Reaction behavior of secondary alcohols in supercritical water

Article abstract of DOI:10.1246/bcsj.80.1828

Benzhydrol and benzoin, which have two benzene subunits, a secondary hydroxy group, and no hydrogen atom on the β-position of the hydroxy group, were treated in supercritical water in the absence of an oxidizing agent or a catalyst. Water played a key role in the product distributions in these reactions. Each reaction proceeded smoothly to give larger amounts of oxidation products, benzophenone (3) and benzil (6), as well as smaller amounts of reduction products, diphenylmethane (4) and benzyl phenyl ketone (7), respectively, in the presence of water, while the ratios of 3:4 and 6:7 were almost 1:1 in both cases in the absence of water. The best yield of benzophenone (63%) was achieved by the reaction of benzhydrol at 460°C for 180 min in 0.35 g mL^-1 water density in the SUS 316 reactor. Hydrogen gas evolution was observed in the reaction of benzhydrol in a quartz tubular reactor.

Full text of DOI:10.1246/bcsj.80.1828

1828 Bull. Chem. Soc. Jpn. Vol. 80, No. 9, 1828–1832 (2007)
Ó 2007 The Chemical Society of Japan
Reaction Behavior of Secondary Alcohols in Supercritical Water
ꢀ1
Pengyu Wang,1 Hiroyuki Kojima,1 Kazuya Kobiro, Koichi Nakahara,2
Toshihiko Arita,3 and Okitsugu Kajimoto3
1Department of Environmental Systems Engineering, Faculty of Engineering, Kochi University of Technology,
185 Miyanokuchi, Tosayamada, Kami 782-8502
2Process Development Department, Engineering and Process Development Division, Technical Development Center,
Suntory Ltd., 5-2-5 Yamazaki, Shimamoto-cho, Mishima-gun, Osaka 618-0001
3Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502
Received March 12, 2007; E-mail: kobiro.kazuya@kochi-tech.ac.jp
Benzhydrol and benzoin, which have two benzene subunits, a secondary hydroxy group, and no hydrogen atom on
the ꢀ-position of the hydroxy group, were treated in supercritical water in the absence of an oxidizing agent or a catalyst.
Water played a key role in the product distributions in these reactions. Each reaction proceeded smoothly to give larger
amounts of oxidation products, benzophenone (3) and benzil (6), as well as smaller amounts of reduction products,
diphenylmethane (4) and benzyl phenyl ketone (7), respectively, in the presence of water, while the ratios of 3:4 and
6:7 were almost 1:1 in both cases in the absence of water. The best yield of benzophenone (63%) was achieved by
the reaction of benzhydrol at 460 ꢁC for 180 min in 0.35 g mLꢂ1 water density in the SUS 316 reactor. Hydrogen gas
evolution was observed in the reaction of benzhydrol in a quartz tubular reactor.
Much attention has been paid to supercritical water (SCW)
as a medium for chemical reactions, since it has quite unique
properties, such as low polarity, high density, low viscosity,
and high solubility of organic materials, which are tunable
simply by changing temperature, pressure, and water density.1
These unique properties have been exploited, for example, in
the field of the waste treatment especially in the presence of
a large excess amount of oxygen.2 Recently, unique organic re-
actions in SCW, such as H–D exchange reaction in supercriti-
cal deuterium oxide,3 Beckmann rearrangement of cyclohexa-
none oxime,4 pinacol rearrangement of 2,3-dimethyl-2,3-
butanediol,4b,5 Cannizzaro reaction of formaldehyde6 and
benzaldehyde,7 Heck reaction,8 C–Si bond cleavage,9 Claisen–
Schmidt reaction,10 and benzil–benzilic acid rearrangement,11
have been also studied.
eight-membered ring bridging over two hydrogen atoms of
the ethanol to give an H2 molecule (Scheme 1).13 Unfortunate-
ly, side reactions, such as dehydration, occurred to give ethene
simultaneously, which hindered knowing the intrinsic alcohol
oxidation ability of SCW. Alternative substrates with no side
reaction should be considered to discuss the inherent oxidation
ability of SCW.
Combining the advantages of the benzene subunit exhibiting
high affinity to SCW14 and secondary alcohol with no hydro-
gen atom on the ꢀ-position of the hydroxy group leading to de-
hydration, benzhydrol (1) and its related compound benzoin
(2) were selected as substrates in order to evaluate the intrinsic
alcohol oxidation ability of SCW. In this paper, we wish to
report the alcohol oxidation property of supercritical water
through secondary alcohols 1 and 2 (Chart 1).
In related studies, we have reported a unique reaction
of ethanol in SCW.12 When ethanol was treated in SCW at
450–500 ꢁC in the absence of an oxidizing agent or a catalyst,
oxidation occurred to give acetaldehyde concomitant with
hydrogen gas generation. Takahashi et al. proposed a water-
catalyzed hydrogen formation mechanism consisting of an
ethanol molecule and two water molecules for the transition
state of the reaction based on theoretical calculations, in which
two water molecules catalyzed the reaction by making an
OH
OH
O
1
2
Chart 1.
H
H
H
H
H
O
H
H
O
O
O
H
O
O
H
O
O
H
H
H
C
H
C
H
C
H
H3C
H3C
H3C
H
H
O
H
H
H
H
Scheme 1.
Published on the web September 13, 2007; doi:10.1246/bcsj.80.1828

P. Wang et al.
Table 1. Reaction of 1 in Supercritical WateraÞ
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1829
Product/%
Mole of 1
/mmol
Temperature
/ꢁC
Water density
/g mLꢂ1 bÞ
Reaction time
/min
Conversion
/%
Entry
3
4
1
2
3
4
5
6
7
8
9
0.272
0.272
0.272
0.272
0.272
1.09
380
400
420
440
460
460
460
460
460
460
440
440
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0
180
180
180
180
180
180
180
20
19
26
77
87
>99
96
>99
38
82
93
>99
86
6
16
46
53
63
60
60
16
53
49
48
50
4
5
4
9
10
10
17
<1
7
7
53
29
2.00
0.272
0.272
0.272
0.272
0.272
60
10
11
12
120
180
180
0.05
a) Under N2, in SUS 316 tubular reactor. b) Value of water density: water (g)/volume of the reactor
(9.9 mL).
OH
O
H2
1
3
4
Scheme 2.
Table 2. Generation of Hydrogen Gas in Supercritical Water Reaction of 1aÞ
ConversionbÞ
/%
Products/%
Temperature
/ꢁC
Reaction time
/min
Entry
H2
3
4
1
2
422
420
10
60
ꢃ1
0.6
1.2
2.4
5.1
1.5
2.8
7
a) Reaction conditions: 0.272 mmol of 1 and 0.34 mL of water in 1 mL quartz tubular
reactor, water density 0.34 g mLꢂ1. b) Conversions was suppressed with low level to
avoid explosion of the quartz tubings by inner pressure of generated hydrogen gas.
tionation between two molecules of alcohol 1 took place ther-
Results and Discussion
mally. In the presence of water, however, the ratio of 3:4
always exceeded unity and increased with increasing water
density (Entries 11, 12, and 4). Even within shorter reaction
time (Entries 8, 9, and 10), the amount of 3 was always larger
than that of 4 at 460 ꢁC and 0.35 g mLꢂ1 water density. These
observations imply that a new reaction path other than the dis-
proportionation occurs at higher water density and higher tem-
perature. Water must play a key role in the new reaction.
Next, a quartz tubular reactor was adopted instead of the
SUS 316 one to ascertain the evolution of hydrogen gas and
to quantify the gaseous products. When alcohol 1 was treated
in supercritical water at 420 ꢁC in the quartz tubular reactor,
evolution of hydrogen gas was observed, as expected, along
with oxidation product 3 and reduction product 4 (Table 2).
The material of the reactor, quartz or SUS 316, influenced
the product distributions in SCW.12 Thus, the product distribu-
tions of the reaction in the quartz tubular reactor were slightly
different from those in the SUS 316 reactor in the present
study. In other words, smaller ratios of 3:4 were obtained in
the quartz tubular reactor than those in the SUS 316 reactor,
although oxidation product 3 was the major product in both re-
actors. The amount of 3 was almost equal to the sum of ob-
Reaction of Benzhydrol (1) in Supercritical Water. Al-
cohol 1 was treated in supercritical water in a SUS 316 tubular
reactor under various conditions (Table 1).15 Small amounts
of benzophenone (3) and diphenylmethane (4) were produced
at the temperature near the critical point (Entry 1). With an
increase in the reaction temperature, the conversion of 1 and
yields of 3 and 4 became higher (Entries 1–5). A remarkable
change was observed at 420 ꢁC (Entry 3). Concerning the reac-
tion time, reaction almost finished within about 120 min
(Entry 10). The required high temperature (>420 ꢁC) as well
as long reaction time (>120 min) suggests that the activation
energy of this reaction is quite high. The best yield of 3 was
achieved at 460 ꢁC for 180 min (Entry 5). A higher concentra-
tion of alcohol 1 has almost no influence on the conversion of
1 and the yield of 3, and a little influence on the yield of 4,
although the yields of 3 were higher than those of 4 in all cases
(Entries 5, 6, and 7) (Scheme 2).
The role of water in the above reaction was examined by
changing the water density. In the absence of water (Entry 11,
pyrolysis), almost equal amounts of oxidation product 3 and
reduction product 4 were obtained, suggesting that dispropor-

1830 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
Reaction of Secondary Alcohols in SCW
tained H2 and 4, showing no discrepancy supposing that reduc-
tion of 1 and/or 3 by the generated hydrogen gave 4 in the re-
action system.16 Prolonged reaction time led to higher conver-
sion of 1 and higher yields of hydrogen and products 3 and 4
(Entry 2).17 The yields of 3 were almost two times higher than
those of 4 in both reactions.
well understood, the water-catalyzed hydrogen formation
mechanism13 seems to be the most favourable one at present
for our experiment in water.
Reaction of Benzoin (2) in Supercritical Water. The
higher homologue benzoin (2) (Scheme 3), which also has
two benzene subunits, a secondary hydroxy group, and a car-
bonyl group, was the next secondary alcohol to be treated in
sub- and super-critical water (Table 3). Oxidation product
benzil (6) and reduction product benzyl phenyl ketone (7) with
small amounts of benzaldehyde (8), which can be derived from
decomposition of 2, 6, and/or 7, were obtained even at low
temperatures (Entries 1 (300 ꢁC) and 2 (340 ꢁC)) and a short
reaction time (10 min), indicating that the reactions of 2 in
sub- and super-critical water proceeded easily as compared
to those of 1. Conversion of 2 and yields of 6 and 7 became
higher with an increase in the reaction temperature (Entries
1, 2, and 6) and then saturated at 380 ꢁC (Entry 10). A longer
reaction time improved conversion of 2 as well as yields of 6
and 7, though small amounts of 1, which should be produced
via benzil–benzilic acid rearrangement of 6, followed by de-
carboxylation, as reported by Comisar and Savage,11 and quite
small amounts of benzophenone (3) and diphenylmethane (4)
from 1, as discussed previously, were obtained. Water density
also played a crucial role in this reaction. In the absence of wa-
ter (Entry 7, pyrolysis), however, reaction of 2 resulted in high
conversion (95%) and almost the same total yield of the oxida-
tion products (ꢃ29%, defined as the sum of 6, 1, 3, and 4) and
reduction product 7 (30%), which was quite similar to the re-
sults of the pyrolysis of alcohol 1 (Entry 11 in Table 1). Con-
version of 2 as well as yields of 6 and 7 became lower with an
increase in the water density (Entries 7–10 and 6), suggesting
disproportionation of 2 was suppressed by water in the reac-
tion. Again, in the presence of water, total yield of the oxida-
tion products as defined above was always larger than the yield
of reduction product 7 in every reaction.
Hatano et al. studied a similar reaction using the same sub-
strate 1 in sub- and super-critical water in a steel bomb reac-
tor.18 They obtained the same products, 3 and 4, as us, though
the ratios of 3:4 were quite different from ours, almost 1:1
under all conditions they tested. No effect of water density on
product distributions was observed in their experiments. They
obtained ether 5 (Chart 2) from their reaction at 200 ꢁC. When
ether 5 was treated under supercritical conditions as a starting
material, the corresponding product ratio of 3:4 was almost
1:1. They concluded, therefore, that equal amounts of 3 and
4 were derived from disproportionation of ether 5, which
was produced in an early stage of the reaction.19 The proposed
reaction mechanism would be quite reasonable if a 1:1 mixture
of 3 and 4 were obtained even in our experiments. Our experi-
ments always gave larger amounts of 3 than those of 4. The
low yield of 4 in our experiments could be attributed to the la-
bility of 4 under the reaction conditions. A control experiment
involving 4 in SCW (460 ꢁC, 180 min, 0.35 g mLꢂ1 water den-
sity), however, resulted in complete recovery of 4 (>99%), in-
dicating that 4 was quite stable under the reaction conditions.
Especially, it is noteworthy that the yield of 3 exceeded 50% to
reach 63% under the reaction conditions of Entry 5 in Table 1.
The observed temperature and water density dependence of the
reaction (Table 1) and the evolution of hydrogen are of consid-
erable importance for discussion of the reaction mechanism. In
our experiment, the formation of ether 5 could be suppressed
by hydrolysis of 5 itself under extreme supercritical condi-
tions, even if ether 5 was generated in the reactions. It is dif-
ficult to put forward a conclusive discussion, though the cru-
cial differences in the reaction behavior between the reported
and ours could be attributed to the difference in the materials
of the metal reactors. Although the reaction mechanism is not
As a conclusion, 2 had higher reactivity than 1 in sub- and
super-critical water. The reaction of 2 in SCW was tempera-
ture- and time-dependent. Compound 2 reacted more rapidly
with an increase in reaction temperature up to 380 ꢁC. Longer
reaction time caused higher conversion of 2 and higher yields
of products. The total amount of oxidation product 6 and its
secondary products (1, 3, and 4) was higher than that of reduc-
tion product 7 in the presence of water.
Ph
Ph
Ph
Ph
O
5
Reaction of Reference Compound Benzyl Alcohol (9) in
SCW. The reaction behavior of benzyl alcohol (9) in SCW,
Chart 2.
OH
O
O
O
O
O
2
6
7
8
O
OH
1
3
4
Scheme 3.

P. Wang et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1831
Table 3. Reaction of 2 in Subcritical and Supercritical WateraÞ
Product/%
Temperature
/ꢁC
Water density
/g mLꢂ1 bÞ
Reaction time
/min
Conversion
/%
Entry
6
7
8
1
3
4
dÞ
dÞ
1
2
3
4
5
6
7
8
9
300
340
380
380
380
380
380
380
380
380
400
0.35cÞ
0.35cÞ
0.35
0.35
0.35
0.35
0
0.05
0.15
0.25
0.35
10
10
0eÞ
1
42
47
27
36
59
66
95
81
73
68
67
8
2
5
1
3
6
1
<1
2
<1
1
4
6
<1
<1
2
3
7
—
—
—
—
—
—
—
—
dÞ
dÞ
dÞ
dÞ
dÞ
dÞ
15
10
15
16
19
26
19
18
16
18
2
<1
1
4
6
5
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
10
10
10
10
10
10
9
30
16
10
7
6
12
12
8
10
11
9
15
a) Reaction conditions: 0.236 mmol of 2, water, under N2 in SUS 316 tubular reactor. b) Value of water density: water
(g)/volume of the reactor (9.9 mL). c) Reaction medium was not homogeneous, because reaction temperature was
under the critical temperature of water. d) Not detected. e) As soon as the temperature reached 380 ꢁC, the reaction
was quenched by rapid cooling of the reactor in ice-water.
which is a primary alcohol, was compared to the reaction be-
havior of 1 and 2 (Scheme 4). When alcohol 9 was treated at
380–440 ꢁC for 180 min in 0.35 g mLꢂ1 water density in the
SUS 316 reactor, oxidation product benzaldehyde (8) and re-
duction product toluene (10) were obtained (Table 4). Lower
conversion of 9 than that of benzhydrol (1) under the same re-
action conditions indicates that the reactivity of 9 is lower than
that of 1. Benzene (11) was also obtained in the reaction,
which should be generated by thermal decomposition of 8.20
The total amount of the oxidation products 8 and 11 in this re-
action is always larger than that of the reduction product 10.
under all conditions examined. Efficient oxidation of 1 was
achieved at 460 ꢁC for 180 min in 0.35 g mLꢂ1 water density in
a SUS 316 reactor to give 63% of 3. Water played a key role in
this reaction. The ratio of 3:4 always exceeded unity and rap-
idly increased with an increase in the water density and tem-
perature. Evolution of hydrogen gas was confirmed in the re-
action of 1 in a quartz tubular reactor. In the reaction of 2, the
total yield of oxidation product 6 and its secondary reaction
products 1, 3, and 4 was also higher than that of reduction prod-
uct 7 in the presence of water. The fact of hydrogen gas evolu-
tion, water density dependence of alcohol reaction, and more
oxidation products than reduction product in SCW suggests
that the water-catalyzed hydrogen generation mechanism is
favorable to explain the reaction behavior of alcohols in SCW.
Conclusion
We demonstrated the reaction behavior of benzhydrol (1)
and its higher homologue benzoin (2), both of which have
two benzene subunits, a secondary hydroxy group, and no hy-
drogen atom on the ꢀ-position of the hydroxy group, in sub-
and super-critical water without any oxidizing agents or cata-
lysts. Oxidation product 3 and reduction product 4 were pro-
duced from the reaction of 1. In the absence of water, almost
a 1:1 (3:4) mixture was obtained, suggesting that disproportio-
nation between two molecules of alcohol 1 occurred thermally.
Higher yields of 3 than that of 4 were always achieved in water
Experimental
1H NMR spectra were obtained on a Varian Unity Inova spec-
trometer operating 400 MHz. GC-MS analyses were performed
on a Shimadzu GCMS-QP 5050. GC analyses were done on a
Shimadzu GC-17A gas chromatograph with CBP-5 and/or DB-1
columns. Benzhydrol and benzyl alcohol were purchased from
Nacalai Tesque Inc., and benzoin was purchased from Wako Pure
Chemical Industries Ltd.
The relevant alcohol and reverse osmosis water, into which
nitrogen gas had been bubbled for 30 min to remove the dissolved
oxygen, were introduced into a SUS316 tubular reactor. The reac-
tor was purged with N2 for 10 min to remove the oxygen in the
reactor and sealed with a screw cap, which was equipped with a
thermocouple for measuring the reactor temperature. The reactor
CH3
OH
O
9
8
10
11
Scheme 4.
Table 4. Reaction of 9 in Supercritical WateraÞ
Product/%
Entry
Temperature
/ꢁC
Water density
/g mLꢂ1 bÞ
Reaction time
/min
Conversion
/%
8
10
11
cÞ
1
2
3
4
380
400
420
440
0.35
0.35
0.35
0.35
180
180
180
180
9
18
26
40
5
<1
2
5
10
—
10
14
21
<1
1
8
a) Reaction conditions: 1.09 mmol of 9, water, under N2 in SUS 316 tubular reactor. b) Value of
water density: water (g)/volume of the reactor (9.9 mL). c) Not detected.

1832 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
Reaction of Secondary Alcohols in SCW
was then put in a molten salt bath, which was kept at an appropriate
temperature, and heated for an appropriate time. It took about 20–
30 s to raise the inner reactor temperature up to 380–460 ꢁC. After
the reaction, reactor was placed into an ice water bath to quench
the reaction. When the reactor was completely cooled down, the
screw cap was opened. The reaction mixture was extracted 3 times
with ether. The organic phase was separated, and the solvent was
evaporated in vacuo to give crude products. The crude products
were purified by using silica gel chromatography (Wako C-200,
ether and hexane) and GPC (JAI gel 1H and 2H, chloroform), if
5
Y. Ikushima, K. Hatakeda, O. Sato, T. Yokoyama, M. Arai,
Angew. Chem., Int. Ed. 1999, 38, 2910.
a) M. Osada, M. Watanabe, K. Sue, T. Adschiri, K. Arai,
6
J. Supercrit. Fluids 2004, 28, 219. b) Y. Tsujino, C. Wakai, N.
Matubayashi, M. Nakahara, Chem. Lett. 1999, 287.
7
Y. Ikushima, K. Hatakeda, O. Sato, T. Yokoyama, M. Arai,
Angew. Chem., Int. Ed. 2001, 40, 210.
R. Zhang, F. Zhao, M. Sato, Y. Ikushima, Chem. Commun.
2003, 1548.
8
9
a) K. Itami, K. Terakawa, J.-i. Yoshida, O. Kajimoto, Bull.
1
necessary. The products were identified using H NMR and GC-
Chem. Soc. Jpn. 2004, 77, 2071. b) K. Itami, K. Terakawa, J.-i.
Yoshida, O. Kajimoto, J. Am. Chem. Soc. 2003, 125, 6058.
10 S. A. Nolen, C. L. Liotta, C. A. Eckert, R. Glaser, Green
Chem. 2003, 5, 663.
11 C. M. Comisar, P. E. Savage, Green Chem. 2005, 7, 800.
12 T. Arita, K. Nakahara, K. Nagami, O. Kajimoto, Tetra-
hedron Lett. 2003, 44, 1083.
13 a) H. Takahashi, H. Hashimoto, T. Nitta, J. Chem. Phys.
2003, 119, 7964. b) H. Takahashi, S. Hisaoka, T. Nitta, Chem.
Phys. Lett. 2002, 363, 80.
14 a) K. Nakahara, T. Arita, K. Nagami, O. Kajimoto, the 8th
Meeting on Supercritical Fluids, Bordeaux, France, April 14, 2002.
b) G. M. Schneider, Ber. Bunsen-Ges. Phys. Chem. 1972, 76, 325.
15 a) H. Kojima, K. Kobiro, T. Arita, O. Kajimoto, K.
Nakahara, the 82nd Autumn Annual Meeting of the Chemical
Society of Japan, Toyonaka, Osaka, September 25, 2002, Abstr.,
No. 3PA-113. b) K. Nakahara, K. Nagami, O. Kajimoto, K.
Kobiro, U.S. Patent 7166753, 2007.
16 When alcohol 1 was treated with and without additional
hydrogen gas in SCW (1: 0.054 mmol, H2: 0 or 0.29 mmol,
440 ꢁC for 180 min in 0.35 g mLꢂ1 water density in SUS 316 reac-
tor), no difference in the product distributions was observed
between the reactions with and without additional hydrogen gas
(with H2, 3: 24%, 4: 15%; without H2, 3: 25%, 4: 13%). But
the possibility of the reduction of 1 not by hydrogen gas generated
in situ but nascent hydrogen in the reaction conditions still
remains. Reduction of 1 and 3 to give 4 in 15% aqueous formic
acid or 15% aqueous sodium formate in supercritical conditions
(460 ꢁC, 60 min) was reported: A. R. Katritzky, E. S. Ignatchenko,
S. M. Allin, R. A. Barcock, M. Siskin, C. W. Hudson, Energy
Fuels 1997, 11, 160.
MS by comparing the spectra with those of authentic samples.
Conversion of the starting materials and yields of the products
were determined using an internal standard method in the GC anal-
ysis. Heptadecane and dodecane were used as internal standards.
Reaction in quartz tubular reactor: To a quartz tubular reactor
was added 1 (50 mg, 0.272 mmol) and water (0.34 mL). The quartz
reactor, which had an inner volume of 1 mL, was sealed with a
flame under N2. The sealed quartz reactor was inserted into the
SUS 316 reactor, which was filled with 4 mL of water, and then
the SUS 316 reactor was closed tightly. The SUS 316 reactor with
the small quartz reactor inside was heated at a desired temperature
by the method similar to that described above. Evolved gases were
identified and quantified with GC.12
¨
We thank Professor Takahiro Hosokawa of Kochi Univer-
sity of Technology and Dr. Kenzo Nagami of Institute for Fun-
damental Research, Suntory Ltd. for their invaluable advice
and fruitful discussions. This work has been financially sup-
ported by CREST of JST (Japan Science and Technology Cor-
poration).
References
1
a) H. Weingartner, E. U. Franck, Angew. Chem., Int. Ed.
¨
2005, 44, 2672. b) A. R. Katritzky, D. A. Nichols, M. Siskin,
R. Murugan, M. Balasubramanian, Chem. Rev. 2001, 101, 837.
c) M. Siskin, A. R. Katritzky, Chem. Rev. 2001, 101, 825. d) D.
Broll, C. Kaul, A. Kramer, P. Krammer, T. Richter, M. Jung,
H. Vogel, P. Zehner, Angew. Chem., Int. Ed. 1999, 38, 2998.
e) P. E. Savage, Chem. Rev. 1999, 99, 603.
2
a) M. Svanstrom, M. Froling, M. Olofsson, M. Lundin,
17 CH4 (0.1%), CO (0.6%), and CO2 (0.5%) were detected in
the early stage of the reaction (10 min, Entry 1, Table 2), whereas
after 60 min, CH4 and CO were not detected. In addition, the
amount of CO2 did not exceed 0.8% (Entry 2, Table 2). When
the reaction was executed under degassed conditions, which were
prepared by freeze-and-thaw procedure, CH4, CO, and CO2 were
not detected. These gaseous products might be derived from the
partial oxidation of substrate 1 by a trace amount of oxygen dis-
solved in water.
¨
¨
Waste Manage. Res. 2005, 23, 356. b) H. C. Lee, J. H. In,
K. Y. Hwang, C. H. Lee, Ind. Eng. Chem. Res. 2004, 43, 3223.
c) M. J. Drews, M. Barr, M. Williams, Ind. Eng. Chem. Res.
2000, 39, 4784. d) T. Mizuno, M. Goto, A. Kodama, T. Hirose,
Ind. Eng. Chem. Res. 2000, 39, 2807. e) H. Schmieder, J.
Abeln, Chem. Eng. Technol. 1999, 22, 903. f) S. F. Rice, R. R.
Steeper, J. Hazard. Mater. 1998, 59, 261. g) P. A. Marrone,
P. M. Gschwend, K. C. Swallow, W. A. Peters, J. W. Tester,
J. Supercrit. Fluids 1998, 12, 239.
18 B. Hatano, J.-i. Kadokawa, H. Tagaya, Tetrahedron Lett.
2002, 43, 5859.
3
a) M. Kubo, T. Takizawa, C. Wakai, N. Matubayasi, M.
Nakahara, J. Chem. Phys. 2004, 121, 960. b) C. R. Yonker, S.
Bai, B. J. Palmer, Preprints of Symposia-American Chemical
Society, Division of Fuel Chemistry, 1999, Vol. 44, p. 377.
c) T. Junk, W. J. Catallo, Tetrahedron Lett. 1996, 37, 3445.
d) J. Yao, R. F. Evilia, J. Am. Chem. Soc. 1994, 116, 11229.
19 Disproportionation of 5 and its homologues was also re-
ported, see: a) C. Waterlot, D. Couturier, M. De Backer, B. Rigo,
Can. J. Chem. 2000, 78, 1242. b) P. Gautret, S. El-Ghammarti, A.
Legrand, D. Couturier, B. Rigo, Synth. Commun. 1996, 26, 707.
c) G. Heinisch, Bull. Soc. Chim. Belg. 1992, 101, 579. d) G.
Heinisch, R. Waglechner, J. Heterocycl. Chem. 1984, 21, 1727.
e) P. D. Bartlett, J. D. McCollum, J. Am. Chem. Soc. 1956, 78,
1441.
4
a) M. Boero, T. Ikeshoji, C. C. Liew, K. Terakura, M.
Parrinello, J. Am. Chem. Soc. 2004, 126, 6280. b) Y. Ikushima,
K. Hatakeda, O. Sato, T. Yokoyama, M. Arai, J. Am. Chem.
Soc. 2000, 122, 1908. c) O. Sato, Y. Ikushima, T. Yokoyama,
J. Org. Chem. 1998, 63, 9100.
20 Y. Nagai, N. Matubayasi, M. Nakahara, Chem. Lett. 2004,
33, 622.