Highly efficient oxidation of alcohols and aromatic compounds catalysed by the Ru-Co-Al hydrotalcite in the presence of molecular oxygen

Article abstract of DOI:10.1039/a809082c

The ruthenium hydrotalcite having cobalt cations, Ru-Co-Al-CO₃ HT, is an effective heterogeneous catalyst for the oxidation of various kinds of alcohols in the presence of molecular oxygen.

Full text of DOI:10.1039/a809082c

Highly efficient oxidation of alcohols and aromatic compounds catalysed by the
Ru-Co-Al hydrotalcite in the presence of molecular oxygen
Tsuyoshi Matsushita, 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. E-mail: kaneda@cheng.es.osaka-u.ac.jp
Received (in Cambridge, UK) 20th November 1998, Accepted 15th December 1998
The ruthenium hydrotalcite having cobalt cations, Ru-Co-
Al-CO HT, is an effective heterogeneous catalyst for the
oxidation of various kinds of alcohols in the presence of
molecular oxygen.
yielding 2.05 g of powder. The structure of the powder was
confirmed by its X-ray diffraction pattern, and the basal spacing
was estimated to be 7.9 Å, which is similar to that of the Ru–
3
Mg–Al–CO
Ru:Co:Al = 0.3:3.0:1.0): Co, 20.1; Al, 7.4; Ru, 7.0%.
Found: Co, 19.5; Al, 7.4; Ru, 7.3%. X-Ray photon spectroscopy
(XPS) for the Ru-Co-Al-CO HT: Co 2p3/2 = 780.6 eV,
FWHM = 3.1 eV; Ru 3d5/2 = 282.7 eV, FWHM = 2.0 eV.
XPS for the Ru-Mg-Al-CO HT: Ru 3d5/2 = 281.7 eV, FWHM
3 3
HT (7.92 Å); calc. for Ru-Co-Al-CO HT
(
From the standpoints of atom economy and environmental
friendliness,1 much attention has been paid to the development
of selective oxidations catalysed by metal compounds using
molecular oxygen as oxidant.3 Hydrotalcites of layered
mineral materials consist of cationic Brucite layers separated by
,2
3
–6
3
= 2.5 eV. The XPS peak positions are refered to Al1s at 73.7
eV].
7
layers of anionic species. Changing the element ratios in the
Brucite layer and selection of different anionic species enables
tuning of the surface basicity.8 Additionally, various metal
elements can be introduced into the Brucite layer via the
A typical example for the oxidation of alcohols is as follows
(Scheme 1). Into a reaction vessel with a reflux condensor were
placed cinnamyl alcohol (0.80 g, 6.0 mmol), the Ru-Co-Al-CO
HT (0.90 g) and toluene (15 ml). The resulting mixture was
stirred at 60 °C under an O atmosphere. After 40 min, the
3
II
III
isomorphic substitution of Mg or Al cations at the octahedral
3
sites, which are expected to be the active sites of the catalysts.
2
1
Thus, the interaction of introduced metal cations (M ) with
hydrotalcite was separated by filtration. GC analysis of the
filtrate showed a quantitative yield of cinnamaldehyde. Re-
moval of the solvent under reduced pressure was followed by
column chromatography on silica to yield cinnamaldehyde
(0.707 g, 89%). Isolated hydrotalcites were washed with
2
1
2
other cations (M ) through M –O–M bonds would lead to
unique catalytic reactions using the functionalised hydro-
talcites. Here, we have designed a highly active catalyst of the
hydrotalcite containing Ru and Co cations for the oxidation of
various alcohols and hydrocarbons in the presence of molecular
oxygen. This heterogeneous catalyst has the advantages of
using molecular oxygen and a simple work-up procedure over
other homogeneous oxidizing reagents.1 Furthermore, this
hydrotalcite is reusable without appreciable loss of activity and
selectivity for the above oxidation.
2 3
aqueous 10% Na CO (30 ml) and water, and could be reused
without appreciable loss of activity for the above oxidation; the
first, second and third runs of the experiment using the spent
hydrotalcites gave cinnamaldehyde with > 92% GC yield.
Ru hydrotalcites having divalent metal cations in place of
II
Mg were examined as catalysts for the oxidation of cinnamyl
II
Various Ru hydrotalcites having divalent metal cations M in
alcohol in the presence of molecular oxygen, as shown in Table
1. Generally, cinnamaldehyde is the main product under the
II
II
place of Mg (Ru:M :Al = 0.3:3.0:1.0) were prepared
according to a modified version of a procedure in the literature.7
A representative example is for the hydrotalcite having cobalt,
R1
R2
CH2OH
R3
R1
R2
CHO
R3
C
C
C
C
aluminum, and ruthenium in the Brucite layer and CO
in the interlayer (Ru-Co-Al-CO HT). mixture of
RuCl ·3H O (1.53 mmol), CoCl ·6H O (15.3 mmol) and
AlCl ·6H O (5.10 mmol) were dissolved in distilled water (10
ml). To an aqueous solution of Na CO (13.3 mmol) and NaOH
46.4 mmol) was slowly added the above solution, and then the
3
anions
3
A
Ru-Co-Al-CO3 HT, O2
toulene, 60 °C
3
2
2
2
OH
R4
O
3
2
2
3
R4
(
resulting mixture was heated at 65 °C for 18 h with stirring. The
obtained slurry was cooled to room temperature and filtered,
washed with distilled water and dried at 110 °C for 12 h,
R5
R5
Scheme 1
Table 1 The oxidation of cinnamyl alcohol with various Ru hydrotalcitesa
Heat of
Conversion Yieldb
adsorption /
c
2
1
Entry
Catalyst
Time
(%)
(%)
J g
1
2
3
4
5
Ru-Co-Al-CO
3
HT
HT
HT
HT
40 min
40 min
40 min
40 min
40 min
100
99
64
23
31
94
92
50
23
20
13.4
13.3
12.9
6.6
Ru-Mn-Al-CO
Ru-Fe-Al-CO
Ru-Zn-Al-CO
Ru-Mg-Al-CO
3
3
3
3
HT
32.1
d
8
h
100
33
95
22
6e
Co-Al-CO
HT + Ru-Mg-Al-CO
HT
40 min
3
3
a
Reaction conditions: cinnamyl alcohol (2.0 mmol), catalyst (0.30 g), toluene (5 ml), 60 °C, O
2
atmosphere. b Yields of cinnamaldehyde were
c
determined by GC analysis using internal standards, based on cinnamyl alcohol. The basicity of the hydrotalcites was estimated by calorimetric heats of
benzoic acid adsorption (ref. 8). Cited from ref. 3. e The physical mixture of the two catalysts which contained the same amounts of Ru and Co as entry
d
1
was used.
Chem. Commun., 1999, 265–266
265

Table 2 The oxidation of various alcohols with Ru-Co-Al-CO
3
HTa
xanthene
fluorene
70 °C, 2 h
70 °C, 3 h
xanthen-9-one 98%
fluoren-9-one 93%
Ru-Co-Al-CO3 HT, O2
chlorobenzene
Con-
version Yieldb
Entry Substrate
Product
Time (%)
(%)
diphenylmethane
120 °C, 6 h benzophenone 95%
CH2OH
CH2OH
CHO
CHO
100 94 (89)c
Scheme 2
1
40 min
positions of aromatic compounds, i.e. xanthene, fluorene and
diphenylmethane, to give the corresponding ketones
(Scheme 2).
2
3
4
1.5 h
2 h
100
99
100
90
CH2OH
CHO
The hydrotalcite catalyst was easily separated from the
reaction mixture and was reusable without an appreciable loss
of activity and selectivity for the above oxidations.
12 h
86
80
E/Z = 3/97 CH2OH
CH2OH
E/Z = 5/95 CHO
In the oxidation of cinnamyl alcohol, the Co-Al-CO
(Co:Al = 3:1) barely catalysed the oxidation, and the activity
of Ru-Co-Al-CO HT was much higher than that of a physical
mixture of Co-Al-CO HT and Ru-Mg-Al-CO HT (Table 1,
entry 6). These results indicate that it is the synergism derived
from interaction of Co and Ru cations in the Ru-Co-Al-CO HT
that enhances the catalytic activity. The XPS results show that
the oxidation state of the Ru cations of Ru-Co-Al-CO HT was
3
HT
5
CHO 12 h
89
71
E/Z = 98/2
CH2OH
E/Z = 94/6
CHO
3
3
3
6
7
8
1 h
100
100
100
96
100
95
3
CH2OH
CHO
50 min
1.5 h
H3C
H3C
3
CH2OH
CHO
higher than that of Ru-Mg-Al-CO
binding energy of Ru-Co-Al-CO
3
HT; the Ru 3d5/2 electron
HT was similar to that of
3
Cl
Cl
9
CH2OH
CHO
3
RuO . Presumably, the Ru cation species with higher oxidation
IV
VI
states, i.e. Ru to Ru , induced by the introduction of Co
9
1 h
1 h
100
92
cations are responsible for high catalytic activity in the above
5
oxidation. From Table 1, the basicity of hydrotalcites is not
OH
O
3
correlated with the catalytic activity for the oxidation. At
1
0
100 96 (98)
present, we think that substitution of Mg cations with divalent
Co cations in the Brucite layer might lead to generation of an
active species having a high oxidation state for the Ru ions, e.g.
OH
O
10
RuNO species.
11
1.5 h
100
100
In conclusion, the ruthenium hydrotalcite having Co cations
was found to be an effective heterogeneous catalyst for the
oxidation of various kinds of alcohols in the presence of
molecular oxygen. This heterogeneous oxidation can be
regarded as an environmentally benign chemical process
because of the use of molecular oxygen, the simple work-up
procedure and the reusability of the hydrotalcite catalyst.
S
N
S
N
CH2OH
CH2OH
CHO
CHO
1
2
3
40 min
7 h
100
99
91
91
1
OH
O
14
2 h
100 97 (82)
HT (0.3 g),
2
atmosphere. Yields of aldehydes and ketones
a
Reaction conditions: substrate (2 mmol), Ru-Co-Al-CO
toluene (5 ml), 60 °C, O
3
b
Notes and references
were determined by GC analysis using internal standards, based on
†
The oxidations of aliphatic allylic alcohols and 2-pyridylmethanol hardly
c
alcohols. Values in parentheses are isolated yields. In the case of the
3
proceeded in the presence of the Ru-Mg-Al-CO HT under these reaction
product isolation experiments, the reaction scale was three times as much as
that given in footnote (a).
conditions.
1
G. W. Parshall and S. D. Ittel, Homogeneous Catalysis, 2nd edn., Wiley,
New York, 1992; C. L. Hill, Advances in Oxygenated Processes, ed.
A. L. Baumstark, JAI, London, 1998, vol. 1, p. 1; M. Hudlucky,
Oxidations in Organic Chemistry, ACS Monograph, Washington, DC,
1990; R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Oxidations of
Organic Compounds, Academic Press, London, 1981.
above conditions. The hydrotalcite with Ru cations in the
3
Brucite layer, Ru-Mg-Al-CO HT, has been previously found to
3
be a good catalyst (entry 5). Substitution of Mg ions with Co
ions in the Brucite layer of the above Ru-Mg-Al-CO HT
drastically enhanced the catalytic activity (entries 1 and 5). The
Ru-Mn-Al-CO HT was also an effective catalyst, while the
2
3
4
5
B. M. Trost, Science, 1991, 254, 1471; Angew. Chem., Int. Ed. Engl.,
3
1
995, 34, 259.
Hydrotalcite: K. Kaneda, T. Yamashita, T. Matsushita and K. Ebitani,
J. Org. Chem., 1998, 63, 1750.
Co: Y. Ishii, T. Iwahama, S. Sakaguchi, K. Nakayama and Y.
Nishiyama, J. Org. Chem., 1996, 61, 4520.
Ru: M. Matsumoto and N. Watanabe, J. Org. Chem., 1984, 49, 3435;
S.-I. Murahashi, T. Naota and N. Hirai, J. Org. Chem., 1993, 58, 7318;
I. E. Mark o´ , P. R. Giles, M. Tsukazaki, I. Chell e´ -Regnaut, C. J. Urch and
S. M. Brown, J. Am. Chem. Soc., 1997, 119, 12 661.
Pd: K. Kaneda, M. Fujii and K. Morioka, J. Org. Chem., 1996, 61, 4503;
K. Kaneda, Y. Fujie and K. Ebitani, Tetrahedron Lett., 1997, 38, 9023;
T. Nishimura, T. Onoue, K. Ohe and S. Uemura, Tetrahedron Lett.,
3
introduction of Fe and Zn cations resulted in low yields of
cinnamaldehyde.
Oxidation of various kinds of alcohols using the Ru-Co-Al-
3
CO HT in toluene was carried out at 60 °C. Typical results for
the oxidation of aromatic and aliphatic alcohols were summa-
rized in Table 2. Cinnamyl alcohol and its derivative gave a,b-
unsaturated aldehydes in almost quantitative yield (entries 1 and
6
2
). In the cases of benzylic alcohols, the corresponding
aldehydes were obtained in high yield (entries 6–11). It is
notable that benzoic acids (over-oxidation products) were
barely detected under the above conditions. Further, the
hydrotalcite catalyst is applicable for the oxidation of aliphatic
allylic alcohols (entries 3–5) and heterocyclic alcohols includ-
ing sulfur and nitrogen species in spite of slow reaction rates
1
998, 39, 6011; K. P. Peterson and R. C. Larock, J. Org. Chem., 1998,
6
3, 3185.
7
8
F. Cavani, F. Trifir o` and A. Vaccari, Catal. Today, 1991, 11, 173.
K. Kaneda, S. Ueno and T. Imanaka, J. Chem. Soc., Chem. Commun.,
1994, 797; K. Kaneda, S. Ueno and T. Imanaka, J. Mol. Catal. A: Chem.,
1995, 102, 135.
(
entries 12 and 13).† A secondary saturated alcohol, octan-2-ol,
was smoothly converted into the corresponding ketone (entry
4), while primary saturated alcohols such as octan-1-ol showed
9 H. Y. H. Chan, C. G. Takoudis and M. J. Weaver, J. Catal., 1997, 172,
36.
0 W.-H. Fung, W.-Y. Yu and C.-M. Che, J. Org. Chem., 1998, 63,
873.
3
1
1
2
extremely low reactivity for this oxidation. Interestingly, the
hydrotalcite could also efficiently oxygenate the benzylic
Communication 8/09082C
266
Chem. Commun., 1999, 265–266