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A green and efficient oxidation of benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2
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Chinese Chemical Letters 19 (2008) 1277–1280 www.elsevier.com/locate/cclet
A green and efficient oxidation of benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2 Ali Ezabadi a, Ghloam Reza Najafi b, Mohammad M. Hashemi b,* a
b
Department of Chemistry, Central Tehran Branch, Azad University, Tehran, Iran Department of Chemistry, Science & Research Branch, Azad University, Tehran, Iran Received 31 March 2008
Abstract Primary and secondary benzylic alcohols were oxidized to the corresponding carbonyl compounds in good to high yields by environmentally friendly and green oxidant, H2O2 catalyzed by montmorillonite K-10 supported cobalt(II) chloride. # 2008 Mohammad M. Hashemi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Green oxidation; Hydrogen peroxide; Montmorillonite K-10; Cobalt(II) chloride
The oxidation of alcohols to their corresponding aldehydes and ketones is of significant importance in organic chemistry, both for fundamental research and industrial manufacturing [1–3]. Traditionally, this reaction is realized by using inorganic oxidants (e.g. Cr(VI) reagents). These reagents, which are neither environmental friendly nor economical, are needed in stoichiometric amounts and hard to be separated from products. Hence, in terms of economical and environmental concern, catalytic oxidation processes with inexpensive and environmental oxidants are extremely valuable. One of favorite oxidant to resort to is hydrogen peroxide due to its environmental impact, since water is the only by product of such oxidative reactions [4]. Although a variety of different catalytic systems for the hydrogen peroxide oxidation of alcohols has been developed [5], there is a growing up interest in the search for new efficient metal catalysts for this concern. Clay and polymer supported reagents have been widely applied in organic synthesis mainly because of the ease of separation of products, readily available commercial clays, simple workup, selectivity and mild reaction conditions. Montmorillonite clays have been extensively used as efficient supports for a variety of organic reagents [6]. During the course of our systematic study on catalytic oxidation we have recently reported some salts supported on montmorillonite as a catalyst for the oxidation [7]. Herein, we reported montmorillonite K-10 supported cobalt (II) chloride as a new catalyst for the oxidation of benzylic alcohols (Scheme 1). In the first step, we turned our attention to the conditions of reaction; therefore, we examined different solvents such as chloroform, acetone, ethyl acetate, acetonitrile and dimethylformamide (DMF). The results suggested that DMF was appropriate solvent for oxidation of primary and secondary benzylic alcohols for our purposes. Subsequently, we
* Corresponding author. E-mail address: [email protected] (M.M. Hashemi). 1001-8417/$ – see front matter # 2008 Mohammad M. Hashemi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.09.010
1278
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
Scheme 1.
Table 1 Oxidation of various benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2 Entry
Substrate
Product
Time (h)
H2 O 2 (mL)
Yield (%) a
1
3.5
2.5
90
2
6
4
90
3
8
4
88
4
1
1.5
85
5
1
5
84
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
1279
Table 1 (Continued ) Time (h)
H2 O 2 (mL)
Yield (%) a
6
3
3
83
7
2
3
80
8
7
7
75
9
8
4
50
Entry
a
Substrate
Product
Isolated yields.
considered three thermal conditions, i.e. room, 80 8C, and reflux temperature. After several experiments, we found that 80 8C is an appropriate temperature for this procedure. Moreover, we carried out reactions without the catalyst or the oxidant. We observed that in absence of the catalyst or the oxidant no reaction occurred. After optimizing the reaction condition, we oxidized different primary and secondary benzylic alcohols. The results are summarized in Table 1. It should be mentioned that all the reactions occurred with complete selectivity for aldehydes or ketones and no other products were detected in the reaction mixture. The structures of products were confirmed by IR and 1H NMR [8] and comparison with authentic samples. To demonstrate the recyclability of the catalyst, it was reused at least three cycles for further oxidation without a significant decrease in yield (Table 2). Table 2 Reuse of the catalyst for oxidation of benzyl alcohol Run
Yield (%)
1 2 3
80 80 76
1280
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
In summary, we have extended successfully the application of montmorillonite K-10 supported cobalt (II) chloride for oxidation of benzylic alcohols by H2O2. This method offers some advantages in terms of simplicity of performance, high yields without side product formation, mild and green reaction conditions. 1. Experimental The catalyst was prepared by adding: montmorillonite K-10 to a solution of cobalt (II) chloride hexahydrate in acetone (0.2 mmol g 1 montmorillonite). The mixture was stirred at room temperature for 2 h. The solvent was then evaporated and the residue was dried at 115 8C for 5 h. In a typical oxidation procedure: to a solution of 1 mmole benzylic alcohol in 10 mL DMF, 1 g catalyst was added. The reaction mixture was stirred at 80 8C and H2O2 was added dropwise by the time indicated in Table 1. The reaction progress was monitored by TLC (eluent: n-hexane:ethyl acetate = 7:3). The reaction mixture was cooled to room temperature and then filtrated to recover the catalyst. The filtrate was extracted with toluene/H2O (15 mL/15 mL). The organic layer was dried over Na2SO4 and the solvent was then evaporated and the product purified by column chromatography over silica gel (eluent: n-hexane:ethyl acetate = 7:3). References [1] [2] [3] [4]
[5]
[6]
[7]
[8]
R.C. Larock, Comprehensive Organic Transformations, VCH, New York, 1999, p. 1234. R.A. Sheldon, J.K. Kochi, Metal-Catalyzed Oxidation of Organic Compounds, Academic, New York, 1981, p. 350. B.M. Trost, I. Fleming, S.V. Ley, Comprehensive Organic Synthesis, vol. 7, Pergamon, Oxford, 1991. (a) G. Strukul (Ed.), Catalytic Oxidations with Hydrogen Peroxide as Oxidant, Kluwer, Dordrecht, The Netherlands, 1992; (b) K. Sato, M. Aoki, M. Ogawa, T. Hashimoto, R. Noyori, J. Org. Chem. 61 (1996) 8310; (c) W.R. Sanderson, Pure Appl. Chem. 72 (2000) 1298. (a) For some examples: S.E. Martin, A. Garrone, Tetrahedron Lett. 44 (2003) 547, and references cited therein; (b) R. Noyori, M. Aoki, K. Sato, Chem. Commun. (2003) 1977; (c) E. Balogh-Hregovich, G. Speier, J. Mol. Cat. A 230 (2005) 79; Z. Weng, G. Liao, J. Wang, X. Jian, Cat. Commun. 8 (2007) 1493; (d) Z.Q. Lei, R.R. Wang, Cat. Commun. 9 (2008) 740; J. Liu, F. Wang, K. Sun, X. Xu, Cat. Commun. 9 (2008) 386. (a) N. Narayanan, T.R. Bala Subramanian, J. Chem. Res. Synop. 4 (1992) 132; (b) D. Li, F. Shi, S. Guo, Y. Deng, Tetrahedron Lett. 45 (2004) 265; (c) B. Tamami, H. Yaganeh, Reac. Func. Poly. 50 (2002) 101; (d) C.R. Harrison, P. Hodge, J. Chem. Soc. Perkin Trans. I (1989) 509; (e) H. Firouzabadi, B. Tamami, N. Goudarzian, M.M. Lakourage, M. Hatam, Synth. Commun. 21 (1991) 2077. (a) A. Ezabadi, G.R. Najafi, M.M. Hashemi, Chinese Chem. Lett. 18 (2007) 1451; (b) M.M. Hashemi, A. Ezabadi, Z. Karimi-Jaberi, Lett. Org. Chem. 2 (2005) 559; (c) M.M. Hashemi, D. Ghazanfari, Y. Ahmadibeni, Z. Karimi-Jaberi, A. Ezabadi, Synth. Commun. 35 (2005) 1103; (d) M.M. Hashemi, Z. Karimi-Jaberi, Monatsh. Chem. 135 (2004) 41; (e) M.M. Hashemi, Z. Karimi-Jaberi, D. Ghazanfari, J. Chem. Res. (2004) 365; (f) M.M. Hashemi, B. Khalili, B. Eftekhari-Sis, J. Chem. Res. (2005) 484; (g) M.M. Hashemi, M. Akhbari, Z. Kaimi-jaberi, Lett. Org. Chem. 3 (2006) 39; (h) M.M. Hashemi, F. Kalantari, Synth. Commun. 30 (2000) 1857. 1 H NMR (300 MHz, CDCl3, d ppm) for selected compounds: Benzaldehyde: 9.8 (s, 1H), 7.4–7.8 (m, 5H), 4-methoxybenzaldehyde: 9.9 (s, 1H), 7.8 (d, 2H, J = 8.4 Hz), 7.0 (d, 2H, J = 8.4 Hz), 3.9 (s, 3H) Acetophenone: 7.8–8.0 (m, 2H), 7.3–7.6 (m, 3H) Benzil: 7.8–8.0 (m, 4H), 7.6–7.7 (m, 2H), 7.3–7.5 (m, 4H).
Chinese Chemical Letters 19 (2008) 1277–1280 www.elsevier.com/locate/cclet
A green and efficient oxidation of benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2 Ali Ezabadi a, Ghloam Reza Najafi b, Mohammad M. Hashemi b,* a
b
Department of Chemistry, Central Tehran Branch, Azad University, Tehran, Iran Department of Chemistry, Science & Research Branch, Azad University, Tehran, Iran Received 31 March 2008
Abstract Primary and secondary benzylic alcohols were oxidized to the corresponding carbonyl compounds in good to high yields by environmentally friendly and green oxidant, H2O2 catalyzed by montmorillonite K-10 supported cobalt(II) chloride. # 2008 Mohammad M. Hashemi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Green oxidation; Hydrogen peroxide; Montmorillonite K-10; Cobalt(II) chloride
The oxidation of alcohols to their corresponding aldehydes and ketones is of significant importance in organic chemistry, both for fundamental research and industrial manufacturing [1–3]. Traditionally, this reaction is realized by using inorganic oxidants (e.g. Cr(VI) reagents). These reagents, which are neither environmental friendly nor economical, are needed in stoichiometric amounts and hard to be separated from products. Hence, in terms of economical and environmental concern, catalytic oxidation processes with inexpensive and environmental oxidants are extremely valuable. One of favorite oxidant to resort to is hydrogen peroxide due to its environmental impact, since water is the only by product of such oxidative reactions [4]. Although a variety of different catalytic systems for the hydrogen peroxide oxidation of alcohols has been developed [5], there is a growing up interest in the search for new efficient metal catalysts for this concern. Clay and polymer supported reagents have been widely applied in organic synthesis mainly because of the ease of separation of products, readily available commercial clays, simple workup, selectivity and mild reaction conditions. Montmorillonite clays have been extensively used as efficient supports for a variety of organic reagents [6]. During the course of our systematic study on catalytic oxidation we have recently reported some salts supported on montmorillonite as a catalyst for the oxidation [7]. Herein, we reported montmorillonite K-10 supported cobalt (II) chloride as a new catalyst for the oxidation of benzylic alcohols (Scheme 1). In the first step, we turned our attention to the conditions of reaction; therefore, we examined different solvents such as chloroform, acetone, ethyl acetate, acetonitrile and dimethylformamide (DMF). The results suggested that DMF was appropriate solvent for oxidation of primary and secondary benzylic alcohols for our purposes. Subsequently, we
* Corresponding author. E-mail address: [email protected] (M.M. Hashemi). 1001-8417/$ – see front matter # 2008 Mohammad M. Hashemi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.09.010
1278
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
Scheme 1.
Table 1 Oxidation of various benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2 Entry
Substrate
Product
Time (h)
H2 O 2 (mL)
Yield (%) a
1
3.5
2.5
90
2
6
4
90
3
8
4
88
4
1
1.5
85
5
1
5
84
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
1279
Table 1 (Continued ) Time (h)
H2 O 2 (mL)
Yield (%) a
6
3
3
83
7
2
3
80
8
7
7
75
9
8
4
50
Entry
a
Substrate
Product
Isolated yields.
considered three thermal conditions, i.e. room, 80 8C, and reflux temperature. After several experiments, we found that 80 8C is an appropriate temperature for this procedure. Moreover, we carried out reactions without the catalyst or the oxidant. We observed that in absence of the catalyst or the oxidant no reaction occurred. After optimizing the reaction condition, we oxidized different primary and secondary benzylic alcohols. The results are summarized in Table 1. It should be mentioned that all the reactions occurred with complete selectivity for aldehydes or ketones and no other products were detected in the reaction mixture. The structures of products were confirmed by IR and 1H NMR [8] and comparison with authentic samples. To demonstrate the recyclability of the catalyst, it was reused at least three cycles for further oxidation without a significant decrease in yield (Table 2). Table 2 Reuse of the catalyst for oxidation of benzyl alcohol Run
Yield (%)
1 2 3
80 80 76
1280
A. Ezabadi et al. / Chinese Chemical Letters 19 (2008) 1277–1280
In summary, we have extended successfully the application of montmorillonite K-10 supported cobalt (II) chloride for oxidation of benzylic alcohols by H2O2. This method offers some advantages in terms of simplicity of performance, high yields without side product formation, mild and green reaction conditions. 1. Experimental The catalyst was prepared by adding: montmorillonite K-10 to a solution of cobalt (II) chloride hexahydrate in acetone (0.2 mmol g 1 montmorillonite). The mixture was stirred at room temperature for 2 h. The solvent was then evaporated and the residue was dried at 115 8C for 5 h. In a typical oxidation procedure: to a solution of 1 mmole benzylic alcohol in 10 mL DMF, 1 g catalyst was added. The reaction mixture was stirred at 80 8C and H2O2 was added dropwise by the time indicated in Table 1. The reaction progress was monitored by TLC (eluent: n-hexane:ethyl acetate = 7:3). The reaction mixture was cooled to room temperature and then filtrated to recover the catalyst. The filtrate was extracted with toluene/H2O (15 mL/15 mL). The organic layer was dried over Na2SO4 and the solvent was then evaporated and the product purified by column chromatography over silica gel (eluent: n-hexane:ethyl acetate = 7:3). References [1] [2] [3] [4]
[5]
[6]
[7]
[8]
R.C. Larock, Comprehensive Organic Transformations, VCH, New York, 1999, p. 1234. R.A. Sheldon, J.K. Kochi, Metal-Catalyzed Oxidation of Organic Compounds, Academic, New York, 1981, p. 350. B.M. Trost, I. Fleming, S.V. Ley, Comprehensive Organic Synthesis, vol. 7, Pergamon, Oxford, 1991. (a) G. Strukul (Ed.), Catalytic Oxidations with Hydrogen Peroxide as Oxidant, Kluwer, Dordrecht, The Netherlands, 1992; (b) K. Sato, M. Aoki, M. Ogawa, T. Hashimoto, R. Noyori, J. Org. Chem. 61 (1996) 8310; (c) W.R. Sanderson, Pure Appl. Chem. 72 (2000) 1298. (a) For some examples: S.E. Martin, A. Garrone, Tetrahedron Lett. 44 (2003) 547, and references cited therein; (b) R. Noyori, M. Aoki, K. Sato, Chem. Commun. (2003) 1977; (c) E. Balogh-Hregovich, G. Speier, J. Mol. Cat. A 230 (2005) 79; Z. Weng, G. Liao, J. Wang, X. Jian, Cat. Commun. 8 (2007) 1493; (d) Z.Q. Lei, R.R. Wang, Cat. Commun. 9 (2008) 740; J. Liu, F. Wang, K. Sun, X. Xu, Cat. Commun. 9 (2008) 386. (a) N. Narayanan, T.R. Bala Subramanian, J. Chem. Res. Synop. 4 (1992) 132; (b) D. Li, F. Shi, S. Guo, Y. Deng, Tetrahedron Lett. 45 (2004) 265; (c) B. Tamami, H. Yaganeh, Reac. Func. Poly. 50 (2002) 101; (d) C.R. Harrison, P. Hodge, J. Chem. Soc. Perkin Trans. I (1989) 509; (e) H. Firouzabadi, B. Tamami, N. Goudarzian, M.M. Lakourage, M. Hatam, Synth. Commun. 21 (1991) 2077. (a) A. Ezabadi, G.R. Najafi, M.M. Hashemi, Chinese Chem. Lett. 18 (2007) 1451; (b) M.M. Hashemi, A. Ezabadi, Z. Karimi-Jaberi, Lett. Org. Chem. 2 (2005) 559; (c) M.M. Hashemi, D. Ghazanfari, Y. Ahmadibeni, Z. Karimi-Jaberi, A. Ezabadi, Synth. Commun. 35 (2005) 1103; (d) M.M. Hashemi, Z. Karimi-Jaberi, Monatsh. Chem. 135 (2004) 41; (e) M.M. Hashemi, Z. Karimi-Jaberi, D. Ghazanfari, J. Chem. Res. (2004) 365; (f) M.M. Hashemi, B. Khalili, B. Eftekhari-Sis, J. Chem. Res. (2005) 484; (g) M.M. Hashemi, M. Akhbari, Z. Kaimi-jaberi, Lett. Org. Chem. 3 (2006) 39; (h) M.M. Hashemi, F. Kalantari, Synth. Commun. 30 (2000) 1857. 1 H NMR (300 MHz, CDCl3, d ppm) for selected compounds: Benzaldehyde: 9.8 (s, 1H), 7.4–7.8 (m, 5H), 4-methoxybenzaldehyde: 9.9 (s, 1H), 7.8 (d, 2H, J = 8.4 Hz), 7.0 (d, 2H, J = 8.4 Hz), 3.9 (s, 3H) Acetophenone: 7.8–8.0 (m, 2H), 7.3–7.6 (m, 3H) Benzil: 7.8–8.0 (m, 4H), 7.6–7.7 (m, 2H), 7.3–7.5 (m, 4H).