[{W(=O)(O2)2(H2O)}2(μ-O)] 2--Catalyzed Epoxidation of Allylic Alcohols in Water with High Selectivity and Utilization of Hydrogen Peroxide

Article abstract of DOI:10.1002/adsc.200303123

A dinuclear peroxotungstate, K₂[{W(=O)(O₂) ₂(H₂O)}₂(μ-O)] · 2 H₂O, exhibits high catalytic performance for the epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide at 305 K in water solvent. The effectiveness of this system is evidenced by high chemo-, regio-, and diastereoselectivity, and stereospecificity for the epoxidation of allylic alcohols. Furthermore, products/catalyst separation can be easily carried out by simple extraction and the catalyst recovered can be reused with the maintenance of the catalytic performance.

Full text of DOI:10.1002/adsc.200303123

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2
ˆ
[{W( O)(O2)2(H2O)}2(m-O)] -Catalyzed Epoxidation of Allylic
Alcohols in Waterwith High Selectivity and Utilization of
Hydrogen Peroxide
Keigo Kamata, Kazuya Yamaguchi, Shiro Hikichi, Noritaka Mizuno*
Department of Applied Chemistry, School of Engineering, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113 8656, Japan
Fax: ( ‡ 81)-3-5841-7220, e-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
Received: July 27, 2003; Accepted: September 2, 2003
(H2O)}2(m-O)] ¥ 2 H2O (I), could act as an effective
Abstract:
A
dinuclear
peroxotungstate,
catalyst for the epoxidation of allylic alcohols using
hydrogen peroxide in water under mild reaction con-
ditions [Eq. (1)]. To our knowledge, the isolated I itself
has never been used for the catalytic epoxidation of
allylic alcohols using hydrogen peroxide in water with-
out additives although I is a previously known com-
pound.[17]
ˆ
K2[{W( O)(O2)2(H2O)}2(m-O)] ¥ 2 H2O, exhibits high
catalytic performance for the epoxidation of various
allylic alcohols with only one equivalent of hydrogen
peroxide at 305 K in water solvent. The effectiveness
of this system is evidenced by high chemo-, regio-,
and diastereoselectivity, and stereospecificity for the
epoxidation of allylic alcohols. Furthermore, prod-
ucts/catalyst separation can be easily carried out by
simple extraction and the catalyst recovered can be
reused with the maintenance of the catalytic per-
formance.
ꢀ1†
Epoxidation of 2-propen-1-ol as a model substrate using
30% aqueous hydrogen peroxide in various solvents was
carried out in the presence of I. The results are
summarized in Table 1. The oxidation did not proceed
in the absence of I (entry 2). Water was the most
effective solvent for the present epoxidation: 96%
Keywords: allylic alcohols; dinuclear peroxotung-
state; epoxidation; hydrogen peroxide
Epoxidation of allylic alcohols is of great importance[1 5] conversion, 99% selectivity to 2,3-epoxy-1-propanol,
because epoxides have been used as raw materials for and 97% efficiency of hydrogen peroxide utilization for
epoxy resins and building blocks for the synthesis of the epoxidation of 2-propen-1-ol (entry 1). The use of
biologically important compounds including natural non-polar toluene, benzene, and dichloromethane sol-
products,[6,7] and chiral carbons are formed by the vents (organic/aqueous biphasic system) gave 2,3-ep-
epoxidation.[1 5] Although many methods for the epox- oxy-1-propanol yields of 90, 80, and 63%, respectively
idation of allylic alcohols have been developed, catalytic (entries 3 5). On the other hand, water-miscible polar
processes with expensive and environmentally-unac- acetonitrile (5% yield) and methanol ( < 1% yield) were
ceptable oxidants such as peracids and hydroperoxides poor solvents probably because of the strong coordina-
in explosive, hazardous, and carcinogenic organic sol- tion to the tungsten center (entries 6 and 7).
vents are still widely used.[8] In this context, the
Table 2 shows the results of epoxidation of various
development of efficient catalytic processes using allylic alcohols with only one equivalent of hydrogen
hydrogen peroxide or molecular oxygen as a green peroxidecatalyzed by Iin water solvent. The pH value of
oxidant in non-explosive solvent, especially water, the reaction media was in the range of 4 5 under the
achieves economical and environmental benefits, and present conditions. The catalyst I was intrinsically stable
is challenging.[9 15]
in the pH range of 2.5 7 as was confirmed by 183W NMR
We reported very recently an efficient and simple and IR spectra. The efficiency of the hydrogen peroxide
route for epoxidation of both internal and terminal utilization was more than 90% in each case. Oxidation of
olefins with hydrogen peroxide catalyzed by the diva- simple primary allylic alcohols proceeded almost quan-
cant lacunary silicotungstate, [(n-C4H9)4N]4[g-Si- titatively and chemoselectively to afford the epoxy
W10O34(H2O)2].[16] During the course of our investiga- alcohols without formation of the corresponding alde-
tion of tungsten-catalyzed oxidation, we found that the hydes and carboxylic acids (entries 1 5). A 100-mmol
ˆ
simple dinuclear peroxotungstate, K2[{W( O)(O2)2- scale epoxidation of the internal allylic alcohol of
Adv. Synth. Catal. 2003, 345, 1193 1196
DOI: 10.1002/adsc.200303123
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Keigo Kamata et al.
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Table 1. Oxidation of 2-propen-1-ol with hydrogen peroxide in various solvents.[a]
Entry
Solvent
Yield [%]
H2O2 efficiency [%]
97
1b
1c
1d
1
water
water (no catalyst)
toluene
benzene
dichloromethane
acetonitrile
methanol
95
1
< 1
2[b]
3
no reaction
90
80
63
2
< 1
< 1
< 1
< 1
< 1
1
91
90
79
95
4
5
6
7
5
< 1
no reaction
[a]
Reaction conditions: 2-propen-1-ol (5 mmol), I (100 mmol, 2 mol %), 30% aqueous H2O2 (5 mmol), solvent (6 mL), 305 K,
10 h. Yields were determined by gas chromatography and 1H NMR with an internal standard technique, and based on allyl
alcohol. Remaining H2O2 after reaction was estimated by potential difference titration of Ce3‡/Ce4‡ (0.1 M of aqueous
Ce(NH4)4(SO4)4 ¥ 2H2O). H2O2 efficiency (%) ˆ products (mol)/consumed H2O2 (mol)  100.
Reaction was carried out in the absence of catalyst.
[b]
2-buten-1-ol (I:H2O2 :substrate ˆ1:5000:5000) showed Table 2. Epoxidation of various allylic alcohols with hydro-
gen peroxide in water catalyzed by I.[a]
a turnover frequency (TOF) of 594 hÀ1 and a turnover
number (TON) of 4200. These values are higher than
those reported to be active for the tungsten-catalyzed
epoxidation of internal allylic alcohols with hydrogen
peroxide: Na2WO4-NH2CH2PO3H2-[CH3(n-C8H17)3N]-
HSO4 in toluene, 86 hÀ1 (TOF) and 43 (TON);[18]
[C5H5N(n-C16H33)]3PW12O40 in 1,2-dichloroethane,
5 hÀ1, 20;[19] [(n-C4H9)4N]2[PhPO3{WO(O2)2}] in 1,2-
dichloroethane,
80 hÀ1,
40;[20]
{WZn[M(H2O)]2
(ZnW9O34)2}q (M: Zn2‡, Mn2‡, Ru3‡, Fe3‡, etc.) in 1,2-
dichloroethane, 167 hÀ1, 1000;[21] Na2WO4-phosphate
buffer-b-d-fructopyranoside in water, 0.4 hÀ1, 10.[22]
For the epoxidation of cis- and trans-allylic alcohols,
ˆ
the configurations around the C C moieties were
retained in the corresponding epoxy alcohols (entries 2,
5, and 6). Such a stereospecific epoxidation suggests that
the free-radical intermediates are not involved in the
epoxidation. Furthermore, regioselective epoxidation
of 3,7-dimethyl-2,6-octadien-1-ol took place at the
electron-deficient allylic 2,3-double bond to afford
only the 2,3-epoxy alcohol in high yield (entry 6). The
epoxidation of secondary b,b-disubstituted allylic alco-
hol (1,3-allylic strained alcohol), 4-methyl-3-penten-2-
ol, proceeded diastereoselectively to form mainly the
threo-epoxy alcohol (entry 7). An allylic alcohol without
1,3-allylic strain, 3-penten-2-ol, gave the erythro-rich
epoxy alcohol (entry 8). These selectivities for the
epoxidations of secondary allylic alcohols are similar
to those for VO(acac)2/TBHP systems,[5,23 25] and differ-
ent from those with dimethyldioxirane[5,25] and TS-1/
urea-hydrogen peroxide.[5,25]
[a]
Reaction conditions: allylic alcohol (5 mmol), I (20 mmol,
0.4 mol %), 30% aqueous H2O2 (5 mmol), water (6 mL),
305 K. Yields were based on allylic alcohol which were
determined by GC and 1H NMR using an internal
standard technique.
[b]
I (100 mmol, 2 mol %).
[c]
Substrate: cis/trans ˆ 13/87, epoxy alcohol: cis/trans ˆ 13/
87.
[d]
Isolated yield.
[e]
[n-(C12H25N(CH3)3)2[W2O3(O2)4(H2O)] (20 mmol) was
used as a catalyst.
3-Buten-2-one was produced as a by-product (7% yield).
[f]
The structural stability of catalyst I was confirmed by
direct observation of the reaction solution with in-situ
IR and UV-vis spectroscopy. No changes in the spectra measurements and the spectrum showed one signal at
were observed during the oxidation. The concentrated
À 704.5 ppm. No spectral changes were observed during
solution of I (0.3 M) was prepared for 183W NMR the reaction. These facts show that I is stable under the
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Adv. Synth. Catal. 2003, 345, 1193 1196

Epoxidation of Allylic Alcohols in Water
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in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.
reaction conditions. Oxidation products could easily be
isolated by simple extraction using dichloromethane (or
pentane) after the oxidation since catalyst I was
completely insoluble in these solvents. Actually, no
leaching of tungsten into the organic phase was con-
firmed by inductively coupled plasma atomic emission
analysis. Therefore, the aqueous phase including the
catalyst could be recovered without loss of the tungsten
species. It is notable that I could be reused for the
epoxidation of 2-buten-1-ol without loss of the high
catalytic performance.
In summary, the dinuclear peroxotungstate I is found
to be an effective homogeneous catalyst for the highly
chemo-, regio-, and diastereoselectivity, and stereospe-
cific epoxidation of allylic alcohols in water with high
efficiency of hydrogen peroxide utilization. The mech-
anistic work is in progress.
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ˆ
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O)] ¥ 2 H2O: H 1.16, O 34.6, K, 11.27 W 52.99%; found: H 1.12,
K 11.98, W 53.19%. IR (400 4000 cmÀ1: KBr disk; below
À1
ˆ
600 cm : polyethylene disk): nˆ966 n(W O), 854 n(O-O), 764
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1
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This workwas supported in part by the Core Research for
Evolutional Science and Technology (CREST) program of
Japan Science and Technology Corporation (JST) and a Grant-
Adv. Synth. Catal. 2003, 345, 1193 1196
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¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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