Heck Coupling Reaction of Iodobenzene and Styrene Using Supercritical Water in the Absence of a Catalyst

Article abstract of DOI:10.1002/chem.200305542

Heck coupling reaction of iodobenzene and styrene proceeds rapidly and selectively in supercritical water even without any catalyst in the presence of base. Both the choice of base and the reaction conditions had a significant effect on the conversion and the selectivity of the coupling products. The addition of a relatively mild base such as potassium acetate facilitated the cross-coupling reaction, while the hydrolysis of phenyl halide was favored in the presence of a strong base. The conversion and the yields of coupling products increased with increasing temperature, reaching a maximum at 650 K near the critical temperature of water, and then decreased as the temperature was further increased. Water density had a significant influence on the reaction rate, showing nearly 30% augmentation with a slight increase in density from 0.45 to 0.56 gcm^-3, but had less effect on the product selectivity. Two possibilities of the role of water responsible for the noncatalytic Heck coupling reaction in supercritical water, that is, ion and water-catalyzed mechanisms have been considered.

Full text of DOI:10.1002/chem.200305542

FULL PAPER
Heck Coupling Reaction of Iodobenzene and Styrene Using Supercritical
Water in the Absence of a Catalyst
[
a, c]
[a, b]
[a, b]
[a]
Rong Zhang,
Osamu Sato,
Fengyu Zhao,
Masahiro Sato, and
[
a, b]
Yutaka Ikushima*
Abstract: Heck coupling reaction of io-
dobenzene and styrene proceeds rapid-
ly and selectively in supercritical water
even without any catalyst in the pres-
ence of base. Both the choice of base
and the reaction conditions had a sig-
nificant effect on the conversion and
the selectivity of the coupling products.
The addition of a relatively mild base
such as potassium acetate facilitated
the cross-coupling reaction, while the
hydrolysis of phenyl halide was favored
in the presence of a strong base. The
conversion and the yields of coupling
products increased with increasing tem-
perature was further increased. Water
density had a significant influence on
the reaction rate, showing nearly 30%
augmentation with a slight increase in
density from 0.4± to 0.±6 gcm , b ut
had less effect on the product selectivi-
ty. Two possibilities of the role of water
responsible for the noncatalytic Heck
coupling reaction in supercritical water,
that is, ion and water-catalyzed mecha-
nisms have been considered.
ꢀ
3
perature, reaching
a
maximum at
6±0 K near the critical temperature of
water, and then decreased as the tem-
Keywords: green chemistry ¥ Heck
reaction ¥ supercritical fluids
Introduction
this reaction in high reactivity and high selectivity, homoge-
neous catalysts generally present problems in the separation,
recovery and regeneration of the catalysts. The problems
could, in principal, be minimized by using heterogeneous
catalysts. However, such heterogeneous systems show quite
slight activities compared with homogeneous catalysts owing
to the paucity of activated sites resulting from the presence
of a phase boundary. Much effort has so far been put into
Among the various ways known to synthesize arylated ole-
fins, the Heck coupling reaction is one of the most useful
methods owing to its tolerance of a wide variety of function-
[
1]
al groups. This powerful carbon±carbon bond forming
process has been practiced on an industrial scale for the pro-
duction of compounds such as the anti-inflammatory drug
Neproxen and the most common UV-B sunscreen agent
the development of new, more active, and more stable cata-
[2]
[3±±]
octyl methoxycinnamate. Heck reactions are most fre-
quently performed in polar aprotic s-donor-type solvents
such as acetonitrile, dimethyl sulphoxide, or dimethylaceta-
mide in the presence of homogenous or heterogeneous cata-
lysts. Although soluble palladium complexes can promote
lysts.
In addition, the use of halogenated aromatic com-
pounds requires the use of stoichiometric amounts of base,
which leads to the formation of large quantities of halide
salt by-products, especially in large-scale processes. To cir-
cumvent these problems, aromatic carboxylic acid anhy-
drides and esters have been used by de Vries and co-work-
[6]
[7]
ers and Goossen et al. respectively. Considering the envi-
ronment, safety and economics, efforts are being directed
toward decreasing the usage of organic solvents in chemical
[
a] Dr. R. Zhang, Dr. O. Sato, Dr. F. Zhao, Dr. M. Sato,
Prof. Dr. Y. Ikushima
Supercritical Fluid Research Center
National Institute of Advanced Industrial Science and Technology
-2-1 Nigatake, Miyagino-ku, Sendai 983-8±±1 (Japan)
[8]
laboratories and industrial processes. Recently, environ-
mentally benign approaches to the Heck reaction have been
4
[
9±11]
developed, such as the application of water,
supercritical CO2
as well as
Fax : (+81) 22-237-±224
[12,13]
[14]
E-mail: y-ikushima@aist.go.jp
and ionic liquids as solvent media.
[
b] Dr. O. Sato, Dr. F. Zhao, Prof. Dr. Y. Ikushima
CREST, Japan Science and Technology Agency (JST)
From the viewpoint of sustainable development, supercrit-
ical water (scH O) should be a more useful replacement for
2
4
-1-8 Honcho, Kawaguchi 332-0012 (Japan)
organic solvents for the following reasons. First, water is a
cheap, safe, and environmentally benign solvent compared
with organic solvents. A new application of water as the re-
action medium will not only reduce the use of harmful or-
ganic solvents, but will also be regarded as an important re-
E-mail: y-ikushima@aist.go.jp
[
c] Dr. R. Zhang
Present address: State Key Laboratory of Coal Conversion
Institute of Coal Chemistry, Chinese Academy of Sciences
Taiyuan, 030001 (P.R. China)
Chem. Eur. J. 2004, 10, 1±01 ± 1±06
DOI: 10.1002/chem.200305542
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1±01

FULL PAPER
[
1±]
search topic in green chemistry. Second, water has unique
physical and chemical properties, and its physicochemical
properties can be influenced greatly with pressure and tem-
perature. For example, the static dielectric constant of water
is 78.± at 298 K, and dramatically decreases to about 6.0 at
in which several alkylarenes, such as stilbene 1 and 1,1-di-
phenylethylene 2 were formed as shown in Scheme 1, be-
sides hydrogen iodide. In addition to the expected coupling
reaction, we observed the hydrogenation of 1!bibenzyl 4
and 2!1,1-diphenylethane 5, and also the hydrogenation of
styrene to ethyl benzene. We observed a high conversion of
styrene, but ethyl benzene and a tarry polymeric material
(styrene oligomers) were the main products.
[16]
the critical point (647.1 K and 22.1 MPa).
nonpolar organic compounds are very soluble or miscible in
scH O. By utilizing these properties it would be possible to
As a result,
2
realize reactivities that cannot
be attained in organic solvents.
This nature along with high dif-
fusivity and low viscosity is ex-
pected to function as an ideal
alternative for apolar organic
[16,17]
solvents.
Experimental re-
sults of Diels±Alder reactions,
hydrolysis of ester and nitriles
Scheme 1. Heck reaction of styrene and iodobenzene.
[18]
in scH O have been reported.
2
[19]
More recently, Sasaki et al. discovered that intramolecular
dehydration between 1-hexyl alcohol and acetamide occur
in scH O without catalyst. scH O is thus expected to play an
In this system, the presence of base, which is necessary to
bind the hydrogen halide formed during CꢀC bond cou-
pling, and the choice of base can have a crucial effect on the
2
2
[3]
important role according to each reaction, and could pro-
vide new reaction pathway.
rate and the product distribution of the Heck reaction.
Thus, the effect of base on the Heck reaction in scH O was
2
The Heck arylation of alkenes has been carried out in hot
investigated. Experiments were carried out in the presence
of N(Et)3, NaOAc, KOAc, K PO , K CO , Na CO ,
compressed water (±33 K) and also in scH O (673 K) in the
2
3
4
2
3
2
3
[20±23]
presence of Pd catalysts.
In the case of the Pd-catalyzed
NaHCO , or NaOH base. The results are shown in Table 1.
3
reaction of iodobenzene and styrene, the yield of coupling
products was less than 2±% and the catalysts were deacti-
vated rapidly. Further, the influence of water on the selectiv-
ity and the reaction mechanism has scarcely been elucidat-
ed. We have demonstrated a remarkable stimulation of rear-
The kind of base has a strong influence on both the conver-
sion and the selectivity in scH O. That is, KOAc base was
2
the most effective for synthesizing coupling compounds such
as stilbene 1. The conversion of iodobenzene and styrene
reached over 70%. High regioselectivity (>9±:±) towards
the internal olefin 1 was observed with only a small amount
of terminal olefin 2, and the yield of double arylated Heck
coupling compound, 1,1,2-triphenylethylene 3 was less than
3%. The yield of stilbene was ±±.6% and the ratio of trans-
to cis-stilbene (E:Z in Table 1) was approximately 81:19. In
addition, white crystals of trans-stilbene can be easily sepa-
rated from the reaction system.
Similarly to the case without base addition, in the pres-
ence of N(Et)3 base, high conversion of styrene was ob-
tained; however, the yield of stilbene 1 was low and ethyl
benzene and the hydrogenated products (4 and 5) were ob-
tained in about 10.± and 6.8% yields, respectively. When a
strong base such as NaOH was used, the conversion of iodo-
rangement or disproportionation using scH O even in the
2
[24,2±]
absence of any acid or base catalysts.
The structural and
electronic properties of water close to above the critical
point have been analyzed by first principles molecular dy-
[26]
[2±]
[27]
namics, in situ IR and Raman spectroscopic measure-
ments. Close at the critical point, where the density is very
low, small clusters, mainly monomer, dimers and trimers, are
predominant, but the clusters exhibit no hydrogen-bonding
network. The significant reduction of the strength of hydro-
gen bonding in H O peculiar near the critical point would
2
+
ꢀ
lead to the activation of protons or H O or OH ions. This
3
might be responsible for the acid and base difunctionality of
scH O. Hence, we attempted to conduct a noncatalytic ary-
2
lation of styrene using scH O,
2
in which the effects of base,
[
a]
Table 1. Effect of base on reaction of styrene and iodobenzene.
Base Conversion [%]
styrene iodobenzene
temperature, water density, and
reactor material on the conver-
sion and product selectivity
were investigated in detail.
Yield [%]
E:Z
1
2
3
6
7
[b]
±
100.0
39.7
±.0
0
0
[
d]
(
3.3)
(1.3)
0 (1.8)
2.3
(1.8)
0
0
0
0
6.3
2±.7
44.3
±8.2
±2.8
±9.4
0
±
±
[
c]
N(Et)
KOAc
NaOAC
3
94.1
72.±
6±.4
60.4
64.6
39.0
±±.2
41.4
4±.1
77.±
6±.6
77.2
100.0
93.1
13.9 (±.0)
±±.6
43.8
42.2
27.8
0
0
0
1.9
±.2
7.7
4.1
3.0
2.0
1.4
0.±
0.1
0.1
0
81:19
81:19
81:19
83:17
81:19
83:17
80:20
Results and Discussion
1.9
1.8
1.2
0.±
0.4
0.3
K
3
PO
4
Na
2
CO
3
Effect of base: We found for
the first time that the coupling
of styrene and iodobenzene can NaOH
be promoted even in the ab-
K
2
CO
3
10.7
10.2
NaHCO
3
9±.0
100.0
7.7
11.±
ꢀ3
[
a] 6±0 K and water density 0.±1 gcm . [b] Ethylbenzene 10.2%. [c] Ethylbenzene 10.±%. [d] The numbers in
sence of any catalysts in scH O, the parentheses are yields of corresponding hydrogenated products.
2
1±02
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2004, 10, 1±01 ± 1±06

Heck Coupling Reactions in Supercritical Water
1±01 ± 1±06
benzene was high and phenol was the main product. Other
bases, such as K PO , K CO , Na CO , and NaHCO , gave
3
4
2
3
2
3
3
results in-between potassium acetate and sodium hydroxide.
Unlike the Heck reactions in organic solvent with cata-
[3]
lysts, the nature of base had no influence on the regiose-
lectivity of the double bond, but there was a slight different
in the E:Z selectivity. Moreover, homocoupling of iodoben-
zene to biphenyl has not been observed in scH O regardless
2
of the base used.
It is noteworthy that in the absence of base or presence of
the N(Et) base, the hydrogenation of styrene and the cou-
3
pling products took place to a large extent. It would be pre-
dicted that the hydrogenation would be caused by the result-
ing hydrogen iodide, because the hydrogenation of styrene
Figure 2. Effect of water density on the conversion of styrene at 6±0 K in
the presence of KOAc conversion.
to ethyl benzene in scH O was shown to proceed only when
2
hydrogen iodide is present. On the other hand, in the ab-
sence of hydrogen iodide the formation of a small amount
of 1-phenylethyl alcohol from styrene in scH O was con-
2
firmed, and so that the hydrogen for the hydrogenation can
only be donated from scH O itself.
2
Effect of temperature and water density: Figure 1 shows the
temperature dependence of the conversion and the yield of
stilbene in the presence of KOAc. One can see an interest-
ing temperature dependence in which both the conversion
and the yield increased, reaching a maximum conversion
and yield at 6±0 K near the critical temperature of water,
and then decreased as the temperature further increased. It
was found that higher temperatures favored the formation
of gaseous products, resulting in the low yield of stilbene.
Furthermore, the E:Z ratio was approximately 81:19 regard-
less of the temperature.
Figure 3. Yields of coupling products under different water densities at
6
±0 K in the presence of KOAc; product 1: stilbene, product 2: 1,1-diphe-
nylethylene, product 3: 1,1,2-triphenylethylene.
modynamic pressure effect on the rate constant at a given
[16]
temperature can be obtained as:
°
ð@ln k=@ PÞT ¼ ꢀV =RT
°
where k is the bimolecular rate constant, V is the reaction
activation volume, R is the gas constant, and P and T are
the pressure and the temperature, respectively. Processes ac-
companied by a decrease in partial molar volume such as a
CꢀC bond formation, in which the distance between two
Figure 1. Influence of temperature on the conversion and the yield of stil-
bene at 2± MPa in the presence of KOAc conversion yield.
carbon atoms decreases from the van der Waals distance to
the bonding distance, are known to be accelerated by pres-
sure and the equilibrium should be shifted toward the side
of products. In most liquid solutions, the values of activation
The effect of water density on the conversion of styrene is
shown in Figure 2. The reaction seems to be significantly ac-
celerated by water density, especially showing nearly 30%
augmentation with a slight increase in density from 0.4± to
3
ꢀ1 [28]
volume are typically in the range of ꢀ30 to 30 cm mol .
Thus, pressure changes in the kilobar range are required to
achieve large variations in rate constant. For example, the
coupling of iodobenzene with ethyl acrylate hardly occurred
at 298 K and atmospheric pressure, but the conversion
ꢀ
3
0
.±6 gcm . The E:Z ratio remained almost unaltered, rang-
ing from 80:20 to 82:18. The yield of the terminal olefin 2
decreased slightly with increasing density, while that of
double arylated product 3 increased with pressure (see
Figure 3).
[29]
reached nearly 100% at 1 GPa. Moreover, for the palladi-
um catalyzed cross-coupling of iodobenzene with 2,3-dihy-
drofuran, very high pressures amounting to 8 kbar has been
reported to increase the turnover number in organic solvent
A significant part of the effect of pressure on the reaction
rate in scH O could be assignable to the thermodynamic
2
pressure effect. For a simple bimolecular reaction, the ther-
Chem. Eur. J. 2004, 10, 1±01 ± 1±06
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Y. Ikushima et al.
FULL PAPER
[
30,31]
systems, owing to an improved lifetime of the catalysts.
onically decreases with increasing temperature above ±73 K
[32]
ꢀ
Unlike the Heck reaction in normal organic solutions, small
pressure changes can make substantial variations in the rate
constant in supercritical fluids because the absolute value of
at 2± MPa,
and so the proton or hydroxide ion (OH )
concentration anticipated from the K concept is not so high
w
near the critical temperature at 2± MPa. However, in scH O
2
[
16]
ꢀ
activation volume is in the orders of liters per mol. As a
the OH or proton adjacent to substrate molecules cannot
result, for the Heck coupling reaction in scH O, increasing
the pressure from 20.3 to 32.1 MPa would elicit 40% aug-
mentation in the conversion.
migrate throughout the hydrogen-bond network near the
critical point. At least ten water molecules are considered to
be required for appreciable interaction between the hydro-
2
[33]
The E:Z ratio was independent of the density, which sug-
gests that there is no large difference in partial molar
volume between the two transition states. The slight de-
crease in the selectivity to terminal olefin might be due to
that the transition state of internal olefin having a relatively
larger dipole moment than that of terminal olefin. There-
fore, the internal olefin transition state would interact more
strongly with the solvent and be favored as the solvent den-
sity increased.
gen-bonding network and proton.
Moreover, the local
ꢀ
proton and OH concentrations would be high when the
transferring ions cannot escape. An increase in local proton
or hydroxide ion concentration around substrate molecules
might induce the enhancement in the rate of reaction.
ꢀ
Hence the OH or proton species could react spontaneously
with substrate molecules to form a transient intermediate
owing to the lower activation energies for bond cleavage
and formation. For the coupling reaction between styrene
ꢀ
and phenyl halide in scH O, it was proposed that the OH
2
Effect of reactor material: We had conducted the scH O re-
removes the b-H of styrene, giving a carbanion. Then the
nucleophilic carbanion attacks iodobenzene at the electro-
philic carbon, resulting in the formation of coupling prod-
ucts.
The second possibility is the direct participation of water
molecules through a transition state involving one or two
water molecules as shown in Scheme 2.
2
action under certain conditions using iron-base stainless
steel (SUS 316) and nickel-base alloy (Inconel 62±) reactors
with the same volume. The conversion and the yields of cou-
pling products are shown in Table 2. For both reactors, the
conversion of styrene reached 70%, while the yield of stil-
bene was 49.3 and ±±.6%, respectively. Moreover, there was
no discernible difference between the two reactors with re-
spect to the selectivity to the coupling products. High regio-
selectivity towards the internal olefins 1 was observed and
the ratio of trans- to cis-stilbene was approximately 81:19.
Thus, the effect of the reactor wall is considered to be negli-
gible. Furthermore, after extracting the products, both or-
ganic and water phases were analyzed by inductively cou-
pled plasma atomic emission spectroscopy (ICP-AES). The
concentrations of nickel, iron, chromium, and molybdenum
in both phases were lower than the identification limitation.
Hence, the possibility of catalytic effect of metal content of
the reaction solution was also excluded.
Scheme 2. Formation of stilbene via a transition state involving two water
molecules.
In the above water-catalyzed model, water molecules
make a hydrogen-bond ring network with the substrate mol-
ecules, and then play a role of a catalyst transferring a
proton along the locally formed hydrogen-bond network.
Stilbene would be formed via a six-membered or eight-
membered ring transition state, which greatly lowers the
energy for bond cleavage and formation. A similar water-
catalyzed mechanism has been proposed for the conversion
[
a]
Table 2. Results of Heck coupling reaction using different reactors.
Reactor
Conversion [%]
styrene iodobenzene
Yield [%]
E:Z
1
2
3
SUS 316
Inconel 62±
71.3
72.±
67.8
77.±
49.3
±±.6
2.1
2.3
2.±
3.0
81:19
81:19
[
a] 6±0 K, 2± MPa, in the presence of KOAc.
[34]
of 2-nitroaniline to benzofurazan and the decarboxylation
[3±]
of acetic acid derivatives in subcritical water. Moreover,
the role of water in the intermolecular hydrogen transfer
has been supported by quantum chemistry calculations. In
general, water molecules make the geometry of the transi-
tion state species less strained, thereby facilitating the for-
mation and cleavage of bonds that lead to the products.
Specifically, for the dehydrogenation reaction of ethanol
to acetaldehyde, the inclusion of two water molecules in
the transition state reduces the activation barrier by
The role of water: Two possibilities for the role of water re-
sponsible for the noncatalytic Heck coupling in scH O, that
2
is, ion and water-catalyzed mechanisms have been consid-
ered. First the supposition implicit in this ion mechanism is
+
that ionic species such as proton, H O , and hydroxide ion
3
originated from water molecules can be activated under su-
percritical state and promote the coupling reaction. Our
[
2±]
[27]
IR and Raman measurements of the hydrogen bonding
of sub- and supercritical water suggest that the tetrahedral
configurations disappear near the critical point, where the
monomer or dimer or trimer structures are predominant.
This result was further supported by a recent first-principle
ꢀ
1
~34 kcalmol and increases the rate constant by nine
[36]
orders of magnitude, compared with those in the absence
of water. Water also facilitates the decomposition of formic
[
37,38]
acid
and the aldol condensation of an aldehyde (formal-
[26]
[39]
molecular dynamics study. The ion product (K ) monot-
dehyde or acetaldehyde) with vinyl alcohol. Thus, it was
w
1±04
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2004, 10, 1±01 ± 1±06

Heck Coupling Reactions in Supercritical Water
1±01 ± 1±06
postulated that stilbene might be formed through a water-
bridged transition state.
It was further confirmed that phenol is obtained over
the temperature was controlled within ꢁ2 K. After the desired reaction
time of 10 min had elapsed, the reactor was removed 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 pure
compounds, and routine quantitative analysis was done using a 30 m DB-
WAX capillary column on a HP-6890 gas chromatograph equipped with
a FID detector, with response factors determined from the analysis of
standard compounds. The product yield was calculated based on styrene.
Each data point was measured at least two times and the errors in the
conversion and yields were less than ±%. The thermodynamic and trans-
port properties of the system at various conditions were determined
±
0% yield by hydrolysis of iodobenzene in scH O. As for
2
the formation of phenol, hydrolysis of chlorobenzene in
NaOH solution under high temperatures (633±663 K) and
high pressures (28±30 MPa) has been used commercially for
the production of phenol.
From the above results, it may be concluded that four
[
40]
competitive reaction processes take place in scH O: hydro-
using steam table.
2
genation, polymerization of styrene, coupling reaction of
styrene with iodobenzene, and hydrolysis of iodobenzene to
phenol. The selectivity would be controlled by the ionic be-
havior of water. The hydrogen halide formed during the re-
action facilitated the polymerization of styrene besides the
hydrogenation of both styrene and the coupling products.
The presence of a base was a key factor for the unusual se-
Acknowledgement
The authors gratefully acknowledge financial support from Japan Society
for the Promotion of Science (JSPS).
lectivity to stilbene in scH O. The cation of the base might
2
promote the removal of iodine via an intermediate com-
posed of an ion±dipole bond between cation and iodine. The
addition of a relatively mild base, such as NaOAc and
KOAc, could scavenge the hydrogen halide and promote
the cross-coupling reaction. When a strong base is use, the
[1] S. B. Solabannavar, Uday V. Desai, R. B. Mane, Green Chem. 2002,
4
, 347±348.
[2] J. G. de Vries, Can. J. Chem. 2001, 79, 1086±1092.
[3] M. Beller, T. H. Riermeier, Eur. J. Inorg. Chem. 1998, 29±3±.
[4] M. Feuerstein, H. Doucet, M. Santelli, Tetrahedron Lett. 2002, 43,
2191±2194.
ꢀ
[
[
±] F. Berthiol, H. Doucet, M. Santelli, Eur. J. Org. Chem. 2003, 1091±
concentration of OH was high, thus the hydrolysis of iodo-
benzene was favored.
1
096.
6] M. S. Stephan, A. J. J. M. Teunissen, G. K. M. Verzijl, J. G. de Vries,
Angew. Chem. 1998, 110, 688±690; Angew. Chem. Int. Ed. 1998, 37,
6
62±664.
Conclusion
[7] L. J. Goossen, J. Paetzold, L. Winkel, Synlett 2002, 1721±1723.
[
[
8] J. An, L. Bagnell, T. Cablewski, C. R. Strauss, R. W. Trainor, J. Org.
Chem. 1997, 62, 2±0±±2±11.
9] S. Mukhopadhyay, G. Rothenberg, A. Joshi, M. Baidossi, Y. Sasson,
Adv. Synth. Catal. 2002, 344, 348±3±4.
The Heck coupling of styrene with iodobenzene occurred in
scH O with high regioselectivity even in the absence of cata-
2
lyst. Both the choice of base and the reaction conditions had
a significant effect on the conversion and the product selec-
tivity. High yields of coupling products were obtained in the
presence of mild bases such as KOAc or NaOAc. The con-
version and the yields of coupling products increased with
increasing temperature, reaching a maximum at 6±0 K near
the critical temperature of water, and then decreased as the
temperature was further increased. Water density had a sig-
nificant influence on the reaction rate, showing nearly 30%
augmentation with an increase in density from 0.4± to
[10] T. Jeffery, Tetrahedron Lett. 1994, 35, 30±1±30±4.
[
[
[
11] Y. Uozumi, T. Kimura, Synlett 2002, 204±±2048.
12] R. S. Gordon, A. B. Holmes, Chem. Commun. 2002, 640±641.
13] S. Fujita, K. Yuzawa, B. M. Bhanage, Y. Ikushima, M. Arai, J. Mol.
Catal. A 2002, 180, 3±±42.
[14] A. J. Carmichael, M. J. Earle, J. D. Holbrey, P. B. McCormac, K. R.
Seddon, Org. Lett. 1999, 1, 997±1000.
[
[
1±] K. Manabe, S. Limura, X. Sun, S. Kobayashi, J. Am. Chem. Soc.
002, 124, 11971±11978.
16] R. W. Shaw, T. B. Bill, A. A. Clifford, C. A. Eckert, E. U. Franck,
2
Chem. Eng. News 1991, 69, 26±39.
[17] P. E. Savage, Chem. Rev. 1999, 99, 603±621.
ꢀ
3
[
18] D. Brˆll, C. Kaul, A. Kramer, P. Krammer, T. Richer, M. Jung, H.
Vogel, P. Zehner, Angew. Chem. 1999, 111, 3180±3196; Angew.
Chem. Int. Ed. 1999, 38, 2998±3014.
0.±6 gcm , but had minor effect on the products selectivity.
Supercritical water might promote the Heck coupling reac-
tion either through an ion reaction process or by taking part
in the formation of cyclic transition state involving one or
two water molecules.
[
19] M. Sasaki, J. Nishiyama, M. Uchida, K. Goto, K. Tajima, T. Ad-
schiri, K. Arai, Green Chem. 2003, 5, 9±±97.
[20] J. Diminnie, S. Metts, E. Parsons, J. Organomet. Chem. 1995, 14,
023±402±.
4
[
21] P. Reardon, S. Metts, C. Crittendon, P. Daugherity, E. Parsons, J. Or-
ganomet. Chem. 1995, 14, 3810±3816.
[
[
22] L. U. Gron, A. S. Tinsley, Tetrahedron 1999, 55, 227±230.
23] L. U. Gron, J. E. LaCroix, C. J. Higgins, K. L. Steelman, A. S. Tins-
ley, Tetrahedron Lett. 2001, 42, 8±±±±8±±7.
Experimental Section
All reactants and solvents were obtained from Wako pure or Aldrich and
were used as-received without further purification. Triply distilled high-
purity water was used for all experiments and deoxygenated by N
prior to use.
[
[
24] Y. Ikushima, K. Hatakeda, O. Sato, T. Yokoyama, M. Arai, Angew.
Chem. 2001, 113, 216±219; Angew. Chem. Int. Ed. 2001, 40, 210±
2
gas
2
13.
2±] Y. Ikushima, K. Hatakeda, M. Sato, O. Sato, M. Arai, Chem.
Commun. 2002, 2208±2209.
The experiments were performed by using an Inconnel 62± batch reactor
3
system with an internal volume of 10.2 cm . A predetermined amount of
[26] M. Boero, K. Terakura, T. Ikeshoji, C. C. Liew, M. Parrinello, Phys.
Rev. Lett. 2000, 85, 324±±3248.
[27] Y. Ikushima, K. Hatakeda, N. Saito, M. Arai, J. Chem. Phys. 1998,
108, ±8±±±8±±7.
substrates and base (1.0 mmol each) and water were loaded into the reac-
tor under argon atmosphere. The reactor vessel was immersed and vigo-
rously 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 and
[28] A. Baiker, Chem. Rev. 1999, 99, 4±3±473.
Chem. Eur. J. 2004, 10, 1±01 ± 1±06
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1±0±

Y. Ikushima et al.
FULL PAPER
[
29] T. Sugihara, M. Takebayashi, C. Kaneko, Tetrahedron Lett. 1995, 36,
±47±±±±0.
[36] H. Takahashi, S. Hisaoka, T. Nitta, Chem. Phys. Lett. 2002, 363, 80±
86.
±
[
[
30] S. Hiller, O. Reiser, Chem. Commun. 1996, 2197±2198.
31] S. Hiller, S. Sartori, O. Reiser, J. Am. Chem. Soc. 1996, 118, 2087±
[37] N. Akiya, P. E. Savage, AIChE J. 1998, 44, 40±±41±.
[38] T. Yagasaki, S. Saito, I. Ohmine, J. Chem. Phys. 2002, 117, 7631±
7639.
[39] E. L. CoitiÊo, J. Tomasi, O. N. Ventura, J. Chem. Soc. Faraday Trans.
1994, 90, 174±±17±±.
[40] A. H. Harvey, A. P. Peskin, S. A. Klein, NIST/ASME Steam Proper-
ties, Formulation for General and Scientific use NIST Standard Ref-
erence Database 10, Version 2.11.
2
088.
32] W. L. Marshall, E. U. Franck, J. Phys. Chem. Ref. Data 1981, 10,
9±±304.
33] Y. P. Sun, M. A. Fox, K. P. Johnston, J. Am. Chem. Soc. 1992, 114,
187±1194.
34] X. G. Wang, L. U. Gron, M. T. Klein, T. B. Brill, J. Supercrit. Fluids
995, 8, 236±249.
3±] A. J. Belsky, P. G. Maiella, T. B. Brill, J. Phys. Chem. A 1999, 103,
2±3±4260.
[
[
[
[
2
1
1
4
Received: September 16, 2003 [F±±42]
1±06
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 1±01 ± 1±06