Reaction of O(3P) atoms with benzene

Article abstract of DOI:10.1524/zpch.218.4.391.29202

The gas-phase reaction of O(³P) atoms with benzene was investigated in a flow system in the pressure range of 50-100 mbar and a temperature of 295 ± 2 K with a focus on the product formation. O₂ concentrations in the carrier gas were in the range of (7.7-84) × 10¹⁴ molecule cm^-3. The primary stable products detected were phenol, benzene oxide/oxepin and a not identified compound with the probable composition C₅H₆O. The yields of phenol and benzene oxide/oxepin were 0.12 ± 0.02 and 0.26 ± 0.06, respectively, being not affected by the experimental conditions. For benzene oxide/oxepin, a rapid consecutive reaction with O(³P) atoms was observed with a rate coefficient of k_{(295 K)} = (1.1 ± 0.1) × 10^-10 cm³ molecule^-1 s^-1 measured at a pressure of 100 mbar. A substance with the formula C₆H₆O₂ (likely oxepin 4,5-epoxide or oxepin 2,3-epoxide), the isomers of muconaldehyde, as well as formic acid, acrolein and trans-butenedial were identified as products of the reaction of O(³P) atoms with benzene oxide/oxepin.

Full text of DOI:10.1524/zpch.218.4.391.29202

Z. Phys. Chem. 218 (2004) 391–403
by Oldenbourg Wissenschaftsverlag, München
Reaction of O(3 P) Atoms with Benzene
∗
By Torsten Berndt and Olaf Böge
Leibniz-Institut für Troposphärenforschung, Permoserstraße 15, 04318 Leipzig,
Germany
Dedicated to Prof. Dr. Klaus Scherzer on the occasion
of his 70th birthday
(Received December 17, 2003; accepted in revised form February 3, 2004)
O(3P) Atoms / Kinetics / Benzene Oxide-Oxepin
The gas-phase reaction of O( 3P) atoms with benzene was investigated in a flow system
in the pressure range of 50–100 mbar and a temperature of 295 2 K with a focus
on the product formation. O2 concentrations in the carrier gas were in the range
of (7.7–84)× 1014 moleculecm−3. The primary stable products detected were phenol,
benzene oxide oxepin and a not identified compound with the probable composition
C5H6O. The yields of phenol and benzene oxide oxepin were 0 12 0 02 and 0 26 0 06,
respectively, being not affected by the experimental conditions. For benzene oxide oxepin,
a rapid consecutive reaction with O( 3P) atoms was observed with a rate coefficient
of k 295 K = 1 1 0 1 ×10−10 cm3 molecule−1 s−1 measured at a pressure of 100 mbar.
A substance with the formula C6H6O2 (likely oxepin 4,5-epoxide or oxepin 2,3-epoxide),
the isomers of muconaldehyde, as well as formic acid, acrolein and trans-butenedial were
identified as products of the reaction of O( 3P) atoms with benzene oxide oxepin.
1. Introduction
In the course of investigations concerning the degradation pathways of aro-
matics in the atmosphere a series of experiments has been performed on the
reaction of O( 3P) atoms with benzene. This experimental work was focused
on the identification of the oxidation products. From the findings arising from
the O( 3P) atom initiated oxidation of benzene, a more comprehensive under-
standing of the degradation pathway for aromatics is expected. This should be
helpful also in the field of atmospheric benzene oxidation where the primary
attack proceeds predominantly via the reaction with OH radicals.
In the literature, beside quite a number of kinetic studies [1], a series
of end product information exists for the reaction of O( 3P) atoms with ben-
zene [2–9]. Phenol is reported to account for more than 95% of the volatile
*
Corresponding author. E-mail: berndt@tropos.de
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392
T. Berndt and O. Böge
products [6] with a formation yield of 0.10–0.14 [3, 4, 7]. In a former study,
an unsteady phenol yield of up to 0.27 was detected [2]. Furthermore, using
the Hg-sensitised decomposition of N2O for O( 3P) atom generation, a pres-
sure dependent CO yield was measured, 0.239 at 49 1 Torr down to 0.143 at
591 6 Torr [4]. As a result of crossed molecular beam studies applying a dis-
charge technique for O( 3P) atom generation, however, the formation of CO
was controversially discussed to be a primary process [8, 9]. Some investiga-
tors observed the deposition of yellow-coloured solid material at the reactor
walls [4, 7]. MS-, NMR- as well as IR-analysis of the coatings did not give
a clear indication for the chemical nature of this material [7]. The elemental
analysis yielded C : H : O = 60 : 5 : 35 (in weight percentages) [7].
From the mechanistic point of view, kinetic data [1] as well as the absence
of a primary H D isotope effect [7] indicate that an electrophilic addition of
O( 3P) atoms to the aromatic ring is favoured yielding a triplet biradical. Tappe
et al. [10] proposed three pathways for the stabilisation of this biradical, i.e. the
formation of a phenoxy radical and an H-atom, the formation of the valence
isomers benzene oxide and oxepin and the formation of phenol, cf. pathways
(1a)–(1c).
Up to now, there is only experimental evidence for the formation of phenol via
pathway (1c). The investigations described here are to improve the knowledge
of the primary stable products from the reaction of O( 3P) atoms with benzene.
2. Experimental
The experiments have been performed in a 4 0 cm i.d. quartz flow tube
(total length: 100 cm) in the pressure range of 50–100 mbar and a tempera-
ture of 295 2 K. Approximately 50 cm downstream of the point of the en-
trance of benzene diluted in N2, O( 3P) atoms were generated in a side-arm
with a microwave discharge (SAIREM GMP 03 K SM) using a mixture of
0.05–0 5 vol% O2 or 18O2 in He. The resulting carrier gas mixture was kept
constant at 20 vol% He and 80 vol% N2. Initial benzene concentrations in
the reaction zone were in the range (3.5–360) × 1015 molecule cm−3 and the
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Reaction of O( 3P) Atoms with Benzene
393
amount of converted benzene was (3.6–5.7) × 1013 molecule cm−3. If needed,
O2 was added to the N2 stream resulting in O2 concentrations after mixing
with the He stream of (7.7–84) × 1014 molecule cm−3. The total gas flow was
2.0–4.0 standard litre min−1 leading to a bulk residence time in the reaction
zone of 0 86–1 2 s. The gas flows were set by calibrated mass flow controllers
(MKS 1259) and the pressure was measured using a capacitive manometer
(Baratron).
For analysis, the main part of the reaction gas was pumped continuously
through a White cell (optical path length: 10 m) for FT-IR measurements
(Nicolet Magna 750). For quantitative determinations, calibrated spectra of
the corresponding reference substances were used. Furthermore, for on-line
GC-MS analysis (Agilent 6890 with MSD 5973), a GC loop was directly con-
nected to the flow tube by means of a heated transfer line. The mass spectra
were recorded in the 70 eV EI mode. For product separation, a HP 5 MS col-
umn, 30 m×0 25 mm was applied. Using the ion trace at m z = 94 u, benzene
oxide oxepin as well as phenol were determined efficiently down to flow-tube
concentrations of about 1010 molecule cm−3.
In a few runs, the gas stream was pumped through a cryo-trap directly at-
tached to the outlet of the flow tube. The cryo-trapping of the reaction products
was performed at liquid argon temperature. Immediately after disconnecting
the trap from the flow tube, the frozen material was dissolved in ether and
analysed subsequently by GC-MS applying the same equipment as described
before.
Additionally, the product formation from the reaction of O( 3P) atoms
with benzene oxide oxepin was investigated in a few runs at a pressure of
100 mbar. The O2 concentration was 1 5×1015 molecule cm−3, the initial ben-
zene oxide oxepin concentration was around 2 8×1013 molecule cm−3 and
(1.0–1.2) × 1013 molecule cm−3 were converted. All other conditions were the
same as described for the reaction with benzene.
2.1 Gases and chemicals
The gases used had stated purities as follows: He (99.999%), O2 (99.9996%),
N2 (99.999%) (Linde) and 18O2 (18O enrichment: 96%) (euriso-top). For fur-
ther purification, the He was passed through an universal trap (Agilent).
Benzene oxide oxepin was prepared by a procedure of Gillard et al. [11].
Briefly, 1,4-cyclohexadiene was monobrominated in the cold, and epoxidation
with MCPBA gave 4,5-dibromocyclohexene oxide. Double dehydrobromina-
tion was performed with DBU yielding benzene oxide oxepin as a yellow
liquid. trans-Butenedial was made by hydrolysis of its bis dimethylacetal.
For this, a solution of the bis dimethylacetal in water acetone was stirred at
room temperature in presence of a sulfonic acid-based cation exchange resin
(Amberlyst-15). After filtration and concentration, the residue was extracted
with methylene chloride. The organic layer was dried over sodium sulfate
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394
T. Berndt and O. Böge
and concentrated afterwards yielding trans-butenedial as yellow crystals. The
bis dimethylacetal of trans-butenedial was synthesised by reacting furan with
bromine in methanol as described by Gree et al. [12]. Phenol ( 99 99%), ben-
zene ( 99 9%), tetramethylethylene ( 99%) and acrolein ( 90%) (Aldrich)
were used as purchased. Formic acid (98%) (Fluka) was dried (CuSO4) just
before use.
2.2 Relative rate coefficient
The rate coefficient for the reaction of O( 3P) atoms with benzene oxide oxepin
(BO) was determined by means of the relative rate technique choosing tetra-
methylethylene (TME) as the reference substance.
From the signals (FT-IR analysis) obtained from the initial concentrations, in-
dex “0”, and the concentration with conversion of the organics in the presence
of O( 3P) atoms after a certain reaction time, index “t”, Eq. (I) follows.
k2
k3
ln [BO]0 [BO]t
=
(I)
ln [TME]0 [TME]t
From the ratio k2 k3, the desired rate coefficient k2 is obtained using the litera-
ture value for k3 [13].
2.3 Formation yield of benzene oxide oxepin
In the course of these experiments, O( 3P) atoms were found to be very reactive
towards benzene oxide oxepin (BO). The rate coefficient k2 is approximately
four orders of magnitude higher as k1. Here pathway (1) stands for the overall
reaction of O( 3P) atoms with benzene, k1 = k1a +k1b +k1c. Considering path-
ways (1) and (2) and defining Yphenol = k1c k1 and YBO = k1b k1, the resulting
rate laws for phenol and BO are as follows:
ꢀ
ꢁ
d phenol
3
= k1Yphenol[O P ][benzene]
(II)
dt
d [BO]
3
3
= k1YBO[O P ][benzene]−k2[O P ][BO]
(III)
dt
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Reaction of O( 3P) Atoms with Benzene
395
Dividing Eq. (III) by Eq. (II), and after integration of the resulting differential
equation an expression for YBO follows assuming a negligible consumption of
benzene (conversion of benzene was around 1% or less).
ꢂ
ꢂ
ꢃꢃ
1
k1 [benzene]0
k2 [BO]t
k2
[phenol]t
=
1−exp −
(IV)
YBO
k1Yphenol [benzene]0
Here again, the index “0” represents the initial conditions and the index “t”
stands for a certain reaction time. For a convenient application in practice, the
value of the exponential term becomes practically negligible for conditions of
k2
[phenol]t
5
10
(V)
k1Yphenol [benzene]0
and Eq. (IV) can be simplified to:
k2 [BO]t
YBO
=
(VI)
k1 [benzene]0
Taking into account the rate coefficients k1 and k2 (see later), Eq. (VI) is valid
for the determination of the formation yield of BO for a benzene conversion of
0 08 0 16%, cf. expression (V).
3. Results and discussion
3.1 Kinetics of O(3 P) + benzene oxide oxepin
The rate coefficient for the reaction of O( 3P) atoms with benzene oxide oxepin
(BO) was measured at 295 2 K and a pressure of 100 mbar (20 vol% He and
80 vol% N2 by means of the relative rate technique. The initial concentra-
tions were (1.1–3.0) × 1013 molecule cm−3 for benzene oxide oxepin BO and
(1.8–5.9) × 1013 molecule cm−3 for the reference substance tetramethylethy-
lene (TME). The experimental findings are plotted in Fig. 1 according to
Eq. (I). The slope is k2 k3 = 1 57 0 11 and the intercept 0 012 0 053. Error
limits given represent 2 values. Using k3 = 6 9×10−11 cm3 molecule−1 s−1
from an Arrhenius expression of a literature review [13],
k2 = 1 1 0 1 ×10−10 cm3 molecule−1 s−1 (295 2 K)
follows. For comparison, rate coefficients for the reaction of O( 3P) atoms
with the structurally related compounds 1,3-cyclohexadiene and 1,3,5-cyclo-
heptatriene at 295 K are reported to be 9 0×10−11 cm3 molecule−1 s−1 [13] and
4 4×10−11 cm3 molecule−1 s−1 [14], respectively.
It is to be noted, that it is impossible to decide whether O( 3P) atoms react
predominantly with benzene oxide or with oxepin. A fast equilibrium is estab-
lished between both valence isomers [15].
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396
T. Berndt and O. Böge
Fig. 1. Experimental data for the determination of the rate coefficient of the reaction of
O( 3P) atoms with benzene oxide oxepin (BO) using tetramethylethylene (TME) as the
reference substance, T = 295 2 K, p = 100 mbar. Data are plotted according to Eq. (I).
Using kinetic measurements performed at low temperature in a solution of
CF3Br pentane, the extrapolation yields k4 = 4 6×107 s−1 and k = 5 9×
−4
106 s−1 for a temperature of 295 K [15]. For initial O( 3P) atom concen-
trations in these experiments of approximately (3–5) × 1013 molecule cm−3,
k2[O( 3P)] 6×103 s−1 can be calculated. Therefore, the establishment of the
equilibrium (4 -4) is very fast compared to the O( 3P) atom reaction via path-
way (2).
3.2 Products from O(3 P) + benzene
Cryo-trapping
To get an overview of the product distribution, experiments have been per-
formed with cryo-trapping using a pressure in the flow tube of 100 mbar.
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Reaction of O( 3P) Atoms with Benzene
397
Fig. 2. GC-MS analysis from cryo-trapping experiments of the products from the reaction
of O( 3P) atoms with benzene; upper part with O( 3P) atom reaction and lower part without
O( 3P) atom reaction.
In order to prevent consecutive reactions of O( 3P) atoms with the pri-
mary stable products, benzene was chosen in a large excess, [benzene] =
3 6×1017 molecule cm−3. The amount of reacted benzene was estimated to be
(3–4) × 1013 molecule cm−3. As a result of GC-MS analysis a series of product
peaks were observed, cf. upper part of Fig. 2. For comparison, the lower part of
Fig. 2 shows the result of a run performed under identical conditions but with-
out O( 3P) atom formation. Beside the toluene impurity, benzene oxide oxepin
and phenol were identified unambiguously as reaction products with the help
of the reference substance in each case. For the peak with the retention time
of about 2.1 min, there is no definite identification. In the corresponding mass
spectrum the parent [M]+ ion was attributed to m z = 82 u. In experiments
where the commonly used 16O2 for the microwave discharge was substituted
by 18O2 producing 18O atoms, the [M]+ ion in the mass spectrum of this sub-
stance was shifted to m z = 84 u. That is a clear indication that this substance
contains one O atom. Taking into account that this unknown substance consists
of C, H and O atoms only, C5H6O can be given as a probable composition. El-
igible species are e.g., the isomers of cyclo-pentenone, pentadienal and pyran
or other. No further effort was made to identify this species. In the runs using
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398
T. Berndt and O. Böge
18O atoms, the signal of the parent [M]+ ion of benzene oxide oxepin as well as
that of phenol at m z = 96 u exceeded clearly the signal intensity at m z = 94 u
confirming the isotope purity of the 18O2 gas and the approach of 18O-labeling
by itself.
On-line product analysis
With a large excess of benzene, 3 6×1017 molecule cm−3, as used in the cryo-
trapping experiments, FT-IR measurements were impossible due to a the strong
light absorption by benzene. On-line GC-MS analysis yielded qualitatively the
same results as for the runs with cryo-trapping. In contrast to the finding of
those experiments, the signal intensity of benzene oxide oxepin compared to
that of phenol and the unknown C5H6O compound was much higher. That
points at a loss of benzene oxide oxepin during the sampling or the sample
handling in the course of the cryo-trapping experiments.
The majority of the experiments has been performed with a benzene con-
centration around 5×1015 molecule cm−3 allowing a determination of the ben-
zene conversion and the products as well by means of FT-IR spectroscopy.
Fig. 3 shows a typical FT-IR spectrum; p = 100 mbar, [benzene] = 4 18 ×
1015 molecule cm−3, conversion of benzene = 1.05%. The reacted benzene ap-
pears as negative absorption and the products as positive absorption, cf. the
lower part of Fig. 3. After spectral subtraction of benzene and phenol, the re-
maining absorption bands were attributed to CO, CO2, carbonylic substances
(band with maximum at 1716 cm−1), formic acid (1119 and 1091 cm−1) and
likely C–H vibrations of aldehydes (band centred at 2819 cm−1, cf. upper
part of Fig. 3). As a result of simultaneous GC-MS runs, the occurrence of
acrolein and trans-butenedial was clearly proved beside the peaks of ben-
zene oxide oxepin, phenol and a small signal of the unknown C5H6O com-
pound. Because of the absence of acrolein and trans-butenedial in experiments
with large excess of benzene, it was concluded that these compounds were
formed in consecutive reactions of O( 3P) atoms with products such as ben-
zene oxide oxepin. There was no experimental confirmation for the occurrence
of formic acid from the GC-MS analysis. It is to be noted, that the observed
formation of CO and CO2 did not arise from the gas-phase reaction of O( 3P)
atoms with benzene, at least not mainly. Nearly the same concentrations of CO
and CO2 were also observed in the absence of benzene in the carrier gas most
likely formed from the microwave discharge.
3.3 Product yields (benzene oxide oxepin, phenol)
Yields of benzene oxide oxepin and phenol were determined using GC-MS
analysis for the detection of benzene oxide oxepin and FT-IR spectroscopy
to measure phenol and the amount of benzene reacted. The majority of
these experiments has been performed with a benzene concentration in the
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Reaction of O( 3P) Atoms with Benzene
399
Fig. 3. Lower part: Typical FT-IR spectrum from the reaction of O( 3P) atoms with ben-
zene. Upper part: Residual spectrum after subtraction of bands from phenol and benzene.
range of (3.6–5.7) × 1015 molecule cm−3 and with a conversion of benzene
of around 1% allowing the application of Eq. (VI) for the calculation of the
formation yield of benzene oxide oxepin. The rate coefficient k1 = 1 85 ×
10−14 cm3 molecule−1 s−1 was taken from literature [13] and k2 from this study,
cf. Sect. 3.1. Formation yields were determined at 50, 80 and 100 mbar for
a constant O2 concentration as well as O2-dependent at a fixed pressure of
80 mbar. For demonstration, Fig. 4 shows the experimental findings from the
O2 dependent measurements. Furthermore, benzene was used in large excess
of (3.5–3.6) × 1017 molecule cm−3 in a set of runs with GC-MS analysis of the
products. Assuming a phenol yield of 0.12, in this case Eq. (IV) was applied for
the calculation of the formation yield of benzene oxide oxepin. The yields are
summarised in Table 1 together with the experimental conditions used. Error
limits represent 2 values. The results were found to be independent of experi-
mental conditions with averaged formation yields of 0 12 0 02 for phenol and
0 26 0 06 for benzene oxide oxepin. The phenol yield from this study is in
good agreement with data published in the literature; ≤ 0 13 [3], 0.13–0.14 [4]
and 0.10 [7].
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400
T. Berndt and O. Böge
Fig. 4. O2-dependent measurements of the formation yields of benzene oxide oxepin and
phenol at a pressure of 80 mbar.
Table 1. Formation yields of phenol Yphenol and benzene oxide oxepin YBO
.
p
mbar
O2
benzene
reacted benzene
1013 molec. cm−3
Yphenol
YBO
1015 molec. cm−3
1015 molec. cm−3
50
80
100
80
2.4
2.3
2.4
3.5
4.6–4.7
4.2
4.5
350–360
4.0–4.4
5.0–5.7
4.4–4.8
3.6–5.7
–
0 11 0 02 0 27 0 01
0 12 0 02 0 24 0 03
0 12 0 01 0 26 0 05
0 12 0 02 0 26 0 04
0.77–8.4
1.8
100
–
0 28 0 04
average:
0 12 0 02 0 26 0 06
3.4 Products from O(3 P) + benzene oxide oxepin
In order to find out whether acrolein and trans-butenedial represent consecu-
tive products of benzene oxide oxepin or not, cf. Sect. 2.2, the products from
the reaction of O( 3P) atoms with benzene oxide oxepin were investigated
in a few runs. In Fig. 5 the result of an on-line GC-MS analysis is given.
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Reaction of O( 3P) Atoms with Benzene
401
Fig. 5. On-line GC-MS analysis of the products from the reaction of O( 3P) atoms with
benzene oxide oxepin. “n.i.” stands for “not identified”.
Using reference substances, acrolein and trans-butenedial were clearly iden-
tified. The peak with a retention time of 7 15 min showed a parent [M]+ ion
at m z = 110 u corresponding to the composition C6H6O2. The fragmentation
pattern with the base signal at [M-28]+ and noteworthy signals at [M-2]+ and
[M-30]+ was equal to that from 1,3-cyclohexadiene 1,2-epoxide indicating that
the substance C6H6O2 contained probably similar structural elements such as
epoxy groups [16]. From the oxidation of benzene oxide oxepin by means
of dimethyldioxirane in solution, the formation of oxepin 4,5-epoxide was
found [17]. For the possible other isomer, oxepin 2,3-epoxide, a fast rearrange-
ment was recommended leading to cis,cis-muconaldehyde [17]. By analogy,
it can be speculated that in the gas-phase reaction of O( 3P) atoms with ben-
zene oxide oxepin the oxepin 4,5-epoxide and or the oxepin 2,3-epoxide is
also formed to be in line with the MS fragment pattern. The absence of the
corresponding reference substances prevented an unambiguous identification
of the substance occurring in the chromatogram at 7 15 min. Furthermore,
from the GC-MS analysis there was experimental evidence for the isomers
of muconaldehyde. The two peaks at 7.9 and 8 0 min were attributed to the
cis,cis- cis,trans-species and the trans,trans-species, respectively, using the
GC-MS data of the respective reference substances of the muconaldehydes
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402
T. Berndt and O. Böge
from a former study [18] The phenol detected by GC-MS, cf. Fig. 5, arose
from wall reactions of benzene oxide oxepin in the transfer line to the GC and
in the GC loop. Phenol was also detectable in the absence of O( 3P) atoms by
means of GC-MS analysis whereas phenol was below the detection limit in
simultaneously performed FT-IR runs.
As a result of FT-IR measurements, beside CO and CO2 formed from the
microwave discharge, the absorption bands measured were nearly identical
to those found from the reaction of O( 3P) atoms with benzene after subtrac-
tion of phenol, cf. upper part of Fig. 3. The absorption bands can be attributed
to formic acid, acrolein, trans-butenedial and, in addition, muconaldehydes.
There were no further, noticeable absorption bands indicating the occurrence
of other carbonylic substances.
It is to be noted, that trans-butenedial is a yellow, crystalline solid with
a melting point of 313–317 K, but sometimes it appears as an oil at room tem-
perature [19, 20]. Boocock and Cvetanovic´ [4] as well as Bonanno et al. [7]
reported the formation of yellow-coloured material deposited at the reactor
walls. In the latter work the result of the elemental analysis of the wall coatings
is given, C : H : O = 60 : 5 : 35 (in weight percentages) [7]. In theory, elemental
analysis of trans-butenedial yields C : H : O = 57.1 : 4.8 : 38.1 roughly in line
with the analysis mentioned by Bonanno et al. [7]. That indicates that the
yellow coatings reported in former studies [4, 7] consisted probably of trans-
butenedial, at least partly.
4. Summary
The gas-phase reaction of O( 3P) atoms with benzene was investigated in a flow
system in the pressure range of 50–100 mbar and a temperature of 295 2 K.
O2 concentrations were in the range of (7.7–84) × 1014 molecule cm−3. The pri-
mary stable products of the title reaction were phenol, benzene oxide oxepin
and a not identified compound with the probable composition C5H6O. The for-
mation of phenol and benzene oxide oxepin was found to be independent of
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Reaction of O( 3P) Atoms with Benzene
403
the experimental conditions used with yields of 0 12 0 02 and 0 26 0 06,
respectively. The formation yield of phenol from this study is in good agree-
ment with literature data. The formation of benzene oxide oxepin is reported
for the first time. A rapid consecutive reaction of O( 3P) atoms with benzene
oxide oxepin was observed, k 295 K = 1 1 0 1 ×10−10 cm3 molecule−1 s−1.
A substance with the formula C6H6O2 (likely oxepin 4,5-epoxide or oxepin
2,3-epoxide), the isomers of muconaldehyde, as well as formic acid, acrolein
and trans-butenedial were detected as products of the reaction of O( 3P) atoms
with benzene oxide oxepin. The occurrence of yellow-coloured coatings from
the reactor wall, as observed in former studies, can be explained with the help
of trans-butenedial.
Acknowledgement
The authors thank Herwig Macholeth for technical assistance and Natalie Heim
for the translation of Ref. [2].
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