A simple and efficient oxidation of alcohols with ruthenium on carbon

Article abstract of DOI:10.1039/b908451g

A simple, efficient, and environmentally-friendly heterogeneous Ru/C-catalyzed oxidation of secondary and primary alcohols without additives under an atmosphere of oxygen has been established. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b908451g

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A simple and efficient oxidation of alcohols with ruthenium on carbonw
Shigeki Mori, Masato Takubo, Kazuya Makida, Takayoshi Yanase, Satoka Aoyagi,
Tomohiro Maegawa,z Yasunari Monguchi and Hironao Sajiki*
Received (in Cambridge, UK) 28th April 2009, Accepted 23rd June 2009
First published as an Advance Article on the web 17th July 2009
DOI: 10.1039/b908451g
A simple, efficient, and environmentally-friendly heterogeneous
Ru/C-catalyzed oxidation of secondary and primary alcohols
without additives under an atmosphere of oxygen has been
established.
Table 1 Optimization of reaction conditions
A method for oxidizing alcohols to the corresponding
aldehydes or ketones is one of the most pivotal reactions in
organic chemistry. Although oxidants such as chromium
and manganese reagents have been employed in such
transformations, the necessity of the use of toxic reagents
and the production of a huge amount of heavy metal waste
make the industrial application difficult from an environ-
mental point of view.1 Use of molecular oxygen as an oxidant
together with a heterogeneous metal catalyst should be an
attractive alternative due to the recoverability, reusability,
and residual metal-free property of the catalyst, minimization
of metal-based waste, generation of water as the sole
by-product, and so on.2 Many immobilized transition-metal
catalysts such as PI Au,3 ARP-Pt,4 Ru/Al2O3,5 Pd/HAP,6
Au-Pd/TiO2,7 and HB-Ru8 have been developed to achieve
the efficient oxidation of alcohols. These catalysts, however,
are generally difficult to access because they are handmade
and/or expensive. Much effort has been devoted to develop
efficient oxidation methods for alcohols using the readily
available carbon-supported metal catalysts.2 Although
Pd/C,9 Pt/C,10 or Au/C11-catalyzed oxidation of alcohols has
been reported, addition of other metals such as Co or Cd,
and use of high pressures of oxygen or air, and reaction
temperature under strong basic conditions are required to
obtain the desired products. Ruthenium is less expensive than
gold, palladium or platinum, but very few Ru/C-catalyzed12
and Ru salt on carbon-catalyzed13 oxidation methods
for alcohols have been developed; for example, pantoyl
lactone could be oxidized to the corresponding diketone by
bubbling oxygen through the lactone at a temperature of
170 1C.12 We report here a mild and efficient Ru/C-catalyzed
Entry
Solvent
1 : 2a
1
Toluene
Toluene
Toluene
DMSO
t-BuOH
MeCN
7 : 93
98 : 2
82 : 18
96 : 4
87 : 13
43 : 57
84 : 16
0 : 100
2b
3c
4
5
6
7d
8e
Toluene
Toluene
a
1
b
The ratio was determined by H NMR analysis. Norits was used
c
in place of 10% Ru/C. The reaction was performed under an argon
d
atmosphere. The reaction was performed at rt. The reaction was
e
performed at 70 1C.
oxygen atmosphere, and the corresponding valerophenone (2)
was obtained in 93% conversion (Table 1, entry 1).14 Either
the use of Norits (without Ru metal) in place of 10% Ru/C or
the absence of oxygen (under an argon atmosphere) hardly
promoted the reaction (entries 2 and 3), indicating that Ru
metal and oxygen are essential for the reaction process.
The oxidation in DMSO or t-BuOH scarcely proceeded
(entries 4 and 5), and moderate conversion was obtained in
MeCN (entry 6). While the oxidation was impeded at rt
(compare entries 1 and 7), raising the temperature to 70 1C
greatly enhanced the reaction efficiency, leading to
quantitative formation of 2 (entry 8).15
a
1-Phenylethanol (3a), 1-(2-tolyl)ethanol (3b), 2,2-dimethyl-
1-phenyl-1-propanol (3c), and substrates bearing an electron-
withdrawing group on the aromatic ring (3d and 3e) were
efficiently oxidized to the corresponding ketones (4a–4e) in
excellent yields (Table 2, entries 1–5), whereas a moderate
yield was obtained from an alcohol possessing an electron-
donating methoxy group (entry 6). 1-(Thiophen-2-yl)ethanol (3g),
possessing a sulfur atom which has the potential to act as a
catalyst poison, was also smoothly transformed to the
corresponding ketone (4g) without a decrease in catalytic
activity (entry 7).
oxidation of
a variety of alcohols under an oxygen
atmosphere.
We performed the oxidation of 1-phenyl-1-pentanol (1)
using 10% Ru/C as a catalyst in toluene (50 1C) under an
Laboratory of Organic Chemistry, Department of Organic and
Medicinal Chemistry, Gifu Pharmaceutical University,
5-6-1 Mitahora-higashi, Gifu 502-8585, Japan.
The oxidation of various primary benzylic alcohols (5a–5g)
efficiently gave aldehydes (6a–6g) without overoxidation to the
corresponding carboxylic acid derivatives (Table 3). It is note-
worthy that thiophene- and pyridine-containing alcohols
(5f and 5g) were also efficiently oxidized to 6f and 6g
E-mail: sajiki@gifu-pu.ac.jp; Fax: (+81) 58-237-5979;
Tel: (+81) 58-237-3931
w Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b908451g
z Current address: Graduate School of Pharmaceutical Sciences,
Osaka University 1-6 Yamada-oka, Suita, Osaka 565-0871, Japan
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(entries 6 and 7). These results indicate that the present
oxidation does not seriously suffer from catalyst poisoning
possibly caused by the heterocyclic moiety.
Table 2 Application to various secondary benzylic alcohols
Encouraged by these results, we applied the present
method to the oxidation of cinnamyl and aliphatic
alcohols (Table 4). While p-nitrocinnamyl alcohol (7a) was
smoothly oxidized to the desired product (8a) at 50 1C
(entry 1), the oxidation of cinnamyl alcohol (7b) to cinnam-
aldehyde (8b) was completed by the elevation of the reaction
temperature to 70 1C (entry 2). The oxidation of secondary
aliphatic alcohols (7c and 7d) to the corresponding ketones
(8c and 8d) was achieved at 90 1C with good yields
(entries 3 and 4), while no desired aldehyde (8e) was
obtained in the case of the primary aliphatic alcohol (7e)
under the present reaction conditions (entry 5). Interestingly,
only 14% of 8e could be obtained together with over-
oxidized decanoic acid (8f) as the major product (59%),
which was presumably produced by the oxidation of the
gem-diol formed by the addition of H2O to the resulting
aldehyde (entry 6).
Time
Product (h)
Yield
(%)a
Entry Substrate
1
2
3
4
5
6
7
R1 = Ph, R2 = Me (3a)
4a
4b
4c
4d
5
24
2
99
86
89
96
95
58
86
R1 = 2-MePh, R2 = Me (3b)
R1 = Ph, R2 = t-Bu (3c)
R1 = 4-ClPh, R2 = Ph (3d)
1
R1 = 4-NO2Ph, R2 = Me (3e) 4e
R1 = 4-MeOPh, R2 = Me (3f) 4f
R1 = 2-Thienyl, R2 = Me (3g) 4g
24
24
24
a
Isolated yield.
Table 3 Application to various primary benzylic alcohols
In conclusion, we have established a simple, efficient, and
Ru/C-catalyzed method for the oxidation of a variety of
secondary and primary benzylic alcohols to the corresponding
ketones without any additives such as bases.16 Furthermore,
oxidation of allylic and aliphatic alcohols has also been
achieved. Further detailed investigations related to the present
method including oxidation under air and reuse of Ru/C are
currently ongoing in our laboratory.
Time
(h)
Yield
(%)a
Entry
Substrate
Product
1
2
3
4
R = 4-ClPh (5a)
R = 4-NO2Ph (5b)
R = 4-BnOPh (5c)
R = 2-HOPh (5d)
1-Naphthyl (5e)
2-Thienyl (5f)
6a
6b
6c
6d
6e
6f
6
24
24
24
24
24
24
82
86
89
79
91
87
Quant.
5
6
7b
3-Pyridyl (5g)
6g
We thank the N.E. Chemcat Corporation for the gift of the
10% Ru/C.
a
b
Isolated yield. The reaction was performed at 90 1C.
Table 4 Application to cinnamyl and aliphatic alcohols
Entry
1
Substrate
Product
Temperature (1C)
Yield (%)a
50
85
2
3
70
90
79
66
4
90
61
5
90
90
0
6b
14
a
b
Isolated yield. The reaction was carried out in toluene–H2O (4 : 1). 59% of decanoic acid (8f) was formed.
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11 S. Carrettin, P. McMorn, P. Johnston, K. Griffin and
G. J. Hutchings, Chem. Commun., 2002, 696–697; L. Prati and
F. Porta, Appl. Catal., A, 2005, 291, 199–203; M. Comotti,
C. D. Pina, R. Matarrese, M. Rossi and A. Siani, Appl. Catal.,
A, 2005, 291, 204–209; N. Dimitratos, J. A. Lopez-Sanchez,
D. Lennon, F. Porta, L. Prati and A. Villa, Catal. Lett., 2006,
108, 147–153; G. J. Hutchings, S. Carrettin, P. Landon,
J. K. Edwards, D. Enache, D. W. Knight, Y.-J. Xu and
A. F. Carley, Top. Catal., 2006, 38, 223–230; A. H. Begli,
C. Baatz, N. Decker, U. Pruesse and K.-D. Vorlop, PCT Int.
Appl., WO2008095629, 2008; Y. Onal, S. Schimpf and P. Claus,
J. Catal., 2004, 223, 122–133.
12 M. Matsumoto and S. Ito, Synth. Commun., 1984, 14, 697–700; the
Ru/C–AcOOH system was used for the oxidation of alkanes:
S.-I. Murahashi, Y. Oda, N. Komiya and T. Naota, Tetrahedron
Lett., 1994, 35, 7953–7956; furthermore, Naota et al. recently
reported that Ru/C was inactive for the aerobic oxidation of
alcohols in water: N. Komiya, T. Nakae, H. Sato and T. Naota,
Chem. Commun., 2006, 4829–4831.
Notes and references
1 R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Oxidations of
Organic Compounds, Academic Press, New York, 1981; W. J. Mijs
and C. R. H. De Jonge, Organic Synthesis by Oxidation with Metal
Compounds, Plenum Press, New York, 1986; B. M. Trost,
I. Fleming and S. V. Ley, Comprehensive Organic Synthesis,
Pergamon, Oxford, 1991, vol. 7.
2 For reviews, see: T. Mallat and A. Baiker, Chem. Rev., 2004, 104,
3037–3058; T. Matsumoto, M. Ueno, N. Wang and S. Kobayashi,
Chem.–Asian J., 2008, 3, 196–214.
3 H. Miyamura, R. Matsubara, Y. Miyazaki and S. Kobayashi,
Angew. Chem., Int. Ed., 2007, 46, 4151–4154.
4 Y. M. A. Yamada, T. Arakawa, H. Hocke and Y. Uozumi, Angew.
Chem., Int. Ed., 2007, 46, 704–706.
5 Y. Yamaguchi and N. Mizuno, Angew. Chem., Int. Ed., 2002, 41,
4538–4542.
6 K. Mori, K. Yamaguchi, T. Hara, T. Mizugaki, K. Ebitani and
K. Kaneda, J. Am. Chem. Soc., 2002, 124, 11572–11573; K. Mori,
T. Hara, T. Mizugaki, K. Ebitani and K. Kaneda, J. Am. Chem.
Soc., 2004, 126, 10657–10666.
7 D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu,
A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely,
D. W. Knight and G. J. Hutchings, Science, 2006, 311, 362–365.
8 T. Matsumoto, M. Ueno, N. Wang and S. Kobayashi,
Chem.–Asian J., 2008, 3, 239–243.
9 M. Hronec, Z. Cvengrosova and J. Kizlink, J. Mol. Catal., 1993,
83, 75–82; T. Mallat and A. Baiker, Catal. Today, 1994, 19,
247–283; G. An, M. Lim, K.-S. Chun and H. Rhee, Synlett,
2007, 95–98.
13 [RuCl2(p-cymene)]2 on carbon–O2 was newly prepared for the
oxidation of benzylic alcohols, organosilanes, and aldoximes:
E. Choi, C. Lee, Y. Na and S. Chang, Org. Lett., 2002, 4,
2369–2371.
14 The general procedure for the oxidation of 1-phenyl-1-pentanol (1)
is as follows: A 15 mL test tube was charged with 1-phenyl-1-
pentanol (1) (164 mg, 1.00 mmol), 10% Ru/C (50.5 mg, 0.05
mmol), toluene (2 mL), and oxygen (balloon). The reaction
mixture was placed on the Chemistation personal organic syn-
thesizer (EYELA, Tokyo), heated at 70 1C, and stirred for 24 h.
The mixture was diluted with ether (10 mL) and filtered using a
membrane filter (Millipore, Millex-LH, 0.45 mm). The filtrate was
concentrated in vacuo and the product ratio was determined by
1H NMR analysis of the residue.
15 No leached ruthenium in the filtrate of the reaction mixture was
detected within the limits of the assay (o1 ppm) by analysis with
inductively coupled plasma atomic emission spectrometry.
16 Addition of inorganic base to the aerobic oxidation system was
recommended by Mueller. See: J. A. Mueller and M. S. Sigman,
J. Am. Chem. Soc., 2003, 125, 7005–7013.
10 C. Bronnimann, Z. Bodnar, R. Aeschimann, T. Mallat and
A. Baiker, J. Catal., 1996, 161, 720–729; T. Mallat,
C. Bronnimann and A. Baiker, Appl. Catal., A, 1997, 149,
103–112; P. Korovchenko, C. Donze, P. Gallezot and
M. Besson, Catal. Today, 2007, 121, 13–21; C. Donze,
P. Korovchenko, P. Gallezot and M. Besson, Appl. Catal., B,
2007, 70, 621–629; I. Reile, A. Paju, M. Eek, T. Pehk and M. Lopp,
Synlett, 2008, 347–350; Y. H. Ng, S. Ikeda, T. Harada, Y. Morita
and M. Matsumura, Chem. Commun., 2008, 3181–3183.
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This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 5159–5161 | 5161