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Simple Heteropoly Acids as Water-Tolerant Catalysts in the Oxidation of Alcohols with 34% Hydrogen Peroxide, A Mechanistic Approach
Simple Heteropoly Acids as Water-Tolerant Catalysts in the Oxidation of Alcohols with 34% Hydrogen Peroxide, A Mechanistic Approach
Journal of the Korean Chemical Society. 2008. Feb, 52(1): 23-29
Copyright © 2008, The Korean Chemical Society
  • Received : December 04, 2006
  • Published : February 20, 2008
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Reza Tayebee

Abstract
Simple Keggin type tungsten and molybdenum heteropoly acids, H 3 PW 12 O 40 and H 3 PMo 12 O 40 , were used as water-tolerant catalysts for the oxidation of alcohols with 34% hydrogen peroxide in normal drinking water. According to our findings, H 3 PW 12 O 40 may be used as a simple, effective, and cheap catalyst for this type of transformation in normal drinking water with excellent yields. Effects of different solvents at 25-80 ℃ and changing concentration of catalyst and substrate on the reaction progress were also studied.
Keywords
INTRODUCTION
Development of effective, safe, and environmentally benign protocols to carry out selective oxidation of alcohols mediated by Lewis acids in water, as the most fundamentally functional transformation in practical and academic organic synthesis, has been a challenge for many years. 1 - 7 A variety of stoichiometric and catalytic routes have been explored to accomplish such a conversion. 8 - 16
However, much of these methods involve the use of expensive reagents, harsh reaction conditions, and leading to the generation of a large amount of toxic waste. 17 , 18 Because of these facts, there is still a need to develop new environmentally benign routes that meet industrial demands for this transformation.
Because of the unique properties of polyoxometalates, they are promising acid, redox and bifunctional catalysts. The catalytic reactions can be performed in homogeneous as well as in heterogenous systems. Polyoxometalates are environment-friendly and economically feasible solid acids due to several advantages such as high catalytic activities, ease of handling, cleaner reaction conditions, non-toxicity and experimental simplicity. 19 These compounds effectively catalyze oxidation of a variety of organic compounds such as olefins, thioethers, and alcohols with several terminal oxidants such as alkyl hydroperoxide, molecular oxygen, iodosyl benzene, as well as hydrogen peroxide. 20 - 23
Now, in continuation to our previous findings, 24 we summarized here our recent developments on different reaction parameters affect oxidation of alcohols with aqueous hydrogen peroxide catalyzed by water-tolerant catalysts, H 3 PW 12 O 40 and H 3 PMo 12 O 40 , in normal drinking water. Role of solvent system, effect of catalyst/substrate mole ratio, and temperature on the reaction progress are presented.
RESULTS AND DISCUSSION
- General
Polyoxometalates are coordination compounds containing d 0 metal-oxygen clusters whose chemical properties can be controlled by transition metal substitution and the counter cation used. One important class of polyoxometalates is heteropoly anions, which are more studied and are useful as catalysts. The two main structures of heteropolyoxometalates are Keggin and Wells-Dawson types ( 1 ). 29
The Keggin structure is roughly spherical and gives a general formula of XM 12 , where X is the heteroatom and M is the addenda d 0 metal atom. Each corner of the heteroatom tetrahedron is associated with an M 3 O 13 unit. Three MO 6 of octahedron unit form a triplet M 3 O 13 by sharing octahedral edges, and four such triplets share the octahedral vertexes and arrange tetrahedrally around the heteroatom, that is, the three-fold shared oxygen atoms in the triplet M 3 O 13 are coordinated to a heteroatom, resulting in a Td symmetric polyoxometalate. Another structure is the Wells-Dawson type structure that is ellipsoidal, of formula X 2 M 18 . This structure consists of two heteroatoms stacked one atop the other, and each end is composed of an M 3 O 13 cap, with two six-metal belts circling the molecule.
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The structure of Keggin (a) and Wells–Dawson (b) heteropoly anion [XM12O40]n-. Red corners, black, and pink (blue) balls represent oxygen atoms, metal ions, and heteroatoms in the structures, respectively.
For catalysis, Keggin -type heteropoly acids with the general formula of H 8-x X x M VI 12 O 40 (where X=Si IV , Ge IV , P V , As V and M=Mo VI , W V ) are of great importance. The considerable number of studies performed during the past years allowed to formulate the selection principles of effective catalysts in the series of Keggin -structure. Their significantly higher Brønsted acidity, compared with the acidity of traditional mineral acid catalysts, is of great importance for catalysis. Using heteropoly acid-based catalysts, it is frequently possible to obtain higher selectivity and successfully solve ecological problems.
- Oxidation of cyclohexanol with H2O2- H3PW12O40catalytic system in different solvents at 25-80 ℃
It is well known that the nature of solvent plays a very important role in the catalytic reactions carried out in liquid phase. 30 , 31 To study the influence of the nature of solvent, the oxidation of cyclohexanol with H 2 O 2 -H 3 PW 12 O 40 catalytic system was carried out in different solvents. Cyclohexanol as model substrate and H 3 PW 12 O 40 as catalyst were conducted in normal water, t butanol, and chloroform, as solvents, at 25-80 ℃ ( 1 ). The results showed that the catalytic performance was strongly affected by the type of solvent. The highest reaction activity was achieved in the system of using water as a solvent. The results showed that efficiency and yield of the reactions in t butanol and chloroform, as organic solvents, were much less than those observed in water. Normal water (electrical conductivity, 550; total dissolved solids, 350; and pH, 8.3) led to complete conversion of cyclohexanol to cyclohexanone with 100% selectivity at 65 ℃ after 2.5 h; whereas, chloroform and t butanol produced <5% of cyclohexanone at the same reaction conditions.
Oxidation of cyclohexanol to cyclohexanone with H2O2-H3PW12O40catalytic oxidation system in different solvents at 25-80℃.a
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aTo a solution of H3PW12O40 (0.018 mmol) and 34% H2O2 (5 mmol) in the appropriate solvent (5 ml) was added cyclohexanol (0.94 mmol). The reaction mixture was stirred by a magnetic stirrer for the required time. Progress of the reactions was followed by the aliquots withdrawn directly and periodically from the reaction mixture, analyzed by gas chromatography.
1 also describes effect of temperature elevation on the oxidation of cyclohexanol. The conversion found to increase substantially with increasing temperature, which suggested that the reaction was intrinsically kinetically controlled. At ambient temperature (25 ℃), the reaction hardly happened; while, the conversion increased with increasing temperature. A sharp increase in the yield occurred by elevation of temperature and 65% of cyclohexanone obtained with H 2 O 2 - H 3 PW 12 O 40 catalytic system in water at 80 ℃ after 1h. Whereas, only 15% of the product observed at ambient temperature at the same time ( 2 ).
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Effect of temperature on the conv.% of cyclohexanol with H2O2-H3PW12O40 catalytic system after 1 h.
- Oxidation of cyclohexanol with H2O2over some Keggin-type heteropoly acids
Based on the effect of solvent, we selected normal water as the solvent for the oxidation of cyclohexanol. Effect of the type and concentration of heteropoly acid on the oxidation of cyclohexanol in normal water is studied. 2 shows that H 3 PW 12 O 40 acted distinctly more efficient than H 3 PMo 12 O 40 and H 4 SiW 12 O 40 in the oxidation of cyclohexanol with H 2 O 2 in normal water. It’s considerable, no conversion of cyclohexanol was observed in the absence of catalyst.
Effect of the type and concentration of heteropoly acid on the yield% of cyclohexanol oxidation in water.a
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aTo a solution of catalyst (0-0.09 mmol) and 34% H2O2 (5 mmol) in normal water (5 ml) was added cyclohexanol (0.94 mmol). The reactions were carried out as described below Table 1.
An increase in the catalyst concentration (with respect to cyclohexanol) resulted in an increase in the conversion. 5-fold increase in concentration of H 3 PW 12 O 40 , from 0.0036 to 0.018 mmol, enhanced the conversion from 29 to 45% in water, as solvent, after 1 h. Moreover, increase in concentration of H 3 PMo 12 O 40 from 0.018 to 0.09 mmol, caused an increase in the conversion from 18 to 26% at the same time. 3 shows the effect of catalyst concentration on the oxidation of cyclohexanol with H 2 O 2 in water.
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Effect of catalyst concentration on the conv.% of cyclohexanol with H2O2 in water after after 1 h.
- Oxidation of some alcohols into their corresponding oxygenated products with H2O2- H3PW12O40-H2O catalytic oxidation system
Treatment of an appropriate alcohol with hydrogen peroxide by the mediation of H 3 PW 12 O 40 in water afforded the corresponding carbonyl compound after the indicated time in 3 . Cyclohexanol, as a secondary alcohol, showed the best results under different mole ratios of sub./cat. It led to complete conversion with sub./cat. mole ratio of 52 after 2.5 h. While, benzyl alcohol showed less reactivity toward oxidation and produced 78% benzaldehyde under the same reaction conditions. n-Butanol, as a linear primary aliphatic alcohol, resulted in the least reactivity and obtained 30% of conversion toward the corresponding aldehyde after 2.5h.
Effect of changing concentration of alcohols was also introduced in 3 . As is expected, conversion decreased by enhancing alcohol concentration. For example, cyclohexanol produced 62, 45, and 13% of conversions with sub./cat. mole ratios of 26, 52, and 260, respectively. However, as is shown in 3 and 4 , turnover frequency, 42 TOF, increases with enhancing concentration of alcohol. This may partly be due to lower deactivation of catalyst during the reaction and higher number of effective collisions between substrate and the catalytically active oxidizing species. Finally, in all cases no over oxidation products, carboxylic acids, were observed even after extended reaction times.
Effect of the type and concentration of some alcohols on the efficiency of H2O2-H3PW12O40-H2O catalytic oxidation system.a
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aTo a solution of H3PW12O40 (0.018 mmol) and 34% H2O2 (5 mmol) in normal water (5 ml) was added the corresponding alcohol (0.47-4.7 mmol). The reactions were carried out as described below Table 1. bTurnover frequency, TOF, was calculated by the expression ([product]/[catalyst])×time (h–1).42
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Effect of alcohol concentration on the TOF in H2O2-H3PW12O40-H2O catalytic oxidation system.
- Catalytically active oxidizing species in H2O2- H3PM12O40-H2O oxidation system
The groups of Venturello 32 , 33 and Ishii 34 - 36 independently developed highly effective and mechanistically closely related polyoxometalates-based catalyst systems for oxygenation of some organic compounds by hydrogen peroxide. Heteropoly acids with the Keggin structure are degraded in the presence of excess H 2 O 2 to form peroxo species {PO 4 [MO(O 2 ) 2 ] 4 } 3- and [M 2 O 3 (O 2 ) 4 (H 2 O) 2 ] 2- (M=W, Mo), which are the true catalytically active intermediate in the oxygenation of organic compounds by hydrogen peroxide catalyzed by H 3 PW 12 O 40 and H 3 PMo 12 O 40 . It is recommended that these two peroxo species are responsible for the oxidation of alcohols with H 2 O 2 -H 3 PM 12 O 40 -H 2 O (M=W and Mo) catalytic oxidation system. 1 represents the general formulation of the catalytic system in the oxidation of alcohols.
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General scheme for the catalytic oxidation of alcohols with H3PM12O40.
The reasons why H 3 PW 12 O 40 showed a higher activity than H 3 PMo 12 O 40 during the catalysis process may be explained considering previous findings in similar oxidation protocols. 37 - 41 Both H 3 PW 12 O 40 and H 3 PMo 12 O 40 are degraded to form the peroxo complexes {PO 4 [MO(O 2 ) 2 ] 4 } 3- and [M 2 O 3 (O 2 ) 4 (H 2 O) 2 ] 2- (M=W, Mo) in the presence of excess H 2 O 2 . The reason may partly be due to the structure and coordination environment of these active species. Ding et al. 41 believe that the observed different efficacy for H 3 PW 12 O 40 and H 3 PMo 12 O 40 in the epoxidation reactions may be related to the different M-O bond order and the different state of electrons filling orbitals of the central metal ion. The electron configuration of atomic tungsten (W) and molybdenum (Mo) are [Xe]4f 14 5d 4 6s 2 and [Kr] 4d 5 5s 1 , respectively. For the {PO 4 [WO(O 2 ) 2 ] 4 } 3- , 5d and 6s orbitals are vacant, while {PO 4 [MoO(O 2 ) 2 ] 4 } 3- has more vacant orbitals, i.e. 4f, 4d, and 5s. It is suggested that the substrate and the active species form an intermediate or transitional state during the catalytic process, and the electrons of substrate enter the vacant orbitals of the metal ions. For {PO 4 [MoO(O 2 ) 2 ] 4 } 3- , there is vacant 4f, 4d, 5s orbitals; whereas, {PO 4 [WO(O 2 ) 2 ] 4 } 3- only having two kinds of vacant orbitals. As a consequence, the intermediate formed by the mediation of {PO 4 [MoO(O 2 ) 2 ] 4 } 3- is comparatively more stable than the one formed by {PO 4 [WO(O 2 ) 2 ] 4 } 3- . Furthermore, the O-O bonds of tungsten complex are longer than that of molybdenum complex; it seems to be essential for the facile transfer of the active oxygen. 41
EXPERIMENTAL
- Materials and Instrumentation
Solvents, reagents, and other chemicals used in this study were of the highest grade available and were purchased commercially. The reagents were stored at 5 ℃ and purified just before use. Silica gel 60 (70-230 mesh, purchased from E-Merck A.G., Darmstadt, Germany) used for column chromatography. Purity of the substances and progress of the reactions were monitored by Gas Chromatography. GLC analyses were performed on a Shimadzu GC-17A instrument equipped with a flame ionization detector using CPB 5-20 (25 m × 0.25 mm, 0.1 to 5.0 μm film thickness) and fused silica WCOT 25 m × 0.32 mm capillary columns with 5.0 μm film thickness. The heteropoly acids H 3 PW 12 O 40 , H 3 PMo 12 O 40 , and H 4 SiW 12 O 40 were prepared and characterized according to literature procedures or were purchased commercially. 25 - 28
- General procedure for oxidation of alcohols to carbonyl compounds in normal drinking water
To a solution of catalyst (0.018 mmol) and 34% H 2 O 2 (5 mmol) in normal water (5 ml) as solvent, was added alcohol (0.94 mmol) and the reaction mixture was allowed to stir at 65 oC for the required time. Progress of the reaction was followed by the aliquots withdrawn directly from the reaction mixture, analyzed by gas chromatography using n-decane as internal standard. After completion of the reaction, products were extracted with 20 ml CHCl 3 . The extract was dried over anhydrous sodium sulfate and then was filtered. The filtrate was concentrated under reduced pressure. Finally, the concentrated filtrate was treated with 2,4-dinitrophenylhydrazine in 6% HCl to give 2,4-dinitrophenylhydrazone of the corresponding carbonyl compound.
- Reusability of H3PW12O40
At the end of the reaction, H 3 PW 12 O 40 recovered by slow drying the aqueous phase of the reaction mixture at 50 ℃ under intense light for 2 h and then at 130 ℃ for 3 h. The regenerated solid acid catalyst was washed with dichloromethane, dried at 130 ℃ for 1 h, and re-used in another reaction. The reusability of the catalyst was studied by using the separated catalyst in another reaction. Therefore, two experiments were done, one with the fresh catalyst and another with the recycled H 3 PW 12 O 40 . It is concluded that there is no considerable deactivation of the catalyst and it is recyclable. The recycled catalyst could be reused for several times without considerable loss of activity. IR spectroscopy of the catalyst confirmed that the Keggin structure was almost retained at least after four repeated runs.
CONCLUSION
To conform to green chemistry, it is important to realize reaction systems in water instead of organic solvents, to use safe reagents, to decrease hazardous inorganic and organic wastes, and to use a minimal amounts of reusable catalysts. 43 Present report established a unique green protocol to achieve some of these goals by using the simplest heteropoly acid catalysts, which offer substantial economic and environmental benefits.
Acknowledgements
The financial support from the research council of Sabzevar University is greatly appreciated.
References
Dirk S. M. , Mickelson E. T. , Henderson J. C. , Tour J. M. 2000 Org. Lett. 2 3405 -    DOI : 10.1021/ol006539j
Suresh S. , Joseph R. , Jayachandran B. , Pol A. V. , Vinod M. P. 1995 Tetrahedron 51 11305 -    DOI : 10.1016/0040-4020(95)00692-2
Webb K. S. , Seneviratne V. 1995 Tetrahedron Lett. 36 2377 -    DOI : 10.1016/0040-4039(95)00281-G
Firouzabadi H. , Jafari A. A. 2005 J. Iran. Chem.Soc 8 85 -    DOI : 10.1007/BF03247201
Li C.-J. 2005 Chem. Rev. 105 3095 -    DOI : 10.1021/cr030009u
Ikeda T. , Tsutumi O. 1995 Science 268 1873 -    DOI : 10.1126/science.268.5219.1873
Hill C. L. , Prosser-McCartha G. M. 1995 Coordn. Chem. Rev 143 407 -    DOI : 10.1016/0010-8545(95)01141-B
Zhan B.Z. , White M.A. , Sham T. K. , Pincock J. A. , Doucet R. J. , Rao K. V. R. , Robertson K. N. , Cameron T. S. 2003 J. Am. Chem. Soc. 125 2195 -    DOI : 10.1021/ja0282691
Moorthy J.N. , Singhal N. , Venkatakrishnan P. 2004 Tetrahedron Lett. 45 5419 -    DOI : 10.1016/j.tetlet.2004.05.044
Wolfson A. , Wuyts S. , De Vos D. E. , Vankelecom I. F. J. , Jacobs P. A. 2002 Tetrahedron Lett. 43 8107 -    DOI : 10.1016/S0040-4039(02)01921-4
Loua J.-D. , Xu Z.-N. 2002 Tetrahedron Lett. 43 8843 -    DOI : 10.1016/S0040-4039(02)02234-7
Xu L. , Trudell M. L. 2003 Tetrahedron Lett. 44 2553 -    DOI : 10.1016/S0040-4039(03)00283-1
Lou J. D. , Wang M. , Zhu L.-Y. , Fang Z.-G. 2003 Catal. Commun. 4 647 -    DOI : 10.1016/j.catcom.2003.10.008
Reddy S. R. , Das S. , Punniyamurthy T. 2004 Tetrahedron Lett. 45 3561 -    DOI : 10.1016/j.tetlet.2004.03.056
Zhan B.Z. , White M. A. , Sham T. K. , Pincock J. A. , Doucet R. J. , Rao K. V. R. , Robertson K. N. , Cameron T. S. 2003 J. Am. Chem. Soc. 125 2195 -    DOI : 10.1021/ja0282691
Zhang S. , Xu L. , Trudell M. L. 2005 Synthesis 11 1757 -
Sato K. , Aoki M. , Takagi J. , Noyori R. 1997 J. Am. Chem. Soc. 119 12386 -
Neumann R. , Gara M. 1995 J. Am. Chem. Soc. 117 5066 -    DOI : 10.1021/ja00123a008
Kozhevnikov I. V. 1998 Chem. Rev. 98 171 -    DOI : 10.1021/cr960400y
Ishii Y. , Ogava M. 1990 In Hydrogen Peroxide Oxidation Catalyzed by Heteropoly Acids Combined with Cetylpyridinium Chloride MY Tokyo vol.3 121 - 145
Kozhevnikov I. V. 1987 Russ. Chem. Rev. 56 811 -    DOI : 10.1070/RC1987v056n09ABEH003304
Dickman M. H. , Pope M. T. 1994 Chem. Rev. 94 569 -    DOI : 10.1021/cr00027a002
Isobe K. , Yagasaki A. 1993 Act. Chem. Res. 26 524 -    DOI : 10.1021/ar00034a002
Tayebee R. , Alizadeh M. H. 2007 Monatshe Chemie 138 763 -    DOI : 10.1007/s00706-007-0660-z
Okun N. M. , Anderson T. M. , Hill C. L. 2003 J. Am. Chem. Soc. 125 3194 -    DOI : 10.1021/ja0267223
ten Brink G. J. , Arends I. W. C. E. , Sheldon R. A. 2000 Science 258 1636 -    DOI : 10.1126/science.287.5458.1636
ten Brink G. J. , Arends I. W. C. E. , Sheldon R. A. 2002 Adv. Synth. Catal. 344 355 -    DOI : 10.1002/1615-4169(200206)344:3/4<355::AID-ADSC355>3.0.CO;2-S
Brevard C. , Schimpf R. , Tourne G. , Tourne C. M. 1983 J. Am. Chem. Soc. 105 7059 -    DOI : 10.1021/ja00362a008
Bonardet J. L. , Carr K. , Fraissard J. , Mc Garvey G. B. , Mc Monagle J. B. , Seay M. , Moffat J. B. 1996 In Microporous metal-oxygen cluster compounds (heteropolyoxometalates); in: Moser, W. R. (Ed.), Advanced Catalysts and Nanostructured Materials, Modern Synthetic Methods Academic Press New York 395 -
Hulea V. , Dumitriu E. , Patcas F. , Ropot R. , Graffin P. , Moreau P. 1998 Appl. Catal. A 170 169 -    DOI : 10.1016/S0926-860X(98)00047-7
Clerici M. G. , Bellussi G. , Romano U. 1991 J. Catal. 129 159 -    DOI : 10.1016/0021-9517(91)90019-Z
Venturello C. , D’Aloisio R. , Bart J. C. J. , Ricci M. 1985 J. Mol. Catal. 32 107 -    DOI : 10.1016/0304-5102(85)85037-9
Venturello C. , D’Aloisio R. 1988 J. Org. Chem. 53 1553 -    DOI : 10.1021/jo00242a041
Ishii Y. , Yamawaki K. , Ura T. , Yamada H. , Yoshida T. , Ogawa M. 1988 J. Org. Chem. 53 3587 -    DOI : 10.1021/jo00250a032
Matoba Y. , Inoue H. , Akagi J. , Okabayashi T. , Ishii Y. , Ogawa M. 1984 Synth. Commun. 14 865 -    DOI : 10.1080/00397918408075730
Ohno A. , Furukawa N. , Ishii Y. , Ogawa M. 1990 In Reviews on Heteroatom Chemistry, vol. 3 MYU Tokyo 121 -
Venturello C. , D’Aloisio R. 1988 J. Org. Chem. 53 1553 -    DOI : 10.1021/jo00242a041
Salle L. , Piquemal J. Y. , Thouvenot R. , Minot C. , Bregeault J. M. 1997 J. Mol. Catal. A 117 375 -    DOI : 10.1016/S1381-1169(96)00257-9
Campbell N. J. , Dengel A. C. , Edwards C. J. , Griffith W. P. 1989 J. Chem. Soc., Dalton Trans. 1203 -    DOI : 10.1039/dt9890001203
Salle L. , Aubry C. , Thouvenot R. , Robert F. , Doremieux-Morin C. , Chottard G. , Ledon H. , Jeanin Y. , Bregeault J. M. 1994 Inorg. Chem. 33 871 -    DOI : 10.1021/ic00083a008
Ding Y. , Gao Q. , Li G. , Zhang H. , Wang J. , Yan L. , Suo J. 2004 J. Mol. Catal. A 218 161 -    DOI : 10.1016/j.molcata.2004.04.019
Anastase P. T. , Warner J. C. 1998 Green Chemistry: Theory and Practice Oxford University Press Oxford