Kinetics and products of the gas-phase reactions of 6-methyl-5-hepten-2-one and trans-cinnamaldehyde with OH and NO3 radicals and O3 at 296 ± 2 K

Article abstract of DOI:10.1021/es950871m

6-methyl-5-hepten-2-one is an atmospheric reaction product of the biogenic emission linalool, and trans-cinnamaldehyde is a model compound for dicarbonyls formed from the OH radical-initiated reaction of naphthalene. These carbonyl compounds react in the atmosphere, and photoloysis and the gas-phase reactions with OH radicals, NO₃ radicals, and O₃ have been investigated. Using relative rate methods, the respective rate constants were obtained for the OH radical, NO₃ radical, and O₃ reactions.

Full text of DOI:10.1021/es950871m

Environ. Sci. Technol. 1996, 30, 1781-1785
In the atmosphere, gas-phase photooxidations of directly
Kinetics and Products of the
Gas-Phase Reactions of
emitted volatile organic compounds lead to the formation
of products, which are often carbonyl compounds more
oxidized and less volatile than the directly-emitted precursor
compounds (2). For a complete understanding of the
atmospheric chemistry of an emitted compound, the
subsequent atmospheric reactions of its reaction products
also need to be known. In this work, we have investigated
the atmospheric chemistry of 6-methyl-5-hepten-2-one
6-Methyl-5-hepten-2-one and
trans-Cinnamaldehyde with OH
and NO Radicals and O at 296
3
3
[
[
(CH3)2CdCHCH2CH2C(O)CH3]and trans-cinnamaldehyde
trans-C6H5CHdCHCHO]. 6-Methyl-5-hepten-2-one is a
(
2 K
product of the OH radical-initiated reaction of linalool
A N N A M . S M I T H , E L I S A B E T H R I G L E R ,
[(CH ) CdCHCH CH C(CH )(OH)CH)CH ] (3), a terpene
3
2
2
2
3
2
E R I C S . C . K W O K , † A N D
emitted from orange blossoms (4) and from certain pine
trees in southern Europe (5), while trans-cinnamaldehyde
is structurally related to commercially unavailable ring-
opened C10-dicarbonyls formed in significant yield from
the OH radical-initiated reaction of naphthalene (6). The
kinetic and product data obtained for these two oxygenated
compounds add significantly to the database concerning
the atmospheric chemistry of products formed from the
atmospheric photooxidations of volatile organic com-
pounds of anthropogenic and biogenic origin.
,
‡
R O G E R A T K I N S O N *
Statewide Air Pollution Research Center, University of
California, Riverside, California 92521
6-Methyl-5-hepten-2-one is an atmospheric reaction
product of the biogenic emission linalool, and
trans-cinnamaldehyde is a model compound for
dicarbonyls formedfromthe OHradical-initiatedreaction
of naphthalene. These carbonyl compounds react
in the atmosphere, and photolysis and the gas-phase
reactions of 6-methyl-5-hepten-2-one and trans-
Experimental Section
The experimental methods used were similar to those
described previously (7, 8). All experiments were carried
out at 296 ( 2 K and 740 Torr total pressure of purified air
at ∼5% relative humidity in a ∼6700-L Teflon chamber
equipped with two parallel banks of black lamps and with
a Teflon-coated fan to ensure rapid mixing of reactants
during their introduction.
3
cinnamaldehyde with OH radicals, NO radicals, and
O
3
have been investigated at 296 ( 2 K and
atmospheric pressure ofair. Usingrelative rate methods,
the respective rate constants obtained for the OH
3
radical, NO
molecule
3
radical, and O
3
reactions were (in cm
-
1
-1
Rate Constant Measurem ents. The rate constants for
the OH radical, NO3 radical, and O3 reactions were measured
using relative rate methods in which the relative disap-
pearance rates of the carbonyl and a reference organic,
whose reaction rate constant with OH radicals, NO3 radicals,
s
units) as follows: for 6-methyl-5-
hepten-2-one: (1.57 ( 0.39) × 10 , (7.5 ( 3.0) × 10-12,
-10
-16
and (3.9 ( 1.5) × 10 ; for trans-cinnamaldehyde:
-
11
-14
(
1
4.8 ( 1.4) × 10 , (1.9 ( 0.7) × 10 , and (2.2 (
-
18
.8) × 10 . trans-Cinnamaldehyde was also observed
or O is reliably known, were measured in the presence of
3
to photolyze. Benzaldehyde was observed and
quantified from the OH radical reaction with trans-
cinnamaldehyde, with a yield of 0.90 ( 0.39. Acetone
OH radicals, NO3 radicals, or O3 (8). Providing that the
carbonyl and the reference organic reacted only with OH
radicals, NO3 radicals, or O3, then,
andCH
from the OH radical and O
-methyl-5-hepten-2-one, with formation yields of
.706 ( 0.054 and 0.59 ( 0.13, respectively, from the
OH radical reaction and 0.302 ( 0.048 and 0.82 (
.21, respectively, from the O reaction. The reaction
3
C(O)CH
2
CH
2
CHOwere observedandquantified
[
carbonyl]t0
3
reactions with
ln
- D )
t
{[carbonyl]
}
6
0
t
[reference organic]t0
k
1
ln
- Dt (I)
{
[
]
}
k2
[reference organic]t
0
3
mechanisms are discussed.
where [carbonyl]t0 and [reference organic]t are the con-
0
centrations of the carbonyl and reference organic, respec-
tively, at time t0; [carbonyl]t and [reference organic]t are
the corresponding concentrations at time t; Dt is a term to
take into account any dilution caused by additions to the
chamber during an experiment (Dt ) 0.0014-0.0028 per
addition); and k1 and k2 are the rate constants for reactions
Introduction
A large number of organic compounds are emitted into the
atmosphere from anthropogenic and biogenic sources (1).
*
Author to whom correspondence should be addressed; tele-
1
and 2, respectively.
phone: (909) 787-4191; fax: (909) 787-5004; e-m ail address:
ratkins@mail.ucr.edu.
OH
†
Present address: Environmental Toxicology Program, University
NO3 + carbonyl f products
(1)
of California, Riverside, CA 92521.
}
‡
O3
Also at Department of Soil and Environmental Sciences.
0
013-936X/96/0930-1781$12.00/0

1996 Am erican Chem ical Society
VOL. 30, NO. 5, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1 7 8 1

TABLE 1
Rate Constant Ratios k
1
/k
2
and Rate Constants k
1
for Gas-Phase Reactions of 6-Methyl-5-hepten-2-one and
at 296 ( 2 K and Atmospheric Pressure
trans-Cinnamaldehyde with OH Radicals, NO
3
Radicals, and O
3
3
-1 -1
k1 (cm molecule
s )
carbonyl
ref compd
k1/k2a
experimentalb
estimatedc
OH Radical Reaction
2.42 ( 0.35
-
10
-11
6
-m ethyl-5-hepten-2-one
trans-2-butene
trans-2-butene
(1.57 ( 0.39) × 10
9.2 × 10
trans-cinnam aldehyde
0.74 ( 0.14
(4.8 ( 1.4) × 10-
11
4.1 × 10
-11
NO3 Radical Reaction
0.80 ( 0.14
6-m ethyl-5-hepten-2-one
trans-cinnam aldehyde
2-m ethyl-2-butene
propene
(7.5 ( 3.0) × 10-
(1.9 ( 0.7) × 10-
12
9.4 × 10
-12
14
-15 d
2.07 ( 0.18
5.1 × 10
O3 Reaction
0.98 ( 0.14
0.23 ( 0.18
16
18
-16
6
-m ethyl-5-hepten-2-one
trans-cinnam aldehyde
2-m ethyl-2-butene
propene
(3.9 ( 1.5) × 10-
4.0 × 10
9.0 × 10
(2.2 ( 1.8) × 10-
-19 d
a
b
(in cm 3 m olecule
-1
s-1
Indicated errors are two least-squares standard deviations. Placed on an absolute basis by use of rate constants k
2
)
-11
-15
at 296 K of k
9.37 × 10
2
-
(OH + trans-2-butene) ) 6.48 × 10
((20%) (2, 17), k
2
(NO
3
+ propene) ) 9.24 × 10
((35%) (2, 15), k
+ 2-m ethyl-2-butene) ) 3.96 × 10
2
(NO
3
+ 2-m ethyl-2-butene)
((35%) (2). c Estim ated
CHdCHCHO]
12
-18
-16
)
((35%) (2, 15), k
2
(O
3
+ propene) ) 9.68 × 10
((25%) (2), and k
2
(O
3
d
as described in refs 15, 16 and 18 unless noted otherwise. Literature rate constants for the structurally related carbonylcrotonaldehyde [CH
3
(
2); see text.
2
-methyl-2-butene were analyzed as described previously
OH
NO3 + reference organic f products
O3
(2)
(12). For the analyses of the carbonyls 6-methyl-5-hepten-
2
samples were collected from the chamber onto Tenax-TA
solid adsorbent with subsequent thermal desorption at
}
3
-one and trans-cinnamaldehyde, 100 cm volume gas
Plots of {ln([carbonyl]t / [carbonyl]t) - Dt} against {ln-
[reference organic]t / [reference organic]t) - Dt} should
therefore be straight lines with slope k1/ k2 and zero
intercept.
0
∼
225-250 °C onto a 30-m DB-5.625 or DB-5 megabore
(
0
column, initially held at 0 (trans-cinnamaldehyde) or 40 °C
(
6-methyl-5-hepten-2-one) and then temperature pro-
-
1
grammed to 250 °C at 8 °C min
.
The initial concentrations of 6-methyl-5-hepten-2-one,
trans-cinnamaldehyde, and the reference organic were
Product Studies. The products formed from the gas-
phase reactions of the OH radical with 6-methyl-5-hepten-
2
1
3
13
13
(
1.9-2.5) ×10 , (0.64-1.3) ×10 , and ∼4.8 ×10 molecule
-one and trans-cinnamaldehyde in the presence of NO
-3
cm , respectively. The reference organics used in these
relative rate measurement experiments are listed in Table
and from the reaction of O3 with 6-methyl-5-hepten-2-one
were investigated. These experiments were carried out as
described above with similar initialreactant concentrations,
except for the absence of the reference organic. As
discussed in detail previously (8, 12, 13), the OH radical
formation yield from the O3 reaction with 6-methyl-5-
hepten-2-one was derived from the measured amounts of
cyclohexanone and cyclohexanol formed from the reaction
of OH radicals with cyclohexane.
Gas samples were collected from the chamber onto
Tenax-TA solid adsorbent, with subsequent thermal des-
orption and analyses by GC-FID (as described above),
combined gas chromatography-mass spectrometry (GC/
MS) with positive ion chemical ionization [using a 60-m
HP-5 fused silica capillary column in a Hewlett Packard
1
.
Hydroxyl radicals were generated from the photolysis
1
4
-3
of 2.4 × 10 molecule cm of methyl nitrite (CH3ONO) in
1
4
air at wavelengths >300 nm (9), and 2.4 × 10 molecule
-3
cm of NO was added to the reactant mixtures to suppress
the formation of O3 and hence of NO3 radicals (9).
Irradiations were carried out at 20% of the maximum light
intensity, corresponding to an NO2 photolysis rate of 1.5
-
3 -1
×
10
s , for 1-6 min. In addition, carbonyl-air mixtures
1
5
-3
with (4.2-6.7) × 10 molecule cm of cyclohexane to
scavenge any OH radicals formed from residual NOx or
impurities in the chamber were irradiated at 20% of the
maximum light intensity for up to 30 min to assess the
importance of photolysis by the black lamps. Nitrate
radicals were generated by the thermal decomposition of
(
HP) 5890 GC interfaced to a HP 5971 mass selective detector
and HP G1072A CI detector, operated in the scanning
mode], and gas chromatography with FTIR detection (GC-
FTIR), using a 30-m DB-5MS capillary column in a HP 5890
GC interfaced to a HP 5965B FTIR detector. GC-FID
response factors for the reactants and products were
measured (6-methyl-5-hepten-2-one, acetone, and ben-
zaldehyde) or estimated using the equivalent carbon
number concept of Scanlon and Willis (14), as described
previously (7, 8).
Chem icals. Acetone, benzaldehyde, trans-2-butene,
trans-cinnamaldehyde, cyclohexane, 2-methyl-2-butene,
6-methyl-5-hepten-2-one, propene, and NO were all of
g98% purity. Methyl nitrite and N O were prepared as
1
4
-3
N2O5 (10) in the presence of (1.2-2.4) × 10 molecule cm
of NO2. Three or four additions of N2O5 [each addition
corresponding to an initial concentration of N2O5 in the
1
3
-3
chamber of (0.5-5) × 10 molecule cm ] were made to
the chamber during an experiment. For the O3 reactions,
1
6
-3
(
(
2.6-3.3) × 10 molecule cm of cyclohexane was used
7, 8, 11) to scavenge >95% of the OH radicals formed from
the reactions of O3 with the reference organics (12) and the
carbonyls. One to three additions of O3 in O2 diluent (each
O3/ O2 addition corresponding to an initial O3 concentration
in the chamber of ∼5 × 10 molecule cm ) were made to
the chamber during an experiment.
1
2
-3
2
5
The concentrations of the carbonyls and reference
organics were measured during these experiments by gas
chromatography with flame ionization detection (GC-FID).
The reference organics propene, trans-2-butene, and
described previously (9, 10) and stored under vacuum at
77 K. NO2 was prepared immediately prior to use by
reacting NO with an excess of O2, and O3 was prepared as
needed by a Welsbach T-408 ozone generator.
1
7 8 2
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 5, 1996

addition to the >CdC< bond (2, 15-17), and the rate
constants for the addition reactions are estimated to be the
same as those for the corresponding reactions of 2-methyl-
2
6
-butene (2, 15, 16, 18). For the OH radical reaction with
-methyl-5-hepten-2-one, H-atom abstraction from the
various C-H bonds is estimated to be minor, accounting
for ∼5% of the overall OH radical reaction (2, 17, 18). The
estimated rate constants for the reactions of OH radicals,
NO3 radicals, and O3 with 6-methyl-5-hepten-2-one are also
given in Table 1, and are within a factor of e1.7 of our
measured values.
The OH radical and NO3 radical reactions with trans-
cinnamaldehyde can proceed by addition to the >CdC<
bond, addition to the aromatic ring, and H-atom abstraction
from the CHO group (2, 15, 18). Addition of OH radicals
and NO3 radicals to the aromatic ring is expected to be of
minor (OH radical) or negligible (NO3 radical) importance
(
2, 15, 17, 18). The OH radical reaction rate constant for
addition to the >CdC< bond can be estimated using the
CHO group substituent factor (18), and the resulting
calculated overall rate constant is given in Table 1. For the
NO3 radical and O3 reactions, trans-cinnamaldehyde is
expected to be of similar reactivity to crotonaldehyde
[
CH3CHdCHCHO] (2, 15, 17), and the rate constants for
the reactions of NO3 radicals and O3 with crotonaldehyde
2) are given in Table 1 and are within a factor of 4 of those
(
FIGURE 1. Plots of eq I for the gas-phase reactions of the OH radical
with6-methyl-5-hepten-2-one andtrans-cinnamaldehyde, withtrans-
we measured for trans-cinnamaldehyde.
Products of the OH Radical and O3 Reactions. The
products of the atmospherically important reactions of
2-butene as the reference organic.
6
-methyl-5-hepten-2-one with OH radicals and O3 and of
trans-cinnamaldehyde with OH radicals were investigated.
-Methyl-5-hepten-2-one. GC-FID, GC-MS, and GC-
Results and Discussion
Photolysis and OH Radical, NO3 Radical, and O3 Reaction
Rate Constants. No photolysis (<1%) of 6-methyl-5-
hepten-2-one was observed over a 30-min period at 20%
of the maximum light intensity. In contrast, photolysis of
trans-cinnamaldehyde at 20% of the maximum light
intensity for 30 min led to the disappearance of 33% of the
trans-cinnamaldehyde, with the appearance of a product
tentatively identified by its infrared (IR) and MS spectra as
cis-cinnamaldehyde. The photolysis rate of trans-cinna-
maldehyde was 0.0129 ( 0.0026 min (the indicated error
is two least-squares standard deviations) under the light
intensityand spectralconditions employed, and the amount
of cis-cinnamaldehyde formed was 57 ( 7% of the trans-
cinnamaldehyde photolyzed (the indicated error is again
two standard deviations).
6
FTIR analyses of irradiated CH3ONO-NO-6-methyl-5-
hepten-2-one-air mixtures and reacted O3-6-methyl-5-
hepten-2-one-cyclohexane (in excess)-air mixtures showed
the formation of acetone plus a second compound in both
reactions. Additionally, cyclohexanone and cyclohexanol
were observed in the O3 reaction, indicating the formation
ofOH radicals (12, 13). The IRspectra ofthe second product
from the OH radical and O3 reactions had absorption bands
-
1
-1
at 1164, 1367, 1740 (strong), 2721, 2817, and 2918 cm
.
-1
The absorption bands at 2721 and 2817 cm are attributed
-1
to the C-H stretch in a CHO group and that at 1740 cm
to a CdO stretch. The methane-CI mass spectra had a
base ion peak at 101 u (unified atom mass unit) and weaker
ion peaks at 129 and 141 u. The 101 u ion peak is therefore
the [M + H]+ ion, and the product of the OH radical and
Representative experimental data obtained from the
kinetic experiments are plotted in accordance with eq I in
Figure 1 for the OH radical reactions with 6-methyl-5-
hepten-2-one and trans-cinnamaldehyde. In allcases, good
straight line plots were observed, and no effect of the initial
NO2 concentrations on the rate constant ratios k1/ k2 were
observed for the NO3 radical reactions. The rate constant
ratios k1/ k2 obtained from least-squares analyses of the
experimental data are given in Table 1. For the reaction
of O3 with trans-cinnamaldehyde, <19% of the initially
present trans-cinnamaldehyde was consumed by reaction,
and the rate constant ratio k1/ k2 given in Table 1 is subject
to significant uncertainties. The measured rate constant
ratios k1/ k2 are placed on an absolute basis as described
in footnote b in Table 1, and the resulting rate constants
k1 are given in Table 1.
O reactions has a molecular weight of 100. These IR and
3
MS data are consistent with the second product of both
reactions being CH C(O)CH CH CHO, as expected from
3
2
2
cleavage of the >CdC< bond (2).
Secondary reactions of the products with the OH radical
occur in the OH radical reaction, and the measured
concentrations of acetone and CH C(O)CH CH CHO were
3
2
2
corrected to take into account their reactions with the OH
radical (19) using measured or estimated rate constants for
the OH radical reactions with acetone and CH C(O)CH -
3
2
CH CHO of 2.15 × 10-13 cm3 molecule-1 s-1 at 296 K (2)
2
and 2.63 × 10-11 cm3 molecule-1 s-1 (18), respectively. The
corrections for secondary reactions were <1% for acetone
and e12% for CH C(O)CH CH CHO. Plots of the amounts
3
2
2
of acetone and CH C(O)CH CH CHO formed, corrected for
3
2
2
The reactions of 6-methyl-5-hepten-2-one with OH
radicals, NO3 radicals, and O3 proceed totally (NO3 radical
and O3 reactions) or mainly (OH radical reaction) by initial
secondary reactions with the OH radical, against the
amounts of 6-methyl-5-hepten-2-one reacted with the OH
radical are shown in Figure 2, and plots of the amounts of
VOL. 30, NO. 5, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1 7 8 3

TABLE 2
Measured Product Yields for Gas-Phase Reactions
of OH Radicals in the Presence of NO with
6
-Methyl-5-hepten-2-one and trans-Cinnamaldehyde
and of O
3
with 6-Methyl-5-hepten-2-one
reaction with
product
OH
O3a
6
-Methyl-5-hepten-2-one
b
b
CH3C(O)CH3
0.706 ( 0.054
0.302 ( 0.048
b
b
CH3C(O)CH2CH2CHO
OH
0.59 ( 0.13
0.82 ( 0.21
0.75c
trans-Cinnamaldehyde
b
C6H5CHO
0.90 ( 0.39
a
In the presence of sufficient cyclohexane to scavenge g95% of the
b
OH radicals form ed. Indicated errors are two least-squares standard
3 2 2
FIGURE 2. Plots of the amounts of acetone and CH C(O)CH CH CHO
deviations com bined with estim ated overall uncertainties in the GC-
FID response factors for 6-m ethyl-5-hepten-2-one and acetone of (5%
each and in the relative GC-FID response factors of 6-m ethyl-5-hepten-
formed, corrected for reaction with the OH radical (see text), against
the amounts of 6-methyl-5-hepten-2-one reacted with the OH radical
in the presence of NO.
2-one and CH C(O)CH CH CHO and of trans-cinnam aldehyde and
3 2 2
c
benzaldehyde of (20%. Derived from the m easured cyclohexanone
plus cyclohexanol yield, assum ing a form ation yield of cyclohexanone
plus cyclohexanol from cyclohexane of 0.50 (12). Estim ated overall
uncertainty is a factor of ∼1.5.
The OH radical reaction with 6-methyl-5-hepten-2-one
proceeds mainly (∼95%) by initial addition to form the
â-hydroxyalkyl radicals CH3C(O)CH2CH2CH(OH) C˙ (CH3)2
and CH3C(O)CH2CH2 C˙ HC(OH)(CH3)2, which rapidly add
O2 to yield the â-hydroxyalkyl peroxy radicals CH3C(O)CH2-
CH2CH(OH)C(O O˙ )(CH3)2 and CH3C(O)CH2CH2CH(O O˙ )C-
(
OH)(CH3)2 (2). These â-hydroxyalkyl peroxy radicals then
react with NO to form the â-hydroxynitrate or the corre-
sponding â-hydroxyalkoxy radical plus NO2 (2). The
â-hydroxyalkoxy radical CH3C(O)CH2CH2CH(OH)C( O˙ )-
(
CH3)2 can isomerize through a six-member transition state
or decompose, with the R-hydroxy radical formed from the
decomposition reaction reacting rapidly with O2 to form
the carbonyl CH3C(O)CH2CH2CHO plus HO2 radical (2):
.
CH3C(O)CH2CH2CH(OH)C(O)(CH3)2
.
FIGURE 3. Plots of the amounts of acetone (4), CH
O), and cyclohexanone plus cyclohexanol (b) formed against the
amounts of 6-methyl-5-hepten-2-one reacted with O in the presence
3
C(O)CH
2
CH
2
CHO
CH C(O)CHCH CH(OH)C(OH)(CH )
(3a)
(3b)
3
2
3 2
(
.
CH3C(O)CH2CH2CHOH + CH3C(O)CH3
3
of sufficient cyclohexane to scavenge g95% of the OH radicals
formed.
O2
CH3C(O)CH2CH2CHO + HO2
acetone, CH3C(O)CH2CH2CHO, and cyclohexanone plus
cyclohexanol formed against the amounts of 6-methyl-5-
hepten-2-one reacted with O3 are shown in Figure 3. Least-
squares analyses of the acetone and CH3C(O)CH2CH2CHO
data lead to the formation yields given in Table 2.
The â-hydroxyalkoxyradicalCH3C(O)CH2CH2CH( O˙ )C(OH)-
(CH ) can react with O or decompose (2):
3
2
2
.
CH3C(O)CH2CH2CH(O)C(OH)(CH3)2
Aleast-squares analysis ofthe amounts ofcyclohexanone
plus cyclohexanol formed against the amounts of 6-methyl-
O2
CH3C(O)CH2CH2C(O)C(OH)(CH3)2 + HO2
(4a)
(4b)
.
5
-hepten-2-one reacted with O3 in the presence of sufficient
CH3C(O)CH2CH2CHO + CH3C(OH)CH3
cyclohexane to scavenge g95% of the OH radicals formed
leads to a {([cyclohexanone] + [cyclohexanol])/ ([6-methyl-
O2
5
-hepten-2-one] reacted)} ratio of 0.377 ( 0.058, where the
HO2 + CH3C(O)CH3
indicated error is two least-squares standard deviations
combined with estimated overall uncertainties in the GC-
FID response factors for the reactants and products of (5%
each. A yield of 0.50 for the formation of cyclohexanone
plus cyclohexanol from the OH radical reaction with
cyclohexane in reacting O3-alkene-air systems (12) is used
to derive the OH radical formation yield given in Table 2.
Our m easured form ation yields of acetone and
CH3C(O)CH2CH2CHO of 0.706 ( 0.054 and 0.59 ( 0.13,
respectively, indicate that decomposition of the intermedi-
ate â-hydroxyalkoxy radicals dominates to form acetone
plus CH C(O)CH CH CHO (reactions 3b and 4b). Other
3
2
2
reaction processes, either hydroxynitrate formation from
1
7 8 4
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 5, 1996

the peroxy radical plus NO2 reaction, isomerization of the
CH3C(O)CH2CH2CH(OH)C( O˙ )(CH3)2 radical (reaction 3a),
and/ or reaction of the CH3C(O)CH2CH2CH( O˙ )C(OH)(CH3)2
radical with O2 (reaction (4a) must also occur.
The O3 reaction with 6-methyl-5-hepten-2-one proceeds
by initial addition to form a primary ozonide (2), which
then rapidly decomposes to either CH3C(O)CH3 plus the
C6H5 C˙ HCH(OH)CHO are expected to react as discussed
above for the â-hydroxyalkyl radicals formed from the OH
radical reaction with 6-methyl-5-hepten-2-one, leading to
the formation of benzaldehyde plus formaldehyde by
decomposition of the intermediate â-hydroxyalkoxy radi-
cals. The acyl radical C6H5CHdCH C˙ O formed in reaction
6a is expected to rapidly add O2 to form the C6H5CHdCHC-
(O)O O˙ radical (2), which in the presence of NO is expected
to also ultimately form, at least in part, benzaldehyde (2).
Our measured high yield of benzaldehyde from the OH
radical reaction with trans-cinnamaldehyde in the presence
of NO is consistent with the above discussion, although we
cannot assess the relative contributions of H-atom ab-
straction from the CHO group versus OH radical addition
to the >CdC< bond of the substituent group.
[CH3C(O)CH2CH2 C˙ HO O˙ ]* biradical or to CH3C(O)CH2CH2-
CHO plus the [(CH3)2 C˙ O O˙ ]* biradical. Our measured
acetone and CH3C(O)CH2CH2CHO formation yields of0.302
(
0.048 and 0.82 ( 0.21, respectively, show that decom-
position of the ozonide to CH3C(O)CH2CH2CHO plus the
(CH3)2 C˙ O O˙ ]* biradical dominates and that the two path-
[
ways sum to unity within the experimental uncertainties.
Our measured yield of OH radicals of ∼0.75 is consistent
with the formation of the [(CH3)2 C˙ O O˙ ]* biradical in ∼70-
8
0% yield, followed by isomerization to the hydroperoxide
Acknowledgments
The authors gratefully acknowledge the support of this
research by the National Science Foundation through Grant
ATM-9414036.
[CH3C(OOH)dCH2]* and subsequent decomposition to
form the OH radical in high yield (12, 20):
[
(CH ) C˙ O O˙ ]* f [CH C(OOH)dCH ]* f
3
2
3
2
Literature Cited
CH C(O) C˙ H + OH (5)
3
2
(
1) Graedel, T. E.; Hawkins, D. T.; Claxton, L. D. Atmospheric
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together with some additional formation of OH radicals
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(
(
2) Atkinson, R. J. Phys. Chem. Ref. Data 1994, Monograph 2, 1-216.
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(
12, 20), where the [(CH3)2 C˙ O O˙ ]* biradical leads to the
(
(
4) Arey, J.; Corchnoy, S. B.; Atkinson, R. Atmos. Environ. 1991, 25A,
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analyses of irradiated CH3ONO-NO-trans-cinnamalde-
hyde-air mixtures showed the formation of benzaldehyde,
together with smallamounts ofcis-cinnamaldehyde formed
from the photolysis of the trans-cinnamaldehyde. Our
measured photolysis rate constant for trans-cinnamalde-
hyde was used to correct for the amounts of trans-
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1
377-1381.
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(
Italy), June 1993; Joint Research Centre, Environment Institute:
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(
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(
(
(
7) Hakola, H.; Arey, J.; Aschmann, S. M.; Atkinson, R. J. Atmos.
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Pollut. Control Assoc. 1981, 31, 1090-1092.
-
11
3
-1
reaction with benzaldehyde of 1.29 × 10 cm molecule
(
(
(
10) Atkinson, R.; Plum, C. N.; Carter, W. P. L.; Winer, A. M.; Pitts, J.
N., Jr. J. Phys. Chem. 1984, 88, 1210-1215.
-
1
s
(2), with the corrections being e14%. Least-squares
11) Greene, C. R.; Atkinson, R. Int. J. Chem. Kinet. 1992, 24, 803-
analyses of the amounts of benzaldehyde formed, corrected
for reaction with the OH radical, against the amounts of
trans-cinnamaldehyde reacted with the OH radical lead to
the benzaldehyde formation yield given in Table 2. The
amounts of cis-cinnamaldehyde formed were consistent
with the amounts of trans-cinnamaldehyde photolyzed and
our measured cis-cinnamaldehyde formation yield.
The OH radical reaction with trans-cinnamaldehyde is
expected to proceed mainly by H-atom abstraction from
the CHO group and initial addition to the >CdC< bond
of the substituent group (2, 17).
8
11.
12) Atkinson, R.; Aschmann, S. M. Environ. Sci. Technol. 1993, 27,
357-1363.
1
(13) Atkinson, R.; Aschmann, S. M.; Arey, J.; Shorees, B. J. Geophys.
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(
(
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(16) Atkinson, R.; Carter, W. P. L. Chem. Rev. 1984, 84, 437-470.
(
(
17) Atkinson, R. J. Phys. Chem. Ref. Data 1989, Monograph 1, 1-246.
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1
695.
(19) Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Winer, A. M.;
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(
M. D. J. Phys. Chem. 1987, 91, 941-946.
OH + C6H5CH CHCHO
.
Received for review November 21, 1995. Revised manuscript
received January 17, 1996. Accepted January 17, 1996.
H2O + C6H5CH CHCO
.
(6a)
(6b)
X
.
C6H5CH(OH)CHCHO and C6H5CHCH(OH)CHO
ES950871M
X
The â-hydroxyalkyl radicals C6H5CH(OH) C˙ HCHO and
Abstract published in Advance ACS Abstracts, March 15, 1996.
VOL. 30, NO. 5, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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