untitled European Journal of Chemistry 3 (3) (2012) 298‐304 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2012 EURJCHEM DOI:10.5155/eurjchem.3.3.298‐304.540 European Journal of Chemistry Journal homepage: www.eurjchem.com Recyclable and reusable nano‐CuFe2O4 catalyzed C‐O cross‐coupling Venkanna Avudoddi, Vinod Kumar Goud Palle and Venkateshwar Rao Pallapothula* Department of Chemistry, Nizam College, Basheerbagh, Nampally, Hyderabad, 500001, India *Corresponding author at: Department of Chemistry, Nizam College, Basheerbagh, Nampally, Hyderabad, 500001, India. Tel.: +91.40.27037934; fax: +91.40.23240806. E‐mail address: pallapothulavrao@gmail.com (V.R. Pallapothula). ARTICLE INFORMATION ABSTRACT Received: 21 October 2011 Received in revised form: 12 March 2012 Accepted: 12 March 2012 Online: 30 September 2012 KEYWORDS An efficient protocol was developed and validated for the synthesis of biaryl/aryl alkyl ethers using CuFe2O4 nano powder as a recyclable catalyst via the reaction between aryl halides and phenols/alcohols. Variety of aryl ethers were synthesized efficiently in the presence of catalytic amount of CuFe2O4, KOH as base, under ligand free conditions in nitrogen atmosphere with DMSO as solvent at 120 oC. The catalyst is air‐stable, inexpensive, magnetically separable and recyclable up to four cycles. Aryl halide Recyclability Nano‐CuFe2O4 Phenol/alcohol C‐O cross‐coupling Heterogeneous catalysis 1. Introduction Diaryl ethers constitute a very important class of organic compounds that are finding widespread applications in numerous fields such as life sciences, chemical, pharmaceutical, polymer and material industries [1‐9]. Biaryl ethers are found in variety of natural compounds such as antifungal peperazinomycin and combretastatin D‐2, antiviral cyclic peptide K‐13, glycopeptides antibiotics vancomycin [10‐12] (Figure 1). The transition metal catalyzed cross‐coupling of aryl halides with phenols is the most straight forward and regular method for the synthesis of biaryl ethers [13]. Despite palladium catalyzed methods to achieve diaryl ether structural scaffold, Hartwig et al reported the synthesis of biaryl ethers using sodium phenoxide and electron‐deficient aryl bromides in the presence of ligand (dppf) [14]. Buchwald and co workers reported the C‐O coupling reaction between aryl halides and phenols by using palladium as a catalyst [15‐19]. In recent past palladium based complexes, [20‐22] were explored for the synthesis of biaryl ethers. However, these methods use the expensive palladium in more than stoichiometric amounts and tedious work up procedure involved in the synthesis of phosphine ligands, would limit its applications to large (or) industrial‐scale production [23‐29]. To widen the applicability of this reaction in all facets, explorations were carried out towards the classical Ullmann type copper [30], catalyzed reactions for the synthesis of biaryl ethers, however these reactions also suffer from limitations such as high catalyst loadings, requirement of high reaction temperature (>220 oC) [31]. During the last decade tremendous research work has been carried out on copper catalyzed reactions and showed that certain additives in combination with copper source enhanced the reaction rate under mild reaction conditions. Thus neocuproine [32], tripod ligands [33], ethylene glycol diactate [34], 1‐naphthoic acid [35], 2,2,6,6‐tetramethyl heptane‐3,5‐dione [36], β‐keto ester [37], triphenyl phosphine [38], 2‐pyridyl acetone [39], were successfully employed as additives. It is thought that these additives increase the efficiency of the catalyst by increasing the solubility of the copper salts and by preventing their aggregation [40]. These metal/ligand based systems suffer from certain limitations, such as high catalyst loading of ligand and require high reaction temperature etc. Dewei Ma and co‐workers reported that the N,N‐dimethyl glycine promoted Ullmann coupling reaction of phenols with aryl halides at 90 oC [41]. Recently, few studies have focused on the use of copper [42‐44], zinc [45], nickel [46], copper/iron [47] and iron [48], based catalytic systems for the synthesis of biaryl ethers by using the cross‐coupling of aryl halide and phenol. However, these aforementioned protocols have one (or) more drawbacks such as use of various well designed ligands, lack of recyclability, high cost of ligands etc. Marc Taillefer et al. reported an efficient, inexpensive and practical copper‐catalyzed method to cross‐couple various phenols with aryl bromides under very mild conditions [49]. Sekar and co‐workers developed an efficient, general, mild and intermolecular Ullmann type synthesis of biaryl and alkyl aryl ethers catalyzed by diol‐copper(I) complex [50‐51]. However, most of these metal‐catalyzed reactions involve expensive catalysts/co‐catalysts causing major problems such as commercialization to the plant scale and recovery of the catalyst. In the recent past, heterogeneous catalysis has received a paramount attention in view of improved efficacy due to recyclability and reusability of the process. Heterogeneous catalysts have become more significant both economically and industrially when compared to homogeneous catalytic systems. B. H. Lipshutz, et al. reported copper‐on‐charcoal (Cu/C) as a heterogeneous catalyst to the synthesize biaryl ethers from aryl bromides with phenol [52]. Now days, chemistry of nanoparticles is more fascinating as these metal nanoparticles offer active sites with extended surface area, recyclability and reusability without the loss of catalytic activity. Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 299 Figure 1. Some of the biologically active molecules containing ether linkage. These prominent features of nanoparticles led us to focus on the aspect of CuFe2O4 nanoparticles [53], as catalyst for the formation of carbon‐oxygen bond. In general, nano scale heterogeneous catalysts provide greater advantages in organic reactions, as they offer higher surface area and lower coordination sites [54‐55], which are responsible for higher catalytic activity and increase the reaction rates. Nano‐CuO [56‐ 57] and CuI [58] were used as active catalysts for the cross‐ coupling of aryl halides with phenols under ligand free conditions. However, till now investigation of nanoparticles as catysts has been utilized in various organic transformations. In this regard, we envisaged the application of commercially available, inexpensive CuFe2O4 nanoparticle as a catalyst for the formation of carbon‐oxygen bonds. Herein, we wish to report a general, mild and efficient magnetically separable CuFe2O4 nanoparticle as catalyst for C‐O cross‐coupling processes. To test the efficiency of the catalytic system, we chose to focus our initial studies on the cross‐coupling of phenol with iodobenzene as model substrates under ligand free conditions. 2. Experimental 2.1. Instrumentation CuFe2O4 (purity ≥ 98.0%) was purchased from Sigma Aldrich. All experiments were carried out under nitrogen atmosphere. Column chromatography was carried out with 60‐ 120 sized mesh silica gel using ethyl acetate and hexane as eluent. Analytical thin layer chromatography (TLC) was performed with silica gel plates and the products were visualized by UV detection. 1H NMR and 13C NMR (Avance 300, Innova 400 MHz and Brucker Gemini 200 MHz) spectra were recorded in CDCl3 using TMS as internal standard. Chemical shifts (δ) are reported in ppm, and spin‐spin coupling constants (J) are in Hz. Melting points were determined on a Fischer‐ Johns melting point apparatus. IR and MS were recorded on a Thermo Nicolet Nexus 670 FT‐IR spectrometer and Finnegan MAT 1020 mass spectrometer operating at 70 eV. 2.2. Synthesis Representative experimental procedure for the synthesis of biaryl ethers by using heterogeneous nano‐CuFe2O4 as a catalyst: Phenol (1.0 mmol), iodobenzene (0.1 mL, 1.0 mmol), nano‐CuFe2O4 (6 mol%, 143 mg), KOH (2.0 equiv.), and were charged in a 25 mL round‐bottomed flask with a condenser, under nitrogen atmosphere, followed by the addition of dry DMSO (2.0 mL) and the reaction mixture was heated at 120 oC under nitrogen atmosphere for 20 h, The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was extracted with ethyl acetate (3x10 mL). The combined organic layers were dried with anhydrous Na2SO4. The solvent was evaporated under vacuum to give the crude product, which was purified by column chromatography with hexane as eluent to yield the expected product 3a (159 mg, 94%) as yellowish oil. The purity of the product was confirmed by 1H, 13C, Mass, and IR spectroscopy. Oxydibenzene [24] (3a) (Table 1, entry 1): Yield: 94%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.35‐ 7.24 (4H, m, ArH), 7.10‐6.93 (6H, m, ArH). 13C NMR (100 MHz, CDCl3, δ, ppm): 157.4, 129.9, 123.1, 118.8. IR: 3442, 2950, 1637, 1480, 752. MS (EI, m/z): 170. 1‐Fluoro‐4‐phenoxybenzene [47] (3b) (Table 1, entry 2): Yield: 89%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.60 (1H, d, J = 8.9 Hz, ArH), 7.37‐7.20 (2H, m, ArH), 7.12‐ 6.88 (4H, m, ArH), 6.78‐6.64 (2H, m, ArH). 13C NMR (75 MHz, CDCl3, δ, ppm): 160.6, 157.5, 153.0, 138.6, 129.8, 123.3, 120.6, 120.4, 118.5, 116.5, 116.2. FT‐IR (KBr, cm‐1): 3450, 2930, 2858, 1598, 1216, 841, 780, 690. MS (EI, m/z): 188. 1‐Phenoxy‐4‐(trifluoromethyl)benzene [38] (3c) (Table 1, entry 3): Yield: 85%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.56 (2H, d, J = 8.5 Hz, ArH), 7.45‐7.32 (2H, m, ArH), 7.23‐7.10 (3H, m, ArH), 7.01 (2H, d, J = 8.5 Hz, ArH). 13C NMR (100 MHz, CDCl3, δ, ppm): 160.8, 155.7, 130.5, 129.9, 127.0, 124.3, 124.1, 119.9, 119.4, 117.9. FT‐IR (KBr, cm‐1): 3445, 2930, 2850, 1485, 1225, 848, 765. MS (EI, m/z): 238. 1‐Chloro‐4‐phenoxybenzene [47] (3d) (Table 1, entry 4): Yield: 88%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.36‐7.22 (4H, m, ArH), 7.11‐7.04 (1H, m, ArH), 7.01‐6.88 (4H, m, ArH). 13C NMR (75 MHz, CDCl3, δ, ppm): 157.0, 156.3, 129.9, 129.7, 123.5, 129.1, 119.3. FT‐IR (KBr, cm‐1): 3448, 2930, 2858, 1583, 1465, 1089, 840, 758, 695. MS (EI, m/z): 204. 1‐Bromo‐4‐phenoxybenzene [60] (3e) (Table 1, entry 5): Yield: 88%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.40 (1H, d, J = 8.9 Hz, ArH), 7.33‐7.23 (3H, m, ArH), 7.10‐ 7.03 (2H, m, ArH), 6.97 (2H, d, J = 7.9 Hz, ArH), 6.86 (1H, d, J = 8.9 Hz, ArH). 13C NMR (75 MHz, CDCl3, δ, ppm): 157.2, 156.5, 132.6, 129.9, 129.6, 123.8, 123.1, 120.5, 119.0, 118.8, 115.3. 300 Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 Table 1. Reaction of aryl halides with phenol using nano copper iron oxide as a catalysta. Entry Arylhalide Nucleophile Product Yield (%) b 1 Iodobenzene Phenol 3a 94 2 1‐Fluoro‐4‐iodobenzene Phenol 3b 89 3 1‐Iodo‐4‐(trifluoromethyl)benzene Phenol 3c 85 4 1‐Chloro‐4‐iodobenzene Phenol 3d 88 5 1‐Bromo‐4‐iodobenzene Phenol 3e 88 6 1‐Iodo‐4‐methoxybenzene Phenol 3f 80 7 1‐Iodo‐4‐methylbenzene Phenol 3g 78 8 1‐Tert‐butyl‐4‐iodobenzene Phenol 3h 73 9 1‐Iodo‐3‐methoxybenzene Phenol 3i 79 10 1‐Iodo‐3,5‐dimethylbenzene Phenol 3j 78 11 1‐Iodonaphthalene Phenol 3k 70 12 2‐Iodonaphthalene Phenol 3l 76 13 1‐Iododecane Phenol 3m 75 14 1‐Iodooctane Phenol 3n 79 15 Bromobenzene Phenol 3a 76 16 1‐Bromo‐4‐fluorobenzene Phenol 3b 70 17 1‐Bromo‐4‐chlorobenzene Phenol 3e 69 18 1‐Bromo‐4‐methoxybenzene Phenol 3f 60 a Reaction conditions: 1 (1.0 mmol), 2 (1.0 mmol), CuFe2O4 (6 mol% , 143 mg), N2, 20 h. b Isolated yield. FT‐IR (KBr, cm‐1): 3450, 2928, 1598, 1490, 1213, 850, 758. MS (EI, m/z): 247. 1‐Methoxy‐4‐phenoxybenzene [24] (3f) (Table 1, entry 6): Yield: 80%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.36‐7.12 (5H, m, ArH), 6.90‐6.82 (2H, m, ArH), 6.77‐6.68 (2H, m, ArH), 3.79 (3H, s, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm):159.5, 155.7, 150.4, 129.7, 122.3, 121.2, 118.1, 116.4, 115.1, 55.3. FT‐IR (KBr, cm‐1): 3448, 2956, 1362, 1179, 758, 693. MS (EI, m/z): 200. 1‐Methyl‐4‐phenoxybenzene [51] (3g) (Table 1, entry 7): Yield: 78%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.31‐7.22 (2H, m, ArH), 7.19‐6.83 (5H, m, ArH), 6.81‐6.73 (2H, m, ArH), 2.33 (3H, s, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 157.8, 154.8, 132.7, 130.2, 129.6, 122.8, 119.6, 118.2, 20.5. FT‐IR (KBr, cm‐1): 3443, 2899, 1591, 1298, 765, 699. MS (EI, m/z): 184. 1‐Tert‐butyl‐4‐phenoxybenzene [24] (3h) (Table 1, entry 8): Yield: 73%. Colour: White solid. M.p.: 52‐53 oC. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.34‐7.22 (4H, m, ArH), 7.06‐6.86 (5H, m, ArH), 1.33 (9H, s, (CH3)3). 13C NMR (75 MHz, CDCl3, δ, ppm): 157.1, 154.4, 145.2, 129.2, 126.3, 123.2, 118.5, 34.3, 31.2. FT‐IR (KBr, cm‐1): 3450, 2960, 1593, 1498, 1368, 754, 695. MS (EI, m/z): 226. 3‐Methoxy‐4‐phenoxybenzene [47] (3i) (Table 1, entry 9): Yield: 79%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.35‐7.24 (2H, m, ArH), 7.21‐7.11 (1H, m, ArH), 7.09‐6.96 (3H, m, ArH), 6.61‐6.50 (3H, m, ArH), 3.75 (3H, s, CH3). 13C NMR (75 MHz, CDCl3, δ, ppm):161.1, 158.5, 157.3, 130.1, 129.5, 123.3, 119.1, 110.9, 108.8, 104.8. FT‐IR (KBr, cm‐1): 3448, 2959, 1590, 1178, 850, 753, 698. MS (EI, m/z): 200. 1,3‐Dimethyl‐5‐phenoxybenzene [24] (3j) (Table 1, entry 10): Yield: 78%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.30‐7.19 (2H, m, ArH), 7.08‐6.91 (2H, m, ArH), 6.84‐ 6.76 (2H, m, ArH), 6.71‐6.56 (2H, m, ArH), 2.28 (6H, s, (CH3)2). 13C NMR (75 MHz, CDCl3, δ, ppm): 158.3, 157.1, 139.4, 132.2, 129.8, 127.6, 124.7, 122.8, 121.8, 120.1, 118.8, 116.8, 21.5. FT‐ IR (KBr, cm‐1): 3446, 2860, 2495, 1640, 1486, 1245. MS (EI, m/z): 198. 1‐Phenoxynaphthalene [57] (3k) (Table 1, entry 11): Yield: 70%. Colour: Colorless oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 8.15 (1H, d, J = 7.9 Hz, ArH), 7.81 (1H, d, J = 7.9 Hz, ArH), 7.55 (1H, d, J = 7.6 Hz, ArH), 7.50‐7.41 (2H, m, ArH), 7.35‐7.22 (3H, m, ArH), 7.10‐6.89 (4H, m, ArH). 13C NMR (75 MHz, CDCl3, δ, ppm): 157.8, 153.1, 135.1, 129.8, 128.2, 127.7, 126.6, 125.8, 125.6, 123.3, 123.1, 122.4, 118.9, 118.5, 113.4. FT‐IR (KBr, cm‐ 1): 3445, 2928, 1600, 1485, 1238, 1165. MS (EI, m/z): 220. 2‐Phenoxynaphthalene [57] (3l) (Table 1, entry 12): Yield: 76%. Colour: White solid. M.p.: 47‐48 oC. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.85‐7.62 (3H, m, ArH), 7.45‐7.19 (6H, m, ArH), 7.12‐6.96 (3H, m, ArH). 13C NMR (75 MHz, CDCl3, δ, ppm):157.2, 155.1, 134.3, 129.8, 129.7, 127.6, 127.2, 126.4, 124.5, 123.2, 120.1, 119.1, 118.8, 114.2. FT‐IR (KBr, cm‐1): 3445, 2923, 1596, 1496, 1245, 1160, 1046. MS (EI, m/z): 220. Decyloxybenzene [57] (3m) (Table 1, entry 13): Yield: 75%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.26‐ 7.15 (2H, m, ArH), 6.90‐6.79 (3H, m, ArH), 3.91 (2H, d, J = 6.9 Hz, CH2), 1.77 (2H, d, J = 6.6 Hz, J = 7.9 Hz, CH2), 1.51‐1.23 (14H, m, (CH2)7), 0.91 (3H, d, J = 6.9 Hz, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 159.2, 129.3, 120.4, 114.6, 67.7, 31.8, 29.7, 29.5, 29.3, 26.1, 22.8, 14.2. FT‐IR (KBr, cm‐1): 3445, 2929, 1597, 1239, 1175. MS (EI, m/z): 234. Octyloxybenzene (3n) (Table 1, entry 14): Yield: 79%. Colour: Yellowish oil. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.26‐ 7.16 (2H, m, ArH), 6.91‐6.78 (3H, m, ArH), 3.91 (2H, d, J = 6.6 Hz, CH2), 1.76 (2H, d, J = 6.6 Hz, J = 7.9 Hz, CH2), 1.52‐1.23 (10H, m, (CH2)5), 0.91 (3H, d, J = 6.6 Hz, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 159.1, 129.2, 120.4, 114.5, 67.6, 31.8, 29.6, 29.4, 29.2, 26.2, 22.8, 14.2. FT‐IR (KBr, cm‐1): 3444, 2921, 1598, 1498, 1245, 1145. MS (EI, m/z): 206. 3. Results and discussion Here, we report a highly efficient, reusable nano‐CuFe2O4 catalyzed O‐arylation of phenols/alcohols with aryl halides in dry DMSO as a reaction medium in presence of nitrogen atmosphere at 120 oC. The reaction of iodo benzene with phenol was selected as a preliminary model reaction for C‐O cross‐coupling (Scheme 1). Here, the reaction conditions were optimized by taking into consideration of parameters such as temperature, solvent, base. No product formation was seen in the presence of CuFe2O4 (6 mol %) at room temperature, while lower yield was observed at 70 oC. Temperature has a significant effect on product control, as temperature increases the yield is also slowly increases to 94% at 120 oC (Table 2, entries 1‐4). As a part of optimization studies, several solvents were screened in the reaction, among these, toluene, dioxane, NMP, DMF were less effective compared to DMSO (Table 2, entries 4‐8). Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 301 Table 2. Nano copper ferrite nanoparticle catalyzed cross coupling of iodobenzene with phenol a. Entry Solvent Base (2 equiv.) Temperature (oC) Yield (%)b 1 DMSO KOH R.t. ‐ 2 DMSO KOH 70 50 3 DMSO KOH 100 80 4 Toluene KOH 120 94 5 Toluene KOH 120 65 6 NMP KOH 120 60 7 DMF KOH 120 58 8 DMSO KOH 120 70 9 DMSO K2CO3 120 60 10 DMSO Cs2CO3 120 62 11 DMSO NaOtBu 120 52 12 DMSO KOtBu 120 50 13 DMSO K3PO4 120 54 a Reaction conditions: 1 (1.0 mmol), 2 (1.0 mmol), CuFe2O4 (6 mol% , 143 mg), N2, 20 h. b Isolated yield. Table 3. Optimization studies of aryl halide and phenol by using different nano catalysts a. Entry Arylhalide Nucleophile Diaryl ether Nano catalyst (6 mol%) Yield (%)b 1 Iodobenzene Phenol 3a Sb2O3 55 2 Iodobenzene Phenol 3a Y2O3 70 3 Iodobenzene Phenol 3a YFe2O4 65 4 Iodobenzene Phenol 3a Bi2O3 53 5 Iodobenzene Phenol 3a CuFe2O4 94 6 Iodobenzene Phenol 3a Co3O4 58 7 Iodobenzene Phenol 3a SnO2 54 8 1‐iodo‐4‐methoxybenzene Phenol 3f Sb2O3 44 9 1‐iodo‐4‐methoxybenzene Phenol 3f Y2O3 56 10 1‐iodo‐4‐methoxybenzene Phenol 3f YFe2O4 45 11 1‐iodo‐4‐methoxybenzene Phenol 3f Bi2O3 42 12 1‐iodo‐4‐methoxybenzene Phenol 3f CuFe2O4 80 13 1‐iodo‐4‐methoxybenzene Phenol 3f Co3O4 43 14 1‐iodo‐4‐methoxybenzene Phenol 3f SnO2 45 a Reaction conditions: Aryl halide (1.0 mmol), phenol (1.0 mmol), CuFe2O4 (6 mol% , 143 mg), N2, 20 h. b Isolated yield. Scheme 1 We have then examined the different bases, KOH, K2CO3, Cs2CO3, NaOtBu, KOtBu, and K3PO4 (Table 2, entries 9‐13). Of these, KOH provided biaryl ether in excellent yield. Next we turned our attention to test different metal oxide nanoparticles such as Sb2O3, Y2O3, YFe2O4, Bi2O3, CuFe2O4, Co3O4 and SnO2 towards C‐O cross‐coupling reaction with aryl halide and phenol under ligand free conditions and the results are summarized in Table 3. After having optimized the reaction parameters for o‐ arylation of phenol with aryl halides, the proposed catalytic system was employed to cross‐couple wide range of commercially available aryl halides/alkyl halides with phenols under ligand free conditions. All the reactions were clean and the corresponding cross‐coupled products were obtained in excellent yields and as shown in Table 1. In the case of aryl halide, substitutions on the aromatic ring played a pivotal role in governing the C‐O cross coupling reaction. The substitution of electron withdrawing groups at para‐position of aryl halide gave the high yield when compared to electron donating groups (Table 1, entries 2‐8). Next, the electron donating groups at para to meta‐position of aryl halide decreased the yield (Table 1, entries 9‐10). In case of aliphatic aryl halides, as the carbon chain length increases, a slight decrease in the product yield was observed (Table 1, entries 13‐14). Aryl bromides were less reactive than the corresponding aryl iodides and good yields were obtained (Table 1, entries 15‐18). In order expand and explore the scope of this catalytic system various phenols/alcohols were treated with iodo benzene under optimized reaction conditions and the results are represented in Table 4. Satisfactory yields were obtained in the case of electron donating and withdrawing substitutions at para and meta‐position of phenols (Table 4, entries 1‐5). In the case of alcohols, as the carbon chain was increased, a slight decrease in the product yield was observed (Table 4, entries 8‐ 9). We were then interested in investigating the recyclability of the nano‐CuFe2O4 catalyst. After completion of the C‐O cross coupling reaction, the reaction mixture was cooled to room temperature and the catalyst was recovered with the help of magnetic bar and washed with ethyl acetate and acetone, air dried and used directly for the cycles without any further purification and the results are summarized in Table 5. The catalyst maintained its high level of activity even after the fourth cycle in C‐O cross‐coupling reaction. The results obtained in our studies support the oxidative addition/reductive elimination type of reaction mechanism for C‐O cross‐coupling reaction (Scheme 2). Initially the ArX oxidatively adds on to the nano‐CuFe2O4 catalyst and forms a complex A followed by replacement of X with a nucleophile in the presence of base forming complex B and reductive elimination affords the O‐arylated product. The newly regenerated heterogeneous nano‐CuFe2O4 catalyst is released to complete the catalytic cycle. The FT‐IR spectroscopic analysis of the CuFe2O4 nanoparticles, indicated that the significant bands, obtained in range of 680‐ 400 cm‐1, proved the presence of CuFe2O4 peaks. 302 Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 Table 4. Reaction of aryl halides with phenol using heterogeneous copper as a catalysta. Entry Aryliodide Nucleophile Product Yield (%) b 1 Iodobenzene 4‐Chlorophenol 3d 87 2 Iodobenzene 4‐Bromophenol 3e 85 3 Iodobenzene p‐Cresol 3g 80 4 Iodobenzene 4‐tert‐Butylphenol 3h 79 5 Iodobenzene 3‐Methoxyphenol 3i 85 6 Iodobenzene Naphthalen‐1‐ol 3k 75 7 Iodobenzene Naphthalen‐2‐ol 3l 80 8 Iodobenzene Decan‐1‐ol 3m 78 9 Iodobenzene Octan‐1‐ol 3n 80 a Reaction conditions: Aryl iodide (1 mmol), phenol/alcohol (1 mmol), CuFe2O4 (6 mol%, 143 mg), base (2.0 equiv.), DMSO (2 mL), 120 oC, 20 h. b Isolated yield. Table 5. Recyclability of nano copper iron oxide as a catalysta. I Nano CuFe2O4 (6 mol%) KOH (2.0 equiv) 120 oC, 20 h OH O DMSO (2 mL) 1a 2a 3a Cycle Product isolated yield (%) Catalyst recovery (%) Native 98 94 1 91 92 2 85 89 3 83 81 a Reaction conditions: 1a (1 mmol), 2a (1 mmol), CuFe2O4 (6 mol %, 143 mg), KOH (2.0 equiv.), DMSO (2 mL), 120 oC, 20 h. ArX O xid ative ad d itio n Base Re du ct ive eli m in at io n = Heterogeneous nano-CuFe2O4 catalyst ArOH ArOAr Ar ArO I II Ar X Scheme 2 These significant peaks appeared both in fresh and reused catalyst (Supplementary Figure S1). In addition, the powder X‐ ray diffraction analysis, [59] showed identical peaks for both the fresh and recovered CuFe2O4 nanoparticles (Supplementary Figure S2). The SEM images of the nano‐CuFe2O4 catalyst before and after the cycles were recorded and it was observed that the morphology and size of the nanoparticle did not change considerably, even after the last cycle (Figure 2). The X‐ray photoelectron spectroscopic [60‐62] (XPS) study of the fresh and used nano‐CuFe2O4 catalyst at the Cu 2p level shows the 2p3/2 lines at 934.6 and 934.8 eV respectively and the Fe 2p level shows the 2p3/2 lines at 710.7 and 710.8 eV respectively, which indicates that Cu is in the +2 and Fe is in +3 oxidation state before and after the reaction. The X‐ray photoelectron spectroscopic (XPS) study of the fresh and used nano‐CuFe2O4 catalyst at the Cu 2p level shows the 2p1/2 lines at 954.7 and 954.9 eV respectively and the Fe 2p level shows the 2p1/2 lines at 724.7 and 724.9 eV respectively, which indicates that Cu is in the +2 and Fe is in +3 oxidation state before and after the reaction (Figure 3). From these experimental data, we can conclude that there was no significant change in the catalytic activity of nano‐CuFe2O4, before and after the reaction. (a) (b) Figure 2. SEM analysis of (a) native nano‐CuFe2O4 catalyst and (b) reused nano‐CuFe2O4 catalyst. 4. Conclusions In summary, we have developed a simple, general and efficient procedure for the synthesis of biaryl ethers by using aryl halides/alkyl halides with phenols/alcohols as substrates employing heterogeneous nano‐CuFe2O4 as a catalyst in DMSO Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 303 [63] as solvent. The catalyst is air‐stable, inexpensive, easily recoverable and recyclable. (a) (b) (c) (d) Figure 3. XPS profiles of (a) Cu 2p orbital of native nano‐CuFe2O4 catalyst (b) Fe 2p orbital of native nano‐CuFe2O4 catalyst (c) Cu 2p orbital of reused nano‐CuFe2O4 catalyst (d) Fe 2p orbital of reused nano‐CuFe2O4 catalyst. Acknowledgements We are grateful to Council of Scientific and Industrial Research, New Delhi for the research fellowships to Avudoddi Venkanna and Palle Vinod Kumar Goud. References [1]. Evano, G.; Blanchard, N.; Toumi, M. Chem. Rev. 2008, 108, 3054‐3131. [2]. Theil, F. Angew. Chem. Int. Ed. 1999, 38, 2345‐2347. [3]. Boger, D. L.; Patane, M. A.; Zhou, J. J. Am. Chem. Soc. 1994, 116, 8544‐ 8556. [4]. Asano, M.; Inoue, M.; Katoh, T. Synlett 2005, 2599‐2602. [5]. Jiang, H.; Leger, J. ‐M.; Huc, I. J. Am. Chem. Soc. 2003, 125, 3448‐3449. [6]. Yamazaki, N.; Washio, I.; Shibasaki, Y.; Ueda, M. Org. Lett. 2006, 8, 2321‐2324. [7]. Bolm, C.; Hildebrand, J. P.; Muniz, Hermanns, K, N. Angew. Chem. Int. Ed. 2001, 40, 3284‐3308. [8]. Matsumoto, Y.; Uchida, W.; Nakahara, H.; Yanagisawa, I.; Shibanuma, T.; Nohira, H. Chem. Pharm. Bull. 2000, 48, 428‐432. [9]. Gu, W. X.; Jing, X. B.; Pan, X. F.; Chan, A. S. C.; Yang, T. K. Tetrahedron Lett. 2000, 41, 6079‐6082. [10]. Goodbrand, H. B.; Hu, N. ‐X. J. Org. Chem. 1999, 64, 670‐674. [11]. Ullmann, F. Chem. Ber. 1904, 37, 853‐854. [12]. Sawyer, J. S. Tetrahedron 2000, 56, 5045‐5065. [13]. Mann, G.; Hartwig, J. F. Tetrahedron Lett. 1997, 38, 8005‐8008. [14]. Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369‐4378. [15]. Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 3395‐3396. [16]. Prim, D.; Campagne, J. M.; Joseph, D.; Andrioletti, B. Tetrahedron 2002, 58, 2041‐2075. [17]. Kataoka, N.; Shelby, Q.; Stambuli, J.; Hartwig, J. J. Org. Chem. 2002, 67, 5553‐5556. [18]. Vorogushin, A. V.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 8146‐8149. [19]. Burgos, C. H.; Barder, T. E.; Huang, X.; Buchwald, S. L. Angew. Chem. Int. Ed. 2006, 45, 4321‐4326. [20]. Mann, G.; Hartwig, J. F. Tetrahedron Lett. 1997, 38, 8005‐8008. [21]. Vorogushin, A. V.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 8146‐8149. [22]. Prim, D.; Campagne, J. M.; Joseph, D.; Andrioletti, B. Tetrahedron. 2002, 58, 2041‐2075. [23]. Palomo, C.; Oiarbide, M.; LIpez, R.; Bengoa, E. G. Chem. Commun. 1998, 2091‐2092. [24]. Cristau, H. J.; Cellier, P. P.; Hamada, S. ; Spindler, J. ‐F.; Taillefer, M. Org. Lett. 2004, 6, 913‐916. [25]. Chen, Y. ‐J.; Chen, H. ‐H. Org. Lett. 2006, 8, 5609‐5612. [26]. Rao, H.; Jin, Y.; Fu, H.; Jiang, Y.; Zhao, Y. Chem. Eur. J. 2006, 12, 3636‐ 3646. [27]. Cai, Q.; Zou, B.; Ma, D. Angew. Chem. Int. Ed. 2006, 45, 1276‐1279. [28]. Altman, R. A.; Buchwald, S. L. Org. Lett. 2007, 9, 643‐646. [29]. Ouali, A.; Spindler, J.‐F.; Jutand, A.; Taillefer, M. Adv. Synth. Catal. 2007, 349, 1906‐1916. [30]. Ullmann, F. Ber. Dtsch. Chem Ges. 1903, 36, 2382‐2384. [31]. Jin, Y.; Liu, J.; Yin, Y.; Fu, H.; Jiang, Y.; Zhao, Y. Synlett, 2006, 1564‐ 1568. [32]. Gujadhur, R. K.; Bates, C. G.; Venkataraman, D. Org. Lett. 2001, 3, 4315‐4317. [33]. Chen, Y. J.; Chen, H. H. Org. Lett. 2006, 8, 5609‐5612. [34]. Weingarten, H. J. Org. Chem. 1964, 29, 3624‐3626. [35]. Marcoux, J. F.; Doye, S.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 10539‐10540. [36]. Buck, E.; Song, Z. J.; Tschaen, D.; Dormer, P. G.; Volante, R. P.; Reider, P. J. Org. Lett. 2002, 4, 1623‐1626. [37]. Lv, X.; Bao, W. J. Org. Chem. 2007, 72, 3863‐3867. [38]. Gujadhur, R. K.; Venkataraman, D. Synth. Commun. 2001, 31, 2865‐ 2879. [39]. Zhang, Q.; Wang, D.; Wang, X.; Ding, K. J. Org. Chem. 2009, 74, 7187‐ 7190. [40]. Kiyomori, A.; Marcoux, J. F.; Buchwald, S. L. Tetrahedron Lett. 1999, 40, 2657‐2660. [41]. Ma, D. ; Cai, Q. Org. Lett. 2003, 5, 3779‐3782. [42]. Kim, J. Y.; Park, J. C.; Kim, A.; Kim, A. Y.; Lee, H. J.; Song, H.; Park, K. H. Eur. J. Inorg. Chem. 2009, 4219‐4223. [43]. Larsson, P. F.; Correa, A.; Carril, M.; Norrby, P. O.; Bolm, C. Angew. Chem. Int. Ed. 2009, 48, 5691‐5693. [44]. Liu, Z.; Larock, R. C. J. Org. Chem. 2006, 71, 3198‐3209. [45]. Paul, S.; Gupta, M. Tetrahedron Lett. 2004, 45, 8825‐8829. [46]. Xu, L. W.; Xia, C. G.; Li, J. W.; Hu, X. X. Synlett. 2003, 2071‐2073. [47]. Mao, J.; Xie, G.; Wu, M.; Guo, J.; Ji, S. Adv. Synth. Catal. 2008, 350, 2477‐ 2482. [48]. Bistri, O.; Correa, A.; Bolm, C. Angew. Chem. Int. Ed. 2008, 47, 586‐588. [49]. Ouali, A.; Spindler, J. F.; Cristau, H. J.; Taillefer, M. Adv. Synth. Catal. 2006, 348, 499‐505. [50]. Naidu, A. B.; Raghunath, O. R.; Prasad, D. J. C.; Sekar, G. Tetrahedron Lett. 2008, 49, 1057‐1061. [51]. Naidu, A. B.; Jaseer, E. A.; Sekar, G. J. Org. Chem. 2009, 74, 3675‐3679. [52]. Lipshutz, B. H.; Unger, J. B.; Taft, B. R. Org. Lett. 2007, 9, 1089‐1092. [53]. Swapna, K.; Murthy, S. N.; Nageswar, Y. V. D. Eur. J. Org. Chem. 2011, 1940‐1946. [54]. Knight, W. D.; Clemenger, K.; de Heer, W. A.; Saunders, W. A. M.; Chou, Y.; Cohen, M. L. Phys. Rev. Lett. 1984, 52, 2141‐2143. [55]. Pacchioni, G. Surf. Rev. Lett. 2000, 7, 277‐306. [56]. Kidwai, M.; Mishra, N. K.; Bansal, V.; Kumar, A.; Mozumdar, S. Tetrahedron Lett. 2007, 48, 8883‐8887. 304 Avudoddi et al. / European Journal of Chemistry 3 (3) (2012) 298‐304 [57]. Jammi, S.; Sakthivel, S.; Rout, L.; Mukherjee, T.; Mandal, S.; Mitra, R.; Saha, P.; Punniamurthy, T. J. Org. Chem. 2009, 74, 1971‐1976. [58]. Sreedhar, B.; Arundhathi, R.; Reddy, P. L.; Kantam, M. L. J. Org. Chem. 2009, 74, 7951‐7954. [59]. Tasca, J. E.; Ponzinibbio, A.; Diaz, G.; Bravo, R. D.; Lavat, A.; Gonzalez, M. G. Top Catal. 2010, 53, 1087‐1090. [60]. Bhadra, S.; Sreedhar, B.; Ranu, B. C. Adv. Synth. Catal. 2009, 351, 2369‐ 2378. [61]. Maity, D.; Kale, S. N.; Ghanekar, R. K.; Xue, J. M.; Ding, J. J. Magn. Magn. Mater. 2009, 321, 3093‐3098. [62]. Kantam, M. L.; Arundhathi, R.; Likhar, P. R.; Damodara, D. Adv. Synth. Catal. 2009, 351, 2633‐2637. [63]. Hunter, D. H.; Cram, D. J. J. Am. Chem. Soc. 1966, 88, 5765‐5776.