Biphasic hydroformylation of substituted allylbenzenes with water-soluble rhodium or ruthenium complexes

Article abstract of DOI:10.1016/j.apcata.2010.12.037

The water-soluble complexes [Rh(CO)(Pz)(L)]₂ and [HRu(CO)(CH₃CN)(L)₃][BF₄] [L = TPPMS (m-sulfonatophenyl-diphenylphosphine) and TPPTS (tris-m-sulfonato- phenylphosphine)] were used for the first time as catalyst precursors for the hydroformylation of eugenol, estragole, safrole and trans-anethole under moderate conditions in biphasic media. Under mild reaction conditions the substrates showed the following reactivity order: eugenol > estragole ≈ safrole > trans-anethole. The use of cetyl-trimethylammonium chloride (CTAC) as phase transfer agent inhibits the isomerization reaction, reaching high selectivity for the hydroformylation products (80-94%). The catalytic phase can be recycled up to four times with a decrease in the activity over time but maintaining its high selectivity.

Full text of DOI:10.1016/j.apcata.2010.12.037

Applied Catalysis A: General 394 (2011) 117–123
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Biphasic hydroformylation of substituted allylbenzenes with
water-soluble rhodium or ruthenium complexes
Luis G. Meleana, Mariandry Rodrigueza, Marynell Romeroa,
Maria L. Alvaradoa, Merlin Rosalesb, Pablo J. Baricellia,∗
a Centro de Investigaciones Químicas, Facultad de Ingeniería, Universidad de Carabobo, Valencia, Venezuela
b Laboratorio de Química Inorgánica, Departamento de Química, Facultad Experimental de Ciencias, Universidad del Zulia, Ado. 526, Maracaibo, Venezuela
a r t i c l e i n f o
a b s t r a c t
Article history:
The water-soluble complexes [Rh(CO)(Pz)(L)]2 and [HRu(CO)(CH3CN)(L)3][BF4] [L = TPPMS (m-
sulfonatophenyl-diphenylphosphine) and TPPTS (tris-m-sulfonato-phenylphosphine)] were used for the
first time as catalyst precursors for the hydroformylation of eugenol, estragole, safrole and trans-
anethole under moderate conditions in biphasic media. Under mild reaction conditions the substrates
showed the following reactivity order: eugenol > estragole ≈ safrole ꢀ trans-anethole. The use of cetyl-
trimethylammonium chloride (CTAC) as phase transfer agent inhibits the isomerization reaction, reaching
high selectivity for the hydroformylation products (80–94%). The catalytic phase can be recycled up to
four times with a decrease in the activity over time but maintaining its high selectivity.
© 2011 Elsevier B.V. All rights reserved.
Received 13 October 2010
Received in revised form
18 December 2010
Accepted 23 December 2010
Available online 4 January 2011
Keywords:
Biphasic hydroformylation
Allylbenzenes
Water-soluble Rh and Ru complexes
1. Introduction
and obtained high regioselectivity towards the linear aldehydes
(80–96%).
The hydroformylation of naturally occurring olefins such as
allylbenzenes, propenyl-benzenes and terpenes, readily available
from biomass, is an important and useful synthetic tool to obtain
oxygenated products relevant in the flavor, food and pharmacy
industries. The aldehydes obtained from the hydroformylation of
allyl-benzenes and propenyl-benzenes are direct synthetic inter-
mediates in the production of substituted 2-methyl-indanons (1)
and ␣-tetralons (2) (Fig. 1) which are important precursors for bio-
logically active compounds [1].
Several groups have studied the hydroformylation of allyl-
benzenes over the years. The homogeneous hydroformylation
of eugenol (3a) and iso-eugenol (4a) at high pressure was per-
formed 30 years ago by Siegel and Himmele [2], who obtained
a mixture of aldehydes (linear and branched) whose distribu-
tion depended on the temperature. Kollár et al. [1] reported
the enantioselective hydroformylation of estragol (3b) and trans-
anethole (4b) using Pt–Sn and Rh with diop and bdpp as
chiral phosphines; however low regioselectivity and ee were
found. Kalck et al. [3] studied the hydroformylation of eugenol,
estragole, safrole (3c) and eugenol–methyl ether with the sys-
tems [Rh(␮-SR)2(CO)2L2] where L = PPh3, P(OPh)3 and P(OMe)3,
In 2001, dos Santos et al. [4] reported a systematic study
of the homogeneous hydroformylation of several allylbenzenes
and propenylbenzenes using the system [Rh(COD)(OAc)2]/L where
L = P(OPh)3, PPh3, P(Cy)3, P(n-Bu)3, P(CH2-Ph)3, dppe, dppp, dppb,
BISBI, NAPHOS. Two important conclusions were drawn from that
study: (i) when monophosphines were used, the activity and
regioselectivity of the reaction depended on the basicity of the
ligand; (ii) the regioselectivity depended on the bite angle of the
diphosphines used with wide-angled ones favoring the linear alde-
hyde almost exclusively.
Recently, Claver et al. [5] reported the hydroformylation of
trans-anethole and estragol using the system [Rh(acac)(CO)2]
with carbohydrate-derived diphosphites. They found high activ-
ity and regioselectivity towards the branched aldehydes in the
hydroformylation of trans-anethole and moderate ones with
estragol.
Despite the interest in the hydroformylation of allyl- and
propenylbenzenes in the homogeneous media, there has been
only one report of a biphasic process to the best of our knowl-
edge. In 2006, Paganelli et al. [6] reported the hydroformylation
of m-di-isopropyl-benzene (5) in homogeneous, heterogeneous
and biphasic systems, as a first step in the preparation of the
mono-alhehyde Florhydral© (6), a patented, marine-scented fra-
grance as seen in Eq. (1). They used the precursors [Rh(COD)Cl]2
and [Rh(CO)2(acac)] with TPPTS and obtained better results in the
∗
Corresponding author. Tel.: +58 241 6004000x305235.
E-mail address: pbaricel@uc.edu.ve (P.J. Baricelli).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.12.037

118
L.G. Melean et al. / Applied Catalysis A: General 394 (2011) 117–123
CO/H2
R
O
H
R
R
O
R
R
R
1
O
H
CO/H2
R
R
O
R
R
R
R
2
Fig. 1. Potential reactions of hydroformylated allylbenzenes.
biphasic system than with any other.
CHO
CHO
H2
CO/H2
5
6
(1)
Our group has shown a long lasting interest in biphasic sys-
tems; we have reported the hydroformylation and hydrogenation
of olefins and light naphtha cuts with water-soluble rhodium,
ruthenium, tungsten and molybdenum precursors [7–11]. More
recently, we have shifted our focus towards functionalizing nat-
urally occurring olefins like allylbenzenes and terpenes, readily
available from biomass, in biphasic media aiming to obtain prod-
ucts of high added-value important in the cosmetic, perfume, and
pharmacological industries. In the present work we report for
the first time the hydroformylation of substituted allylbenzenes
[eugenol (3a), estragole (3b), safrole (3c), and trans-anethole (4b)]
with rhodium and ruthenium water-soluble complexes in a bipha-
sic media.
2.2. Biphasic aqueous hydroformylation of allylbenzenes
In a typical experiment, the catalyst precursor (0.0044 mmol)
and the phase transfer agent (CTAC, 0.006 mmol) were dissolved in
5 mL of deoxygenated water and added into a stainless steel reactor
(25 mL, Parr) fitted with internal mechanical stirring, a temperature
control unit, and a sampling valve. The system was purged three
times, then pressurized to 2.07 MPa with syn-gas (CO/H2 = 1:1) and
warmed to 80 ◦C. Once the desired temperature was achieved, a
solution of the substrate (2.2 mmol) in 5 mL of toluene was added
via a high-pressure burette and this was taken as the initial reaction
time. Samples of the reaction mixture were periodically extracted
and the system total pressure was adjusted via a high pressure
reservoir. Once the samples were extracted, they were cooled, the
phases separated and the organic phase analyzed by GC and GC–MS
techniques.
2. Experimental
2.1. General procedure
All manipulations were carried out under nitrogen using stan-
dard Schlenk techniques. Organic solvents were dried and purified
by distillation over standard agents under N2 prior to use. All
other chemicals were commercial products and were used with-
out further purification. All gases were of high purity (>99.9%) and
were purchased from Aga Gases-Venezuela. [Rh(CO)(Pz)(L)]2 and
[HRu(CO)(CH3CN)(L)3][BF4] (L = TPPMS and TPPTS) were synthe-
sized according to published methods [7–10]. GC analyses were
performed on a Hewlett Packard 5971 Plus Series II chromato-
graph with a flame ionization detector in an Ultra-1, DB-1, (10%
dimethyl polysiloxane), 25 m, 0.32 mm, 0.52 ␮m column to sepa-
rate the products. Quantification was achieved by using heptane as
the internal standard and all peaks were identified by GC/MS on
a Digital Technology 5890/5971 coupled system using a Quadrex
PONA 10% dimethyl polysiloxane, 25 m, 0.52 ␮m column.
3. Results and discussion
3.1. Biphasic hydroformylation of allylbenzenes with
water-soluble rhodium complexes
A preliminary study was conducted to determine the best oper-
ational conditions for the biphasic hydroformylation of eugenol
as model molecule using the binuclear water-soluble precursor
[Rh(CO)(Pz)(TPPMS)]2. As shown in Eq. (2), eugenol (3a), under
hydroformylation conditions, can undergo several competing
transformation: isomerization to iso-eugenol (4a), hydrogenation
to form the saturated product (7a) and hydroformylation to cre-
ate the linear (8a) and branched (9a and 10a) aldehydes. In order
to determine the best reaction conditions, the following param-

L.G. Melean et al. / Applied Catalysis A: General 394 (2011) 117–123
119
Table 1
Determination of optimal reaction conditions for the hydroformylation of eugenol (3a) with [Rh(CO)(Pz)(TPPMS)]2.
No.
[CTAC] (mM)
P CO/H2 (MPa)
[3a] M
T (◦C)
Conv.
TON
Selectivity
l/b
TOF (h−1
)
4a
7a
8a
14%
33%
31%
34%
9a
27%
55%
56%
50%
1
2
3
4
0
1.52
1.52
1.52
1.52
0.44
0.44
0.44
0.44
80
80
80
80
96%
96%
98%
480
480
489
501
40%
11%
8%
19%
1%
5%
1.93
1.67
1.81
1.47
160
160
163
167
1.25
2.5
5.0
100%
3%
13%
5
2
6
7
1.25
1.25
1.25
1.25
0.69
1.52
2.07
3.45
0.44
0.44
0.44
0.44
80
80
80
80
99%
96%
98%
94%
495
480
489
471
32%
11%
6%
1%
1%
1%
0%
19%
33%
31%
28%
48%
55%
62%
51%
2.53
1.67
2.00
1.82
165
160
163
157
20%
8
9
6
10
11
1.25
1.25
1.25
1.25
1.25
2.07
2.07
2.07
2.07
2.07
0.44
0.44
0.44
0.44
0.44
60
70
80
90
44%
98%
98%
96%
98%
219
489
489
480
489
16%
14%
6%
30%
31%
4%
1%
1%
1%
1%
28%
35%
31%
27%
31%
52%
51%
62%
42%
37%
1.86
1.46
2.00
1.56
1.19
73
163
163
160
163
100
12
6
13
14
15
1.25
1.25
1.25
1.25
1.25
2.07
2.07
2.07
2.07
2.07
0.22
0.44
0.66
0.88
1.32
80
80
80
80
80
97%
98%
99%
72%
50%
243
489
744
720
750
9%
6%
26%
24%
28%
0%
1%
1%
1%
4%
36%
31%
28%
28%
25%
55%
62%
45%
47%
43%
1.53
2.00
1.61
1.68
1.72
81
163
248
240
250
Conditions: Rh = 0.0044 mmol, t = 3 h, H2O = toluene = 5 mL, stirring = 960 rpm.
eters were systematically varied: concentration of phase-transfer
reagent, reaction temperature, pressure of syn-gas and substrate
concentration; the reaction time, volume of the organic and aque-
ous phases and stirring rate were kept constant for ease of analysis
and comparison; the results are summarized in Table 1.
The total pressure of syn-gas also has a marked effect on the
product distribution. As the pressure rises, the amount of alde-
hydes obtained increments accordingly till it reaches a maximum
of 93% for a pressure of 2.07 MPa (CO/H2 = 1:1); this behavior can
be explained by the complex equilibrium present in a biphasic
H
HO
O
8a
HO
OMe
OMe
3a
+
HO
HO
O
H
OMe
OMe
O
H
9a
7a
HO
HO
OMe
OMe
10a
4a
(2)
As it can be seen from entries 1 to 4, the addition of the phase-
transfer agent cetil-trimethylammonium chloride has little effect
on the total conversion of eugenol; however, it affects the product
distribution dramatically. CTAC has been reported by dos Santos
et al. [12] as an aid in the biphasic hydroformylation of terpenes;
however it has never been studied with allylbenzenes. In the
absence of CTAC, the isomerization and hydrogenation products
account for half of those obtained. The addition of a little con-
centration of CTAC (1.25 mM) inhibits to a great extent those side
reactions, reaching a product selectivity of 88% towards the desired
aldehydes; further increments on the amount of CTAC have little
effect on the reaction.
medium. A further increment in the working pressure (3.45 MPa)
results in a drop in the activity of the catalyst, evidencing that the
equilibrium shifts again depending on the reaction conditions to
form inactive poly-hydride or poly-carbonyl species.
The temperature of the reaction has an important influence on
the total conversion. At low temperature (60 ◦C) the substrate does
not react favorably. As the temperature increases, the conversion
also increases, however, at temperatures too elevated (>90 ◦C) all
the competing reactions are also favored, decreasing the selectivity
towards the aldehydes.
The variation in the substrate concentration clearly shows evi-
dence of saturation kinetics. The TON and TOF of the catalyst

120
L.G. Melean et al. / Applied Catalysis A: General 394 (2011) 117–123
Table 2
Biphasic hydroformylation of allylbenzenes with [Rh(CO)(Pz)(TPPMS)]2.
Substrate
Conv.
Product distribution
Isomer
l/b
TOF (h−1
)
7
8
9
10
Eugenol, 3a
Safrole, 3c
Estragole, 3b
Anethole, 4b
98%
88%
99%
35%
6%
19%
26%
11%
1%
1%
1%
3%
62%
46%
43%
6%
32%
34%
27%
30%
0%
0%
3%
1.94
1.35
1.43
0.07
61
55
62
22
51%
Conditions: Rh = 0.0044 mmol, [substrate] = 0.44 M, [CTAC] = 1.25 mM, H2O = toluene = 5 mL, t = 8 h, T = 80 ◦C, P = 2.07 MPa (CO/H2 1:1), stirring = 960 rpm.
Table 3
Biphasic hydroformylation of allylbenzenes with [Rh(CO)(Pz)(TPPTS)]2.
Substrate
Conv.
Product distribution
Isomer
l/b
TOF (h−1
)
7
8
9
10
Eugenol, 3a
Safrole, 3c
Estragole, 3b
Anethole, 4b
94%
98%
99%
28%
11%
29%
39%
27%
0.6%
0.5%
0.5%
4%
55%
38%
37%
19%
34%
32%
23%
31%
0%
0%
0.4%
19%
1.62
1.19
1.61
0.38
59
61
62
18
Conditions: Rh = 0.0044 mmol, [substrate] = 0.44 M, [CTAC] = 1.25 mM, H2O = toluene = 5 mL, t = 8 h, T = 80 ◦C, P = 2.07 MPa (CO/H2 1:1), stirring = 960 rpm.
increase steadily with the substrate concentration until they reach
maximum values of around 750 and 250 h−1 respectively for a con-
centration of 0.66 M and remain constant for higher concentrations.
The l/b ratios in all reactions stay in the range of 1.5–2.5 which are
characteristic of rhodium systems without any excess of phosphine
added. A concentration of 0.44 M was chosen for further studies
since it’s product distribution was more satisfactory: high selec-
tivity towards aldehydes with small amounts of isomerization and
hydrogenation products detected.
In order to rule out the participation of metallic rhodium in the
hydroformylation reactions, the well-known mercury test was car-
ried out performing the hydroformylation of eugenol under the best
operational condition but adding one drop of mercury to the reac-
tion mixture [13,14]. The reaction showed no interference of the
Hg in the course of the hydroformylation of eugenol, confirming
the absence of metallic particles or colloids during the catalysis.
The metal content in the organic phase was determined by atomic
absorption analysis in each run and the results show that less than
5 ppm were present in the organic phase, indicating that practically
all of the rhodium remains in the aqueous phase.
Once the best operational conditions were determined
([CTAC] = 1.25 mM, T = 80 ◦C, P syn-gas (2.07 MPa, CO/H2 = 1:1),
[substrate] = 0.44 M), they were employed in the biphasic hydro-
formylation of several allylbenzenes. Estragole (3b) and trans-
anethole (4b) react as depicted in Eq. (3), while safrole (3c) reacts as
described in Eq. (4); in all cases isomerization, hydrogenation and
hydroformylation products are formed. The results of the reactions
are shown in Table 2.
H
MeO
O
8b
MeO
3b
+
MeO
MeO
O
H
O
H
9b
7b
MeO
MeO
10b
4b
(3)

L.G. Melean et al. / Applied Catalysis A: General 394 (2011) 117–123
121
H
O
O
8c
O
O
O
3c
+
O
O
O
H
O
O
O
H
9c
7c
O
O
O
O
10c
4c
(4)
The reaction time was extended to 8 h since the other substrates
the hydroformylation of different allylbenzenes was studied; the
results are summarized in Table 4.
are not as reactive as eugenol under the reaction conditions. This
inhibited reaction is probably due to solubility difficulties since
estragole, anethole and safrole lack the hydroxyl group present in
eugenol which increases its hydrophilicity and favors the biphasic
reaction. All substrates with a terminal olefin reach high conver-
sions while trans-anethole, bearing an internal olefin, only reaches a
moderate conversion due to its difficulty to coordinate to the metal
center. In all cases, the selectivity for hydroformylation products
(7–10) is high (70–94%) with l/b ratios typical for rhodium systems
without any excess of phosphine added to the reaction mixture,
which demonstrates that our catalyst precursor is highly efficient
in this reaction system.
When the phosphine in the catalyst precursor was changed
to TPPTS, keeping all reaction conditions the same for the sake
of comparison, two interesting results were obtained: the con-
versions were not affected and the selectivity dropped slightly,
increasing the amount of isomerization products as can be seen
in Table 3. This increase in the amount of isomerization prod-
uct can be explained by the well known tensoactive properties
of the TPPMS which are absent in the TPPTS [15]. As it was
explained earlier, the concentration of the phase-transfer addi-
tive plays an important role in the product distribution of this
biphasic reaction and when the phosphine was changed, it had
the same effect as lowering the concentration of CTAC in the sys-
tem. An interesting consequence of this increase of isomerization
is that in the reaction of anethole, the linear aldehyde (8c) was
observed in a significant amount, which could only derive from
estragole.
The most remarkable difference between the Rh and Ru sys-
tems is that asides from eugenol, all other substrates show sluggish
conversions. Safrole and estragole only reached moderate val-
ues of 15% and 30% respectively, while trans-anethole, with its
unreactive internal olefin, only reached a trace conversion. How-
ever, the selectivity towards the hydroformylation products is very
high (88–100%) for those substrates; the hydrogenation reaction is
inhibited in all cases except for eugenol and the isomerization one
is also diminished, which are unexpected, gratifying results.
When the phosphine in the catalyst precursor was changed to
TPPTS, once again the isomerization reaction was enhanced as it
occurred in the rhodium system, and it is explained by the lack of
tensoactive properties of the TPPTS. Also, it can be seen in Table 5,
that the reactions of safrole and estragole achieved higher con-
versions with TPPTS than with TPPMS; this can be explained by
the higher solubility of the TPPTS in water compared to that of
its monosulfonated analog, which makes the ruthenium system
slightly more active.
3.3. Evaluation of the recycling of the water-soluble complexes
Arguably, the greatest benefit of a biphasic system is the ability
of easily separate the aqueous phase containing the catalyst from
the organic phase where the products are present and reusing the
catalyst by loading fresh substrate [16]. In this order of ideas, we
evaluated the recycling ability of our systems of rhodium and ruthe-
nium in the biphasic hydroformylation of eugenol, the results are
presented in Figs. 2 and 3.
3.2. Biphasic hydroformylation of allylbenzenes with
water-soluble ruthenium complexes
The catalytic aqueous phase in the rhodium systems can be recy-
cled in four consecutive reactions; both the TPPTS and TPPMS show
a decrease in the activity over time due most likely to the oxidation
of the phosphine when it comes in contact with air. The presence of
the tensoactive additive (CTAC) makes the phase separation diffi-
cult, requiring a long period of time to be achieved resulting in the
decrease of the activity. The effect is evident to a lesser extent when
the TPPTS is used, once again due to its lack of tensoactive prop-
erties. In both cases the selectivity towards the aldehydes remains
high (>80%).
The optimal reaction conditions were determined using
[HRu(CO)(CH3CN)(TPPMS)3][BF4] and eugenol as model substrate.
Traditionally, ruthenium is less active in hydroformylation than
rhodium, thus it was not surprising that the Ru precursor
required hasher conditions than its Rh counterpart, being neces-
sary 6.21 MPa of syn-gas (CO/H2 = 1.1), a temperature of 100 ◦C,
a concentration of CTAC of 1.25 mM, a [substrate] = 0.44 M and
a reaction time of 10 h for the reaction to achieve moderate to
high conversions. Once the reaction conditions were determined,
When the recycling of the ionic ruthenium precatalyst
[HRu(CO)(CH3CN)(TPPMS)3][BF4] was evaluated and interesting

122
L.G. Melean et al. / Applied Catalysis A: General 394 (2011) 117–123
Table 4
Biphasic hydroformylation of allylbenzenes with [HRu(CO)(CH3CN)(TPPMS)3][BF4].
Substrate
Conv.
Product distribution
Isomer
l/b
TOF (h−1
)
7
8
9
10
Eugenol, 3a
Safrole, 3c
Estragole, 3b
Anethole, 4b
99%
15%
30%
2%
13%
12%
5%
7%
0%
0%
0%
48%
53%
62%
0%
32%
35%
33%
60%
0%
0%
0%
1.50
1.51
1.88
N/A
50
8
15
1
0%
40%
Conditions: Ru = 0.0044 mmol, [substrate] = 0.44 M, [CTAC] = 1.25 mM, H2O = toluene = 5 mL, t = 10 h, T = 100 ◦C, P = 6.21 MPa (CO/H2 1:1), stirring = 960 rpm.
Table 5
Biphasic hydroformylation of allylbenzenes with [HRu(CO)(CH3CN)(TPPTS)3][BF4].
Substrate
Conv.
Product distribution
Isomer
l/b
TOF (h−1
)
7
8
9
10
Eugenol, 3a
Safrole, 3c
Estragole, 3b
Anethole, 4b
92%
42%
41%
3%
21%
25%
37%
42%
4%
0%
1%
0%
45%
44%
42%
10%
30%
31%
20%
34%
0%
0%
0%
1.50
1.42
2.10
0.21
46
21
21
2
14%
Conditions: Ru = 0.0044 mmol, [substrate] = 0.44 M, [CTAC] = 1.25 mM, H2O = toluene = 5 mL, t = 10 h, T = 100 ◦C, P = 6.21 MPa (CO/H2 1:1), stirring = 960 rpm.
phine. Current experiments focused on different phase transfer
agents and inert atmosphere techniques are under way aiming to
solve the recycling difficulties encounter to date, results will be
published elsewhere in due course.
4. Conclusions
The hydroformylation of allylbenzenes (eugenol, safrole,
estragole and anethole) was achieved for the first time with water-
soluble catalyst precursors of rhodium and ruthenium in biphasic
media; which represents an interesting new alternative to obtain
aldehydes of high added-value in the pharmaceutical and fine
chemical industry. In general, the rhodium complexes required
milder reaction conditions of pressure and temperature than their
ruthenium counterparts. The use of CTAC as a phase transfer agent
was needed in order to favor the hydroformylation reaction since
in its absence the isomerization of the substrates was considerable.
When the TPPMS in the catalyst precursors was changed for TPPTS,
the reaction conversions increased slightly; however the selectiv-
ity towards the aldehydes decreased in favor of the corresponding
isomerization product due to the lack of tensoactive properties of
the TPPTS. The catalytic phases can be recycled up to four times;
their activity decreased with time while their selectivity remained
high towards aldehydes.
Fig. 2. Recycling of rhodium complexes in the hydroformylation of eugenol.
result was obtained. In the first cycle a high conversion was
achieved as reported above; however it required a long induc-
tion period of about 1 h before the reaction proceeded. Once the
phases were separated and the aqueous one reused with fresh
eugenol/toluene, the reaction reached its maximum conversion in
1 h, without any induction time; evidence that the active species are
already formed and stable in the catalytic phase. Unfortunately, a
second reuse was not possible due to the oxidation of the phos-
Acknowledgements
We thank FONACIT (Caracas) for the financial support project
F-97-003766, CONIPET project 97-003777 and CDCH-UC projects
UAC-397-08 and 2006-005. We are grateful to the CYTED project
V.9, Laboratory of synthesis and characterization of new materials
– IVIC and the University of Carabobo for permitting the publication
of this work.
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