Stereoselective hydrogenation of tetralin to cis-decalin over a carbon-supported rhodium catalyst in supercritical carbon dioxide solvent

Article abstract of DOI:10.1246/cl.2006.188

cis-Decalin was selectively obtained with high cis/trans ratio (83%) over a carbon-supported rhodium catalyst at 333 K under 6 MPa of hydrogen and 15 MPa of carbon dioxide. Copyright

Full text of DOI:10.1246/cl.2006.188

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Chemistry Letters Vol.35, No.2 (2006)
Stereoselective Hydrogenation of Tetralin to cis-Decalin over a Carbon-supported
Rhodium Catalyst in Supercritical Carbon Dioxide Solvent
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1
ꢀ1
Norihito Hiyoshi, Eiichi Mine, Chandrashekhar V. Rode, Osamu Sato, and Masayuki Shirai
Research Center for Compact Chemical Process, National Institute of Advanced Industrial Science and Technology (AIST),
-2-1 Nigatake, Miyagino, Sendai 983-8551
Homogeneous Catalysis Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
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(Received September 9, 2005; CL-051160; E-mail: m.shirai@aist.go.jp)
cis-Decalin was selectively obtained with high cis/trans
ratio (83%) over a carbon-supported rhodium catalyst at 333 K
under 6 MPa of hydrogen and 15 MPa of carbon dioxide.
of carbon-supported catalysts expressed as turnover number
(TON, in parentheses) based on the number of surface metal
atoms were found to be in the following order: Rh/C (6500) >
Pd/C (400) > Pt/C (320) > Ru/C (120), indicating that Rh/C
was the most active catalyst among the carbon-supported cata-
lysts. This result was similar to the hydrogenation of naphthalene
in supercritical carbon dioxide. Martins et al. reported that an
alumina-supported platinum catalyst was active for the hydroge-
12
nation of tetralin in supercritical carbon dioxide at 493 K.
Cyclic saturated hydrocarbons such as decahydronaphtha-
lene (decalin), bicyclohexane, methylcyclohexane, etc. are pro-
posed as new mobile hydrogen storage media for proton ex-
8
1
change membrane fuel cells. Hydrogen can be obtained by cat-
alytic dehydrogenation of the cyclic saturated hydrocarbons to
the corresponding aromatic compounds and stored by the hydro-
genation of the aromatic products. For hydrogen production
from decalin, cis-isomer is more preferable, because dehydro-
genation rate of cis-decalin is faster than that of trans-decalin.1b
Also, cis-decalin can be used to produce sebatic acid that is used
in the manufacture of 6,10-Nylon and softeners. Thus, the ster-
eoselective hydrogenation of tetrahydronapnthalene (tetralin)
to cis-decalin is an industrially important reaction. The hydroge-
nation of tetralin is also important for the production of a high
We also checked the activity of an alumina-supported platinum
catalyst, but it showed much lower activity (TON ¼ 120) than
Rh/C in supercritical carbon dioxide at 333 K.
Figure 1a shows the reaction profile for the hydrogenation of
tetralin over Rh/C under 6 MPa of hydrogen and 15 MPa of
carbon dioxide at 333 K. From the beginning of the reaction,
cis- and trans-decalin were formed in almost constant cis/trans
ratio (cis/(cis + trans) = 0.83), and small amount of octahy-
dronaphthalene (octalin) (we could not determine the position
of carbon–carbon double bond from GC-MS analysis) was also
detected. Beyond 100 min of reaction, the amount of octalin de-
creased gradually, and all tetralin was hydrogenated to cis- and
trans-decalin after 150 min. The yield of cis-decalin reached
82% after 150 min. The cis/trans ratio did not vary even after
longer reaction time (>150 min), indicating that isomerization
of cis- to trans-decalin did not occur. We also carried out some
hydrogenation experiments in an organic solvent (n-heptane) to
investigate the solvent effect on the tetralin hydrogenation over
Rh/C (Figure 1b). The initial hydrogenation activity was found
to be much higher in supercritical carbon dioxide (r ¼ 12
2
performance diesel fuel. The hydrogenation of tetralin is usual-
ly performed at high temperature (>390 K), and coking during
3
reaction causes the catalyst deactivation. As against this, hydro-
genation with supported metal catalysts in supercritical carbon
dioxide solvent has several advantages; 1) higher solubility of
hydrogen in supercritical carbon dioxide, thereby controlling
the product selectivity and activity, 2) easy separation of prod-
ucts and catalysts, and 3) maintaining clean active site in solid
4
,5
surfaces by washing with supercritical carbon dioxide solvent.
We have reported that carbon-supported metal catalysts are ef-
fective for the hydrogenation of aromatic compounds at lower
ꢂ1
ꢂ1
ꢂ1
mmolꢁg ꢁmim ) than that in n-heptane (r ¼ 5:9 mmolꢁg
ꢁ
6
–11
ꢂ1
temperature in supercritical carbon dioxide.
In this paper,
mim ). Also, the selectivity to cis-decalin (= cis-decalin/
(cis-decalin + trans-decalin + octalin) ꢃ 100) in supercritical
carbon dioxide (78% at 70% conversion) was higher than that
we report that cis-decalin is obtained by stereoselective hydroge-
nation of tetralin in supercritical carbon dioxide over a carbon-
supported rhodium catalyst at low temperature.
Catalysts used in this work, viz. carbon-supported, 5 wt %
rhodium (Rh/C), palladium (Pd/C), platinum (Pt/C), and ruthe-
nium (Ru/C) were commercially available from Wako Pure
Chemical Ind., Ltd., Japan. The dispersion values of metal par-
ticles on charcoal were determined by a hydrogen adsorption
2
2
1
1
0
.5
.0
.5
.0
.5
0
2.5
2.0
1.5
1.0
0.5
0
(
a)
(b)
6
method. All catalysts were used without further reduction for
the hydrogenation of tetralin. The hydrogenation of tetralin
(
2.3 mmol) was carried out in high-pressure stainless-steel reac-
tors (50 mL capacity). After the reaction was over, the unreacted
tetralin and products were recovered with acetone, which
showed a material balance of more than 95%. The quantitative
analysis was conducted with GC-MS and GC-FID.
The activities of various catalysts for the hydrogenation of
tetralin were examined after 30 min of reaction at 333 K under
0
50
Time/min
100
150
0
50
Time/min
100
150
Figure 1. The hydrogenation of tetralin over Rh/C (0.002 g)
under hydrogen pressure 6 MPa at 333 K. (a) Carbon dioxide
15 MPa (0.69 mol); (b) n-heptane 20 mL (0.14 mol). ( ) Tetra-
lin; ( ) cis-decalin; ( ) trans-decalin; ( ) octalin.
6
MPa of hydrogen and 10 MPa of carbon dioxide. The activities
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.2 (2006)
189
in n-heptane (74% at 70% conversion). It is reported that, in
liquid-phase hydrogenation of tetralin, cis-isomer is directly
formed via the hydrogenation of octalin intermediate adsorbed
on an active site and the trans-isomer is formed via flipping of
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6
0
0
85
80
(
a)
(b)
1
,9
2
,3,4,5,6,7,8,10-octahydronaphthalene (ꢀ -octalin) intermedi-
40
20
0
75
ate, in which ꢀ1,9-octalin desorbs from the active site and re-ad-
sorbs on its other side, followed by its further hydrogenation to
give trans-decalin.13 We also investigated the isomerization of
cis- to trans-decalin over Rh/C in carbon dioxide solvent. Al-
though trans-decalin is the thermodynamically stable isomer,
cis to trans isomerization did not occur under 6 MPa of hydrogen
and 15 MPa of carbon dioxide from 313 to 343 K.
70
14
65
0
5
10
15
0
5
10
15
H pressure/MPa
H pressure/MPa
2
2
Figure 3. Effect of hydrogen pressure on the hydrogenation of
tetralin over Rh/C (0.002 g) at 333 K. Initial tetralin 2.3 mmol;
reaction time 30 min. ( ) Carbon dioxide pressure 15 MPa;
Figure 2 shows the effect of reaction temperature on the hy-
drogenation of tetralin over Rh/C under 6 MPa of hydrogen and
15 MPa of carbon dioxide. As the reaction temperature increased
from 313 to 343 K, the conversion of tetralin increased from 12
to 50%, but the selectivity to cis-decalin decreased from 78 to
(
) n-heptane 20 mL.
ity to cis-decalin increased from 76 to 79% with increase in hy-
drogen pressure from 6 to 12 MPa in supercritical carbon diox-
ide. On the other hand, the selectivity to cis-decalin was lower
75%. The cis/trans ratio decreased from 0.87 to 0.82. The cis/
trans ratio was almost constant regardless of the conversion at
(
73%) in n-heptane and almost constant regardless of hydrogen
the same temperature. The density of carbon dioxide decreases
ꢂ3
pressure. Higher selectivity to cis-decalin in supercritical carbon
dioxide than in n-heptane could be explained by the rapid direct
from 0.78 to 0.51 gꢁcm with increasing temperature from
313 to 343 K at 15 MPa of carbon dioxide pressure. In a separate
1,9
hydrogenation of ꢀ -octalin intermediate to produce more cis-
1,9
experiment at 25 MPa of carbon dioxide pressure, it was found
that the selectivity to cis-decalin slightly increased (form 76.3
to 76.5%) with decrease in the density of carbon dioxide from
decalin, and/or lower possibility of the desorption of ꢀ -octa-
1,9
lin intermediate to solvent due to lower solubility of ꢀ -octalin
in carbon dioxide solvent. Also, the increase in the selectivity to
cis-decalin with increasing hydrogen pressure in supercritical
carbon dioxide is probably due to higher concentration of hydro-
gen atoms on surface at higher hydrogen pressure leading to
0
3
.79 (25 MPa of carbon dioxide) to 0.61 gꢁcmꢂ3 (15 MPa) at
33 K. Thus, the decrease in the selectivity to cis-decalin with
increasing temperature shown in Figure 2 was mainly due to
1
,9
the thermal effect, inducing activation of the flipping of ꢀ
octalin intermediate at higher reaction temperature.
-
enhance hydrogenation rate of ꢀ1,9-octalin intermediate.8
Figure 3a shows the effect of hydrogen pressure on conver-
sion of tetralin after 30 min of the reaction in supercritical carbon
dioxide and n-heptane solvent. All tetralin was converted to dec-
alin after longer reaction time under the reaction conditions. The
conversion of tetralin increased linearly with increase in hydro-
gen pressure for both supercritical carbon dioxide and n-heptane
solvents. The increase in the conversion would be caused by
increase in the concentration of surface hydrogen atoms with in-
creasing hydrogen pressure. However, it is noteworthy that the
conversion of tetralin was two times higher in supercritical car-
bon dioxide than in n-heptane under the same hydrogen pressure.
This would be due to higher solubility of hydrogen in supercrit-
ical carbon dioxide than in n-heptane. Figure 3b shows the effect
of hydrogen pressure on selectivity to cis-decalin. The selectiv-
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Published on the web (Advance View) January 14, 2006; DOI 10.1246/cl.2006.188