Catalysis Communications 11 (2010) 1109–1115

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Catalysis Communications

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Preparation and characterization of P4MVPMnO4/SBA-15 as an efficientheterogeneous oxidant: An organic–inorganic hybrid polymer

Roozbeh Javad Kalbasi ⁎, Majid Kolahdoozan ⁎, Keinaz Shahabian, Farzad ZamaniDepartment of Chemistry, Islamic Azad University, Shahreza Branch, 311-86145, Shahreza, Isfahan, Iran

⁎ Corresponding authors. Tel.: +98 321 3292072; faxE-mail addresses: rkalbasi@iaush.ac.ir (R.J. Kalbasi),

(M. Kolahdoozan).

1566-7367/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.catcom.2010.05.020

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 April 2010Received in revised form 24 May 2010Accepted 28 May 2010Available online xxxx

Keywords:Organic–inorganic hybrid polymerHeterogeneous oxidantKMnO4

SBA-15Solvent-less oxidation

This work is concerned about the preparation and characterization of MnO4− supported poly (4-methyl

vinylpyridinium)/SBA-15 which was effectively employed as a heterogeneous oxidant for oxidation ofaromatic alcohols. P4MVPMnO4/SBA-15 exhibited excellent activity and selectivity under mild and solvent-less conditions.

: +98 321 3293095.kolahdoozan@iaush.ac.ir

l rights reserved.

© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Hybrid organic–inorganic polymers had attracted considerableinterest because of their unique properties. These materials combinesome advantages of polymer compounds (easy processing withconventional techniques, elasticity and organic functionalities) withproperties of inorganic oxides (hardness, thermal and chemicalstability, and transparency). Thus, the syntheses of hybrid organic–inorganic polymers with new framework structures are highlydesirable [1–7].

Functional polymers are specified as very efficient catalystsupports, since they provide the stabilizing steric bulk of theirframework and several binding sites for simultaneous interactionswith the particles and the substrates [8]. Poly (4-vinylpyridine)(P4VP) is particularly attractive because of the strong affinity of thepyridyl group for metallic nanoparticles and because of its ability forinteracting with polar species through hydrogen bonding. Moreover,P4VP could be quaternizedwith different kinds of alkyl halides and actas a catalyst with high catalytic activity in organic reactions [9].

Adsorption onto solid supports is known as a cause for change inthe chemical properties of many reagents and the selectivity andreactivity in various reactions [10,11]. Well-known oxidant, potassi-

um permanganate is one of the most striking examples of such achange in chemical activity that has been reported [12]. Permanga-nate has beenwidely used as a strong, easily handled, readily availableand versatile oxidant that reacts with alcohols, alkenes, aldehydes,saturated C–H bonds and other functionalities [10,13–16].

In continuation of our study to develop new organic-inorganichybrids, we found that the poly (4-methyl vinylpyridinium iodide)/SBA-15 is an excellent candidate for iodide exchange with perman-ganate in order to prepare a heterogeneous oxidant (P4MVPMnO4/SBA-15) using the shakingmethod. Herein, wewill introduce a simpleand eco-environmental friendly catalyst for the effective conversionof aromatic alcohols to their corresponding aldehyde or ketonederivatives under mild and heterogeneous conditions.

2. Experimental method

2.1. Catalyst characterization

The BET specific surface areas and BJH pore size distribution of thesamples were determined by adsorption–desorption of nitrogen atliquid nitrogen temperature, using a Series BEL SORP 18. The X-raypowder diffraction (XRD) of the catalysts was carried out on a BrukerD8Advance X-ray diffractometer using nickel filtered Cu Kα radiationat 40 kV and 20 mA. Moreover, the samples were analyzed by FT-IRspectroscopy (using a Nicolet 400D in KBr matrix in the range of4000–400 cm−1). Scanning electron microscope (SEM) studies wereperformed on Philips, XL30, SE detector and themanganese content of

Fig. 1. XRD powder patterns of the calcinated samples: (a) mesoporous silica SBA-15,(b) P4VP/SBA-15 and (c) P4MVPMnO4/SBA-15.

1110 R.J. Kalbasi et al. / Catalysis Communications 11 (2010) 1109–1115

the catalysts was estimated by atomic absorption spectrometer (AAS)(Perkin-Elmer, AAnalyst 300).

2.2. Catalyst preparation

Mesoporous silica SBA-15 was prepared through the addition ofH3PO4 as described in the literature recently [17].

P4MVPMnO4/SBA-15 composite was synthesized as the following:At first, into a 50 mL round-bottomed flask 4-vinyl pyridine (2 mL,

0.019 mol), benzoylperoxide (0.132 g), SBA-15 (2 g) and THF (20 mL)were added. The solution was stirred with magnetic stirrer andrefluxed for 6 h at 65 °C. Then the solution was filtered and washedwith THF (2×10 mL). The white precipitate was dried in air overnightto yield 3.4 g of poly 4-vinylpyridine/SBA-15 (P4VP/SBA-15).

In the second step, the obtained P4VP/SBA-15, CH3I (2.9 mL) andCH2Cl2 (20 mL) were added to a 50 mL round-bottomed flask. Thesolution was stirred with magnetic stirrer and refluxed for 6 h at40 °C. This mixture was filtered and washed with CH2Cl2 (2×10 mL)and the yellow precipitate was dried in air to yield 4.2 g of poly 4-methyl vinylpyridinium iodide/SBA-15 (P4MVPI/SBA-15). Theamount of iodide in P4MVPI/SBA-15 was determined by ICP-MS(inductively coupled plasma mass spectrometry). Iodide content ofP4MVPI/SBA-15 was 8 mmol g−1.

In the third step, a series of solutionswith varying KMnO4 amounts(1.13 g to 8.77 g of KMnO4 in 20 mL H2O) was added to the obtainedP4MVPI/SBA-15 at room temperature. Themixture was stirred for 2 h.Then it was filtered and washed sequentially with deionized water toremove excess MnO4

− and dried in 50 °C to yield P4MVPMnO4/SBA-15composite. The procedure for prepare P4MVPMnO4/SBA-15 is given inScheme 1.

In order to specify the amount of MnO4−, the known amount of the

catalysts was decomposed by perchloric acid, nitric acid, fluoric acidand hydrochloric acid. Then the manganese content was estimated byatomic absorption spectrometer.

2.3. General procedure for oxidation of aromatic alcohols

A typical oxidation of aromatic alcohols was performed as thefollowing: 1 mmol (0.1 ml) of benzyl alcohol (or another alcohol) and0.12 g of the oxidant catalyst (P4MVPMnO4/SBA-15) were added to10 mL round-bottomed flask. Then, the mixture was stirred undernitrogen atmosphere at 80 °C. The progress of reaction wasmonitoredby Thin Layer Chromatography (TLC). After Completion of thereaction, for the reaction work-up, the catalyst was removed fromthe reaction mixture by the filtration, so the products and theunconverted reactants were analyzed by gas chromatography andcolumn chromatography.

The products were identified with 1H NMR, 13C NMR and FT-IRspectroscopy techniques. Quantitative analyses were conducted with

Scheme 1. Synthesis of P

an Agilent 6820 GC equipped with a FID detector with the internalstandard method. Isolated yield was obtained by using columnchromatography, together with GC yield.

3. Results and discussion

3.1. Catalyst characterization

Powder X-ray diffraction patterns of mesoporous silica SBA-15,P4VP/SBA-15 and P4MVPMnO4/SBA-15 samples are shown in Fig. 1.The samples showed a typical mesoporous structure with three sharppeaks, including one strong peak (100) and twoweak peaks (110) and(200) at 2θ ranging between 0.5° and 3°, corresponding to a highlyordered hexagonal mesoporous silica framework [18]. TheP4MVPMnO4/SBA-15 sample showed the same pattern, indicatingthat the long-range order of the SBA-15 framework was well retainedafter the immobilization. However, it was observed that the intensityof these characteristic diffraction peaks decreases slightly in theP4MVPMnO4/SBA-15 as compared with pure mesoporous silica SBA-15, which was probably due to the presence of guest moieties ontothe mesoporous framework of SBA-15, resulting in the decrease ofcrystallinity.

The FT-IR spectra of mesoporous silica SBA-15, P4VP, P4VP/SBA-15,P4MVPI/SBA-15 and P4MVPMnO4/SBA-15 with varying MnO4 contentwas shown in Fig. 2. The characteristic band at 1050–1080 cm−1 wasdue to the Si–O stretching in Si–O–Si structure, which was seen in allsamples. In the spectrum of P4VP/SBA-15, the band appeared at

4MVPMnO4/SBA-15.

Fig. 2. FTIR spectra of (a) mesoporous silica SBA-15, (b) P4VP, (c) P4VP/SBA-15,(d) P4MVPI/SBA-15, (e) P4MVPMnO4(21.2%)/SBA-15, (f) P4MVPMnO4(35.58%)/SBA-15,(g) P4MVPMnO4(45.45%)/SBA-15, (h) P4MVPMnO4(52.65%)/SBA-15, (i) P4MVPMnO4

(58.16%)/SBA-15, (j) P4MVPMnO4(63.47%)/SBA-15 and (k) P4MVPMnO4(67.61%)/SBA-15.

1111R.J. Kalbasi et al. / Catalysis Communications 11 (2010) 1109–1115

1602 cm−1was the stretching vibration absorptionof C–Nbond and thebands at 1558, 1496 and 1415 cm−1 were attributed to the stretchingvibration absorption of C=C bond [19,20]. In the spectra of P4MVPI/SBA-15 and P4MVPMnO4/SBA-15, a peak at 1640 cm−1 was ascribed tothe C–N(CH3-pyridinium)bondabsorption. This observation confirmed

Table 1Surface data of MnO4-supported poly (4-methyl vinylpyridine)/SBA-15.

Sample BET surface area(m2 g−1)

Pore volume(cm3 g−1)

Pore diameter(nm)

Mesoporous silica SBA-15 1430 1.9 9.9P4VP/SBA-15 1180 1.51 9.42P4MVPMnO4(63.47%)/SBA-15 807 1.03 8.89

the N-alkylation of pyridine ring. The broad bands located at 515 to750 cm−1 can be ascribed to the Mn–O and Mn–O–Mn vibrations ofMnO4, respectively [21,22].

The specific area and the pore size of mesoporous silica SBA-15,P4VP/SBA-15 and P4MVPMnO4/SBA-15 had been calculated usingBrunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH)methods, respectively (Table 1). It was clear that P4VP/SBA-15 andP4MVPMnO4/SBA-15 exhibit a smaller specific area, pore size andvolume in comparison with those of pure SBA-15, which might bedue to the presence of polymer on the surface of the SBA-15 [17].Although these textural properties were smaller than those foundfor mesoporous silica SBA-15, P4MVPMnO4/SBA-15 had still meso-porous form and did not block the pores of the SBA-15, therefore, itwas suitable to act as an oxidant catalyst in oxidation reaction.

Fig. 3 gave the scanning electron microscopy (SEM) photographsof SBA-15, P4VP/SBA-15 and P4MVPMnO4/SBA-15 composite. It wasobvious that before hybridization the surface of SBA-15 wassomewhat coarse and irregular, whereas after hybridization withP4VP, the surface of SBA-15 becomes more smooth (Fig. 3.b). Inaddition, Fig. 3.c shows some changes in the surface of catalyst afterthe quaternization of pyridine group and exchange of iodide ion withMnO4

−.

3.2. Effect of reaction conditions on the benzyl alcohol oxidation

The oxidation of benzyl alcohol was chosen as a model reaction totest the catalytic activity of the poly (4-methyl vinylpyridiniumpermanganate)/SBA-15 for oxidation of alcohols.

The oxidation of 0.4 mmol benzyl alcohol was carried out withseveral common organic solvents using 0.12 g of the catalyst(Table 2). As can be seen, toluene and 1,2-dichloromethane werenot suitable solvents for this catalytic system, because their polaritywere not enough high.Water as solvent was weakly active and gainedno yield and selectivity. The mass transfer is probably retardedbecause water may form a film layer on the catalyst surface, and thusthe possibility of benzyl alcohol diffusing to active sites was reduced[23,24]. On the other hand, by using acetonitrile and also THF as thereaction solvent, the catalyst led to the good yield and selectivityduring the oxidative reaction, among which acetonitrile was the bestone with 100% selectivity at 80% yield. It was likely that the catalystremains coated by aprotic solvent and benzyl alcohol and benzalde-hyde diffused better through aprotic solvent than through water.Interestingly, as can be seen, the solvent-free reaction gave 82% yieldwith 100% selectivity to benzaldehyde. So, the solvent-free conditionwas chosen in other experiments.

Effect of reaction temperature on the progress of benzyl alcoholoxidation was studied in the temperature range of 25–80 °C byemploying 0.12 g of the catalyst for oxidation of 0.4 mmol benzylalcohol at solvent-free condition. The percentage of yield increasedfrom 48% to 82% with the increase in temperature from 25 °C to 80 °C,without any substantial loss of reaction selectivity (100%). Thisreaction was classified as very slow reaction, kinetically controlled forwhich reaction temperature influences the progress of the reactionsignificantly [25].

The effect of MnO4− amount on oxidation reaction was investigated

using 0.12 g of the catalyst and 0.4 mmol of benzyl alcohol. The resultsshowed that by increasing the amount ofMnO4

−, the percentage of yieldalso was increased (Table 3). With further increase in the MnO4

−

amount, the percentage of yield remained the same. Moreover, lowor high MnO4

− content did not have any effect on the selectivity(100%). In addition, the activities of SBA-15, P4VP/SBA-15, and P4MVPI/SBA-15 as catalyst in the oxidation of benzyl alcohol were investigated.The synthesized materials did not show any activity for the oxidationof benzyl alcohol to produce benzaldehyde.

In order to study the amount of Mn leaching, wemeasured amountof Mn in the solution after the reaction by Atomic Absorption. The Mn

Fig. 3. Scanning electron microscopy (SEM) photographs of (a) SBA-15, (b) P4VP/SBA-15 and (c) P4MVPMnO4(63.47%)/SBA-15.

1112 R.J. Kalbasi et al. / Catalysis Communications 11 (2010) 1109–1115

was not observed in the solution. In addition, we measured theamount of Mn on the catalyst by Atomic Absorption before and afterthe reaction. The changing in amount of Mn is attributed to theleached and used Mn. It was found that no appreciable decrease in

Table 2Effect of solvent on oxidation of benzyl alcohol over P4MVPMnO4/SBA-15.a

Solvent Yieldb (%)

CH3CN 80CH3OH 55H2O –

C7H8 10THF 77CH2Cl2 40free-Solvent c 82

a Reaction conditions: benzyl alcohol (0.4 mmol), catalyst (0.12 g, P4MVPMnO4

(45.45%)/SBA-15), reaction time=10 min, T=reflux.b GC yield.c Reaction temperature=80 °C.

Table 3Effect of MnO4

− amount on oxidation of benzyl alcohol over P4MVPMnO4/SBA-15.a

Catalyst Amount of KMnO4b

(g)Mn content(mmol g−1) c

Yieldd

(%)

P4MVPMnO4(21.2%)/SBA-15 1.13 0.59 56P4MVPMnO4(35.58%)/SBA-15 2.32 0.78 66P4MVPMnO4(45.45%)/SBA-15 3.50 1.11 82P4MVPMnO4(52.65%)/SBA-15 4.67 1.35 88P4MVPMnO4(58.16%)/SBA-15 5.84 1.67 93P4MVPMnO4(63.47%)/SBA-15 7.30 1.90 96P4MVPMnO4(67.61%)/SBA-15 8.77 1.93 96

a Reaction conditions: benzyl alcohol (0.4 mmol), catalyst (0.12 g, P4MVPMnO4/SBA-15), reaction time=10 min , solvent-free, T=80 °C.

b Used in experimental procedure.c Estimated by atomic absorption spectrometer (AAS).d GC yield.

amount of Mn was observed after first reaction. So the leaching of theMn from the surface was not seen.

The variation of catalytic activity with the amount of catalyst wasstudied using 0.4 mmol of benzyl alcohol. The values are shown inTable 4. In general, there was an upward trend of benzaldehyde yieldby raising catalyst amounts, and the selectivity remains constant(100%).

The effect of benzyl alcohol amount on the percentage of yield wasstudied by varying mole from 0.2 mmol to 2 mmol, where otherparameters were kept constant. The yield of benzaldehyde decreasedwith the increase in moles of benzyl alcohol (Table 5). Moreover, itwas observed that the sole product was benzaldehyde.

Table 4Effect of catalyst amount on oxidation of benzyl alcohol over P4MVPMnO4/SBA-15.a

Amount of catalyst (g) Yield b (%)

0.08 700.1 800.12 960.14 96

a Reaction conditions: benzyl alcohol (0.4 mmol), P4MVPMnO4(63.47%)/SBA-15,reaction time=10 min, solvent-free, T=80 °C.

b GC yield.

Table 5Effect of alcohol amount on oxidation of benzyl alcohol over P4MVPMnO4/SBA-15.a

Alcohol amount (mmol) Time (min) Yield b (%)

0.2 5 980.4 10 961 45 902 60 60

a Reaction conditions: catalyst (0.12 g, P4MVPMnO4(63.47%)/SBA-15), solvent-free,T=80 °C.

b GC yield.

Table 6Solvent-free oxidation of various aromatic alcohols over P4MVPMnO4/SBA-15.a

Entry Substrate Product Time (min) Yieldb (%)

145

90

2 30 75

3 45 70

4 45 70

5 30 75

6 90 40

7 90 35

8 60 40

9 40 80

10 30 98

11 30 94

1230

95

(continued on next page)

1113R.J. Kalbasi et al. / Catalysis Communications 11 (2010) 1109–1115

Table 6 (continued)

Entry Substrate Product Time (min) Yieldb (%)

13 40 95

14 60 80

15 60 85

16120

60

17 150 50

a Reaction conditions: alcohol (1 mmol), catalyst (0.12 g, P4MVPMnO4(63.47%)/SBA-15), solvent-free, T=80 °C.b GC yield.

1114 R.J. Kalbasi et al. / Catalysis Communications 11 (2010) 1109–1115

The reusability of the catalyst was studied by using P4MVPMnO4/SBA-15 in recycling experiments. In order to regenerate the oxidantcatalyst, after completion the reaction, it was separated by filtration,washed several times with deionized water and acetone, then driedand used it in the subsequent run. By using regenerated sample aftersix cycles, the yield just decreased by 10% and the selectivity wasconstant (100%).

3.3. Oxidation of various aromatic alcohols over P4MVPMnO4/SBA-15

The P4MVPMnO4/SBA-15 catalyst also showed good activity andselectivity in some other oxidation reactions using different kinds ofaromatic alcohols. The results were given in Table 6. In all cases, theselectivity for carbonyl compounds was 100%. The substituent effectwas observed over benzyl alcohols. As the substituent was varyingfrom electron-withdrawing (entries 2–8) to electron-donating(entries 9–13), the yield of aldehyde remarkably increased from35% to 98%. Benzohydrol and its substitute (entries 14 and 15)indicate high yield (80% and 85%) with 100% selectivity to thecorresponding ketones. Primary aromatic alcohols (entries 16 and 17)also showed reasonable yield of 60% and 50% respectively and highselectivity of 100% to the aldehyde products.

4. Conclusion

In conclusion, our studies showed that the iodide exchange withpermanganate on poly 4-methyl vinylpyridine/SBA-15 serve as highlyactive heterogeneous oxidant catalyst for the solvent-free oxidation ofbenzyl alcohol and its substituted homologues. The existence of bothorganic and inorganic phase in this composite has had the critical

effect on the catalytic activity. The merit of this methodology was thatit was simple, fast, mild, and efficient. Therefore it is believe that thesynthetic method reported here would greatly contribute to theenvironmentally greener and safer process.

Acknowledgements

The support by Islamic Azad University, Shahreza Branch (IAUSH)Research Council and Center of Excellence in Chemistry is gratefullyacknowledged.

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