Hydroxyl radical as a strong electrophilic species

Article abstract of DOI:10.1016/S0968-0896(02)00048-2

In order to clarify an index which could be used as proof of the presence of hydroxyl radical, a new standard isomer distribution ratio of phenols formed from aromatic hydroxylation with [(4-bromophenyl)diazenyl](phenyl)methyl hydroperoxide 4, which is a stable source of hydroxyl radical, under a new appropriate photolysis condition in the presence or absence of benzoquinones is reported. We also demonstrated the strong electrophilic properties of hydroxyl radical in reference to earlier results of electron density calculations.

Full text of DOI:10.1016/S0968-0896(02)00048-2

Bioorganic & Medicinal Chemistry 10 (2002) 2283–2290
Hydroxyl Radical as a Strong Electrophilic Species
Hiroshi Marusawa,a,* Kazuhiko Ichikawa,b Nozomu Narita,b
Hiromu Murakami,b Keiichi Itob and Takahiro Tezukab,*
aMedical Supplies & Systems, Fujisawa Pharmaceutical Co., Ltd., 10-2 Kanda-Tomiyamacho,
Chiyoda-ku, Tokyo 101-0043, Japan
bDepartment of Chemistry, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8575, Japan
Received 19 November 2001;accepted 19 January 2002
Abstract—In order to clarify an index which could be used as proof of the presence of hydroxyl radical, a new standard isomer
distribution ratio of phenols formed from aromatic hydroxylation with [(4-bromophenyl)diazenyl](phenyl)methyl hydroperoxide 4,
which is a stable source of hydroxyl radical, under a new appropriate photolysis condition in the presence or absence of benzo-
quinones is reported. We also demonstrated the strong electrophilic properties of hydroxyl radical in reference to earlier results of
electron density calculations. # 2002 Elsevier Science Ltd. All rights reserved.
Introduction
proof for the presence of hydroxyl radical as Walling
and Johnson studied,24 there still remain many ambi-
guities25 concerning whether or not, or which isomer
ratio of phenols reveals the participation of hydroxyl
radical correctly. Various ortho:meta:para isomer ratios
of phenols have been reported in aromatic hydroxy-
lation with hydroxyl radicals generated from Fenton’s
reagent26À28 or by radiolysis of water.29À31 Variation in
the ratios is thought to arise from positional isomeriza-
tion of the initially formed hydroxycyclohexadienyl
radicals 6 under aqueous acidic conditions, for example,
via radical cations24 7 prior to oxidation to phenols as
shown in Scheme 3 or by NIH shift rearrangements32
via arene oxide intermediates33 and so on. In addition,
molecular oxygen present in the reactant was found to
be incorporated into phenols and changed the isomer
ratios.34 Although many trials to clarify the mechanism
have also been put forward, several reactive species are
produced together with hydroxyl radical in the reac-
tions,31,35 which make the analysis of the reaction
mechanism more complicated. Furthermore, even with
Fenton’s reagent, there are some papers describing pro-
duction of another reactive intermediate36,37 instead of
hydroxyl radical.
Oxidative stress1,2 and the damage3 that results from it
have been implicated in a wide number of disease pro-
cesses including atherosclerosis,4 autoimmune dis-
orders,5,6 rheumatoid arthritis,7 neuronal degeneration,8
cardiovascular diseases9 and cancer.10 Reactive oxygen
species (ROS) are ubiquitous and occur naturally in all
aerobic species, coming from both exogenous and
endogenous sources.11 In particular, hydroxyl radical
among a number of ROS is quite reactive12 and readily
damages biological molecules13 including DNA.14,15
A
number of compound16À18 have been demonstrated in in
vitro and in vivo experiments to protect against oxida-
tive damage by inhibiting or quenching hydroxyl radi-
cal. As such, there is a need to establish proof19
regarding the presence or absence of the hydroxyl radi-
cal as a reactive intermediate species in chemical and
biological processes. In vivo measurement of highly
reactive hydroxyl radicals in humans is very difficult and
specific markers are currently under investigation
(amino acid hydroxylation, protein, DNA adducts, and
aromatic probes).20 These are all based on the ability of
hydroxyl radical to attack the benzene rings of aromatic
compounds smoothly and produce hydroxylated com-
pounds, particularly isomer ratios of phenols that can
be measured directly.21À23
In order to prevent positional isomerization and hence
to get intrinsic isomer ratios which accurately reflect the
position of hydroxyl radical attack, it is desirable to
carry out reaction in an anhydrous medium in the pre-
sence of a good oxidant under deaerated conditions,
with argon or nitrogen gas. In 1975 Tezuka et al.38
found that a-azohydroperoxide such as [(4-bromo-
However, even in chemical processes where the isomer
ratios in aromatic hydroxylation have been used as
*Corresponding author. Fax: +81-3-5256-5370;
e-mail: hiroshi_marusawa@po.fujisawa.co.jp
phenyl)diazenyl](phenyl)methyl
hydroperoxide
439
0968-0896/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(02)00048-2

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H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
Scheme 1.
Scheme 2.
Scheme 3.
generates the hydroxyl radical by photolysis instead of
thermolysis40 under anhydrous conditions and we sub-
sequently investigated aromatic hydroxylation41 using 4
as an efficient hydroxyl radical generator. In this report,
we describe a new standard isomer ratio of phenols
formed from aromatic hydroxylation with 4 under a
new appropriate photolysis condition in the presence or
absence of benzoquinones as a good oxidant and
demonstrate the strong electrophilic properties of
hydroxyl radical in reference to previous results42,43 of
electron density calculations.
decomposed in the presence or absence of benzo-
quinones under argon gas, and yielded cresol 8a,
methoxyphenol 8b or nitrophenol 8c, respectively
together with benzaldehyde, bromobenzene and so on.
All products in the reaction of 4 in toluene are shown
in Scheme 2. During hydroxylation in the absence of
benzoquinones, the initially formed isomeric hydro-
xycyclohexadienyl radicals 6 disproportionate to give
phenols 8a–8c, as shown in Scheme 3. In the presence of
oxidant such as benzoquinones on the other hand, the
isomeric radicals 6a–6c are converted to phenols 8a–8c
efficiently by an electron transfer oxidation as shown in
Scheme 4.
Chemistry
Hydrazone 3 derived from p-bromophenylhydrazine 2
and benzaldehyde 1 was oxidized by molecular oxygen
in benzene to give a-azohydroperoxide 4 as yellow
crystals as shown in Scheme 1. a-Azohydroperoxide 4 in
toluene 5a, anisole 5b or nitrobenzene 5c were photo-
Results and Discussion
We initially selected K3Fe(CN)6 as an oxidant for
cyclohexadienyl radical intermediate 6 because it is
often used in aqueous media to prevent hydration and/or

H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
2285
Scheme 4.
rearrangement reactions,44 and tried to compare an isomer
distribution ratio of phenols in this system with that
with Fenton’s reagent. We chose toluene as the sub-
strate and carried out the reaction with hydroxyl radi-
cals generated from 4 by photolysis with a high pressure
mercury lamp through a Pyrex filter in toluene and
water (1:1) in the absence or presence of K3Fe(CN)6 as
the oxidant with vigorously stirring and thorough bub-
bling of argon gas constantly, and analyzed the isomer
ratios and yields of the produced cresols, as indicated in
Table 1. The isomer ratios in both cases were found to
be almost the same while the yield of cresols increased in
the presence of K3Fe(CN)6. This result was the desired
outcome, even though the increase is small. We thus
moved on to experiments in anhydrous media to
increase the efficacy of the oxidant.
p-benzoquinone while that of nitrophenol did not
increase. The ortho:meta:para ratio of each phenol, on
the other hand, showed a constant value within experi-
mental error in the absence or presence of p-benzoquin-
one. It is important to note that the yield of phenols was
more than doubled, except for nitrophenol, in the case
of coexistence with the oxidant, while the isomer ratios
remained constant in each case. This implies that the
oxidation of the cyclohexadienyl radicals 6a and 6b by
p-benzoquinone is so efficient that the isomer ratio of
cresol and hydroxyanisole reflects the isomer ratio of
the position at which hydroxyl radical first attacked. In
other words, the isomer ratio in the case of the oxida-
tion is almost the same as that of disproportionation,26
and so we confirmed that this system with 4 in anhy-
drous media works very well for eliciting the correct
isomer ratio regardless of oxidant. In terms of why the
yield of both cresol and methoxyphenol increased more
than doubled, we think that the intermediate cyclohex-
adienyl radicals 6, which actually should have converted
into biphenyls41 as byproducts, might also form phenols
instead in the presence of p-benzoquinone. In addition,
it seemed that p-benzoquinone did not abstract a
hydrogen atom from 4 and not interfere with the
photodecomposition of 4.
We tried to find a new standard isomer distribution
ratio of phenols that would be obtained by the reaction
with hydroxyl radicals generated from 4 by photolysis in
anhydrous media in the absence or presence of an oxi-
dant. We chose p-benzoquinone as the oxidant because
there was a report30 that the rate of electron transfer
oxidation of cyclohexadienyl radical 6b by p-benzoqui-
none under radiolytic conditions in aqueous media is
fast and nearly equal to the diffusion controlled rate
(k6109 MÀ1 sÀ1). In order to investigate the substituent
group effect for hydroxyl radical attack at a benzene
ring, we selected toluene 5a, anisole 5b and nitrobenzene
5c as substrates. The photolysis of 4 in these aromatics
with a high pressure mercury lamp through a Pyrex fil-
ter under argon gas gave cresol, methoxyphenol and
nitrophenol, respectively, in the isomer ratios and yields
listed in Table 2.
Furthermore, in order to minimize absorption of light
by p-benzoquinone, reaction was next carried out using
Table 2. The isomer ratios and yields of cresols, methoxyphenols and
nitrophenols in the presence or absence of p-benzoquinonea,b
It can be clearly seen from Table 2 that the yield of both
cresol and methoxyphenol increased in the presence of
X
CH3
OCH3
NO2
0.05 M
p-Benzoquinonec 0 M 0.05 M
0 M
0.05
0 M
Table 1. The isomer ratios and yields of cresols in the presence or
aÀd
ortho
meta
para
Yielde (%)
SOMO 6 (ev)f
71
9
21
8
73
11
16
25
84
0d
16
14
À8.5ꢀ8.9h
80
2
18
51
26
48
26
16
29
46
25
14
absence of K3Fe(CN)3
À8.6ꢀ9.0g
À9.8ꢀÀ10.0i
a
A Pyrex filter was used.
b Data obtained by repeating the experiment several times.
c Concentration of p-benzoquinone in aromatics.
K3Fe(CN)3e (M)
Cresol ortho:meta:para
Yield (%)
0
0.05
70:10:20
71:10:19
5
7
d Only a trace of m-methoxyphenol was detected by GLC.
e Yields are based on the original amount of 4 (0.01 M).
f
a
Electron density of the HOMO of these aromatics was calculated by
CNDO/2.
A Pyrex filter was used.
b Yields are based on the original amount of 4 (0.01 M).
c Data obtained by repeating the experiment several times.
d Heterogeneous reaction system (water/toluene=1:1).
e Concentration of K3Fe(CN)3 in toluene and water (1:1).
g
ortho (À8.6990eV):meta (À9.0337eV):para (À8.6201eV).45
hortho (À8.5603eV):meta (À8.8541eV):para (À8.4977eV).
i
ortho (À10.0119eV):meta (À9.8419eV):para (À10.0106eV).45

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H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
a Corning glass filter 5–60 which passes only light
between 360 and 490 nm. We selected toluene as a typi-
cal example for the solvent and performed the appro-
priate photolysis of 4 in toluene with p-benzoquinone
with a high pressure mercury lamp through this filter
whereby more than 90% of light was absorbed by 4
(p-benzoquinone: e420=12; 4: e420=180 in toluene). We
chose a 0.005 M concentration of p-benzoquinone so as
to minimize absorption by the oxidant. In addition, we
also used 2-methylbenzoquinone and 2,5-di-tert-butyl-
benzoquinone as an oxidant instead of p-benzoquinone
and performed the same irradiation experiments with
the Corning filter as the new appropriate photolysis
condition.
case of nitrobenzene, supporting the proposition that an
electron transfer oxidation by p-benzoquinone occurs
when an electron-donating group is substituted in 5.
This probably is related to the fact that 6a and 6b pos-
sess a higher SOMO energy (À8.6–À9.0 eV45 and À8.5–
À8.9 eV, respectively) compared with 6c (À9.8–À10.0
eV)45 calculated by CNDO/2, and 6a and 6b might
interact more easily with the LUMO (À2.1 eV) of p-
benzoquinone. In other words, it seems that 6c is more
stabilized to delocalize the radical charge between the
nitro substituent group and the ring, and that such an
electron transfer oxidation did not take place.
The isomer ratios observed in this study are consistent
with those under argon in the absence of oxidant within
experimental errors, as reported by us.41 On the basis of
our present and previous studies, we propose a new
standard isomer distribution ratio of cresol, methoxy-
phenol and nitrophenol as ortho:meta:para=72:10:18,
82:1:17 and 27:47:26, respectively, in which the error is
less than 10%, as shown in Table 4. The isomer ratios
reported in this study, therefore, provide a correct value
for the position of aromatics attacked by hydroxyl
radical in anhydrous organic media. As for the derived
ratios, additional factors need to be considered. As we
reported, the HOMO electron density of aromatics
strongly controls the site of hydroxyl radical attack at
the aromatic ring.42 We therefore also calculated the
ortho:meta:para values of the HOMO coefficients for
anisole by CNDO/2 according to the method of Eber-
hardt and Yoshida45 and made a comparison between
the calculated results, including their data,45 and the
experimental isomer ratios for hydroxylation of toluene,
anisole and nitrobenzene observed in this study. As
shown in Table 4, the experimental ratios are fairly
consistent with the HOMO coefficients, but the ortho
isomer values of 8a and 8b in this study are a little
higher than the values of HOMO coefficients, as well as
in the case of 5a and 5b. This fact, together with a high
HOMO electron density and coefficient at the ipso-
position45 of these aromatics and formation of a small
amount of phenol in the reaction of 5a and 5b with 4 in
Table 5, suggests that the ipso isomer46,47 must be taken
into account. Therefore, we think that the rearrange-
ment of the ipso to ortho isomers increases and this
derives a high isomer ratio of the ortho-oriented isomer
of 6a and 6b in this study.
As shown in Table 3, the isomer ratio of cresol in this
case was found to be almost the same as that observed
with the Pyrex filter within experimental error. In addi-
tion, the yields of cresol had the same tendency to
increase when oxidant was added. All the observations
in Tables 2 and 3 demonstrate that benzoquinone acts
as the oxidant for 6 in its ground state and also do not
resist photodecomposition of 4. In other words, we
confirmed that at least the intermediate radicals 6a and
6b were converted to the phenols 8a and 8b efficiently by
electron transfer oxidation by benzoquinones, as shown
in Scheme 4.
Finally, we consider further the data in Table 2 to
demonstrate the electrophilic property of hydroxyl
radical in reference to the previous results of electron
density calculations. Comparison of the yields in Table
2 indicates that oxidation by p-benzoquinone is very
effective in the toluene and anisole cases, but not in the
Table 3. The isomer ratios and yields of cresols in the presence of
p-benzoquinone derivativesa,b
Oxidant
Concentrationc ortho:meta: Yieldd
(M)
para
(%)
None
p-Benzoquinone
2-Methyl-p-benzoquinone
2,5-di-tert-Butyl-p-benzoquinone
—
71:9:20
67:13:20
66:11:23
67:14:19
8
18
21
19
0.005
0.005
0.005
aA Corning 5-60 filter was used.
Comparing these new standard isomer distribution
ratios with those obtained from radiolysis of water or
reaction with Fenton’s reagent, it is interesting to note
bData obtained by repeating the experiment several times.
cConcentration of p-benzoquinone in toluene.
dYields are based on the original amount of 4 (0.01 M).
Table 4. The standard isomer ratio of phenols observed and the calculated HOMO coefficients of the aromatics
Benzenes
Isomer ratio observeda
ortho:meta:parab (%)
HOMO coefficientsc
ortho:meta:para
Toluene
Anisole
Nitrobenzene
72:10:18
82:1:17
27:47:26
0.6392 (39%):0.4646 (28%):0.5282 (32%)45
0.6754 (41%):0.4408 (27%):0.5295 (32%)
0.0287 (36%):0.0374 (47%):0.0136 (17%)45
aData obtained by the observed isomer ratio of phenols.
bData obtained by repeating the experiment several times.
cHOMO coefficients were calculated by CNDO/2.

H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
2287
Table 5. The yields of phenol in the presence or absence of p-benzo-
quinonea,b
by using this system under the appropriate photolysis
condition. In the presence of oxidant, the yield of phe-
nols with an electron-donating group in the aromatic
increased while the isomer ratio of the phenols is almost
the same as in the absence of the oxidant. In addition to
this, the yield and isomer ratio of phenol with an
electron-withdrawing group is almost constant in the
presence or absence of oxidant. Therefore it is demon-
strated that the new standard isomer distribution ratio
should be correct and that hydroxyl radical possesses
stronger electrophilic properties, compared to others
such as phenyl and methyl radicals.
X
CH3
OCH3
p-Benzoquinonec (M)
0
2
0.005
5
0
9
0.005
15
Yieldd (%)
aA Corning 5-60 filter was used.
bData obtained by repeating the experiment several times.
cConcentration of p-benzoquinone in toluene or anisole.
dYields are based on the original amount of 4 (0.01 M).
Experimental
Table 6. The isomer ratios of phenols in the reaction of toluene,
anisole and nitrobenzene with a-azohydroperoxide 4, radiolysis of
water and Fenton’s reagent
Toluene and benzene were treated with concentrated
sulfuric acid, washed with H2O, 5% NaOH aqueous
solution and H2O, dried over calcium chloride, and then
distilled. Anisole of guaranteed grade was treated with
5% NaOH aqueous solution, washed with H2O, dried
over calcium chloride, and distilled. Nitrobenzene of
guaranteed grade was dried over calcium chloride, and
distilled. These solvents were prepared by bubbling
argon gas for at least 10 min prior to use. p-Benzo-
quinone and 2,5-di-tert-butylbenzoquinone were recrys-
tallized from a mixture of ethanol and n-hexane (1:1)
and 2-methylbenzoquinone was sublimed before use.
Potassium ferricyanide, 1,1,1,3,3,3-hexamethyldisilazane
and pyridine were of guaranteed grade. A glass column
(3.0 mmÂ3.0 m) or a glass capillary column (20 m) was
used in a Shimadzu 6-AM gas chromatograph, with a
flame ionization detector (FID). Nitrogen was used as
the carrier gas. The packing materials and operating
conditions for separation of phenols are described
below. The average isomer ratios and yields of phenols
were obtained by repeating the same reaction run two
or three times. The proton nuclear magnetic resonance
(1H NMR) spectra were recorded at 60 MHz on a Var-
ian EM360A Spectrometer using tetramethylsilane
(TMS) as an internal reference. The infrared (IR) spec-
tra were recorded on a Hitachi 215 infrared spectro-
photometer. The ultraviolet (UV) spectra were recorded
on a JASCO UVIDEC-1 spectrophotometer. The ESI
mass spectra (ESI-MS) were recorded on a Plateform
LC-MS Spectrometer (Micromass). The mass spectra
(MS) were recorded on a Hitachi RMU-6M mass
spectrometer by GC-mass system.
Phenols
a-Azohydroperoxide
Radiolysis
of water
ortho:meta:para ortho:meta:para
Fenton’s
reagent
4
ortho:meta:paraa
Cresol
Methoxyphenol
Nitrophenol
72:10:18
82:1:17
27:47:26
49:20:3129
46:0b:5430
30:9:6131
71:5:2426
85:4:1127
24:30:4628
aData obtained by repeating the experiment several times.
bOnly a trace of m-methoxyphenol was detected.
that the ratios in this study differs from those by radi-
olysis, while there is a similar tendency with those from
the Fenton’s reagent, except for the ratios of nitrophe-
nols, as shown in Table 6. It seems to us that the dis-
crepancy of these values between radiolysis of water and
this study is strongly associated with facile formation of
the radical cation 7 in aqueous media (k6108 MÀ1
s
À1).30 As described, we could not achieve electron
transfer oxidation in this system with nitrobenzene and
p-benzoquinone, and are unable to deduce which ratio
is more precise. However, it is clearly demonstrated in
this study that attack of hydroxyl radical takes place
mainly at ortho–para positions when an electron-donating
group is substituted in 5 and it occurs mainly at the
meta position when an electron-withdrawing group is
substituted in 5. It is interesting to note that the ioni-
zation potential of hydroxyl radical (À13.0 eV)48 is the
lowest among other radicals such as phenyl radical
(À9.24 eV)48 and methyl radical (À9.84 eV),48 and it
suggests that hydroxyl radical has a strong electron
accepting property. In addition to this, we also recog-
nized that a 2Âpara/meta (p/m) value of 5b calculated
from the new isomer ratio was found to be 34.0 and this
value is much higher than that of phenyl radical (2p/m=
1.44),49 methyl radical (2p/m=1.47)
Therefore, we could finally confirm the strong electro-
philic properties of hydroxyl radical from both the
observed and calculated data.
49
and so on.
Preparation of [(4-bromophenyl)diazenyl](phenyl)methyl
hydroperoxide 4. To a solution of 4-bromophenyl-
hydrazine hydrochloride (3.58 g, 16.0 mmol) and
sodium acetate (1.97 g, 24.0 mmol) in water (50 mL)
and ethanol (50 mL) was added dropwise benzaldehyde
(1.63 mL, 16.0 mmol) at room temperature and the
resulting precipitate was filtered and purified by recrys-
tallization from carbon tetrachloride to give 3.90 g
(89.0%) of benzaldehyde 4-bromophenylhydrazone as
milk-white crystals. A suspension of benzaldehyde
4-bromophenylhydrazone (2.12 g, 7.70 mmol) in dry
benzene (20 mL) was stirred at room temperature in the
Conclusion
We discovered that 4 is a very good source for genera-
tion of hydroxyl radical in anhydrous media by photo-
lysis, and determined the new standard isomer
distribution ratio of phenols in aromatic hydroxylation

2288
H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
shade while oxygen gas was bubbled through the solu-
tion until 4-bromophenylhydrazone was completely
converted to 4. The suspension gradually turned yellow.
After stirring for 6 h, the resulting precipitate was fil-
tered and purified by recrystallization from benzene to
give 1.43 g (60.5%) of 4 as yellow crystals: mp 114–
115 ꢁC (dec., lit.50,51 mp 107–108 ꢁC). 1H NMR
(60 MHz, CD3CN)] d 6.05 (1H, s), 7.4–7.6 (5H, m), 7.7–
7.8 (4H, m), 10.35 (1H, s). IR (KBr, cmÀ1) 845 (o–o).
UV–vis [(CH3CN) lmax, nm (log e)]: 287 (4.22), 413
(2.36). ESI-MS m/z: 308 (MÀH)À. Anal. Calcd for
C13H11O2N2Br: C 50.81, H 3.58, N 9.12, Br 26.06.
Found: C 51.01, H 3.98, N 9.34, Br 25.98.50,51 The
molecular structure of 4, BrO2N2C13H1152 was identified
by X-ray crystal graphic analysis. Compound 4 is stable
at room teperature and can be stored at 4 ꢁC in the dark
for a couple of months. Biological activity tests such as
chemical carcinogen and inhibition of photosynthesis
were done.53,54
HP60–80;FID at 80 ꢁC constant) and the yields of
bromobenzene and benzaldehyde were determined.
b. From the solution utilized above, the solvent was
removed under the reduced pressure at room tem-
perature, and the resulting residue was analyzed by
GLC (3 mmÂ3 m, glass column, KG02 on Uniport
HP60–80;FID with temperature programing for 1 ꢁC/
min from 130 to 180 ꢁC) and the yields of cresol, benzyl
alcohol and bromomethyldiphenyl (X) were determined.
c. To the above residue was added fluorenone as an
internal standard, and the products were analyzed by
GLC (3 mmÂ3 m glass column, SF-96 on Uniport B
10% 60–80;FID at 160 ꢁC constant) and the yields of
dibenzyl and ditolyl were determined.
The structure assignment of these compounds was made
by GC-mass and GLC in comparison with the authentic
samples. Bromomethyldiphenyl (X) was separated from
the reaction mixture as a mixture of two components A
and B (a mixture of isomers) which have the following
spectroscopic properties. A: 1H NMR (60 MHz, CD3CN)
d 2.13 (3H, s;CH 3), 7.10–7.47 (8H, m;aromatic). MS m/z:
Photodecomposition of [(4-bromophenyl)diazenyl](phe-
nyl)methyl hydroperoxide 4 in toluene and water or aqu-
eous potassium ferricyanide solution. To a toluene
solution (10 mL) of 4 (61.5 mg, 0.20 mmol) in a Pyrex
tube was added distilled water (10 mL) or 1.0 mM
potassium ferricyanide solution (329 mg in 10 mL dis-
tilled water, pH=6.2). The mixtures were stirred vigor-
ously while they were irradiated with a 400 W high-
pressure mercury lamp (UVL-400P, Rikougakusangyo)
under argon gas at 12–15 ꢁC for 3 h. After removal of
the aqueous solution by filtration, each organic layer
was separated and dried over calcium chloride. To each
solution was added naphthalene as an internal standard,
and the mixture was directly analyzed by GLC (3
mmÂ3 m glass column, KG02 on Uniport HP60–80;FID
with temperature programing for 3 ꢁC/min from 80 to
180 ꢁC) and the yield of o-cresol was determined. From
each solution utilized above, the solvent was removed
under reduced pressure and the resulting residue was
treated with 1,1,1,3,3,3-hexamethyldisilazane. The mix-
tures including the trimethylsilyl ethers of cresols were
analyzed by GLC (3 mmÂ3 m glass column, KG02 on
Uniport HP60–80;FID at 80 ꢁC constant) and the
ortho/meta/para isomer ratio of cresols was determined.
1
248, 246 (1:1) (M)+, 167, 152. B: H NMR (60 MHz,
CD3CN) d 2.35 (3H, s;CH ), 7.20–7.35 (8H, m;aro-
3
matic). MS m/z: 248, 246 (1:1) (M)+, 167, 152.
Photodecomposition of 4 in anisole in the absence or pre-
sence of p-benzoquinone. 4 (92 mg, 0.30 mmol) and var-
ious concentrations of p-benzoquinone [(0 mg, 0 mmol),
(64.9 mg, 0.60 mmol), (162 mg, 1.5 mmol) or (324 mg, 3.00
mmol)] were dissolved in anisole (30 mL), respectively,
and the mixtures in a Pyrex tube were irradiated for 3 h in
the same manner as in the case of toluene. After removal of
excess solvent under reduced pressure at room tempera-
ture, each resulting residue was treated with 1,1,1,3,3,3-
hexamethyldisilazane and pyridine to analyze methox-
yphenols. After addition of naphthalene as an internal
standard, each trimethylsilyl ether of o-, m-, p-methox-
yphenol was analyzed by GLC (OV-101 glass capillary
column, 20 m; FID at 110 ꢁC constant) and the yield and
isomer ratio of the methoxyphenols were determined.
Photodecomposition of 4 in nitrobenzene in the absence
or presence of p-benzoquinone. 4 (92 mg, 0.30 mmol)
and various concentrations of p-benzoquinone [(0 mg, 0
mmol), (64.9 mg, 0.60 mmol), (162 mg, 1.5 mmol) or
(324 mg, 3.00 mmol)] were dissolved in nitrobenzene (30
mL), respectively and the mixtures in a Pyrex tube were
photolyzed in the same manner as described above. To
each reaction mixture was added 1,1,1,3,3,3-hexamethyl-
disilazane and pyridine to analyze nitorophenols. After
addition of benzophenone as an internal standard, each
trimethylsilyl ether of o-, m-, p-nitorophenol was ana-
lyzed by GLC (3 mmÂ3 m glass column, SF-96 on Uni-
Photodecomposition of 4 in toluene in the absence or pre-
sence of p-benzoquinone. 4 (92 mg, 0.30 mmol) and var-
ious concentrations of p-benzoquinone [(0 mg, 0 mmol),
(64.9 mg, 0.60 mmol), (162 mg, 1.5 mmol) or (324 mg,
3.00 mmol)] were dissolved in toluene (30 mL), respec-
tively, and the mixtures in a Pyrex tube were irradiated
for 3 h in the same manner as above. Each reaction
mixture was analyzed by GLC (KG-02 glass column) in
the same manner described above. The reaction mixture
in the absence of p-benzoquinone was devided into the
two parts of equal volume and one was used to analyze
cresol as described above. The other was used for ana-
lyzing bromobenzene, benzaldehyde, benzyl alcohol,
bromomethyldiphenyl, dibenzyl, ditolyl as follows.
ꢁ
port B 10% 60–80;FID at 160 C constant) and the yield
and isomer ratio of the nitrophenols were determined.
Photodecomposition of 4 in toluene in the absence or pre-
sence of p-benzoquinone by using a 400 W high pressure
mercury lamp with a Corning glass filter 5–60. 4 (92 mg,
0.30 mmol) and each concentration of p-benzoquinone
a. To the reaction mixture was added naphthalene as an
internal standard, and the mixture was directly analyzed
by GLC (3 mmÂ3 m glass column, KG02 on Uniport

H. Marusawa et al. / Bioorg. Med. Chem. 10 (2002) 2283–2290
2289
[(0 mg, 0 mmol) or (16.2 mg, 0.15 mmol) were dissolved
in toluene (30 mL), respectively, and the mixtures in a
Pyrex tube were irradiated through a Corning glass filter
with a 400 W high pressure mercury lamp under argon
gas at 22 ꢁC for 3 h. To each reaction mixture was
added naphthalene as an internal standard, then the
mixture was analyzed by GLC (3 mmÂ3 m glass col-
umn, KG02 on Uniport HP60–80;FID with tempera-
ture programing for 3 ꢁC/min from 70 to 180 ꢁC) and
the yield and isomer ratio of cresols, and the yield of
phenol were determined.
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Photodecomposition of 4 in anisole in the absence or pre-
sence of p-benzoquinone by using a 400 W high pressure
mercury lamp with a Corning glass filter 5–60. 4 (92 mg,
0.30 mmol) and each concentration of p-benzoquinone
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