Gas-phase reaction of hydroxyl radicals with m-, o- and p-cresol

Article abstract of DOI:10.1002/kin.20186

The gas-phase reaction of oxygenated aromatic compounds m-cresol,o-cresol. and p-cresol with hydroxyl radicals has been studied by GC-MS. Experiments have been performed in a large-volume photoreactor (8000 L) at 294 ± 2 K and atmospheric pressure. The relative kinetic method was used to determine the rate constants for these reactions, with 1,3,5-trimethylbenzene as a reference compound. The rate constants obtained are k_OH(m-cresol) = (5.88 ± 0.92) × 10-¹¹ cm³ molecule^-1 s^-1, k_OH(o-cresol) = (4.32 ± 0.52) × 10 ^-11 cm³ molecule^-1 s^-1, and k _OH(p-cresol) = (4.96 ± 0.75) × 10^-11 cm ³ molecule^{-1 s-1}. The degradation products observed and their respective molar yields were methyl-1,4-benzoquinone 12.4 ± 1.2%, 5-methyl-2-nitrophenol 1.5 ± 0.3%, and 3-methyl-2-nitrophenol 1.4 ± 0.3% from m-cresol, methyl-1,4-benzoquinone 5.6 ± 0.9%, and 6-methyl-2-nitrophenol 4.7 ± 0.8% from o-cresol. and 4-methyl-2-nitrophenol 17.2 ± 2.5% from p-cresol. This kinetic and product data are compared with the literature, and the reaction mechanisms are discussed. Our results are in accordance with the previous studies (Atkinson, J Phys Chem Ref Data 1989, Monograph (1), 1-246; Atkinson and Aschmann. Int J Chem Kinet 1990, 22, 59-67; Atkinson et al., Environ Sci Technol 1992, 26, 1397-1403; Atkinson et al., J Phys Chem 1978, 82, 2759-2805; Olariu et al., Atoms Environ 2002, 36, 3685-3697; Semadeni et al., Int J Chem Kinet 1995, 27, 287-304) and confirm the methyl-1,4-benzoquinone yields determined by a different experimental technique (long-path Fourier transform infrared FT-IR (Olariu et al., 2002)).

Full text of DOI:10.1002/kin.20186

Gas-Phase Reaction
of Hydroxyl Radicals with
m-, o- and p-Cresol
1
1
2
´
CECILE COEUR-TOURNEUR, FRAN C¸ OISE HENRY, MARIE-ANDREE JANQUIN,
LAURENT BRUTIER1
1Ecosyst e` mes Littoraux et C oˆ tiers, UMR CNRS 8013, Universit e´ du Littoral C oˆ te d’Opale, 32 avenue Foch,
2 930 Wimereux, France
6
2Ecosyst e` mes Littoraux et C oˆ tiers, UMR CNRS 8013, Universit e´ des Sciences et Technologiques de Lille,
BP 80, 28 avenue Foch, 62 930 Wimereux, France
Received 8 July 2005; revised 9 February 2006; accepted 13 February 2006
DOI 10.1002/kin.20186
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The gas-phase reaction of oxygenated aromatic compounds m-cresol, o-cresol,
and p-cresol with hydroxyl radicals has been studied by GC-MS. Experiments have been per-
formed in a large-volume photoreactor (8000 L) at 294 ± 2 K and atmospheric pressure. The
relative kinetic method was used to determine the rate constants for these reactions, with
1
,3,5-trimethylbenzene as a reference compound. The rate constants obtained are kOH(m-
−11
3
−1 −1
−11
3
cresol) = (5.88 ± 0.92) × 10
cm molecule
s
, kO H (o-cresol) = (4.32 ± 0.52) × 10
cm
−1 −1
cm molecule s . The degra-
−1
−1
−11
3
molecule
s
, and kO H (p-cresol) = (4.96 ± 0.75) × 10
dation products observed and their respective molar yields were methyl-1,4-benzoquinone
1
2.4 ± 1.2%, 5-methyl-2-nitrophenol 1.5 ± 0.3%, and 3-methyl-2-nitrophenol 1.4 ± 0.3% from
m-cresol, methyl-1,4-benzoquinone 5.6 ± 0.9%, and 6-methyl-2-nitrophenol 4.7 ± 0.8% from
o-cresol, and 4-methyl-2-nitrophenol 17.2 ± 2.5% from p-cresol. This kinetic and product data
are compared with the literature, and the reaction mechanisms are discussed. Our results are
in accordance with the previous studies (Atkinson, J Phys Chem Ref Data 1989, Monograph (1),
1–246; Atkinson and Aschmann, Int J Chem Kinet 1990, 22, 59–67; Atkinson et al., Environ Sci Tech-
nol 1992, 26, 1397–1403; Atkinson et al., J Phys Chem 1978, 82, 2759–2805; Olariu et al., Atmos
Environ 2002, 36, 3685–3697; Semadeni et al., Int J Chem Kinet 1995, 27, 287–304) and confirm the
methyl-1,4-benzoquinone yields determined by a different experimental technique (long-path
Fourier transform infrared FT-IR (Olariu et al., 2002)). ꢀC 2006 Wiley Periodicals, Inc. Int J Chem
Kinet 38: 553–562, 2006
INTRODUCTION
ognized today [7–12]. The major sources of aromatic
hydrocarbons in the atmosphere are emissions from
motor vehicles and solvent use [13–15].
Besides their carcinogenic and mutagenic effects on
living organisms and human health [16,17], the main
importance of aromatic hydrocarbons is their role as
precursors for the formation of photo-oxidants [9,18]
and secondary organic aerosols [11,12,19,20].
The importance of the contribution of aromatic hydro-
carbons to problems of urban air pollution is well rec-
Correspondence to: Cecile Coeur-Tourneur; e-mail: cecile.
cœur@univ-littoral.fr.
ꢀ
c 2006 Wiley Periodicals, Inc.

554
COEUR-TOURNEUR ET AL.
In the atmosphere, aromatic compounds react
mainly with OH radicals. Phenol, the cresols, and
the dimethylphenols are formed in significant yields
1,3,5-trimethylbenzene 0.3–0.5 ppmv, o-cresol 0.3–1.2
ppmv, p-cresol 0.3–1.0 ppmv, m-cresol 0.3–1.1 ppmv,
and NO 1.3–1.5 ppmv.
(
2–60%) from the gas-phase reactions of OH radi-
The mixture within the chamber was homogenized
by a fan working sequentially. Irradiation was pro-
vided artificially by 10 fluorescence tubes (Philips
400–800 nm, 40 W).
cal with benzene, toluene, and the xylenes, respec-
tively [1,21–33]. In contrast with results from previ-
ous studies [1,21–28,30–32], Bohn and Zetzsch [34],
Klotz et al. [29], Knispel et al. [35], and Volkamer
et al. [33,36] have observed a pronounced depen-
dency between the NOx concentrations and the distri-
bution of the aromatic degradation products. The phe-
nol yields formed from the benzene reaction with OH
were found essentially constant for NOx levels of up
to several 10 ppb and decrease for elevated NOx con-
centrations (>100 ppb) [33]. In the opposite, toluene,
p-xylene, and 1,3,5 trimethylbenzene exhibit a ten-
dency to form higher yields of phenol-type products
when the NOx concentrations increase [36]. These
effects of the product distribution on the NOx indi-
cate a change in the oxidation mechanisms and are
of particular importance because most smog cham-
ber studies are performed with high NOx concentra-
tions and may therefore not be representative of the
troposphere.
Relative Rate Method
The experimental technique used for the determination
of the OH rate constant was a relative method, with
1,3,5-trimethylbenzene as a reference compound. This
method is based on the simultaneous monitoring of
the disappearance of the cresols and reference organic
which rate constant is known.
Providing that the cresols and the reference organic
reacted only with OH radicals, then:
ln([cresol]0/[cresol]t ) = k1/k2 ln([reference
organic]0/[ reference organic]t ) (I)
where [cresol] and [reference organic] are the con-
0
0
While phenol and the cresols react slowly with O3
centrations of the cresols and the reference organic at
[37], the reactions of these hydroxylated aromatic hy-
time t = 0, [cresol] and [reference organic] are the
t
t
drocarbons with OH [38] and NO3 radicals [21,39]
are fast and result in phenol, cresol, and dimethylphe-
nol lifetimes in the troposphere which are significantly
shorter than those of their parent aromatic hydrocar-
bons [40–42].
In this work, we have determined the forma-
tion yields of nitrophenol isomers and methyl-1,4-
benzoquinone from the hydroxyl radical reaction with
the cresols in the presence of NOx . Additionally, we
have used a relative rate method to determine the
rate constants for the gas phase reactions of OH with
o-, m-, and p-cresol at 294 ± 2 K and atmospheric
pressure.
corresponding concentrations at time t, and k and
k2 are the rate constants for reactions (1) and (2),
respectively.
1
OH + cresol → products (k1)
(1)
OH + reference organic → products (k2) (2)
Thus, plots of ln([cresol]0/[cresol]t ) against ln-
[reference organic]0/[reference organic]t ) should
(
yield straight lines of slope k1/k2 and zero
intercept.
Hydroxyl Radical
EXPERIMENTAL
The OH radicals were generated by methyl nitrite
Experimental System
(CH3ONO) photolysis in air in the presence of NO.
3
The experiments were performed in a 8-m (2 m ×
An excess of NO was added to avoid the formation
of O3 and NO3 radicals. Methyl nitrite was synthe-
sized using the method described by Atkinson et al.
[43], by addition of 50% H2SO4 to a saturated solution
of sodium nitrite (NaNO2) in methanol. The methyl
nitrite, which bubbles out of the NaNO2solution, was
then transferred into the smog chamber using a pure he-
lium stream. As this system is very reactive, care was
taken to eliminate light leaks before the inception of the
experiment. Methyl nitrite photolysis leads to hydroxyl
2
m × 2 m) cubic evacuable Plexiglas reaction cham-
ber, at atmospheric pressure 760 Torr, room temper-
ature 294 ± 2 K, and moderate relative humidity
4
0–45%. Purified air was supplied by an LGCAD 140
(Dominick Hunter) pure air generation system.
The 1,3,5-trimethylbenzene and the cresols were in-
troduced into the chamber after vaporization at 503 K.
NO was directly injected with a gas-tight syringe. The
initial concentrations of the different reactants were

GAS-PHASE REACTION OF HYDROXYL RADICALS WITH m-, o-, AND p-CRESOL
555
radical formation as follows:
p-cresol > 98% (Merck products); 1,3,5-trimethy-
lbenzene99%, 5-methyl-2-nitrophenol97%, 4-methyl-
2-nitrophenol 99%, 3-methyl-2-nitrophenol 99%, and
methyl-1,4-benzoquinone > 99% (Acros Organics
products); and NO > 99% (Air Liquide Chemical
Company).
CH3ONO + hꢀ (ꢁ ≥ 295 nm) → CH3O + NO
CH3O + O2 → HCHO + HO2
HO2 + NO → OH + NO2
RESULTS AND DISCUSSION
Cresol Rate Constants
Analytical Conditions
An analysis of the composition of the reactive mixture
was achieved before and regularly during the irradia-
tion time (every 15 or 30 min during 7 h). Gaseous sam-
ples were collected at room temperature, onto stain-
less steel tubes filled with Tenax TA (60–80 mesh).
The organic compounds were then thermally desorbed
onto a 30-m DB-5 megabore fused silica capillary col-
umn held at 323 K for 5 min and then programmed
Preliminary experiments were performed into the smog
chamber to verify that the 1,3,5-trimethylbenzene, and
the cresols were solely removed via the reaction with
OH radicals. No wall deposition and photolysis losses
were observed for these hydrocarbons. Moreover, no
reaction was detected with CH3ONO/NO/air in the
dark.
A series of CH3ONO-NO-cresol-1,3,5-trimethy-
lbenzene-air irradiations were carried out. In order
to avoid GC interferences, the following mixtures of
cresols were used: o- and p-cresol and o- and m-cresol.
The hydroxyl radical concentrations, as calculated
from the decay rates of the reference organic, were in
−1
to 523 K at 5 K min . Analyses were performed
by gas chromatography-mass spectrometry (GC-MS),
and the total ion chromatograms (TIC) were recorded.
In order to improve the detection limits, the analy-
ses were also performed in single ion resolution (SIR)
for nitrophenol isomers (m/z = 153) and methyl-1,4-
benzoquinone (m/z = 122).
6
−3
the range (1–4) × 10 molecule cm
.
The experimental data are plotted in accordance
with Eq. (I) in Fig. 1. All the plots show good
linearity. Table I lists the measured ratios k1/k2
obtained from the analysis of the data according
to Eq. (I) and the resulting rate constants k1 for
Chemicals
The chemicals used and their purity levels were
as follows: o-cresol > 99%, m-cresol > 99%, and
Figure 1 Plots of Eq. (I) for reactions of the OH radicals with m-, o-, and p-cresol, with 1,3,5-trimethylbenzene as the reference
organic. The data for o- and p-cresol have been displaced vertically by 1 and 2 units, respectively, for clarity.

556
COEUR-TOURNEUR ET AL.
Table I Rate Constant Ratios k /k and Rate Constants k for the Gas-Phase Reaction of OH Radicals with the Cresols
1
2
1
at 294 ± 2 K and Atmospheric Pressure, Together with Literature Experimental Data and Estimated Rate Constants
−
11
3
−1 −1
k1 (×10
cm molecule s )
k1/k2a
This Workb
Literature
c
m-Cresol
o-Cresol
p-Cresol
1.02 ± 0.16
5.88 ± 0.92
6.78 ± 1.10; RR : 296 K [2]
5
.17 ± 0.51; RR: 299 K [6]
.57 ± 0.32; RR: 300 K [4]
5
6
.40 ± 0.22; Estimated: 298 K [1]
5
.67; Estimated: 298 K [6]
0.75 ± 0.09
0.86 ± 0.13
4.32 ± 0.52
4.96 ± 0.75
4.26 ± 0.68; RR: 296 K [2]
4
4
.65 ± 0.39; RR: 301 K [6]
.25 ± 0.37; RR: 300 K [4]
4
.20 ± 0.13; Estimated: 300 K [1]
4
.00; Estimated: 298 K [6]
4.84 ± 0.89; RR: 296 K [2]
5
4
4
.22 ± 0.52; RR: 301 K [6]
.22 ± 0.66; RR: 301 K [6]
.31 ± 0.20; RR: 300 K [4]
4
.60 ± 0.16; Estimated: 298 K [1]
4
.94; Estimated: 298 K [6]
a
Indicated errors are two standard deviations of the regression analysis and do not take into account the uncertainty in the reference compound
rate constant.
b
Placed on an absolute basis by use of rate constant k
2
for the reactions of the OH radical with 1,3,5-trimethylbenzene at 294 K of
k
2(1,3,5
c
-
trimethylbenzene) = (5.75 ± 0.92) × 10− cm molecule
11
3
−1 −1
s [.44].
Relative rate method.
the reaction of OH radicals with the cresols. The
cresol rate constants are determined from 1,3,5-
trimethylbenzene as reference, with the recommended
ceeds mainly (93%) via electrophilic addition of OH to
the aromatic ring [38]. The rate constants for o-cresol
and p-cresol are close and agree within the combined
error limits. These results were expected since the pos-
sible addition sites for the OH radical are the same for
both isomers. For m-cresol, the electrophilic addition
has more possibilities, which explains the higher value
for m-cresol rate constant compare to o- and p-cresols.
−11
3
value k1,3,5-trimethylbenzene = (5.75 ± 0.92) × 10
cm
−
1
−1
molecule
s [44]. The errors quoted in Table I are
two standard deviations of the regression analysis and
do not take into account the uncertainty in the reference
compound rate constant.
The available literature experimental rate constants
for the reactions of the OH radicals with the cresols at
room temperature are also given in Table I. The present
rate constants for the three cresols are in good agree-
ment with those of previous studies [1,2,4,6]. The ex-
perimental cresol rate constants have also been com-
pared with the values calculated with the structure–
activity relationship (SAR) based on group reactivity
Product Studies
Product identification was typically made from exper-
iments conducted at the highest reactant concentra-
tions. GC/MS analyses of gas samples collected from
the gas-phase reactions of OH radical in the pres-
ence of NO with the cresols showed the formation
x
[45]. The experimental and calculated data are in good
of methyl-1,4-benzoquinone, 5-methyl-2-nitrophenol,
agreement for the three cresols (within a factor 2).
As shown in Table I, the reactivity of the
cresol isomers takes the order: kOH(o-cresol) < kOH(p-
cresol) < kOH(m-cresol), with the following rate con-
and 3-methyl-2-nitrophenol from m-cresol, methyl-
1,4-benzoquinone and 6-methyl-2-nitrophenol from
o-cresol, and 4-methyl-2-nitrophenol from p-cresol.
These product identifications were based on match-
ing the GC retention times and mass spectra with
those of authentic samples recorded under the
same conditions. Authentic samples of 6-methyl-2-
nitrophenol are apparently not commercially available.
For this compound, probable identification was derived
from the mass spectra of the nitrophenol standards
3
−1 −1
−11
,
stants (in cm molecule
s
): (4.32 ± 0.52) × 10
−11
−11
(4.96 ± 0.75) × 10 , and (5.88 ± 0.92) × 10
for
o-cresol, p-cresol, and m-cresol, respectively. This or-
derwasexpectedfromaconsiderationofthecompound
structure and is attributed to the position of the methyl
group. The reaction of OH radicals with cresols pro-

GAS-PHASE REACTION OF HYDROXYL RADICALS WITH m-, o-, AND p-CRESOL
557
−
13
3
−1 −1
s at 294 K [3] is
complemented by interpretation of the compound frag-
mentation pattern.
(9.0 ± 0.2) × 10 cm molecule
a factor 30 lower than for the reaction of the OH radical
with phenol, it was expected that secondary reactions
of methylnitrophenols in the OH radical reactions of
the cresols were also negligible.
For the correction of the yields of methyl-1,4-
benzoquinone, the following OH rate constant was
In order to determine the formation yields of the
products, it is necessary to correct the product concen-
trations for further reaction. The experimental condi-
tions were such that the NO concentrations were suffi-
ciently high to suppress the formation of O3 and hence
NO3. Thus, the reactions with O3 and NO3 are con-
sidered to be of negligible importance. Furthermore,
the wall adsorption and photolysis of these compounds
were also not significant and only loss process due to
the reaction with OH radicals was taken into consider-
ation for the yield correction.
The approach for determining corrections uses a
two-stepmechanism, theformationofaproduct(P)due
to reaction of OH + cresols, followed by OH reaction
with P. Other processes are assumed to be negligible.
This approach yields an expression of the following
form [46]:
−
11
used: k(
methyl-1,4-benzoquinone)
−1 −1
s [47]. The maximum correctionfac-
= (2.35 ± 0.47) × 10
3
cm molecule
tors were about 1.5 for methyl-1,4-benzoquinone.
Product concentrations (with the correction factor
applied to each data point) have been plotted against the
amount of cresol isomers reacted (Figs. 2–4). Primary
product yields were computed from the slope of an
linear least-squares fit to the corrected data. Table II
lists the yields of the identified products from the gas-
phase reactions of OH radicals with the cresols together
with the literature experimental data. Indicated errors
are two standard deviations of the regression analysis.
In the present work, methyl-1,4-benzoquinone was
identified as the main degradation product from the OH
reaction with m-cresol, with a yield of 12.4 ± 1.2%.
This product has been previously detected by Olariu
et al. [5] with a similar yield 11.3 ± 2.5%, but was
not determined by Atkinson et al. [3]. 5-Methyl-2-
nitrophenol and 3-methyl-2-nitrophenol were also de-
tected from m-cresol with the yields of 1.5 ± 0.3% and
1.4 ± 0.3%, respectively. These results are in good
agreement with Atkinson et al. [3], whereas Olariu
et al. [5] have not detected (interferences) 3-methyl-
2-nitrophenol and reported higher yield 4.4 ± 1.5%
for 5-methyl-2-nitrophenol. Olariu et al. [5] have
[
cresol]t
1
−
(
k1 − k3)
k1
[
cresol]0
F =
∗ (
k
k
3
1
[cresol]t
cresol]0
[cresol]t
)
−
[
[cresol]0
where F represents the correction factor, k1 is the rate
constant for the reaction of OH with the cresols, and
k3 is the rate constant for the reaction of OH + P. This
expression was applied to the data for all compounds
having non-negligible corrections.
For methylnitrophenol isomers, no rate constant is
available for the reaction with OH. However, since the
OH radical reaction rate constant for 2-nitrophenol of
Figure 2 Plots of the corrected concentrations of methyl-1,4-benzoquinone, 5-methyl-2-nitrophenol, and 3-methyl-2-
nitrophenol versus the amounts of m-cresol reacted with the OH radicals in the presence of NOx . The 5-methyl-2-nitrophenol
data have been scaled vertically by 0.05 ppm for clarity.

558
COEUR-TOURNEUR ET AL.
Figure 3 Plots of the corrected concentrations of methyl-1,4-benzoquinone and 6-methyl-2-nitrophenol versus the amounts of
o-cresol reacted with the OH radicals in the presence of NOx . The 6-methyl-2-nitrophenol data have been scaled vertically by
0
.05 ppm for clarity.
Figure 4 Plots of the corrected concentrations of 4-methyl-2-nitrophenol versus the amounts of p-cresol reacted with the OH
radicals in the presence of NOx .
also observed 3-methyl-4-nitrophenol as a degrada-
tion product from m-cresol with a formation yield of
a formation yield of 5.6 ± 0.9%. The second prod-
uct identified was a methyl-2-nitrophenol isomer. As
its retention time does not correspond with those
of the standards (3-methyl-2-nitrophenol, 4-methyl-2-
nitrophenol, and 5-methyl-2-nitrophenol), it was sup-
posed to be 6-methyl-2-nitrophenol (to our knowledge,
there is no standard for this isomer). To determine
its formation yield, its response factor was assumed
to be in the same order of magnitude than those of
other isomers and we took the mean value of the re-
sponse factors of the three standards available. The
6-methyl-2-nitrophenol was detected with a yield of
4
.3 ± 1.6%. This compound was not observed in our
study. Our identifications were performed both by mass
spectrometry and by comparing the retention time of
the degradation products with those of the methyl nitro-
phenolisomerstandards, andthereisnodoubtaboutthe
formation of 3-methyl-2-nitrophenol and 5-methyl-2-
nitrophenol and the absence of 3-methyl-4-nitrophenol
in our experiments.
From o-cresol, two degradation products were ob-
served. Methyl-1,4-benzoquinone was formed with

GAS-PHASE REACTION OF HYDROXYL RADICALS WITH m-, o-, AND p-CRESOL
559
Table II Formation Yields of the Products from the Gas-Phase Reactions of OH Radicals with the Cresols in the
Presence of NOx , at 294 ± 2 K and Atmospheric Pressure, Together with Literature Experimental Data
Yield (%)
Reactant
Product
This Worka
Literature
Not determined [3]
m-Cresol
Methyl-1,4-benzoquinone
12.4 ± 1.2
1
1.3 ± 2.5 [5]
5
-Methyl-2-nitrophenol
-Methyl-2-nitrophenol
1.5 ± 0.3
1.4 ± 0.3
5.6 ± 0.9
4.7 ± 0.8
17.2 ± 2.5
1.6 ± 0.1 [3]
4
.4 ± 1.5 [5]
3
1.6 ± 0.1 [3]
Not detected [5]
Not determined [3]
o-Cresol
Methyl-1,4-benzoquinone
-Methyl-2-nitrophenol
4-Methyl-2-nitrophenol
6
.8 ± 1.0 [5]
6
5.1 ± 1.5 [3]
6
.8 ± 1.5 [5]
10 ± 4 [3]
.6 ± 2.2 [5]
p-Cresol
7
a
Indicated errors are two standard deviations of the regression analysis.
−
1
−1
s for 3-methyl-1,2-dihydroxybenzene
4
.7 ± 0.8%. These values are close to those of Olariu
molecule
−
10
3
−1
et al. [5]. Atkinson et al. [3] have also observed 6-
methyl-2-nitrophenol with a similar yield but have not
determined methyl-1,4-benzoquinone.
and k = (1.56 ± 0.33) × 10
cm molecule
OH
−
1
s
for 4-methyl-1,2-dihydroxybenzene [47]. Taking
into account the amounts of cresols which reacted, the
OH rate constants of the dihydroxymethylbenzenes
and the formation yields determined by Olariu et al.
[5], we have calculated the residual dihydroxymethyl-
benzene concentrations into the simulation chamber.
These residual concentrations were around 0.30–0.35
ppm and were below our detection limits for the
dihydroxymethylbenzenes estimated to 0.45–0.50
ppm. These detection limits were determined in
single ion resolution (SIR m/z = 124) and were two
order of magnitude higher than those of cresols,
methyl-1,4-benzoquinone, and methylnitrophenols.
In Olariu et al. [47], analyses were performed in
situ by long-path Fourier transform infrared (FT-IR)
absorption spectroscopy. In our work and those of
Atkinson et al. [3], gas samples were collected into
Tenax solid adsorbent, with subsequent thermal des-
orption and analysis using combined gas chromatog-
raphy/mass spectrometry (GC/MS). This analytical
procedure gives high dihydroxymethylbenzene detec-
tion limits and does not allow their detection from the
OH radical reaction with cresols.
At 298 K, it has been estimated that, respectively,
about 9% and 7% of the overall reactions of OH with
phenol and cresols proceed via H-atom abstraction [1],
the remainder being addition. As observed by Atkinson
et al. [3] and Olariu et al. [5], the yields of nitrophe-
nols measured in the OH-radical induced oxidation of
phenol and cresols are similar (uncertain to ± 50%) to
the calculated fraction of the reaction proceeding by
the H-atom abstraction from the OH group. This re-
sult is also observed in our experiments for the yields
For p-cresol, the only product identified was
-methyl-2-nitrophenol with a yield of 17.2 ± 2.5%;
4
this value is twice higher than in previous works [3,5].
Previous studies have shown the dependency be-
tween the NOx concentrations and the distribution
of the aromatic degradation products [29,33–36]. The
yields of the phenol-type products formed from the OH
reaction with benzene decrease for NOx concentrations
higher than 100 ppb, while those formed from the OH
reaction with toluene, p-xylene, and 1,3,5 trimethyl-
benzene increase with increasing NOx concentrations.
Our experiments and those of Atkinson et al. [3] and
Olariu et al. [5] were performed with NOx concen-
trations in the same range (0.5–10 ppm) and did not
allow to conclude on the possible influence of the NOx
concentrations on the yields of the cresol degradation
products.
Olariu et al. [5] have observed dihydroxymethyl-
benzenes as main degradation products from OH reac-
tion with cresols, with yields around 65–75%. These
compounds were not measured in Atkinson’s work. In
our experiments, we were also unable to detect the for-
mation of dihydroxymethylbenzenes. Either these sub-
stances were formed below the detection limits or ef-
fective wall losses prevented their identification using
the GC-MS technique. The wall losses of the dihy-
droxymethylbenzenes were tested into our simulation
chamber and could not explain the fact that these com-
pounds were not detected in our experiments.
The dihydroxymethylbenzenes have high OH
rate constants: kOH = (2.05 ± 0.43) × 10−
10
cm
3

560
COEUR-TOURNEUR ET AL.
of methylnitrophenols formed from the reaction of OH
with the cresol isomers. The formation of the methylni-
trophenols from the gas-phase reaction of OH radicals
with cresols is therefore produced via the following
reaction scheme, e.g. for o-cresol + OH [3,5]:
Platz et al. [48] and Olariu et al. [5] have performed
experiments to study the atmospheric chemistry of phe-
noxy radicals, and they did not observe the formation
of 1,4-benzoquinone. Moreover, in our experiments,
For 4-methyl-2-nitrophenol formed from the OH
radical initiated oxidation of p-cresol, the determined
yield exceeds the fraction of the reaction proceeding by
the H-atom abstraction from the OH group. Thus, this
product could be formed via the OH radical addition
to the aromatic ring at positions meta- or ortho- to the
OH group:
the combined yields of the methylnitrophenols and
methyl-1,4-benzoquinone formed from the reactions
of OH with o- and m-cresol exceed the ≈7% fraction
of the reaction estimated to be proceeding by the
H-atom abstraction from the OH group. These results
tend to assume that the methyl-1,4-benzoquinone is
Three mechanisms could be proposed to explain
methyl-1,4-benzoquinone formation from OH-radical
reaction with o-cresol and m-cresol: one correspond-
ing to the H-atom abstraction from the hydroxyl group
and the two others proceeding by OH addition to the
aromatic ring (at positions either para- or ipso- to the
OH group), e.g. for o-cresol [5]:
formed mainly via the OH addition to the aromatic
ring; however, it is not possible to estimate the fraction
of the reaction proceeding by each of the two different
OH-addition channels proposed.
OH radical is a strong electrophile, and it adds
preferentially at the electron-rich sites of an aromatic

GAS-PHASE REACTION OF HYDROXYL RADICALS WITH m-, o-, AND p-CRESOL
561
ring. In the case of m-cresol, the hydroxyl substitutent
has a dominant ortho- para-directing effect. In the
case of o-cresol, the methyl substitutent has also a
significant effect on the electronic structure and the
OH addition at the ipso position of the methyl group
can be of considerable importance [49]. The addition
of OH radicals to aromatic rings at position substituted
with the alkyl group can be of appreciable importance
in the OH oxidation of aromatic substrates [50–52].
These results tend to speculate that for m- and
o-cresol the OH addition to the aromatic ring is in
favor of the para- rather than the ipso-position of the
OH group.
14. Piccot, S. D.; Watson, J. J.; Jones, J. W. J Geophys Res
1992, 97, 9897–9912.
15. Westerholm, R.; Almen, J.; Li, H.; Rannung, U.; Rosen,
A. Atmos Environ 1992, 26B, 79–90.
1
6. Dumdei, B. E.; Kenny, D.; Shepson, P. B.; Kleindienst,
T. E.; Nero, C. M.; Cupitt, L. T.; Claxton, L. D. Environ
Sci Technol 1988, 22, 14–30.
1
1
7. Shepson, P. B.; Kleindienst, T. E.; Edney, E. O.; Narnie,
G. R.;Pittman, J. H.;Cupitt, L. T.;Claxton, L. D. Environ
Sci Technol 1985, 19, 249–255.
8. Derwent, R. G.; Jenkin, M. E.; Saunders, S. M.; Pillings,
M. J. Atmos Environ 1998, 32, 2429–2441.
19. Hurley, M. D.; Sokolov, O.; Wallington, T. J.; Takekawa,
H.; Karasawa, M.; Klotz, B.; Barnes, I.; Becker, K. H.
Environ Sci Technol 2001, 35, 1358–1366.
2
0. Kleindienst, T. E.; Smith, D. F.; Edney, E. O.; Driscoll,
D. J.; Speer, R. E.; Weathers, W. S. Atmos Environ 1999,
33, 3669–3681.
The authors gratefully acknowledge the financial support
for this research (The National Program for Atmospheric
Research-PNCA and the “Contrat de Plan Etat-R e´ gion Nord-
Pas de Calais”–CPER) and the technical staff who has con-
tributed to the simulation chamber achievement (B. Lunaud,
D. Menu, E. Lecuyer, and P. Philippe).
21. Atkinson, R.; Aschmann, S. M.; Arey, J. Int J Chem
Kinet 1991, 23, 77–97.
22. Atkinson, R.; Aschmann, S. M.; Arey, J.; Carter, W. P.
L. Int J Chem Kinet 1989, 21, 801–827.
23. Atkinson, R.; Carter, W. P. L.; Darnall, K. R.; Winer, A.
M.; Pitts, J. N. J. Int J Chem Kinet 1980, 12, 779–837.
2
4. Atkinson, R.; Carter, W. P. L.; Winer, A. M. J Phys Chem
983, 87, 1605–1610.
5. Atkinson, R.; Lloyd, A. C. J Phys Chem Ref Data 1984,
3, 315–444.
1
BIBLIOGRAPHY
2
1
1
2
3
4
5
6
7
8
. Atkinson, R. J Phys Chem Ref Data 1989, Monograph
1), 1–246.
. Atkinson, R.; Aschmann, S. M. Int J Chem Kinet 1990,
2, 59–67.
. Atkinson, R.; Aschmann, S. M.; Arey, J. Environ Sci
Technol 1992, 26, 1397–1403.
26. Berndt, T.; B o¨ ge, O. Phys Chem Chem Phys 2001, 3,
4946–4959.
27. Kenley, R. A.; Davenport, J. E.; Hendry, D. G. J Phys
Chem 1981, 85, 2740–2746.
28. Klotz, B.; Sorensen, S.; Barnes, I.; Becker, K. H.;
Etzkorn, T.; Volkamer, R.; Platt, U.; Wirtz, K.; Martin-
Reviejo, M. J Phys Chem A 1998, 102, 10289–10299.
29. Klotz, B.; Volkamer, R.; Hurley, M. D.; Sulbaeck
Andersen, M. P.; Nielsen, O. J.; Barnes, I.; Imamura,
T.; Wirtz, K.; Becker, K. H.; Platt, U.; Wallington,
T.; Washida, N. Phys Chem Chem Phys 2002, 4,
4399–4411.
30. Smith, D. F.; Kleindienst, T. E.; McIver, C. D. J Atmos
Chem 1999, 34, 339–364.
31. Smith, D. F.; McIver, C. D.; Kleindienst, T. E. J Atmos
Chem 1998, 30, 209–228.
32. Takagi, H.; Washida, N.; Akimoto, H.; Nagasawa, K.;
Usui, Y.; Okuda, M. J Phys Chem 1980, 84, 478–483.
33. Volkamer, R.; Klotz, B.; Barnes, I.; Imamura, T.; Wirtz,
K.; Washida, N.; Becker, H.; Platt, U. Phys Chem Chem
Phys 2002, 4, 1598–1610.
(
2
. Atkinson, R.; Darnall, K. R.; Pitts, J. N. J. J Phys Chem
1
978, 82, 2759–2805.
. Olariu, R. I.; Klotz, B.; Barnes, I.; Becker, K. H.;
Mocanu, R. Atmos Environ 2002, 36, 3685–3697.
. Semadeni, M.; Stocker, D. W.; Kerr, J. A. Int J Chem
Kinet 1995, 27, 287–304.
. Atkinson, R.; Aschmann, S. M. Int J Chem Kinet 1994,
2
6, 929–944.
. Calvert, J.; Atkinson, R.; Becker, K. H.; Kamens, R.; Se-
infeld, J.; Wallington, T.; Yarwood, G. The Mechanisms
of Atmospheric Oxidation of the Aromatic Hydrocar-
bons; Oxford University Press: New York, 2002.
. Derwent, R. G.; Jenkin, M. E.; Saunders, S. M. Atmos
Environ 1996, 30, 181–199.
9
1
0. Lewis, A. C.; Carslaw, N.; Marriott, P. J.; Kinghorn, R.
M.; Morrison, P.; Lee, A. L.; Bartle, K. D.; Pilling, M.
J. Nature 2000, 405, 778–781.
34. Bohn, B.; Zetzsch, C. Phys Chem Chem Phys 1999, 1,
5097–5107.
11. Odum, J. R.; Jungkamp, T. P. W.; Griffin, R. J.; Flagan,
R. C.; Seinfeld, J. Science 1997, 276, 96–99.
35. Knispel, R.; Koch, R.; Siese, M.; Zetzsch, C. Ber Bun-
senges Phys Chem 1990, 94, 1375–1379.
1
2. Odum, J. R.; Jungkamp, T. P. W.; Griffin, R. J.; Forstner,
H. J. L.; Flagan, R. C.; Seinfeld, J. Environ Sci Technol
36. Volkamer, R.; Uecker, J.; Wirtz, K.; Platt, U.
In Proceedings of EUROTRAC Symposium, 2002;
Margraf-Verlag; Weikersheim, 2002; pp. 1–5.
37. Atkinson, R.; Carter, W. P. L. Chem Rev 1984, 84,
437–470.
1
997, 31, 1890–1897.
1
3. Dearth, M. A.; Glerczak, C. C.; Siegl, W. O. Environ Sci
Technol 1992, 26, 1573–1580.

562
COEUR-TOURNEUR ET AL.
3
8. Atkinson, R. J Phys Chem Ref Data 1994, Monograph
2), 11–216.
47. Olariu, R. I.; Barnes, I.; Becker, K. H.; Klotz, B. Int J
Chem Kinet 2000, 32, 696–702.
(
3
9. Carter, W. P. L.; Winer, A. M.; Pitts, J. N. J. Environ Sci
Technol 1981, 15, 829–831.
0. Atkinson, R. Atmos Environ 1990, 24A, 1–41.
1. Grosjean, D. J Air Waste Manage Assoc 1990, 40,
48. Platz, J.; Nielsen, O. J.; Wallington, T. J.; Ball,
J. C.; Hurley, M. D.; Staccia, A. M.; Schneider, W.
F.; Schested, J. J Phys Chem A 1998, 102, 7964–
7974.
4
4
1
397–1402.
49. Albarran, G.; Schuler, R. H. J Phys Chem A 2005, 109,
9363–9370.
4
4
2. Grosjean, D. Sci Total Environ 1991, 100, 367–414.
3. Atkinson, R.; Carter, W. P. L.; Winer, A. M.; Pitts, J. N.
J. J Air Pollut Control Assoc 1981, 31, 1090–1092.
4. Atkinson, R.; Aschmann, S. M. Int J Chem Kinet 1989,
50. Johnson, D.; Raoult, S.; Lesclaux, R.; Krasnoperov, L.
N. J Photochem Photobiol A 2005, 176, 98–106.
51. Schuler, R. H.; Albarran, G.; Zajicek, J.; George, M. V.;
Fessenden, R. W.; Carmichael, I. J Phys Chem A 2002,
106, 12178–12183.
52. Uc, V. H.; Garcia-Cruz, I.; Hernandez-Laguna, A.;
Vivier-Bunge, A. J Phys Chem A 2000, 104, 7847–
7855.
4
2
1, 355–365.
4
4
5. Atkinson, R. Int J Chem Kinet 1987, 19, 799–828.
6. Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.;
Winer, A. M.; Pitts, J. N. J. J Phys Chem 1982, 86,
4
563–4569.