Noncatalytic Heck coupling reaction using supercritical water

Article abstract of DOI:10.1039/b302683c

Heck coupling of iodobenzene with styrene can be promoted in supercritical water without using catalyst, and the conversion reaches over 70% within 10 min in the presence of base, such as KOAc, in which case the yield of stilbene is 55.6% (both trans- and

Full text of DOI:10.1039/b302683c

Noncatalytic Heck coupling reaction using supercritical water
Rong Zhang,a Fengyu Zhao,ab Masahiro Satoa and Yutaka Ikushima*ab
a Supercritical Fluid Research Center, National Institute of Advanced Industrial Science and Technology,
4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan. E-mail: y-ikushima@aist.go.jp;
Fax: +81-22-237-5224; Tel: +81-22-237-5211
b CREST, Japan Science and Technology Corporation (JST), Honcho, Kawaguchi 332-0012, Japan
Received (in Cambridge, UK) 10th March 2003, Accepted 24th April 2003
First published as an Advance Article on the web 2nd June 2003
Heck coupling of iodobenzene with styrene can be promoted
in supercritical water without using catalyst, and the
conversion reaches over 70% within 10 min in the presence
of base, such as KOAc, in which case the yield of stilbene is
55.6% (both trans- and cis-stilbene).
and degassed by N2 gas prior to use. A predetermined amount of
substrates and base (1.0 mmol each) and water were loaded into
the reactor in argon atmosphere. The reactor vessel was
immersed and vigorously shaken in a molten salt bath. The heat-
up time to raise the reactor temperature from 293 K to the
reaction temperature was within 30 s. Pressure was calculated
using a steam table. After a preselected reaction time of 10 min,
the reactor was withdrawn from the molten salt bath and rapidly
quenched in an ice–water bath. All of the products were
extracted with dichloromethane and identified by GC-MS and
1H-NMR, and each concentration was determined by using GC-
FID. The product yield was calculated based on styrene.
We first found that coupling of styrene and iodobenzene can
be promoted even in the absence of any catalysts in scH2O, in
which several alkylarenes, such as stilbene (I and II) and
1,1-diphenylethylene (III), were formed as shown in Scheme 1,
besides hydrogen iodide. Furthermore, the effect of base on the
Heck reaction in scH2O was investigated. Experiments were
carried out in the presence of NEt3, NaOAc, KOAc, K2CO3,
Na2CO3, NaHCO3, or NaOH base. The results are shown in
Table 1. The kind of base had a strong influence on both the
conversion and the selectivity in scH2O. That is, KOAc base
was the most effective for synthesizing coupling compounds
such as stilbene (I and II). The conversion of iodobenzene and
styrene reached over 70% and the yield of stilbene (both trans-
and cis-stilbene) was 55.6%. In addition, white crystals of trans-
stilbene can be easily separated from water.
In the absence of base or in the presence of NEt3 base, high
conversion of styrene was obtained; however, only small
amounts of the coupling products were formed and the main
products were polymeric compounds. Furthermore, ethylben-
zene and diphenylethane compounds that were the hydro-
genated products of styrene and the coupling products (I, II, and
III) were obtained in about 10 and 6% yields, respectively. It
would be predicted that the hydrogenation would be caused by
the resulting hydrogen iodide, because the hydrogenation of
styrene to ethylbenzene in scH2O was shown to proceed only
when hydrogen iodide was present. Moreover, in the absence of
hydrogen iodide the formation of a small amount of 1-phenyl-
ethyl alcohol from styrene in scH2O was confirmed, and so one
cannot deny the donation of hydrogen from scH2O itself for the
hydrogenation. When relatively strong bases K2CO3, Na2CO3,
NaHCO3, and NaOH were used, the conversion of iodobenzene
was high and phenol was the chief product. Homocoupling of
iodobenzene to biphenyl has not been observed in scH2O
regardless of the base used.
The Heck reaction is an extremely valuable method for carbon–
carbon bond formation and is now widely used in the fine
chemical and pharmaceutical manufacturing industries.1,2
However, its practical production has been restricted due to the
disadvantages of using environmentally damaging solvents and
transition metal catalysts, such as palladium, and of problems
associated with catalyst–product separation and side reactions
such as decomposition, which would take place during the
distillation after the reaction. Recently, environmentally benign
approaches to the Heck reaction have been developed, such as
the application of water with a water-soluble ligand,3 phase-
transfer catalysts,4,5 as well as supercritical CO2 and ionic
6,7
liquids8 as solvent media.
Supercritical water (scH2O) should be a more useful
replacement for organic solvents because water is the most
environmentally acceptable solvent and its physicochemical
properties can be changed widely with pressure and tem-
perature. For example, the static relative permittivity of water is
78.5 at 298 K, and dramatically decreases to about 6.0 at the
supercritical point.9 As a result, nonpolar organic compounds
are very soluble or miscible in scH2O. This nature, along with
high diffusivity and low viscosity, is expected to allow it to
function as an ideal alternative to organic solvents.10
The Heck arylation of alkenes has been carried out in hot
compressed water (533 K) and also in scH2O (673 K) in the
presence of Pd catalysts.11–14 In the case of Pd-catalysed
reaction of iodobenzene and styrene, the yield of coupling
products was less than 25% and the catalysts were deactivated
rapidly. Further, the influence of water on the selectivity and the
reaction mechanism has scarcely been elucidated.15 We have
recently demonstrated a remarkable stimulation of rearrange-
ment or disproportionation using scH2O even in the absence of
any acid or base catalysts.16,17 This might be due to the acid and
base difunctionality of scH2O. In this paper we attempted to
conduct noncatalytic arylation of styrene with iodobenzene
using scH2O. It will be shown that high reaction rate and high
selectivity are possible in water near its critical point.
The experiments were performed by using an Inconnel 625
batch reactor system with an internal volume of 10.2 cm3.
Triply distilled high-purity water was used for all experiments
Scheme 1 Heck reaction of iodobenzene and styrene.
This journal is © The Royal Society of Chemistry 2003
1548
CHEM. COMMUN., 2003, 1548–1549

Table 1 Effect of base on coupling of iodobenzene and styrene at 650 K and 25 MPa
Conversion (%)
Yield (%)
I
Initial
Base
pH value
Styrene
Iodobenzene
II
III
IV
V
VI
a
—
6.5
10.8
7.2
100.0
94.1
65.4
72.5
64.6
39.0
55.2
41.4
39.7
45.1
65.6
77.5
100.0
93.1
5.0 (3.3)
13.9 (2.0)
35.3
45.1
23.1
8.7
8.5
6.2
0
0 (1.3)c
0 (1.8)
0
2.0
3.0
0.5
0
0
0
6.3
0
44.3
58.2
52.8
59.4
0
0
0
0
5.2
7.7
4.1
b
NEt3
NaOAc
KOAc
Na2CO3
K2CO3
NaHCO3
NaOH
0 (3.0)
8.5
10.5
4.7
2.0
1.7
1.5
0 (1.8)
1.9
2.3
1.2
0
7.2
10.0
10.0
9.0
95.0
100.0
0
0
0
0
12.0
11.5
a Ethylbenzene 10.2%. b Ethylbenzene 10.5%. c The numbers in parentheses are yields of corresponding hydrogenated products.
formation of phenol, hydrolysis of chlorobenzene in NaOH
solution under high temperature (633–663 K) and high pressure
(28–30 MPa) has been used commercially for the production of
phenol.23 We confirmed that phenol is obtained in over 50%
yield by hydrolysis of iodobenzene in the presence of a
relatively strong base.
In summary, the unusual properties of water near its critical
point provide a novel method for extending the Heck reaction
into water. The choice of base had a significant effect on
product selectivity. The best result was obtained using KOAc,
which is a relatively mild base. The conversion reached 70%
and the yield of stilbene was 55.6% (both trans- and cis-
stilbene) within 10 min.
The authors gratefully acknowledge financial support from
the Japan Society for the Promotion of Science (JSPS).
Fig. 1 Influence of temperature on the conversion and the yield of stilbene
at 25 MPa in the presence of KOAc.
Notes and references
1 A. de Meijere and F. E. Meyer, Angew. Chem., Int. Ed. Engl., 1994, 33,
2379.
2 F. Berthiol, H. Doucet and M. Santelli, Tetrahedron Lett., 2003, 44,
1221.
3 S. Mukhopadhyay, G. Rothenberg, A. Joshi, M. Baidossi and Y. Sasson,
Adv. Synth. Catal., 2002, 344, 348.
Fig. 1 shows the temperature dependence of the conversion
and the yield of stilbene at 25 MPa in the presence of KOAc.
One can see an interesting temperature dependence in which
both the conversion and the yield increased, reaching maximum
conversion and yield at 650 K near the critical temperature of
water, and then decreased with increasing temperature.
The change of hydrogen bonding is presumed to be a key
factor for understanding the above results. Our Raman18 and
IR17 measurements of the hydrogen bonding of sub- and super-
critical water suggest that the tetrahedral configurations dis-
appear near the critical point, where the monomer or dimer or
trimer structures are predominant. This result was further
supported by a recent first-principle molecular dynamics
study.19 The ion product (Kw) monotonously decreases with
increasing temperature above 573 K at 25 MPa,20 and so the
proton or hydroxide ion (OH2) concentration anticipated from
the Kw concept is not so high near the critical temperature at 25
MPa. However, in scH2O the OH2 or proton adjacent to
substrate molecules cannot migrate throughout the hydrogen
bonding network near the critical point, and hence the OH2 or
proton species could react spontaneously with substrate mole-
cules to form a transient intermediate owing to lower activation
energies for bond breakage and formation. At least 10 water
molecules are considered to be required for appreciable
interaction between the hydrogen bonding network and pro-
ton.21 Moreover, the local proton and OH2 concentrations
would be high when the transferring ions cannot escape.
Considering the experimental results, a general mechanism
for the coupling reaction in scH2O is postulated as follows. The
OH2 removes the b-H of styrene, giving a carbanion. Then the
nucleophilic carbanion attacks iodobenzene at the electrophilic
carbon, resulting in the formation of coupled products. The
hydrogen iodide formed during the reaction facilitates the
polymerisation of styrene and the hydrogenation of styrene and
both coupling products. The addition of a relatively mild base,
such as NaOAc and KOAc (see Table 1, initial pH value is less
than 8.0), can not only neutralize hydrogen iodide, but also
promote the removal of iodine via an intermediate composed of
an ion–dipole bond between cation and iodine.22 As for the
4 T. Jeffery, Tetrahedron Lett., 1994, 35, 3051.
5 J. X. Wang, Z. L. Y. Hu, B. Wei and L. Bai, J. Chem. Res. (S), 2000,
484.
6 R. S. Gordon and A. B. Holmes, Chem. Commun., 2002, 640.
7 S. Fujita, K. Yuzawa, B. M. Bhanage, Y. Ikushima and M. Arai, J. Mol.
Catal. A, 2002, 180, 35.
8 A. J. Carmichael, M. J. Earle, J. D. Holbrey, P. B. McCormac and K. R.
Seddon, Org. Lett., 1999, 1, 997.
9 R. W. Shaw, T. B. Bill, A. A. Clifford, C. A. Eckert and E. U. Franck,
Chem. Eng. News, 1991, 69(51), 26.
10 P. E. Savage, Chem. Rev., 1999, 99, 603.
11 J. Diminnie, S. Metts and E. J. Parsons, Organometallics, 1995, 14,
4023.
12 P. Reardon, S. Metts, C. Crittendon, P. Daugherity and E. J. Parsons,
Organometallics, 1995, 14, 3810.
13 L. U. Gron and A. S. Tinsley, Tetrahedron, 1999, 40, 227.
14 L. U. Gron, J. E. LaCroix, C. J. Higgins, K. L. Steelman and A. S.
Tinsley, Tetrahedron Lett., 2001, 42, 8555.
15 D. Broll, C. Kaul, A. Kramer, P. Krammer, T. Richter, M. Jung, H.
Vogel and P. Zehner, Angew. Chem., Int. Ed., 1999, 38, 2998.
16 Y. Ikushima, K. Hatakeda, O. Sato, T. Yokoyama and M. Arai, Angew.
Chem., Int. Ed., 2001, 40, 210.
17 Y. Ikushima, K. Hatakeda, M. Sato, O. Sato and M. Arai, Chem.
Commun., 2002, 2208.
18 Y. Ikushima, K. Hatakeda, N. Saito and M. Arai, J. Chem. Phys., 1998,
108, 5855.
19 M. Boero, K. Terakura, T. Ikeshoji, C. C. Liew and M. Parrinello, Phys.
Rev. Lett., 2000, 85, 3245.
20 W. L. Marshall and E. U. Franck, J. Phys. Chem. Ref. Data, 1981, 10,
295.
21 Y. P. Sun, M. A. Fox and K. P. Johnston, J. Am. Chem. Soc., 1992, 114,
1187.
22 K. S. Lin and H. P. Wang, Environ. Sci. Technol., 1999, 33, 3278.
23 K. Weissermel and H.-J. Arpe, Industrial Organic Chemistry: Im-
portant Raw Materials and Intermediates, Wiley-VCH Verlag GmbH,
2002.
CHEM. COMMUN., 2003, 1548–1549
1549