Highly efficient oxidation of alcohols to carbonyl compounds in the presence of molecular oxygen using a novel heterogeneous ruthenium catalyst

Article abstract of DOI:10.1016/S0040-4039(02)01678-7

A ruthenium cation combined with microcrystals of cobalt hydroxide and cerium oxide acted as a highly efficient heterogeneous catalyst for the oxidation of various types of alcohols to carbonyl compounds under atmospheric pressure of molecular oxygen at 60°C. Especially, primary aliphatic alcohols could be oxidized to afford the carboxylic acids in high yields.

Full text of DOI:10.1016/S0040-4039(02)01678-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7179–7183
Highly efficient oxidation of alcohols to carbonyl compounds in
the presence of molecular oxygen using a novel heterogeneous
ruthenium catalyst
Hongbing Ji, Tomoo Mizugaki, Kohki Ebitani and Kiyotomi Kaneda*
Department of Chemical Science and Engineering, Graduate School of Engineering Science, Osaka University,
1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
Received 1 July 2002; revised 8 August 2002; accepted 9 August 2002
Abstract—A ruthenium cation combined with microcrystals of cobalt hydroxide and cerium oxide acted as a highly efficient
heterogeneous catalyst for the oxidation of various types of alcohols to carbonyl compounds under atmospheric pressure of
molecular oxygen at 60°C. Especially, primary aliphatic alcohols could be oxidized to afford the carboxylic acids in high yields.
© 2002 Elsevier Science Ltd. All rights reserved.
The selective oxidation of alcohols to the corresponding
carbonyl compounds plays an important role in organic
synthesis.1 Even at present, however, stoichiometric
amounts of hazardous and/or toxic inorganic oxidants
that generate copious amounts of wastes are used.2
Much attention has been paid to the use of molecular
oxygen as a ‘green’ oxidant to achieve the effective
oxidation of alcohols in the presence of transition metal
catalysts.3,4 Recently, we have developed highly active
heterogeneous ruthenium catalysts for aerobic alcohol
oxidations based on the unique characteristics of inor-
ganic matrices, i.e. hydrotalcites and hydroxyap-
atites.4b,d,e In this paper, a Ru cation combined with
cobalt hydroxide and cerium oxide, Ru–Co(OH)2–
CeO2, was found to be an effective heterogeneous cata-
lyst for the oxidation of various alcohols to carbonyl
compounds under atmospheric pressure of O2. Notably,
the present catalyst showed high activity for the oxida-
tion of primary aliphatic alcohols to carboxylic acids
(Scheme 1).4c,f
The Ru–Co(OH)2–CeO2 catalyst was prepared as fol-
lows. To 30 ml of aqueous Na2CO3 (13.3 mmol) and
NaOH (46.4 mmol) was slowly added a mixture of
Co(NO3)2·6H2O (10.2 mmol), Ce(NO3)3·6H2O (5.1
mmol), and RuCl3·nH2O (Ru: 1.53 mmol) dissolved in
20 mL of distilled water, and the resultant mixture was
heated at 65°C for 18 h with vigorous stirring. The dark
brown slurry was filtered, washed with distilled water
and dried at 110°C for 12 h, yielding 2.15 g of black
powder [Anal. Co, 33.6; Ce, 25.7; Ru, 6.4. XPS: Ru
3p3/2=464.4 eV, FWHM=4.9 eV; Co 2p3/2=780.8 eV,
FWHM=2.6 eV].5
The black powder exhibited high catalytic activity for
the oxidation of various kinds of alcohols in the pres-
ence of molecular oxygen as summarized in Table 1.6
Allylic alcohols (entries 1, 3 and 4), benzylic alcohols
(entries 5–8), and secondary alcohols (entries 9–13)
gave high yields of the corresponding carbonyl com-
pounds. A heteroaromatic alcohol of 2-thiophen-
methanol could be also oxidized quantitatively to
2-thiophencarboxaldehyde (entry 8). The notable ability
of the Ru–Co(OH)2–CeO2 catalyst over other heteroge-
neous Ru catalysts was the oxidation of cyclohexanol
to cyclohexanone in high yield (entry 10). Sterically
hindered secondary alcohols, i.e. borneol and adaman-
tanol, could be smoothly converted to the correspond-
ing ketones in quantitative yields (entries 12 and 13).
Furthermore, the Ru–Co(OH)2–CeO2 could be reused
with retention of its high catalytic activity (entry 2).7,8
Scheme 1.
Keywords: oxidation; alcohols; carbonyl compounds; molecular oxy-
gen; ruthenium catalyst.
Encouraged by the above results, the oxidation of
primary aliphatic alcohols, e.g. 1-octanol, was exam-
* Corresponding author. Tel./fax: +81-6-6850-6260; e-mail: kaneda@
cheng.es.osaka-u.ac.jp
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01678-7

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H. Ji et al. / Tetrahedron Letters 43 (2002) 7179–7183
a
Table 1. Aerobic oxidation of various alcohols catalyzed by Ru–Co(OH)2–CeO2
ined using various Ru catalysts under atmospheric O2
pressure as shown in Table 2. Notably, the Ru–
Co(OH)2–CeO2 was found to be a highly efficient cata-
lyst for the oxidation of 1-octanol to octanoic acid at
60°C (entry 1). This Ru catalyst was more effective for
the aerobic oxidation of primary alcohols than the
RuHAP and Ru/CeO2 (entries 3 and 4).4c,f In a separate
experiment using this Ru–Co(OH)2–CeO2 catalyst,
octanal was smoothly oxidized to octanoic acid even at
room temperature in the air (Scheme 2), while slow
oxidation occurred with Co(OH)2–CeO2 catalyst.4c,9
Without the Ce component, the yield of octanoic acid
was low in spite of a high conversion of 1-octanol
(entry 2). It can be said that a combination of Ru with
both Co and Ce elements is necessary to achieve high
yield of the carboxylic acid.
Table 3 shows the results for the oxidation of various
primary alcohols using the Ru–Co(OH)2–CeO2 cata-
lyst.10 Aliphatic alcohols were smoothly oxidized to the

H. Ji et al. / Tetrahedron Letters 43 (2002) 7179–7183
7181
Table 2. Aerobic oxidation of 1-octanol using various types of heterogeneous Ru catalystsa
Entry
Catalystb
Conv. of 1-octanol (%)c
Yields (%)c
Octanoic acid
Octanal
1
2
3
4e
5
6
7
Ru–Co(OH)2–CeO2
Ru–Co–Al–CO3
Ru/CeO2
100
90
30
95
58
97
63
28
0
1
0
1
26
0
94
48
15
B1
d
RuHAP
Ru–Mg–Ce–CO3
Ru–Mg–Al–CO3
Co(OH)2–CeO2
16
B2
0
a Reaction conditions: 1-octanol (2 mmol), catalyst (0.3 g, Ru: 6 wt%), benzotrifluoride (5 mL), O2 flow, 60°C, 4 h.
b Molar ratio: Co/Ce/Ru=Co/Al/Ru=Mg/Ce/Ru=Mg/Al/Ru=2/1/0.3.
c Conversion and yields were determined by GC using an internal standard method.
d Prepared by the literature procedures (Ref. 4c).
e Data from Ref. 4e.
Scheme 2.
Table 3. Oxidation of various primary alcohols catalyzed by Ru–Co(OH)2–CeO2 in the presence of molecular oxygena

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H. Ji et al. / Tetrahedron Letters 43 (2002) 7179–7183
corresponding carboxylic acids in excellent yields
(entries 1–6). Addition of water improved the catalytic
activity to attain a high yield of the branched car-
boxylic acid (entry 4). a,v-Primary diols were selec-
tively transformed into the corresponding lactones in
high yields (entries 7 and 8). Intramolecular competitive
oxidation of 1,4-pentanediol having primary and sec-
ondary hydroxyls gave methyl-g-butyrolactone in 87%
yield (entry 9). To the best of our knowledge, this
Ru–Co(OH)2–CeO2 is the most effective catalyst for the
one-pot oxidation of primary aliphatic alcohols into
carboxylic acids using atmospheric pressure of O2 as a
sole oxidant.
Millar, J. G.; Oehlschlager, A. C.; Wong, J. W. J. Org.
Chem. 1983, 48, 4404; RuCl3/H5IO6: (b) Carlsen, P. H.
J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J. Org.
Chem. 1981, 46, 3936; CrO3/H5IO6: (c) Zhao, M.; Li, J.;
Song, Z.; Desmond, R.; Tschaen, D. M.; Grabowski, E.
J. J.; Reider, P. J. Tetrahedron Lett. 1998, 39, 5323:
TEMPO/NaClO: (d) Zhao, M.; Li, J.; Mano, E.; Song,
Z.; Tschaen, D. M.; Grabowski, E. J. J.; Reider, P. J. J.
Org. Chem. 1999, 64, 2564; (e) Yasuda, K.; Ley, S. V. J.
Chem. Soc., Perkin Trans. 1 2002, 1024.
3. For typical examples of Ru complex-catalyzed homoge-
neous oxidations of alcohols in the presence of molecu-
lar oxygen, see: (a) Ba¨ckvall, J.-E.; Chowdhury, E. L.;
Karlsson, U. J. Chem. Soc., Chem. Commun. 1991, 473;
(b) Murahashi, S.-I.; Naota, T.; Hirai, N. J. Org. Chem.
1993, 58, 7318; (c) Marko´, I. E.; Giles, P. R.; Tsukazaki,
M.; Chelle´-Regnaut, I.; Urch, C. J.; Brown, S. M. J.
Am. Chem. Soc. 1997, 119, 12661; (d) Hanyu, A.;
Takezawa, E.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett.
1998, 39, 5557; (e) Masutani, K.; Uchida, T.; Irie, R.;
Katsuki, T. Tetrahedron Lett. 2000, 41, 5119; (f) Dijks-
man, A.; Marino-Gonza´lez, A.; Payeras, A. M. I.;
Arends, I. W. C. E.; Sheldon, R. A. J. Am. Chem. Soc.
When 2,6-di-tert-butyl-p-cresol as a radical scavenger
was added in the oxidation of 1-octanol, octanal was
formed in a quantitative yield without formation of the
corresponding carboxylic acid. The present oxidation
might proceed via a Ru–alkoxide intermediate, fol-
lowed by b-hydride elimination to give an aldehyde.11
An efficient transformation of aldehyde to carboxylic
acid might involve a free radical process. As previously
noted, the oxidation of aldehyde to carboxylic acid was
slow using Ce-free Ru catalyst, i.e. Ru–Co–Al–CO3.
High activity of this Ru catalyst might be due to a high
oxidation state of the Ru species, e.g. Ru(IV), arising
from the Co component.12 The radical process of the
aldehyde oxidation13 would be also facilitated by the
synergism among the Ru, Co, and Ce components.
´
2001, 123, 6826; (g) Csjernyik, G.; Ell, A. H.; Fadini, L.;
Pugin, B.; Ba¨ckvall, J.-E. J. Org. Chem. 2002, 67, 1657.
4. For typical examples of aerobic alcohol oxidations using
heterogeneous catalysts, see: Ru: (a) Matsumoto, M.;
Watanabe, M. J. Org. Chem. 1984, 49, 3435; (b)
Kaneda, K.; Yamashita, T.; Matsushita, T.; Ebitani, K.
J. Org. Chem. 1998, 63, 1750; (c) Vocanson, F.; Guo, Y.
P.; Namy, J. L.; Kagan, H. B. Synth. Commun. 1998,
28, 2577; (d) Matsushita, T.; Ebitani, K.; Kaneda, K.
Chem. Commun. 1999, 265; (e) Yamaguchi, K.; Mori,
K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem.
Soc. 2000, 122, 7144; Pd: (f) Akada, M.; Nakano, S.;
Sugiyama, T.; Ichitoh, K.; Nakao, H.; Akita, M.; Moro-
oka, Y. Bull. Chem. Soc. Jpn. 1993, 66, 1511; (g) Ebi-
tani, K.; Fujie, Y.; Kaneda, K. Langmuir 1999, 15, 3557;
(h) Nishimura, T.; Kakiuchi, N.; Inoue, M.; Uemura, S.
Chem. Commun. 2000, 1245; (i) Kakiuchi, N.; Maeda,
Y.; Nishimura, T.; Uemura, S. J. Org. Chem. 2001, 66,
6620; (j) Kakiuchi, N.; Nishimura, T.; Inoue, M.;
Uemura, S. Bull. Chem. Soc. Jpn. 2001, 74, 165; Ni: (k)
Choudary, B. M.; Kantam, M. L.; Rahman, A.; Reddy,
Ch. V.; Rao, K. K. Angew. Chem., Int. Ed. 2001, 40,
763.
In conclusion, the Ru cation combined with Co(OH)2
and CeO2 acted as an excellent heterogeneous catalyst
for aerobic oxidation of various types of alcohols,
including cyclic alcohols and primary aliphatic alco-
hols, to the corresponding carbonyl compounds under
mild reaction conditions. This heterogeneous Ru cata-
lyst provides a green oxidation protocol for the direct
production of aliphatic carboxylic acids from the alco-
hols using atmospheric pressure of molecular oxygen.
Acknowledgements
This work was supported by the Grant-in-Aid for
Scientific Research from Ministry of Education, Cul-
ture, Sports, Science and Technology of Japan
(11450307). We are grateful to the Department of
Chemical Science and Engineering, Graduate School of
Engineering Science, Osaka University, for scientific
support via ‘Gas-Hydrate Analyzing System (GHAS)’.
5. XRD measurement of the black powder proved the for-
mation of small crystals of Co(OH)2 and CeO2. Ru
K-edge XAFS (Spring-8, BL10B, 2000A0278) revealed
that the Ru4+ cation exists as a monomeric species on
the surface of Co(OH)2 and CeO2. The curve-fitting
analysis of k3-weighted EXAFS showed that four oxy-
gen atoms surround the isolated Ru species.
References
6. A typical procedure for the large scale oxidation of
alcohols is as follows. A mixture of cinnamyl alcohol
(20 mmol, 2.68 g), Ru–Co(OH)2–CeO2 (0.30 g, Ru 0.20
mmol), and benzotrifluoride (5 mL) was stirred at 80°C
for 24 h under atmospheric O2 pressure. After the reac-
tion, the solid catalyst was separated by filtration, and
the Kugelrohr distillation of the residue gave 2.43 g of
pure cinnamaldehyde (92%).
1. (a) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxi-
dations of Organic Compounds; Academic Press: New
York, 1981; (b) de Nooy, A. E. J.; Basemer, A. C.;
Bekkum, H. V. Synthesis 1996, 1153; (c) Arends, I. W.
C. E.; Sheldon, R. A. Appl. Catal. A: Gen. 2001, 212,
175.
2. For typical examples of primary aliphatic alcohol oxida-
tions using inorganic oxidants, see: CrO3/H2SO4: (a)

H. Ji et al. / Tetrahedron Letters 43 (2002) 7179–7183
7183
7. After the oxidation of cinnamyl alcohol, the solid catalyst
was separated by filtration and washed with 10% of aqueous
Na2CO3 and then deionized water, followed by drying at
110°C. The used catalyst was subjected to the oxidation of
cinnamyl alcohol at 60°C for 1 h to give 90% yield of
cinnamaldehyde.
mmol, 2.60 g), Ru–Co(OH)2–CeO2 (0.30 g), and benzotri-
fluoride (5 mL) was stirred at 80°C under an atmospheric
O2 pressure. After 30 h, the solid catalyst was separated
by filtration. Removal of the solvent under the reduced
pressure and distillation of the residue gave 2.30 g of pure
octanoic acid (90%).
11. Chatt, J.; Shaw, B. L.; Field, A. E. J. Chem. Soc. 1964, 3466.
12. Kaneda, K., et al., to be submitted.
8. Filtration of the heterogeneous mixture gave a solution
devoid of any oxidizing ability. This result clearly shows
that active Ru species did not leach from the Ru–Co(OH)2–
CeO2 catalyst during the oxidation reaction.
9. A temperature of 140°C was required for the oxidation of
octanal to octanoic acid when the Ru/CeO2 catalyst was
used.4c
13. Typical examples of homogeneous oxidation of aldehydes
in the presence of molecular oxygen: Ni: (a) Yamada, T.;
Rhode, O.; Takai, T.; Mukaiyama, T. Chem. Lett. 1991,
5; (b) Howarth, J. Tetrahedron Lett. 2000, 41, 6627; Co:
(c) Bhatia, B.; Iqbal, J. 1992, 33, 7961; Fe: (d) Mizuno, N.;
Hirose, T.; Tateishi, M.; Iwamoto, M. J. Mol. Catal. 1994,
88, L125.
10. A typical procedure for the large scale oxidation of primary
aliphatic alcohols is as follows. A mixture of 1-octanol (20