Rate constant and products for the reaction of Cl atom with n-butyraldehyde

Article abstract of DOI:10.1002/kin.20228

The photooxidations of n-butyraldehyde initiated by Cl atom were carried out at room temperature (298 ± 2K) and 1 atm pressure. The rate coefficient for the reactions of Cl atom with n-butyraldehyde was determined as k = (2.04 ± 0.36) × 10^-10 cm³ molecule ^-1 s^-1 by using relative rate techniques. The photooxidation products of n-butyraldehyde reaction with Cl atom were also studied by using both gas chromatography-mass spectrometry (GC-MS) and gas chromatography techniques. C₂H₅CHO, CH₃CHO, CO and CO₂ were the major products observed. In the absence of NO, the observed yields of C₂H₅CHO, CH₃CHO, and CO were 60%, 3%, and 9%, respectively. However, when NO was introduced into the reaction chamber and the initial ratios of [NO]₀/[n-butyraldehyde] ₀ were between 1 and 8, the yield of C₂H₅CHO decreased to 33%, whereas that of CH₃CHO and CO rose up to 21% and 25%, respectively. On the basis of mechanism data deduced in this study and the fraction molar yields, the approximate branching ratios for Cl atom attack at -C(O)H, α-, β-, and γ-positions in n-butyraldehyde could be derived as ≥42%, <25%, 21%, and ≤12%, respectively.

Full text of DOI:10.1002/kin.20228

Rate Constant and Products
for the Reaction of Cl Atom
With n-Butyraldehyde
HAI WU,1 YUJING MU2
,2
1
National Institute of Metrology of China, Beijing 100013, P.R. China
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P.R. China
2
Received 21 February 2006; revised 12 June 2006, 24 July 2006; accepted 10 October 2006
DOI 10.1002/kin.20228
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The photooxidations of n-butyraldehyde initiated by Cl atom were carried out at
room temperature (298 ± 2K) and 1 atm pressure. The rate coefficient for the reactions of Cl
−
10
3
−1 −1
atom with n-butyraldehyde was determined as k = (2.04 ± 0.36) × 10
cm molecule s
by using relative rate techniques. The photooxidation products of n-butyraldehyde reaction
with Cl atom were also studied by using both gas chromatography-mass spectrometry (GC-MS)
and gas chromatography techniques. C2H5CHO, CH3CHO, CO and CO2 were the major prod-
ucts observed. In the absence of NO, the observed yields of C2H5CHO, CH3CHO, and CO were
6
0%, 3%, and 9%, respectively. However, when NO was introduced into the reaction chamber
and the initial ratios of [NO]0/[n-butyraldehyde]0 were between 1 and 8, the yield of C2H5CHO
decreased to 33%, whereas that of CH3CHO and CO rose up to 21% and 25%, respectively. On
the basis of mechanism data deduced in this study and the fraction molar yields, the approxi-
mate branching ratios for Cl atom attack at C(O)H, α-, β-, and γ-positions in n-butyraldehyde
could be derived as ≥42%, <25%, 21%, and ≤12%, respectively. ꢀC 2007 Wiley Periodicals, Inc.
Int J Chem Kinet 39: 168–174, 2007
INTRODUCTION
of free radicals such as HO2, OH, and RO2 in the lower
atmosphere [6]. As sources of free radicals in the atmo-
sphere and precursors in the organic aerosols, aldehy-
des play a significant role in urban photochemical smog
and in the regional ozone layer. In addition, aldehydes
are also the precursors of peroxyacyl nitrates, which are
phytotoxic and strongly eye-irritating compounds [7].
The atmospheric oxidation of aldehydes is mainly
initiated by photolysis and their reaction with OH rad-
icals during daytime, and, to a lesser extent, with NO3
radicals during nighttime. Previous studies have shown
that the rate constants for the reactions of Cl atoms with
certain aldehydes can be much larger than those of
corresponding molecules with OH radicals [8,9]. Even
though the concentration of Cl atoms is lower than that
of OH radicals, their faster rates of reactions with alde-
hydes can make Cl atom reactions competitive with OH
Recently, several aliphatic aldehydes (e.g., n-
butyraldehyde) have been identified and quantified in
vehicle emissions [1,2]. n-Butyraldehyde and higher
aldehydes have been observed in ambient air and in
the emissions of various plant species [3,4]. Aldehydes
can significantly contribute to secondary aerosol for-
mation through heterogeneous reactions [5]. Photodis-
sociation of aldehydes represents an important source
Correspondence to: Yujing Mu; e-mail: yjmu@mail.rcees.ac.cn.
Contract grant sponsor: NSF (China).
Contract grant number: 20277044.
Contract grant sponsor: 973 Project.
Contract grant number: 2002CB410800.
ꢀ
c 2007 Wiley Periodicals, Inc.

RATE CONSTANT AND PRODUCTS FOR THE REACTION OF Cl ATOM WITH n-BUTYRALDEHYDE
169
reactions. Ambient measurements of tetrachloroethene
and other volatile organic compounds suggested that
Kinetic Study of the Reaction of Cl atom
With n-Butyraldehyde
3
−3
Cl atom concentrations are less than 10 atoms cm in
the global troposphere but may be significantly higher
Kinetic experiments of the reaction of Cl atoms with n-
butyraldehyde were carried out at 298 ± 2K and 1 atm.
The Cl atoms were generated through photodegrada-
tion of molecular chlorine using fluorescent lamps.
The rate constant for the gas-phase reaction of Cl
atoms with n-butyraldehyde was determined using a
relative rate method. The decays of n-butyraldehyde
and of a suitable reference compound, whose rate con-
stant with Cl atoms was reliably known, were moni-
tored in parallel in the presence of Cl atoms.
4
−3
in the marine boundary layer (in 10 atoms cm range)
10–12]. Spicer et al. predicted that maximum chlorine
atom levels occur shortly after sunrise with a peak con-
[
5
−3
centration of 1.3 × 10 atoms cm in both the remote
marine boundary layer and coastal urban areas, and
suggested that Cl atoms play a potential important role
in the atmospheric chemistry of such areas [13].
The reliable data of the rate coefficients and the at-
mospheric oxidation mechanisms for the reaction of
Cl atoms with aldehydes are useful in the estimation
of the photochemical ozone creation potential (POCP).
To our knowledge, there are still no reports about the
kinetic and mechanistic data for the reaction of n-
butyraldehyde with Cl atoms. Besides kinetic study
for the reaction of Cl atoms with n-butyraldehyde,
the present work also includes product studies of
the photooxidation of n-butyraldehyde initiated by Cl
atoms.
Cl2 + hν(λ = 365 nm) → 2Cl
(1)
(2)
(3)
k2
Cl + n-butyraldehyde −→ products
k3
Cl + reference −→ products
Provided that n-butyraldehyde and the reference are
removed solely by reaction with Cl atoms, then
ꢀꢁ
ꢁ
ꢂ ꢃ
n − butyraldehyde
k
2
0
ln
ꢂ
=
n − butyraldehyde
k3
t
EXPERIMENTAL
ꢄ[
ꢅ
reference]
0
·
ln
(I)
[
reference]t
The experimental systems used for the present study
have been described in detail elsewhere [14], and are
only briefly presented here.
where [n-butyraldehyde]0 and [reference]0 are the con-
centrations of the n-butyraldehyde and reference com-
pound, respectively, at time t0; [n-butyraldehyde]t and
Indoor Teflon Bag Reaction Chamber
[reference] are the corresponding concentrations at
t
time t; and k2 and k3 are the rate constants for re-
All experiments were performed using a Teflon bag
of approximately 100 L hung inside a ligneous box
of about 1 m volume. The Teflon film of 0.14-mm
thickness was adopted here to reduce the interference
by penetration of the reactant and product molecules.
Four fluorescent tubes (30 W, Academy of Electric
Lamp-House in Beijing) were set on the inner wall
of the cabinet surrounding the Teflon bag. These four
actions (2) and (3), respectively. Kinetic experiments
were performed using both propane and isopropanol
as reference compounds in order to ensure the accurate
rate coefficients for the reaction of n-butyraldehyde
with Cl atoms. The initial reactant concentrations (in
3
−
3
14
units of molecule cm ) were as follows: Cl2, 5 × 10
14
14
14
to 7 × 10 ; n-butyraldehyde, 7 × 10 to 9 × 10 ;
14
14
propane, ∼9 × 10 ; and isopropanol, ∼9 × 10 .
The concentration–time behaviors of n-butyraldehyde
and reference compounds were monitored over a
“black lamps” provided UV radiation, with intensity
maximum around 365 nm. Aluminum foil covering the
inner wall of the cabinet reflected UV light to enhance
the light efficiency and to prevent the leakage of UV
light.
A mercury-free greaseless vacuum system was used
for all experiments. Pressure measurements were done
with an MKS Baratron capacitance manometer, MKS
100–120-min irradiation period by using a gas chro-
matography with flame ionization detector (GC-FID,
HP5890, Agilent Technologies). Successful quantita-
tive analyses for both sets of kinetic experiments were
achieved on a 2 m × 3-mm Teflon column packed with
GDX 103 (60–80 mesh).
270 B. Measured amounts of the reagents were flushed
from Pyrex bulbs into the Teflon reaction chamber by
a stream of air, which was purified by passing through
Products of the Reaction of Cl Atom
With n-Butyraldehyde
˚
desiccant, charcoal, and 5 A molecular sieve. A mass
−1
flow meter (range = 0–5000 mL min , ShengYe Tech-
Product investigations were also carried out in the
reaction chamber at room temperature and 1 atm. The
nology Company, Beijing) controlled the flow rate.
International Journal of Chemical Kinetics DOI 10.1002/kin

1
70
WU AND MU
Cl atoms were generated through photodegradation
of Cl2 by fluorescent lamps. Products were identified
and quantified by GC-MS and GC-FID, respectively.
Determination of n-butyraldehyde, propionaldehyde,
and acetaldehyde was done by GC-FID (HP5890,
Agilent Technologies), equipped with a 2 m × 3-mm
Teflon column packed with GDX 103 (60–80 mesh).
CO and CO2 were measured by GC-FID (GC112A,
Shanghai Precision & Scientific Instrument Co., Ltd.,
Shanghai, China) with a methanizer [15], equipped
with a 1.2 m × 3-mm Teflon column packed with
TDX-01 (60–80 mesh).
About 1000-mL gas samples were collected from
the chamber onto Tenax-TA solid adsorbent in liq-
Figure
1 Plots of ln([n-butyraldehyde]0/[n-butyralde-
hyde]t ) vs. ln([reference]0/[reference]t ) for Cl atom reac-
tions with n-butyraldehyde.
uid nitrogen, with subsequent thermal desorption at
◦
1
80 C into a 100-mL syringe. It was then analyzed by
combined GC-MS, using a 0.32 mm × 30 m × 20-µm
◦
HP-PLOT Q capillary column, initially held at 85 C
kinetic data obtained from two experiments plotted
according to Eq. (I). Least-squares analysis of these
data led to the rate coefficient ratios of k(Cl + n-
butyraldehyde)/k(Cl + isopropanol) = 2.39 ± 0.15 and
k(Cl + n-butyraldehyde)/k(Cl + propane) = 1.39 ±
◦
or 1 min and then temperature programmed to 250 C
◦
−1
at 3 in , in a HP6890 GC interfaced to an HP 5973
mass selective detector.
0.04, respectively. On the basis of the values of
Chemicals
−
11
3
−1 −1
k(Cl + isopropanol) = 8.6 × 10
cm molecul
s
The chemicals used and their stated purities were
n-butyraldehyde (99%), propionaldehyde (99%), iso-
propanol (99%), frpm Aldrich Chemical Co. The chlo-
rine gas was prepared by dropwise addition of HCl
to KMnO4 in our laboratory. n-Butyraldehyde, propi-
onaldehyde, isopropanol, and Cl2 were further purified
by repeat freeze, pump, and thaw cycles and fractional
distillation before use. Acetaldehyde (1.03 mg/mL in
water), propane (1.2% in N2), CO (5.28 ppm in N2),
CO2 (511 ppm in N2), and standard gases were ob-
tained from National Research Center for Certified
Reference Materials, China.
−10
3
−1
and k(Cl + propane) = 1.4 × 10
cm molecule
−1
s
at 298 K [16], the rate constant of k(Cl + n-
butyraldehyde) could be calculated as (2.06 ± 0.13) ×
−10
−10
3
−1 −1
10
and (1.95 ± 0.06) ×10
cm molecule s .
The quoted errors were twice the standard deviation
arising from the least-squares fit of the straight lines
but not including the estimate of the errors in the
reference rate constants. We estimated that potential
systematic errors of ± 10% associated with uncer-
tainties in the reference rate constants for k(Cl + n-
butyraldehyde). Propagating this additional uncer-
tainty gave k(Cl + n-butyraldehyde) = (2.06 ± 0.34) ×
−10
−10
3
−1 −1
10
and (1.95 ± 0.26) ×10
cm molecule s .
The two rate constants based on different references
agreed with each other to within 5%. We chose to
cite a final value for k(Cl + n-butyraldehyde), which
was the average of those determined using the two
different reference compounds together with error
limits that encompass the extremes of the individual
determinations. Hence, k(Cl + n-butyraldehyde) =
RESULTS AND DISCUSSION
Relative Rate Constant for the Reaction
of Cl Atom With n-Butyraldehyde
Some tests on n-butyraldehyde/isopropanol or
propane/air mixtures in the chamber showed that losses
of the compounds to the wall or via photolysis were
−10
3
−1 −1
(2.04 ± 0.36) × 10
cm molecule s . This work
<3% for all processes over a 2-h period. In compari-
provided the first rate constant for the reaction of Cl
atoms with n-butyraldehyde.
sion to the measured decays for the compounds during
the kinetic experiments, the contributions from wall
loss and photolysis were negligible. Mixtures of n-
butyraldehyde and isopropanol/propane with Cl2 were
stable in the dark for about 2 h in the reaction chamber.
Kinetic investigations were performed by
irradiation of n-butyraldehyde/Cl2/propane or
isopropanol/air mixtures. Figure 1 illustrates the
As for n-butyraldehye, the rate constant for Cl atom
−
10
−3 −1
s ) is al-
reaction (k = 2.04 × 10
molecule cm
most 1 order of magnitude higher than that for OH radi-
−
11
−3 −1
s ) [16].
cal reaction (k = 2.4 × 10 molecule cm
In free troposphere, the concentration of OH radicals is
nearly 100 times higher than Cl atoms, so the reaction
of Cl atom may be less important than the reaction of
International Journal of Chemical Kinetics DOI 10.1002/kin

RATE CONSTANT AND PRODUCTS FOR THE REACTION OF Cl ATOM WITH n-BUTYRALDEHYDE
171
OH radicals. In the marine boundary layer or coastal
area, the reaction of Cl atom with n-butyraldehyde
could compete with OH reactions because of the high
Cl atom concentration.
tion, one unidentified products was also observed. The
GC peak of the unknown product eluted before but
very close to the retention time of n-butyraldehyde.
This unknown product was identified probably as 3-
hydroxy-1-propionaldehyde or its isomers by GC-MS
(
see the following discussion).
The reaction of Cl atoms with n-butyraldehyde pro-
Product Study of the Cl Atom Initiated
Oxidation of n-Butyraldehyde
ceeded by the oxidation of the radicals formed fol-
lowing H-atom abstraction from the C H bonds [16].
The alkyl radicals formed after H-atom abstraction
at the C(O)H, i.e., α-, β-, and γ-positions in n-
butyraldehyde, would add O2 to give corresponding
acylperoxy radicals and alkylperoxy radicals.
The products of the Cl atom initiated oxida-
tion of n-butyraldehyde were studied by the UV
irradiation of n-butyraldehyde/Cl2/NO/air and n-
butyraldehyde/Cl2/air mixtures. Initial concentrations
−
3
(
in molecule cm
units) were as follows: n-
14
14
14
butyraldehyde, 5 × 10 to 8 × 10 ; Cl2, 4 × 10 to
14
14
1
1 × 10 ; NO, 0 to 40 × 10 . Typical plots of the con-
CH3CH2CH2C(O)OO• Radical. In the absence of
NOx, the acylperoxy radical reacts with itself (4) and,
to a lesser extent, reacts with HO2 radicals, leading
to the formation of organic acids and peroxyacids (5a,
5b). In the presence of NOx, it also reacts with NO to
form CH3CH2CH2C(O)O• radical (6), and react with
NO2 to form CH3CH2CH2C(O)OONO2(7).
centrations of reactant and major products for irradia-
tion of n-butyraldehyde/Cl2/air mixtures over the time
period of analysis are illustrated in Fig. 2. The mix-
tures were irradiated for a period ranging between 100
and 130 min, and the main observed products gave the
carbon balance of about 65%, which indicates the pres-
ence of other oxidation products that we did not detect.
Acetaldehyde, propionaldehyde, CO, and CO2 were
the main products observed in all experiments. In addi-
2CH3CH2CH2C(O)OO•
→
2CH3CH2CH2C(O)O• + O2 (4)
CH3CH2CH2C(O)OO• + HO2
→
→
CH3CH2CH2C(O)OH + O3 (5a)
CH3CH2CH2C(O)OOH + O2
(5b)
CH3CH2CH2C(O)OO• + NO
CH3CH2CH2C(O)O• + NO2 (6)
CH3CH2CH2C(O)OO• + NO2
CH3CH2CH2C(O)OONO2
→
→
(7)
CH3CH2CH2C(O)O• → CH3CH2CH2 • + CO2 (8)
The alkoxy radical CH3CH2CH2C(O)O• is ex-
pected to rapidly decompose to CH3CH2CH2 • and CO2
(
8). The alkyl radical of CH3CH2CH2 • finally converts
to a certain amount of propionaldehyde.
In the absence of NOx, the alkylperoxy radicals
formed after the H-atom abstraction at α-, β-, and
γ-positions in n-butyraldehyde then predominantly
react with acylperoxy radical to form alkoxy rad-
ical, or with HO2 radicals leading to form hy-
droperoxide species (9), although the self-reaction of
these alkylperoxy radicals is less important. When
NO is added, these alkylperoxy radicals are ex-
pected to easily react with NO (10). The contri-
bution of the channel (10b) forming organic ni-
trates (RONO ) in these RO + NO reactions is
Figure 2 Plots of product concentrations for the Cl atom
reaction with n-C3H7CHO with or without added NO:
(
[
A):[n-C3H7CHO] = 74, [NO] = 0; (B) [n-C3H7CHO] = 79,
13
−3
.
NO] = 330; in units of ×10 molecule cm
2
2
International Journal of Chemical Kinetics DOI 10.1002/kin

1
72
WU AND MU
considered to be small (≤7%) [17].
The reaction of O2 with CH3CH(O•)CH2CHO would
lead to the product acetyl acetaldehyde (14). How-
ever, acetyl acetaldehyde was not observed in our ex-
periments, which was probably due to its concentra-
tion below the detection limit. So the O2 reaction of
)CH CHO could be negligible.
ꢁ
R(OO•)CHO + HO2 → R OOH + O2
(9)
R(OO•)CHO + NO → R(O•)CHO + NO2 (10a)
R(ONO2)CHO (10b)
CH3CH(O•
→
2
The alkoxy radical R(O•)CHO then reacts via a
number of pathways, involving decomposition, iso-
merization through a six-membered transition state,
and reaction with oxygen [18]. But not all of these
reaction pathways are possible for these three alkoxy
radicals.
CH2(O•)CH2CH2CHO Radical. Previous studies in-
dicated that the reactions of n-butoxy radicals were
dominated by the reaction with O2 and 1,5-H shift
−14
3
−1 −1
isomerization (kO = 1.4 × 10
cm molecule
s
2
18
−3
[20], taking [O2] = 4.9 × 10 molecule cm , kO •
2
4
−1
−1 −1
[O2] = 6.9 × 10
s
; kdecompostion = 3.93 × 10
s
5
−1
[
21], kisomerization = 1.8 × 10 s [22].). On the ba-
sis of reactions of n-butoxy radical, the reactions of
CH2(O•)CH2CH2CHO radicals might be also dom-
inated by reaction with O2 or isomerization, with
the decomposition being negligible. The reaction of
CH2(O•)CH2CH2CHO with O2 will lead to 1,4-
butanedial (15). However, 1,4-butanedial was not ob-
served by GC-MS, probably because 1,4-butanedial
does not appear elute from the GC columns [23].
CH3CH2CH(O•)CHO Radical. This alkoxy radical
either decomposes or reacts with O2. On the basis of
the reactions of CH3C(O)CH(O•)CH2CH3 radicals of
similar structure formed from 2-pentanone, for which
the decomposition dominated over its reaction with
O2 [19], CH3CH2CH(O•)CHO radical would mainly
decompose to propionaldehyde plus one •CHO radi-
cal (11). One •CHO radical reacts with O2 to give a
molecule of CO. No CH3CH2C(O)CHO was detected
during our experiments, which also indicated that the
reaction of CH3CH2CH(O•)CHO with O2 (12) could
be neglected.
CH2(O•)CH2CH2CHO + O2
→
HC(O)CH2CH2CHO + HO2 (15)
The radical CH2(O•)CH2CH2CHO is isomerized to
form HOCH2CH2CH2C(•)O radical (16), which would
lead to the formation of 3-hydroxy-1-propionaldehyde
after reaction with O2 (17) and subsequent decomposi-
tion (18). Hence, the unidentified product eluted before
the retention time of n-butyraldehyde was expected to
be 3-hydroxy-1-propionaldehyde. The concentration
of 3-hydroxy-1-propionaldehyde was roughly esti-
mated by comparing to the propionaldehyde standard,
and finally the production yield is found to be about
CH3CH2CH(O•)CHO
→
CH3CH2CHO + •CHO
CH3CH2CH(O•)CHO + O2
CH3CH2C(O)CHO + HO2 (12)
(11)
→
CH3CH(O•)CH2CHORadical. Thealkoxyradical ei-
ther decomposes or reacts with O2. On the basis of the
reaction of CH3C(O)CH2CH(O•)CH3 radicals of sim-
ilar structure formed from 2-pentanone [19], the de-
composition of CH3CH(O•)CH2CHO radical mainly
leads to acetaldehyde plus •CH2CHO radical (13).
2%.
CH2(O•)CH2CH2CHO
→
HOCH2CH2CH2C(•)O
(16)
CH3CH(O•)CH2CHO → CH3CHO + •CH2CHO
(13)
HOCH2CH2CH2C(•)O + O2
The decomposition pathway followed by the reactions
of •CH2CHO radical under tropospheric conditions re-
sults in the formation of CHOCHO or HCHO plus
CO. However, CHOCHO was not detected in our ex-
periment, which was probably because the flame ion-
ization detector is not a proper detector for the analysis
of glyoxal.
→
HOCH2CH2CH2C(O)OO• (17)
HOCH2CH2CH2C(O)OO•
HOCH2CH2CHO + CO2
→
(18)
The products were investigated by gas chromatog-
raphy using the mixture containing seven different con-
14
centrations of NO between 0 and 40 × 10 (all in units
CH3CH(O•)CH2CHO + O2
−3
of molecules cm ). Product formation yield of pro-
pionaldehyde was corrected for its secondary reaction
→
CH3C(O)CH2CHO + HO2 (14)
International Journal of Chemical Kinetics DOI 10.1002/kin

RATE CONSTANT AND PRODUCTS FOR THE REACTION OF Cl ATOM WITH n-BUTYRALDEHYDE
173
Table I Yields of C2H5HO, CH3CHO, and CO from the Cl-initiated Photooxidation of n-C3H7CHO
Initial Concentration
1
3
−3
)
(
×10 molecule cm
Product Yield
CH3CHO
C3H7CHO
Cl2
NO
NO2
[NO]0/[C3H7CHO]0
C2H5CHO
CO
52
62
74
73
72
73
59
79
48
36
87
79
110
64
87
52
75
46
0.0
0.0
0.0
34
0
0
0
0
0
0
0
0
62
0
0
0
0.5
1
1.9
2.5
4.2
8
0.61
0.59
0.60
0.36
0.32
0.32
0.33
0.32
0.33
0.03
0.02
0.03
0.13
0.22
0.20
0.19
0.20
0.20
0.09
0.09
0.07
0.13
0.23
0.27
0.25
0.26
0.26
69
138
145
330
386
with Cl atoms [24], while the formation yields of ac-
etaldehyde, CO2, and CO were derived in the early
stages of the reaction (about 20% n-butyraldehyde
was consumed). Product formation yields of CO, ac-
taldehyde, and propionaldehyde are listed in Table
the formation of peroxy-n-butyrylnitrate. The NO is
rapidly decreased after the initiation of the reaction
and NO2 is formed, so the main fate of the acylperoxy
radicals will be the formation of corresponding stable
acyl peroxynitrate and not lower aldehyde [17,25].
Regarding the increase in product yields of
CH3CHO and CO, a similar trend for acetaldehyde
was reported by Cheema and coworkers [26] when
they studied the mechanisms of Cl atom reaction
with propanol. In this work, the reason might be
that the degradation of alkylperoxy radicals to alkoxy
radicals is the key process for both formation of
CH3CHO and CO. In absence of NOx, the reaction
of CH3CH(OO•)CH2CHO with other peroxy radicals
including acylperoxy radicals and HO2 will be the
dominant degradation process. Since the reaction of
CH3CH(OO•)CH2CHO with HO2 radicals could lead
to formation of hydroperoxide species without gener-
ating CH3CH(O•)CH2CHO radicals, a relatively small
amount of CH3CH(O•)CH2CHO was formed, and
therefore the product yield of CH3CHO was low. When
sufficient NO was added into the mixture, the reaction
of CH3CH(OO•)CH2CHO with NO would dominate
over the other reactions of CH3CH(OO•)CH2CHO.
Then almost all CH3CH(OO•)CH2CHO radicals were
transformed to CH3CH(O•)CH2CHO, which led to a
high product yield. We thought that the steady yields of
acetaldehyde at high [NO]0/[propanol]0 ratios were ap-
propriate to determine the branching ratios for Cl attack
on n-butyraldhyde. Hence, the branching ratios of Cl
attack at α- and β-positions in n-butyraldehyde were
derived by considering the formation yields for CO and
acetaldehyde as 25% and 21%, respectively. Consider-
ing that CO might partly come from the degradation of
1
and also plotted against [NO]0/[n-butyraldehyde]0
(the subscript “0” means the initial concentrations),
which are illustrated in Fig. 3. When there was no
NO present in the mixture, the observed yields of
C2H5CHO, CH3CHO, and CO were 60%, 3%, and 9%,
respectively. However, the yields of CO and acetalde-
hyde rose, whereas that of propionaldehyde decreased
as the ratio of [NO]0/[n-butyraldehyde]0 increased.
In addition, the formation yields of the three com-
pounds were nearly constant for the ratios of [NO]0/[n-
butyraldehyde]0, between 1 and 8 (the production
yields for CO and acetaldehyde and propionaldehyde
were 25%, 21%, and 33%, respectively). The decrease
in propionaldehyde production yield might be due to
•
2
CH CHO (formed after Cl attack at β-position), the
Figure 3 Plots of the product formation yields against the
ratio of [NO]0/[n-C3H7CHO]0 in Cl atom reactions with
n-C3H7CHO.
branching ratio of Cl attack at α-position should be the
high limit.
International Journal of Chemical Kinetics DOI 10.1002/kin

1
74
WU AND MU
The product yield of CO2 (44% in the absence of
7. Finlayson-Pitts, B. J.; Pitts, J. N., Jr. In Chemistry of the
Upper and Lower Atmosphere—Theory, Experiments
and Applications; Academic Press: San Diego, 2000.
NO) may be taken to estimate an approximate branch-
ing ratio of Cl attack at C(O)H function group in
n-butyraldehyde. In the absence of NO, the radical
of CH3CH2CH2C(O)OO• may predominantly undergo
self-reactions and cross-reactions with other alkylper-
oxy radicals to produce CO2, and, to a certain extent,
with HO2 radicals to generate acids and peracids. Con-
sidering that about 2% CO2 is contributed by reaction
8
. Albaladejo, J.; Ballesteros, B.; Jim e´ nez, E.; Mart ´ı n, P.;
Mart ´ı nez, E. Atmos Environ 2002, 36, 3231.
9
. Th e´ venet, R.; Mellouki, A.; Le Bras, G. Int J Chem Kinet
2000, 32, 676.
10. Wingenter, O. W.; Blake, D. R.; Blake, N. J.; Sive, B. C.;
Rowland, F. S.; Atlas, E.; Flocke, F. J Geophys Res 1999,
104(D17), 21819.
(
18), it might be suggested that at least 42% reaction oc-
11. Singh, H. B.; Thakur, A. N.; Chen, Y. E.; Kanakidou,
M. Geophys Res Lett 1996, 23(12), 1529.
curs at C(O)H in n-butyraldehyde. So the branching
ratios for Cl atoms attack at C(O)H, α-, β-, and γ-
positions in n-butyraldehyde are ≥42%, ≤25%, 21%,
and ≤12%, respectively.
12. Rudolph, J.; Koppmann, R.; Plass-D u¨ lmer Ch. Atmos
Environ 1996, 30, 1887.
1
3. Spicer, C. W.; Chapman, E. G.; Finlayson-Pitts, B. J.;
Plastridge, I. A.; Hubbe, J. M.; Fast, J. D.; Berkowitz,
C. M. Nature 1998, 394, 353.
According to the branching ratios of Cl atom attack
at C(O)H, α-, β-, and γ-positions and k(Cl + n-
−
10
3
−1 −1
s ,
14. Wu, H.; Mu, Y.; Zhang, X.; Jiang, G. Int J Chem Kinet
003, 35, 81.
butyraldhyde) = 2.04 × 10
cm molecule
2
the partial rate coefficients for the groups of n-
15. Yonemura, S.; Sudo, S.; Tsuruta, H.; Kawashima, S. J
Atmos Chem 2002, 43, 1.
butyraldhyde can be obtained approximately as follow-
−
11
ing: k( C(O)H) = 8.6×10 , k(α CH2 ) = 5.1 ×
1
6. Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley,
J. N.; Hampson, R. F., Jr.; Hynes, R. G.; Jenkin,
M. E.; Kerr, J. A.; Rossi, M. J.; Troe, J. In Sum-
mary of Evaluated Kinetic and Photochemical
Data for Atmospheric Chemistry (Web version
February 2006). Available at http://www.iupac-
kinetic.ch.cam.ac.uk/summary/IUPACsumm web latest.
pdf.
−11
−11
1
2
0
, k(β CH2 ) = 4.3 × 10 , and k(γ CH3) =
−11
3
−1 −1
.4 × 10
cm molecule s , respectively. The
partial rate constant for Cl attack at C(O)H ob-
tained by this study is close to the upper limit of
cm molecule s reported by
Kegley-Owen et al. [27]. Coincidently, our derived
−11
3
−1 −1
(
7.5 ± 0.8) × 10
values of k( C(O)H), k(β CH2 ), and k(γ CH3)
−
11
17. Cavalli, F.; Geiger, H.; Barnes, I.; Becker, K. H. Environ
Sci Technol 2002, 36, 1263.
agree well with k(α CH2OH) = 8.7 × 10
,
−11
k(β CH2 ) = 4.7 × 10 , and k(γ CH3) =
1
1
8. Atkinson, R. Int J Chem Kinet 1997, 29, 99.
9. Atkinson, R.; Tuazon, E.C.; Aschmann, S. M. Environ
Sci Technol 2000, 34, 623.
−11
3
−1 −1
2
.2 × 10
cm molecule s obtained by Cheema
et al. [26] from the analysis of the Cl-initiated
oxidation of 1-propanol.
2
2
2
0. Hein, H.; Hoffmann, A.; Zellner, R. Phys Chem Chem
Phys 1999, 1, 3743.
1. Balestra-Garcia, C.; Le Bras, G.; Mac Leod, H. J Phys
Chem 1992, 96, 3312.
2. Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L. P.
J Phys Chem 1981, 85, 2698.
BIBLIOGRAPHY
1
2
3
4
5
6
. Grosjean, D.; Grosjean, E.; Getler, A. W. Environ Sci
Technol 2001, 35, 34.
. Kawamura, K.; Steinberg, S.; Kaolan, I. R. Atmos Env-
iron 2000, 34, 4175.
. Grosjean, E.; Rasmussen, R. A.; Grosjean, D. L. Atmos
Environ 1998, 32, 3371.
. Kerstine, W.; Galbally, I.; Yu, Y.; Hooper, M. J Geophys
Res 1998, 103, 10605.
. Jang, M.; Kamens, R. M. Environ Sci Technol 2001, 35,
23. Reisen, F.; Aschmann, S. M.; Atkinson, R.; Arey J. En-
viron Sci Technol 2003, 37, 4664.
24. Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Winer,
A. M.; Pitts, J. N., Jr. J Phys Chem 1982, 86, 4563.
25. Picquet, B.; Doussin, J. F.; Durand-Jolibois, R.; Carlier,
P. Phys Chem Chem Phys 2001, 3, 2595.
26. Cheema, S. A.; Holbrook, K. A.; Oldershaw, G. A.;
Wlker, R. W. Int J Chem Kinet 2002, 34, 110.
27. Kegley-Owen, C. S.; Tyndall, G. S.; Orlando, J. J.; Fried,
A. Int J Chem Kinet 1999, 31, 766.
4758.
. Grosjean, D. Environ Sci Technol 1982, 16, 254.
International Journal of Chemical Kinetics DOI 10.1002/kin