vibration near 1625 cm−1 were observed for both in Fig. 4(a) and (b). The significant features observed for Fig. 4(b) are the appearance of the peaks at 1002 cm−1 (Si O stretching) and at 2874 cm−1 ( CH2 stretching). Several peaks at 650, 1091, 1159, 3495 cm−1 can be attributed

4.1.2. TEM, SEM and EDX elemental analysis The TEM and SEM images of the synthesized CoFe2 O4 @SiO2 – DASA are shown in Figs. 2 and 3. These images confirmed the formation of single-phase CoFe2 O4 nanoparticles, with spherical morphology. The average nanoparticle diameter of CoFe2 O4 @SiO2 –DASA was estimated to be ca. 25–30 nm based on the TEM image, which is also in accordance with the result calculated by the Scherrer formula. The presence of C, O, Fe, Co, Si and S atoms was observed in the EDX spectrum (Fig. 4). 4.1.3. FT-IR analysis Fig. 5 shows the Fourier transform infrared (FTIR) spectra of both the unfunctionalized and functionalized magnetic nanoparticles.

Fig. 4. EDS spectrum of CoFe2 O4 @SiO2 –DASA.

X.-N. Zhao et al. / Applied Catalysis A: General 482 (2014) 258–265

263

Table 1 Screening of reaction conditions for the Ritter reactiona .

a

4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumbers(cm )

Entry

Catalyst (mg)

Temperature (◦ C)

Time (h)

Yield (%)

1 2 3 4 5 6 7 8 9 10

No 10 10 10 10 10 10 5 15 10

80 25 40 60 80 90 100 80 80 80

6 4 4 4 4 4 4 4 4 4

Trace Trace 56 73 90 90 90 70 90 91b

a

Fig. 5. IR spectra of CoFe2 O4 @SiO2 (a) and CoFe2 O4 @SiO2 –DASA (b).

to the characteristic absorption of sulfonic acid groups. The peak at 650 cm−1 was associated with the S O stretching vibration, and the broad peak in the range of 3000–3600 cm−1 was originated from the stretching of O H bond in the sulfonic acid groups. 4.2. Catalytic activity of CoFe2 O4 @SiO2 –DASA We have chosen the Ritter reaction as the model reaction to evaluate the catalytic performance of CoFe2 O4 @SiO2 –DASA, using the coupling of diphenyl methanol with acetonitrile as the standard reaction under solvent-free conditions. The results of these experiments are summarized in Table 1. Only a trace amount of the desired product was observed on TLC plate in the absence of the catalyst after 6 h at 80 ◦ C (Table 1, entry 1). To our delight, the reaction could proceed smoothly in the presence of 10 mg CoFe2 O4 @SiO2 –DASA, resulting in a desired product in 90% yield

b

Experimental conditions: diphenyl methanol (1 mmol), acetonitrile (1 mmol). 10 mmol Scale.

(Table 1, entry 5). To further improve the efficiency of the reaction, the amount of catalyst and temperature were also examined. However, none of them could produce a higher yield, even at higher temperature. We also examined the feasibility of the present method for large-scale synthesis with diphenyl methanol with acetonitrile. The reaction was found to proceed smoothly affording the desired product in 91% yield within 4 h, almost similarly in all respects with 1 mmol scale (Table 1, entry 9). After optimizing of the reaction conditions, a broad range of structurally diverse alcohols and nitriles was further evaluated and the results are depicted in Table 1. Initially, the reaction of different alcohols with acetonitrile was studied. The results demonstrated that benzylic, and secondary alcohols as well as tertiary alcohol are all good substrates in this reaction, and the corresponding amides are formed in good to excellent yields (Table 2, entries

Table 2 Ritter reaction catalyzed by CoFe2 O4 @SiO2 –DASAa . Entry

Alcohol

Nitrile

Product

Time (h)

Yield (%)b

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

PhCH2 OH 2-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH Ph2 CHOH PhCH2 CMe2 OH Ph3 COH PhCH CHCH2 OH Ph2 CHOH Ph2 CHOH Ph2 CHOH Ph2 CHOH Ph2 CHOH Ph2 CHOH PhCH2 OH PhCH2 OH 2-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH Ph3 COH PhCH2 OH 2-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH 4-MeC6 H4 CH2 OH Cyclohexanol Borneol Borneol

CH3 CN CH3 CN CH3 CN CH3 CN CH3 CN CH3 CN CH3 CN 4-FC6 H4 CN 4-ClC6 H4 CH2 CN 4-BrC6 H4 CN 4-ClCH2 C6 H4 CN Ph2 CHCN 1-Naphthonitrile C6 H5 CN 4-ClC6 H4 CH2 CN 4-ClC6 H4 CH2 CN 4-ClC6 H4 CH2 CN 4-ClC6 H4 CH2 CN 4-ClCH2 C6 H4 CN 4-ClCH2 C6 H4 CN 4-ClCH2 C6 H4 CN 4-FC6 H4 CN 4-BrC6 H4 CN 1-Naphthonitrile C6 H5 CN C6 H5 CN 4-ClCH2 C6 H4 CN

3a 3b 3c 3d 3e 3f 3g 3h 3i 3j 3k 3l 3m 3n 3o 3p 3q 3r 3s 3t 3u 3v 3w 3x 3y 3z 3aa

4 4 4 4 4 4 4 4 3 4 3 4 4 4 4 4 4 4 3 3 3 4 4 4 4 4 4

83 86 87 90 85 83 80 88 86 83 89 86 87 91 83 85 86 80 96 90 95 83 81 79 91 90 87

a b

Reaction conditions: alcohol (1 mmol), nitrile (1 mmol), CoFe2 O4 @SiO2 –DASA (0.27 g), 80 ◦ C. Isolated yield.

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Table 3 Comparison of our results with previously reported methods. Catalyst

Reaction conditions

Product

Time

Yield (%)

1 2 3 4 5 6 7 8 9 10 11

o-Benzenedisulfonimide (10 mol%) 2,4-Dinitrobenzenesulfonic acid (10 mol%) FeCl3 ·6H2 O (10 mol%) I2 (20 mol%) Ca(HSO4 )2 (100 mol%) Sulfated tungstate (20 wt%) SBNPSA (0.1 g) ␥-Fe2 O3 @SiO2 –HClO4 (0.1 g) Silica sulfuric acid (20 mg) Nanocat-Fe–OSO3 H (0.1 g) CoFe2 O4 @SiO2 –DASA (0.1 g)

Reflux Reflux H2 O, 150 ◦ C H2 O, 110 ◦ C 80 ◦ C Solvent-free, 100 ◦ C Solvent-free, 80 ◦ C Solvent-free Toluene, 90 ◦ C Solvent-free, 90 ◦ C Solvent-free, 80 ◦ C

5a 5a 5a 5a 5n 5a 5a 5a 5n 5n 5a

8h 15 h 0.5 h 5h 2.5 h 6h 15 min 5h 8h 4h 4h

89 [31] 86 [32] 96 [34] 80 [36] 89 [37] 88 [38] 98 [39] 95 [41] 91 [42] 84 [44] 90 (this work)

Isolated yield (%)

Entry

of toxic or volatile solvents, higher yields, and facile recovery and recyclability of the catalyst used.

100 90 80 70 60 50 40 30 20 10 0

Acknowledgment 0

1

2

3

4

5

6

Cycles

Fig. 6. Reusability of the catalyst.

1–6). Moreover, allylic alcohol can also participate in this reaction to give expected amide 3g in a slightly lower yield (Table 2, entry 7). Unfortunately, primary alcohols such as 1-adamantanemethanol, 2-phenylethan-1-ol and 3-phenylpropan-1-ol are inert under these conditions and no reaction occurred even under forcing conditions. Reactions of a variety of substituted benzonitriles with diphenyl methanol were also surveyed. As shown in Table 2, the reactions proceeded efficiently to furnish the desired products in high yields. Similarly, 2,2-diphenylacetonitrile and 1-naphthonitrile also reacted very efficiently to give the corresponding amides 3l and 3m in 86% and 87% yields, respectively. 4.3. Recycling of the catalyst The reusability of the catalyst was evaluated under the reaction conditions described above for the model reaction. After completion of the reaction, the catalyst could be easily recovered by applying a strong external permanent magnet, followed by washing with ethyl acetate to remove residual product, dried under vacuum, and reused directly for the next cycle without further treatment. The catalyst was used over six runs, and no obvious loss in the catalytic activity was observed (Fig. 6). Notably, the SEM analysis of recycled catalyst revealed that the morphology and size of the particles were unaltered after six cycles (Fig. 2). This indicated that the developed catalyst had great recyclability in this reaction. Finally, in order to show the merit of the present method, CoFe2 O4 @SiO2 –DASA catalyst was compared with other catalysts reported earlier in the synthesis of 5a or 5n. As can be seen in Table 3, the results clearly indicated that this magnetic solid sulfamic acid is an equally or more efficient catalyst for Ritter reaction. 5. Conclusion In summary, we have demonstrated the first successful synthesis of a magnetic CoFe2 O4 nanoparticle immobilized diamine-N-sulfamic acid catalyst and its application in Ritter reaction between alcohols and nitriles. The method described herein compares favorably with hitherto known methodologies, especially in terms of easy and green work-up procedures, absence

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