1
206 Bull. Chem. Soc. Jpn., 77, No. 6 (2004)
Table 2. Formation of CH3CHO from Fenton Reaction of CH3CH2OH
Oxidation of Ethanol Induced by Polyphenols
Amount of CH3CHO formed/mM
Without H2O2
Yield/%
Additive
With H2O2
Corrected value
Based on Fe(II)
—
Pyrogallol (1)
Catechol (2)
46.8
43.2
22.7
7.7
8.9
8.2
39.1
34.3
14.5
98
86
36
ed 200 mL of a solution of FeSO4 7H2O (1 mM) and DTPA
1 mM) in H2O, and subsequently 150 mL of 5.88 mM H2O2
was added at room temperature. Into this solution was then added
amount of H2O2 down to 110 mM. This fact supports the above
consideration.
ꢅ
(
2
together with 1.5 mL of EtOH. The amount of 1 (or 2) and Fe(II)
.5 mL of 10 mM pyrogallol (1) or catechol (2) in EtOH–H2O (1:1)
We thank Dr. Kenzo Nagami (Institute for Fundamental
Research, Suntory Limited) for inspiration, encouragement,
and valuable discussions throughout this work.
used corresponded to 5 mM and 40 mM, respectively. The resulting
solution was stirred at 60 C under argon for 60 min. As a refer-
ꢃ
ence, the same reaction was performed in the absence of 1 or 2.
An analysis of CH3CHO was carried out by the same procedure
as mentioned above. Even without adding H2O2, the oxidation
was found to slightly take place, because air was not rigorously ex-
cluded. Consequently, the amount of CH3CHO formed in the Fen-
ton reaction was corrected by using the amount of CH3CHO
formed in the absence of H2O2. The results are given in Table 2.
Formation of Purpurogallin (6) from Pyrogallol (1) and O2.
Into a 100 mL of phosphate buffer solution (100 mM, pH 7.5) con-
taining CH3CH2OH (30 mL) was added 1 (1 mmol, 72.02 mg),
References
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6
0 C for 40 min. The products were immediately and rigorously
extracted with ether (200 mL), and dried over Na2SO4. The evap-
oration of ether gave a light brown powder which contained pur-
purogallin (6) (22.88 mg, 0.10 mmol, 20% based on 1) and 1
(
72.02 mg, 0.57 mmol, 57%) by NMR analysis. From an analysis
of the H2O2 formed, its amount was found to be 0.58 mmol. The
authentic purpurogallin (6) was prepared from sodium iodate and
4
5
L. Bravo, Nutr. Rev., 56, 317 (1998).
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6
1
by the reported procedure.28 1H NMR (400 MHz, DMSO-d6) ꢄ
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1
3
1
H, J ¼ 9:43 Hz), 7.34 (d, 1H, J ¼ 11:47 Hz); C{ H} NMR
6
(100.5 MHz, DMSO-d6) ꢄ 111.7 (C-9), 116.3 (C-4a), 118.0
(C-1), 125.0 (C-8), 134.5 (C-3), 135.8 (C-7), 136.2 (C-9a), 153.0
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If the following assumptions (1)–(3) based on Scheme 5 are val-
id, the amount of H2O2 formed is nearly consistent with that ex-
pected: (1) The pyrogallol (1) consumed (1.0 mmol ꢂ 0.57 mmol
=
(
0.43 mmol) produces an equimolar amount of H2O2
0.43 mmol). (2) The consumed 1 is quantitatively transformed in-
to purpurogallin (6) (0.43 mmol/2 = 0.21 mmol). (3) The amount
of 6 isolated is 0.10 mmol, and therefore a part of 6 formed
7
a) K. Kondo, M. Kurihara, N. Miyata, T. Suzuki, and M.
2
9
(
0.21 mmol ꢂ 0.10 mmol) is oxidized by O2 to give 0.11 mmol
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M. Kurihara, N. Miyata, T. Suzuki, and M. Toyoda, Arch.
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K. Fukuhara, T. Tanaka, T. Suzuki, N. Miyata, and M. Toyoda,
Tetrahedron Lett., 41, 485 (2000).
of H2O2. From these assumptions, the expected amount of H2O2
formed becomes 0.54 mmol (0.43 mmol þ 0.11 mmol), which is
nearly equal to the observed value of 0.58 mmol. Note that based
on Scheme 5, the expected amount of H2O2 is to be 1.5 equivalent
of 1 used. However, under the conditions using phosphate buffer
8
J. Alanko, A. Riutta, P. Holm, I. Mucha, H. Vapaatalo, and
T. Mets a¨ -Ketel a¨ , Free Radical Biol. Med., 26, 193 (1999).
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(
Fig. 2a), 100 mM of 1 produced 200 mM of H2O2. This amount
exceeded the expected value of 150 mM. Therefore, unknown
processes for the production of H2O2 must be involved, in which
the phosphate buffer may take part. Since the phosphate buffer acts
as a reductant,30 it could induce the regeneration of 1 from the in-
termediate quinone (hydroxyl-3,5-cyclohexadiene-1,2-dione)
9
Chem., 45, 30 (1997). b) Y. Hanasaki, S. Ogawa, and S. Fukui,
Free Radical Biol. Med., 16, 845 (1994). c) G. Cao, E. Sofic,
and R. L. Prior, Free Radical Biol. Med., 22, 749 (1997). d) F.
Hayakawa, T. Kimura, T. Maeda, M. Fujita, H. Sohmiya, M. Fujii,
and T. Ando, Biochim. Biophys. Acta., 1336, 123 (1997).
10 M. Mochizuki, S.-I. Yamazaki, K. Kano, and T. Ikeda, Bio-
chim. Biophys. Acta., 1569, 35 (2002); and see also: I. Nakanishi,
K. Fukehara, K. Ohkubo, T. Simada, H. Kansui, M. Kurihara, S.
(
Scheme 5). The regenerated 1 again produces H2O2. Involvement
of such a process explains 200 mM production of H2O2 from
00 mM of 1. In place of the phosphate buffer, the use of MOPS
buffer (3-(N-morpholino)propanesulfonic acid) decreased the
1