SnO2âSiO2 Mesoporous Composite: A Very Active Catalyst for

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SnO2-SiO2 Mesoporous Composite: A Very Active Catalyst for Regioselective Synthesis of Aromatic Ketones with Unusual Catalytic Behavior K. Raveendranath Reddy, dupati venkanna, M. Lakshmi Kantam, Suresh Kumar Bhargava, and Pavuluri Srinivasu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b00910 • Publication Date (Web): 19 Jun 2015 Downloaded from http://pubs.acs.org on June 23, 2015

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Industrial & Engineering Chemistry Research

SnO2-SiO2 Mesoporous Composite: A Very Active Catalyst for Regioselective Synthesis of Aromatic Ketones with Unusual Catalytic Behavior K. Raveendranath Reddy,† D. Venkanna,† M. Lakshmi Kantam,† Suresh K. Bhargava,‡ and Pavuluri Srinivasu*,† †

Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India

‡

Advanced Materials and Industrial Chemistry Group, School of Applied Sciences, RMIT University, Melbourne-3001, Australia

ABSTRACT: Aromatic ketones (R-Ar-CO-R′) have been prepared directly through C-C bond formation using aromatics, aryl, and alkyl acid halides to undergo Friedel–Crafts reaction over reusable and catalytically active ordered SnO2-SiO2 three-dimensional mesoporous composite (PS-4) catalyst, which found to be superior to modified zeolites, functionalized MCM-41 and supported heteropolyacid catalysts.

1. INTRODUCTION Afford Regio selective monoarylation and alkylation of aromatics with electrophilic reagents, such as aryl and alkyl acid halides is of great potential significance in the organic synthesis and specialty chemical industry.1,2 Despite of the tremendous applications both in biological and medicinal chemistry, major challenges still remain as traditional strategies to produce aromatic ketones often suffers from complicated reaction procedures and environmental issues. In addition, soluble metal halides, protic acids, trifluoroacetic anhydride, methanesulfonic anhydride in stoichiometric amounts,3 homogeneous catalysts such as Zn(OTf)2.6H2O, Hf(OTf)4 in LiClO4-MeNO2, and (PhCN)2PtCl2/AgSbF6 in catalytic amounts4,5 have been used to produce aromatic ketones, which restricts its use in industry due to high process cost, toxicity, and possible contamination of metal catalysts in the products. Unfortunately, homogeneous catalytic processes available today for preparation of aromatic ketones are generally far from ideal. In view of this, heterogenization of the homogeneous metal catalysts favours industrial catalytic processes due to its ease of handling, simple workup and regenerability. In recent years, mesoporous materials have been applied as important class of materials in wide range of applications including green catalysis,6 fuel cells,7 solar cells and drug delivery systems8 because of their unique structural and textural properties such as high specific surface area, high thermal stability, large and uniform narrow range pore size distribution. Thus, various mesoporous catalysts have been involved in Aldol,9 Friedel-Crafts,10 and Diels-Alder processes.11 These mesoporous materials with two and threedimensional (2D &3D) structures have been synthesized by using either cationic or an anionic or a neutral surfactant as a structure directing agent to enhance their properties. In addition, 3D nanostructured materials show superior performance over 2D materials in diffusion of reactants, which avoids pore blocking. Recently, 3D mesoporous cubic Ia3d material with bicontinuous structure of two enantiomeric pore

systems has been synthesized using Pluronic P123 and nbutanol, which possess large pore diameter, high surface area and a large pore volume. On the hand, metal oxides are the most common surfaces of particular interest in heterogeneous catalysis due to their applications in several industrial processes. However, in order to get higher catalytic performance, metal oxides are immobilized in mesoporous channels as they show low specific surface area and small pore diameter. In particular, tin oxide (SnO2) based heterogeneous acid catalysts such as Sn-MFI, Sn-Beta zeolite, Sn-MCM-48 have been used in several important reactions, including Baeyer-Villiger (BV) oxidations,12 Meerwein-PonndorfVerley reductions,13 Mukaiyama-aldol condensations14 and isomerisation of sugars.15 In addition, there are several reports on the use of heterogeneous acid catalysts to produce aromatic ketones including zeolite β,16 bentonite,17 P2O5/Al2O3,18 Fe3O4,19 nafion/SBA-15,20 TiO2-ZrO2,21 Fe/K10,22 sulfated alumina,23 WO3/ZrO2,24 sulfated zirconia,25 heteropoly acids26 and SiC-based solid acid catalysts.27 However, the use of harsh reaction conditions and several synthesis steps increase the number of products, which elegantly circumvent these systems for commercialization of the technology. Therefore, development of recyclabe green catalytic stystem for synthesis of aromatic ketones is of considerable interest. In addition, the use of mesoporous silica with 3D network structure (MPS) as a support presents significant advantages owing to its unique textural properties and thermal stability. However, to the best of our knowledge, no 3D composite system has yet been employed for synthesis of aromatic ketones. In the present strategy, we envisioned an alternative approach by preparing SnO2/SiO2 3D mesoporous composite heterogeneous acid catalysts that would provide green process for synthesis of aromatic ketones. The catalytic performance of the composite catalysts for direct synthesis of aromatic ketones by C-C bond formation are investigated regarding the yield of aromatic compounds, and more attention is paid to amount of catalyst, reaction temperature and aryl, alkyl acid

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halide to aromatics mole ratio to optimize C-C bond formation reaction conditions. In addition, the catalysts are characterized by various physicochemical techniques such as powder X-ray diffraction (XRD), Nitrogen-sorption, FourierTransform Infrared Spectroscopy (FTIR) and UV-vis spectroscopy. Further, the catalytic activity and reusability of the catalyst have been investigated to develop regioselective method that could produce aromatic ketones with high yield than that of modified zeolites and supported heteropolyacids. 2. EXPERIMENTAL SECTION 2.1. Materials. P-123, n-butanol, hydrochloric acid, tetraethyl ortho silicate [Si(OC2H5)4, TEOS], tin chloride (SnCl4·5H2O) and other chemicals and solvents were purchased from Sigma-Aldrich and were analytical grade. All the products were purified by using ACME silica gel (60-120 Mesh). 2.2. Synthesis Procedure for PS-4 Materials. The ordered large mesoporous silica with Ia3d symmetry is prepared using a mixture of amphiphilic triblock copolymer, Pluronic P123 (EO20PO70EO20, MW = 5800, Aldrich), n-butanol as structure directing mixture in hydrochloric acid solution. Tetraethyoxysilane (TEOS, Aldrich, 98%) as a silica source. Pluronic P123 (4.5 g) was completely dissolved in 162 g of hydrochloric acid solution, followed by addition of 4.5 g of butanol, which was stirred at 35 °C. After that, 9.6 g of TEOS was added at once to the above homogeneous solution. The resulting gel was stirred for 20 h at the same temperature and aged at 90 °C for 20 h. After hydrothermal treatment, the obtained solid was filtered, dried and calcined at 550 °C for complete removal of the polymer. The obtained sample is denoted as MPS. A series of different tin loaded mesoporous silica composites were prepared by suspending SnCl4.5H2O in ethanol (10ml) and mesoporous silica (200 mg). The mixtures were stirred at room temperature for 6 h and subsequently raised the temperature of hot plate to 50 °C to remove the solvent. The tin oxide and mesoporous silica composite were obtained by oxidizing the mixture at 550 °C for 5 h. Finally obtained samples are designated as PS-4(X), where X indicates weight % of SnO2 in 3D mesoporous silica composite. 2.3. Characterizations. X-ray powder diffraction (XRD) patterns of all catalysts were recorded on a Rigaku Ultima- IV (M/s. Rigaku Corporation, Japan) using Ni filtered CuKα radiation (λ = 1.5406 A° ) with a scan speed of 1° min−1 and a scan range of 0.7°–80° at 40 kV and 30 mA. Both low angle and wide angle XRD patterns of the catalyst samples recorded to characterize the crystallinity and mesoporous ordering of the samples. The N2 adsorption–desorption isotherms were performed at 77 K using QuadraSorb SI (M/s Quantachrome Instruments Corporation, USA) system after degasification under vacuum at 423 K for 12h. The specific surface areas were evaluated using the BrunauerEmmett-Teller (BET) method in the P/Po range 0.05 - 0.35. Pore size was calculated by using the Barrett-Joyner-Halenda (BJH) method from the desorption branch of isotherm. The total pore volume was taken by a single point method at P/Po = 0.99. The FTIR spectra of all samples recorded on PerkinElmer - Spectrum GX Spectrometer in the range of 400-4000 cm-1 by using KBr pellets having 1 wt% of the sample. The UV–vis diffused reflectance spectra of calcined samples were recorded on Shimadzu UV–Vis spectrophotometer (UV-3600) in the UV–vis range 200–800 nm. Spectral grade BaSO4 was taken as reference for the reflectance spectra.

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2.4. Typical Procedure for Synthesis of Aromatic Ketones.

In a 15 ml round bottom pressure tube, mixture of catalyst (50 mg), acid chloride(1.0 mmol) and nitro methane(0.5 ml) were taken. To this mixture, aromatic substrate (1 mmol) was added at room temperature and stirred with a magnetic stirrer at 80 ºC for certain period of time until the reaction is completed (monitored by TLC). The reaction mixture is diluted with ethyl acetate and the catalyst is separated from reaction mixture by centrifugation. The ethyl acetate extract was washed with an aqueous saturated solution of sodium bicarbonate and dried over anhydrous sodium sulfate. After solvent evaporation under reduced pressure, the pure product was separated by column chromatography. The isolated compounds are identified and confirmed by different spectral analysis. The products are characterized by 1H-NMR, and 13CNMR using Bruker Avance (300 MHz) or Varian Unity (400 MHz) spectrometer (TMS as an internal standard and CDCl3 as solvent).

2.5. Analytical Data. 1-(4-Methoxyphenyl) Ethanone. White solid; mp 36 - 38 oC. IR (KBr): 2840, 1674, 1600, 1254, 1174, 1026, 957, 835, 570 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.88 (d, J = 9.06 Hz, 2H), 6.87 (d, J = 9.06 Hz, 2H), 3.85 (s, 3H), 2.51 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 196.6, 163.3, 130.4, 130.1, 113.5, 55.3, 26.2. MS (EI, 70 eV): m/z (%) = 150 (25) [M+], 135(100), 107(27), 92(30), 77(55), 63(22). Anal Calcd for C9H10O2: C, 71.98; H, 6.71. Found: C, 71.91; H, 6.68. 1-(2, 4, 6-Trimethoxyphenyl) ethanone. Light brown solid; mp 98 - 102 oC. IR (KBr): 2981, 1690, 1600, 1455, 1239, 1123, 1026, 820, 571 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 6.10 (s, 2H), 3.82 (s, 3H), δ 3.79 (s, 6H), δ 2.46 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 201.6, 162.2, 158.2, 113.5, 90.4, 55.7, 55.3, 32.4. MS (EI, 70 eV): m/z (%) = 210 (21) [M+], 195(100), 180(16), 152(17), 137(20), 122(5), 109(6), 69(7). Anal Calcd for C11H14O4: C, 62.85; H, 6.71. Found: C, 62.79; H, 6.70. 1-(6-Methoxynaphthalen-2-yl) ethanone. White crystalline solid; mp 107 - 109 oC. IR (KBr): 2934, 1673, 1620, 1475, 1358, 1275, 1200, 1019, 859, 817 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 8.31 (s, 1H), 7.95 (d, J = 10.77 Hz, 1H), 7.78 (d, J = 8.89 Hz, 1H), 7.69 (d, J = 8.89 Hz, 1H), 7.14 (d, J = 10.77 Hz, 1H), 7.07 (s, 1H), 3.92 (s, 3H), 2.64 (s, 3H); 13C NMR (75 MHz, CDCl3, ppm): δ = 197.7, 159.6, 137.2, 132.5, 131.0, 129.9, 127.7, 127.0, 124.5, 119.6, 105.7, 55.3, 26.5. MS (EI, 70 eV): m/z (%) = 200 (75) [M+], 185(100), 157(15), 142(10), 114(16). Anal Calcd for C13H12O2: C, 77.98; H, 6.04. Found: C, 77.95; H, 5.96. 1-p-Tolylethanone. Colourless liquid; IR (Neat): 2922, 1656, 1603, 1276, 1178, 836, 730, 699 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.81 (d, J = 8.12 Hz, 2H), 7.24 (d, J = 8.12 Hz, 2H), 7.20 (s, CDCl3, 1H), 2.55 (s, 3H), 2.42 (s, 3H). 13 C NMR (75 MHz, CDCl3, ppm): δ = 197.6, 143.6, 134.5, 129.1, 128.3, 26.3, 21.4. MS (EI, 70 eV): m/z (%) = 134 (85) [M+], 119(76), 105(8), 91(100), 77(9), 65(75). Anal Calcd for C9H10O: C, 80.56; H, 7.51. Found: C, 80.45; H, 7.46. 1-(3, 4-Dimethylphenyl) ethanone: Pale yellow liquid; IR (Neat): 2966, 1682, 1607, 1358, 1267, 1182, 955, 832, 765, 595 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.58 (d, J = 8.31 Hz, 1H), 6.97-7.03 (m, 2H), 2.52 (s, 3H), 2.49 (s, 3H), 2.34 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 198.0, 142.5, 136.7, 135.0, 129.7, 129.3, 126.0, 26.4, 19.9, 19.6. MS (EI, 70 eV): m/z (%) = 148 (20) [M+], 133(69), 120(13),


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100

MPS PS-4 (2) PS-4 (5) PS-4 (10) PS-4 (15)

(b)

Intensity (a.u)

Intensity (a.u)

(a)

1

2

3

4

PS-4 (2) PS-4 (5) PS-4 (10) PS-4 (15)

20

5

40

60

Angle (2theta)

2theta (degree) 0.6

(c)

(d)

MPS PS-4(2) PS-4(5) PS-4(10) PS-4(15)

0.5 -1

Amount adsorbed (cm g )

0.4

3

0.3

Dv

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 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2

0.1

0.0

0.2

0.4

0.6

0.8

1.0

5

10

15

20

Pore diameter (nm)

Relative pressure (P/PO)

Figure 1. (a) Powder XRD patterns of MPS and PS-4 materials; (b) wide-angle XRD patterns; (c) nitrogen adsorption-desorption isotherms of MPS and PS-4 materials, and (d) the corresponding pore size distribution.

105(100), 85(20), 77(75), 56(20), 43(90). Anal Calcd for C10H12O: C, 81.04; H, 8.16. Found: C, 81.01; H, 8.15. 1-(Furan-2-yl) ethanone: Pale yellow liquid; IR (Neat): 3131, 1676, 1568, 1468, 1392, 1359, 1289, 1165, 1099, 1021, 960, 909, 766, 625 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ 7.58 (d, J= 1.52 Hz, 1H), 7.18 (d, J=3.5 Hz, 1H), 6.54 (m, 1H), 2.48 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 186.1, 153.0, 145.8, 116.5, 112.1, 25.9. MS (EI, 70 eV) m/z (%) = 110 (79) [M+], 95(100), 81(3), 67(16). Anal Calcd for C6H6O2: C, 65.45; H, 5.49. Found: C, 65.41; H, 5.46. 1-(Thiophen-2-yl) ethanone: Yellow liquid; IR (Neat): 3096, 2924, 1662, 1517, 1415, 1358, 1273, 933, 854, 726, 590 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.66 (d, J = 3.77 Hz, 1H), 7.60 (d, J = 5.28 Hz,1H), 7.10 (t, J = 4.52 Hz, 1H), 2.55 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 190.6, 144.4, 133.6, 132.3, 128.0, 26.8. MS (EI, 70 eV): m/z (%) = 126 (10) [M+], 111(20), 83(18), 69(60), 56(49). Anal Calcd for C6H6SO: C, 57.11; H, 4.79; S, 25.41. Found: C, 57.02; H, 4.76; S, 25.39.

1-(5-Chloro-2-methoxyphenyl) ethanone: Yellow liquid; IR (Neat): 2926, 2852, 1677, 1597, 1485, 1400, 1268, 1179, 1022, 812, 646 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.66 (s, 1H), 7.36 (d, J = 9.0 Hz, 1H), 6.87 (d, J = 9.0 Hz, 1H), 3.91 (s, 3H), 2.56 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 198.3, 157.4, 133.1, 130.0, 129.1, 125.9, 113.1, 55.8, 31.7. MS (EI, 70 eV): m/z (%) = 184 (12) [M+], 169(93), 126(36), 111(35), 85(33), 75(69), 63(100). Anal Calcd for C9H9ClO2: C, 58.55; H, 4.91. Found: C, 58.49; H, 4.90. 4-Methoxyphenyl-(Phenyl) methanone. White solid; mp 5863 oC. IR (KBr): 2962, 2840, 1650, 1598, 1255, 1174, 1027, 846, 741 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.78 (d, J = 9.06 Hz, 2H), 7.71 (d, J = 9.82 Hz, 2H), 7.51 (t, J = 7.92 Hz, 1H), 7.42 (t, J = 8.3 Hz, 2H), 6.91 (d, J = 9.82 Hz, 2H), 3.86 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 195.2, 163.0, 138.1, 132.3, 131.6, 129.9, 129.5, 127.9, 113.4, 55.27. MS (EI, 70 eV): m/z (%) = 212 (63) [M+], 135(100), 105(25), 92(25), 77(56), 64(14). Anal Calcd for C14H12O2: C, 79.22; H, 5.70. Found: C, 79.21; H, 5.69.



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Table 1. Physicochemical Properties of Calcined PS-4 Catalysts

a0a (nm)

surface area (m2 g-1)

PS-4(15)

23.1

468

6.3

0.40

PS-4(10)

24.0

632

7.7

0.59

PS-4(5)

23.2

684

7.6

0.75

PS-4(2)

23.0

726

7.6

0.95

MPS

24.5

748

10.6

1.34

catalyst

a: unit cell parameter 3, 4-Dimethoxyphenyl-(phenyl) methanone. White crystalline solid; mp 89-93 oC. IR (KBr): 2932, 2311, 1648, 1589, 1512, 1271, 1230, 1128, 1023, 835, 710 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.72 (d, J = 7.91 Hz, 2H), 7.52 (t, J = 7.43 Hz, 1H), 7.41-7.46 (m, 3H), 7.31 (d, J = 7.91 Hz, 1H), 6.82 (d, J = 7.91 Hz, 1H), 3.93 (s, 3H), 3.92 (s, 3H); 13C NMR (75 MHz, CDCl3, ppm): δ = 195.6, 152.9, 148.9, 138.2, 131.9, 130.2, 129.7, 128.2, 125.5, 112.0, 109.7, 56.1, 56.0. MS (EI, 70 eV): m/z (%) = 242 (69) [M+], 211(9), 165(100), 128(15), 105(39), 77(65). Anal Calcd for C15H14O3: C, 74.36; H, 5.82. Found: C, 74.20; H, 5.81 Phenyl (2, 4, 6-trimethoxyphenyl) methanone. White solid; mp 103-107 oC. IR (KBr): 2942, 2310, 1669, 1595, 1413, 1267, 1127, 1031, 951, 918, 813, 723 cm -1. 1H NMR (300 MHz, CDCl3, ppm): δ = 7.79 (d, J = 7.01 Hz, 2H), 7.49 (t, J = 7.55 Hz, 1H), 7.38 (t, J = 7.55 Hz, 2H), 7.13 (s, 2H), 3.85 (s, 3H), 3.69 (s, 6H); 13C NMR (75 MHz, CDCl3, ppm): δ = 195.0, 162.4, 158.7, 138.2, 132.9, 129.4, 128.2, 110.8, 90.6, 55.7, 55.4. MS (EI, 70 eV): m/z (%) = 272 (29) [M+], 255(20), 195(100), 180(8), 152(7), 137(13), 105(11), 77(24). Anal Calcd for C16H16O4: C, 70.57; H, 5.92. Found: C, 70.51; H, 5.90. 6-Methoxynaphthalen-2-yl)(phenyl) methanone. Pale yellow crystalline solid; mp 83-86 oC. IR (KBr): 2935, 2310, 1652, 1622, 1479, 1279, 1211, 1169, 1028, 894, 859, 720, 635 cm -1. 1 H NMR (300 MHz, CDCl3, ppm): δ = 7.11-8.15 (m, 11H), 3.92 (s, 3H). 13C NMR (75 MHz, CDCl3, ppm): δ = 196.1, 159.6, 138.2, 136.9, 132.6, 131.9, 131.8, 130.9, 129.9, 128.1, 127.6, 126.9, 126.5, 119.6, 105.7, 55.3. MS (EI, 70 eV): m/z (%): 262 (73) [M+], 185(97), 157(42), 142(37), 127(16), 114(62), 105(43), 77(100), 63(13). Anal Calcd for C18H14O2: C, 82.42; H, 5.38. Found: C, 82.18; H, 5.26. 3. RESULTS AND DISCUSSION 3.1. Characterization of PS-4 Catalysts: The structural characterization of PS-4 and MPS materials by X-ray diffraction are shown in Figure 1a, which illustrates well resolved characteristic planes of (211) and (220) signifying body-centered cubic Ia3d symmetry. Exceptionally, the XRD pattern suggests the structural order is well maintainted even after incorporation of tin oxide into MPS material. In addition, the shifting of the most intense Bragg peak to lower 2θ values

pore diameter (nm)

pore volume (cm3 g-1)

indicates that the unit cell parameter (a0) of 23 nm for PS-4(2) increases to 24 nm for PS-4(10) material. The results cleary confirm that the expansion of unit cell size is accompanied with the considerable enlargement of pore diameter of PS-4 materials. The wide angle XRD patterns of PS-4 materials (Figure 1b) show broad diffraciton peak originating from MPS, implying that finely dispersed tin oxides partilces composites are formed with interaction of hydroxyl group of the MPS material. On the other hand, it is interesting to note that with increasing tin oxide amount in MPS channels, tetragonal rutile crystalline phases of tin oxide peaks (JCPDS 41-1445) are detected for PS-4(15) material. The texture and pore network structure of PS-4 materials are assessed by using nitrogen sorption studies. The nitrogen adsoroption-desorption isotherms of PS-4 materials demonstrate type IV isotherms with H1 hysteresis loops (Figure 1c) indicate of high-quality large-porous materials. The textural parameters of PS-4 and MPS materials are summarized in Table 1. The unitcell parameter (a0) is calculated from XRD data, specific surface area is obtained from Brunauer-Emmett-Teller (BET) method, Barret-Joyner-Halenda (BJH) method is used to get pore diameter from the maxium position on pore size distribution, and total pore volume is estimated from the amout of nitrogen gas adsorbed. The specific surface and pore volume are systematically decreases from 726 m2 g-1 and 0.95 cm3 g-1 for PS-4(2) to 468 m2 g-1 and 0.40 cm3 g-1 for PS-4(15) respectively, with increasing tin oxide loading in MPS channels. Notably, the capillary condensation step shifts to lower relative pressure, revealing the mesopore diameter of PS-4 materials significantly decreases from 7.6 to 6.3 nm (Figure 1d), which is because of occupation of tin oxide nanoparticles in mesochannels. The above results reveal that the systematic tunning in textural properties of PS-4 materials upon incorporation of crystalline tin oxide species in threedimension porous network structure. FTIR spectra of PS-4 materials determine the progressive consumption of surface silonol groups in MPS material after incorporation of SnO2 species. The FTIR spectra of PS-4 materials show bands centered at about 1624 cm-1 and a broad band at 3450 cm-1 attributed to Si-OH bending and water hydroxyl streching vibrations respectively (Figure 2a). In addition, the IR band at 800 cm-1 asymmetric streching and 1074 cm-1 band with a sholder peak is correspond to Si-O-Si symmetric stretching vibrations. The intensity of Si-OH streching vibration band at


4000

3500

resolution trasmission electron microscopy (HRTEM). Figure 3 shows that the material comprises ordered mesoporousity with linear arry of pores and pore channels. The HRTEM observations are consistent with aforementioned nitrogen sorption and XRD results. Pyridine adsorbed FTIR is used to evaluate the acidity strength and nature of acidic sites on PS-4 catalysts. The band at ~1539 cm-1 is usually assigned to Br∅nsted acidic sites, exists in all PS-4 catalysts (Figure 4). It is noted that regardless of amount of tin oxide incorporation, the intensity of Br∅nsted acidic sites practically unchanged. In addition, coordinately bounded pyrindine band at ~1450 cm-1 is characteristic of pyridine adsorbed on Lewis acid sites.30 The fact that the intensity of both Lewis and Br∅nsted acidic sites associated peak at ~1498 cm-1 increases with increasing tin oxide loading up to PS-4(10) catalyst. These results suggest that the Lewis acidic sites of PS-4 materials having more tin oxide loading, retain extra pyridine compare to others.

3000

2500

-1

800 cm

-1 1074 cm

MPS PS-4(2) PS-4(5) PS-4(10) PS-4(15)

-1 1624 cm

-1 3450 cm

Transmittance (%)

(a)

2000

1500

1000

500

-1

Wavenumber (cm )

1.8

206 nm 251 nm

1.6

-0.06

(b) PS-4 (2) PS-4 (5) PS-4 (10) PS-4 (15)

1.4 1.2

B 1539 cm-1

-0.05

L 1450 cm-1 B+L 1489 cm-1

-0.04

1.0

Absorbance (a.u)

Absorbance(a.u)

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 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-1 676 cm -1 558 cm

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0.8 0.6 0.4 0.2

-0.03

(d)

-0.02

(c) (b)

-0.01

0.0 200

300

400

500

600

700

800

(a) 0.00

Wave length (nm) 1540

Figure 2. (a) FTIR spectra and (b) UV-vis DRS spectra of PS-4 materials.

558 cm-1 in PS-4 materials gradually increases with inceasing tin oxide incorporation signifies the surface modifiation in MPS materials. Interestingly, the additional IR band at 676 cm-1 for PS-4(15) implies the Sn-O-Sn vibrational modes.28 On the other hand, in order to prove charge-transfer bands and tin oxide coordiantion number in PS-4 materials UV-vis diffuse reflectance specra is employed. The spectra of PS-4 materials show two intense absorption bands at 205-215 nm and 240-250 nm, which are correspond to charge trasfer transition (CT) from O2- to Sn4+ in tetrahedral coordination with silica pore walls and the latter peak is mainly assigned to the SnO2 formation.29 The PS-4(15) material consists of larger aggregates of SnO2 particles in MPS network, which is in contrast to PS-4(2), PS(5) and PS-4(10) materials due to higher loading of SnO2 particles (Figure 2b). Thus, it can be conclude that the efficient formation of tin oxide nanoparticles in MPS channels and subsequent tunable surface acidic properties of PS-4 materials. Further, to investigate the structural properties, PS-4 material is examined by high

1520

1500

1480

1460

1440

1420

1400

-1

Wave number (cm )

Figure 3. Infrared spectra pyridine adsorbed on PS-4 catalysts: (a) PS-4(15), (b) PS-4(10), (c) PS-4(5) and PS-4(2).

100 nm

Figure 4. HRTEM image of PS-4(10) catalyst.



100

catalyst. Among the catalysts tested, PS-4(10) has shown high yield of aromatic ketones because of large pore size and ordered three-dimensional pore structure. For further studies, PS-4(10) has been preferred as best catalyst to investigate the effect of solvent, effect of reaction temperature, effect of amount of catalyst and acetyl chloride to anisole mole ratio under optimized reaction conditions. Direct synthesis of aromatic ketones through C-C bond formation of aniosole and acetyl chloride has been carried out to heterogenize the reaction over PS-4 catalyst using different solvents at 80 °C. It is interesting to note that poor yields are obtained when tetrahydrofuran (THF) solvent is used. On the other hand, when acetonitrile and ethylene dichloride (EDC) are employed as

PS-4(2) PS-4(5) PS-4(10) PS-4(15)

80

Yield (%)

60

40

20

0 0

10

20

30

40

50

100

Time (min)

Figure 5. Effect of PS-4 on the yield of aromatic ketones. (reactions were carried out using of acid chloride (1.0 mmol), aromatic substrate (1 mmol), PS-4 catalyst and 0.5 ml of nitro methane.

80

Yield (%)

60

PS-4(10) (30mg) PS-4(10) (40mg) PS-4(10) (50mg) PS-4(10) (60mg)

40

100 20

80

Yield (%)

60

0 0

10

20

30

40

50

Time (min)

40

Figure 7. Effect of amount of PS-4 on the yield of aromatic ketones.

20 0 30

50

80

100

Temperature (ºC) Figure 6. Effect of temperature in PS-4 catalytic system on the yield of aromatic ketones.

120 100

. 3.2. Catalytic studies. In order to achieve environmentally friendly chemical process for direct synthesis of aromatic ketones by C-C coupling reaction over PS-4 catalysts, the reactions have been efficiently tested with anisole, and acetyl chloride as aromatic substrate and acylating agent, respectively. To determine the best reaction conditions for obtaining excellent yields of corresponding C-C bond formation product, the influence of different PS-4 catalysts has been explored at reaction temperature of 80 °C (Figure 5). The yield of 4-methoxy acetophenone (PMAP) increases from 51% for PS-4(2) to 92% for PS-4(10). The yield remained constant when the reaction is carried out over PS-4(15) catalyst. It is important to note that the reaction resulted without any product, when the reaction is employed without PS-4 catalyst, which signifies the role of the

Yield (%)

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80 60 40 20 0 0.5

1

1.5

Acetyl chloride : Anisole Figure 8. Effect of acetyl choloride to anisole mole ratio over PS-4 on the yield of aromatic ketones.


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Table 2: Direct Synthesis of Aromatic Ketones through C-C Coupling Reaction over PS-4(10)a catalyst

O R

PS-4(10) catalyst,

+ R'

80

Cl

oC,

R CH3NO2 COR'

O

OMe O CH3

MeO

O CH3

CH3 MeO

a

OMe

MeO

b

time= 0.5 hr, 92% yield

c


O


O CH3

Me

CH3 CH3

O

Me

O

Me

d time= 1.0 hr, 82% yield

e time= 1.0 hr, 86% yield

f time= 0.5 hr, 81% yield

OMe O

O CH3

CH3

Ph

S

g

O

i

h




OMe O

O MeO

MeO

Cl

O Ph

Ph

Ph

MeO

MeO

OMe

j time= 0.5 hr, 84% yield

k time= 0.5 hr, 81% yield

a

MeO

l time= 0.5 hr, 70% yield

Reaction conditions: acid chloride (1 mmol), aromatic compound (1 mmol), PS-4(10) catalyst (50 mg), and CH3NO2 (0.5 ml) at 80 °C



100 80

Yield (%)

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 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

60 40 20 0 1

2

3

4

5

No. of cycle Figure 9. Recyclability of the PS-4 catalyst.

Scheme 1. Plausible Mechanism Involved in Synthesis of Aromatic Ketones with Acid chloride over PS-4 Catalyst

Lewis acidic sites

PS-4 Product

Acylium ion Arenium ion

solvent for the same reaction showed 28% and 66% yield respectively. Among the solvents tested nitro methane is found to be the best with 92% yield of corresponding acetophenone over PS-4(10) catalyst (Figure S3). Thus, nitro methane is used as a solvent for further optimization of reaction conditions. In the synthesis of aromatic ketones through C-C bond formation reaction over PS-4 catalyst, the reaction temperature has played significant affect. The yield of aromatic ketones systematically increases from 28 to 92% with increasing reaction temperature from 30 to 80 °C respectively (Figure 6). However, a further increase in the reaction temperature to 100 °C, did not alter the product yield% greatly. The above results suggest that at reaction temperature of 80 °C, PS-4(10) is an

Page 8 of 11

efficient catalyst for synthesis of aromatic ketones. Further to obtain maximum yield of aromatic ketones, the reaction is optimized by varying the amount of PS-4 catalyst needed as shown in Figure 7. The product yield increased with catalyst amount, and when 50 mg catalyst is used the maximum yield (92%) is observed. The catalyst amount of 60 mg does not affect the yield of aromatic ketones significantly. In addition, the yield of aromatic ketones is also influence by the acetyl chloride to anisole mole ratio and is tuned from 0.5 to 1.5 with 50 mg of PS-4(10) catalyst at 80 °C (Figure 8). This study reveals that yield of aromatic ketones increases from 47 to 92% with increasing mole ratio and remained constant after further increasing mole ratio. These results provide clear evidence of a pathway to synthesize aromatic ketones through CC coupling reaction of aromatics, aryl, and alkyl acid halides, undergo Friedel–Crafts reaction. The scope of the reaction is investigated using a variety of aromatic compounds and acetyl/benzoyl chlorides under optimized reaction conditions, and the results are summarized in Table 2. The reaction between electron-releasing groups such as -OCH3, -CH3 on aromatic ring and acid halides resulted in 72 to 92% yield of corresponding aromatic ketones (Table 2, entries a-d). In addition, five membered heterocyclic compounds both furan and thiophene reacted with acid halides and produced good yields (Table 2, entries f, g). Significantly, the reaction of 4-chloro anisole with acid halide also proceeded well with 82% yield of desired aromatic ketone at ortho-position to methoxy group (Table 2, entry h). It is quite interesting to note that PS-4 catalytic system is also effective for the reaction of anisole, 1,2-dimethoxy benzene, 1,3,5-trimethoxy benzene, and 2methoxy naphthalene with bulky benzoyl halides afforded 70 to 86% yield of the corresponding product (Table 2, entries il). Significantly, the reaction of anisole and electronwithdrawing 4-fluoro-benzoyl chloride also proceeded well to furnish 89% yield of corresponding 4-fluoro-4-methoxy benzophenone (Figure S2). The above substituent effects clearly disclose that the protocol also affords useful alternative for synthesis of electron-withdrawing substituted aromatic ketones. One of the interesting features in this study is that the PS-4 catalyst exhibit higher catalytic activity with excellent regioselectivity of aromatic ketones under mild reaction conditions than that of modified zeolites, functionalized MCM-41, and supported heteropolyacids,20,27,31 which is attributed because of its high surface area, ordered porosity and acidity ascribed from SnO2 incorporation in porous SiO2 network. The above results demonstrate that PS-4 catalytic system presented direct synthesis of aromatic ketones through C-C bond formation from aromatics, aryl, and alkyl acid halides. The reusability performance of PS-4 catalyst for synthesis of aromatic ketones is depicted in Figure 9. The PS-4 catalyst is recovered from reaction mixture, washed, dried, activated and redispersed in a freshly prepared reaction solution identical to the initial run. It is noteworthy to mention that because of robustness of the PS-4 catalyst, the high yield of aromatic ketones is maintained without much loss of activity up to five reaction cycles. Note that the absence of tin metal ion in the reaction solution is confirmed by ICP analysis, which suggests


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that there is no leaching of tin metal from PS-4 catalyst occurred during the reaction. The plausible pathway involved for this process is depicted in Scheme 1. The acidic centers in PS4 catalyst facilitates for formation of acyl carbonium ion. Then, the carbonyl carbon becomes more electrophilic, which helps to produce arenium ion through nucleophilic attraction, thereby generating the corresponding aromatic ketones. 4. CONCLUSIONS In summary, for the purpose of developing mesoporous composite catalyst for green process, we have constructed ordered PS-4 catalyst with high specific surface area and tunable lare pore size. The composite catalyst is successfully empolyed for variety of aromatic compounds with acetyl/benzoyl chlorides to synthesize aromatic ketones under mild reaction conditions. In comparison with other porous and heteropolyacid catalysts, PS-4 catalyzes aromatic compounds with high yield and regioselectivity. Our results suggest that PS-4 catalysts are highly active, can be recovered and potentially resuasble. The operational simplity and environmental friendlyness of this protocol affords a useful alternative for synthesis of various aromatic ketone intermediates in speciality and fine chemical industry. ASSOCIATED CONTENT Supporting Information 1 H & 13C NMR spectra of all the products. This material is available free of charge via the Internet at http://pubs.acs.org/. ACKNOWLEDGEMENTS One of the authors K R thanks UGC-New Delhi, India for the award of the research fellowship. REFERENCE (1) Harrington, P. J.; Lodewijk, E. Twenty Years of Naproxen Technology. Org. Process Res. Dev. 1997, 1, 72-76. (2) (a) Franck, H. G. Industrial Aromatic Chemistry; Springer: Berlin 1988. (b) Horsely, J. A. Producing bulk and fine chemicals using solid acids. Chemtech 1997, 10, 45- 49. (c) Bauer, K.; Garbe, D.; Surberg, H. Common fragrance and flavor materials. WHC Vertagsgesellschaft: Weinheim 1990, 83. (3) (a) Olah, G. A. Friedel-Crafts and Related Reactions, Vol. IIV, Willey inter science, Newyork 1973. (b) Surette, J. K. D.; Green, L.; Singer, R. D. 1-Ethyl-3-methylimidazolium halogenoaluminate melts as reaction media for the Friedel–Crafts acylation of ferrocene. Chem. Commun. 1996, 2753-2754. (c) Galli, C. Acylation of arenes and heteroarenes with in-situ generated acyl trifluoroacetates. Synthesis 1979, 303-304. (d) Smyth, T. P.; Corby, B. W. Toward a clean alternative to Friedel−Crafts acylation: In-situ formation, observation, and reaction of an acyl bis(trifluoroacetyl)phosphate and related structures. J. Org. chem. 1998, 63, 8946-8951. (e) Nishimoto, Y.; Arulananda Babu, S.; Yasuda, M.; Baba, A. Esters as acylating reagent in a Friedel-Crafts reaction: Indium tribromide catalyzed acylation of arenes using dimethylchlorosilane. J. Org. Chem. 2008, 73, 9465–9468. (f) Wilkinson, M. C. “Greener” Friedel−Crafts acylations: A metal- and aalogen-free methodology. Org. lett. 2011, 13, 2232-2235. (g) Guchhait, S. K.; Kashyap, M.; Kamble, H. ZrCl4-mediated regio- and chemoselective Friedel-Crafts acylation of indole. J. Org. Chem. 2011, 76, 4753–4758.

(4) (a) Fu1rstner, A.; Voigtlander, D.; Schrader, W.; Giebel, D.; Reetz, M. T. A “hard/soft” mismatch enables catalytic Friedel−Crafts acylations. Org. Lett. 2001, 3, 417-420. (b) He, F.; Wu, H.; Chen, J.; Su, W. Unexpectedly high activity of Zn(OTf)2· 6H2O in catalytic Friedel–Crafts acylation reaction. Synth. Commun., 2008, 38, 255264. (5) (a) Ogoshi, S.; Nakashima, H.; Shimonaka, K.; Kurosawa, H. Novel role of carbon monoxide as a Lewis acid catalyst for FriedelCrafts reaction. J. Am. Chem. Soc. 2001, 123, 8626-8627. (b) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Catalytic Friedel-Crafts acylation reactions using hafnium triflate as a catalyst in lithium perchloratenitromethane. Tetrahedron Lett.., 1995, 36, 409-412. (6) Srinivas, M.; Srinivasu, P.; Bhargava, S. K.; Lakshmi Kantam, M. Direct synthesis of two-dimensional mesoporous copper silicate as an efficient catalyst for synthesis of propargylamines. Catal. Today 2013, 208, 66-71. (7) Su, F.; Zeng, J.; Bao, X.; Yu, Y.; Lee, J. Y.; Zhao, X. S. Preparation and characterization of highly ordered graphitic mesoporous carbon as a Pt catalyst support for direct methanol fuel cells. Chem. Mater. 2005, 17, 3960–3967. (8) (a) Srinivasu, P.; Islam, A.; Singh, S. P.; Han, L.; Kantam, M. L.; Bhargava, S. K. Highly efficient nanoporous graphitic carbon with tunable textural properties for dye-sensitized solar cells. J. Mater. Chem. 2012, 22, 20866-20869. (b) Srinivasu, P.; Singh, S. P.; Islam, A.; Han, L. Metal-free counter electrode for efficient dye-sensitized solar cells through high surface area and large porous carbon. Int. J. Photoenergy, 2011, Article ID 617439. (c) Chiola, V.; Ritsko, J. E.; Vanderpool, C. D. Process for producing low-bulk density silica. US Pat. 3556725, 1971. (d) Radu, D. R.; Lai, C. Y.; Wiench, J. W.; Pruski, M.; Lin, V. S. Y. Gatekeeping layer effect: A poly (lactic acid)coated mesoporous silica nanosphere-based fluorescence probe for detection of amino-containing neurotransmitters. J. Am. Chem. Soc. 2004, 126, 1640-1641. (e) Huh, S.; Chen, H. T.; Wiench, J. W.; Pruski, M.; Lin, V. S. Y. Cooperative catalysis by general acid and base bifunctionalized mesoporous silica nanospheres. Angew. Chem. Int. Ed. 2005, 44, 1826-1830. (9) Xie, Y.; Sharma, K. K.; Anan, A.; Wang, G.; Biradar, A. V.; Asefa, T. Efficient solid-base catalysts for aldol reaction by optimizing the density and type of organoamine groups on nanoporous silica. J. Catal. 2009, 265, 131-140. (10) Kubczyk, T. M.; Williams, S. M.; Kean, J. R.; Davies, T. E.; Taylorb, S. H.; Graham, A. E. Nanoporous aluminosilicate catalyzed Friedel–Crafts alkylation reactions of indoles with aldehydes and acetals. Green Chem. 2011, 13, 2320-2325. (11) Kugita, T.; Ezawa, M.; Owada, T.; Tomita, Y.; Namba, S.; Hashimoto, N.; Onaka, M. MCM-41 as a highly active catalyst for Diels–Alder reaction of anthracene with p-benzoquinone. Micropor. Mesopor. Mater. 2001, 44- 45, 531-536. (12) Corma, A.; Nemeth, L. T.; Renz, M.; Valencia, S. Sn-zeolite beta as a heterogeneous chemoselective catalyst for Baeyer–Villiger oxidations. Nature 2001, 412, 423-425. (13) Corma, A.; Domine, M. E.; Valencia, S. Water-resistant solid Lewis acid catalysts: Meerwein–Ponndorf–Verley and Oppenauer reactions catalyzed by tin-beta zeolite. J. Catal. 2003, 215, 294-304. (14) Matsuo, J.; Murakami, M. The Mukaiyama Aldol Reaction: 40 Years of Continuous Development. Angew. Chem. Int. Ed. 2013, 52, 9109 – 9118. (15) Dapsens, P. Y.; Mondelli, C.; Jagielski, J.; Hauert, R.; PérezRamírez, J. Hierarchical Sn-MFI zeolites prepared by facile top-down methods for sugar isomerisation. Catal. Sci. Technol. 2014, 4, 23022311. (16) (a) Serrano, D. P.; Garcia, R. A.; Otero, D. Friedel–Crafts acylation of anisole over hybrid zeolitic-mesostructured materials. Appl. catal. A: Gen. 2009, 359, 69-78. (b) Moreau, P.; Finiels, A.; Meric, P.; Fajula, F. Acetylation of 2-methoxynaphthalene in the presence of beta zeolites: influence of reaction conditions and textural properties of the catalysts. Catal. Lett. 2003, 85, 199-203. (c) Casagrande, M.; Storaro, L.; Lenarda, M.; Ganzerla, R. Highly selective Friedel–Crafts



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acylation of 2-methoxynaphthlene catalyzed by H-BEA zeolite. Appl. Catal. A: Gen. 2000, 201, 263-270. (17) Hu, R. J.; Li, B. G. Novel Solid Acid Catalyst, Bentonitesupported polytrifluoromethanesulfosiloxane for Friedel–Crafts acylation of ferrocene. Catal. Lett. 2004, 98, 43-47. (18) Hajipour, A. R.; Zarei, A.; Khazdooz, L.; Ruoho, A. E. Simple and Efficient Procedure for the Friedel–Crafts Acylation of aromatic compounds with carboxylic acids in the presence of P2O5/Al2O3 under heterogeneous conditions. Synth. Commun. 2009, 39, 2702-2722. (19) Cano, R.; Miguel, Y.; Ramon, D. J. Catalyzed addition of acid chlorides to alkynes by unmodified nano-powder magnetite: synthesis of chlorovinyl ketones, furans and related cyclopentenone derivatives, Tetrahedron. 2013, 69, 7056-7065. (20) Martínez, F.; Morales, G.; Martín, A.; Grieken, R. V. Perfluorinated Nafion-modified SBA-15 materials for catalytic acylation of anisole. Appl. Catal. A: Gen. 2008, 347, 169-178. (21) Ghiaci, M.; Kalbasi, R. J.; Mollahasani, M.; Aghaei, H. Vapor phase acylation of phenol with ethyl acetate over H3PO4/TiO2-ZrO2. Appl. Catal. A: Gen. 2007, 320, 35-42. (22) Cornelis, A.; Gerstmans, A.; Laszlo, P.; Mathy, A.; Zieba, I. Friedel-Crafts acylations with modified clays as catalysts. Catal. Lett. 1990, 6, 103-110. (23) Arata, K.; Hino, M. Benzoylation of toluene with benzoyl chloride and benzoic anhydride catalyzed by solid superacid of sulfatedsupported alumina. Appl. Catal. 1990, 59, 197-204. (24) Arata, K.; Nakamura, M.; Shouji, M. Friedel-Crafts acylation of toluene catalyzed by solid superacids. J. Mol. Catal. A: Chem. 2004, 207, 51-57. (25) Matsuhashi, H.; Miyazaki, H.; Kawamura, Y.; Nakamura, H.; Arata, K. Preparation of a solid superacid of sulfated tin oxide with acidity higher than that of sulfated zirconia and its applications to Aldol condensation and benzoylation. Chem. Mater. 2001, 13, 30383042. (26) De Castro, C.; Primo, J.; Corma, A. Heteropolyacids and largepore zeolites as catalysts in acylation reactions using α, β-unsaturated organic acids as acylating agents, J. Mol. Catal. A: Chem. 1998, 134, 215-222. (27) Wine, G.; Tessonnier, J. P.; Pham-Huu, C.; Ledoux, M. J. Beta zeolite supported on a macroscopic pre-shaped SiC as a high performance catalyst for liquid-phase benzoylation. Chem. Commun. 2002, 2418-2419. (28) (a) Lenza, R. F. S.; Vasconcelos, W. L. Preparation of Silica by Sol-Gel Method Using Formamide. Mat. Res. 2001, 4, 189-194. (b) Farrukh, M. A.; Heng, B. T.; Adnan, R. Surfactant-controlled aqueous synthesis of SnO2 nanoparticles via the hydrothermal and conventional heating methods. Turk. J. Chem. 2010, 34, 537-550. (c) Acarbas¸ O.; Suvac, E.; Dogan, A. Preparation of nanosized tin oxide (SnO2) powder by homogeneous precipitation. Ceram. Int. 2007, 33, 537542. (29) (a) Wark, M.; Rohlfing, Y.; Altindag, Y.; Wellmann, H. Optical gas sensing by semiconductor nanoparticles or organic dye molecules hosted in the pores of mesoporous siliceous MCM-41. Phys. Chem. Chem. Phys. 2003, 5, 5188-5194. (b) Liu, Z. C.; Chen, H. R.; Huang, W. M.; Gu, J. L.; Bu, W. B.; Hua, Z. L.; Shi, J. L. Synthesis of a new SnO2/mesoporous silica composite with room-temperature photoluminescence. Micropor. Mesopor. Mater. 2006, 89, 270-275. (30) (a) Corma, A. Inorganic solid acids and their use in acidcatalyzed hydrocarbon reactions. Chem. Rev. 1995, 95, 559-614. (b) Juan, J. C.; Zhang, J.; Yarmo, M. A. Structure and reactivity of silica-supported zirconium sulfate for esterification of fatty acid under solvent-free condition. Appl. Catal. A: Gen. 2007, 332, 209-215. (31) Cardoso, L. A. M.; Alves. Jr. W.; Gonzaga, A. R. E.; Aguiar, L. M. G.; Andrade, H. M. C. Friedel–Crafts acylation of anisole with acetic anhydride over silica-supported heteropolyphosphotungstic acid (HPW/SiO2). J. Mol. Catal. A: Chem. 2004, 209, 189-197.


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Abstract SnO2-SiO2 Mesoporous Composite: A Very Active Catalyst for Regioselective Synthesis of Aromatic Ketones with Unusual Catalytic Behavior K. Raveendranath Reddy,† D. Venkanna,† M. Lakshmi Kantam,† Suresh K. Bhargava,‡ and Pavuluri Srinivasu*,†

100 nm

Aromatic ketones (R-Ar-CO-R) have been prepared directly through C-C bond formation using aromatics, aryl, and alkyl acid halides to undergo Friedel–Crafts reaction over reusable and catalytically active ordered SnO2-SiO2 three-dimensional mesoporous composite (PS-4) catalyst, which found to be superior to modified zeolites, functionalized MCM-41 and supported heteropolyacid catalysts.


SnO2âSiO2 Mesoporous Composite: A Very Active Catalyst for

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