Gold nanoparticle-catalyzed cyclocarbonylation of 2-aminophenols

Article abstract of DOI:10.1039/c2gc36851j

Gold nanoparticles supported on hydrotalcite acted as a highly efficient catalyst for the cyclocarbonylation of 2-aminophenols to 2-benzoxazolinones without any additives. After the cyclocarbonylation, the hydrotalcite-supported gold nanoparticles could be reused without loss of catalytic efficiency.

Full text of DOI:10.1039/c2gc36851j

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Gold nanoparticle-catalyzed cyclocarbonylation of
2-aminophenols†
Cite this: Green Chem., 2013, 15, 608
Received 21st November 2012,
Accepted 21st December 2012
Akifumi Noujima,a Takato Mitsudome,a Tomoo Mizugaki,a Koichiro Jitsukawaa and
Kiyotomi Kaneda*a,b
DOI: 10.1039/c2gc36851j
www.rsc.org/greenchem
Gold nanoparticles supported on hydrotalcite acted as a highly additives such as iodides10 and PPh3.11 These catalytic
efficient catalyst for the cyclocarbonylation of 2-aminophenols to systems, however, have suffered from several drawbacks, such
2-benzoxazolinones without any additives. After the cyclocarbo- as the difficulty of separating the homogeneous metal species
nylation, the hydrotalcite-supported gold nanoparticles could be from the product, as well as the reuse of the catalysts. Despite
reused without loss of catalytic efficiency.
heterogeneous catalysis having significant advantages in the
above issues, there has been only one example of a hetero-
geneous catalyst for the cyclocarbonylation of 2-aminophenol
using Pd/C with I2.10c
In recent years, green and sustainable organic synthesis using
gold nanoparticle (Au NP) catalysts has attracted great inter-
est.1 In this context, the catalysis of Au NPs in liquid-phase
organic transformations with CO remains quite rare,2–5
whereas Au NP-catalyzed gas-phase reactions with CO have
been widely studied.6 The carbonylation of anilines to ureas
and carbamates catalyzed by Au NPs has previously been
demonstrated.2 We also recently discovered that Au NPs sup-
ported on basic supports such as hydrotalcite [HT: Mg6Al2-
CO3(OH)16] and Al2O3 catalyzed the double-carbonylation of
amines to oxamides.3 In our continuing studies on the cata-
lysis of Au NPs in liquid-phase reactions, we herein found that
HT-supported Au NPs (Au/HT) could act as a highly efficient
heterogeneous catalyst for the cyclocarbonylation of 2-amino-
phenols to 2-benzoxazolinones.
Cyclocarbonylations of 2-aminophenols to 2-benzoxazoli-
nones are of significant importance because 2-benzoxazoli-
nones and their derivatives are valuable compounds for
extensive applications as intermediates for organic synthesis,
fine chemicals, and pesticides.7 Catalytic carbonylations are
alternative green methods for traditionally stoichiometric
reactions using toxic phosgene or its derivatives with 2-amino-
phenols, producing large amounts of HCl.8 The cyclocarbony-
lations of 2-aminophenols have been carried out using Se
metals with Et3N9 and homogeneous Pd complexes with
The present Au/HT catalyst could efficiently promote the
cyclocarbonylation of 2-aminophenols under non-flammable
conditions. This catalyst system provided excellent yields of
the corresponding 2-benzoxazolinones without any additives
which have been necessary in previous cyclocarbonylations.9–11
Moreover, the catalytic activity of Au NPs was found to be
remarkably high among metal NPs, and the Au/HT catalyst
could be reused without loss of its activity or selectivity.
The Au/HT catalyst was prepared according to the pro-
cedure in our previous work.12 Briefly, HT was added to the
aqueous solution of HAuCl4. After the subsequent addition of
NH3 solution, the resulting mixture was further stirred. Then,
the obtained slurry was filtered and washed with deionized
water to afford HT-supported AuIII species. Treatment of the
resulting solid with an aqueous solution of KBH4 afforded the
Au/HT as a reddish purple powder with a mean diameter of
2.7 nm.
Initially, the catalytic activity of Au/HT was tested in the
cyclocarbonylation of 2-aminophenol (1) in 1,2-dimethoxy-
ethane under 50 atm of CO/O2 (48/2) at 110 °C, i.e., the non-
flammable condition.13 Au/HT showed high catalytic activity
in the cyclocarbonylation to afford 2-benzoxazolinone (2) in
99% yield without any formation of byproducts (Table 1,
entry 1). The cyclocarbonylation did not proceed in the
absence of O2, which demonstrated the necessity of O2 in the
cyclocarbonylation (entry 2). When using Au/HT with different
Au NP sizes, the size of Au NPs on HT affected the catalytic
activity; the yield of 2 increased with decreasing mean particle
size (d) of Au NPs (entries 1 and 3–6).14 When Au/HT was
removed from the reaction mixture at 40% conversion of 1,
further stirring of the resulting filtrate under similar reaction
aDepartment of Materials Engineering Science, Graduate School of Engineering
Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
E-mail: kaneda@cheng.es.osaka-u.ac.jp; Fax: +81 6-6850-6260;
Tel: +81 6-6850-6260
bResearch Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama,
Toyonaka, Osaka 560-8531, Japan
†Electronic supplementary information (ESI) available: Experimental details,
EXAFS analysis and TEM images. See DOI: 10.1039/c2gc36851j
608 | Green Chem., 2013, 15, 608–611
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Table 1 Cyclocarbonylation of 1 to 2 using various catalystsa
Table 2 Cyclocarbonylation of various 2-aminophenols with Au/HTa
Time
(h)
Conv.b
(%)
Yieldb
(%)
Conv.b (%)
Yieldb (%)
Entry Substrate
Product
Entry
Catalyst
d (nm)
1
2
2
2
3
99
99
99
99
99
98
98
99
1
Au/HT
Au/HT
Au/HT
Au/HT
Au/HT
Au/HT
Rh/HT
Pd/HT
2.7
2.7
5.8
7.9
12
99
<1
95
88
81
59
10
12
5
99
<1
95
86
81
56
7
2c
3d
4
2c
3
4
5
6
7
8
9
20
5
3
97
96
6
3
Pt/HT
10
11
12
13
14
15
16
17d
18
Ru/HT
Ag/HT
Cu/HT
Au/Al2O3
Au/CeO2
Au/TiO2
Au/HAP
Au/HAP + Na2CO3
Au/SiO2
3
3
4
97
92
87
75
91
63
0
0
0
97
92
82
72
87
62
6
7
6
4
99
99
97
96
3.6
3.8
3.7
3.0
3.0
2.2
8
6
99
95
a Reaction conditions: catalyst (1.8 mol%),
1
(0.25 mmol).
a Reaction conditions: Au/HT (0.10 g, Au: 1.8 mol%), substrate
(0.25 mmol). b Determined by GC or HPLC using an internal standard
technique. c Reuse 1. d Reuse 2.
b Determined by GC using an internal standard technique. c In the
absence of O2. d 1.0 mmol of Na2CO3 was added.
conditions did not afford 2 (see Fig. 3S in ESI†). From the ICP
analysis, no leaching was confirmed in the filtrate (detection
limit: <0.1 ppm). These results indicated that the cyclocarbony-
lation of 1 proceeded on the solid surface of Au/HT.
Next, a series of metal NPs was supported on HT and then
tested under similar reaction conditions (entries 7–12).4b In
contrast to the result using Au/HT, platinum group metals
such as Rh, Pd, Pt, and Ru NPs on HTs gave extremely low
yields of 2 (entries 7–10)15 and coinage metals of Ag and Cu
NPs did not have any catalytic activity (entries 11 and 12).
These results highlighted the fact that Au NPs have remarkably
high and unique catalytic activity for the cyclocarbonylation
among metal NPs. The effect of supports on the Au NP-cata-
lyzed cyclocarbonylation was further investigated using Au NPs
deposited on various inorganic supports such as SiO2, TiO2,
Scheme 1 Cyclocarbonylation of 1,2-phenylenediamine with Au/HT.
Scheme 2 10 mmol-scale cyclocarbonylation of 1 using Au/HT.
Al2O3, CeO2 and hydroxyapatite (HAP). Basic supports such as present carbonylation system, converting to the cyclic urea
Al2O3 and CeO2 as well as HT were found to be effective 2-benzimidazolinone in high yield (Scheme 1).
(entries 13 and 14). The use of non-basic supports of TiO2,
Au/HT also worked well under preliminary scale-up con-
HAP and SiO2 resulted in lower yields of 2 (entries 15, 16 and ditions; a 10 mmol-scale cyclocarbonylation of 1 proceeded to
18). Notably, addition of Na2CO3 to the Au/HAP catalyst system afford 2 with high efficiency (Scheme 2). In this reaction, the
enhanced the yield of 2, confirming that bases have a positive turnover number reached up to 2000.16 In the present Au/HT
effect on the cyclocarbonylation (entry 16 vs. entry 17).
catalyst system, the obtained 2-benzoxazolinone products were
The cyclocarbonylation of 2-aminophenol derivatives using easily isolated from the reaction mixture and purified by
Au/HT was investigated under the optimized reaction con- recrystallization due to the absence of additives. Moreover, the
ditions. 2-Aminophenols with electron donating and withdraw- used Au/HT could be easily recovered by simple filtration after
ing substituents were successfully transformed to the the reaction and reused without loss of its catalytic efficiency
corresponding 2-benzoxazolinones in high yields (Table 2, (Table 2, entries 2 and 3).
entries 1 and 4–7). Au/HT also efficiently catalyzed 3-amino-2-
Taking into consideration the positive effect of bases in the
naphthol to the corresponding 2-oxazolinone (entry 8). Fur- cyclocarbonylation of 1 (vide supra), a plausible reaction mech-
thermore, 1,2-phenylenediamine could be applied in the anism is proposed in Scheme 3. Initially, CO adsorbs on the
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4 For the Au NP–CO/H2O catalyst system for chemoselective
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Scheme 3 Plausible reaction mechanism.
surface of Au NPs on HT. Then, nucleophilic attack of
the N atom of 1 toward CO on the Au NPs occurs, affording a
[Au-carbamoyl]− and H+ through the activation of N–H of 1 by
a basic site of HT.17 Subsequent β-elimination of the [Au-carba-
moyl]− gives a [Au–H]− and an isocyanate intermediate,18 fol-
lowed by intramolecular attack of the hydroxyl group of 1,
yielding 2.19 The resulting [Au–H]− and H+ react with O2 to
form water, regenerating the catalyst.
In conclusion, hydrotalcite-supported Au NPs showed high
catalytic activity for the cyclocarbonylation of 2-aminophenols
to 2-benzoxazolinones under non-flammable conditions. The
present Au NP-catalyzed system did not require any additives
such as PPh3 and I2 that have been necessary in previously
reported cyclocarbonylations. The significantly unique cata-
lysis of Au/HT with high activity was also disclosed. Moreover,
the solid Au/HT was easily recovered by simple filtration and
reusable with no decrease in catalytic activity. This study also
clearly showed that the cooperative contribution of small
Au NPs with basic supports was important to achieve highly
efficient cyclocarbonylation of 2-aminophenols.
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This work was supported by a Grant-in-Aid for Young Scien-
tists (A) (23686116) from the Japan Society for the Promotion
of Science (JSPS). We thank Dr Uruga, Dr Tanida and Dr Nitta
(SPring-8) for XAFS measurements. One of the authors
A. N. thanks the JSPS Research Fellowships for Young Scien-
tists. The TEM experiments were carried out at a facility of the
Research Center for Ultrahigh Voltage Electron Microscopy,
Osaka University.
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14 For the preparation of Au/HTs with different size Au NPs, 18 For the generation of the isocyanate intermediate during
see: A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa
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16 TON is calculated based on the total amount of Au 19 The intramolecular nucleophilic attack of
a
phenoxy
atoms.
oxygen to the isocyanate intermediate was proposed. See:
17 The activation of the N–H group of amines by a basic site
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