Formation of 2-Hydroxyethyl Hydroperoxide in-an OH-lnaiated Reaction of Ethylene in Air in the Absence of NO SHIRO H A T A K E Y A M A , * HAIPING LAI,+ AND KENTARO MURANO Global Environment Division, National Institute for Environmental Studies, Tsukuba, Ibaraki 305, Japan
Introduction The reactions of hydroxyl radicals with hydrocarbons play a major role in the chemistry of the troposphere. The formation of alkylperoxyl radicals is assumed to be an important step after the initial attack of OH and the subsequent addition of an oxygen molecule. In the presence of sufficient NO, as is typical for polluted air, alkylperoxyl radicals are reduced by NO to alkoxy1 radicals. In the absence of NO, however,the next reaction step of alkylperoxyl radicals is the reaction with HO2. Formation of hydroperoxideaccording to following reaction was pointed out as the sole reaction path (1, 2).
ROO
+ H02
-
ROOH
+ 0,
(1)
In the reaction of alkenes, little information has been reported about the formation of hydroperoxidesin the NOfree reaction with OH, although the reaction kinetics of the intermediate, HOOCH2CH200 radical, with HO2 was studied recently by several groups (3-6). The formation of hydroperoxides from ozone-alkene reactions, on the other hand, is a topic that has recently received much attention (7-11). Hydroperoxides are important as a potential cause of damage to plants (12).In previous studies which dealt with ozone-ethylene reactions, the formation of methyl hydroperoxide had been reported. It is very difficult to expect the formation of methyl hydroperoxide from this reaction because (i) there has been no report of the formation of methyl radicals in ozone-ethylene reactions under atmospheric conditions and (ii)formation of methyl hydroperoxiderequires methyl radicals as we reported recently (10). Here we report the first observation of the formation of 2-hydroxyethyl hydroperoxide (HOCH2CH200H)as a product of OH-ethylene reactions in air in the absence of NO.
Experimental Section
A 4-m3photochemical reaction chamber (details reported elsewhere (7)) was employed to conduct experiments with * To whom correspondence should be addressed. Present address: Green Blue Inc., 6-7-9, Minamiooi, Shinagawaku, Tokyo 140, Japan. +
0013-936X/95/0929-0833$09.00/0
@ 1995 American Chemical Society
concentrations in the parts per million by volume (ppmv) range. Ozone reactions in air were made with initial ethylene and ozone concentrations of 5.5-10.0 and 0.51.3 ppm, respectively. After ozone was almost consumed, the products were collected in water with a mist chamber (8). OH reactions in air in the absence of NO were made employing H202 as the source of OH radicals. The initial concentration of ethylene was 7-12 ppm. Introduction of H202 into the chamber was done in a manner similar to that reported in our previous paper (1.5). The initial concentration of gaseous H202 within the chamber was -30 ppm. Introduction of H202was continued throughout the experimentto maintain the concentration of OH radical. Xe arc lamps with quartz windows were used to photolyze the H202. Concentrations of ozone and ethylene were monitored with a chemiluminescent ozone analyzer (Monitor Labs Model 8410E) and an FID gas chromatograh (ShimadzuGC-GA), respectively. Reactionsproducts were collected intermittently with a mist chamber. Analyses of the peroxidic products were made with a high-performance liquid chromatograph equipped with a fluorescence detector (formation of fluroescent dimer of p-hydroxyphenylacetic acid in the presence of peroxides was used) (10). Calibrations of peroxides other than methyl hydroperoxide were carried out with standard solutions of H202. Methyl hydroperoxide standard was prepared according to the method of Vaghjiani and Ravishankara (16).
Results and Discussion Ozone-Ethylene Reactions. The reaction of ozone with ethylene gave three distinct peroxidic products. The liquid chromatograph peaks 1and2 showninFigure 1correspond to H202 and hydroxymethyl hydroperoxide (HMHP,HOCHZOOH), respectively. The molar yields of H202 and HMHP indryairwere 1.1%and2.8%,respectively. Peak3 appeared very soon after that of methyl hydroperoxide. The yield of this compound was estimated to be -2% on assumption that this hydroperoxide has the same efficiency as H202 to form the dimer of p-hydroxyphenylaceticacid. This peak was assigned to methyl hydroperoxide in previous studies (7-9, 11). However, the retention time of peak 3 (9.4f 0.06 min) was slightly shorter than that of methyl hydroperoxide (9.6 st 0.06 min). Reactions of ozone with each of the alkenes that have a methyl group attached to the double bond gave a product peak at 9.6 min. For example, propene, 2-butene, isoprene, 1-methyl cyclohexene, and a-pinene gave peaks identical to that of the methyl hydroperoxide standard. Thus, we conclude that peak3 in the chromatogram shown in Figure 1 is not methyl hydroperoxide. The results of HPLC analysis of alkyl hydroperoxides reported by Kurth (I 7) are useful for the identification of the compound that gives rise to peak 3. They found that the alkyl hydroperoxides (C,) have retention times similar to thoseof 1-hydroxyalkylhydroperoxides (C, + 1). As stated in the Introduction, ethylene does not have a methyl group and hence, assuming that hydroxyethyl hydroperoxides
VOL. 29, NO. 3, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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0
6' 0
0
0
0
8
0
*t I
"0
0
0
50
0
0
100
150 200
1
250
Time/mi n L
1
1
1
4
I
0 3 6 9 1 2 Retention Time (Min) FIGURE 1. Chromatogram of the products of the ozone-ethylene reaction: (1) H202, (2) hydroxymethyl hydroperoxide (HMHP), (3) 2-hydroxyethyl hydroperoxide (2-HEHP).
FIGURE 3. Molar yield of 2-HEHP plotted against reaction time. Yields were not corrected for the possible decay of 2-HEHP by photolysis and/or OH reactions.
visible even in the initial stage of the reaction. After the accumulation of ozone (formed by the irradiation of oxygen with Xe arc lamps with quartz windows), HMHP was formed (Figure2b). The yield of this compound was nearly constant during the reaction (Figure3). Thus, we conclude that this is a direct product of the OH-ethylene reaction. Formation Mechanism of 2-HEHP. On account of the above two observations, we propose that the compound which gave rise to the liquid chromatogram peak at a retention time of 9.4 min was 2-HEHP. If this proposition is correct, then the formation mechanism is quite simple:
+ OH - HOCH,-CH, HOCH,-CH, + 0, -.. HOCH,-CH,OO HOCH,-CH,OO + HO, 2-HEHP + 0, CH,=CH,
--
0 3 6 9 1 2 0 3 6 9 1 2 Retention Time (Miii)
Retelltion Time (Min)
FIGUREZ. (a) Chromatogramof the products of OH-ethylene reaction after 5 min of photoirradiation. (b) Chromatogram of the products of OH-ethylene reaction after 100 min of photoirradiation.
have chromatographic peaks close to that for methyl hydroperoxide, it is possible that peak 3 is due to 2-hydroxyethyl hydroperoxide (2-HEHP). Formation of 2-HEHP can be easily explained by OH reactions with ethylene, if we take into account the generation of OH in ozone-alkene reactions (I 6-22). In order to check the possibility of OH reactions, OH-ethylene reactions were examined. OH-Ethylene Reactions. OH reactions of ethylene in air in the absence of NO produced a compound that showed an HPLC peak at a retention time of 9.4 min. Figure 2 shows chromatograms of the products obtained with 5- (a) and 100-min photoirradiation (b). The 9.4-min peak was 834 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 3, 1995
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(2)
(3) (4)
HOz radicals are very abundant in this reaction system because of OH-H2O2 reactions. This is the first example to show the formation of hydroperoxides in OH-alkene reactions. At present, the evidence is rather indirect because of the difficultyofthe synthesis of 2-HEHP. More direct evidence is needed to confirm the formation of 2-HEHP in this reaction system.
Acknowledgments The authors are grateful to Hiroyulu Hiramatsu (Forum Engineering, Inc.) for his assistance in conducting chamber experiments. This study was supported by the Global Environment Research Program Budget of the Japan Environment Agency.
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(5) Murrells, T. P.; Jenkin, M. E.; Shalliker, S. J.; Hayman, G. D. J. Chem. SOC.Faraday Trans. 1991, 87, 2351-2360. (6) Atkinson, R.; Baulch, D. L.; Cox, R. A,; Hampson, R. F., Jr,; Kerr, J. A.; Troe, J. 1. Phys. Chem. Ref: Datu 1992,21, 1125-1568. (7) Hellpointner, E.; Gab, S. Nature (London) 1989, 337, 631-634. (8) Hewitt, C. N.; Kok, G. L.; Fall, R. Nature (London) 1990, 344, 56-58. (9) Hewitt, C. N.; Kok, G. L. J. Atmos. Chem. 1991, 12, 181-194. (10) Hatakeyama, S.; Lai, H.; Gao, S.; Murano, K. Chem. Lett. 1993, 1287-1290. (11) Horie, 0.:Neeb. P.: Limbach, S.: Moortaat, ., G. K. Geoahvs. .~ Res. Lett. 1994, 21, 1523-1526. (12) Hewitt, N.; Terrv, G. Environ. Sci. Technol. 1992,26, 1890-1891. (13) Izumi, K.; Mizubchi, M.; Yoshioka, M.; Murano, K.; Fukuyama, T. Enuiron. Sci. Technol. 1984, 18, 116-118. (14) Hatakeyama, S.; Lai, H.; Gao, S.; Murano, K. Nippon Kagaku Kaishi 1993, 998-1000. (15) Hatakeyama, S.; Izumi, K.; Fukuyama, T.; Akimoto,H.;Washida, N. 1. Geophys. Res. 1991, 96, 947-958.
(16) Vaghjiani, G. L.; Ravishankara, A. R. 1.Phys. Chem. 1989, 93, 1948- 1959. (17) Kurth, H. H.; Gab, S.; Turner, W. V.; Kettrup, A. Anal. Chem. 1991, 63, 2586-2589. (18) Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L. P.; Hurley, M. D. 1. Phys. Chem. 1987, 91, 941-946. (19) Atkinson, R.; Aschmann, S. M.; h e y , J.; Shorees, B. J , Geophys. Res. 1992, 97, 6065-6073. (20) Paulson. S. E.; Flagan, R. C.: Seinfeld, J. H. Int. I. Chem. Kinet. 1992, 24, 103-12< (21) Paulson, S. E.; Seinfeld, J. H. Enuiron. Sci. Technol. 1992, 26, 1165-1 173. (22) Atkinson, R.; Aschmann, S. M. Environ. Sci. Technol. 1993, 27, 1357-1363. '
Received f o r review October 3, 1994. Accepted December 8, 1994.
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