P.A. Robles-Dutenhefner et al. / Journal of Catalysis 265 (2009) 72–79
73
[13–15], one of the most abundant sesquiterpenes found in rela-
tively large amounts in Indian turpentine oil. Oxygenated deriva-
tives of isolongifolene occupy a vintage place in modern perfume
industry because of their extremely rich woody and floral odor
[16–19]. Most of the reported processes for the oxidation of isol-
ongifolene are non-catalytic reactions employing traditional oxi-
dants in stoichiometric amounts (permanganates, dichromates,
peroxo compounds, etc.) [16–22]. These reactions usually result
in the complex mixtures of oxygenated products.
NOVA-1200 instrument, nitrogen, ꢁ196 °C). Samples were out-
gassed for 2 h at 300 °C before analysis. Specific surface areas and
average pore diameter were determined by the Brunauer–Em-
mett–Teller (BET) equation. The pore size distributions were
calculated from the desorption isotherms using the Barrett–Joy-
ner–Halenda (BJH) method.
Transmission electron microscopy (TEM) images were obtained
using a JEOL-JEM 1200 instrument operating at an accelerating
voltage of 120 kV.
Terpenic compounds, in general, are an important renewable
feedstock for flavor and fragrance industries. For several years,
we have been interested in catalytic transformations of terpenes
to value-added chemicals, in particular, via cobalt [23–26] and pal-
ladium [27–30] catalyzed oxidations. The most abundant non-
functionalized monoterpenes, such as limonene and pinenes, have
been mainly used in our previous works.
In the present work, we report a simple and efficient aerobic
oxidation of isolongifolene into a conjugated ketone, which is
highly important for perfume industry and can be obtained in
excellent yields under mild solvent-free conditions. A Co-MCM-
41 material, which contains cobalt incorporated into the frame-
work, is used as a heterogeneous, low cost, and easily recyclable
catalyst. The performance of Co-MCM-41 is compared with that
of a silica-included cobalt material prepared by a conventional
sol–gel method without the surfactant.
Powder X-ray diffractometry (XRD) measurements were per-
formed on a Rigaku model Geigerflex-3034 equipment using a
Co(Ka) radiation scanning from 4 to 70° (2h) to register the pres-
ence of cobalt oxide phases. Samples were dried previously and
pulverized.
Small-angle X-ray scattering (SAXS) experiment at the D11A-
SAXS beam line was performed at the LNLS synchrotron laboratory,
Campinas, Brazil. The SAXS setup was equipped with a Si(111)
monochromator, giving a horizontally focused X-ray beam. The
incident X-ray wavelength k was 1.5494 Å, and the scattering angle
2h was approximately 0–10°.
X-ray photoelectron spectroscopy (XPS) measurements were
performed on
a VG-Microtech Multilab 3000 spectrometer
equipped with a hemispherical electron analyzer and a Mg(Ka)
ðh
m
¼ 1253:6 eV; 1 eV ¼ 1:6302 ꢀ 10ꢁ19 JÞ 300 W X-ray source.
The spectra were collected at a pass energy of 50 eV.
Temperature-programmed reduction with hydrogen (H2-TPR)
was performed on a Quantachrome-ChemBET 300 instrument
equipped with a thermal conductivity detector. The experiments
were performed between 30 and 900 °C (10 °C/min) in a flow of
a N2/H2 mixture containing 5 vol% of H2.
2. Experimental
All reagents were purchased from commercial sources and were
used as received. Isolongifolene was kindly donated by Professor
J.C. Bayón (Universidad Autónoma de Barcelona).
2.2. Catalytic oxidation experiments
2.1. Catalyst preparation and characterization
Reactions were carried out in a glass reactor equipped with a
magnetic stirrer and a sampling system and connected to a gas
burette to monitor the oxygen uptake. In a typical run, a mixture
of isolongifolene (14 mmol), dodecane (4.4 mmol, internal stan-
dard), and the catalyst (0.1–0.2 g, ca. 2.8–5.6 wt%) was intensively
stirred at 80 °C and at an oxygen pressure of 1 atm for the reported
time. The reactions were followed by measuring the uptake of oxy-
gen and by gas chromatography (GC) using dodecane as an internal
standard (Shimadzu 17 instrument, Carbowax 20 M capillary col-
umn, temperature program: 80 °C, isothermal, 3 min; 10 °C/min
up to 220 °C; and 220 °C, isothermal, 5 min). At appropriate time
intervals, stirring was stopped and after the quick settling of the
catalyst aliquots were taken, diluted 20-fold with cyclohexane,
and were analyzed by GC.
The 5.0 wt% Co/SiO2 catalyst (denoted as Co–SiO2/sol–gel) was
prepared by a sol–gel method using tetraethoxysilane (0.9 g, TEOS,
Sigma–Aldrich) and CoCl2 ꢀ 6H2O (15.2 g, Sigma–Aldrich) as pre-
cursors. The sol was obtained from a TEOS/ethanol/water mixture
in a 1/3/10 molar ratio with the addition of HCl and HF (up to pH
2.0) as catalysts. The sample was prepared in a monolithic shape,
dried at 110 °C for 48 h, and thermally treated for 2 h at 900 °C
in air.
The catalyst 3.3 wt% Co/MCM-41 catalyst (denoted as Co-MCM-
41) was prepared by the direct incorporation of Co into the MCM-41
framework aiming for the isomorphous substitution of Si by Co ions.
TEOS and CoCl2 ꢀ 6H2O (Sigma–Aldrich) were used as precursors,
and hexadecyltrimethylammonium bromide (C16-TAB, Sigma–Al-
drich) was used as a structure template. The C16-TAB solution in
water was added to the solution of TEOS (2.5 g) in aqueous tetra-
methylammonium hydroxide (TMAOH, 25 wt%, Sigma–Aldrich).
The mixture was stirred for 30 min before CoCl2 (1.2 g) and remain-
ing TEOS (21.0 g) were added. After additional mixing at 40 °C for
24 h, the mixture was placed in an autoclave at 100 °C for 24 h
and was then cooled to room temperature. The resulting solid was
recovered by filtration, washed first with de-ionized water and then
with ethanol, and dried at 40 °C. The pre-dried solid was heated
from room temperature to 550 °C under flowing nitrogen and was
calcinated for 3 h at 550 °C under flowing air to remove the residual
organics. The TEOS/C16-TAB/TMAOH/water molar ratio was 1.0/
0.12/0.28/26.2.
Catalyst recycling experiments were performed as follows: after
the reaction, the catalyst was centrifuged, washed with cyclohex-
ane, and reused. To control metal leaching, the catalyst was re-
moved at the reaction temperature after 2 h and the solution was
allowed to react further.
Products 2–5 were isolated by column chromatography (silica)
using mixtures of hexane and CH2Cl2 as eluents, and were identi-
fied by GC/MS (Shimadzu QP2010-PLUS instrument, 70 eV) and
NMR (Bruker DRX-400 instrument, tetramethylsilane, CDCl3).
Isolongifolen-9-one (2): MS (m/z/rel.int.): 218/43 (M+); 203/10
(M+–CH3); 176/40; 175/90; 162/67; 147/60; 133/23; 119/30;
105/33; 91/42; 77/23; 55/28; 43/23; 41/100. 1H NMR, dH (J, Hz):
0.99 (s, 3H, C14H3); 1.05 (s, 3H, C12H3); 1.09 (s, 3H, C15H3); 1.14
(s, 3H, C13H3); 1.29–1.33 (m, 1H, C5HH); 1.41 (d, 1H, C11HH,
2J = 10.0); 1.57–1.65 (m, 1H, C4HH); 1.68 (dd, 2J = 10.0, 3J = 2.0,
The determination of total Co contents was done by inductively
coupled plasma atomic emission spectrometry (ICP-AES) on a
Spectro Ciros CCD instrument.
The textural characteristics of the catalysts were determined
from nitrogen adsorption isotherms (Autosorb-Quantachrome
C
11HH); 1.73–1.77 (m, 1H, C4HH); 1.91–1.98 (m, 2H, C3H, C5HH);
2.07 (d, 1H, C8HH, 2J = 16.0); 2.38 (d, 1H, C8HH, 2J = 16.0); 5,70 (s,
1H C10H). 13C NMR, dC: 24.33 (C4); 24.57 (C13); 25.40 (C14); 25.76
(C12); 26.97 (C15); 27.83 (C5); 34.45 (C7); 36.70 (C11); 44.12 (C2);