Ozonolysis of phenols in aqueous solution

Article abstract of DOI:10.1039/b301824p

In the ozonolysis of phenol in aqueous solution at pH 3, 7 and 10 the following products were quantified: catechol, hydroquinone, 1,4-benzoquinone, cis,cis-muconic acid, H₂O ₂, 2,4-dihydroxybiphenyl and 4,4-dihydroxybiphenyl. At pH 10, material balance (products vs. phenol consumption) is obtained. Singlet dioxygen, O₂(¹Δ_g), and OH are formed as short-lived intermediates. The precursor of the latter, O₃^-, and a phenoxyl radical is suggested to arise from electron transfer from phenol/phenolate to ozone. Addition of OH to phenol gives rise to dihydroxyclohexadienyl radicals which add dioxygen and eliminate HO₂ thereby forming catechol/hydroquinone. In competition and catalysed by H⁺ and OH^-, the dihydroxycyclohexadienyl radical eliminates water yielding a phenoxyl radical. At pH 10, they readily oxidise catechol and hydroquinone. This reforms phenol (accounting for the low phenol consumption) and yields higher-oxidised products, eventually 1,4-benzoquinone, cis,cis-Muconic acid can be accounted for by the Criegee mechanism, while O₂(¹Δ_g) is released on the way to (some of the) catechol and hydroquinone. Similar reactions proceed with hydroquinone (products: 1,4-benzoquinone, 2-hydroxy-1,4-benzoquinone and H₂O₂, with high yields of O₂(¹Δ_g) and OH) and with catechol (products: 2-hydroxy-1,4-benzoquinone, cis,cis-muconic acid, H₂O₂ with high yields of O₂(¹Δ_g) and OH). Material balance is not obtained for these two systems. Pentachlorophenolate, pentabromophenolate and 2,4,6-triiodophenolate ions give rise to halide ions, O₂(¹Δ_g) (58%/48%/10%) and OH (27%/2%/0%). It is suggested that together with O₂(¹Δ_g) the corresponding ortho- and para-quinones plus a halide ion are formed. Further halide ion is released upon the hydrolysis of these and other products. For pentachlorophenolate the material balance with respect to the short-lived intermediates is 85%. With the bromo- and iodophenolates the O₂(¹ Δ_g) yields are substantially lowered, most likely due to release of triplet (ground state) dioxygen induced by the heavy atom effect.

Full text of DOI:10.1039/b301824p

View Article Online / Journal Homepage / Table of Contents for this issue
Ozonolysis of phenols in aqueous solution
a
b
Eino Mvula† and Clemens von Sonntag*
a
Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstrasse 15, D-04318 Leipzig,
Germany
b
Max-Planck-Institut für Strahlenchemie, Stiftstrasse 34-36, P.O. Box 101365,
D-45470 Mülheim an der Ruhr, Germany. E-mail: Clemens@vonSonntag.de
Received 14th February 2003, Accepted 28th March 2003
First published as an Advance Article on the web 14th April 2003
In the ozonolysis of phenol in aqueous solution at pH 3, 7 and 10 the following products were quantified: catechol,
hydroquinone, 1,4-benzoquinone, cis,cis-muconic acid, H O , 2,4-dihydroxybiphenyl and 4,4-dihydroxybiphenyl.
2
2
1
ؒ
At pH 10, material balance (products vs. phenol consumption) is obtained. Singlet dioxygen, O ( ∆ ), and OH are
formed as short-lived intermediates. The precursor of the latter, O3 , and a phenoxyl radical is suggested to arise
from electron transfer from phenol/phenolate to ozone. Addition of OH to phenol gives rise to dihydroxycyclo-
hexadienyl radicals which add dioxygen and eliminate HO thereby forming catechol/hydroquinone. In competition
and catalysed by H and OH , the dihydroxycyclohexadienyl radical eliminates water yielding a phenoxyl radical.
At pH 10, they readily oxidise catechol and hydroquinone. This reforms phenol (accounting for the low phenol
consumption) and yields higher-oxidised products, eventually 1,4-benzoquinone. cis,cis-Muconic acid can be
2
g
ؒ
Ϫ
ؒ
ؒ
2
ϩ
Ϫ
1
accounted for by the Criegee mechanism, while O ( ∆ ) is released on the way to (some of the) catechol and
2
g
hydroquinone.
Similar reactions proceed with hydroquinone (products: 1,4-benzoquinone, 2-hydroxy-1,4-benzoquinone and
1
ؒ
H O , with high yields of O ( ∆ ) and OH) and with catechol (products: 2-hydroxy-1,4-benzoquinone, cis,cis-
2
2
2
g
1
ؒ
muconic acid, H O with high yields of O ( ∆ ) and OH). Material balance is not obtained for these two systems.
Pentachlorophenolate, pentabromophenolate and 2,4,6-triiodophenolate ions give rise to halide ions, O ( ∆ )
58%/48%/10%) and OH (27%/2%/0%). It is suggested that together with O ( ∆ ) the corresponding ortho- and
2
2
2
g
1
2
g
ؒ
1
(
2 g
para-quinones plus a halide ion are formed. Further halide ion is released upon the hydrolysis of these and other
products. For pentachlorophenolate the material balance with respect to the short-lived intermediates is 85%.
1
With the bromo- and iodophenolates the O ( ∆ ) yields are substantially lowered, most likely due to release of
2
g
triplet (ground state) dioxygen induced by the heavy atom effect.
Introduction
dimerisation products of phenoxyl radicals have, in fact,
8,9
already been reported.
The ozonide radical, O3 , is only stable at high pH. It is in
Ϫ
Ozonation is widely used in drinking-water processing for dis-
ؒ
Ϫ
1,2
infection as well as for the removal of unwanted contamin-
ؒ
Ϫ
20
ؒ
equilibrium with O and O [reaction (2), pK = 6.26], and O
3
2
ants. There is an increasing concern about potential unwanted
ؒ
21
is in equilibrium with OH [reaction (3), pK = 11.8]. At all pH
a
by-products. Phenol and its derivatives often pose a problem.
Moreover, the omnipresent natural organic matter (NOM)
may contain phenolic groups. The aim to degrade phenols with
ozone has led to a large number of studies, in particular of its
values relevant for water processing, equilibria (2) and (3) are
ؒ
fully shifted towards OH.
ؒ
Ϫ
ؒ
Ϫ
O3
O ϩ O
2
(2)
(3)
4–16
parent,
but a detailed mechanistically-oriented study is still
missing. For a better understanding of the underlying pro-
cesses, especially also for an assessment of potential by-product
formation, such a study is urgently needed.
Upon deprotonation of phenol (pK = 10), the ozone rate
constant increases as much as six orders of magnitude (cf. Table
ؒ
ؒ
Ϫ
ϩ
OH
O
ϩ H
ؒ
As a consequence, the reactions of OH with phenol must be
a
8
taken into account. There is also the intriguing observation
that the consumption of phenol is low despite its high rate of
reaction with ozone. Thus, it is expected that the reaction of
ozone with phenol is much more complex than has been
thought before. In the present paper, some of these complexities
are disentangled. Although the main thrust of the paper is dir-
ected to the elucidation of the ozonolysis of phenol, data on the
ozonolysis of hydroquinone, catechol and highly halogenated
phenols will also be presented. The chemistries of the latter are
mechanistically quite interesting.
2
). Due to this large difference in rates, ozone reacts practically
only with the phenolate in equilibrium in neutral and slightly
acidic solutions. For studying the reactions specific to phenol,
the pH has to be lowered to <4.
Upon the ozonolysis of phenol, OH is formed.
recently suggested that this is due to an electron transfer from
ؒ
15–17
We have
7
18
7
phenolate/phenol to ozone [E (phenol) = 0.86 V ; E (ozone) =
17
1
.03 V] [reaction (1)], and this will be substantiated in the
present paper.
Ϫ
ؒ
ؒ
ϩ
ؒ
Ϫ
PhO /PhOH ϩ O3
PhO /PhOH ϩ O3
(1)
Experimental
Phenol, hydroquinone, catechol, pentachlorophenol, penta-
bromophenol and 2,4,6-triiodophenol were commercially avail-
able in high purity and used as received. For the quantification
of the products, cis,cis-muconic acid, 1,2,4-trihydroxybenzene,
In reaction (1), a phenoxyl radical is formed either directly or
19
via the phenol radical cation which is a strong acid (pK = Ϫ2)
a
and readily deprotonates. In the ozonolysis of phenol, the
1
,4-benzoquinone (resublimed) and 4,4Ј-dihydroxybiphenyl
†
On leave from the University of Namibia, Windhoek, Namibia
were also available as reference material. For the calibration of
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6
1749

View Article Online
ؒ
ؒ
2
-hydoxy-1,4-benzoquinone, 1,2,4-trihydroxybenzene was oxid-
OH ϩ (CH ) S᎐O
CH S(O)OH ϩ CH
3
(4)
3
2
᎐
3
22
ised with 1,4-benzoquinone, a reaction which proceeds
quantitatively.
Solutions were made up in Milli-Q-filtered (Millipore) water.
A dioxygen-fed ozonator (Philaqua, Gladbeck) was used to
produce the ozone stock solutions. Their ozone content was
23
Subsequent oxidation of methanesulfinic acid to methane-
sulfonic acid by some oxidising species does not materially alter
the assay as long as both are measured. Methanesulfinic acid is
ؒ
34
known to undergo a very efficient OH-induced autoxidation,
24,25
3
but this seems not to be the reason for the formation of methane-
sulfonic acid here, since the methanesulfinic acid to methane-
sulfonic acid ratio does not dependent on the DMSO concen-
tration. From the data shown in Table 1 (see below), it is
estimated that in the ozonolysis of phenol the OH radical yield
must be ∼22% at pH 10 and close to that at pH 7. It is recalled
that at both pH values the reacting species is the phenolate ion.
In the Bu OH assay, the measured products, formaldehyde
and 2-hydroxy-2-methylpropionaldehyde, result from the bi-
determined spectrophotometrically using ε(260)
= 3300 dm
Ϫ1
Ϫ1
mol cm . When the ozonation was carried out at pH 10, the
pH was lowered to pH 4 immediately after ozonation in order
to minimise the autoxidation of phenolic products and the
degradation of 1,4-benzoquinone.
Ozone rate constants were determined directly by stopped
flow by following the decay of ozone at 260 nm at a more than
ten-fold substrate concentration or with fast ozone reactions by
competition using buten-3-ol (k = 7.9 × 10 dm mol s )
as competitor. Stopped-flow experiments were carried out with
the help of a Biologic (SF3) instrument equipped with a diode
array system (Tidas–16, J&M, Aalen) for optical detection.
Formaldehyde yields were determined using the Hantzsch
method. Organic (hydro)peroxides and H O were quantified
with molybdate-activated iodide, either by following the kinet-
ics of this reaction or by post-column derivatisation.
The products were separated by HPLC on a reversed phase
column (RP18, 25 cm) using 25% methanol and 0.1% phos-
1
7
ؒ
t
26
4
3
Ϫ1 Ϫ1 27,28
t
molecular decay of the Bu OH-derived peroxyl radicals [e.g.,
reactions (5)–(7)].
35
ؒ
2(CH
)
)
C(OH)CH
OO
OO
3
3
2
2
2
2
29
ؒ
2CH O ϩ O ϩ 2 C(CH ) OH (5)
2 2 3 2
2
2
30
17,27,31
ؒ
ؒ
2(CH
C(OH)CH
2HC(O)C(CH
)
OH ϩ H
O
(6)
3
2
2
2
Ϫ1
2(CH ) C(OH)CH OO
3 2 2
HC(O)C(CH ) OH ϩ
O ϩ HOCH C(CH ) OH (7)
phoric acid in water as eluent at a flow rate of 1 ml min
3 2
[retention times (min): 1,2,4-trihydroxybenzene (3), hydro-
2
2
3 2
quinone (7.5), 2-hydroxy-1,4-benzoquinone (9), 1,4-benzo-
quinone (10), catechol (13), cis,cis-muconic acid (16.8), cis,
trans-muconic acid (17.5) and phenol (25)]. Under these
conditions, 2-hydroxy-1,4-benzoquinone and 1,4-benzoquin-
one peaks were not well resolved. A better separation was
obtained with 10% methanol and 0.1% phosphoric acid in
water as eluent [2-hydroxy-1,4-benzoquinone (14), 1,4-benzo-
quinone (16)] or water as an eluent [2-hydroxy-1,4-benzo-
quinone (4), 1,4-benzoquinone (45)]. 4,4Ј-Dihydroxybiphenyl
ؒ
To arrive at the OH yield in this assay in ozone reactions, the
formaldehyde yield has to be approximately doubled; the yield
of 2-hydroxy-2-methylpropionaldehyde is typically 1.3–1.4
17
times that of formaldehyde.
In the presence of other radicals or reducing agents such as
hydroquinone, they may undergo additional reactions, i.e. not
only self-termination reactions. This seems to have occurred in
the phenol system as well. The hydroquinone yield is reduced
and the 1,4-benzoquinone yield enhanced with respect to the
unscavenged system (see below). Thus, besides concluding that
(
3
10.5) and 2,4Ј-dihydroxybiphenyl (14) were separated using
0% acetonitrile in water as eluent. Upon standing, cis,cis-
ؒ
OH must play an important role, its quantification is not as
muconic acid partially isomerises into cis,trans-muconic acid,
and this has been accounted for whenever cis,cis-muconic acid
yields are reported.
precise as with the DMSO system.
ؒ
Ϫ
The yield of O2 may be determined with tetranitromethane
TNM, reaction (8)].
[
Halide ions were determined by ion chromatography (Dionex
DX100) on a AS9-HC column (with Ion Pac AG9-HC as pre
O2ؒϪ
ϩ C(NO2)
4
2
2 3
Ϫ
ؒ
O ϩ C(NO ) ϩ NO2
(8)
Ϫ3
Ϫ3
Ϫ3
column); eluent: 1.8 × 10 mol dm Na CO –1.7 × 10 mol
2
3
Ϫ3
Ϫ1
dm NaHCO at 1 ml min for chloride (10 min) and bromide
3
In peroxyl radical chemistry, the TNM assay is a very com-
36,37
Ϫ3
Ϫ3
Ϫ3
Ϫ3
(
25 min); 2 × 10 mol dm Na CO –0.75 × 10 mol dm
2
3
mon procedure,
but in ozone reactions this assay is not as
NaHCO for iodide (30 min). Methanesulfinic acid (5.8) and
3
straightforward (for the special requirements see ref. 17).
methanesulfonic acid (6.8) were separated on the AG14/AS14
Ϫ4
Ϫ3
Ϫ4
column; eluent: 4.5 × 10 mol dm Na CO –4.25 × 10 mol
2
3
Products of phenol ozonolysis
Ϫ3
dm NaHCO3.
Singlet dioxygen, O ( ∆ ), yields were determined by measur-
1
In the ozonolysis of phenol, the major products are hydro-
quinone, catechol, 1,4-benzoquinone and cis,cis-muconic acid.
At low phenol conversions, their yields increase nearly linearly
with increasing ozone concentration (Fig. 1).
Similar catechol (12.4%) and hydroquinone (8.6%), but
higher muconic acid (12.3%) yields were reported before. There
2
g
12
ing its fluorescence as has been described elsewhere.
Kinetic simulations were carried out with the help of the
Chemical Kinetics Simulator
TM
software, version 1.01 (from
IBM, Almaden Research Center).
8
are also low yields of the dimers of the phenoxyl radicals,
such as 2,4Ј-dihydroxybiphenyl and 4,4Ј-dihydroxybiphenyl
Results and discussion
(
determined at pH 10, cf. Table 1).
Scavenging experiments
Using only the small guard column for chromatography to
ؒ
speed up the elution of phenol and of the dihydroxybiphenyls
gave no evidence for the formation of high-molecular-weight
material.
It has been mentioned in the Introduction that OH is formed in
the reaction of ozone with phenol. This conclusion is based on
ؒ
OH-scavenging experiments with DMSO and tertiary butanol
Bu OH). This approach has been discussed in detail in recent
t
(
Phenol consumption
17,32
studies,
and only a brief account will be given here for a
better understanding of the results presented below.
Compared to phenol, DMSO and Bu OH react with ozone at
negligible rates even if present at reasonable excess (cf. Table 2).
The DMSO assay is superior, since scavenging of OH yields
For measuring the destruction of phenol as a function of the
ozone concentration, lower phenol concentrations have to be
used. Under these conditions and at pH ∼7, only 0.48 mol
phenol are destroyed per mol ozone consumed (Fig. 2).
t
ؒ
immediately the detected product, methanesulfinic acid which is
formed in 92% yield [reaction (4)].
An even more pronounced deviation from stoichiometry
(0.33) has been reported before. The value of such measure-
33
8
1
750
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6

View Article Online
Table 1 Ozonolysis of phenol. Products and their yields in % of ozone consumed. When more than one value is given, further runs at four or five
ؒ
t
ؒ
Ϫ
different ozone concentrations were carried out. Some experiments were carried out in the presence of scavengers ( OH: Bu OH, and DMSO; O
:
2
tetranitromethane, TNM; see text)
Product (Scavenger)
≤ pH 3
pH 6–7
pH 10
a
a
Hydroquinone
Hydroquinone (Bu OH)
1.6/1.1
—
4.8/1.8
—
13.3/16
< 1
13.6
2
4.6/4.6
13
2.8
2.0
—
—
0.8
—
20
—
32
—
1
—
∼1
∼1
8
11
—
16
4
—
—
—
2
t
Catechol
Catechol (Bu OH)
t
a
1
1
,4-Benzoquinone
,4-Benzoquinone (Bu OH)
9.6/10.4/6.1
t
—
a
cis,cis-Muconic acid
cis,cis-Muconic acid (Bu OH)
4.8/4.0/3
t
—
—
—
Absent
10/11
—
—
—
3
—
—
8.5
—
4
2
,4Ј-Dihydroxybiphenyl
,4Ј-Dihydroxybiphenyl
1
12
Singlet dioxygen, O ( ∆ )
5.6
2
g
t
Formaldehyde (Bu OH)
-Hydroxy-2-methylpropionaldehyde (Bu OH)
14/13/12
15.4
—
—
—
Absent
2.6
4.8
t
2
Methanesulfinic acid (DMSO)
Methanesulfonic acid (DMSO)
Nitroform anion (TNM)
Organic (hydro)peroxide
Organic (hydro)peroxide (Bu OH)
Hydrogen peroxide
Hydrogen peroxide (Bu OH)
Hydrogen peroxide (DMSO)
Phenol consumption
Phenol consumption (Bu OH)
t
t
16
—
—
59
—
33
13
48
42
a
a
a
t
a
—
—
a
Ϫ4
Ϫ3
At [phenol] = 2.5 × 10 mol dm ; —: not determined.
Ϫ3
Ϫ3
Ϫ4
Ϫ3
Fig. 1 Ozonolysis of phenol (3 × 10 mol dm ) in aqueous solution
at pH 7. Yields of hydroquinone (∆), catechol (ꢀ), 1,4-benzoquinone
(
Fig. 2 Ozonolysis of phenol (2.5 × 10 mol dm ) in aqueous
solution. Consumption of phenol as function of the ozone
concentration at pH 3 (ꢀ), 7 (ᮀ) and 10 (᭹).
a
᭺) and cis,cis-muconic acid (᭹) as
a function of the ozone
concentration.
At pH 7, the consumption value is higher, in agreement with
a now higher k for the reaction of ozone with phenol (kobs
≈
obs
Ϫ1 Ϫ1
ments is debatable. In general, consumption yields can only be
measured at a reasonable turnover of the substrate, otherwise
the deviation from the untreated sample is too small. As a con-
sequence, at a low turnover large errors are involved, because
small changes of a large value have to be measured. At high
conversions, which yield a reasonable decrease of the substrate
concentration that can be measured with confidence, the com-
petition of the products for the reagent (here: ozone) consumes
the reagent and hence results in a low substrate consumption
yield. At pH 3, the yields of the major products are indeed all
much lower than when the experiments were carried out at a
6
3
1
0 dm mol s ), but major aspects that were discussed for the
situation at pH 3 persist.
At pH 10, the rate of reaction of phenol and that of all
9
3
Ϫ1 Ϫ1
phenolic products is about the same (kobs ≈ 10 dm mol s ),
and the rate constants of cis,cis-muconic acid and of 1,4-benzo-
quinone are now lower. Under such conditions, the competi-
tion of phenol and its products is now “on equal terms”, and
the consumption value, although still somewhat too low, is now
meaningful. The fact that it is below unity is of importance as
far as mechanistic aspects are concerned.
∼
10-fold higher phenol concentration (Table 1). Thus, the com-
Mechanistic considerations
petition in the reactions between phenol plus ozone and ozone
5
0
plus products must have been effective. At this pH, the rate
While in the case of olefins the Criegee mechanism dominates
27,51
3
3
Ϫ1 Ϫ1
constant of ozone with phenol is only 1.3 × 10 dm mol s ,
while those of the potential products are all one to two orders
of magnitude higher (Table 2). Thus, they readily interfere
leading to a low consumption value, i.e. this value is of no
significance as far as the mechanism is concerned.
and free-radical pathways are typically absent,
free radicals
ؒ
play an important role in the ozonolysis of phenol, since OH is
formed in ∼22% yield. The reactions of OH with phenol are
well known. The electrophilic OH adds preferential to the
ortho- (48%) and para-positions (36%) [reactions (9) and (10)].
ؒ
ؒ
52
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6
1751

View Article Online
3
Ϫ1 Ϫ1
Table 2 Compilation of rate constants (unit: dm mol
s ) relevant for the present study. These values were used for modelling
Reaction
Rate constant
Reference
3
9
5
5
Phenol ϩ O3
Phenolate ϩ O3
Catechol ϩ O3
products
products
products
1.3 × 10
1.4 × 10
3.1 × 10
38
38
39
5
.2 × 10 at pH 7
This work
39
This work
This work
This work
This work
This work
This work
40
41
21
21
42
42
42
42
42
6
Hydroquinone ϩ O3
products
1.5 × 10
2
1
6
.3 × 10 at pH 7
6
.8 × 10 at pH 3
6
Pentachlorophenolate ϩ O3
Pentabromophenolate ϩ O3
products
products
products
1.2 × 10
1.7 × 10
6.8 × 10
2.5 × 10
4 × 10
6
6
2
1
,4,6-Triiodophenolate ϩ O3
,4-Benzoquinone
3
4
cis,cis-Muconic acid
ؒ
Ϫ
ؒ
O ϩ O
3
Ϫ
9
O
ϩ O3
1.6 × 10
∼ 1 × 10
∼ 1 × 10
2
2
ؒ
10
10
8
OH ϩ Phenol
OH-adduct radicals
ؒ
OH ϩ Phenolate ion
OH-Adduct radicals
OH-Adduct radicals ϩ O2
OH-Adduct-peroxyl radicals
OH-adduct radicals
products
2
2 × 10 (2k)
9
OH-adduct-peroxyl radicals
1.2 × 10
ؒ
5
Ϫ1
Ϫ1
HO2 ϩ products
1.3 × 10 s
3
p-OH-Adduct radical
o-OH-Adduct radical
p-OH-Adduct radical
o-OH-Adduct radical
Phenoxyl ϩ H O
Phenoxyl ϩ H O
Phenoxyl ϩ H O (H -catal.)
Phenoxyl ϩ H O (H -catal.)
1.8 × 10 s
2
Very slow
1.7 × 10
(1.1–2.1) × 10
2
ϩ
9
42
42
43
44
2
ϩ
8
9
2
2
Phenoxyl Products
2.6 × 10 (2k)
9
2
.3 × 10 (2k)
ؒ
Ϫ
9
Phenoxyl ϩ O2
products
≥ 1 × 10
cf. ref. 45
46
47
48
48
21
21
49
8
2
Semiquinone
hydroquinone ϩ 1,4-benzoquinone
3.1 × 10
3
Ϫ1
Cyclohexadienone
Phenol
3.8 × 10 s
t
Ϫ3
O ϩ Bu OH
products
products
products
products
∼1 × 10
8
6 × 10
7 × 10
3
O ϩ DMSO
3
ؒ
ؒ
t
8
OH ϩ Bu OH
OH ϩ DMSO
O2 ϩ C(NO2)4
9
ؒ
Ϫ
Ϫ
ؒ
9
O ϩ C(NO ) ϩ NO
2 × 10
2
2
3
2
Addition to the meta-position [reaction (11), 8%] and phenoxyl
radical formation [reactions (12)/(17) and (13), 8%] are of lesser
importance. In acidic and basic solutions, the dihydroxycyclo-
hexadienyl radicals rapidly eliminate water giving rise to further
minor in comparison (for potential additional decay pathways
42
see ref. 54).
53
phenoxyl radicals [reactions (14)–(16)].
ؒ
Ϫ
The formation of O2 in these reactions may, in principle,
ؒ
Ϫ
induce a chain reaction, since O
readily reacts with ozone
2
ؒ
Ϫ
ؒ
48
giving rise to O3 [reaction (23)] and hence to OH.
ؒ
Ϫ
ؒ
Ϫ
O2 ϩ O3
O ϩ O3
(23)
2
However at pH 10, the reaction of ozone with phenolate is so
fast that this reaction can be neglected at the phenol concen-
Ϫ3
Ϫ3
trations used ([phenol] = 3 × 10 mol dm ). Even at pH 7 the
3
Ϫ1
rate of reaction of ozone with phenol is too fast (∼3 × 10 s )
to allow reaction (23) to compete effectively (≤2% of total
ozone reaction). At pH 3, its contribution is ∼3% as has been
Ϫ3
determined with the help of the TNM assay ([TNM] = 1 × 10
Ϫ3
mol dm ). This assay can only be carried out with confidence
at this low pH, because the hydroquinone anion reacts too
rapidly with TNM, even at the low concentrations in equi-
librium present at pH ∼7. At pH 3, however, this reaction is
sufficiently slow, and the nitroform anion yield is significant.
The low value observed under these conditions is due to the
Ozone is generated from dioxygen, and dioxygen is always
present in excess over ozone. Therefore, one has to take into
account that the dihydroxycyclohexadienyl radicals react with
ϩ
rapid H -catalysed water elimination which prevents dioxygen
ؒ
ؒ
Ϫ
42
dioxygen [e.g., reactions (18) and (19)], and release HO /O
from reacting with the dihydroxycyclohexadienyl radicals.
2
2
ؒ
2
41
ؒ
[
pK (HO ) = 4.8] [reactions (20) and (22)] (for rate constants
These data now allow us to distinguish between OH form-
ation by an electron transfer [reactions (1)–(3)] or via an O2
a
42
ؒ
Ϫ
see Table 2). The main products from these reactions are
hydroquinone and catechol (the analogous routes to the latter
are not shown). There are competing reactions, but they are
-
induced reaction as favoured in a study on methoxylated ben-
55,56
zenes.
There, it has been suggested that the ozone adducts of
1
752
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6

View Article Online
Ϫ1
the type formed according to reaction (24) may decompose into
two radicals one of which being O2 [reaction (25)].
energy by 105 kJ mol but violates the spin conservation rule.
ؒ
Ϫ
Spin orbit coupling (heavy atom effect) as in the halide ions
1
1
bromide [54% O ( ∆ )] and iodide [14% O ( ∆ )] are typical
2
g
2
g
12
examples. Long lifetimes of the ozone adduct may also allow
58
the release of triplet dioxygen. A case in point may be the
59
triethylamine system. Thus, it is possible that in basic solu-
1
tions the O ( ∆ ) yield does not necessarily fully reflect the yield
2
g
of reactions such as (26).
At pH 7, the yields of 1,4-benzoquinone and H O match.
This may be accidental (cf. the low H O yield at pH 10, where
ؒ
ؒ
2
Ϫ
ؒ
At pH 3, the HO /O yield is 3% (see above), while the OH
2
2
2
yield at this pH is about the same as that at the higher pH
values, i.e. ∼22%, as is evident from the very similar formalde-
hyde yields in the presence of Bu OH under these three condi-
tions. We, therefore, exclude the superoxide pathway [reactions
2
2
hydroquinone is expected to autoxidise quite fast autocatalyti-
t
60,61
cally
to these products). If not, reactions (34)–(39) should
be considered which are, in major aspects, analogous to the
established Criegee mechanism. The 1,4-addition pathway is
supported by products observed in the ozonolysis of methoxy-
ؒ
(
25), (23), (2) and (3)] as a major contribution to OH
formation.
At pH 7, the water elimination reactions (14) and (15) are too
slow (cf. Table 2) to compete with the addition of dioxygen [cf.
reactions (18) and (19)]. Due to some competing reactions, the
yield of catechol is 40% and that of hydroquinone is 30% of the
OH yield, i.e. lower than that of their precursors, the corre-
sponding dihydroxycyclohexadienyl radicals. From these data,
62
lated benzenes.
ؒ
42
we calculate that a catechol yield of ∼9% and a hydroquinone
ؒ
yield of ∼7% is formed via OH. The much higher catechol
(
∼14%) and hydroquinone yields (∼15%, Table 1) clearly show
that there must be further routes to these products. The observ-
1
12
ation that O ( ∆ ) is among the products strongly indicates
2
g
that reactions (24), (26)–(28) take place. A similar reaction
sequence leading to hydroquinone can be written for an ozone
attack at the para position.
Protonation of the para-adduct gives rise to a hydrotrioxide
[
reaction (40)]. Hydrotrioxides are common intermediates in
63–69
the ozonolysis of aliphatic compounds, e.g., of alcohols.
They yield the corresponding carbonyl compound, often with
very few side reactions. Mechanistic details are not yet fully
elucidated. Reaction (41), assisted by a water molecule as a
relay to allow for a six-membered transition state, could also be
a route to 1,4-benzoquinone and H O , but this must remain a
2
2
tentative suggestion.
In the context of the formation of 1,4-benzoquinone and
ؒ
ؒ
H O , the fate of HO /O
2
Ϫ
must be discussed. Its yields are
2
2
2
ؒ
42
abundant at pH 7 (∼70% of the OH yield, i.e. ∼15% of
reacted ozone). At pH 10 it is lower because of the competition
Ϫ
of the OH -induced water elimination and dioxygen addition.
In competition, the ozone adduct may close the ring yielding
the Criegee intermediate [reactions (29) and (30)]. Ring opening
and water elimination gives rise to cis,cis-muconic acid [reac-
tions (31) and (32)]. In all other systems that have been investi-
gated thus far, the α-hydroxyhydroperoxide eliminated H O
It can undergo two radical–radical reactions, self-termination
and a reaction with the phenoxyl radical. The self-termination
6
3
Ϫ1 Ϫ1 41
is slow at pH ∼7 (kobs< 10 dm mol s ), but its reaction with
4
5
phenoxyl radicals is fast. Reduction by electron transfer has
70,71
been considered
(this would contribute to the low value of
2
2
2
7,51
[cf. reaction (33)],
and a water elimination has never been
phenol consumption), but addition seems to be an even more
45,72
observed. In the present system, however, the elimination of
H O2 seems not to occur. The high molar absorption co-
2
important pathway.
In the present system, this could contri-
bute to 1,4-benzoquinone formation [reactions (42)–(44)].
efficients of muconic systems would have allowed us to detect
the aldehyde in the HPLC chromatogram. Interestingly, cis,cis-
muconic acid is even observed in basic solutions, conditions
that normally favour the elimination of H O . Reactions such
2
2
as (33) are reversible, and this could account for the formation
of cis,cis-muconic acid despite the fact the k33 is very likely
much larger than k32 [reaction (32) is irreversible].
The analogous reaction, addition to the ortho position,
would lead to 1,2-benzoquinone. There is no evidence for its
formation. This is not surprising, since it is a stronger oxidant
than 1,4-benzoquinone and would oxidise hydroquinone, i.e.
the final product of this reaction would again be 1,4-benzo-
quinone. Since other reactions compete for the phenoxyl radi-
The yield of cis,cis-muconic acid strongly depends on the pH.
It is highest at low pH and low at high pH (Table 1). The inverse
1
has been observed for the O ( ∆ ) yields. This can be accounted
2
g
for by equilibrium (29). At high pH, the hydrotrioxide anion
will have a longer lifetime allowing a more efficient elimination
1
ؒ
Ϫ
ؒ
41
of O ( ∆ ) [reaction (26)]. Concomitantly, the yield of catechol
cals as well, some O2 /HO2 will remain and slowly decay
forming H O and dioxygen.
2
g
(
and hydroquinone) are increased [cf. reactions (27) and (28)].
2
2
The present system seems to be related to the ozonolysis of
At pH 10 (to some extent also at pH 7), catechol and hydro-
quinone are largely dissociated. Their monoanions react readily
with the phenoxyl radicals [e.g., reaction (45)]. This reaction
consumes phenoxyl radicals and reforms phenol [reaction (46)].
It mainly accounts for the low consumption of phenol at
1
pyrimidines, where O ( ∆ ) is only released, when ozone is
2
1
g
2,57
reacted with the anion.
1
Although the O ( ∆ ) yield often matches that of the corre-
2
g
sponding product, there are cases, where release of triplet
ground state) dioxygen takes place. This process is lower in
73
(
this pH. The semiquinone radicals [pK = 4, equilibrium (47)]
a
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6
1753

View Article Online
disproportionate yielding 1,4-benzoquinone and hydroquinone
similarly at pH 7 it is impossible to put up a material balance
based on the observed products. The best condition for trying a
material balance is pH 10. At this pH, we observe ∼1% hydro-
quinone, 20% catechol, 32% 1,4-benzoquinone and 2% dimers
[reaction (48)].
(
3% correcting for the missing ones). The dimers contain two
phenol units, and their yield has to be doubled for a material
balance. The sum of this is ∼59%. A few percent, e.g. products
ؒ
derived from OH addition to the meta-position and reactions
ؒ
competing with the HO -elimination (together ∼3%), must
2
remain undetected. It has been discussed above that the con-
sumption value determined with a low phenol concentration is
always on the low side. Thus, product yields (∼62%) and phenol
consumption (∼59%) are in reasonable agreement.
Hydroquinone and catechol
At pH 10, phenoxyl radicals are formed in ∼22% yield via
The quantifiable products of the ozonolysis of hydroquinone
and catechol at pH ∼7 are given in Table 3.
reaction (1). Further phenoxyl radicals are generated upon the
Ϫ
OH -induced water elimination from the dihydroxycyclo-
It is seen from this table that the material balance is
incomplete, and it is not adequate to discuss the chemistries of
hydroquinone and catechol ozonolysis in detail. In many
aspects, they follow similar lines as depicted above for their
parent, phenol. Hydroxyl radicals are major intermediates in
both systems (hydroquinone: ∼33%; catechol: ∼22%). Their
formation is connected with that of semiquinone radicals,
and further semiquinone radicals may be formed upon the
hexadienyl radicals [reactions (14)–(16)]. These reactions com-
pete with the addition of dioxygen [e.g., reactions (18) and (19)].
The dioxygen concentration in the ozone stock solution was
Ϫ3
Ϫ3
close to 1.25 × 10 mol dm (saturation), while the phenol solu-
tion which was reacted with the ozone stock solution was air-
Ϫ4
Ϫ3
Ϫ
saturated ([O ] = 2.5 × 10 mol dm ). If the OH -induced
2
ϩ
water elimination is as fast as the fast H -induced reaction (∼2 ×
0 dm mol s ) only a fraction of the dihydroxycyclohexa-
9
3
Ϫ1 Ϫ1
ؒ
1
reaction of OH with hydroquinone/catechol (detailed studies
dienyl radicals are converted into phenoxyl radicals, the major
part (>50%) still reacts with dioxygen, i.e. the phenoxyl radical
yield is ∼30% at pH 10. The dimer yields formed under these
conditions, e.g. 4,4Ј-dihydroxybiphenyl [reactions (49) and
as for phenol are not available). The 1,4-semiquinone radicals
disproportionate into hydroquinone and 1,4-benzoquinone.
Correspondingly, the 1,2-semiquinone radicals could dispro-
portionate into catechol and 1,2-benzoquinone (not detected,
(
50)], are low in comparison, altogether a few percent including
the other dimers, 2,2Ј-dihydroxybiphenyl, 2-phenoxyphenol and
-phenoxyphenol. The latter were not quantified in the present
study, but according to a detailed study on the dimerisation of
possibly unstable under our conditions). Another major inter-
1
mediate is O
( ∆
) (hydroquinone: 16%, catechol: 14%). The
2
g
4
corresponding product could be 1,2,4-trihydroxybenzene if
ozone adds preferentially to the ortho-positions of these
substrates [cf. reactions (26)–(28)]. This product is not
observed. This is not surprising, because it is readily oxidised to
44
phenoxyl radicals, the ones measured here represent 70% of the
total dimer yield. High dimer yields have been reported in earlier
8,9
22
studies, but they were not related to ozone consumption
2-hydroxy-1,4-benzoquinone by 1,4-benzoquinone, whereby
1
,4-benzoquinone is reduced to hydroquinone, the educt
[reaction (51), for the kinetics of this reaction see ref. 23].
The substituted phenols that make up the dimers have also
lower reduction potentials than phenol and are readily oxidised
by the phenoxyl radical. The rearrangement of cyclo-
2
-Hydroxy-1,4-benzoquinone is a major product in both
t
44
systems. Yet in the presence of Bu OH which does not interfere
with O ( ∆ ) formation, it is practically no longer present as
shown for the hydroquinone system. Under these conditions,
1
hexadienones [cf. reactions (21), (28) and (50)] is speeded up by
2
g
74,75
proton catalysis
(and likely also by base catalysis). In neu-
the yield of 1,4-benzoquinone is strongly enhanced, i.e. the
tral solution, it occurs at the sub-millisecond time scale (Table
t
Ϫ3
Ϫ3
Bu OH-derived peroxyl radicals certainly interfere at one stage.
2
). At the phenol concentration used here (3 × 10 mol dm ),
Quinones are good radical scavengers. Whether 2-hydroxy-1,4-
benzoquinone, which is deprotonated under these conditions
and combines the properties of a quinone and an enolate, is
capable of scavenging the Bu OH-derived peroxyl radicals has
the intrinsic half-life of the ozone reaction is ∼0.25 ms at pH 7
and < 1 µs at pH 10. Of course, the time required for complete
mixing is much higher, but these values indicate the time scale
of the reaction during the mixing procedure. At a typical ozone
46
t
Ϫ4
Ϫ3
not yet been studied.
concentration of 1 × 10 mol dm , the phenoxyl yield is ∼3 ×
Ϫ5
Ϫ3
In the ozonolysis of catechol, the Criegee-type product,
cis,cis-muconic acid, is formed in a ∼10% yield. The corre-
sponding products that might have been formed in the ozon-
olysis of hydroquinone (potentially a complex mixture of
non-muconic compounds) were not detected.
1
0
mol dm . They decay with a (first) half-life of 150 µs.
Thus in the batch experiment, the time scale of all these
reactions may be at least similar. This will be different upon
continuous ozonation. As the ozonation proceeds, the cyclo-
hexadienones have plenty time to rearrange. Upon continuous
ozonation this may eventually lead to the formation of high-
molecular-weight products, especially at high turnovers, but
with our batch system and with low turnovers significant
amounts of oligomerisation products were not observed.
Halogenated phenols
Pentachlorophenol has been used in many countries, e.g. in
China, for years in large quantities as a herbicide and to fight
snail fever. Although discontinued, some drinking-water
resources are still contaminated due to its slow biodegradation.
Material balance
76,77
From the above discussion, it is obvious that at low pH and
Its ozonolysis has already found some attention.
Here, we
1
754
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6

View Article Online
Ϫ3
Ϫ3
Table 3 Ozonolysis of hydroquinone and catechol (3 × 10 mol dm ). Products and their yields in % of ozone consumed. Some experiments were
ؒ
t
carried out in the presence of OH scavengers, Bu OH and DMSO
Product
Hydroquinone
Catechol
1
1
1
2
2
2
1
,4-Benzoquinone
13/12
36/32
30
11
<1
<1
Absent
16
Absent
Absent
Absent
7.4
—
—
t
,4-Benzoquinone (Bu OH)
,4-Benzoquinone (DMSO)
-Hydroxy-1,4-benzoquinone
-Hydroxy-1,4-benzoquinone (Bu OH)
-Hydroxy-1,4-benzoquinone (DMSO)
t
,2,4-Trihydroxybenzene
Absent
14
1
Singlet dioxygen, O ( ∆ )
2
g
Hydrogen peroxide
5.6
14
5.1
—
7.2
Absent
—
Absent
11
—
t
Hydrogen peroxide (Bu OH)
Hydrogen peroxide (DMSO)
Organic (hydro)peroxides
10.4
Absent
1.9
Absent
21/20
Absent
23
t
Organic (hydro)peroxides (Bu OH)
Formaldehyde
t
Formaldehyde (Bu OH)
2
2
-Hydroxy-2-methylpropionaldehyde
-Hydroxy-2-methylpropionaldehyde (Bu OH)
t
—
Methanesulfinic acid (DMSO)
Methanesulfonic acid (DMSO)
Substrate consumption
6
27
47
48
Absent
22
47
a
a
t
a
Hydroquinone consumption (Bu OH)
—
a
Ϫ4
Ϫ3
At [substrate] = 2.5 × 10 mol dm ; —: not measured.
1
12
t
ؒ
17
Table 4 Yields of halide ions, O ( ∆ ), formaldehyde in the presence of Bu OH, and OH calculated from the latter data, expressed as % of ozone
2
g
ؒ
t
consumed, in the ozonolysis of some halogenated phenolates. Some experiments were carried out in the presence of the OH scavenger Bu OH
1
t
ؒ
Phenolate
Halide ion
O ( ∆ )
CH O (Bu OH)
OH
2
g
2
Pentachlorophenolate
Pentabromophenolate
235
340
106
58
48
10
13
1
Absent
27±4.5
2
Absent
2
,4,6-Triiodophenolate
have included pentabromophenol and 2,4,6-triiodophenol,
because in our study on the OH-induced reactions of this class
shown to be two-fold, addition to the ring [47%, e.g. reaction
ؒ
78
(55)] and electron transfer (53%). The sequence of reactions
ؒ
of compounds we had noticed most interesting substituent
for the ortho- OH-adduct is shown in reactions (55) and (56).
78
effects (addition to the ring vs. electron transfer). These halo-
78
genated phenols have low pK values (ranging from 4.5 to 6.6).
a
While the phenolates are reasonably soluble in water, the
phenols are not. Hence, only the ozonolysis of the phenolates
was studied. Their rate constants with ozone, realised to be high
77
but unknown, were determined by competition against buten-
In reaction (55), a geminal chlorohydrine is formed. Geminal
4
3
Ϫ1 Ϫ1
3
-ol for which a rate constant of 7.9 × 10 dm mol
s
is
chlorohydrins loose HCl within less than a few µs [cf. reaction
27
27
reported. It yields formaldehyde in 100% yield, and since
formaldehyde is not a product of the ozonolysis of the halogen-
ated phenolates, the competition can be based on this product.
The rate constants obtained from these data (not shown) are
compiled in Table 2.
79,80
(
56)].
Kinetic details (decay of the intermediates formed
in these reactions including that of the pentachlorophenoxyl
radical, release of HCl at short and long times) have been
78
measured, but mechanistic suggestions remained tentative.
However, a typical feature of these reactions is the release of
1
12
ؒ
In Table 4, the yields of halide ion, O ( ∆ ) and of OH are
2
g
ؒ
more than one chloride ion per OH, and this feature is also
shown. In the case of pentachlorophenolate, the chloride yield
increased with time. For obtaining quasi-stable conditions, hal-
ide ion yields were therefore measured one day after ozonolysis.
No attempt has been made to follow the kinetics of halide ion
reflected in the ozonation data shown in Table 4. Furthermore,
tetrachloro-1,4-benzoquinone is well known to hydrolyse quite
81
rapidly in two distinct steps [reactions (57) and (58)].
ؒ
release. The OH yields were calculated from the formaldehyde
t
yields in the presence of a large excess of Bu OH.
For pentachlorophenolate, a reasonable ozone balance
ؒ
(
∼85%) with respect to the short-lived intermediates, OH and
1
O ( ∆ ), is obtained. As an example, the process that must
occur, when the ortho-ozone-adduct releases O ( ∆ ) are shown
2
g
1
In the case of pentabromophenolate, the ozone balance vs.
2
g
1
ؒ
O ( ∆ ) plus OH seems to be much poorer. However as in the
in [reactions (52)–(54)].
2
g
12
case of the bromide and iodide ions, the heavy atom effects are
likely to have broken the spin conservation rule, and the O ( ∆ )
1
2
g
yield reflects the ozone addition/dioxygen elimination pathway
only to some extent. In the case of the 2,4,6-triiodophenolate,
1
this must be a fortiori so, and a substantial drop in the O ( ∆ )
2
g
yield is indeed observed (Table 4). We, therefore, tentatively
suggest that with the latter two practically only the ozone addi-
tion/dioxygen elimination pathway occurs. This now raises the
question, why with 2,4,6-triiodophenolate the iodide yield is
The resulting product is tetrachloro-1,2-benzoquinone, and
tetrachloro-1,4-benzoquinone (chloranil) is formed, when
ozone adds to the para position. The reaction of OH has been
ؒ
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6
1755

View Article Online
stoichiometric with respect to ozone consumption, while with
pentabromophenolate ∼3 mol bromide are released per mol
ozone reacted. Considering the dramatic drop in the rate of
hydrolysis of tetrachloro-1,4-benzoquinone to 2-hydroxy-
trichloro-1,4-benzoquinone, it is possible that the quinones
derived from 2,4,6-triiodophenolate do not yet hydrolyse on the
time scale that we are concerned with here.
34 R. Flyunt, O. Makogon, M. N. Schuchmann, K.-D. Asmus and
C. von Sonntag, J. Chem. Soc., Perkin Trans. 2, 2001, 787.
3
3
5 M. N. Schuchmann and C. von Sonntag, J. Phys. Chem., 1979, 83,
7
80.
6 C. von Sonntag and H.-P. Schuchmann, Angew. Chem., Int. Ed.
Engl., 1991, 30, 1229.
37 C. von Sonntag and H.-P. Schuchmann, in Peroxyl Radicals,
81
ed. Z. B. Alfassi, Wiley, Chichester, 1997, p. 173.
8 J. Hoigné and H. Bader, Water Res., 1983, 17, 185.
9 M. D. Gurol and S. Nekouinaini, Ind. Eng. Chem. Fundam., 1984,
3
3
Conclusion
2
3, 54.
4
4
0 A. Leitzke and C. von Sonntag, unpublished results.
1 B. H. J. Bielski, D. E. Cabelli, R. L. Arudi and A. B. Ross, J. Phys.
Chem. Ref. Data, 1985, 14, 1041.
Natural waters always contain some organic matter (NOM).
This material, often related to lignin, may contain phenolic
groups. As shown in the present study, ozonolysis of phenols in
4
2 E. Mvula, M. N. Schuchmann and C. von Sonntag, J. Chem. Soc.,
Perkin Trans. 2, 2001, 264.
ؒ
aqueous solution gives rise to large amounts of OH. This now
ؒ
3
explains, why OH formation is observed at the early stages of
an ozone treatment in drinking-water processing.
43 G. N. R. Tripathi and R. H. Schuler, J. Chem. Phys., 1984, 81, 113.
4
4
4 M. Ye and R. H. Schuler, J. Phys. Chem., 1989, 93, 1898.
5 N. d’Alessandro, G. Bianchi, X. Fang, F. Jin, H.-P. Schuchmann and
C. von Sonntag, J. Chem. Soc., Perkin Trans. 2, 2000, 1862.
Acknowledgements
46 M. N. Schuchmann, E. Bothe, J. von Sonntag and C. von Sonntag,
J. Chem. Soc., Perkin Trans. 2, 1998, 791.
47 M. Capponi, I. Gut and J. Wirz, Angew. Chem., Int. Ed. Engl., 1986,
26, 344.
This paper is dedicated to Silvia Braslavsky on occasion of her
6
0th birthday. E. M. would like to thank the German Academic
4
8 P. Neta, R. E. Huie and A. B. Ross, J. Phys. Chem. Ref. Data, 1988,
7, 1027.
9 K.-D. Asmus, A. Henglein, M. Ebert and J. P. Keene, Ber. Bunsen-
Ges. Phys. Chem., 1964, 68, 657.
0 R. Criegee, Angew. Chem., 1975, 87, 765.
1 A. Leitzke, E. Reisz, R. Flyunt and C. von Sonntag, J. Chem. Soc.,
Perkin Trans. 2, 2001, 793.
Exchange Service (DAAD) for a stipend. The continuing
support by Professor Dr R. Mehnert, enabling us to finalise
the work at the IOM, is highly appreciated.
1
4
5
5
References
1
2
3
4
5
6
7
8
K. V. Ellis, Crit. Rev. Environ. Control, 1991, 20, 341.
U. von Gunten, Water Res., 2003, 37, 1443.
52 N. V. Raghavan and S. Steenken, J. Am. Chem. Soc., 1980, 102, 3495.
53 E. J. Land and M. Ebert, Trans. Faraday Soc., 1967, 63, 1181.
54 X.-M. Pan, M. N. Schuchmann and C. von Sonntag, J. Chem. Soc.,
Perkin Trans. 2, 1993, 289.
55 M. Ragnar, T. Eriksson, T. Reitberger and P. Brandt, Holzforschung,
1999, 53, 423.
56 M. Ragnar, T. Eriksson and T. Reitberger, Holzforschung, 1999, 53,
292.
57 R. Flyunt, J. A. Theruvathu, A. Leitzke and C. von Sonntag,
J. Chem. Soc., Perkin Trans. 2, 2002, 1572.
U. von Gunten, Water Res., 2003, 37, 1469.
H. R. Eisenhauer, J. – Water Pollut. Control Fed., 1968, 40, 1887.
J. Mallevialle, T. S. M. Eau, 1975, 70, 107.
M. D. Gurol and R. Vatistas, Water Res., 1987, 21, 895.
M. Jarret, A. Bermond and C. Ducause, Analysis, 1983, 11, 185.
M. L. Konstantinova, S. D. Razumvskii and G. E. Zaikov, Bull.
Acad. Sci. USSR, Div. Chem. Sci., 1991, 266.
9
M. L. Konstantinova, S. D. Razumvskii and G. E. Zaikov, Bull.
Acad. Sci. USSR, Div. Chem. Sci., 1991, 271.
58 P. S. Nangia and S. W. Benson, J. Am. Chem. Soc., 1980, 102, 3105.
59 F. Muñoz and C. von Sonntag, J. Chem. Soc., Perkin Trans. 2, 2000,
2029.
1
1
1
0 Y. Ku, W.-J. Su and Y.-S. Shen, Ozone: Sci. Eng., 1996, 18, 443.
1 D. Lesczynska, Environ. Prot. Eng., 1982, 8, 105.
2 F. Muñoz, E. Mvula, S. E. Braslavsky and C. von Sonntag, J. Chem.
Soc., Perkin Trans. 2, 2001, 1109.
3 Y. Yamamoto, E. Niki, H. Shiokawa and Y. Kamiya, J. Org. Chem.,
60 P. Eyer, Chem.-Biol. Interact., 1991, 80, 159.
61 V. Roginsky and T. Barsukova, J. Chem. Soc., Perkin Trans. 2, 2000,
1575.
1
1
979, 44, 2137.
62 E. Mvula and C. von Sonntag, unpublished results, 2002.
63 F. Kovac and B. Plesnicar, J. Am. Chem. Soc., 1979, 101, 2677.
64 B. Plesnicar, in The Chemistry of Functional Groups. Peroxides,
ed. S. Patai, Wiley, London, 1983, p. 483.
65 M. N. Schuchmann and C. von Sonntag, J. Water Supply Res. Tech.-
Aqua, 1989, 38, 311.
66 J. Cerkovnik and B. Plesnicar, J. Am. Chem. Soc., 1993, 115, 12169.
67 J. Koller and B. Plesnicar, J. Am. Chem. Soc., 1996, 118, 2470.
68 B. Plesnicar, J. Cerkovnik, T. Tekavec and J. Koller, J. Am. Chem.
Soc., 1998, 120, 8005.
69 B. Plesnicar, J. Cerkovnik, T. Tekavec and J. Koller, Chem. Eur. J.,
2000, 6, 809.
70 M. Jonsson, J. Lind, T. Reitberger, T. E. Eriksen and G. Merényi,
J. Phys. Chem., 1993, 97, 8229.
71 E. P. L. Hunter, M. F. Desrosiers and M. G. Simic, Free Radical Biol.
Med., 1989, 6, 581.
72 F. Jin, J. Leitich and C. von Sonntag, J. Chem. Soc., Perkin Trans. 2,
1993, 1583.
1
1
1
4 C.-R. Huang and H.-Y. Shu, J. Hazard. Mater., 1995, 41, 47.
5 S.-K. Han, K. Ichikawa and H. Utsumi, Water Res., 1998, 32, 3261.
6 H. Utsumi, S.-K. Han and K. Ichikawa, Water Sci. Tech., 1998, 38,
1
47.
1
7 R. Flyunt, A. Leitzke, G. Mark, E. Mvula, E. Reisz, J. A.
Theruvathu and C. von Sonntag, J. Phys. Chem. B, 2003, in the
press.
8 P. Wardman, J. Phys. Chem. Ref. Data, 1989, 18, 1637.
9 W. T. Dixon and D. Murphy, J. Chem. Soc., Faraday Trans. 2, 1976,
1
1
7
2, 1221.
2
2
0 A. J. Elliot and D. R. McCracken, Radiat. Phys. Chem., 1989, 33, 69.
1 G. V. Buxton, C. L. Greenstock, W. P. Helman and A. B. Ross,
J. Phys. Chem. Ref. Data, 1988, 17, 513.
2
2
2 K. C. Kurien and P. A. Robins, J. Chem. Soc. (B), 1970, 855.
3 J. von Sonntag, E. Mvula, K. Hildenbrand and C. von Sonntag,
to be published.
2
2
4 E. J. Hart, K. Sehested and J. Holcman, Anal. Chem., 1983, 55, 46.
5 L. Forni, D. Bahnemann and E. J. Hart, J. Phys. Chem., 1982, 86,
73 G. E. Adams and B. D. Michael, Trans. Faraday Soc., 1967, 63,
2
55.
6 F. Muñoz and C. von Sonntag, J. Chem. Soc., Perkin Trans. 2, 2000,
61.
7 P. Dowideit and C. von Sonntag, Environ. Sci. Technol., 1998, 32,
112.
1171.
2
2
2
74 R. Bausch, H.-P. Schuchmann, C. von Sonntag, R. Benn and
H. Dreeskamp, J. Chem. Soc., Chem. Commun., 1976, 418.
75 R. Benn, H. Dreeskamp, H.-P. Schuchmann and C. von Sonntag,
Z. Naturforsch. B: Anorg. Chem. Org. Chem., 1979, 34, 1002.
76 A. R. Freshour, S. Mawhinney and D. Bhattacharyya, Water Res.,
1996, 30, 1949.
77 X. Fang, Y. He, J. Liu and J. Wu, Radiat. Phys. Chem., 1998, 53, 441.
78 X. Fang, H.-P. Schuchmann and C. von Sonntag, J. Chem. Soc.,
Perkin Trans. 2, 2000, 1391.
79 R. Köster and K.-D. Asmus, Z. Naturforsch. B: Anorg. Chem. Org.
Chem., 1971, 26, 1108.
80 R. Mertens, C. von Sonntag, J. Lind and G. Merényi, Angew. Chem.,
Int. Ed. Engl., 1994, 33, 1259.
6
1
8 J. A. Theruvathu, R. Flyunt, C. T. Aravindakumar and C. von
Sonntag, J. Chem. Soc., Perkin Trans. 2, 2001, 269.
9 T. Nash, Biochem. J., 1953, 55, 416.
0 A. O. Allen, C. J. Hochanadel, J. A. Ghormley and T. W. Davis,
J. Phys. Chem., 1952, 56, 575.
1 R. Flyunt, A. Leitzke and C. von Sonntag, Radiat. Phys. Chem.,
2
3
3
3
3
2
003, in the press.
2 E. Reisz, W. Schmidt, H.-P. Schuchmann and C. von Sonntag,
Environ. Sci. Technol., 2003, in the press.
3 D. Veltwisch, E. Janata and K.-D. Asmus, J. Chem. Soc.,
Perkin Trans. 2, 1980, 146.
81 D. H. Sarr, C. Kazunga, M. J. Charles, J. G. Pavlovich and M. D.
Aitken, Environ. Sci. Technol., 1995, 29, 2735.
1
756
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 7 4 9 – 1 7 5 6