Formation mechanism of peroxides in reactions of cyclic olefins with ozone in air

Article abstract of DOI:10.1246/cl.2001.1248

We carried out reactions of methyl-substituted cyclohexenes and α-pinene with ozone in air and elucidated the mechanisms of formation of the minor products (peroxides and formic acid). Peroxyacetic acid was formed only from the cyclohexenes with a methyl group on the double bond, whereas formic acid was produced in higher yields from the cyclohexenes without a methyl group on the double bond. These differences in product yields allowed us to elucidate the mechanism of formation of the products.

Full text of DOI:10.1246/cl.2001.1248

1248
Chemistry Letters 2001
Formation Mechanism of Peroxides in Reactions of Cyclic Olefins with Ozone in Air
Shiro Hatakeyama,* Subramanian Sivanesan,† and Taichiro Urabe
National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506
†Departmet of Chemical Engineering, A.C. College of Technology, Anna University, Chennai 600 025, India
(Received September 14, 2001; CL-010910)
We carried out reactions of methyl-substituted cyclohex-
attained by monitoring the decomposition of BHMP
(bis(hydroxymethyl) peroxide, HOCH2OOCH2OH). BHMP
was prepared by Marklund’s method.11 It decomposed to
HMHP and H2O2 gradually as reported by Marklund11 in dilute
phosphoric acid at pH 3.5.
enes and α-pinene with ozone in air and elucidated the mecha-
nisms of formation of the minor products (peroxides and formic
acid). Peroxyacetic acid was formed only from the cyclohex-
enes with a methyl group on the double bond, whereas formic
acid was produced in higher yields from the cyclohexenes with-
out a methyl group on the double bond. These differences in
product yields allowed us to elucidate the mechanism of forma-
tion of the products.
It is currently believed that anthropogenic and/or secondary
atmospheric pollutants are closely related to forest decline.1
Organic hydroperoxides are among the most important of these
pollutants. Isoprene and various monoterpenes are emitted into
the atmosphere by forest trees,2,3 and these natural olefins rap-
idly react with ozone,4 forming organic hydroperoxides as
products.5
Previously, we studied reactions of ozone with C5–C7
cycloolefins and found that many kinds of Cn and Cn–1 particu-
late products are formed in addition to gaseous products.6
However, in that study, we ignored the minor products formed
during the reactions. Nevertheless, these minor products are
worth studying, since they are important from the environmen-
tal viewpoint.
Here, we have studied the reactions of ozone with various
cyclic olefins having a methyl group on the ring and measured
the yields of the minor products, i.e., gaseous peroxides (as for
general mechanisms and major products of ozone–olefin reac-
tions. See references7,8). The position of the methyl group dra-
matically influenced the yields of the products, which were
used to elucidate the reaction mechanisms.
The studied alkenes—α-pinene, 1-methylcyclohexene, 3-
methylcyclohexene, and 4-methylcyclohexene (Wako)—were
degassed by repeated freeze–thaw cycles before use.
The chromatogram in Figure 1 shows the peroxide prod-
ucts formed during the reaction of ozone with 1-methylcyclo-
hexene. The yields of the products are listed in Table 1. In
Table 1, the yields of formic acid, MHP, and PAA for the upper
set of reactants (1-methylcyclohexene and α-pinene) are in
clear contrast with those for the lower set of reactants (3-
methylcyclohexene and 4-methylcyclohexene).
Scheme 1 shows the initial Criegee cleavage at the double
bond of 1-methylcyclohexene as well as 3-methylcyclohexene
A 6-m3 photochemical reaction chamber9 was employed to
conduct experiments in the ppmv range. After the chamber was
filled with purified air to a pressure of 105 kPa, ozone was
introduced into the chamber (1–2 ppmv). The concentration of
ozone was monitored with a chemiluminescence ozone analyz-
er. Then, one of the reactant alkenes was measured volumetri-
cally and introduced into the chamber (2–5 ppmv) with a
stream of pure nitrogen. The concentrations of alkene and
formic acid product were measured by FTIR spectroscopy.
The concentrations of hydrogen peroxide, methyl
hydroperoxide (MHP), hydroxymethyl hydroperoxide
(HOCH2OOH, HMHP), and peroxyacetic acid (PAA) were
_
measured with an HPLC fluorescence detector system after
sampling with a mist chamber as reported previously.5 For cal-
ibration, MHP was prepared according to the method described
by Vaghjiani and Ravishankara.10 Identification of HMHP was
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1249
and subsequent formation of peroxides and formic acid from
the substituted Criegee intermediates (RR´COO-type biradical).
On the basis of the difference in the structures of the intermedi-
ates, we can assume that the fully substituted Criegee interme-
diate [A] can form PAA. The Criegee intermediate with an H
atom can form formic acid. Using the reaction of ozone with 2-
methyl-2-butene as a model (in which the ratio of the yield of
(CH3)2COO to the yield of CH3CHOO is 7:3 12), we can easily
rationalize the low yield of formic acid in the reaction of ozone
with 1-methylcyclohexene.
The yields of PAA are very interesting. It is clear from
Table 1 that a methyl group at the 3- or 4-position of cyclohex-
ene does not promote PAA formation. This suggests that only
the Criegee intermediate that has a methyl group at the radical
carbon can form PAA. As pointed out by Niki et al.13 and
Martinez and Herron,14 a doubly substituted Criegee intermedi-
ate can isomerize to reactive acetyl esters, and subsequent reac-
tions can take place as follows:
cyclohexenes gave high yields of formic acid, we can assume
that only a hydrogen-substituted Criegee intermediate ([B] or
[C] in Scheme 1) should be able to produce formic acid. Thus,
after transformation of [B] or [C] to a methylenedioxy-type
biradical [D] or [E], respectively, formic acid can be formed via
one-electron transfers as shown in Scheme 2.
This research was supported by the Global Research Fund
of the Ministry of Environment, Japan (Studies on the Impacts
of Controlling Techniques for the Emission of Acid-Precursors
on the Formation Processes of Acidic and/or Oxidative
Substances; C-3 (1997–1999)).
References and Notes
1
S. Fox and R. A. Mickler, Eds., “Impact of Air Pollutants
on Southern Pine Forests,” Springer, Berlin, 1995, p 513.
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2
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7
8
A possible reaction mechanism for the production of
formic acid is illustrated in Scheme 2. Since 3- and 4- methyl-
9
H. Akimoto, M. Hoshino, G. Inoue, F. Sakamaki, N.
Washida, and M. Okuda, Environ. Sci. Technol., 13, 471
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11 S. Marklund, Acta Chem. Scand., 25, 3517 (1971).
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M. D. Hurley, J. Phys. Chem., 91, 941 (1987).
14 R. I. Martinez and J. T. Herron, J. Phys. Chem., 91, 946
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