P.J. Baricelli et al.
Molecular Catalysis 497 (2020) 111189
conventional TPPTS ligand provided the preferential formation of the
lineal aldehydes, while with the tetrasulfonate diphosphines (DPPETS
and DPPPTS) the regioselectivity was switched to the branched isomer.
In biphasic catalysis, CTAB has been used as a phase transfer agent. In
the toluene/water systems the presence of the surfactant increases the
conversion. However, the role and mechanism of action on the inter-
action of surfactant and system components is not well understood. In
our group, we have focused to study a very interesting alternative in
biphasic catalysis, which is the system organic and ionic liquids phase.
Baricelli et al. [10] reported the activity and selectivity of the biphasic
ionic liquid/toluene system using the catalytic precursor [Rh(CO)(Pz)
(TPPMS)]2 in the modification of naturally occurring olefins in the
hydroformylation of terpenes and allylbenzenes, as well as in the hy-
2.3. Surface tension measurement
Surface tension of the different systems was determined at room
temperature using a Cole Palmer Model 21 tensiometer and du Noüy
ring method with a platinum-iridium ring with a circumference of 6 cm.
All solutions were allowed to stand for 24 h to achieve equilibrium.
Surface tension was obtained by plotting surface tension versus the
logarithm of the solute concentration. Aqueous 10 % (w/v) stock solu-
tions were prepared for the samples TPPTS, TPPMS, rhodium complex,
rhodium complex-H2/CO-TPPTS, cetyltrimethylammonium bromide
(CTAB), as well as 1:1 wt ratio mixture of TPPTS/CTAB and TPPMS/
CTAB. Diluted solution was prepared from stock solution on concen-
tration interval of 0,099 and 2,0 %.
drogenation of α,β-unsaturated aldehydes. This catalyst showed good
behavior during it reuse up to five times without any loss of the activity
or selectivity.
2.4. Catalytic recycling experiments
In the present work we report for the first time the in situ hydro-
formylation of natural olefins (eugenol, estragole and safrole) in
The catalytic phase was reused from 2 to 5 times. The general pro-
cedure for the recycling experiments is similar to that described in the
prior section. Once the samples were extracted, they were cooled, the
phases separated under aerobic condition and the organic phase
analyzed. The catalytic ionic liquid phase was mixed with a fresh
organic phase that contain the substrate (10 mmol) in toluene (1 mL),
introduced again into the autoclave purged three times with syn-gas (1:1
CO + H2), then charged with the required pressure and heated to the
desired temperature, and finally the procedure re-started.
biphasic media BMIm-BF4/toluene with [Rh(COD)(μ-OMe)]2 in pres-
ence of TPPTS as the catalytic precursor. Additionally, we conducted
interaction studies between the CTAB and the components present in the
catalytic system in aqueous media by means of surface tension mea-
surements. We intend to do a first approach about the interfacial phe-
nomena related to the role of CTAB like as agent mass transfer.
2. Experimental
3. Results and discussion
2.1. General procedure
3.1. Biphasic hydroformylation of eugenol
All manipulations were carried out under nitrogen using standard
Schlenk techniques [11]. Organic solvents were dried and purified by
distillation over standard agents under N2 or Ar prior to use. All other
chemicals were commercial products and were used without further
purification. All gases were of high purity (99.99 %) and were purchased
from Aga-Gases (Venezuela).
A preliminary study was conducted in order to determine the best
operational conditions for the biphasic hydroformylation of eugenol as
model molecule using the binuclear water-soluble catalytic system [Rh
(COD)(μ-OMe)]2/TPPTS. Similar reaction conditions than those used for
our group in aqueous biphasic systems [9] were employed for ionic
liquid/toluene biphasic medium, except pressure and temperature,
which were determinate and obtaining new values of 110 ◦C and 55
bars, respectively, and thus completing the best operational parameters.
The BMIm-BF4 was selected due to its hydrophilic properties, which let a
very good solubility of the catalytic precursor and TPPTS in the ionic
liquid phase. Once the reaction conditions were determined, the
hydroformylation of eugenol was studied. The reproducibility of this
reaction was also confirmed; the results are summarized in Table 1.
[Rh(COD)(μ-OMe)]2 [12] and TPPTS [13] were prepared according
to published procedures. Eugenol, estragole and safrole were purchased
from Aldrich and bubbled with argon or nitrogen prior to use. Toluene
was refluxed with sodium/benzophenone and cetyltrimethylammoniun
bromide (CTAB) was purchased from Aldrich and used as received.
Infrared spectra were recorded in a Perkin Elmer Spectrum 1000
FTIR using samples as KBr disks. 1H and 31P{1H} NMR spectra were
recorded on a Bruker 500 MHz spectrometer, using deuterated solvents.
All chemical shifts are reported in parts per million (ppm) relative to
–
As it can be seen from runs I IV in Table 1, the conversion and
tetramethylsilane (1H) or 85 % H3PO4
(
31P). GC analyses were per-
reproducibility of the hydroformylation of eugenol is very good with 99
% of total conversion and 94 % of selectivity towards the aldehydes (70
% lineal and 30 % branched, l/b ≈ 2.3), obtaining a turnover frequency
(TOF) of (32 ± 1) TON minꢀ 1 [TON = 1920 in 1 h, TON (turnover
number) = mol products/mol catalyst]. These results are very similar to
those reported for our groups for aqueous biphasic system [9]. However,
in our BMIm-BF4 system, no cetyltrimethylammoniun bromide (CTAB)
as phase transfer agent was used because completely inhibits the
hydroformylation reaction probably due to the stabilization of the ionic
species from the ionic liquid interacting with the ones from the CTAB in
the interphase of the system and hindering the interaction ionic
liquid-catalytic precursor-substrate [10]. In other words, the catalytic
activity of the system [Rh(COD)(OAc)]2/L was lost completely. How-
ever, the hydroformylation of eugenol could be performed in aqueous
biphasic system as was reported by our group [9]; in this case, the
addition of small amounts of CTAB accelerated the reaction signifi-
cantly, promoting a complete conversion of eugenol in only 20 min with
excellent selectivity (95 %) for aldehydes. In our study showed in Fig. 1,
the amount of CTAB was varied from 0 until 1 × 10-2 M, in order to
establish the maximum reaction rate in our system. The used amount of
CTAB was 1 × 10-3 M. Similar results were published by dos Santos et al.
[14] and Chen et al. [15] for aqueous similar systems. However, our
formed on a Hewlett Packard 5971 Pluss Series II chromatograph with a
flame ionization detector in an ultra-1, DB-1, (10 % dimethyl polix-
ilosane), 25 m, 0.32 mm, 0.52 μm column to separate the products.
Quantification was achieved by using n-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 polix-
ilosane, 25 m, 0.52
μm.
2.2. Biphasic hydroformylation of natural olefins
In
a typical experiment, the catalyst precursor [Rh(COD)
(
μ
-OMe)]2(0.25 × 10ꢀ 5 mol) in 1 mL of ionic liquid BMI-BF4 and the
solution of the corresponding substrate eugenol, estragole or safrole (10
mmol) in 1 mL of toluene and TPPTS (5 × 10ꢀ 5 mol), were introduce
into a stainless steel reactor (Parr instruments, 5 mL) equipped with a
magnetic stirring bar. The system was purged three times and loaded to
the required syn-gas (CO/H2, 1:1) pressure; then the reactor was sub-
merged in a glycerin bath and adjusted to the desired temperature.
When the reaction was completed, the reactor was cooled and slowly
vented, the phases were separated and the organic phase was analyzed
by GC and GC–MS techniques.
2
Baricelli, Pablo J.
