Products of the gas-phase photooxidation reactions of 1 -propanol with OH radicals

Article abstract of DOI:10.1002/(SICI)1097-4601(1999)31:11<810::AID-JCK8>3.0.CO;2-W

An experimental investigation of the hydroxyl radical initiated gas-phase photooxidation of 1-propanol in the presence of NO was carried out in a reaction chamber using gas chromatography mass spectrometry. The products identified in the OH radical reactions of 1-propanol were propionaldehyde and acetaldehyde, with corresponding formation yields of 0.719 ± 0.058 and 0.184 ± 0.030, respectively. Errors represent ± 2σ. The experimental product yields were compared to predictions made using chemical mechanisms.

Full text of DOI:10.1002/(SICI)1097-4601(1999)31:11<810::AID-JCK8>3.0.CO;2-W

Products of the Gas-Phase
Photooxidation Reactions
of 1-Propanol with OH
Radicals
K. AZAD, J. M. ANDINO
University of Florida, Department of Environmental Engineering Sciences, P.O. Box 116450, Gainesville, Florida 32611
Received 16 February 1999; accepted 8 July 1999
ABSTRACT: An experimental investigation of the hydroxyl radical initiated gas-phase pho-
tooxidation of 1-propanol in the presence of NO was carried out in a reaction chamber using
gas chromatography mass spectrometry. The products identified in the OH radical reactions
of 1-propanol were propionaldehyde and acetaldehyde, with corresponding formation yields
of 0.719 Ϯ 0.058 and 0.184 Ϯ 0.030, respectively. Errors represent Ϯ2␴. The experimental
product yields were compared to predictions made using chemical mechanisms. ᭧ 1999 John
Wiley & Sons, Inc. Int J Chem Kinet 31: 810–818, 1999
INTRODUCTION
Once emitted into the atmosphere, alcohols can re-
act with oxidizing species such as hydroxyl radicals
(OB H), nitrate radicals (NO ), and ozone (O ) [8,9] to
The alcohols present in ambient air are a result of both
biogenic and anthropogenic sources. Anthropogenic
emissions of alcohols occur through their use in fuels
and as industrial solvents [1]. 1-Propanol, in particular,
is widely used as a chemical solvent in the manufac-
turing of disk drives, computers, semiconductors, and
various electronic components. 1-Propanol is also
used in the esterfication of acetic acid, a common in-
gredient found in vinegar. Alcohols such as tert-butyl
alcohol (TBA) [1,2–4], ethanol [4,5], and methanol
3
3
produce a number of radicals and products, and con-
vert NO to NO . The subsequent photolysis of NO is
2
2
the main reaction mechanism for the formation of
tropospheric ozone. During daytime hours, reaction
with the OH radical is the most prominent loss mech-
anism [8]. Kinetic studies of the OH radical reaction
with alcohols have already been performed [2–4,10–
15]. However, there are relatively few studies that
have investigated the products from the OB H initiated
reactions of alcohols. Summarized in Table I are the
products of the OH radical reaction of alcohols cur-
rently available in the literature. In order to accurately
assess the impact of alcohols on tropospheric ozone
production, a knowledge of the products of the
OB H-initiated photooxidation of these species is
needed.
In their study of the OH radical reactions of 2-bu-
tanol [17] and 2-pentanol [17], Baxley and Wells ob-
served products that could only occur from the direct
reaction of oxygen with the ␣-hydroxy alkyl radical.
For the reactions of 2-butanol, the products observed
were methyl ethyl ketone and acetaldehyde. Methyl
[4,6] have been used in oxygenated fuels to reduce
automobile emissions of carbon monoxide and hydro-
carbons [7]. The addition of alcohols to fuels promotes
better combustion by allowing for engine operation at
a high octane rating [1,7]. Since alcohols are highly
volatile compounds, significant evaporative emissions
result from their use as solvents and fuel additives.
Hence, it is important to determine their atmospheric
degradation pathways in the troposphere.
Correspondence to: J. M. Andino
Contract grant sponsor: National Science Foundation
Contract grant number: ATM-9702791
1999 John Wiley & Sons, Inc.
᭧
CCC 0538-8066/99/110810-09

GAS-PHASE PHOTOOXIDATION REACTIONS OF 1-PROPANOL
811
Table I Products of OH Radical Reaction with Alcohols
Compound
Principle Products
HCHO
Ref.
Methanol
Ethanol
CH OH
Formaldehyde
Acetaldehyde
Acetone
[2],[15],[16]
[2],[16]
[16]
3
CH CH OH
CH CHO
3
2
3
2-Propanol
-Butanol
CH CH(OH)CH3
(CH ) CO
3
3 2
2
CH CH CH(OH)CH
2-Butanone
CH CH COCH
3
[16],[17]
3
2
3
3
2
Acetaldehyde
2-Pentanone
Propionaldehyde
Acetaldehyde
Acetone
CH CHO
3
2
-Pentanol
CH CH CH(OH)CH
CH COCH CH CH
3
[17]
3
2
3
3
2
2
CH CH CHO
3
2
CH CHO
3
t-Butyl Alcohol
(CH ) COH
(CH ) CO
[2],[3]
3
3
3 2
Formaldehyde
Acetone
HCHO
Methyl Butenol
(CH )C(OH)"CHCH2
(CH ) CO
[18],[19]
3
3 2
Formaldehyde
Glycolaldehyde
Formic Acid
Carbon Dioxide
Carbon Monoxide
Methoxy Acetone
Methyl Formate
Acetaldehyde
Acetone
HCHO
C(OH)CH OH
C(OH)HO
CO2
CO
2
1
-Methoxy-2-
propanol
CH CH(OH)CH OCH
CH C(O)CH OCH
[20]
[21]
3
2
3
3
2
3
CH OCHO
3
CH CHO
3
2
,4-Dimethyl-2-
pentanol
(CH ) C(OH)CH CH(CH )
(CH ) CO
3
2
2
3
2
3 2
2-Methylpropanal
(CH ) CHCHO
3 2
4
4
-Methyl-2-pentanone
-Hydroxy-4-methyl-2-pentanone
CH C(O)CH CH(CH )
3 2 3 2
CH C(O)CH C(OH)(CH )
3
2
3
2
3
2
2
,5-Dimethyl-3-
hexanol
CH CH C(CH )(OH)
Acetone
2-Butanone
(CH ) CO
CH CH C(O)CH
3 2 3
(CH ) CHCHO
3 2
CH C(O)CH CH(CH )
3 2 3 2
CH C(O)CH C(OH)(CH )
3 2 3 2
HC(O)OCH CH CH CH
3
HC(O)OCH CH OH
2 2
[21]
3
2
3
3 2
CH CCH(CH )
2
3
2
2
4
4
-Methylpropanal
-Methyl-2-pentanone
-Hydroxy-4-methyl-2-pentanone
-Butoxyethanol
-Ethoxyethanol
CH CH CH CH OCH CH OH
Butyl Formate
Ethylene Glycol Monoformate
Butoxyacetaldehyde
[20],[22]
3
2
2
2
2
2
2
2
2
CH CH CH CH OCH C(O)H
3
2
2
2
2
3-Hydroxybutyl Formate
HC(O)OCH CH CHOHCH
2
2
3
Propionaldehyde
Ethyl Formate
CH CH CHO
3
2
CH CH OCH CH OH
CH CH O(O)CH
[23]
3
2
2
2
3
2
Ethylene Glycol Monoformate
Ethylene Glycol Monoacetate
Ethoxyacetaldehyde
Propionaldehyde
HC(O)OCH CH OH
2 2
CH C(O)OCH CH OH
3
2
2
CH CH OCH C(O)H
3
2
2
cis-3-Hexen-1-ol
CH CH CHCHCH CH OH
CH CH CHO
[24],[25]
3
2
2
2
3
2
Acetaldehyde
CH CHO
2
Methylglyoxal
CH COCHO
3
Allyl Alcohol
CH CHCH OH
Formaldehyde
Hydroxyacetaldehyde
Formaldehyde
HCHO
[24]
[24]
2
2
CH OHCH HO
2
2
3
-Buten-1-ol
CH CHCH CH OH
HCHO
2
2
2
ethyl ketone can only be formed by the OB H abstraction
of the ␣-hydrogen and the subsequent reaction of the
observations were made for 2-pentanol. The mecha-
nisms proposed by Stemmler et al. in their studies of
2-butoxyethanol [22] and 2-ethoxyethanol [23] with
the OH radical, also suggested that the reaction of the
␣
-hydroxy alkyl radical with O . To determine the role
2
of atmospheric oxygen in its reaction with ␣-hydroxy
1
8
alkyl radical, 2-butanol was labeled with O. The re-
␣-hydroxy alkyl radical with O proceeds via hydro-
2
1
8
sulting methyl ethyl ketone, CH CH CB ( O)CH , was
gen abstraction rather than O addition. Consequently,
3
2
3
2
1
8
analyzed for the presence of O. The results showed
that methyl ethyl ketone contained only O and no
O. Hence, atmospheric oxygen merely abstracts a
the ␣-hydroxy radicals produced in the reactions of 1-
propanol with H are expected to react with oxygen in
a similar manner.
1
8
1
6
hydrogen atom from the ␣-hydroxy alkyl radical and
does not attach to form a peroxy radical [17]. Similar
The structure activity relationship (SAR) [26]
was used to determine the percent of OB H attack on the

8
12
AZAD AND ANDINO
Table II Hydroxyl Radical Attack Sites and Estimated Alkyl Radical Distribution of 1-Propanol
Abstraction Site
Reaction
& Distribution
CH CH CH OH ϩ OB H : CH CH CH OB
Site I
Site II
Site III 21%
Site IV 3%
2.6%
73.4%
3
2
2
3
2
2
:
:
:
CH CH CB HOH
3
2
CH CB HCH OH
3
2
CB H CH CH OH
2
2
2
carbon centers of 1-propanol. Table II shows the pos-
sible attack sites by the OH radical. The main degra-
dation pathway is expected to be hydrogen abstraction
by the OH radical from the secondary carbon center
in 1-propanol (site II), followed by the reactions of the
resulting intermediate alkyl, peroxy, and alkoxy radi-
cals [8,9,27,28].
The products that are predicted to form from the
OB H initiated photooxidation of 1-propanol are pre-
sented in Table III. The OH radical initiated reaction
of 1-propanol is expected to proceed primarily by hy-
drogen abstraction from the secondary carbon (site II)
to form the corresponding ␣-hydroxy radical, which
tion are identified and used to derive the atmospheric
reaction mechanisms. The information collected in
this study adds to the existing kinetic and mechanistic
database of alcohols.
EXPERIMENTAL PROCEDURE
Apparatus and Materials
Experiments were performed in a new indoor photo-
chemical reactor designed to study gas-phase reaction
kinetics and mechanisms. The reactions were con-
᭨
can then react with O to form propionaldehyde and
ducted in a batch reactor composed of 2 mil Tedlar
2
HOB . While there are no data available on the
film (SKC Inc.), with a volume of approximately 100
L. The Tedlar chamber was suspended inside a
2
᭨
1
-propanol/OB H reaction products, investigations of the
-propanol/OB H radical rate constant have been made
1
wooden cabinet. Eight fluorescent black lamps (Syl-
vania F40/350BL, maximum @ 350 nm) in two banks
of four surrounded the chamber, and were used to ini-
tiate the chemistry. The lamps were mounted on a re-
flective surface to provide for uniformity in irradiation.
A fan installed inside of the cabinet ensured that there
was an even temperature distribution around the cham-
ber.
[
4,11–13]. The recommended 1-propanol/OB H rate
Ϫ12 3 Ϫ1 Ϫ1
constant is 5.53 ϫ 10 cm molecule
s
[8]. Using
5
an OB H atmospheric concentration of 8.7 ϫ 10 mol-
Ϫ
3
ecule cm [29], the lifetime of 1-propanol is 2.4 days.
This study elucidates the atmospheric chemistry of
1
-propanol. The products of the 1-propanol/OB H reac-
The reactants were introduced into the chamber by
two methods: direct syringe injection and via an eva-
cuable glass manifold system. A 10 ␮L Hamilton sy-
ringe was used to inject the organic compounds into a
stream of zero air (99.999% purity, Strate Welding)
flowing into the chamber. The injection was made into
Table III Possible Products Formed from the OH
Radical Initiated Reactions of 1-Propanol
OB H Attack Site
Site I
Products
Propionaldehyde
Acetaldehyde
௡
a septum placed inside a Swagelock union tee that
9
OH Group
was connected to the inlet of the chamber. The flo-
wrate of air was monitored using a calibrated rota-
meter (Porter Instrument Co.) and a stopwatch. The
chamber was filled with 78–80 liters of the air/reac-
tant mixture. Since the final volume of the chamber,
the volume of the reactant injected, the density, and
the molecular weight of the reactant were known, the
final concentration of the reactant inside the chamber
was easily calculated.
Formaldehyde
Site II
Secondary Carbon
Propionaldehyde
Propionic Acid
Formic Acid
Hydroxyacetaldehyde
Acetol
Acetaldehyde
Formaldehyde
Hydroxyacetaldehyde
3-Hydroxypropionaldehyde
Formaldehyde
(9OH Group)
Site III
Secondary Carbon
Site IV
Primary Carbon
A custom designed evacuable glass manifold sys-
tem (Chemglass) was used to admit known amounts

GAS-PHASE PHOTOOXIDATION REACTIONS OF 1-PROPANOL
813
of highly volatile reactants (such as methyl nitrite and
nitric oxide) to the chamber. The system contained a
glass bulb and two MKS Baratron pressure gauges
with a combined range of 10 to 10 Torr. The vol-
ume of the glass bulb was calibrated using a gravi-
metric method. The reactants were flushed into the
chamber from the manifold using zero grade air
were obtained from Aldrich with stated purities of
99.5ϩ%, 97%, and 99.5ϩ%, respectively. 1-Propanol
was introduced into the chamber without further pu-
rification. Nitric oxide was taken from a standard
cylinder supplied by Liquid Carbonic. Methyl nitrite
was synthesized according to the method of Taylor
et al. [30]. The methyl nitrite was purified using the
glass manifold system and stored at room temperature
in a stainless steel lecture bottle. The purity of the
methyl nitrite was verified using a Fourier Transform
Infrared (FTIR) spectrometer and was found to be
Ͼ99ϩ%.
Three experiments were performed in which the re-
actants were irradiated for 30–50 min in 3–5 min
intervals. All experiments were performed at 298 Ϯ
2 K and atmospheric pressure. Prior to each set of ex-
periments, zero air was introduced into the chamber
and photolyzed for 20 min to remove any free radicals
that may have been present in the chamber. At the end
of an experiment, the chamber was cleaned by
flushing it several times with zero air. After flushing,
GC-MS samples were taken to check for cross con-
tamination.
The products were identified based on their reten-
tion time and mass spectra as compared to standards.
Standards of all potential products identified in Table
III (with the exception of formaldehyde and 3-hydrox-
ypropionaldehyde) were injected from the chamber
into the GC-MS, and full calibration curves were de-
veloped. 3-Hydroxypropionaldehyde was not com-
mercially available, and formaldehyde could not be
analyzed via the techniques employed in this study. In
all cases, samples were subjected to the same temper-
ature program used in the experiments, and the cor-
responding peak areas obtained. Two samples were
taken for each concentration to check for internal con-
sistency of the GC-MS. The m/z values used for quan-
tifying 1-propanol, propionaldehyde, and acetalde-
hyde were 43, 57, and 43, respectively. The duplicate
samples were found to have peak areas within 5% of
each other. Plots of peak area versus concentration
were generated, and response factors determined.
These factors were then used to quantify the products
during the experimental runs.
Additional studies were conducted with the organ-
ics to characterize losses due to photolysis and inter-
action with the walls of the chamber. Wall losses were
quantified by placing the organics in the chamber and
leaving them in the dark for time periods typically
used in the studies. Losses due to photolysis were
quantified by subjecting the organics to photolysis for
time periods typically used in the actual experiments.
In each case, samples were taken in 5–10 min inter-
vals and compared to samples taken at time zero.
Ϫ3
3
(
(
99.999% purity, Strate Welding). A mechanical pump
Marvac Scientific Co., Model A20) operating at 15
L/min was used to exhaust the chamber prior to and
after the experiments.
The reaction chamber was interfaced to a gas chro-
matograph-mass spectrometer (Finnigan-MAT, GCQ
Model 9001), which provided the necessary analytical
tool to aid in the positive identification and quantifi-
cation of the products. The GC consisted of a heated
6
-port sampling valve that was kept at a constant tem-
perature of 150ЊC to keep the organics in their gaseous
phase, and prevent condensation. A diaphragm pump
was used to extract samples from the chamber directly
into the GC-MS system. The samples were drawn
from the chamber through the loop at 1 lpm before
being injected onto the column. A J&W Scientific DB-
WAX capillary column of dimension 30 m ϫ 0.25 mm
ϫ 0.25 ␮m was used to separate the organics. The GC
carrier gas was helium (99.999% purity, Bitec), with
a linear velocity of 45 cm/s. The temperature program
started at 35ЊC, was held for one minute, then ramped
at 10ЊC/min to 150ЊC, and held at that temperature for
one minute. Mass spectral analyses were performed in
positive electron ionization mode.
Methyl nitrite was used as the source of hydroxyl
radicals in the reaction chamber. Hydroxyl radicals are
produced from the photolysis of methyl nitrite in air
via the following mechanism:
CH ONO ϩ h␯ !: CH OB ϩ NO
(1)
(2)
(3)
3
3
CH OB ϩ O !: CH O ϩ HOB
3
2
2
2
HOB ϩ NO !: OB H ϩ NO
2
2
Nitric oxide was added to the chamber with methyl
nitrite to minimize the accumulation of ozone, and
maximize the reduction of peroxy radicals to alkoxy
radicals.
Product Study
The typical starting concentrations of the reactants ad-
mitted into the chamber were 16–18 ppm of 1-pro-
v
panol, 15–20 ppm of methyl nitrite, and 9–12 ppm
v
v
of NO. 1-propanol. Propionaldehyde and acetaldehyde

8
14
AZAD AND ANDINO
Secondary Product Study
ondary reactions with the OH radical. The calculated
ranges of the correction factors for propionaldehyde
and acetaldehyde were 1.1–2.7 and 1.1–2.1, respec-
tively. The formation of acetaldehyde was also ob-
served in the propionaldehyde/OB H reactions with a
molar yield of 0.585 Ϯ 0.049. Hence, the acetaldehyde
yield obtained from the 1-propanol/OB H reactions was
corrected for the secondary source. The corrected mo-
lar formation yields for propionaldehyde and acetal-
dehyde were 0.719 Ϯ 0.058 and 0.184 Ϯ 0.030, re-
spectively. The errors are two least-squares standard
deviations.
Since the primary products formed in the OH radical
reactions of 1-propanol also react with the OH radical,
separate studies were performed to elucidate the nature
and yields of secondary products. Secondary product
studies were performed for propionaldehyde. Propi-
onaldehyde was introduced into the chamber with
methyl nitrite and nitric oxide using the same experi-
mental method as the initial product study. The con-
centrations used in the propionaldehyde/OB H studies
were 5–6 ppm of propionaldehyde, 20–22 ppm of
v
v
methyl nitrite, and 4–5 ppm of NO. Propionaldehyde
v
The corrected yields for propionaldehyde and ac-
etaldehyde account for about 85 Ϯ 8% of the reacted
carbon. Hence, almost all of the reacted carbon is ac-
counted for. Some of the remaining carbon may be
present as other carbonyl compounds, but none were
observed within the detection limits of the GC-MS.
GC-MS characteristics of acetol, hydroxyacetalde-
hyde, propionic acid, and formic acid, obtained from
the injections of standards from the chamber into the
GC were not observed in the 1-propanol/OB H chro-
matograms. 3-Hydroxypropionaldehyde could not be
analyzed since it was not commercially available.
Propionaldehyde may form as a result of hydrogen
abstraction by OB H from site I or site II (see Table II).
Acetaldehyde is expected to form as a result of hydro-
gen abstraction by OB H from any of the possible sites,
except for abstraction from the primary carbon (site
IV). Hydrogen abstraction from site I forms the alkoxy
radical, CH CH CH OB , which can react with O to
was injected into the chamber without further puri-
fication. The results were analyzed on the GC-MS.
The primary product yields obtained for the
1
-propanol/OB H studies were corrected for interfer-
ences observed in the secondary product studies.
RESULTS AND DISCUSSION
Losses due to photolysis and interaction with the walls
of the chamber were quantified, and were each within
the analytical uncertainty of the GC/MS (ϳ5%).
Therefore, wall losses and losses due to photolysis
were deemed negligible.
The first generation products can react with OH
radicals, thus their formation yields were corrected ac-
cording to the method of Atkinson [8], and using the
rate constants available in the literature [8]. The cor-
rection factor, F, was calculated using Equation I. The
raw molar yields were multiplied by the correction fac-
tor to obtain the true molar yields.
3
2
2
2
yield propionaldehyde and HOB (Reaction 6), or de-
2
compose to produce formaldehyde and an acetyl rad-
ical, CH CB H (Reaction 7),
3
2
[
1-Propanol]t
CH CH CH OB ϩ O !:
1
Ϫ
3
2
2
2
k4 Ϫ k
5
[1-Propanol]
0
5
CH CH CHO ϩ HOB , (6)
3
2
2
F ϭ
ͭ
ͮ
k
k4
[1-Propanol]
t
[1-Propanol]
t
k4
Ϫ
ͩ[1-Propanol]
ͪ
Decomposition
0
[1-Propanol]0
CH CH CH OB 9
:
3
2
2
(
I)
CH CB H ϩ HCHO. (7)
3
2
The rate constants k and k are for the following re-
actions:
Oxygen rapidly reacts with the acetyl radical to form
an acetyl peroxy radical, which continues to react with
NO to either yield peroxy acetyl nitrate (PAN) or the
4
5
1
-Propanol ϩ OB H !: Product
(4)
(5)
corresponding acetyl alkoxy radical and NO . The al-
2
koxy radical can react with oxygen to form acetalde-
hyde or decompose to form formaldehyde. Hydrogen
abstraction by OB H from site II, estimated by the
SAR technique as the most probable hydrogen
abstraction site, forms the ␣-hydroxy alkyl radical,
CH CH CB HOH, which is expected to yield pro-
Product ϩ OB H !: Secondary Product
Product Study
Analysis of irradiated CH ONO-NO-1-propanol-air
mixtures indicated the formation of propionaldehyde
and acetaldehyde. The yields were corrected for sec-
3
3
2
pionaldehyde in a direct reaction with oxygen (Reac-
tion 8),

GAS-PHASE PHOTOOXIDATION REACTIONS OF 1-PROPANOL
815
CH CH CB HOH ϩ O !:
Table IV Measured and Predicted Product Yields for
the Gas-Phase Reactions of 1-Propanol with OH
Radicals
3
2
2
CH CH CHO ϩ HOB
(8)
3
2
2
Our results indicate the absence of propionic and for-
mic acids. Thus, the competing reaction of the ␣-hy-
droxy alkyl radical to form the ␣-hydroxyperoxy rad-
ical (Reaction 9), and eventually propionic and formic
acids is negligible.
Yield
Product
Experimentala
Predictedb
Propionaldehyde
Acetaldehyde
0.719 Ϯ 0.058
0.184 Ϯ 0.030
0.757
0.177
a
Indicated errors are 2 least-squares standard deviations.
Predicted as described in text.
CH CH CB HOH ϩ O !:
b
3
2
2
CH CH CH(O(OB )OH. (9)
3
2
The results obtained here are consistent with the
results obtained in similar studies involving the pro-
duction of the intermediate ␣-hydroxy alkyl radicals
rate constant for the alkoxy radical decomposition and
O reactions were determined by calculating the en-
2
thalpies of reaction using the NIST Structures and
Properties Database Estimation Program [32] in com-
bination with the estimation technique of Atkinson [9].
The rate constants for alkoxy radical decomposition,
kd, were determined using Equation II,
[15–17,20–23]. Previous studies of the reactions of
2
-butanol [17] and 2-pentanol [17] with the OH radical
indicated that the major products observed were
formed due to the OH radical hydrogen abstraction
from the secondary carbon. Initial estimates by the
SAR also predicted that OB H attack on 1-propanol at
the secondary carbon containing the alcohol group was
the most probable site. With a recovery of 71.9 Ϯ
Ϫ
E
d
/RT
Ϫ1
k ϭ A e
s ,
(II)
(III)
(IV)
d
d
1
4
Ϫ1
where A ϭ 2 ϫ 10 d s ,
5
1
.8% of the reacted carbon as propionaldehyde in the
-propanol/OB H reactions and the absence of propionic
d
E ϭ a ϩ 0.36⌬H ,
and formic acids, this study confirms that the main
reaction pathway (at the secondary carbon site of 1-
d
d
A is the pre-exponential factor, d is the reaction path
propanol) involves hydrogen abstraction by O from
d
2
degeneracy, R is the ideal gas constant, T is the tem-
the ␣-hydroxy alkyl radical (Reaction 8), rather than
perature in Kelvin, ⌬H is the decomposition enthalpy
O addition (Reaction 9). The formation of acetalde-
d
2
Ϫ
1
in kcal mol , and E is the activation energy in kcal
hyde at a smaller yield indicates that other reaction
pathways for OH abstraction from 1-propanol will oc-
cur, but are less important.
d
Ϫ
1
mol . The activation energy is dependent on the alkyl
leaving-group, represented in Equation IV by param-
eter a. Reported [9] values of a (in kcal mol ) are:
Ϫ
1
methyl, 15.5; primary alkyl, RCB H , 11.1; secondary
2
Mechanism Predictions
alkyl, R R CB H, 9.3; tertiary alkyl, R R R CB , 7.9; and
1
2
1
2
3
CB H OH, 10.0. The rate constant for the reaction of the
The reaction mechanisms for the OB H initiated pho-
tooxidation of 1-propanol were developed and imple-
mented using the SAPRC Atmospheric Photochemical
Mechanism Preparation Program [31]. The mecha-
nisms did not include secondary reactions of products
since the experimental raw yields were corrected for
secondary reactions. Hence a direct comparison of pre-
dicted and experimental yields was made.
2
alkoxy radical with O is calculated using Equation V:
2
Ϫ
19
k
ϭ 4.0 ϫ 10 ne(Ϫ0.28⌬HO2),
(V)
O2
where kO2 is the rate constant for the alkoxy radical
3
Ϫ
1
Ϫ1
reaction with O in cm molecule s , n is the num-
2
ber of abstractable hydrogen atoms in the alkoxy rad-
The rate constants for the individual OH radical
initiated abstraction steps were determined using the
SAR technique and the recommended overall OH rad-
ical rate constant. The rate constants for the 1-propyl
ical, and ⌬HO2 is the enthalpy of the alkoxy radical
reaction with O . The completed mechanisms were im-
2
plemented into the Carter modeling program [31], and
time-concentration profiles were generated. Predicted
product yields were determined by calculating the ra-
tio of product concentration to the change in the con-
centration of the reactant species, and were compared
to experimental yields. Presented in Table IV are the
predicted and experimental yields of the products.
radical reaction with O [8] was used as an estimate
2
for the rate constant of O2 addition to the
DCH CH CH OH radical. Except for the alkoxy radi-
2
2
2
cal reactions, the rate constants for all the other reac-
tions were directly obtained from Atkinson [8]. The

8
16
AZAD AND ANDINO
Figure 1 Amount of propionaldehyde formed, corrected for reaction with the OH radical, against the amount of 1-propanol
reacted. Data points (Ⅲ) represent experimental values. The dashed line represents the predicted yield.
Figure 2 Amount of acetaldehyde formed, corrected for reaction with the OH radical, against the amount of 1-propanol
reacted. Data points (Ⅲ) represent experimental values. The dashed line represents the predicted yield.

GAS-PHASE PHOTOOXIDATION REACTIONS OF 1-PROPANOL
817
Observed and predicted concentrations of propi-
onaldehyde and acetaldehyde are presented in Figures
experimental yield. The experimental yield of acetal-
dehyde is also in excellent agreement with current es-
timates. A tabulation of the 1-propanol reactions ap-
pears in Table V. Note that methyl nitrite, methyl
1
and 2, respectively. Clearly, the exclusion of reac-
tions leading to the formation and subsequent reaction
of the ␣-hydroxyperoxy radical produces a propion-
aldehyde yield that is in excellent agreement with the
radical, and NO reactions were also included in the
x
overall mechanism used for modeling.
3
Table V 1-Propanol Mechanisms (in cm , molecule, s units)
Rxn No.
k (298 K)
Reaction
Source
1
-Propanol Reactions
Ϫ
13
12
12
13
P1)
P2)
P3)
P4)
1.44 ϫ 10
4.06 ϫ 10
1.16 ϫ 10
1.66 ϫ 10
PROP ϩ HOD ϭ CH (CH ) OD ϩ H O
26,8
26,8
26,8
26,8
3
2 2
2
Ϫ
PROP ϩ HOD ϭ CH CH CHOH ϩ H O
3
2
2
Ϫ
PROP ϩ HOD ϭ CH CHCH OH ϩ H O
3
2
2
Ϫ
PROP ϩ HOD ϭ CH CH CH OH ϩ H O
2
2
2
2
Site I Hydrogen Abstraction
CH (CH ) OD ϩ O ϭ PROPIONALDEHYDE ϩ HO D
Ϫ15
P5)
P6)
P7)
8.24 ϫ 10
32,9
8
8
3
2 2
2
2
Ϫ
11
3.8 ϫ 10
3.8 ϫ 10
CH (CH ) OD ϩ NO ϭ NITRITE
3
2 2
Ϫ
11
3
CH (CH ) OD ϩ NO ϭ NITRATE
3
2 2
2
P8)
P9)
1.04 ϫ 10
7 ϫ 10
CH (CH ) OD ϭ CH CH ϩ FORMALDEHYDE
32,9
8
3
2 2
3
2
Ϫ
12
CH CH ϩ O ϭ CH CH O D
3
2
2
3
2
2
Ϫ12
P10)
P11)
P12)
P13)
P14)
P15)
8.82 ϫ 10
CH CH O D ϩ NO ϭ CH CH OD ϩ NO
8
8
8
8
8
32,9
3
2
2
3
2
2
Ϫ14
8 ϫ 10
CH CH O D ϩ NO ϭ NITRATE
3
2
2
Ϫ
11
11
15
4.4 ϫ 10
2.8 ϫ 10
9.5 ϫ 10
CH CH OD ϩ NO ϭ NITRITE
3
2
Ϫ
Ϫ
CH CH OD ϩ NO ϭ NITRATE
3
2
2
CH CH OD ϩ O ϭ ACETALDEHYDE ϩ HO D
3
2
2
2
Ϫ1
3.36 ϫ 10
26.1 ϫ 10
CH CH OD ϭ FORMALDEHYDE ϩ DCH
3
2
3
Site II Hydrogen Abstraction
Ϫ12
P16)
CH CH CHOH ϩ O ϭ PROPIONALDEHYDE ϩ HO D
8
3
2
2
2
Site III Hydrogen Abstraction
Ϫ
12
12
P17)
P18)
P19)
P20)
P21)
P22)
P23)
P24)
P25)
11.6 ϫ 10
8.45 ϫ 10
CH CHCH OH ϩ O ϭ CH CH(O D)CH OH
8
8
8
8
8
32,9
32,9
32,9
8
3
2
2
3
2
2
Ϫ
CH CH(O D)CH OH ϩ NO ϭ CH CH(OD)CH OH ϩ NO
3
2
2
3
2
2
Ϫ
13
11
11
4.5 ϫ 10
CH CH(O D)CH OH ϩ NO ϭ NITRATE
3
2
2
Ϫ
3.8 ϫ 10
CH CH(OD)CH OH ϩ NO ϭ NITRITE
3
2
Ϫ
3.8 ϫ 10
CH CH(OD)CH OH ϩ NO ϭ NITRATE
3
2
2
Ϫ14
1.16 ϫ 10
CH CH(OD)CH OH ϩ O ϭ ACETOL ϩ HO D
3
2
2
2
5
4.7 ϫ 10
CH CH(OD)CH OH ϭ ACETALDEHYDE ϩ CH OH
3
2
2
6.22
9.4 ϫ 10
CH CH(OD)CH OH ϭ HYDROXYACETALDEHYDE ϩ DCH
3
2
3
Ϫ
12
DCH OH ϩ O ϭ FORMALDEHYDE ϩ HO D
2
2
2
Site IV Hydrogen Abstraction
DCH CH CH OH ϩ O ϭ DOO9CH CH CH OH
Ϫ
12
Estimatea
P26)
P27)
P28)
P29)
P30)
P31)
P32)
P33)
P34)
P35)
P36)
P37)
P38)
P39)
8 ϫ 10
2
2
2
2
2
2
2
Ϫ12
8.72 ϫ 10
1.8 ϫ 10
3.8 ϫ 10
3.8 ϫ 10
DOO9CH CH CH OH ϩ NO ϭ CH CH CH OH9O ϩ NO
8
8
8
2
2
2
2
2
2
2
Ϫ
13
11
11
DOO9CH CH CH OH ϩ NO ϭ NITRATE
2
2
2
Ϫ
DO9CH CH CH OH ϩ NO ϭ NITRATE
2
2
2
Ϫ
DO9CH CH CH OH ϩ NO ϭ NITRATE
8
2
2
2
2
Ϫ15
8.24 ϫ 10
2.02 ϫ 10
DO9CH CH CH OH ϩ O ϭ 3-HYDROXYPROPIONALDEHYDE ϩ HO D
32,9
32,9
8
8
8
8
8
32,9
32,9
2
2
2
2
2
2
DO9CH CH CH OH ϭ FORMALDEHYDE ϩ DCH CH OH
2
2
2
2
2
Ϫ12
3 ϫ 10
DCH CH OH ϩ O ϭ DOO9CH CH OH
2
2
2
2
2
Ϫ12
8.82 ϫ 10
DOO9CH CH OH ϩ NO ϭ DO9CH CH OH ϩ NO
2
2
2
2
2
Ϫ14
8 ϫ 10
DOO9CH CH OH ϩ NO ϭ NITRATE
2
2
Ϫ
11
3.8 ϫ 10
3.8 ϫ 10
7.58 ϫ 10
3.97 ϫ 10
DO9CH CH OH ϩ NO ϭ NITRITE
2
2
Ϫ
11
DO9CH CH OH ϩ NO ϭ NITRATE
2
2
2
Ϫ15
DO9CH CH OH ϩ O ϭ HYDROXYACETALDEHYDE ϩ HO D
2
2
2
2
3
DO9CH CH OH ϭ FORMALDEHYDE ϩ DCH OH
2
2
2
a
Estimated using the rate constant in [8] for the 1-propyl radical ϩO reaction.
2

8
18
AZAD AND ANDINO
CONCLUSIONS
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