1
346
Chemistry Letters Vol.35, No.12 (2006)
Hydration of ꢀ-Pinene in a Triphasic System Consisting of ꢀ-Pinene, Water,
and Cs H PW O –SiO Composite
2
:5 0:5
12 40
2
Ã
Naoto Horita, Yuichi Kamiya, and Toshio Okuhara
Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810
(Received September 8, 2006; CL-061041; E-mail: oku@ees.hokudai.ac.jp)
Cs2:5H0:5PW12O40–SiO2 composite combined with (3-
in acid-catalyzed reactions, even in the presence of a large ex-
9
aminopropyl)triethoxysilane exhibited greater activity and
selectivity for hydration of ꢀ-pinene at 333 K in a triphasic
system (ꢀ-pinene/water/solid acid) compared to previously
reported water-tolerant catalysts such as zeolites, polymer-resins
cess of water, while a Cs2.5–SiO2 composite combined with
(3-aminopropyl)triethoxysilane (APS) is an insoluble and sedi-
1
0
mentable water–tolerant solid acid. Here, we demonstrate the
high activity and selectivity of the Cs2.5–SiO2 composite for
the hydration of ꢀ-pinene in a triphasic system (ꢀ-pinene/wa-
ter/solid acid), which is a desirable system for easy separation
of the product (oil phase) from an oil–water biphase.11 The
Cs2.5–SiO2 composite is a more efficient catalyst than other
water–tolerant solid acids, including high-silica zeolite (H-
ZSM-5, H-ꢁ, and H-mordenite), ion-exchange resins (Amberlyst
15 and Nafion-H), and liquid acids (H PW O and H SO ).
(
Amberlyst 15 and Nafion-H), oxides, and liquid acids such as
H3PW12O40 and H2SO4. The selectivity toward alcohols, includ-
ing mono- and dialcohols, was approximately 80% over
Cs2:5H0:5PW12O40–SiO2 composite.
Terpenic alcohols, such as ꢀ-terpineol, 1,8-terpin, and their
derivatives, have applications in perfume and pharmaceutical in-
dustries and have drawn attention as a raw material for electronic
and optical materials. Currently, the practical synthesis of ter-
penic alcohols involves hydration of ꢀ-pinene using H2SO4 as
a catalyst. However, replacement of H2SO4 with a solid acid
is desirable from an environmental point of view. Although
3
12 40
2
4
1
0
Cs2.5–SiO2 composites
2
were prepared using SiO2
[Aerosil 50 (A-50), 48 m g ; and CARiACT Q-30 (Q-30),
À1
2
À1
126 m g ], APS (Merck), and Cs2.5. The SiO2 (1.3 g) was
3
added to a toluene solution of APS (85.6 mmol; 200 cm ) at
room temperature under N . After mixing the suspension for
2
2 h at room temperature, the solid was separated by filtration.
3
1
hydration of ꢀ-pinene over solid acids such as H-ꢁ zeolite,
polymeric membrane containing heteropolyacid, and supported
The solid recovered was dispersed in water (26 cm ) acidified
3
2
with 6% HCl (6 cm ), then separated, and dried at 373 K
(SiO –APS). To an aqueous suspension of SiO –APS, a colloi-
heteropolyacid3 have been conducted in a biphasic system,
consisting of a solid acid and homogeneous solution including
2
2
9
dal aqueous solution of Cs2.5, prepared in advance, was added
to obtain the Cs2.5–SiO composite, with 14 wt % of SiO –APS.
ꢀ-pinene, water, and cosolvent, the activity and selectivity
toward alcohols were unsatisfactory.
2
2
Hydration of ꢀ-pinene was performed in
a
batch
3
Few solid acids possess acceptable activity for hydrolysis,
hydration, or esterification, in which water participates as either
reactor (Pyrex, 15 cm ) at 333 K with 0.64 mmol of ꢀ-pinene,
6 cm of water, and 40 mg of catalyst. The products were
3
4
–8
a reactant or product. However, an acidic Cs salt of 12-tung-
stophosphoric acid, Cs2:5H0:5PW12O40 (Cs2.5), is highly active
analyzed by FID-GC equipped with a capillary column (NB-1,
0.25 mm  60 m).
a
Table 1. Catalytic data for hydration of ꢀ-pinene over solid and liquid acids
b
c
2
TOFd
Conv.
Selectivity /%
II III IV + V
Acid amount k  10
Entry
Catalyst
À1
À1
À1
/
%
I + II + III
I
/mmol g
/h
/h
Solid acid
1
Cs2.5–(SiO2(A-50)–APS)
Cs2.5–(SiO2(A-50)–APS)
Cs2.5–(SiO2(Q-30)–APS)
H-ꢁ (Si/Al = 25)
86
62
40
69
3
0
0
44
16
75
67
79
50
0
—
—
51
43
30 41
60
45 29
4
5
5
25
33
21
50
100
—
—
0.08f
0.08f
0.08f
0.72
0.80
0.71
0.48
4.70
0.80
4.3
8.8
4.1
2.0
0.5
<0:1
—
—
e
2
3
4
5
6
7
8
9
2
2.0
1.0
2.4
0.1
—
—
1.2
0.4
13 19 18
H-ZSM-5 (Si/Al = 30)
0
—
—
0
—
—
0
—
—
6
H-mordenite (Si/Al = 20)
SiO2–Al2O3
Amberlyst 15
26 19
18 21
49
57
<0:1
<0:1
Nafion-H
5
Liquid acid
1
1
0
1
H3PW12O40
H2SO4
40
73
77
75
39 35
31 38
3
6
23
25
1.04
20.1
1.1
0.5
b
0.2
<0:1
a
3
Reaction conditions: ꢀ-pinene 0.64 mmol, water 6 cm , catalyst 40 mg, temperature 333 K, and reaction time 48 h. I monocyclic
terpenic monoalcohols, II monocyclic terpenic dialcohols, III bicyclic terpenic monoalcohols, IV monocyclic terpens, and V bicy-
clic terpenes (see Scheme 1). First-order rate constant. Turnover frequency (h ) = initial reaction rate (mmol g h )/acid
c
d
À1
À1 À1
À1
e
3
3
3
amount (mmol g ). Reaction was conducted in a mixture of water (3 cm ) and 1,4-dioxiane (3 cm ), instead of water (6 cm ).
Estimated by temperature programmed desorption of benzonitrile.
f
Copyright Ó 2006 The Chemical Society of Japan