Sulfate Grafted Iron Stabilized Zirconia Nanoparticles as Efficient

Article pubs.acs.org/IECR

Sulfate Grafted Iron Stabilized Zirconia Nanoparticles as Efficient Heterogenous Catalysts for Solvent-Free Synthesis of Xanthenediones under Microwave Irradiation Satish Samantaray,†,‡ Purabi Kar,† Garudadhawj Hota,† and Braja Gopal Mishra*,† †

Department of Chemistry, National Institute of Technology, Rourkela, Rourkela 769008, Odisha, India Department of Chemistry, Temple City Institute of Technology & Engineering, Khurda 752057, Odisha, India

‡

S Supporting Information *

ABSTRACT: Sulfate grafted iron stabilized zirconia nanoparticles (SO42−/xFe−Zr−O) are prepared by a coprecipitation method followed by sulfate ion grafting. The SO42−/xFe−Zr−O materials have been characterized using XRD, UV−vis, FTIR, Raman, SEM, and TEM techniques. XRD study indicated incorporation of iron ions (up to 20 mol %) into the zirconia lattice, resulting in the formation of a substitutional solid solution. The vibrational features corresponding to the SO and S−O stretching of anchored sulfate species are observed in the FTIR study. The Raman study indicated the presence of nanosize hematite and tetragonal zirconia phase in the composite oxide. The presence of iron oxide in the zirconia lattice improves the sulfate retention capacity of the host zirconia. The SO42−/xFe−Zr−O materials are found to be efficient catalysts for the synthesis of structurally diverse xanthenediones by one-pot condensation of dimedone with aryl aldehydes under solvent-free conditions and microwave irradiation.

1. INTRODUCTION Synthesis of fine and specialty chemicals involving nonpolluting and atom-efficient catalytic protocols is one of the most exciting research areas in synthetic chemistry.1−12 Recently, solid acids have been increasingly used in many fine chemical synthesis processes. Among several solid acids studied, the sulfate grafted metal oxides are the most promising catalytic materials for fine chemical synthesis.1,3,4,10−12 These materials contain strong acidic sites on their surfaces often termed as “superacidic” which are capable of catalyzing carbonium ion reactions under mild conditions.1,3 The relatively simple method of preparation of sulfated metal oxides catalysts makes them one of the attractive classes of heterogeneous catalysts. Ardizzone et al. have studied the acidic sites over the surface of sulfate zirconia by X-ray photoelectron spectroscopy (XPS) for samples prepared by hydrothermal and sol−gel methods. The structure crystallinity of the zirconia precursor and the presence of bidentate zirconium−sulfate surface complex strongly influences the amount and strength of the acidic sites.13 The nature of acidic sites on sulfated metal oxides has also been studied using DRIFT spectroscopy of adsorbed pyridine molecules in conjugation with density functional calculations. The sulfated metal oxides contain both Lewis and Brønsted acidic sites, the relative population of which depends on the degree of hydroxylation of the surface.14An alternative model involving the redox properties of sulfated zirconia and transition metal doped sulfated zirconia has also been proposed to explain their catalytic activities for n-butane isomerization reaction.15 The sulfated metal oxides have been found to catalyze a number of fine chemical synthesis processes under mild conditions compared to other conventional catalyst materials. Sulfated metal oxides such as sulfated zirconia have been used as catalysts for the synthesis of dihydroprimidones, bis© 2013 American Chemical Society

(indolylmethane), aspirin, Friedel−Crafts acylation, esterification of acids with alcohols, and protection of carbonyl compounds.3,12,16−19 The acidic strength of sulfated zirconia depends on parameters such as the preparation conditions, sulfate density, amount of surface exposed, and nature of crystalline phases of ZrO2.11,20 The sulfate retention capacity, surface area, and the number of active sties on the sulfated zirconia can be enhanced by preparing transition metal doped zirconia and subsequent sulfate grafting or by supporting a small amount of noble metals on the sulfated zirconia. The incorporation of transition metal ions such as Al, Mo, Cu, Fe, Co, and Cr into the zirconia lattice enhances the catalytic activity and stability of the host sulfated metal oxide.20 Jentoft et al. have studied the thermal and mechanical stability of sulfated zirconia particles under different conditions of storage. It has been observed that the sulfated zirconia catalyst undergoes phase transformation upon thermal or mechanical treatment or adsorption of water, resulting in loss of activity. The presence of Fe and Mn as promoters stabilizes the tetragonal phase, making promoted catalysts much more stable during storage or treatment.21Although there are reports on the preparation, characterization, and catalytic application of sulfated metal oxides, there is a lot of scope to explore the application of this important class of materials as catalysts for the synthesis of biologically relevant molecules. In continuation of our interest to explore novel catalytic applications of surface and structurally modified zirconia, 2,5−8 in the present investigation we have synthesized SO42−/Fe2O3−ZrO2 materiReceived: Revised: Accepted: Published: 5862

December 31, 2012 March 19, 2013 April 8, 2013 April 8, 2013 dx.doi.org/10.1021/ie303648b | Ind. Eng. Chem. Res. 2013, 52, 5862−5870

Industrial & Engineering Chemistry Research

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material in 150 mL of 0.5 M sulfuric acid and stirring the aqueous suspension for 24 h. The solid particles were subsequently filtered and washed with 0.05 M sulfuric acid (20 mL portions three times) and calcined at 500 °C for 2 h to obtain the SO42−/xFe−Zr−O materials. 2.3. Characterization Techniques. The XRD patterns of the pure ZrO2, xFe−Zr−O, and SO42−/xFe−Zr−O materials were recorded using a Philips PAN analytical diffractometer using Ni filtered Cu Kα1 (λ = 1.5405 Å) radiation in the range 20−80° at a scan rate of 2 deg/min. The FTIR spectra of SO42−/xFe−Zr−O composite oxides were obtained using a Perkin-Elmer FTIR spectrophotometer with KBr pellets. The spectra from UV−vis diffuse reflectance spectroscopy (DRS) of the synthesized materials were recorded using a Model 2450 Shimadzu spectrometer with a BaSO4 coated integration sphere. Confocal micro-Raman spectra were recorded on a Horiba Jobin-Yvon LabRam HR spectrometer using a 17 mW internal He−Ne laser source with an excitation wavelength of 632.8 nm. Scanning electron micrographs (SEM) were taken using a JEOL JSM-6480 LV microscope (acceleration voltage 20 kV). The sample powders were deposited on a carbon tape before mounting on a sample holder. Transmission electron micrographs (TEM) of the samples were recorded using PHILIPS CM 200 equipment using carbon coated copper grids. The specific surface area of the composite oxides was determined by the BET method using N2 adsorption/ desorption at 77 K on an AUTOSORB 1 Quantachrome instrument. The number of acid sites in the composite oxide materials was obtained using theromgravimetric analysis of adsorbed n-butylamine.6 The sulfate grafted composite oxide samples pretreated at 400 °C for 2 h were exposed to reagent grade n-butylamine for 48 h in a desiccator. Thermogravimetric analysis of the samples was then performed in a nitrogen atmosphere from room temperature to 550 °C at a rate of 20 °C/min. The percentage weight loss corresponding to the temperature range 250−450 °C was calculated and the acidity was obtained assuming each base molecule interacted with a single acidic site in the composite oxide. Prior to the thermogravimetric analysis the samples were flushed with nitrogen gas for 30 min at room temperature to remove the physisorbed n-butylamine molecules. Melting points were measured using a LABTRONICS LT-110 model and are uncorrected. 1H NMR spectra were recorded with a Bruker spectrometer at 400 MHz using TMS as internal standard. Reactions were monitored by thin layer chromatography (TLC) on 0.2 mm silica gel F-254 plates. All the reaction products are known compounds and are identified by comparing their physical and spectral characteristics with the literature reported values. 2.4. Synthesis of Xanthenediones. Typically, a neat mixture of 4-nitrobenzaldehyde (1 mmol), dimedone (2 mmol), and SO4−2/xFe−Zr−O (100 mg) was exposed to microwave irradiation. The reaction was carried out at 900 W for the specified time with an intermittent cooling interval of 60 s after every 60 s of microwave irradiation. The progress of the reaction was monitored by TLC. On completion of reaction, the crude product was dissolved in ethyl acetate (15 mL). The catalyst was separated by centrifugation at 4000 rpm for 15 min. The final product was obtained by evaporating the excess solvent in a vacuum and upon recrystallization from ethanol.

als by a two-step process involving coprecipitation followed by sulfation. The synthesized materials are characterized using Xray diffraction (XRD), UV spectrosopy, Fourier transform infrared spetroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analytical techniques. The catalytic activities of these materials have been studied for the environmentally benign synthesis of xanthenediones under solvent-free conditions using microwaves as the energy source. Xanthenes and their derivatives such as 1,8-dioxooctahydroxanthenes (xanthenediones) are important classes of biologically active heterocyclic compounds which show potential antibacterial, anti-inflammatory, and antiviral activities.22,23 These heterocyclic molecules are also used as dyes, as fluorescent probes, and in laser technologies because of their valuable spectroscopic properties.24,25 Xanthenediones also occur as constituent units in a large number of natural products; hence they occupy a prominent position in medicinal chemistry.26 Owing to their attractive biological activity, the synthesis of this category of heterocyclic compounds has received much attention in recent years. The most efficient way of synthesizing xanthenediones involves the condensation of dimedone with aryl aldehydes in the presence of acidic catalysts. The various catalytic systems employed for this condensation reaction include, among others, Amberlyst-15, ionic liquids, sodium hydrogen sulfate, polyaniline-p-tolulenesulfonate salt, Fe3+−montmorillonite, HClO4−SiO2, PPA− SiO2, ZrOCl2·8H2O, and H3PW12O40/MCM-41.27−31Most of the catalysts studied so far are homogeneous catalysts or supported catalysts or polymers which suffer from drawbacks such as longer reaction time, harsh reaction conditions, toxic solvents, deactivation, and handling of the catalyst. In this investigation, we have evaluated the catalytic activity of SO42−/ xFe−Zr−O materials for the synthesis of xanthenediones by condensation of dimedone and aryl aldehydes under solventfree conditions using microwaves as the energy source.

2. MATERIALS AND METHODS 2.1. Preparation of Fe2O3(x mol %)−ZrO2 Nanocomposite Oxide. The Fe2O3−ZrO2 catalysts were prepared by a coprecipitation method using zirconium oxychloride (ZrOCl2·8H2O) and iron nitrate (Fe(NO3)3·9H2O) (SD Fine Chemicals, India, 99.9%) as precursor salts and liquid ammonia as the precipitating agent. Initially, 200 mL of double distilled water was adjusted to pH 9.0 by addition of liquid ammonia. To this solution the required amount of precursor salt solution was added dropwise (20 mL/h) under constant stirring. The pH of the solution was continuously monitored and maintained at the same pH by dropwise addition of ammonia solution. After completion of the precipitation process, the aqueous mixture was allowed to stir for 12 h followed by filtration and multiple washing in double distilled water (until Cl− free). The coprecipitated material was dried at 120 °C for 12 h in a hot air oven and calcined at 500 °C for 2 h to obtain the Fe2O3− ZrO2composite catalyst. Using this procedure, Fe2O3−ZrO2 catalysts with Fe2O3 contents of 2, 5, 10, 20, and 50 mol % were prepared. The Fe2O3−ZrO2 catalysts are referred to as xFe− Zr−O in the text, where x represents the mole percent of Fe2O3 present in the composite oxide. 2.2. Preparation of Sulfate Grafted Fe2O3(x mol %)− ZrO2 Catalysts (SO42−/xFe−Zr−O). The sulfate grafted Fe2O3(x mol %)−ZrO2(SO42−/xFe−Zr−O) material was prepared by suspending 5 g of the calcined xFe−Zr−O 5863

dx.doi.org/10.1021/ie303648b | Ind. Eng. Chem. Res. 2013, 52, 5862−5870


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Figure 3. Variation of cell volume with iron content for xFe−Zr−O nanocomposite oxides.

Figure 1. XRD patterns of (a) ZrO2, (b) 2Fe−Zr−O, (c) 5Fe−Zr−O, (d) 10Fe−Zr−O, (e) 20Fe−Zr−O, and (f) 50Fe−Zr−O.

Figure 4. XRD patterns of (a) SO42−/2Fe−Zr−O, (b) SO42−/5Fe− Zr−O, (c) SO42−/10Fe−Zr−O, (d) SO42−/20Fe−Zr−O, and (e) SO42−/50Fe−Zr−O.

(Figure 1b−f). No diffraction peaks corresponding to the presence of crystalline Fe2O3 species are observed up to 20 mol % iron oxide content in the composite oxide. However, the 50Fe−Zr−O material shows additional diffraction peaks at 2θ values of 24.2, 33.1, 35.7, 40.9, 49.4, and 54.1° corresponding to the rhombohedral α-Fe2O3 (hematite) phase in the composite oxide.32 The phase transformation behavior of zirconia has been widely studied in the literature.5,6,33−36 The selective stabilization of the tetragonal phase depends on critical crystallite size and the presence of phase stabilizer either in the bulk or at the zirconia surface.5,33,34 The tetragonal phase of zirconia is stabilized effectively in the presence of aliovalent impurity ions in the zirconia lattice.35,36 The presence of aliovalent dopants such as Fe3+ ions induces oxygen ion vacancy in the crystal lattice of zirconia, which in turn helps in the stabilization of the tetragonal phase. For oversized dopants, the oxygen vacancy resides near the Zr ion, whereas for undersized dopants, both ions compete for the oxygen vacancies, resulting in 6-fold oxygen coordination and a large distortion of the

Figure 2. XRD patterns indicating a gradual shift to higher 2θ value for the (111) peak of tetragonal zirconia phase with iron oxide content: (a) ZrO2, (b) 2Fe−Zr−O, (c) 5Fe−Zr−O, (d) 10Fe−Zr−O, (e) 20Fe−Zr−O, and (f) 50Fe−Zr−O.

3. RESULTS AND DISCUSSION 3.1. Characterization of the Sulfate Grafted Fe2O3− ZrO2 Composite Oxides. The X-ray diffraction patterns of the xFe−Zr−O composite oxides prepared by the coprecipitation method are presented in Figure 1. Pure zirconia prepared by precipitation shows characteristic reflections at 2θ values of 24.3, 28.3, 31.5, 34.9, and 50.4° corresponding to the presence of a mixture of monoclinic and tetragonal phases (Figure 1a). The percentage tetragonal phase present in the zirconia sample is 58% calculated using Toroya’s method.6 The iron doped zirconia materials, on the other hand, show reflections corresponding to the presence of tetragonal zirconia only 5864



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Figure 5. Fourier line profile analysis plot for SO42−/xFe−Zr−O materials: (−•−) SO42−/2Fe−Zr−O, (−▲−) SO42−/5Fe−Zr−O, (−▼−) SO42−/ 10Fe−Zr−O, (−◆−) SO42−/20Fe−Zr−O, and (−■−) SO42−/ZrO2.

Figure 7. UV−vis spectra of (a) SO42−/ZrO2, (b) SO42−/2Fe−Zr−O, (c) SO42−/5Fe−Zr−O, (d) SO42−/10Fe−Zr−O (e) SO42−/20Fe− Zr−O, and (f) SO42−/50Fe−Zr−O.

to the contraction in the lattice that occurred due to substitution of Zr4+ ions by Fe3+ ions in the zirconia lattice. Iron oxide is known to form a substitutional type solid solution with zirconia.33,35,36 Fe3+ ions (0.65 Å) being smaller in size compared to Zr4+ ions (0.79 Å), the substitution of Fe3+ ions results in shrinkage of the lattice. Figure 4 shows the XRD patterns of the sulfate grafted FeZr materials (SO42−/xFe−Zr− O). All the materials show the diffraction peaks corresponding to the presence of the tetragonal phase of the host. There is no apparent change in the peak position and intensity as a result of grafting of sulfate ions. The microstructural parameters of the sulfate grafted Fe−Zr−O nanocomposite oxides are calculated using the Fourier transformation of the broadened XRD profiles following the Warren and Averbach method37 using the software BREADTH, the details of which are available in the literature.38 The calculated volume-weighted distributions (PV) as a function of the Fourier length (L) for the SO42−/xFe−Zr−

Figure 6. FTIR spectra of (a) SO42−/ZrO2, (b) SO42−/2Fe−Zr−O, (c) SO42−/5Fe−Zr−O, (d) SO42−/10Fe−Zr−O, (e) SO42−/20Fe− Zr−O, and (f) SO42−/50Fe−Zr−O.

surrounding next nearest neighbor cation network.33,35,36 With increase in the iron oxide content in the composite oxide, the diffraction peaks of tetragonal zirconia are found to shift progressively to higher 2θ values (Figure2). The peak positions (2θ), full width at half-maximum (fwhm), have been calculated for each peak using the software peakfit, and the indexing of the peaks is carried out using POWD software. The variation in the cell volume with iron content in the composite oxide is shown in Figure 3. The cell volume is found to decrease linearly with increase in the iron content. The decrease of cell volume is due 5865



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Figure 10. Transmission electron micrograph of SO42−/10Fe−Zr−O material.

Scheme 1. One-Pot Synthesis of Xanthenediones Using SO42−/xFe−Zr−O Catalyst Figure 8. Raman spectra of (a) SO42−/2Fe−Zr−O, (b) SO42−/20Fe− Zr−O, and (c) SO42−/50Fe−Zr−O.

sulfate grafted composite oxides with low iron oxide contents (2 and 5 mol %). The plots become increasing broadened with increase in iron content in the composite oxides. The crystallite sizes of the sulfate grafted materials, calculated from the Fourier plots, are in the range 10−30 nm. An inverse correlation is observed between the crystallite size and the root-mean-square strain. The FTIR spectra of sulfate grafted xFe−Zr−O materials in the spectral region of 900−1800 cm−1 are presented in Figure6. All the sulfate grafted Fe−Zr−O samples show a prominent and broad band around 1635 cm−1. This band can be assigned to the bending vibration of the structural O−H group and the coordinated water molecules present on the surface of the sulfate grafted materials. In addition, the sulfate grafted composite oxides exhibit a series of IR bands in the frequency range 900−1450 cm−1 characteristic of the vibrational features of anchored sulfate groups.17,18,35,39 In the present study, a group of spectral bands are observed in the region of 950−1250 cm−1 along with a well-defined IR band at 1401 cm−1.The band at 1401 cm−1 can be attributed to the partially ionized SO stretching vibrations of the anchored bidentate sulfate group.35,40 In the spectral region of 950−1250 cm−1, a series of discrete peaks are observed at 990, 1050, 1140, and 1205 cm−1 which are assigned to the various vibrational modes of the S−O bonds of sulfate species connected to the zirconia surface. The FTIR spectral analysis indicates the presence of anchored bidentate sulfate species on the composite oxides with partially ionized bonds. This ionic structure of the sulfate group in the presence of adsorbed water molecules is believed to be responsible for the Brønsted acidity in sulfated zirconia catalysts.17

Figure 9. SEM images of (a) SO42−/ZrO2, (b) SO42−/2Fe−Zr−O, (c) SO42−/5Fe−Zr−O, (d) SO42−/10Fe−Zr−O, (e) SO42−/20Fe−Zr−O, and (f) SO42−/50Fe−Zr−O.

O samples are given in Figure 5. The pure sulfate zirconia shows a wide distribution function indicating the material to be polycrystalline with a broad particle size distribution. Comparable narrow distribution functions are observed for 5866



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Table 1. Physicochemical Characteristics and Catalytic Activity of SO42−/xFe−Zr−O Nanocomposite Catalysts entry

catalyst

sulfur content (wt %)

surf. area (m2/g)

acidic sitesa (mmol g−1)

time (min)

yieldb (%)

reaction ratec (mmol h−1 m−2 × 10−2)

reaction ratec (mmol h−1 g−1)

1 2 3 4 5 6

SO42−/ZrO2 SO42−/2Fe−Zr−O SO42−/5Fe−Zr−O SO42−/10Fe−Zr−O SO42−/20Fe−Zr−O SO42−/50Fe−Zr−O

1.8 2.1 2.3 3.0 2.6 2.2

51 62 73 84 75 56

0.38 0.41 0.48 0.60 0.52 0.40

20 16 15 12 14 18

72 76 79 90 84 80

4.4 4.8 4.7 5.6 5.0 4.9

21 30 35 48 38 28

a

Acidity calculated by TGA of adsorbed n-butyl amine. bRefers to pure and isolated yield. cCalculated with respect to the 4-NO2 benzaldehyde conversion in the reaction mixture analyzed using Gas chromatography

shifted as the number of oxygen ions coordinated to the Fe3+ions increases. It has also been reported that the Fe3+ present in small nonstoichiometric nanooxide clusters of the type FexOy shows a charge transfer transition in the range 300− 400 nm whereas bulk type Fe2O3 particle shows UV absorption above 450 nm.42−44 In the present study, the peak between 260 and 280 nm can be assigned to the isolated octahedral iron species. As the Fe2O3 content increases, this peak is found to be red-shifted and reappear in the range 300−400 nm. With increase in Fe2O3 content it is likely that small FexOy type nanoclusters are formed which exist in a well-dispersed state in the composite oxide matrix. For SO42−/50Fe−Zr−O composite oxides a broad band was observed at 490 nm indicating the presence of bulk type Fe2O3 particles (Figure 7f). From the UV−vis study, it can be concluded that the SO42−/xFe−Zr−O materials with low iron oxide loading contain predominantly well-dispersed isolated Fe3+ species. At higher iron oxide content, the small FexOy type nanoclusters along with bulk type particles are present on the zirconia matrix. The Raman spectra of the SO42−/xFe−Zr−O materials containing 2, 20, and 50 mol % iron oxide are presented in Figure 8. Raman spectroscopy is a simple and versatile technique used for microstructural analysis of crystalline materials. The Raman technique has been effectively used to probe the existence of hematite nanostructure in iron oxide samples.45−47 Hematite belongs to the D63d crystal group and shows seven phonon lines (two A1g modes and five Eg modes) in its Raman spectrum.45,46 In the present study, the SO42−/ 2Fe−Zr−O composite material shows broad Raman bands with maxima at 148, 269, 320, 462, 613, and 642 cm −1 corresponding to the presence of tetragonal zirconia phase (Figure 8a). The additional Raman bands observed at 228 cm−1 can be assigned to the A1g mode and those at 296 and 411 cm−1 can be assigned to the Eg modes of hematite phase present in the SO42−/2Fe−Zr−O material. All the assigned Raman bands match well with the literature reported values and indicate the selective stabilization of the tetragonal phase of zirconia in the composite oxide.48 With increase in iron content, the band intensity corresponding to the tetragonal phase decreases. Concurrently, the bands corresponding to the hematite phase gain intensity. In the case of SO42−/50Fe−Zr−O all the phonon lines which are diagnostics of hematite phase are only observed in the Raman spectra (Figure 8c).45 The other notable feature of the Raman spectra of the hematite phase has been the asymmetric broadening of the peaks and their appearance at higher wavenumbers for SO42−/2Fe−Zr−O compared to SO42−/20Fe−Zr−O and SO42−/50Fe−Zr−O materials. For example, the Eg phonon line observed at 292 cm−1 for SO42−/50Fe−Zr−O is blue-shifted to 296 cm−1 for SO42−/2Fe−Zr−O material. The blue shifting of the band

Figure 11. Effect of (I) microwave power and (II) catalyst amount on the yield and reaction time of 9-(4-nitrophenyl)-3,4,6,7-tetrahydro3,3,6,6-tetramethyl-2H-xanthene-1,8(5H,9H)-dione evaluated using SO42−/10Fe−Zr−O catalyst.

The UV−vis DRS spectra of SO42−/xFe−Zr−O materials with different Fe2O3 contents are presented in Figure7. Pure sulfated ZrO2 shows a sharp and intense band at 214 nm with an absorption edge around 300 nm. ZrO2 is a direct band gap insulator which shows an interband transition in the UV region of the spectrum. The monoclinic form of ZrO2 has two direct interband transitions at 5.93 and 5.17 eV, whereas the tetragonal form has a band gap of 5.1 eV.41 In the present case the peak at 214 nm can be assigned to the O2− → Zr4+ charge transfer transition arising from the host zirconia matrix (Figure 7a). The presence of Fe2O3 in the zirconia matrix significantly modifies the UV absorption feature of the zirconium dioxide. The SO42−/xFe−Zr−O materials with low Fe2O3 content (2 and 5 mol %) show a prominent band in the range 260−280 nm (Figure 7b,c). This band can be assigned to isolated octahedral Fe3+ species anchored to the zirconia surface. Iron in the Fe3+ state exhibits two ligand to metal charge transfer (LMCT) transitions, corresponding to the t1 → t2 and t1 → e electronic transitions.42−44 However, depending upon the coordination environment of the Fe3+ species, these transitions differ widely in energies and appear in different regions of the spectrum. Ferric ion in an isolated state shows UV absorption features with peaks below 300 nm. For example, Fe3+ ions isomorphously substituted in the silicate framework show two peaks at 215 and 241 nm.43 Similarly, Fe3+ in isolated octahedral state shows LMCT transitions around 280 nm in Fe3+ doped alumina sample.42 Thus the CT bands are red5867



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Table 2. SO42−/10Fe−Zr−O Catalyzed Synthesis of Xanthenediones under Solvent-Free Condition and Microwave Irradiation

low iron oxide content samples. This observation corroborates the UV−vis study. The Raman analysis of the SO42−/xFe−Zr− O samples clearly indicates the presence of nanosize tetragonal zirconia and hematite phases in the composite oxides. Scanning electron micrographs of SO4 2−/xFe−Zr−O materials are shown in Figure 9. The pure sulfated zirconia shows agglomerated particles of irregular shape and size (Figure 9a). Addition of iron species to the sulfated zirconia matrix marginally changes the morphology of the sulfated zirconia. At low iron content, the material appears to possess a nonhomogeneous distribution in shape and size. With increasing iron content, the morphology of the particle changes from irregular to spherical-like shape (Figure 9 d−f). The transmission electron micrograph of SO42−/10Fe−Zr−O material is shown in Figure 10. The electron micrograph indicates the presence of 20−40 nm size particles of irregular shape. The particles are present in a highly agglomerated state. 3.2. Catalytic Studies for Synthesis of Xanthenediones. The catalytic activity of SO42−/xFe−Zr−O catalyst is evaluated for the synthesis of xanthenediones by one-pot multicomponent condensation of dimedone and aromatic aldehydes (Scheme 1). Initially, the condensation reaction of dimedone (2 mmol) and 4-nitrobenzaldehyde (1 mmol) is taken as a model reaction and reaction parameters such as catalyst composition, catalyst amount, microwave power, and reaction stoichiometry are varied to obtain the optimized protocol. Table 1shows the catalytic activity of sulfate grafted zirconia based nanocomposite oxides having different iron contents. It can be observed that, under the identical reaction conditions, the SO42−/10Fe−Zr−O nanocomposite oxide shows the highest catalytic activity in a short reaction time span. This catalyst also displays high surface area, more acidic sites, and the highest percent of sulfur retaining capacity on the surface determined from energy dispersive X-ray spectroscopic analysis. The catalytic activities of the sulfated Fe−Zr−O materials are found to correlate well with the sulfate content and surface acidity of the composite oxide (Table 1). As described by Arata and Hino, the sulfate ions act as bidentate ligands and coordinate to the surface of the metal oxide. The surface metal ions which are coordinated to the sulfate species act as Lewis acidic sites, whereas the coordinated water molecules are responsible for generation of Brønsted acidity.50 In the present study, the observation of an increase in the sulfate retention capacity in the presence of iron oxide is responsible for the enhancement in the number of acidic sites of the composite oxide which is reflected in the higher catalytic activity of the sulfate grafted composite oxide. A comparison of the catalytic activity of the composite oxides in terms of the reaction rate indicated that the SO42−/10Fe−Zr−O material was superior compared to other catalysts (Table 1). Hence, the SO42−/10Fe−Zr−O catalyst is chosen for further catalytic experiments in the present study. In order to study the effect of microwave power on the yield of the model reaction, the microwave power is varied between 360 and 900 W (Figure 11, panel I). It has been observed that, at higher irradiation power (900 W), the reaction time is considerably shortened and the yield of the product is improved. Thus, we have fixed the microwave power at 900 W for further reaction. Further, the catalyst amount in the reaction mixture is varied in the range 50−100 mg for reaction involving 1 mmol of aryl aldehyde (Figure 11, panel II). It is observed that, at low catalyst amount (50 mg), the time taken for completion of the reaction is high and the yield is less. For reactions involving 75 and 100 mg of

a

All the reactions were carried out using aromatic aldehyde 1 (1 mmol), 5,5-dimethyl-1,3-cyclohexanedione 2 (2 mmol), and 100 mg of SO42−/10Fe−Zr−O catalyst under microwave irradiation. bThe catalyst recyclability of SO42−/10Fe−Zr−O material is studied for three consecutive cycles for synthesis of product 3f (yield: 90%, first; 88%, second; 83%, third).

maxima and the asymmetric broadening has been observed earlier for titania nanoparticles and has been ascribed to the phonon confinement effect.49 In the present study, it is likely that the hematite phase is present in a well-dispersed state in the form of nanoclusters and particles in the zirconia matrix for 5868



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(2) Kumar, D.; Mishra, B. G.; Swapna, M. S. Sulfated Zirconia Catalyzed One-Pot Benign Synthesis of 3,4-Dihydropyrimidin-2(1H)ones under Microwave Irradiation. Chem. Lett. 2006, 35, 1074. (3) Reddy, B. M.; Patil, M. K. Organic Syntheses and Transformations Catalyzed by Sulfated Zirconia. Chem. Rev. 2009, 109, 2185. (4) Melo Júnior, C. A. R.; Albuquerque, C. E. R.; Carneiro, J. S. A.; Dariva, C.; Fortuny, M.; Santos, A. F.; Egues, S. M. S.; Ramos, A. L. D. Solid Acid Catalyzed Esterification of Oleic Acid Assisted by Microwave Heating. Ind. Eng. Chem. Res. 2010, 49, 12135. (5) Samantaray, S.; Mishra, B. G. Combustion Synthesis, Characterization and Catalytic Application of MoO3-ZrO2 Nanocomposite Oxide towards One Pot Synthesis of Octahydroquinazolinones. J. Mol. Catal. A: Chem. 2011, 339, 92. (6) Samantaray, S.; Hota, G.; Mishra, B. G. Physicochemical Characterization and Catalytic Applications of MoO3-ZrO2 Composite Oxides towards One Pot Synthesis of Amidoalkyl Naphthols. Catal. Commun. 2011, 12, 1255. (7) Naik, M. A.; Mishra, B. G.; Dubey, A. Combustion Synthesized WO3−ZrO2 Nanocomposites as Catalyst for the Solvent-Free Synthesis of Coumarins. Colloids Surf., A 2008, 317, 234. (8) Samantaray, S.; Sahoo, S. K.; Mishra, B. G. Phosphomolybdic Acid Dispersed in the Micropores of Sulfate Treated Zr-Pillared Clay as Efficient Heterogeneous Catalyst for the Synthesis of β-Aminocarbonyl Compounds in Aqueous Media. J. Porous Mater. 2011, 18, 573. (9) Amali, A. J.; Rana, R. K. Trapping Pd(0) in NanoparticleAssembled Microcapsules: An Efficient and Reusable Catalyst. Chem. Commun. 2008, 4165. (10) Sowmiya, M.; Sharma, A.; Parsodkar, S.; Mishra, B. G. Nanosized Sulfated SnO2 Dispersed in the Micropores of Al-Pillared Clay as an Efficient Catalyst for the Synthesis of Some Biologically Important Molecules. Appl. Catal., A: Gen. 2007, 333, 272. (11) Mishra, M. K.; Tyagi, B.; Jasra, R. V. Effect of Synthetic Parameters on Structural, Textural, and Catalytic Properties of Nanocrystalline Sulfated Zirconia Prepared by Sol−Gel Technique. Ind. Eng. Chem. Res. 2003, 42, 5727. (12) Arata, K. Organic Syntheses Catalyzed by Superacidic Metal Oxides: Sulfated Zirconia and Related Compounds. Green Chem. 2009, 11, 1719. (13) Ardizzone, S.; Bianchi, C. L.; Signoretto, M. Zr (IV) Surface Chemical State and Acid Features of Sulphated-Zirconia Samples. Appl. Surf. Sci. 1998, 136, 213. (14) Raj, K. J. A.; Prakash, M. G.; Shanmugam, R.; Krishnamurthy, K. R.; Viswanathan, B. Surface Acidic Properties of Sulphated Fe2O3TiO2. Indian J. Chem. A 2011, 50A, 1050. (15) Vera, C. R.; Yori, J. C.; Parera, J. M. Redox Properties and Catalytic Activity of SO42−-ZrO2 Catalysts for n-Butane Isomerization. Role of Transition Metal Cation Promoters. Appl. Catal., A 1998, 167, 75. (16) Khder, A. S.; El-Sharkawy, E. A.; El-Hakam, S. A.; Ahmed, A. I. Surface Characterization and Catalytic Activity of Sulfated Tin Oxide Catalyst. Catal. Commun. 2008, 9, 769. (17) Tyagi, B.; Mishra, M. K.; Jasra, R. V. Solvent Free Synthesis of Acetyl Salicylic Acid over Nano-crystalline Sulfated Zirconia Solid Acid Catalyst. J. Mol. Catal. A: Chem. 2010, 317, 41. (18) Sinhamahapatra, A.; Sutradhar, N.; Ghosh, M.; Bajaj, H. C.; Panda, A. B. Mesoporous Sulfated Zirconia Mediated Acetalization Reactions. Appl. Catal., A: Gen. 2012, 140, 87. (19) Qi, X.; Guo, H.; Li, L. Efficient Conversion of Fructose to 5Hydroxymethylfurfural Catalyzed by Sulfated Zirconia in Ionic Liquids. Ind. Eng. Chem. Res. 2011, 50, 7985. (20) Chen, F.; Yu, S.; Dong, X.; Zhang, S. Environmentally Friendly Efficient One-Pot Electrochemical Synthesis of 2,4-Dimethylanisole by Selective Oxidation of m-Xylene in Methanol with Metals Promoted Sulfated Zirconia. Ind. Eng. Chem. Res. 2011, 50, 13650. (21) Klose-Schubert, B. S; Jentoft, R. E.; Jentoft, F. C. The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated

catalyst, the reaction time is found to be identical; however, a marginally better yield is observed in the latter case. Hence, in the present study, we have fixed the catalyst amount at 100 mg for efficient condensation of reactants. After optimizing the various parameters, in order to further validate the generality of this protocol, we have used different aryl aldehydes bearing electron-donating and -withdrawing groups in the optimized protocol. Under identical reaction conditions, all the aryl aldehydes reacted efficiently to give the corresponding xanthenediones in high yields and purities (Table 2). The para-substituted aldehydes are found to give better yields of the products compared to the ortho-substituted aldehydes because of steric hindrance in the product formation. In order to study the recyclability of the catalyst, after completion of the reaction, the catalyst is regenerated by washing with 10 mL of ethyl acetate followed by heat treatment at 450 °C for 2 h. The regenerated catalyst is used for three consecutive cycles without any significant loss in catalytic activity (product 3f; 90%, first cycle; 88%, second cycle; 83%, third cycle).

4. CONCLUSIONS In this investigation, the sulfate grafted Fe2O3−ZrO2 nanocomposite oxides prepared by coprecipitation and postsulfation steps have been demonstrated as efficient catalysts for the solvent-free synthesis of xanthenediones. The Fe3+ ions substitute for the Zr4+ ions in the zirconia lattice to form a substitutional solid solution which has been ascertained from XRD study. The presence of Fe2O3 improves the sulfate retention capacity as well as the number of surface active sites and the catalytic activities of the composite oxides. The iron oxide component is found to be present in a highly dispersed state in the form of isolated octahedral Fe3+ ions and small nonstoichiometric (FexOy) nanooxide clusters in the composite oxide. The sulfate grafted Fe2O3−ZrO2 nanocomposite oxides are highly active for the microwave assisted solvent-free synthesis of a variety of octahydroxanthenes. The synthetic protocol developed in this investigation using surface and structurally modified zirconia as catalyst is found to be advantageous in terms of simple experimentation, preclusion of toxic solvents, recyclable catalyst, and high yields and purities of the synthesized compounds.

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ASSOCIATED CONTENT

S Supporting Information *

Physical and spectral data of some selected compounds. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank the Council of Scientific and Industrial Research (CSIR), New Delhi, for financial support. REFERENCES

(1) Climent, M. J.; Corma, A.; Iborra, S. Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals. Chem. Rev. 2011, 111, 1072. 5869



Article

by the Behavior of Sulfated Zirconia Catalysts. Top. Catal. 2011, 54, 398. (22) ElAshry, E. S. H.; Awad, L. F.; Ibrahim, El. S. I.; Bdeewy, O. K. Microwave Irradiation for Accelerating the Synthesis of Acridine and Xanthene Derivatives from Dimedone. ARKIVOC 2006, 178. (23) Lambert, R. W.; Martin, J. A.; Merrett, J. H.; Parkes, K. E. B.; Thomas, G. J. Pyrimidine Nucleosides. PCT Int. Patent Appl. WO9706178, Feb 20, 1997. (24) Ahmad, M.; King, T. A.; Ko, D. K.; Cha, B. H.; Lee, J. Performance and Photostability of Xanthene and Pyrromethene Laser Dyes in Sol-Gel Phases. J. Phys. D: Appl. Phys. 2002, 35, 1473. (25) Bhowmik, B. B.; Ganguly, P. Photophysics of Xanthene Dyes in Surfactant Solution. Spectrochim. Acta, Part A 2005, 61, 1997. (26) Wang, H. K.; Morris-Natschke, S. L.; Lee, K. H. Recent Advances in the Discovery and Development of Topoisomerase Inhibitors as Antitumor Agents. Med. Res. Rev. 1997, 17, 367. (27) Das, B.; Thirupathi, P.; Reddy, K. R.; Ravikanth, B.; Nagarapu, L. An Efficient Synthesis of 1,8-Dioxo-octahydroxanthenes Using Heterogeneous Catalysts. Catal. Commun . 2007, 8, 535. (28) Kantevari, S.; Bantu, R.; Nagarapu, L. TMSCl Mediated Highly Efficient One-Pot Synthesis of Octahydroquinazolinone and 1,8Dioxo-octahydroxanthene Derivatives. ARKIVOC 2006, 136. (29) Song, G.; Wang, B.; Luo, H.; Yang, L. Fe3+-Montmorillonite as a Cost-Effective and Recyclable Solid Acidic Catalyst for the Synthesis of Xanthenediones. Catal. Commun. 2007, 8, 673. (30) Fang, D.; Gong, K.; Liu, Z. L. Synthesis of 1,8-Dioxooctahydroxanthenes Catalyzed by Acidic Ionic Liquids in Aqueous Media. Catal. Lett. 2009, 127, 291. (31) Karthikeyan, G.; Pandurangan, A. Heteropolyacid (H3PW12O40) Supported MCM-41: An Efficient Solid Acid Catalyst for the Green Synthesis of Xanthenedione Derivatives. J. Mol. Catal. A: Chem. 2009, 311, 36. (32) Wu, C.; Yin, P.; Zhu, X.; Yang, C. O.; Xie, Y. Synthesis of Hematite (α-Fe2O3) Nanorods: Diameter-Size and Shape Effects on Their Applications in Magnetism, Lithium Ion Battery, and Gas Sensors. J. Phys. Chem. B 2006, 110, 17806. (33) Figueroa, S.; Desimoni, J.; Rivas, P. C.; Cervera, M. M.; Caracoche, M. C. Hyperfine Study on Sol-Gel Derived-Hematite Doped Zirconia. Chem. Mater. 2005, 17, 3486. (34) Chang, S. M.; Doong, R. N. Chemical-Composition-Dependent Metastability of Tetragonal ZrO2 in Sol-Gel-Derived Films under Different Calcination Conditions. Chem. Mater. 2005, 17, 4837. (35) Chen, L.; Hu, J.; Richards, R. M. Catalytic Properties of Nanoscale Iron-Doped Zirconia Solid-Solution Aerogels. ChemPhysChem 2008, 9, 1069. (36) Navío, J. A.; Hidalgo, M. C.; Colón, G.; Botta, S. G.; Litter, M. I. Preparation and Physicochemical Properties of ZrO2 and Fe/ZrO2 Prepared by a Sol-Gel Technique. Langmuir 2001, 17, 202. (37) Warren, B. E.; Averbach, B. L. The Effect of Cold-Work Distortion on X-ray Patterns. J. Appl. Phys. 1950, 21, 595. (38) Balzar, D.; Ledbetter, H. Voigt-Function Modeling in Fourier Analysis of Size- and Strain-Broadened X-ray Diffraction Peaks. J. Appl. Crystallogr. 1993, 26, 97. (39) Jadhav, S. V.; Jinka, K. M.; Bajaj, H. C. Synthesis of Nopol via Prins Condensation of β-Pinene and Paraformaldehyde Catalyzed by Sulfated Zirconia. Appl. Catal., A: Gen. 2010, 390, 158. (40) Li, X.; Nagaoka, K.; Lercher, J. A. Labile Sulfates as Key Components in Active Sulfated Zirconia for n-Butane Isomerization at Low Temperatures. J. Catal. 2004, 227, 130. (41) Scheithauer, M.; Grasselli, R. K.; Knozinger, H. Genesis and Structure of WOx/ZrO2 Solid Acid Catalysts. Langmuir 1998, 14, 3019. (42) Bordiga, S.; Buzzoni, R.; Geobaldo, F.; Lamberti, C.; Giamello, E.; Zecchina, C.; Leofanti, G.; Petrini, G.; Tozzola, G.; Vlaic, G. Structure and Reactivity of Framework and Extra Framework Iron in Fe-Silicalite as Investigated by Spectroscopic and Physicochemical Methods. J. Catal. 1996, 158, 486. (43) Kumar, M. S.; Schwidder, M.; Grünert, W.; Brückner, A. On the Nature of Different Iron Sites and Their Catalytic Role in Fe-ZSM-5

DeNOx Catalysts: New Insights by a Combined EPR and UV/VIS Spectroscopic Approach. J. Catal. 2004, 227, 384. (44) Gervasini, A.; Messi, C.; Carniti, P.; Ponti, A.; Ravasio, N.; Zaccheria, F. Insight into the Properties of Fe Oxide Present in High Concentrations on Mesoporous Silica. J. Catal. 2009, 262, 224. (45) Jubb, A. M.; Allen, H. C. Vibrational Spectroscopic Characterization of Hematite, Maghemite, and Magnetite Thin Films Produced by Vapor Deposition. ACS Appl. Mater. Interfaces 2010, 2, 2804. (46) Li, S.; Zhang, H.; Wu, J.; Ma, X.; Yang, D. Shape-Control Fabrication and Characterization of the Airplane-like FeO(OH) and Fe2O3 Nanostructures. Cryst. Growth Des. 2006, 6, 351. (47) Fan, H. M.; You, G. J.; Li, Y.; Zheng, Z.; Tan, H. R.; Shen, Z. X.; Tang, S. H.; Feng, Y. P. Shape-Controlled Synthesis of SingleCrystalline Fe2O3 Hollow Nanocrystals and Their Tunable Optical Properties. J. Phys. Chem. C 2009, 113, 9928. (48) Bersani, D.; Lottici, P. P.; Ding, X. Z. Phonon Confinement Effects in the Raman Scattering by TiO2 Nanocrystals. Appl. Phys. Lett. 1998, 72, 73. (49) Spielbauer, D.; Mekhemer, G. A. H.; Bosch, E.; Knözinger, H. nButane Isomerization on Sulfated Zirconia. Deactivation and Regeneration as Studied by Raman, UV-VIS Diffuse Reflectance and ESR Spectroscopy. Catal. Lett. 1996, 36, 59. (50) Arata, K.; Hino, M. Solid Catalyst Treated with Anion XVIII. Benzoylation of Toluene with Benzoylchloride and Benzoic Anhydride Catalysed by Solid Superacid of Sulphate Supported Alumina. Appl. Catal. 1990, 59, 197.

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