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Cellulose as an e

Department of Chemistry, College of Sc

97175-615, Iran. E-mail: manaseri@birja

+98 561 2502065; Tel: +98 561 2502065

Cite this: RSC Adv., 2014, 4, 39870

Received 30th June 2014Accepted 22nd August 2014

DOI: 10.1039/c4ra06450j

www.rsc.org/advances

39870 | RSC Adv., 2014, 4, 39870–398

fficient support for Mn(salen)Cl:application for catalytic oxidation of sulfides tosulfoxides

Arezou Mohammadinezhad, Mohammad Ali Nasseri* and Mehri Salimi

Supported Mn(salen)Cl was prepared by immobilization of a homogeneous Mn(salen)Cl complex onto

cellulose and characterized by FT-IR, TGA and atomic absorption spectroscopy. This heterogeneous

catalyst is able to effectively catalyze the oxidation of aromatic sulfides in good yield under mild

conditions. The catalytic activity of Mn(salen)Cl and [Mn(salen)Cl–cellulose] in this reaction was

investigated. The heterogeneous catalyst showed higher catalytic activity with respect to the neat

Mn(salen)Cl complex. The key advantages of this process are cost effectiveness of the catalyst,

reusability of the catalyst and easy work-up.

Introduction

Sulfones are valuable synthetic intermediates for the construc-tion of chemically and biologically important molecules.1–5

Aromatic sulfones have been shown to be useful in therapy, inparticular as antipsychotic agents.6 A number of drugs closelyrelated to the sulfonamides (e.g. dapsone) have been usedeffectively in the long-term treatment of leprosy.7 Thiosulfo-nates, on the other hand, are powerful sulfenylating agents,8–11

with antimicrobial and fungicidal activities12,13 and someindustrial uses.14 Application of functionalized carbon nano-tube-poly(arylene sulfone) composite membranes for directmethanol fuel cells has been reported.15

The immobilization of catalysts has several importantpotential advantages such as recycle and reuse ability, relativelysafe handling, reduced environmental impact upon work-up,good thermal and chemical stabilities and good dispersion ofthe active catalytic site.16 Thus, search for suitable supports inorder to immobilize salen complex is still a tempting challengein the eld of heterogeneous catalysis. A number of solidmaterials as supports, carbon nanober, graphene, ionicliquids, mesoporous silica, zeolite, SBA-15, metal oxides andpolymers have broadly been investigated.

Many attempts have been focused on the development ofnew ligand-derived polymeric supports for the attachment ofmetals and the design of new approaches to increase the cata-lytic activity.17 An important material within this group iscellulose. Cellulose is the most widely spread organic polymerfound in nature, since it constitutes the main component of themembrane of plant cell. It is well-known that cellulose is a very

iences, University of Birjand, Birjand

nd.ac.ir; malinasseri@yahoo.com; Fax:

74

important and fascinating biopolymer and an almost inex-haustible and renewable rawmaterial.18 It was widely applied asan efficient support and/or template for the synthesis of inor-ganic materials. For example, palladium nanoparticles weresynthesized on the cellulose matrix and employed as an activecatalyst for the hydrogenation reaction of phenol and the Heckcoupling of styrene and iodobenzene.19 In recent years, cellulosehas gained renewed signicance as a raw material and stillpossesses a high potential for future applications.20–22

In this work, we synthesized [Mn(salen)Cl–cellulose] as anefficient, green and new catalyst for the oxidation of suldes.Also, we reported comparison of the catalytic activity of homo-geneous Mn(salen)Cl complex and heterogeneous Mn(salen)Clcomplex in the oxidation reaction. Oxidation reaction carriedout using a variety of oxidants. Among these oxygen donors,oxone is the best oxidant.23–30

ExperimentalMaterials and methods

All chemicals and solvents were purchased fromMerck or Flukaand were used without purication.

The structure of Mn(salen)Cl–cellulose was obtained byinterpretation of the spectra TGA50 (Shimadzu-Japan) on aplatinum cell, FT-IR 4300 (Shimadzu-Japan) on a range from400 to 4000 cm�1 and atomic absorption spectroscopy (AA-6300Shimadzu-Japan).

Preparation of catalyst

3-trimethoxysilylpropylamine (10 mmol, 1.76 ml) was added toa suspension of salicylaldehyde (10 mmol, 1.044 ml) in absoluteethanol (10 ml) in ambient temperature. The solution instantlybecame yellow, indicating the formation of the schiff base. Aer

This journal is © The Royal Society of Chemistry 2014

Fig. 1 Derivative TG (DTG) curve Mn(salen)Cl–cellulose.

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30 min, Mn(CH3COO)2$4H2O (5 mmol, 1.225 g) was added tothe solution, and the mixture was further stirred for 2 h toformation Mn(salen) complex. LiCl (29.15 mmol, 1.224 g) wasthen added. Aer adding 3 g cellulose and stirring the mixtureovernight at room temperature, product was isolated byremoving the solvent. The crude product was washed withwater, EtOH and ether, respectively. Further drying of the solidproduct was carried out in an oven at 80 �C for 8 h.

General procedure for catalytic oxidation of methyl phenylsulde

A mixture of 1 mmol methyl phenyl sulde (MPS) and oxone (1mmol, 0.614 g) was added to a stirring solution of Mn(salen)Cl–cellulose (0.3 g) in H2O (3 ml) at room temperature for therequired period of time (30 min). Aer completion of the reac-tion (TLC), the catalyst was ltered and the mixture wasextracted with diethyl ether (3 � 5 ml), the organic layer waswashed with brine (5 ml), dried over MgSO4, and concentrated.Purity determinations of the products were accomplished byTLC on silica-gel polygram SILG/UV 254 plates.

Results and discussionCharacterization of catalyst

The synthetic procedure is shown in Scheme 1. Spectroscopictechniques including FT-IR, TGA and atomic absorption anal-ysis were used to study the structural of the manganese(III)–salen complex. A series of calculations on the catalyst wereperformed with the Gaussian 98W.

The loading of Mn on cellulose was 0.266 mmol g�1 esti-mated by AAS. The derivative TG (DTG) curve of Mn(salen)Cl–cellulose is shown in the Fig. 1. The recorded curve showed two-step weight loss at temperatures ranging from 30 to 800 �C. Therst derivative peak is observed at 332.25 �C and its area found60% of the total. The total weight loss is about 87.709%. Themass loss from 265 �C to 420 �C and 440 �C to 575 �C is theresult of the thermal decomposition of cellulose.31 On the otherhand, the weight loss from 440 �C to 575 �C can also attribute tothe decomposition of schiff base groups. Covalent bands areresponsible for high thermal stability of catalyst and it causedthat the catalyst stable up to 300 �C.

Scheme 1 Preparation of cellulose supported Mn(III) catalyst.

This journal is © The Royal Society of Chemistry 2014

Fig. 2 shows the FT-IR spectra of the cellulose, Mn(salen)Cland supported complexes of Mn. The spectrum of Mn(salen)Clshows a band at 1632 cm�1 is due to imine n(C]N) and anotherband at 1596 cm�1 attributed to the aromatic ring vibrations(Fig. 2C). The peak at 646 cm�1 is assigned to the stretchingvibrations of the Mn–O bond of the complex. In addition, theobserved peaks in the region of 1300–1600 cm�1 are due to C–O,C–N and aromatic ring. In Fig. 2B, cellulose exhibited bands at

Fig. 2 FT-IR spectra of: (A) [Mn(salen)Cl–cellulose] (B) Cellulose and(C) [Mn(salen)Cl].

RSC Adv., 2014, 4, 39870–39874 | 39871

Table 1 Effect of solvent on the oxidation of methyl phenyl sulfidecatalyzed by [Mn(salen)Cl–cellulose]a

Entry Solvent Sulfone% Sulfoxide% Time (min)

1 H2O 0 98 302 Toluene 5 10 1803 CH3CN 10 60 304 CH3OH 5 80 305 CH3CH2OH 10 70 306 CH3CH2OCOCH3 24 45 1207 1,4-Dioxane 15 0 1808 DMF 10 60 1809 Acetone 20 50 12010 DMSO 35 53 6011 n-Hexane 5 20 18012 Dichloromethane 5 10 180

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3200–3500 cm�1 and 1000–1300 cm�1 that related to OH, C–Oand an anomeric carbon. There were some differences betweenthe FT-IR spectra of the pure catalyst (Fig. 2C) and supportedcatalyst (Fig. 2A). In the spectrum of Mn(salen)Cl–cellulose(Fig. 2A), the vibration intensity of bonds became very weak.

In the present study, the molecular equilibrium geometrywas computed with the Gaussian 98W soware system. Theresults of this study show that the Si–O distance in thecatalyst is about 1.69798 �A and Si–O–C valence angle in thissystem is about 120.48961�. We also calculate the chargedistribution in the present catalyst. Our study shows that theelectron densities at Si and O are 1.43 and �0.793 respec-tively. This charge distribution indicates that the Si–O bondis electrostatic.

13 THF 14 65 12014 Chloroform 15 10 18015 Solvent free 0 0 180

a Reaction conditions: methyl phenyl sulde (1 mmol), catalyst (0.3 g),solvent (2 ml), oxone (1 mmol), T ¼ 25 �C.

The effect of solvent on the oxidation of methyl phenyl suldewith oxone catalyzed by Mn (salen)Cl–cellulose

To nd the optimized conditions, methyl phenyl sulde wasused as a model substrate. The oxidation reactions were carriedout in various solvents at room temperature. According to theTable 1, H2O is the best solvent with a high yield (entry 1). Thereaction in the methanol, ethanol and other polar solventcarried out in moderate to good yield that can be attributed tothe polarity of solvents.

The effect of different oxidants on the oxidation of methylphenyl sulde with oxone catalyzed by Mn(salen)Cl–cellulose.

The effect of different oxidants on the catalytic activity ofMn(salen)Cl–cellulose in the oxidation of methyl phenyl suldewas studied. We chose different oxidants such as oxone, KIO4,UHP and H2O2. The results are summarized in Table 2. WhenKIO4, UHP and H2O2 were used as the oxygen source in H2O,Mn(salen)Cl–cellulose, produced low methy phenyl sulfoxide.Oxone is a strong, cheap and versatile oxidizing agent. Theresults showed that in the presence of oxone as a oxygen sourcehigher yield was obtained.

Fig. 3 Reusability of catalyst in the oxidation reaction. Reaction time¼30 min.

39872 | RSC Adv., 2014, 4, 39870–39874

Oxidation of sulde with oxone catalyzed by Mn(salen)Cl–cellulose

Aer optimization of the reaction conditions, we extendedsubstrates to aromatic suldes (Table 3). We have observed thatthe formation of sulfoxide is favored along with sulfone in H2Omedia (Table 1, entry 1). We have therefore decided to explorethe possibility of achieving selective oxidation of suldes tosulfoxide by conducting the reaction in H2O. Our initialattempts to obtain pure sulfoxide using MPS in oxone (0.5mmol) as a model substrate were unsuccessful. On the otherhand, sulfoxide could be achieved from MPS, in excellent yieldat room temperature within a reasonably short reaction time byusing 1mmol oxone. A substrate/oxidant molar ratio of 1 : 1 wasoptimized for better yield of MPS into sulfoxide under thereaction conditions. We have also compared the catalyticactivity of Mn(salen)Cl and Mn(salen)Cl–cellulose in this reac-tion. As shown in Table 3, the TOF (h�1) for Mn(salen)Cl–cellulose was higher than a neat complex.

Comparison of catalytic activity of Mn(salen)Cl and Mn(salen)Cl–cellulose

In order to show the effect of immobilization on the catalyticactivity of Mn(salen)Cl in the sulde oxidation with oxone, we

Table 2 Effect of different oxidants on the oxidation of methyl phenylsulfide catalyzed by [Mn(salen)Cl–cellulose]a

Entry Oxidant Yield of sulde (%) Time (min)

1 Oxone 98 302 UHP 40 6003 H2O2 40 6004 KIO4 10 6005 None 7 600

a Reaction conditions: methyl phenyl sulde (1 mmol), catalyst (0.3 g),solvent (2 ml), oxone (1 mmol), T ¼ 25 �C.

This journal is © The Royal Society of Chemistry 2014

Table 3 Oxidation of aromatic sulfides with oxone catalyzed by Mn(salen)Cl and [Mn(salen)Cl–cellulose]a

Entry Suldes Time (min)

Yield (%) TOF(h�1)

Mn(salen)ClMn(salen)Cl–cellulose

Mn(salen)Cl Mn(salen)Cl–celluloseSulfoxide Sulfone Sulfoxide Sulfone

1 30 40 5 98 0 10 24.5

2 240 45 3 90 5 1.406 2.812

3 240 33 2 70 10 1.031 2.187

4 240 42 10 76 12 1.312 2.375

5 30 37 5 90 0 9.25 22.5

6 30 41 13 80 14 10.25 20

7 60 49 2 96 0 6.125 12

8 300 36 4 73 6 0.9 1.825

a Reaction conditions: suldes (1 mmol), oxone (1 mmol), catalyst (0.3 g), H2O (2 ml), T ¼ 25 �C.

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repeated all reactions under optimization conditions. Theresults are summarized in Table 3. Our results showed that theTOF (h�1) (Turn Over Frequency) for the Mn(salen)Cl–cellulosecatalyst was higher than the Mn(salen)Cl catalyst. One probableexplanation is that the ligands of Mn(salen)Cl complex is notoxidized when complex attach to cellulose, and therefore thecatalytic activity of Mn(salen)Cl does not reduce.

Catalyst reusability and stability

It is important to verify the stability of the heterogeneouscatalyst since metal leaching from catalyst becomes responsiblefor decreasing of the catalytic activity in successive cycles. Toassess long-term stability and reusability of [Mn(salen)Cl–cellulose], oxidation of methyl phenyl sulde was chosen asmodel reaction, and recycling experiments were carried outwith a single sample of the catalyst. Aer each experiment, thecatalyst was ltered, washed with H2O, dried and reused. Aerreusing catalyst for four consecutive times, the yield was 92%(Fig. 3).

This journal is © The Royal Society of Chemistry 2014

We have additionally analysed the liquid phase for traces ofMn by atomic absorption spectroscopy, but failed to nd anytraces of Mn. Further, we have utilised Sheldon's hot ltrationtest. The Sheldon test shows that in the case of [Mn(salen)Cl–cellulose] we observed 6% of leached Mn aer four consecutivetimes of reaction. The results showed that the catalytic activityof Mn(salen)Cl–cellulose is appropriate for more than four timereuse.

Conclusions

Mn(salen)Cl complex was successfully immobilized on tocellulose. Owing to the abilities of support to highly disperse theactive complexes, and to control the local concentrations of thereactant and product around active sites, the immobilizationled to an increase in catalytic performance in the oxidationreactions. It observed that the catalytic activity of Mn(salen)Clcomplex can be modied by attaching to cellulose throughcovalent bonding. So that, in comparison with the unhybridizedMn(salen)Cl, the oxidation of suldes catalyzed by Mn(salen)Cl–cellulose with oxone showed higher yield. The

RSC Adv., 2014, 4, 39870–39874 | 39873

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heterogeneous catalyst also remarkably alters ratio of sulfoxide/sulfone that was attributed to the immobilization mode andsupport effect of heterogeneous catalyst. The immobilizedcatalyst could be easily recovered.

Acknowledgements

The authors are thankful to the University of Birjand ResearchCouncil for the support of this work.

Notes and references

1 E. N. Prilezhaeva, Russ. Chem. Rev., 2000, 69, 367–408.2 Z. Jin, P. C. Vandort and P. L. Fuchs, Phosphorus, SulfurSilicon Relat. Elem., 1994, 95, 1–19.

3 S. Patai and Z. Rappoport, Synthesis of Sulfones, Sulfoxidesand Cyclic Suldes, John Wiley, Chichester, 1994.

4 N. S. Simpkins, Sulfones in Organic Synthesis, PergamonPress, Oxford, 1993.

5 M. Mikolajczyk, Tetrahedron, 1986, 42, 5459–5495.6 G. Andrew, F. Ian, L. Andrew, P. Andrew, W. Graham,G. Vincenzo, European Patent, EP1511727, 2007.

7 G. A. Ellard, P. T. Gammon, H. S. Helmy and R. J. W. Rees,Nature, 1972, 239, 159–160.

8 T. F. Parsons, J. D. Buckman, D. E. Pearson and L. Field, J.Org. Chem., 1965, 30, 1923–1926.

9 G. Palumbo, C. Ferreri, C. D'Ambrocio and R. Caputo,Phosphorus, Sulfur Silicon Relat. Elem., 1984, 19, 235–238.

10 K. Fujiki and E. Y. Yoshida, Synth. Commun., 1999, 29, 3289–3293.

11 K. Fujiki, S. Akieda, H. Yasuda and Y. Sasaki, Synthesis, 2001,7, 1035–1042.

12 J. P. Weidner and S. S. Block, J. Med. Chem., 1964, 7, 671–673.13 S. S. Block and J. P. Weidner, Mech. React. Sulfur Compd,

1967, 2, 235.14 N. S. Zerov, N. V. Zyk, E. K. Beloglazkina and

A. G. Kutateladze, Sulfur Rep., 1993, 14, 223.15 S. H. Joo, C. Pak, E. A. Kim, Y. H. Lee, H. Chang, D. Seung,

Y. S. Choi, J. B. Park and T. K. Kim, J. Power Sources, 2008,180, 63–70.

39874 | RSC Adv., 2014, 4, 39870–39874

16 (a) F. Coccia, L. Tonucci, N. Alessandroc, P. D'Ambrosioc andM. Bressanc, Inorg. Chim. Acta, 2013, 399, 12–18; (b)E. Ramirez, S. Jansat, K. Philippot, P. Lecante, M. Gomez,A. M. Masdeu-Bulto and B. Chaudret, J. Organomet. Chem.,2004, 689, 4601–4610; (c) D. E. De Vos, M. Dams, B. F. Selsand P. A. Jacobs, Chem. Rev., 2002, 102, 3615–3640.

17 (a) B. Clapham, T. S. Reger and K. D. Janda, Tetrahedron,2001, 57, 4637–4663; (b) N. E. Leadbeater and M. Marco,Chem. Rev., 2002, 102, 3217–3274.

18 A. Lejeune and T. Deprez, Cellulose: Structure and Properties,Derivatives and Industrial Uses, Nova Science Publishers Inc,New York, USA, 2010.

19 K. Srinivasan, P. Michaud and J. K. Kochi, J. Am. Chem. Soc.,1986, 108, 2309.

20 R. L. Hammonds, M. S. Harrison, T. C. Cravanas,W. H. Gazzola, C. P. Stephens and R. S. Benson, Cellulose,2012, 19, 1923–1932.

21 R. J. Maurer, A. F. Sax and V. Ribitsch, Cellulose, 2012, 20, 25–42.

22 B. Duchemin, A. Thuault, A. Vicente, B. Rigaud,C. Fernandez and S. Eve, Cellulose, 2012, 19, 1837–1854.

23 P. Malik and D. Chakraborty, Tetrahedron Lett., 2012, 53,5652–5655.

24 S. P. Das, J. J. Boruah, H. Chetry and N. S. Islam, TetrahedronLett., 2012, 53, 1163–1168.

25 V. Mirkhani, M. Moghadam, S. Tangestaninejad, I. M. poor-Baltork and N. Rasouli, Catal. Commun., 2008, 9, 2411–2416.

26 B. R. Travis, M. Sivakumar, G. O. Hollist and B. Borhan, Org.Lett., 2003, 5, 1031–1034.

27 T. W. Bell, Y. M. Cho, A. Firestone, K. Healy, J. Liu, R. Ludwigand S. D. Rothenberger, Org. Synth., 1993, 87, 87.

28 M. Uyanik, M. Akakura and K. Ishihara, J. Am. Chem. Soc.,2009, 131, 251–262.

29 A. P. Thottumkara, M. S. Bowsher and T. K. Vinod, Org. Lett.,2005, 7, 2933–2936.

30 C. Bolm, A. S. Magnus and J. P. Hildebrand, Org. Lett., 2000,2, 1173–1175.

31 Y. P. Chauhan, R. S. Sapkal, V. S. Sapkal and G. S. Zamre, Int.J. Chem. Sci., 2009, 7(2), 681–688.

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