Kinetics and mechanisms of the tropospheric reactions of menthol, borneol, fenchol, camphor, and fenchone with hydroxyl radicals (OH) and chlorine atoms (Cl)

Article abstract of DOI:10.1021/jp212076g

Relative kinetic techniques have been used to measure the rate coefficients for the reactions of oxygenated terpenes (menthol, borneol, fenchol, camphor, and fenchone) and cyclohexanol with hydroxyl radicals (OH) and chlorine atoms (Cl) at 298 ± 2 K and atmospheric pressure. The rate coefficients obtained for the reactions of the title compounds with OH are the following (in units of 10^-11 cm³ molecule^-1 s^-1): (1.48 ± 0.31), (2.65 ± 0.32), (2.49 ± 0.30), (0.38 ± 0.08), (0.39 ± 0.09) for menthol, borneol, fenchol, camphor, and fenchone, respectively. For the corresponding reactions with Cl atoms the rate coefficients are as follows (in units of 10^-10 cm³ molecule^-1 s^-1): (3.21 ± 0.26), (3.40 ± 0.28), (2.72 ± 0.13), (2.93 ± 0.17), (1.59 ± 0.10), and (1.86 ± 0.29) for cyclohexanol, menthol, borneol, fenchol, camphor, and fenchone, respectively. The reported error is twice the standard deviation. Product studies of the reactions were performed using multipass in situ FTIR (Fourier transform infrared spectroscopy) and solid-phase microextraction (SPME) with analysis by GC-MS (gas chromatography-mass spectrometry). A detailed mechanism is proposed to justify the observed reaction products.

Full text of DOI:10.1021/jp212076g

Article
pubs.acs.org/JPCA
Kinetics and Mechanisms of the Tropospheric Reactions of Menthol,
Borneol, Fenchol, Camphor, and Fenchone with Hydroxyl Radicals
(
OH) and Chlorine Atoms (Cl)
†
́ ́
Antonio A. Ceacero-Vega, Bernabe Ballesteros, Iustinian Bejan, Ian Barnes, Elena Jimen
ez,†
†
‡
‡
,†
́
and Jose Albaladejo*
†Departamento de Química Física, Facultad de Ciencias y Tecnología Química, Universidad de Castilla-La Mancha, Avenida Camilo
Jose Cela, s/n. 13071 Ciudad Real, Spain
́
‡
FB-C Physical Chemistry Department, University of Wuppertal, Gauss Strasse 20, 42119 Wuppertal, Germany.
ABSTRACT: Relative kinetic techniques have been used to
measure the rate coefficients for the reactions of oxygenated
terpenes (menthol, borneol, fenchol, camphor, and fenchone)
and cyclohexanol with hydroxyl radicals (OH) and chlorine
atoms (Cl) at 298 ± 2 K and atmospheric pressure. The rate
coefficients obtained for the reactions of the title compounds
−
11
3
−1
with OH are the following (in units of 10 cm molecule
−1
s ): (1.48 ± 0.31), (2.65 ± 0.32), (2.49 ± 0.30), (0.38 ±
0
.08), (0.39 ± 0.09) for menthol, borneol, fenchol, camphor, and fenchone, respectively. For the corresponding reactions with Cl
−10
3
−1 −1
atoms the rate coefficients are as follows (in units of 10 cm molecule s ): (3.21 ± 0.26), (3.40 ± 0.28), (2.72 ± 0.13),
(
2.93 ± 0.17), (1.59 ± 0.10), and (1.86 ± 0.29) for cyclohexanol, menthol, borneol, fenchol, camphor, and fenchone,
respectively. The reported error is twice the standard deviation. Product studies of the reactions were performed using multipass
in situ FTIR (Fourier transform infrared spectroscopy) and solid-phase microextraction (SPME) with analysis by GC−MS (gas
chromatography−mass spectrometry). A detailed mechanism is proposed to justify the observed reaction products.
3
1
. INTRODUCTION
quenched to ground-state oxygen atoms, O( P), or react with
15
water vapor to form OH radicals, although it is now
recognized that the ozonolysis of alkenes and in particular
the photolysis of nitrous acid (HONO) can be important
Monoterpenes are a very important group of nonmethane
volatile organic compounds (NMVOCs) of natural origin
which are actively involved in the chemistry of the troposphere.
NMVOCs of natural origin are generally referred to as biogenic
volatile organic compounds (BVOCs). They are emitted in
large amounts to the atmosphere in a wide variety of different
forms mainly from vegetation.
detected in indoor environments due to the use of consumer
cleaning products and air fresheners and release from building
and furnishing materials. On a global scale, the emissions of
16
sources of OH radicals, particularly in urban areas.
Until fairly recently the chlorine atom initiated oxidation of
NMVOCs has generally only been considered to be of
importance in coastal and marine air environments and in the
Arctic troposphere during springtime where it is believed that
the main source of chlorine atoms is the photolysis of chlorine-
containing compounds generated in the heterogeneous
However, in a recent field
study nitryl chloride (ClNO ), a gaseous photolytic Cl atom
precursor, was observed in continental regions far from coastal
and marine regions, suggesting that Cl chemistry may possibly
be ubiquitous in the atmosphere and play a significantly more
important role than previously thought in the oxidizing capacity
of the troposphere particularly in the early morning.
Rate coefficients for the reactions of Cl atoms with organic
compounds are generally a factor of 10 higher than the
thus although the
average concentration of chlorine atoms is much lower than
that of OH radicals, the two reactions can compete with one
1
−5
BVOCs have also been
17
6
7
1
5,18,19
−1
reactions of sea-salt aerosols.
BVOCs have been estimated to be 1150 TgC year , of which
4
11% is attributed to monoterpenes. In North America the total
2
−1
BVOC emissions have been estimated to be 84 TgC year of
which 25% is allocated to monoterpenes and sesquiterpenes.
In Europe the estimated amounts of monoterpenes for July
3
8
2
003 ranged from 338 to 1112 Gg. The emissions rates of
20
1
BVOCs generally depend on temperature and light intensity.
BVOCs are known to contribute significantly to the formation
of secondary organic aerosols (SOAs) and tropospheric
ozone,
play an important role in the chemistry of regional-scale air
pollution.
9
2
1,22
1
0,11
corresponding OH rate coefficients,
and thus can, depending on time and location,
1
2−14
The tropospheric degradation of monoterpenes
will primarily occur via reaction with OH radicals during the
daytime and with NO radicals at night-time. The main source
Received: December 14, 2011
Revised: March 21, 2012
Published: March 26, 2012
3
of OH radicals in the atmosphere is generally assumed to be the
1
photolysis of O to generate O( D) atoms which are either
3
©
2012 American Chemical Society
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Figure 1. Structure and names, IUPAC and common, of the oxygenated terpenes and cyclohexanol studied in this work.
another in areas where the chlorine atom concentration is
sufficiently high. Degradation mechanisms of VOCs initiated by
OH radical and Cl atom are often very similar, in particular, for
saturated VOCs. In mechanistic studies, Cl-initiated degrada-
tion is often used as a surrogate for the analogue OH reaction
since the experiments with Cl atoms are generally easier to
perform.
2. EXPERIMENTAL SYSTEMS
This section has been divided into three subsections for ease of
presentation. The first one briefly describes the relative rate
technique used in two different laboratories at the University of
Castilla-La Mancha (UCLM) and at the University of
Wuppertal (UW). The experimental setups employed at
UCLM and UW are described separately in subsections 2.2
and 2.3, respectively.
To date, kinetic and mechanistic studies on the reactions of
OH, NO , and Cl with terpenes have mainly been focused on
unsaturated species.
2.1. Relative Rate Technique. The relative rate method is
3
23−29
a well-established technique for measuring the reactivity of Cl
23
atoms and OH radicals with organic compounds where the
decay of the compound under investigation is measured relative
to the decay of a reference hydrocarbon whose rate coefficient
with the oxidant is well-known. In the present study the decay
of the oxygenated terpene and the reference hydrocarbon (ref)
due to the reaction with the oxidant X (Cl or OH) can be
described by the following reactions
In this work relative kinetic and mechanistic studies have
been performed at atmospheric pressure and room temperature
for the reactions of OH radicals and Cl atoms with the
oxygenated terpenes: borneol, fenchol, menthol, camphor, and
fenchone (Figure 1). To our knowledge, only the reactions of
camphor with OH, NO , and O have been investigated
3
3
30
previously. Reissell et al., using relative rate methods, have
3
−1 −1
obtained rate coefficients (in cm molecule
±
s
units) of (4.6
1.2) × 10− , < 3 × 10 , and <7 × 10 for the reactions of
OH, NO , and O with camphor at 298 ± 2 K and 740 Torr
OH/Cl + oxygenated terpene → products ki
OH/Cl + ref → products kref
(1)
(2)
12
−16
−20
3
3
total pressure of purified air, respectively. Reissell et al. also
identified the products of the OH reaction. The yield for the
formation of acetone was directly determined by gas
chromatography to be (0.29 ± 0.04). Using in situ atmospheric
pressure ionization tandem mass spectrometry (API-MS), they
found evidence for the formation of dicarbonyl, hydroxycar-
bonyl, carbonyl-nitrate, and hydroxycarbonyl-nitrate com-
pounds in the reaction system.
where k and k are the rate coefficients for reactions of the
i
ref
oxidant with the oxygenated terpene and the reference
hydrocarbon, respectively. Provided that the oxygenated
terpene and reference hydrocarbon are lost only by reactions
1 and 2, it can be shown that
⎛
⎞
⎛ ⎛
⎞⎞
[
terpene]0
ki
[reference]0
ln⎜
⎟ =
⎜ln⎜
⎟⎟
⎟
⎜
⎝ [terpene] ⎠ kref ⎝ ⎝ [reference] ⎠⎠
t
t
(3)
The structure of three of the oxygenated terpenes chosen for
study in this work (borneol, fenchol, and menthol) contains the
cyclohexanol structural element. The kinetics and products of
the reaction of OH radicals with cyclohexanol has been
where [terpene] , [reference] , [terpene] , and [reference] are
0
0
t
t
the concentrations of the oxygenated terpene and the reference
hydrocarbon at times t = 0 and t, respectively. According to eq
31
3, the linear least-squares analysis of ln([terpene]
/[terpene] )
0 t
investigated by Bradley et al., but to our knowledge there is
no kinetic information on the reaction of Cl atoms with
cyclohexanol. For this reason and for purposes of comparing
the product profiles with those obtained for the oxygenated
terpenes containing the cyclohexanol structure, a kinetic and
product study of the reaction of chlorine atoms with
cyclohexanol has also been performed.
against ln([reference] /[reference] ) plots yields k /k from
0
t
i
ref
the slope and a zero intercept. Provided that kref is known, the
rate coefficient of the reactions 1, k , can then be determined by
i
multiplying the slope by kref.
Equation 3 relies on the assumption that both the
oxygenated terpene and the reference hydrocarbon are
removed solely by reaction with the oxidant (Cl or OH). To
verify this assumption, various tests were performed to assess
possible complications in the experiments through reaction of
the reactants with the radical precursors (Cl , SOCl , H O , or
The kinetic data obtained in this work allow establishing the
dominant tropospheric removal process for the title oxygenated
terpenes. In addition, the accompanying product study allows
proposing a reaction mechanism for the main product forming
channels.
2
2
2
2
CH ONO), photolysis, and reactant loss on the walls. These
3
tests are previously described by Ceacero-Vega et al. for the
4
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3
2
reactions of the oxidants with 1,8-cineole, and they showed
that the potential interferences for both the oxygenated
terpenes and the reference hydrocarbons are negligible.
In a chemical reaction the yield of a primary product B, α, is
given by the ratio between the formation rate of B and the
disappearance rate of the terpene:
DSQ II) or a FID (flame ionization detector). Chlorine atoms
were produced by either the photolysis of Cl or SOCl in the
2
2
bath gas (synthetic air or He), and OH radicals by the
photolysis of H O . Experiments were also performed in the
2
2
absence of radiation to check for dark reactions and wall losses.
Products studies on the reactions of OH and Cl with
cyclohexanol, borneol, and fenchol were performed in the 200
L Teflon bag at 298 ± 2 K and 720 ± 5 Torr total pressure of
synthetic air, using the solid-phase microextraction sampling
technique (SPME) and analysis with GC−MS and FID. SPME
is a sampling technique which does not use a solvent and has
d[B]
dt
d[terpene]
α =
−
dt
(4)
However, B can subsequently react with the oxidants (OH/
Cl); therefore, in order to obtain the correct concentration of B
formed in the reaction, the measured concentration has been
corrected by the amount of B consumed by the oxidant. This
method is described in detail in various publications.
concentration correction factor F is given by the following
been shown to be very effective in the study of organic
32,38−44
compounds.
In this work, a 50/30 μm divinylbenzene/
carboxen/polydimethylsyloxane fiber is used, which was
exposed during experiments to the chamber contents for
typically 20 min. The absorbed compounds were then desorbed
at 270 °C in the heated injection port of the GC-MS
instrument. Identification of reaction products was made by
comparison of the mass spectra with a library of mass spectra
and the mass spectra of commercial samples when available.
For quantification of the product yields, SPME sampling in
conjunction with the GC-FID system was used. Tests were
made to ensure that the FID response was linear to the
detected reactant/product over the range of concentrations
used in the experiments.
33−35
The
expression
[
terpene]t
1
−
ki/k
p
[terpene]0
kp/ki
F =
×
ki
[terpene]t
([
terpene]0
[terpene]t
[terpene]0
−
)
(5)
where k is the rate coefficient for the reaction of oxygenated
terpene with the oxidant (OH or Cl), and k is the rate
coefficient for the reaction of the primary product with the
oxidant. The slopes of plots of the corrected product
concentration versus the amount of reacted oxygenated terpene
will give the product yield.
i
p
2
.3. Experimental Systems at the University of
Wuppertal (UW). Only a brief description of the experimental
systems at UW is given here since the systems have been
45−47
described in detail elsewhere.
The experiments were
performed at 298 ± 2 K and 760 ± 10 Torr total pressure of
synthetic air or nitrogen in two cylindrical reactors, a 1080 L
quartz glass and a 480 L borosilicate glass chamber, each closed
at both ends by aluminum flanges. Each chamber is equipped
with a pumping system consisting of a turbo-molecular pump
backed by a double-stage rotary fore pump which enables the
reactors to be evacuated to about 10− Torr. Magnetically
coupled Teflon mixing fans are mounted inside each chamber
to ensure homogeneous mixing of the reactants with the bath
gas. The photolysis system for the 1080 L reactor consists of 32
superactinic fluorescent lamps (Philips TL05 40 W: 320−480
nm, λmax = 360 nm), which are spaced evenly around the
reaction vessel while for the 480 L reactor it consists of 20 such
lamps which are likewise spaced evenly around the chamber.
The chambers each contain a White type multiple-reflection
mirror system for sensitive in situ long path absorption
monitoring of reactants and products in the IR spectral range
2
.2. Experimental Systems at the University of
Castilla-La Mancha (UCLM). The experimental systems at
UCLM consist of two environmental chambers equipped with
FTIR or GC-MS and GC-FID analytical techniques. A detailed
description of the chamber setup with FTIR has previously
been presented for studies on the reaction of Cl atoms with
linear and branched alcohols, and that of the chamber setup
with GC-MS and GC-FID for the reaction of Cl atoms with
3
36,37
THP (tetrahydropyran);
therefore, only a brief description
of the chamber experimental systems is given here. The
reaction chamber with FTIR as the detection method consists
of a 16 L borosilicate glass cylinder containing a multipass
optical reflection system, which is coupled to a Nexus Thermo
Nicolet FTIR spectrometer equipped with a liquid nitrogen
cooled mercury cadmium telluride (MCT) detector for online
infrared spectroscopy. A total path length of 96 m was used,
and infrared spectra were obtained by coadding 64 scans with a
resolution of 2 cm . The chamber is surrounded by 4 evenly
spaced UV fluorescent lamps (Philips TL-K 40 W, λmax = 365
nm) that continuously irradiate the gas sample. Liquid and
gaseous compounds were introduced directly into the cell by
expansion from a glass manifold system and mixed in synthetic
air or helium at 298 ± 2 K and 720 ± 5 Torr of total pressure.
Compounds in the solid state or liquids with a low vapor
pressure were introduced into the chamber by flowing the bath
gas through a heated glass bulb which contained the
compounds.
−1
−1
4000−700 cm . The White systems are set for total optical
path lengths of 51.6 and 484.7 m in the 480 and 1080 L
chamber, respectively. IR spectra were recorded with a spectral
resolution of 1 cm− using Nicolet Magna 550 (480 L reactor)
and Nicolet Nexus (1080 L reactor) FTIR spectrometers each
equipped with liquid nitrogen cooled MCT detectors.
1
Chlorine atoms were generated by the photolysis of Cl , and
2
OH radicals were generated by the photolysis of CH ONO in
3
the presence of NO. As described in subsection 2.1,
experiments were performed to test for complicating factors
such as reaction with radical precursors, photolysis, or wall loss
of the compounds under investigation. The tests showed that
such potential interferences were negligible.
The experimental system with GC-MS and GC-FID
analytical methods consisted of either a 100 or 200 L Teflon
bag, surrounded by 8 lamps emitting in the visible (Philips TL
4
0 W, λmax = 365 nm) and 8 UV lamps (Philips TUV G 36 W,
2.3. Chemicals and Reactant Concentrations. The
chemical purities of the reagents used were as follows: synthetic
air (Praxair, 99.999%), 1-butene (Messer Griesheim, grade 2.0),
propene (Messer Griesheim, 2.8; Praxair 99.8%), 1,3-butadiene
3
6
λmax = 254 nm). Gas samples from the reactor were analyzed
by a GC (Thermo Electron Co., model Trace GC Ultra)
coupled to a mass spectrometer (Thermo Electron Co., model
4
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(
(
Aldrich, 99%), camphor (Sigma-Aldrich, ≥ 95%), borneol
The slope of such plots corresponds to the rate coefficient
ratio k /k . The values of k /k extracted from linear-least-
Sigma-Aldrich, ≥ 99%), Cl (Messer Griesheim, 99.8%, Praxair
2
i
ref
i
ref
9
9.999%), fenchol (Sigma-Aldrich, > 97), fechone (Sigma-
squares analyses of these plots are summarized in Table 1.
The absolute rate coefficients for the OH-reaction with the
oxygenated terpenes given in Table 1 have been obtained by
multiplying the rate coefficient ratio with the appropriate value
of the rate coefficient for reaction of OH with the reference
Aldrich, ≥ 99.5%), H O (Scharlau, 50%), He (Praxair,
9
2
2
9.995%), nitrogen (Air Liquide, 99.999%), synthetic air (Air
Liquide, 99.99%, and Praxair 99.99%), NO (Praxair, 99.999%),
n-octane (Sigma-Aldrich, ≥ 99.0%), SOCl (Sigma-Aldrich, ≥
2
compound. Rate coefficients used (×10− cm molecule s )
at 298 K for the OH-reaction with 1-butene, propene, and n-
23
11
3
−1 −1
9
9.0%), tetrahydropyran (Sigma-Aldrich, 99%), cyclohexane
(
Sigma-Aldrich, 99%), cyclohexanol (Sigma-Aldrich, 99%). All
48
compounds were used without further purification.
octane were (3.14 ± 0.62), (2.63 ± 0.39), and 8.11,
The initial concentration ranges used in the experiments
performed at UCLM and UW were (0.6−11.7) ppmV for the
oxygenated terpenes, (1.1−46.4) ppmV for the reference
respectively. Table 1 shows rate coefficients obtained with two
different reference hydrocarbons that are in excellent agree-
ment; therefore, the reported rate coefficient for these reactions
compounds, (1.8−24.7) ppmV for Cl , (4.4−11.7) ppmV for
is the average of the individual determinations. Thus, k for the
2
i
SOCl , (23.2−46.4) ppmV for H O , and (1.9−22.3) ppmV for
reactions of the oxygenated terpenes with OH at 298 K and
2
2
2
−11
3
NO.
720 Torr total pressure are the following (in units of 10 cm
molecule− s ): (2.65 ± 0.32) for borneol, (2.49 ± 0.30) for
fenchol, (1.48 ± 0.31) for menthol, (0.38 ± 0.08) for camphor,
and (0.39 ± 0.08) for fenchone, as Table 1 shows.
1
−1
3. RESULTS AND DISCUSSION
3.1. Relative Rate Coefficients for OH Reactions. The
experimental data obtained from the kinetic investigations on
the reactions of OH with borneol and fenchol at UW and
menthol, camphor, and fenchone at UCLM have been analyzed
in accordance with eq 3. Figure 2 (lower plot) shows several
The rate coefficients obtained for the bicyclic oxygenated
terpenes studied in this work are of the same order of
magnitude as those for bicylic alkanes of similar size such as
bicyclo[2.2.2]octane, bicyclo[3.3.0]octane, bicyclo[2.2.1]-
heptane, cis-bicyclo[4.3.0]nonane, and trans-bicyclo[4.3.0]-
−11
3
nonane where values in the range (0.51−1.65) × 10
cm
have been reported. The rate coefficient for
the reaction of OH with 1,8-cineole at 293 K and 760 Torr total
molecule−
1
s
−1
23
32
pressure reported by our research groups is also of the same
order of magnitude, (1.04 ± 0.12) × 10− cm molecule s .
Rate coefficients for the reactions of OH with the oxygenated
terpenes can only be compared with the previous study on the
11
3
−1 −1
30
reaction of OH with camphor by Reissell et al. They reported
a rate coefficient of (0.46 ± 0.12) × 10− cm molecule
11
3
−1 −1
s
for the reaction of OH with camphor, which is in agreement
with the value obtained in this work. The rate coefficient
obtained for the reaction of OH radicals with fenchone is very
similar to that for camphor, which is expected since they both
have very similar structures.
For the remaining of the oxygenated terpenes, k can be
i
compared with that of the reaction of OH with cyclohexanol,
which has a similar but simpler structure than borneol, fenchol,
and menthol. As mentioned in the Introduction, Bradley et al.
−
11
3
reported a rate coefficient of (1.90 ± 0.05) × 10
cm
molecule−
1
s
−1
for the reaction of OH with cyclohexanol at 293
K and 760 Torr total pressure. This value is similar to the
values obtained in the present work for the alcoholic terpenes
31
(
menthol, borneol, and fenchol).
A rate coefficient of (6.97 ± 1.39) × 10− cm molecule
12
3
−1
s− is reported in the literature for the reaction of OH with
1
23
cyclohexane. This value is only slightly higher than the value
of (6.39 ± 0.12) × 10− cm molecule
12
3
−1 −1
s
reported for the
49
reaction of OH with cyclohexanone by Dagaut et al., whereas
Figure 2. Examples of relative rate data for the reactions of OH
for cyclohexanol and menthol the rate coefficients are
(lower) and Cl atoms (upper) with oxygenated terpenes using
−11
3
−1
significantly higher, (1.90 ± 0.05) × 10
cm molecule
different reference compounds. For clarity the near-zero y-intercepts
have been shifted on some plots.
−131
−11
3
−1 −1
s
and (1.58 ± 0.32) × 10
cm molecule
s
(this
work), respectively. Whereas the ketone group has a
deactivating −I effect on the OH reactivity, Nelson et al.
reported that the −OH group in linear alcohols has a long-
range activating effect on reactivity that can stretch over five
50
examples of plots of eq 3 for these OH-reactions where
propene or 1-butene was used as reference compound. For all
compounds the plots show good linearity and pass through the
origin.
carbon atoms. The same tendency would seem to apply for
the bicyclic oxygenated terpenes (borneol, fenchol, camphor,
and fenchone). The rate coefficients for these compounds are
also much higher than that of 5.12 × 10− cm molecule
12
3
−1 −1
s
4
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Table 1. Rate Coefficients for the Reactions of Oxygenated Terpenes with OH Radicals at 298 K and 720 Torr of Pressure in
a
Air
1
1
(
ki ± 2σ) × 10
3 −1
detection
technique
(ki ± 2σ) × 1011
3 −1
(cm molecule s−1
average
)
terpene
borneol
exptl syst
ref
OH source
(k /k ) ± 2σ
(cm molecule s−1
)
i
ref
b
UW (480 L)
1-butene
propene
1-butene
propene
FTIR
CH ONO/NO 0.84 ± 0.01
2.64 ± 0.53
2.66 ± 0.38
2.54 ± 0.51
2.47 ± 0.37
1.48 ± 0.31
0.38 ± 0.08
0.39 ± 0.09
2.65 ± 0.32
3
b
UW (480 L)
FTIR
CH ONO/NO 1.01 ± 0.01
3
b
fenchol
UW (480 L)
FTIR
CH ONO/NO 0.81 ± 0.01
2.49 ± 0.30
3
b
UW (480 L)
FTIR
CH ONO/NO 1.01 ± 0.01
3
c
menthol
camphor
UCLM (200 L) n-octane
GC-FID/SPME
GC-FID/SPME
GC-FID/SPME
H O2
2
1.83 ± 0.08
0.47 ± 0.02
0.48 ± 0.02
1.48 ± 0.31
0.38 ± 0.08
0.39 ± 0.09
c
UCLM (200 L) n-octane
H O2
2
c
fenchone UCLM (200 L) n-octane
H O2
2
a
11
3
1 1
11
3
1 1 48
11
cm3
k1‑butene = (3.14 ± 0.62) × 10
cm molecule
s
; kpropene = (2.63 ± 0.39) × 10
cm molecule
s
.
kn‑octane = 8.11 × 10

1
1 23
b
c
molecule
s
.
UW: University of Wuppertal. UCLM: University of Castilla − La Mancha.
Table 2. Rate Coefficients for the Reactions of Cyclohexanol, Menthol, Borneol, and Fenchol with Cl atoms at 298 K and 720
a
Torr, using FTIR as Detection Technique and Cl as Cl Source
2
1
0
(
ki ± 2σ) × 10
3 ‑1 ‑1
(
cm molecule s )
average
(ki ± 2σ) × 1010 (cm molecule s )
3
‑1 ‑1
compd
exptl syst
ref
bath gas
(k /k ) ± 2σ
i ref
b
cyclohexanol
UCLM (16 L)
propene
propene
1-butene
1-butene
propene
propene
1-butene
1-butene
propene
propene
propene
1-butene
1,3-butadiene
cyclohexane
1-butene
1-butene
propene
propene
air
He
air
air
air
He
air
N2
air
air
He
air
air
air
air
N2
air
air
air
1.44 ± 0.01
1.44 ± 0.02
1.09 ± 0.01
1.17 ± 0.01
1.51 ± 0.02
1.53 ± 0.04
0.89 ± 0.01
0.91 ± 0.01
1.23 ± 0.01
1.22 ± 0.02
1.25 ± 0.02
0.92 ± 0.02
0.66 ± 0.01
0.89 ± 0.02
0.98 ± 0.01
0.98 ± 0.02
1.28 ± 0.02
1.29 ± 0.02
1.03 ± 0.02
3.21 ± 0.45
3.21 ± 0.45
3.20 ± 0.46
3.44 ± 0.49
3.36 ± 0.47
3.40 ± 0.48
2.62 ± 0.38
2.67 ± 0.38
2.74 ± 0.38
2.72 ± 0.38
2.79 ± 0.38
2.70 ± 0.39
2.76 ± 0.27
2.73 ± 0.55
2.88 ± 0.41
2.88 ± 0.42
2.86 ± 0.40
2.96 ± 0.30
3.03 ± 0.44
3.21 ± 0.26
3.40 ± 0.28
2.72 ± 0.13
b
UCLM (16 L)
b
UCLM (16 L)
c
menthol
borneol
UW (480 L)
b
UCLM (16 L)
b
UCLM (16 L)
c
UW (480 L)
c
UW (480 L)
c
UW (480 L)
b
UCLM (16 L)
b
UCLM (16 L)
b
UCLM (16 L)
b
UCLM (16 L)
b
UCLM (16 L)
c
fenchol
UW (1080 L)
2.93 ± 0.17
c
UW (1080 L)
c
UW (1080 L)
b
UCLM (16 L)
b
UCLM (16 L)
1-butene
a
−10
3
−1 −1
−10
3
−1 −1 21
−10
cm3
kpropene = (2.23 ± 0.31) × 10 cm molecule s ; k
= (2.94 ± 0.42) × 10 cm molecule s . k1,3‑butadiene = (4.20 ± 0.40) × 10
b c
1‑butene
−1
−1 54
−10
3
−1 −1 55
molecule s . kcyclohexane = (3.08 ± 0.12) × 10 cm molecule s .
Wuppertal.
UCLM: University of Castilla − La Mancha. UW: University of
reported for the reaction of OH with the alkane bicyclo[2.2.1]-
heptane which has a similar carbon number. The reaction of
OH radicals with the oxygenated terpenes proceeds by
borneol and fenchol it is underestimated. For the bicyclic
ketones, camphor and fenchone, the measured rate coefficients
are factors of ∼2.5 lower than the calculated SAR values.
2
3
51
hydrogen atom abstraction from the various −CH − groups
The SAR of Kwok and Atkinson includes a factor to
account for activation of H-atom abstraction from C−H bonds
on the β-carbon to the carbonyl group, which is attributed to
the formation of a hydrogen-bonded transition state. However,
n
(n = 1−3) in the compounds. The magnitude of the OH rate
coefficients for the oxygenated terpenes will depend on the
number of primary, secondary, and tertiary H-atoms in the
carbon skeleton and the effect neighboring substituent has on
their OH reactivity. This is the premise of the structure and
53
a recent study on the reaction of OH with cycloketones
concluded that this β-activation is absent in cyclopentanone
and cyclohexanone but occurs for cyclooctanone and cyclo-
heptanone. This conclusion is in agreement with the discussion
51
activity relationship (SAR) method for estimating rate
coefficients.
49
The SAR estimated rate coefficients for menthol, borneol,
fenchol, camphor, and fenchone are the following (in units of
of Dagaut et al. The cyclic ketones investigated in this study,
camphor and fenchone, have each two C5 rings. If the rate
coefficients for OH with camphor and fenchone are calculated
with the Kwok and Atkinson SAR without incorporation of a β-
−11
3
−1 −1
10
cm molecule s ): 2.79, 1.64, 1.40, 0.99, and 1.19,
respectively. In the SAR calculations for menthol, borneol, and
fenchol, the updated substituent factors for effects of OH
substituent on H-atom abstraction at the α- and β-positions as
−
11
3
activation factor, a rate coefficient of 0.58 × 10
cm
molecule−
1
s
−1
is obtained for both reactions which is in
52
reported by Bethel et al. have been used. The measured rate
coefficient for OH with the monocyclic alcohol menthol is
overestimated by the SAR whereas for the bicyclic alcohols
excellent agreement with the measured rate coefficients and
vindicates the conclusions on β-activation in ring systems
49
53
reported by Dagaut et al. and Aschmann et al.
4
101
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Article
Table 3. Rate Coefficients Obtained for the Reactions of Camphor and Fenchone with Chlorine Atoms at 298 K and 720 Torr
a
of Pressure
1
0
(
k ± 2σ ) × 10
i
3 ‑1 ‑1
1
0
(
k ± 2σ ) × 10
(cm molecule s )
average
i
3
‑1 ‑1
compd
exptl syst
ref
propene
bath gas detection technique Cl source (k /k ) ± 2σ (cm molecule s )
i ref
b
camphor
UW (1080 L)
air
N2
air
air
air
air
N2
air
air
air
He
FTIR
Cl2
0.70 ± 0.01
0.70 ± 0.01
0.57 ± 0.01
0.70 ± 0.01
0.55 ± 0.01
0.63 ± 0.01
0.64 ± 0.01
0.61 ± 0.01
0.82 ± 0.02
0.78 ± 0.03
0.84 ± 0.06
1.56 ± 0.22
1.56 ± 0.22
1.68 ± 0.24
1.56 ± 0.22
1.62 ± 0.23
1.85 ± 0.27
1.88 ± 0.27
1.80 ± 0.26
1.83 ± 0.26
1.72 ± 0.26
1.86 ± 0.30
1.59 ± 0.10
b
UW (1080 L)
propene
FTIR
Cl2
b
UW (1080 L)
1-butene
propene
FTIR
Cl2
c
UCLM (16 L)
FTIR
Cl2
c
UCLM (16 L)
1-butene
1-butene
propene
FTIR
Cl2
b
fenchone
UW (1080 L)
FTIR
Cl2
1.86 ± 0.29
b
UW (1080 L)
FTIR
Cl2
b
UW (480 L)
1-butene
propene
FTIR
Cl2
c
UCLM (16 L)
FTIR
Cl2
c
UCLM (200 L)
tetrahydropyran
SPME/GC-MS
SPME/GC-MS
SOCl2
SOCl2
c
UCLM (200 L)
tetrahydropyran
a
−10
3
−1 −1
= (2.94 ± 0.42) × 10−10 cm molecule s . ktetrahydropyran = (2.21 ± 0.32) × 10−10
3
−1 −1 21
k
= (2.23 ± 0.31) × 10 cm molecule s ; k
propene
1‑butene
3
−1 −1 36
b
c
cm molecule s . . UW: University of Wuppertal. UCLM: University of Castilla − La Mancha.
All the compounds have the same number of −CH and
As for reactions of the oxygenated terpenes with OH, the
3
−
CH − groups, but they differ in the number of available
reactivity of these compounds toward Cl atoms will be mainly
determined by the types of abstractable H-atoms. On this basis,
one would expect the following reactivity trend: menthol >
borneol ≈ fenchol > camphor ≈ fenchone. As can be seen in
Tables 2 and 3, that is the experimentally observed trend.
The rate coefficients for the reactions of Cl with camphor
and fenchone can be compared with the rate coefficient for the
reaction of Cl with cyclohexanone. An averaged published value
2
>
CH− groups: one for camphor and fenchone, two for borneol
and fenchol, and four for menthol. On this basis, one would
expect menthol to be the most reactive compound, borneol and
fenchol to be similar in reactivity and slightly slower, and
camphor and fenchone to be the slowest and also similar in
reactivity. Except for menthol, the observed reactivity follows
this trend. The reason for the higher reactivity of the bicyclic
compounds, borneol and fenchol, toward OH compared to
menthol is not presently clear. Further measurements are
necessary to validate the rate coefficients reported here for the
reactions of OH with these compounds before any definitive
conclusions regarding the reactivity trend can be made.
of (1.74 ± 0.15) × 10− cm molecule
10
3
−1 −156−58
s
is available
for this reaction which is similar to the rate coefficient
measured in this work for the reaction of fenchone and
camphor with Cl atoms. The rate coefficients for all the
oxygenated terpenes are of the same order of magnitude as that
measured for the reaction of chlorine atoms with 1,8-cineole of
3.2. Relative Rate Coefficients for Cl Reactions. Figure
10
3
−1 −1 32
(
2.20 ± 0.11) × 10− cm molecule s .
2
(upper) shows examples of the kinetic data obtained from
Using the SAR method developed for estimating rate
investigations on the reactions of the oxygenated terpenes with
Cl atoms plotted according to eq 3. The plots for all of the
compounds show good linearity and pass through the origin.
ki/kref rate coefficient ratios obtained for cyclohexanol and the
oxygenated terpenes from the linear least-squares analysis of
the kinetic data are listed in Tables 2 and 3. The rate
coefficients for the reactions of the title compounds with Cl
were put on an absolute basis using the following values (in
55
coefficients for the reactions of Cl with organics−, the
10
3
estimated rate coefficient for cyclohexanol (2.94 × 10 cm
molecule− s ) is in very good agreement with the
experimentally determined one. A substituent factor for the
OH alcoholic group of 0.90, which has been derived from
several reactions of aliphatic alcohols with Cl, was used in that
estimation. Similar agreement is found for the reactions of Cl
with menthol, borneol, and fenchol where the SAR estimated k
1
−1
units 10− cm molecule s ) for the reactions of Cl with the
10
3
−1 −1
(in 10− cm molecule
10
3
−1 −1
s
units) values are 3.29, 2.99, and
21
reference compounds: propene (2.23 ± 0.31), 1-butene (2.94
2
1
54
2.99, respectively. However, for camphor and fenchone the
±
(
0.42), 1,3-butadiene (4.20 ± 0.40), and cyclohexane
55
−
10
3
−1
SAR method provides values of 2.24 × 10 cm molecule
1 3
3.08 ± 0.12). Tables 2 and 3 show the rate coefficients
−
−10
−1 −1
s , and 2.65 × 10 cm molecule s , respectively, when
using a factor of 0.17 for the contribution of the carbonyl group
obtained from experiments performed in different reactors and
bath gases, and using different reference compounds. k was
i
to the reactivity derived from the rate coefficient of cyclo-
observed to be independent of those experimentally, and
therefore, an average of the individual determinations is also
reported in Tables 2 and 3.
56−58
hexanone with chlorine atoms,
which are somewhat higher
than the corresponding values obtained experimentally in this
work.
−
10
cm3
The rate coefficient of (3.21 ± 0.26) × 10
molecule−
1
s
−1
obtained for the reaction of Cl with cyclo-
4
. PRODUCT STUDIES AND MECHANISM
hexanol can be compared with the rate coefficients for the
reactions of Cl atoms with the linear alcohols hexanol and 1-
heptanol which have a similar number of carbon atoms. Nelson
et al. have reported rate coefficients of (2.90 ± 0.09) and (3.49
Product studies have been performed on the reactions of Cl
atoms and OH radicals with borneol and fenchol by irradiation
of oxygenated terpene/Cl /air or oxygenated terpene/H O /air
2
2
2
10
3
−1 −1
±
1
0.18) × 10− cm molecule s for the reactions of Cl with
mixtures at 298 K and 720 Torr total pressure. A product study
has also been performed for the reaction of chlorine atoms with
cyclohexanol. Reaction products, once identified, were
corrected for secondary consumption using eq 5, and their
50
-hexanol and 1-heptanol, respectively. The rate coefficient
obtained in this work for cyclohexanol with chlorine atoms is in
good agreement with these values.
4
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Article
yields were then extracted from plots of the corrected
concentration of the products versus the amount of reacted
oxygenated terpene (or cyclohexanol). With all the exper-
imental results and well-established VOC degradation pathways
in the atmosphere, mechanisms have been elucidated for the
reactions of OH radicals and Cl atoms with borneol (see
below).
reported a cyclohexanone yield of (55.0 ± 0.6)% for the
31
reaction of OH radicals with cyclohexanol which is much
higher than the value for reaction with chlorine atoms
measured in this work. This difference is probably due to the
fact that reactions of Cl atoms with VOCs are much less site
specific than the corresponding OH radical reactions. The SAR
method estimates that approximately 11% and 58% of the Cl
and OH reactions, respectively, will occur at the H from tertiary
carbon site which is in accordance with the reported
cyclohexanone yield in this work and that of Bradley et al.
Cyclohexanone is detected as main product of reaction. The
formation of cyclohexanone is initiated by the abstraction of a
tertiary hydrogen atom from the >CHOH− entity of
cyclohexanol to give the 1-hydroxycyclohexyl radical which
reacts immediately with O to give cyclohexanone and a HO
15
4.1. Product Study on the Cl + Cyclohexanol Reaction.
Figure 3 shows an example of a gas chromatogram of a sample
2
2
radical. A similar mechanism has been proposed for the
formation of cyclohexanone from the reaction of cyclohexanol
31
with OH radicals. Cyclohexene and chlorocyclohexane are
detected as minor product of the reaction. The source of these
compounds is currently unknown, but it is suspected that they
are formed heterogeneously.
4
.2. Product Study of the Reactions of Borneol and
Fenchol with OH Radicals. Product studies were performed
on the reactions of borneol and fenchol with OH radicals in the
200 L reactor at UCLM at 298 K and 720 Torr total pressure.
Mixtures of borneol/H O /air and fenchol/H O /air were
Figure 3. Gas chromatograms of samples from a Cl /cyclohexanol/air
reaction mixture before and after photolysis.
2
2
2
2
2
taken before and after irradiation of a cyclohexanol/Cl /air
irradiated over periods of 3 min. Figure 5 shows an example of
a chromatogram before and after irradiation of a fenchol/
H O /air mixture. The only identified product for fenchol was
2
mixture in the 200 L chamber at UCLM. Cyclohexanone,
chlorocyclohexane, and cyclohexene were identified by
comparison of their mass spectrum with the corresponding
spectra from a spectral library and also the mass spectrum
generated experimentally from a commercial sample of the
compound. Cyclohexanone is present as an impurity in
cyclohexanol. This initial amount of cyclohexanone was
considered in the yield corrections.
2
2
fenchone, and for borneol, the only detected product was
camphor. Figure 5 shows a collection of chromatographic peaks
with values of m/z = 166 and 168 obtained in the product study
on the reaction of fenchol with OH. This behavior was also
observed in the reaction of borneol with OH. The peaks with
m/z = 166 can be assigned to a dicarbonyl secondary product
Figure 4 shows plots of the corrected and uncorrected
concentrations of cyclohexanone versus the amount of reacted
(
with formula of C H O ) produced by the reaction of
10 14 2
camphor (or fenchone) with the OH radicals as was proposed
30
by Reissell et al. They proposed a collection of structures for
these compounds. The peaks with m/z = 168 can be tentatively
assigned to formation of hydroxycarbonyl compounds.
Unfortunately, these compounds could not be quantified,
since they are not commercially available.
Quantification has only been possible for camphor and
fenchone. Reaction yields have been obtained from plots of
corrected amount of camphor (or fenchone) formed versus
reacted borneol (or fenchol). Figure 6 shows an example of
such plots for the formation of camphor from the reactions of
hydroxyl radicals and chlorine atoms with borneol. The rate
coefficients obtained in this work for the reactions of camphor
and fenchone with OH radicals were used to correct for
secondary OH consumption of the compounds. The maximum
values of the correction factors F were 1.16 and 1.09 for
camphor and fenchone, respectively. The linearity of the
corrected concentration versus the reacted borneol is very good
for both the OH and Cl reactions. For the reaction of OH
radicals with borneol an average camphor yield of (49.0 ±
Figure 4. Plot of the concentration of cyclohexanone formed in the
reaction of Cl atoms with cyclohexanol as a function of the amount of
reacted cyclohexanol with and without correction for secondary
reactions using eq 5.
1
.0)% has been obtained, whereas for the reaction of OH with
cyclohexanol. The secondary consumption of cyclohexanone
fenchol a yield of (60.9 ± 2.6)% has been obtained for the
formation of fenchone. Cyclohexanone, camphor, and fenchone
will be formed from cyclohexanol, borneol, and fenchol,
respectively, via a mechanism involving abstraction of the
tertiary hydrogen atom attached to the carbon bonded to the
OH group. Bradley et al. have reported a yield of (55.0 ± 0.6)%
was corrected according to eq 5, assuming a rate coefficient k
p
−10
3
−1
for cyclohexanone to be (1.75 ± 0.15) × 10 cm molecule
−1
56−58
s .
The maximum correction factor F was 1.43. The yield
of cyclohexanone in the Cl-reaction is (9.1 ± 0.6)%, where the
reported error is twice the standard deviation. Bradley et al.
4
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Article
Figure 5. Gas chromatograms of samples from a fenchol/H O /air reaction mixture before and after photolysis.
2
2
fenchol), respectively. Figure 7 shows an example of a
mechanism proposed for the formation of products with m/z
1
68 from the reaction of borneol and OH radicals. Products
with m/z 170 have not been detected which implies that the
nonradical forming channels between the peroxy radicals are
probably minor and that the alkoxy radical forming channel
dominates.
4
.3. Product Studies of Borneol and Fenchol with Cl
Atoms. Analogous to the OH, product studies were performed
on the reactions of borneol and fenchol with Cl atoms in the
2
00 L reactor at UCLM at 298 K and 720 Torr total pressure.
Mixtures of borneol/Cl /air and fenchol/Cl /air irradiated over
2
2
periods of 90 s. Again, only formation of camphor and
fenchone from the reactions of Cl with borneol and fenchol
could be identified and quantified. The same collection of
chromatographic peaks with m/z = 166 and 168 were also
obtained in both cases. The yields of camphor and fenchone
were determined as outlined in the OH product section, and an
example is shown in Figure 6 for the formation of camphor
from the reaction of Cl with borneol. The concentrations of
camphor and fenchone were corrected for secondary
consumption by Cl using the rate coefficients determined in
this work (Table 3). The maximum correction factors were
Figure 6. Examples of camphor formed in the reaction of Cl atoms
and OH radicals with borneol as a function of the amount of reacted
borneol with and without correction for secondary reactions using eq
5.
for cyclohexanone formation from of the reaction of OH with
3
1
cyclohexanol. The SAR method predicts that for cyclo-
hexanone, camphor, and fenchone this reaction channel will
account for around 58% of the total reaction, which is in good
agreement with the observed carbonyl product yields.
The SAR method predicts that ∼15% of the attack of OH
occurs at the other tertiary hydrogen site in both borneol and
fenchol; however, no experimental evidence has been reported
for this pathway. Attack at the second tertiary H-atom will
probably lead to ring opened products, but they have not been
detected. Attack of OH at the primary hydrogens is predicted
to be of only minor importance (∼3.5%) whereas attack at the
secondary hydrogens is predicted to be around 24%.
On the basis of the results obtained in this study and
knowing the degradation pathways for VOCs in the
atmosphere, mechanisms have been proposed for the reaction
of radicals with borneol and fenchol. The formation of camphor
and fenchone from the reaction of OH with borneol and
fenchol is completely analogous to the formation of cyclo-
hexanone from the reaction of OH radicals with cyclohexanol.
The formation of the products with m/z values of 168 and
1
.16 and 1.46 for the reaction of Cl with camphor and
fenchone, respectively.
Yields for the formation of camphor and fenchone from the
reactions of Cl with borneol and fenchol were (13.6 ± 0.2)%
and (19.6 ± 0.8)% (Table 4). These yields are somewhat
higher than the yield of (9.1 ± 0.6)% for the formation of
cyclohexanone from the reaction of cyclohexanol with chlorine
atoms. As discussed for the analogous reactions with OH
radicals, the Cl atom reactions will proceed via abstraction of
the available hydrogen atoms in the molecules. The SAR
method for Cl reactions predicts that for both borneol and
fenchol about 11% of the reaction will proceed via abstraction
of the tertiary hydrogen atom attached to the carbon atom
bonded to the OH group. It is interesting to note that, as in the
analogous OH reactions, the yield of camphor from the
reaction of Cl with borneol is lower than the yield of fenchone
from the reaction of Cl with fenchol. This can be due to steric
1
−
70 can be explained by the attack of OH radicals at the
CH − positions in camphor or borneol (fenchone or
2
4
104
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Article
Figure 7. Proposed mechanism for the formation of products with m/z = 168 from the reactions of borneol with OH radicals or chlorine atoms.
Table 4. Primary Reaction Yields for Cyclohexanone,
Camphor, and Fenchone from the Reactions of
Cyclohexanol, Borneol, and Fenchol, Respectively, with
tropospheric lifetime (τ) of any VOC due to its reaction an
oxidant X is defined according to eq 6
a
1
Chlorine Atoms and OH Radicals
τ =
kx[X]
(6)
compd
reaction product
YOH (%)
YCl (%)
b
cyclohexanol
borneol
cyclohexanone
camphor
55.0 ± 0.6
49.0 ± 1.0
9.1 ± 0.6
13.6 ± 0.2
where k is the rate coefficient of the VOC with the oxidant X
x
(
in this work Cl atoms or OH radicals) which is present in the
fenchol
fenchone
60.9 ± 2.6
b
19.6 ± 0.8
31
atmosphere in a concentration [X]. For the estimation of the
tropospheric lifetimes of the title compounds with respect to
reaction with OH and Cl, the following average oxidant
a
Errors are twice the standard deviation. From by Bradley et al.
6
−3
concentrations were considered: 10 radical cm for OH
60
3
−3
radicals6 and an upper limit of 10 atom cm for chlorine
0,61
effects or underestimation of substituent effects, as discussed for
the OH reactions.
The SAR method predicts that approximately 52% of the
attack of Cl occurs at the −CH − groups and this attack can
give compounds with chromatographic peaks m/z = 166 and
atoms.
In marine environments, high Cl concentrations are
thought to be formed shortly after sunrise as a result of the
photochemistry of Cl-precursors. Spicer et al. observed high
concentrations of Cl2 at night and estimated a peak Cl
18
2
5
−3
concentration of 1.3 × 10 atom cm , which has also been
used in the estimation of τ under these specific conditions.
Table 5 shows the calculated tropospheric lifetimes of
cyclohexanol and the oxygenated terpenes due to reactions
with hydroxyl radicals and chlorine atoms.
The global tropospheric lifetime for reactions of OH-group-
containing compounds with hydroxyl radicals is around 13 h,
whereas for camphor and fenchone τ is 67 h. For the reactions
with Cl, using a Cl average concentration of 10 atom cm ,
global lifetimes of 38 days for the reactions of the alcohols and
68 days for the reactions of camphor and fenchone are
calculated. Using a higher Cl atom concentration, which
prevails in coastal and marine areas, the tropospheric lifetimes
of the alcoholic terpenes due to the Cl-reaction are around 7 h,
while they are around 12 h for camphor and fenchone. In the
light of these results, it can be concluded that the main gas
phase mechanism for removal of these compounds in the
atmosphere will be reaction with hydroxyl radicals; never-
1
68. No experimental evidence for attack at the >CH− group
could be found, despite the fact that SAR estimates put an
importance of 10% on this reaction pathway. The peaks with
m/z = 168 can be tentatively assigned to hydroxycarbonyl
compounds with formula C H O according to the
1
0
16
2
mechanism proposed by Reissell et al. in 2001. The peaks
with m/z = 166 can be tentatively assigned to dicarbonyl
compounds with formula C H O . A mechanism based on the
3
−3
1
0
14
2
experimental data obtained in this study is shown in Figure 7
for the attack of Cl at the −CH − groups in borneol. The
mechanism is analogous to that proposed for reaction of the
compound with OH radicals.
2
5
. ATMOSPHERIC IMPLICATIONS
Volatile organic compounds are, in general, chemically removed
from the troposphere mainly by reaction with the tropospheric
oxidants such as OH, NO , O , and halogen atoms. The
3
3
4
105
dx.doi.org/10.1021/jp212076g | J. Phys. Chem. A 2012, 116, 4097−4107

The Journal of Physical Chemistry A
Article
(
10) Hoffmann, T.; Odum, J. R.; Bowman, F.; Collins, D.; Klockow,
Table 5. Tropospheric Lifetimes of Cyclohexanol and
Oxygenated Terpenes Due to Reactions with Hydroxyl
Radicals and Chlorine Atoms
D.; Flagan, R. C.; Seinfeld, J. H. J. Atmos. Chem. 1997, 26, 189−222.
(11) Kotzias, D.; Hjorth, J. L.; Skov, H. Toxicol. Environ. Chem. 1989,
2
0−1, 95−99.
(
kCl ± 2σ) ×
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AUTHOR INFORMATION
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22) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Hampson, R. F.; Kerr, J.
■
A.; Troe, J. J. Phys. Chem. Ref. Data 1989, 18, 881−1097.
Corresponding Author
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(
(
23) Atkinson, R.; Arey, J. Chem. Rev. 2003, 103, 4605−4638.
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*Phone: +34 902 204 100. Fax: +34 902 204 130. E-mail: jose.
albaladejo@uclm.es.
Notes
1
(
497−1502.
The authors declare no competing financial interest.
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J. Chem. Kinet. 1999, 31, 491−499.
ACKNOWLEDGMENTS
The authors gratefully thank the Spanish Ministerio de
(
(
27) Gill, K. J.; Hites, R. A. J. Phys. Chem. A 2002, 106, 2538−2544.
■
28) Martinez, E.; Cabanas, B.; Aranda, A.; Martin, P. Environ. Sci.
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31) Bradley, W. R.; Wyatt, S. E.; Wells, J. R.; Henley, M. V.;
Educacio
́
n y Ciencia (CGL2004-03355/CLI, CGL2007-
(
3
(
5
6
1835/CLI, and CGL2010-19066 projects) and the Junta de
Comunidades de Castilla-La Mancha (PAI-05-062 and PCI08-
123-0381 projects) for financial support of this research work.
0
́
́
Also, A.A.C.-V. thanks the Spanish Ministerio de Educacion y
(
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Wuppertal (BES-2005-10258).
Graziano, G. M. Int. J. Chem. Kinet. 2001, 33, 108−117.
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