HBr−H2O2: A Facile Protocol for Regioselective Synthesis of

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HBr-H2O2: A Facile Protocol for Regioselective Synthesis of Bromohydrins and r-Bromoketones and Oxidation of Benzylic/Secondary Alcohols to Carbonyl Compounds under Mild Aqueous Conditions Rajendra D. Patil, Girdhar Joshi, and Subbarayappa Adimurthy* Analytical Science Discipline, Central Salt & Marine Chemicals Research Institute (CSIR), G. B. Marg, BhaVnagar-364002 India

HBr-H2O2 is efficiently activated in water under mild conditions, allowing the bromohydroxylation of various styrenes. HBr-H2O2 is more economic and easy to handle and offers sufficiently high regioselectivity (100%) for bromohydrin synthesis. Further activation of bromohydrin with a catalytic amount of HBr (50 mol %) and H2O2 in water affords R-bromoketones in moderate to good yields in a single step. Oxidation of benzylic/ secondary alcohols to the corresponding carbonyl compounds has been achieved with the HBr (10 mol %) and H2O2 efficiently in aqueous dioxane under ambient conditions. 1. Introduction

2. Experimental Section

Bromohydrins and R-bromoketones are compounds of high practical utility. These bromo intermediates are useful in the synthesis of numerous functionalized compounds such as antitumor and antibacterial agents and antioxidants1 as well as specialty chemicals, agrochemicals, and pharmaceuticals.2 There are many known methods for the synthesis of bromohydrins either by the reaction of alkenes with NBS (N-bromosuccinimide)3 or by the ring-opening of an epoxide with the addition of halo acids.4 The direct use of HBr for the selective synthesis of bromohydrins from olefins has not been explored. However, the HBr-H2O2 system has been reported for a number of elegant bromination reactions by J. Iskra and co-workers5 including the R-bromination of ketones. Our study on various vicinal functionalizations of olefins6 and the one-pot synthesis of R-bromoketones from olefins revealed that limited literature reports are available for the access to R-bromoketones from olefins.7 On the other hand, the development of sustainable, efficient, and selective catalysts for the oxidation of alcohols to aldehydes is a fundamental goal in chemistry. During recent decades, manifold transition metal-catalyzed reactions have been discovered which have significantly improved organic transformations. Notably, most of the applications are based on complexes of precious metals such as palladium,8 platinum,9 gold,10 ruthenium,11 and other metal catalysts.12-16 TEMPO-imidazolium salts are efficient metal-free oxidants reported recently for the oxidation of various alcohols.17 The limited availability of these metals and their high price make it highly desirable to search for more economical and environmentally friendly alternatives. On the basis of our previous study, selective oxidation of various organic substrates with bromate in combination with a catalytic amount of bromide could be achieved under ambient conditions.18 Our present study shows that HBr-H2O2 can regioselectively provide bromohydrins and R-bromoketones from olefins (Scheme 1) and is effective for the selective oxidation of benzylic/secondary alcohols to the corresponding carbonyl compounds under mild conditions (Scheme 2).

General Procedure for the Synthesis of Bromohydrins from Olefins. Representative procedure for 2-bromo-1-phenylethanol (Table 1, entry 1): To a reaction mixture containing styrene (0.52 g, 5.0 mmol), water (15 mL), and 46% aqueous HBr (6.0 mmol, 1.2 equiv) was added 30% aqueous H2O2 (7.5 mmol, 1.5 equiv) during a period of 1 h at room temperature. The above reaction mixture was then refluxed for 5 h (TLC). After completion of the reaction, a sample was withdrawn and analyzed by GC-MS, which showed 100% formation of the desired bromohydrin (2-bromo-1-phenylethanol) based on GC area %. To isolate the product, it was extracted with ethyl acetate (15 mL × 3). The combined organic layers were washed with dilute solutions of Na2S2O3. Finally it was dried over anhydrous Na2SO4 and concentrated under reduced pressure to get a crude product, which was purified by column chromatography on silica gel (hexane-ethyl acetate 95:5) to afford the pure 2-bromo-1phenylethanol (1.81 g, 9.02 mmol) in 94% yield. The spectroscopic data (1H and 13C NMR) was in good agreement with the reported data.6c A similar procedure was followed for the syntheses of bromohydrins listed in Table 1. General Procedure for the Synthesis of r-Bromoketones from Olefins. Representative procedure for 2-bromo-1-phenylethanone (Table 3, entry 1): The first stage of obtaining bromohydrin was followed as mentioned above (general procedure for the synthesis of bromohydins). The above reaction Scheme 1

Scheme 2

* Corresponding author. Fax: +91-278-2567562. E-mail: sadimurthy@ yahoo.com. 10.1021/ie100492r  2010 American Chemical Society Published on Web 07/21/2010

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mixture was allowed to attain room temperature, and another 0.5 equiv of 46% aqueous HBr (2.5 mmol) was added followed by the gradual addition of 1.5 equiv of 30% aqueous H2O2 (7.5 mmol w.r.t. styrene) during 1 h. The stirring of the reaction mixture was further continued at room temperature for 18 h. The product was extracted with ethyl acetate (3 × 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate, and the sample was analyzed by GC-MS. GC-MS analysis showed 94% desired bromoketone (2-bromo-1-phenylethanone) formation based on GC area %. (Caution: All the compounds are lachrymatic, and proper care should be taken in handling). The aqueous part remaining (containing 0.7 equiv of bromide) after obtaining the bromoketone above was utilized further to get bromohydrin. To the above aqueous layer was added a further amount of the styrene (0.36 g, 3.5 mmol) followed by the gradual addition of 30% aqueous H2O2 (5.25 mmol, 1.5 equiv) for 1 h and then reflux for 5 h. GC-MS analysis showed 100% desired bromohydrin formation, and it was isolated in 93% yield. The same procedure was followed for reutilization of aqueous part (from Table 3) for the corresponding bromohydrin synthesis as mentioned in Table 4. General Procedure for the Oxidation of Benzylic/Secondary Alcohols to Corresponding Carbonyl Compounds. Representative procedure for 4-methylbenzaldehyde (Table 5, entry 8): To a solution of 4-methylbenzyl alcohol (0.5 g, 4.1 mmol) in dioxane (5 mL) was added 0.1 equiv of 46% aqueous HBr and 1.2 equiv of 30% aqueous H2O2. The mixture was stirred at room temperature for 15 h (TLC). After completion of the reaction, the product was extracted with ethyl acetate (15 mL × 3). The combined organic extracts were washed with 2% sodium thiosulfate solution if required and dried over anhydrous sodium sulfate. The organic solvent was evaporated, and the crude product thus obtained was subjected to column chromatography to get 88% (0.432 g) isolated yield. The spectroscopic data (IR, 1H NMR, and 13C NMR) are in good agreement with the reported values.19 The above procedure followed for the oxidation of secondary alcohols to ketones (Table 6). 3. Results and Discussion In our previous studies, we have screened different solvent conditions for the synthesis of bromohydrins and observed that the dibromo impurity is inevitably formed.6a,c In the reaction of alkenes with aqueous HBr-NaNO2, J. Iskra and co-workers obtained dibromo derivatives as sole products under optimized conditions,5a but they also achieved 53% bromohydrin with aqueous HBr alone at room temperature.5d The presence of the dibromo impurity not only decreased the yield of the desired bromohydrin but also demanded the purification of products particularly in case of bromohydrin synthesis. In view of our ongoing search for sustainable processes for the regioselective synthesis of bromohydrins, we found that using the appropriate conditions allows the synthesis of regioselective bromohydrins from olefins (Scheme 1), and oxidation of benzyl alcohols to aldehydes, and secondary alcohols to ketones, without using any transition metals, by simply employing 10 mol % hydrobromic acid (HBr) (Scheme 2) under aqueous conditions. Initially, the synthesis of styrene bromohydrin was carried out by stirring the reaction mixture of styrene, aqueous hydrobromic acid (46 wt %), and hydrogen peroxide (30 wt %) at room temperature. GC-MS analysis showed the formation of 65% bromohydrin, 19% bromoketone, and 15% dibromo derivatives. When the same reaction was carried out by the controlled addition of H2O2 at room temperature (1 h) and the

Table 1. Synthesis of Bromohydrins with HBr-H2O2

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a

a Conditions: Styrenes/indene (5.0 mmol), HBr (1.2 equiv), H2O2 (1.5 equiv), 1.0 h RT, and 5.0 h reflux. b GC conversions. c GC yields of desired bromohydrin; yields in parentheses refer to isolated products. d 96:4 and 98:2 regioisomers observed in entries 2 and 8, respectively.

reaction mixture was refluxed at 100 °C for 5 h in water, styrene bromohydrin was obtained with 100% selectivity (Table 1, entry 1). Under reflux conditions, the initially formed dibromo derivative (at room temp) underwent debromination selectively (under reflux) at the benzylic position20 to provide further bromohydrin, thereby eliminating the dibromo impurity during the reaction. A further advantage of the reaction at reflux is the avoidance of bromoketone formation probably due to decomposition of excess H2O2. Simple organic extraction and evaporation of solvent provides analytically pure bromohydrins in many cases. In this way, neat bromohydrin could be obtained as a sole product without any tedious purification. However, at room temperature the initially formed bromohydrin undergoes further oxidation and provides bromoketone. Further, when the reaction was carried out in organic solvents (for example, 1,4-dioxane, dichloromethane, dichloroethane, acetonitrile), the dibromo derivative was observed as the major product, which does not undergo further debromination even under reflux conditions to provide the bromohydrin as indicated above. Hence, water is the only choice for the selective synthesis of bromohydrins. Considering the wide utility of these bromohydrins, we undertook the study for the synthesis of bromohydrins from olefins employing HBr-H2O2 as a cost-effective reagent under mild reaction conditions which can be implemented in industry as well as undergraduate laboratories. Inspired by the high yield and selectivity of the above reaction, we extended our study toward other styrenes. All the styrenes were selectively converted to corresponding bromohydrins in excellent yields, and results are presented in Table 1. As shown in Table 1, styrenes with electron-releasing (Table 1, entries 2 and 3) and electron-withdrawing (Table 1, entries 4 and 5) substituents were neatly converted to the corresponding bromohydrins. However, 2-chlorostyrene provided 91% of the

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Table 2. Optimization of Conditions for r-Bromoketone Synthesis

Scheme 3

product distribution (%)c entry

conditions

conversionb

2

3

4

1a 2a 3a 4d 5e 6

1.5HBr-3H2O2, water, 25 h 1.7HBr-3H2O2, water, 25 h 2HBr-3H2O2, water, 25 h 2BrOH, water, 25 h 2NBS, water, 24 h 1.7HBr-2.5H2O2, water, 10 h, RT 1.7HBr-2.5H2O2, water-dioxane (1:1), 10 h, RT 1.7HBr-2.5H2O2, dioxane, 10 h, RT

100 100 100 100 100 100

78 94 93 92 81 25

22 04 02 05 19 61

00 00 00 00 00 10

100

28

52

18

99

18

24

57

7 8

Table 3. Synthesis of r-Bromoketones from Olefins with HBr-H2O2a

a Initially 1.5 eqv 30% aqueous H2O2 was added gradually at RT for 1.0 h then 5 h reflux and followed by the addition of rest of H2O2 at RT, 19 h (for entries 1-3). b By GC conversion. c Yields based on GC area %. d Reagent from our previous reference,7 and reaction carried out under the present conditions. e Data taken from refence.5d

corresponding bromohydrin along with 6% bromoketone (Table 1, entry 6). In the case of 3-nitrostyrene, 87% bromohydrin formation was observed along with 13% dibromo derivative (Table 1, entry 7). Particularly, only in the case of 3-nitrostyrene debromination was not observed due to the strong electronwithdrawing property of nitro group at the meta position. Other substrates such as indene were also neatly (100%) converted to the corresponding bromohydrin (Table 1, entry 8). To broaden the scope of the present system, and for the access to R-bromoketones from olefins, we optimized the reaction conditions in a single-step synthesis of bromoketomes from olefins (Table 2). As shown in Table 2, by increasing the amount of HBr from 1.5 to 2.0 equiv, the desired bromoketone yield (by GC) was also increased from 78% to 94% (Table 2, entries 1-3). When the reaction of entry 2 was conducted at room temperature, bromohydrin was obtained as the major product rather than the desired bromoketone (entry 6). Further, conducting the reaction in organic solvent led to bromohydrin (entry 7) and dibromo derivatives (entry 8) as major products. The results from Table 2 suggest that to obtain the desired bromoketone, the conditions of entry 2 were considered optimal. We subjected various styrenes and indene to these optimized conditions to obtain the corresponding R-bromoketones. The results are shown in Table 3. The lower yields of bromoketones in the cases of 3-nitrostyrene and indene are due to the low miscibility of the corresponding bromohydrin intermediate in water compared to the rest of the substrates. To the best of our knowledge, as indicated in the Table 3, the direct single-step synthesis of R-bromoketones from olefins with HBr-H2O2 under mild conditions is a new and efficient process not yet reported in the literature. Even though 1.7 equiv of HBr is employed for the synthesis of bromoketones from styrenes, only 1 equiv of bromide is consumed for the desired conversion, the rest of the bromide (0.7 equiv) remaining in the water phase after workup. To ensure maximum atom efficiency as mentioned above, we added a further 0.7 equiv of the corresponding styrene and H2O2 (1.5 equiv w.r.t. styrene) to the water phase containing the unreacted 0.7 equiv of bromide and used the same reaction conditions as mentioned in Table 1, to obtain the complete yield of bromohydrin. Thus, maximum bromide atom efficiency results in either

a Under the optimized conditions of Table 2 (entry 2); yields are based on GC area %. b 1.0 equiv of HBr was used. cRest is a dibromo impurity.

bromoketone and/or bromohydrin with zero effluent discharge, representing an environmentally benign process. The schematic representation for obtaining either bromohydrin and/or bromoketone is shown in Scheme 3, and the representative examples for utilization of the bromide from the effluent (water phase from Table 3) to obtain bromohydrins are presented in Table 4. As evidenced from the results of Table 4, maximum bromide atom efficiency was achieved and the corresponding bromohydrins were obtained in excellent yields and with high selectivity. The aqueous effluent containing bromide could be utilized either for the same or different styrenes as desired. Finally, to evaluate the efficiency of the present reagent system, we also carried out the selective oxidation of benzylic alcohols to aldehydes, and secondary alcohols to ketones, using a catalytic amount of HBr (0.1 equiv) and aqueous H2O2 (1.2 equiv) in aqueous dioxane at room temperature. It is known that at room temperature HBr-H2O2 generates molecular bromine, and in aqueous medium the molecular bromine disproportionates to HBr and HOBr (eqs 1 and 2).5c HOBr is a good selective and mild oxidizing agent for a number of organic substrates (eq 3).7,18 Thus, a general mechanism for the synthesis of bromohydrins/R-bromoketones with the present system is

Ind. Eng. Chem. Res., Vol. 49, No. 17, 2010 Table 4. Synthesis of Bromohydrin from the Aqueous Effluent Containing Bromide (from Table 3) under the Conditions of Table 1

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Table 5. Oxidation of Benzylic Alcohols to Aldehydes

a GC conversions. b GC yields of bromohydrins based on area % yields in parentheses refer to isolated products. c 89:4, 95:2, and 87:4 regioisomers are obtained in entries 2-4, respectively. a Isolated yields after separation by column chromatography. benzoic acid.

Scheme 4

b

15%

Table 6. Oxidation of Secondary Alcohols to Ketones

proposed (Scheme 4). A similar mechanism operates for the oxidation of alcohols. 2HBr + H2O2 f Br2 + H2O

(1)

Br2 + H2O f HOBr + HBr

(2)

RCH(OH)R1 + HOBr f RC(O)R1 + HBr + H2O

(3)

HBr-H2O2 has been reported to oxidize a number of secondary alcohols at 80 °C,21 but the reported procedure does not include the oxidation of benzylic alcohols to aldehydes with this system. We observed that the present system is effective for the selective oxidation of benzylic alcohols to aldehydes as well as secondary alcohols to ketones in aqueous dioxane at room temperature. We further observed that when the oxidation of benzyl alcohol was carried out under the present conditions (HBr: 0.1 equiv and aqueous H2O2: 1.2 equiv) with only water at room temperature, the conversion of alcohols to aldehydes was not efficient as in case of dioxane medium (Table 5, entry 1), where complete conversion was observed. Under the conditions of aqueous dioxane as solvent with HBr (0.1 equiv) and aqueous 30% H2O2 (1.2 equiv) at room temperature, a series of benzylic alcohols were selectively converted to the corresponding aldehydes in excellent yields. These results are summarized in Table 5. Benzyl alcohol provided 78% isolated yield of benzaldehyde along with 15% benzoic acid. Except for benzyl alcohol, other alcohols neatly converted to the corresponding aldehydes. Both electron-withdrawing as well as electron-releasing alcohols

a

Isolated yields after separation by column chromatography.

provided selective aldehydes in good isolated yields. Since HBr is a nonprecious and broadly available in common chemical laboratories, it can be generally used for the oxidation of various benzylic alcohols to aldehydes in a catalytic amount (10 mol %) as an alternate to the precious metal catalysts.8-11 The generality of the present catalytic system proved to be very fruitful for the oxidation of secondary alcohols to ketones under the same reaction conditions (Table 6). All secondary alcohols were selectively and efficiently converted to the corresponding ketones in excellent yields. The oxidation reactions of secondary alcohols were completed within 8 h, compared to 20 h reaction time for the oxidation of benzyl alcohols (Table 5) studied in the present investigation. 4. Conclusions In summary, the present method describes an efficient, selective, and environmentally benign method for the synthesis

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of bromohydrins and R-bromoketones using the HBr-H2O2 system in water under mild conditions. The dibromo impurity generated during the bromohydrin synthesis is selectively converted to bromohydrin by refluxing in water. This conversion is possible only when the reaction is carried out in water but not in any organic solvent media. Further, the HBr (0.7 equiv) generated during the conversion of bromohydrin to R-bromoketones is utilized to get back bromohydrin by charging a fresh substrate under the conditions specified. Therefore, the present system generates absolutely zero effluent, representing an environmentally benign process. Catalysis with HBr (10 mol %) is a highly efficient and selective method for the oxidation of various benzylic alcohols to aldehydes, and secondary alcohols to ketones, in aqueous dioxane medium at room temperature. Furthermore, the versatility toward a range of styrenes to obtain either bromohydrins or R-bromoketones and for the selective oxidation of benzylic/secondary alcohols to carbonyl compounds, simple reaction conditions, and excellent yields of the products make this method a facile, ideal, and attractive synthetic tool. Acknowledgment The authors gratefully acknowledge DST, New Delhi, India, for the financial support of this project under the Green Chemistry Task Force Scheme [No.SR/S5/GC-02A/2006]. We thank Miss Daksha Kuvadia, H. Brahmbhatt, and Mr. Hitesh of our Analytical Division for conducting GC-MS and NMR analyses. We thank Dr. S. H. R. Abdi and Dr. R. I. Kureshi for chiral HPLC analysis of a sample. R.D.P. and G.J. are thankful to CSIR, New Delhi, India, for the award of Senior Research Fellowships. Literature Cited (1) Butler, A.; Walker, J. V. Marine Haloperoxidases. Chem. ReV. 1993, 93, 1937. (2) (a) Larock, R. C. ComprehensiVe Organic Transformations, 2nd ed.; VCH: New York, 1999, 715-719. (b) Bryan, L.; Charles, K. F.; Chiu, R. F.; Hank, J. M.; Joshua, R.; Harry, T. An Optimized Process for Formation of 2,4-Disubstituted Imidazoles from condensation of Amidines and R-Haloketones. Org. Process Res. DeV. 2002, 6, 682. (c) Takayuki, T.; Saeko, I.; Hiroshiand, S.; Koichiro, O. TiCl4-n-Bu4NI as a Reducing Reagent: Pinacol Coupling and Enolate Formation from R-Haloketones. J. Org. Chem. 2000, 65, 5066. (3) (a) Langman, A. W.; Dalton, D. R. Organic Syntheses; John Wiley & Sons: New York, 1988, Coll. Vol. VI, 184-186. (b) Guss, C. O.; Rosenthal, R. Bromohydrins from Olefins and N-Bromosuccinimde in water. J. Am. Chem. Soc. 1955, 77, 2549. (c) Dalton, D. R.; Dutta, V. P.; Jones, D. C. Bromohydrin formation in dimethyl sulphoxide. J. Am. Chem. Soc. 1968, 90, 5498. (d) Mernya´k, E.; Scho¨necker, B.; Lange, C.; Ko¨tteritzsch, M.; Go¨rls, H.; Wo¨lfling, J.; Schneider, G. Addition Reactions at the 16(17) Double Bond of 3-Methoxy-13R-estra-1,3,5(10),16-tetraene. Steroids 2003, 68, 289. (4) (a) Sharghi, H.; Eskandari, M. M. Conversion of Epoxides into Halohydrins with Elemental Halogen Catalyzed by Thiourea. Tetrahedron 2003, 59, 8509. (b) Niknam, K.; Nasehi, T. Cleavage of Epoxides into Halohydrins with Elemental Iodine and Bromine in the Presence of 2,6bis[2-(o-aminophenoxy)methyl]-4-bromo-1-methoxybenzene (BABMB) as Catalyst. Tetrahedron 2002, 58, 10259. (c) Sharghi, H.; Niknam, K.; Pooyan, M. The Halogen- Mediated Opening of Epoxides in the Presence of Pyridine-Containing Acrocycles. Tetrohedron 2001, 57, 6057. (d) Kotsuki, H.; Shimanouchi, T. A Facile Conversion of Epoxides to β-Halohydrins with Silica Gel-Supported Lithium Halides. Tetrahedron Lett. 1996, 37, 1845. (5) (a) For a review, see Podgorseˇk, A.; Zupan, M.; Iskra, J. Oxidative Halogenation with Green Oxidants: Oxygen and Hydrogen Peroxide. Angew. Chem., Int. Ed. 2009, 48, 8424. (b) Podgorseˇk, A.; Eissen, M.; Fleckenstein, J.; Stavber, S.; Zupan, M.; Iskra, J. Selective Aerobic Oxidative Dibromination of Alkenes with Aqueous HBr and Sodium Nitrite as a Catalyst. Green Chem. 2009, 11, 120. (c) Podgorseˇk, A.; Stavber, S.; Zupan, M.; Iskra, J. Bromination of Ketones with H2O2-

HBr “On Water”. Green Chem. 2007, 9, 1212. (d) Podgorseˇk, A.; Stavber, S.; Zupan, M.; Iskra, J. Environmentally Benign Electrophilic and Radical Bromination ‘On Water’: H2O2-HBr System versus N-bromosuccinimide. Tetrahedron 2009, 65, 4429. (e) Podgorseˇk, A.; Stavber, S.; Zupan, M.; Iskra, J. Free Radical Bromination by the H2O2-HBr System On Water. Tetrahedron Lett. 2006, 47, 7245. (6) (a) Adimurthy, S.; Ramachandraiah, G.; Bedekar, A. V.; Ghosh, S.; Ranu, B. C.; Ghosh, P. K. Eco-friendly and Versatile Brominating Reagent Prepared from a Liquid Bromine Precursor. Green Chem. 2006, 8, 916. (b) Adimurthy, S.; Ghosh, S.; Patoliya, P. U.; Ramachandraiah, G.; Agrawal, M.; Gandhi, M. R.; Upadhyay, S. C.; Ghosh, P. K.; Ranu, B. C. An Alternative Method for the Regio- and Stereoselective Bromination of Alkenes, Alkynes, Toluene Derivatives and Ketones using a Bromide/ Bromate Couple. Green Chem. 2008, 10, 232. (c) Agrawal, M. K.; Adimurthy, S.; Ganguly, B.; Ghosh, P. K. Comparative Study of the Vicinal Functionalization of Olefins with 2:1 Bromide/Bromate and Iodide/Iodate Reagents. Tetrahedron 2009, 65, 2791. (7) Patil, R. D.; Joshi, G.; Adimurthy, S.; Ranu, B. C. Facile One-Pot Synthesis of R-Bromoketones from Olefins using Bromide/Bromate Couple as a Nonhazardous Brominating Agent. Tetrahedron Lett. 2009, 50, 2529. (8) (a) Wang, H.; Deng, S. X.; Shen, Z. R.; Wang, J. G.; Ding, D. T.; Chen, T. H. Facile Preparation of Pd/Organoclay Catalysts with High Performance in Solvent-Free Aerobic Selective Oxidation of Benzyl Alcohol. Green Chem. 2009, 11, 1499. (b) Feng, B.; Hou, Z.; Wang, X.; Hu, Y.; Li, H.; Qiao, Y. Selective Aerobic Oxidation of Styrene to Benzaldehyde Catalyzed by Water-Soluble Palladium(II) Complex in Water. Green Chem. 2009, 11, 1446. (c) Jenzer, G.; Sueur, D.; Mallat, T.; Baiker, A. Partial Oxidation of Alcohols in Supercritical Carbon Dioxide. Chem. Commun. 2000, 2247. (9) (a) Ng, Y. H.; Ikeda, S.; Harada, T.; Morita, Y.; Matsumura, M. An Efficient and Reusable Carbon-Supported Platinum Catalyst for Aerobic Oxidation of Alcohols in Water. Chem. Commun. 2008, 3181. (b) Nielsen, R. J.; Goddard, W. A., III. Mechanism of the Aerobic Oxidation of Alcohols by Palladium Complexes of N-Heterocyclic Carbenes. J. Am. Chem. Soc. 2006, 128, 9651. (c) Polshettiwar, V.; Varma, R. S. Nanoparticle-Supported and Magnetically Recoverable Palladium (Pd) Catalyst: A Selective and Sustainable Oxidation Protocol with High Turnover Number. Org. Biomol. Chem. 2009, 7, 37. (d) Wang, T.; Shou, H.; Kou, Y.; Liu, H. Base-free Aqueous-Phase Oxidation of Non-Activated Alcohols with Molecular Oxygen on Soluble Pt Nanoparticles. Green Chem. 2009, 11, 562. (e) Maity, P.; Gopinath, C. S.; Bhaduri, S.; Lahiri, G. K. Applications of a High Performance Platinum Nanocatalyst for the Oxidation of Alcohols in Water. Green Chem. 2009, 11, 554. (10) (a) Mitsudome, T.; Noujima, A.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. Efficient Aerobic Oxidation of Alcohols using a HydrotalciteSupported Gold Nanoparticle Catalyst. AdV. Synth. Catal. 2009, 351, 1890. (b) Ni, J.; Yu, W. J.; He, L. H.; Sun, Y.; Cao, H. He.; Fan, K. N. A Green and Efficient Oxidation of Alcohols by Supported Gold Catalysts using Aqueous H2O2 under Organic Solvent-free Conditions. Green Chem. 2009, 11, 756. (11) (a) Yu, H.; Fu, X.; Zhou, C.; Peng, F.; Wang, H.; Yang, J. Capacitance Dependent Catalytic Activity of RuO2 · xH2O/CNT Nanocatalysts for Aerobic Oxidation of Benzyl Alcohol. Chem. Commun. 2009, 2408. (b) Kato, C. N.; Shinohara, A.; Moriya, N.; Nomiya, K. Water-Soluble Organometallic Ruthenium(II) Complexes Supported on Dawson-Type Polyoxotungstates as Precatalysts: Selective Oxidation of Alcohols with 1 atm Molecular Oxygen. Catal. Commun. 2006, 7, 413. (12) Iron: (a) Dressen, M. H. C. L.; Stumpel, J. E.; van de Kruijs, B. H. P.; Meuldijk, J.; Vekemans, J. A. J. M.; Hulshof, L. A. The Mechanism of the Oxidation of Benzyl Alcohol by Iron(III) Nitrate: Conventional Versus Microwave Heating. Green Chem. 2009, 11, 60. Aluminum: (b) Lei, Z.; Wang, R. Oxidation of Alcohols using H2O2 as Oxidant Catalyzed by AlCl3.. Cat. Commun. 2008, 9, 740. Titanium: (c) Yurdakal, S.; Palmisano, G.; Loddo, V.; Alagoz, O.; Augugliaro, V.; Palmisano, L. Selective Photocatalytic Oxidation of 4-Substituted Aromatic Alcohols in Water with Rutile TiO2 Prepared at Room Temperature. Green Chem. 2009, 11, 510. (13) Chen, Y. L.; Chou, T. C. Kinetics and Mechanism of Anodic Oxidation of n-Butanol by Nickel Peroxide. Ind. Eng. Chem. Res. 1996, 35, 2172. (14) Sawayama, Y.; Shibahara, H.; Ichihashi, Y.; Nishiyama, S.; Tsuruya, S. Promoting Effect and Role of Alkaline Earth Metal Added to Supported Ag Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol. Ind. Eng. Chem. Res. 2006, 45, 8837. (15) Li, Y.; Nakashima, D.; Ichihashi, Y.; Nishiyama, S.; Tsuruya, S. Promotion Effect of Alkali Metal Added to Impregnated Cobalt Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol. Ind. Eng. Chem. Res. 2004, 43, 6021.

Ind. Eng. Chem. Res., Vol. 49, No. 17, 2010 (16) Choudhary, V. R.; Dumbre, D. K.; Oxidation of Benzyl Alcohol to Benzaldehyde by tert-Butyl Hydroperoxide over Nanogold Supported on TiO2 and other Transition and Rare-Earth Metal Oxides. Ind. Eng. Chem. Res. 2009, 48, 9471. (17) Miao, C. X.; He, L. N.; Wang, J. Q.; Wang, J. L. TEMPO and Carboxylic Acid Functionalized Imidazolium Salts/Sodium Nitrite: An Efficient, Reusable, Transition Metal-Free Catalytic System for Aerobic Oxidation of Alcohols. AdV. Synth. Catal. 2009, 351, 2209. (18) Joshi, G.; Bhadra, S.; Ghosh, S.; Agrawal, M. K.; Ganguly, B.; Adimurthy, S.; Ghosh, P. K.; Ranu, B. C. Making Full Use of the Oxidizing Equivalents in Bromate in the Selective Oxidation of Thiols, Sulfides, and Benzylic/Secondary Alcohols into Disulfides, Sulfoxides, and Aldehydes/ Ketones. Ind. Eng. Chem. Res. 2010, 49, 1236. (19) Surendra, K.; Krishnaveni, N. S.; Reddy, M. A.; Nageswar, Y. V. D.; Rama Rao, K. Mild Oxidation of Alcohols with o-Iodoxybenzoic

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Acid (IBX) in Water/Acetone Mixture in the Presence of β-Cyclodextrin. J. Org. Chem. 2003, 68, 2058. (20) Verevkin, S. P.; Krasnykh, E. L.; Wright, J. S. Thermodynamic Properties of Benzyl Halides: Enthalpies of Formation, Strain Enthalpies, and Carbon-Halogen Bond Dissociation Enthalpies. Phys. Chem. Chem. Phys. 2003, 5, 2605. (21) Jain, S. L.; Sharma, V. B.; Sain, B. Highly Efficient and Selective Oxidation of Secondary Alcohols to Ketones under Organic Solvent and Transition Metal free Conditions. Tetrahedron 2006, 62, 6841.

ReceiVed for reView March 5, 2010 ReVised manuscript receiVed July 1, 2010 Accepted July 6, 2010 IE100492R