Environ. Sci. Technol. 1989, 23, 177-181
(6) Stahl, R. G.; Lier, J. G.; Davis, E. M. Arch. Environ. Contam. Toxicol. 1984, 13, 179. (7) Wachter, R. A.; Blackwood, T. R. U.S. Environmental Protection Agency, Report No. EPA-600/2-78-004m;1978. (8) Stadnechenko, T. Econ. Geol. 1934,29, 511. (9) U.S. Environmental Protection Agency, Cincinnati, OH; Report No. EPA-600/4-79-020;1979. (10) Menzel, D.; Vaccaro, R. Limnol. Oceanogr. 1964, 9, 138. (11) Goldberg, M. C.; DeLong, L.; Sinclair, M. Anal. Chem. 1973, 45, 89. (12) Maxwell, J. R.; Pillinger, C. T.; Eglington, G. Q. Rev. Chem. SOC.1971, 25, 571. (13) Radway, J. C.; Tuttle, J. H.; Fendinger, N. J.; Means, J. C. Appl. Environ. Microbiol. 1987, 53, 1056. (14) Helz, G.; Dai, J. H.; Kijak, P. J.; Fendinger, N. J.; Radway, J. C. Appl. Geochem. 1987,2,427. (15) Stahl, R. G.; Davis, E. M. J. Test. Eual. 1984, May, 163.
(16) Anderson, W. C.; Youngstrom, M. P. J. Environ. Eng. Diu. (Am. SOC.Civ. Eng.) 1976, 102, 1239. (17) Swift, M. C. Water Resources Research Center, University of Maryland, College Park, MD.; Report No. A-062-MD. (18) Swann, P. D.; Evans, D. G. Fuel 1979,58, 276. (19) Barrick, R. C.; Furlong, E. T.; Carpenter, R. Environ. Sci. Technol. 1984, 18, 846. (20)
Fendinger, N. J. PbD. Dissertation, University of Maryland, Dept. of Chemistry, College Park, MD, 1987.
Received for review November 19, 1987. Revised manuscript received July 6, 1988. Accepted July 10,1988. This work was supported by Grant P97-84-04 from Maryland's Department of Natural Resources,Power Plant Siting Program. Contribution No. 1963 of the University of Maryland Center for Environmental and Estaurine Studies.
Rate Constant Measurements for the Reaction of the Hydroxyl Radical with Cyclohexene, Cyclopentene, and Glutaraldehyde Jerry D. Rogers Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090-9055 ~~~
~
Fourier transform infrared spectroscopy was used to measure relative rate constants at 298 f 3 K for the reactions of hydroxyl radicals with cyclohexene, cyclopentene, and glutaraldehyde by photolyzing HONO in air containing ppm levels of one of these species and trans2-butene or propene as reference compounds. The rate constants (X10" cm3 molecule-' s-') measured were as follows: 5.40 f 1.10 for cyclohexene, 4.99 f 1.07 for cyclopentene, and 2.23 f 0.46 for glutaraldehyde, using an absolute rate constant of (6.37 f 1.27) X cm3 molecule-'~-' for the reaction of OH with trans-2-butene; and 6.1 f 1.0 for cyclohexene, 5.7 f 1.0 for cyclopentene, and 2.53 f 0.39 for glutaraldehyde, usin an absolute rate cm molecule-l s-' for constant of (2.63 f 0.39) X propene. The analysis of rate data for mixtures of cyclohexene and cyclopentene showed that cyclopentene reacted slightly slower with OH than did cyclohexene; the measured ratio was 0.940 f 0.024.
f
Introduction Federal standards for the total suspended particulate (TSP) loading in the atmosphere are 260 pg m-3 averaged over 24 h and 75 pg mP3averaged annually (1). The annual TSP standard is difficult to meet in many urban areas (2). In the Los Angeles basin, for example, the maximum daytime TSP concentrations of 150 pg m-3 (3) are below the 24-h standard, but the annual average is 100 pg m-3 (4). Organic matter contributes significantly to this TSP loading and can be up to one-third or more of the particulate concentration in Los Angeles (3). The organic aerosol loading, however, is less in other urban areas such as Detroit, for which one study found that organic carbon accounted for 14% of the TSP (5). Much of the organic fraction of suspended particulate matter is composed of difunctional organic species, especially dicarboxylic acids such as succinic acid, glutaric acid, and adipic acid. These difunctional organic aerosol components have been shown to be products of the photochemical degradation of cyclic alkenes by ozone and by hydroxyl radicals ( 6 ) . Atmospheric reactions of cyclopentene, for example, first yield glutaraldehyde, which can undergo further oxidation to form glutaric acid and other-
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0013-936X/89/0923-0177$01.50/0
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oxygenated species (7). Hatakeyama et al. (8)have shown that about 1 4 %of cyclopentene and about 3-13% of cyclohexene are converted into aerosol particles. Thus, the ambient concentrations of 10 ppb measured for cyclopentene (9,lO) and for cyclohexene (9) in Los Angeles could yield up to 3 pg m-3 of aerosol from cyclopentene and up to 9 pg m-3 of aerosol for cyclohexene. The 24-h-averaged concentrations of succinic, glutaric, and adipic acids each range from 0.2 to 0.5 pg m-3 in Los Angeles (11),although higher daytime values of 1.2 pg m-3 for glutaric acid and 1.6 pg m-3 for adipic acid have also been reported (12). Glutaric acid has been detected in rural areas of the Ohio River valley at concentrations of 0.002-0.05 pg m-3 (13). Altogether, organic acids account for 10-20% of the total organic aerosol fraction (3,6,14). The dialdehyde precursors to dicarboxylic acids are also a component of the organic aerosol material; in Los Angeles, for example, concentrations of 0.03-0.3 pg m-3 have been reported for the glutaraldehyde precursor of glutaric acid (14). The purpose of this work was to measure rate constants for some of the reactions that are important in the transformation of cyclic alkenes into organic aerosols. The most abundant cyclic alkenes in urban areas are cyclopentene and cyclohexene (9, I O ) , and while several measurements of the rate constant for the OH-cyclohexene reaction have been reported (15-20), only one measurement of the rate constant for the OH-cyclopentene reaction has been published (15). Because measurements of rate constants are, in general, difficult to make and may be subject to unsuspected systematic errors due to unrecognized side reactions, it is important to have an independent measurement of the rate constant for the reaction of OH with cyclopentene. Therefore, rate constants were measured here for the reaction of OH radicals with cyclopentene and with cyclohexene by the relative rate technique under simulated atmospheric conditions at 298 f 3 K. The rate constant for the OH-cyclohexene reaction was included in the study because an accurate measurement of this rate constant ensures that the experimental technique is adequate. The rate constant for the reaction of OH with glutaraldehyde was also measured because this dialdehyde is a product of OH attack on cyclopentene.
0 1989 American Chemical Society
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The results obtained for glutaraldehyde can also be used to estimate the rate constant for adipaldehyde, which is the initial dialdehyde product in the photooxidation of cyclohexene. The measurement reported here for glutaraldehyde is apparently the first reported rate constant for OH reacting with a dialdehyde, and the results are compared with the rate constants for the reaction of OH with monoaldehydes. The rate constants reported here for cyclohexene, cyclopentene, and glutaraldehyde are important input parameters to chemical models for the prediction of the contribution of cyclic alkenes to TSP levels in urban areas. Experimental Section The rate constants for the OH radical reacting with the organics (HCJ were determined by the relative rate technique (21). In a mixture of the HC1 and a reference organic compound (HC2)for which the OH rate constant is well-established, the following initial reactions take place: OH
+ HC1
OH
+ HC2
kl
-
products
k2
(1)
products (2) If the two compounds are consumed only by reaction with OH, then 1n ([HClI,/[HClI,) = W k z ln ([HCzI,/[HC2I,), (3) where kl and k2 are the rate constants for reactions 1 and 2, respectively, and [HC], and [HC], are hydrocarbon concentrations at time zero and a t time t, respectively. Plots of In ([HClIO/[HCl],) vs In ([HC2],/[HC2],) should thus yield straight lines with slopes of k l / k z . If the value of k2 is known for the reference compound, Fz, can be calculated. trans-2-Butene was chosen as the reference organic compound for the relative rate measurements with cyclopentene and cyclohexene because the rate constant for the reaction of OH with trans-Zbutene is well-established (22), and the rate constants for the cyclic alkenes are expected (15) to be close to that for trans-Bbutene. trans-2-Butene is also attractive as a reference compound because the reaction product with OH is only acetaldehyde, providing for a simple infrared spectrum. Although trans-2-butene was initially used as a reference compound for glutaraldehyde also, the rate constant for the OH-glutaraldehyde reaction proved to be closer to that for propene, so propene was employed as a reference for the dialdehyde in some experiments. The gas mixtures used in this study were composed of 10 ppm (1ppm = 2.45 X 1013molecule ~ m - each ~ ) of the organic of interest and the reference organic compound in air at 298 f 3 K and a total pressure of 700 Torr. The samples were irradiated for a total of 10-20 min. Measurements were made on four mixtures of cyclohexene and trans-2-butene of various initial concentrations. For cyclopentene, five mixtures with trans-2-butene were used, and for glutaraldehyde, six mixtures with trans-2-butene and two mixtures with propene were used. Data were also obtained during the irradiations of two mixtures of cyclohexene and cyclopentene. The literature rate constants for the reaction of OH with propene and with trans-2butene were checked by irradiating two gas mixtures of propene and trans-Zbutene. Separate experiments with each hydrocarbon in air showed that both wall losses and photolysis of the hydrocarbons were insignificant over the time scale of the experiments. The trans-2-butene (high-purity) and propene (CP-grade) samples were obtained from Scott Specialty Gases, as was the diluent hydrocarbon-free air. The glutaraldehyde (grade I) was
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obtained from Sigma. Cyclopentene and cyclohexene were obtained from Aldrich. Hydroxyl radicals were generated by the photolysis of HONO added to the gas mixtures. The HONO was prepared by the reaction of dilute sulfuric acid with sodium nitrite solution, by the method of Nash (23)and Cox (24). Ten to twenty ppm of HONO was generated by this technique, along with lesser amounts of NO, NO2, and HZO. The NO minimizes the formation of ozone, which could also react with the alkenes, and no ozone was detected in our experiments. The reactor was a 3-m base path length White cell operated a t a 96-m optical path length. The cell was constructed of stainless steel and had a volume of 600 L (25). Ultraviolet radiation was provided by 12 black lights (GE F40BL) mounted inside the cell. A HONO photolysis rate s-l was calculated from exconstant of (3.4 f 1.1)X periments using only trans-2-butene/HONO/NO, mixtures in air by assuming that free radicals were in steady state. Infrared spectra of the gas mixtures were measured on a Digilab FTS-2O/C Fourier transform infrared spectrometer interfaced to the White cell. The spectrometer was equipped with a mercury cadmium telluride (MCT) detector. Spectra were measured at l-cm-l resolution (8192 data points) with boxcar apodization. Each spectrum was the average of eight scans, giving a time resolution of -30 s. As many spectra as possible under these conditions were taken over the 10-20-min duration of the irradiations. The precision of the measurements was estimated from the concentrations determined from repeated spectral measurements just before the irradiations began. Three such repeated spectra for each initial gas mixture suggested a precision better than 1% in the concentration measurements. Concentrations of species in the gas mixtures were obtained by subtracting calibrated infrared spectra of the pure compounds from the spectra measured at various times during the irradiations. Selected absorption coefficients (in units of Torr-l m-l; base 10) are as follows: propene, 0.994 f 0.037 a t 912 cm-l (peak to valley); trans-2-butene, 0.130 f 0.007 a t 960 cm-l (peak to Q-R valley); cyclopentene, 0.591 f 0.012 at 2949 cm-' (peak to base line); cyclohexene, 0.441 f 0.022 at 720 cm-l (peak to valley); glutaraldehyde, 0.75 f 0.05 at 2715 cm-l (peak to base line). The calibration of cyclopentene reference spectra was difficult because the Beer's law plots of absorbance vs cyclopentene concentration showed significant curvature for most of the sharp Q-branch frequencies. However, the absorbance a t 2949 cm-l was linear with cyclopentene concentration. Absorption coefficients for most of these species have not been reported in the literature. For glutaraldehyde, however, an absorption coefficient of 0.584 Torr-' m-l was reported by Hatakeyama et al. (26). The absorption coefficient measured here for glutaraldehyde is almost 30% higher than their value. Although the reason for this difference is not clear, the rate constant calculations are unaffected, since the ratio of the concentrations at any two times appearing in eq 3 is equal to the absorbance ratio a t those two times. Thus, the rate measurements are independent of the magnitude of the absorption coefficients. Results Plots of In ([HCl],/[HCl],) vs In ([HCzIo/[HC~It) are shown in Figure 1 for cyclohexene vs trans-2-butene, Figure 2 for cyclopentene vs tran-2-butene, and Figure 3 for glutaraldehyde vs trans-2-butene and vs propene. The
14
8 5 -
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3 2X 5 -
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-
1.0
-
08
-
06
-
0.4
-
0.2
-
r 0
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-
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C
I
0 0
0.2
0.4
0.6
0.8
1.0
1.2
1.4 1.6
1.8
In ([trans-2-b~tene]~/[trans-2-butene]t)
Flgure 1. Plot of eq 3 for cyclohexene vs trans-Bbutene. The data represent the results from the Irradiation of four Initial gas mixtures.
r
5
1
1.4
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-
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2
-
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-
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-
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0.2 -
r
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06
0
0.8
10
1.2
1.4
In ([~yc~opentene]~/[cyciopentene]~)
Flgure 4. Plot of eq 3 for cyclohexene vs cyclopentene. The data represent the results from the irradiation of two initial gas mixtures.
Table I. Hydrocarbon Rate Constant Ratios for Reaction with OH
rate constant ratio this work" literature
-~
6 ;
K
0.2 0 4
l 2-
hydrocarbon mixture
1.0-
0
00
cyclohexene/trans-2-butene cyclopenteneltrans-2-butene cyclopentenelcyclohexene glutaraldehydeltrans-2-butene glutaraldehydelpropene propenel trans-2-butene
~
~~
0.848 f 0.036 0.784 f 0.061 0.940 f 0.024 0.99 f 0.04 (15) 0.350 f 0.017 0.96 f 0.04 0.365 f 0.019 0.412 A 0.009 (27)
The uncertainties are the 26 scatter about the least-squares lines fit to the data points. 0.2
0.4
0.6
0.8
1.0
1.2 1.4
1.6
1.8
In ([trans-2-b~tene]~/[trans-2-butene]t)
Flgure 2. Plot of eq 3 for cyclopentene vs trans-2-butene. The data represent the results from the irradiation of five initial gas mixtures.
Table 11. Rate Constants for the Reaction of OH with Cyclohexene, Cyclopentene, and Glutaraldehyde at 298 f 3 K
hydrocarbon cyclohexene
10" X kl,cms molecule-1 s-l this work I" IP literature 5.40 i 1.1
6.1 f 1.0
cyclopentene 4.99 f 1.07 5.7 f 1.0 glutaraldehyde 2.23 f 0.46 2.53 f 0.39
-= OW' 0 0.4
'
1
'
'
'
'
0.8
1.2
1.6
2.0
2.4
2.8
'
3.2
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Figure 3. Plot of eq 3 for glutaraldehyde vs trans-Bbutene ( 0 )and vs propene (m). The data for trans-2-butene represent the results from the irradiation of six Initial gas mixtures, and the data for propene are from two initial gas mixtures.
rate constant for the reaction of OH with cyclopentene relative to cyclohexene was also measured to provide a direct comparison of the reaction rates of these two species with OH. These results are plotted in Figure 4. Figures 1-4 also include the least-squares lines fit to the data points, according to eq 3. The slopes of the fitted lines give the ratio of k l / k z and are listed in Table I, along with the 2a error limits determined from the fits. We have also included in Table I our measured ratio for the rate of reaction of OH with trans-2-butene relative to propene. The intercepts of the least-squares lines were all zero, within 1 standard deviation, as expected from eq 3. Reference rate constants of (6.39 f 1.27) X cm3 molecule-1 s-I for trans-2-butene and (2.63 f 0.39) X lo-'' cm3 molecule-' s-' for propene for reaction with OH (27)
6.43 f 0.17 (15),6.41 f 0.25 (16), 5.17 f 0.52 (17), 6.2 (I@, 7.34 f 1.47 (19), 6.24 (20) 6.39 f 0.23 (15)
" Placed on an absolute basis by using rate constant for the reaction of OH with trans-2-butene of k2 = (6.39 f 1.27) X lo-'' cms molecule-' 8-l (27). *Relative to a rate constant of k , = (2.63 f 0.39) cm3 rnolecule-'~-~(27) for the reaction of OH with propene. were used to place the rate constants on an absolute basis. These reference rate constants are in agreement with the values recommended by Atkinson (22). The results are given in Table 11; the uncertainties in the reference rate constants are explicitly included in the uncertainties for the rate constants measured for cyclopentene, cyclohexene, and glutaraldehyde. The rate data were also analyzed by plotting In [HC] vs t for each-of the two hydrocarbon species in the irradiated mixtures. This was done to check on the accuracy of the initial concentrations [HC],used in fitting eq 3 to the data. The plots of In [HC] vs t exhibited pseudofirst-order behavior, indicating that the OH concentration quickly reached steady-state conditions. The rate constant ratios determined by analyzing the data in this fashion were within 1-3% of the values obtained from the plots of Figures 1-4. The initial measurements of the rate constant for the reaction of OH with glutaraldehyde relative to trans-2Environ. Sci. Technol., Vol. 23, No. 2, 1989
179
butene showed very different rates of consumption of the two hydrocarbons. The glutaraldehyde rate constant proved to be closer to that for propene, and several experiments were made using propene as the reference organic compound. To ensure that the literature values for the OH rate constants for these two reference species were consistent, the relative rates of reaction of propene and trans-2-butene with OH were measured. The OH rate constant for propene relative to that for trans-2-butene was 0.365 f 0.019 (2u), which agrees to within the uncertainties with the recommended ratio of 0.41 f 0.10 (22). This agreement demonstrates that our measurement method is free of unsuspected systematic errors. Either trans-2-butene or propene is thus satisfactory for use as a reference compound in deriving the rate constant for the OH-glutaraldehyde reaction, within the present uncertainty limits. The validity of the method is also supported by the good agreement between the experiments in which the rate constant for OH reacting with cyclopentene vs cyclohexene was measured directly and those in which the reaction rates for each cycloalkene were individually measured relative to trans-2-butene. Discussion The hydroxyl radical reacts with cyclic alkenes predominately by addition to the double bond (29).The rate constant for this reaction with cyclohexene has been measured several times by the relative rate technique. The literature values summarized in Table I1 for this rate constant show considerable variation, ranging from a low of (5.17 f 0.52) X lo-'' (17)up to (7.34 f 1.47) X lo-'' cm3 molecule-' s-l (19). The value of (5.40 f 1.10) X 10-l1 cm3 molecule-' s-' obtained here relative to trans-2-butene is somewhat lower than the most recent value of (6.43 f 0.17) X lo-'' cm3 molecule-' s-' reported by Atkinson et al. (15). Atkinson et al. (15) also reported the only previous measurement of the rate constant for the OH-cyclopentene reaction; their value of (6.39 f 0.23) X loe1' cm3 molecule-' s-l is 28% higher than the value of (4.99 f 1.07) X lo-'' cm3 molecule-' s-' reported here. Our rate constant measurements for cyclohexene and cyclopentene appear to be significantly lower than recent literature measurements. However, uncertainties in the reference rate constants used in relative rate techniques contribute to the overall uncertainties and could account for part of the apparent discrepancies. These uncertainties in the reference rate constants are included in the rate constants reported here. However, the uncertainty estimates in the relative rate measurements by Atkinson et al. (15)do not include the uncertainty in the reference rate constant. A better way of comparing our results with other measurements is thus to use the measured rate constant ratios reported in Table I. These rate constant ratios are independent of the assumed value of the reference rate constant and thus avoid the uncertainties introduced by the value assumed for the reference rate constant. The rate constant ratio of 0.365 f 0.019 measured here for propene relative to trans-2-butene is seen to be 11% less than the value of 0.412 f 0.009 measured by Atkinson and Aschmann (27). Furthermore, if we assume that the relative rate constant measurements made by Atkinson et al. (15)may be combined with those made by Atkinson and Aschmann (27), then ratios of 1.05 f 0.06 for cyclohexene and 1.04 f 0.06 for cyclopentene relative to trans-2-butene are obtained. Our values of 0.848 f 0.036 for cyclohexene and 0.784 f 0.061 for cyclopentene relative to trans-2butene are thus seen to be about 20-25% lower than the values derived from ref 15 and 27. The reason for these discrepancies is not clear.
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Differences in the ring strain energies and the number of CH, groups of cyclopentene and cyclohexene suggest that they might react at different rates with OH radicals. However, the ratio of the rate constant for cyclopentene to that for cyclohexene calculated from the data reported by Atkinson et al. (15) is 0.99 f 0.04 and thus would indicate no difference in the two rate constants. The rate constants reported here give a ratio of 0.92 f 0.08, also indicating that the two alkenes react with OH at the same rate, within the experimental uncertainties. We also made a direct measurement of the reaction rate of cyclopentene relative to cyclohexene. This measurement yielded a ratio of 0.940 f 0.024 (2u) and suggests that cyclopentene reacts slightly slower with OH than cyclohexene. However, the ratio is sufficiently close to 1.0 that there is no clear difference in the two rate constants. The relative rate measurements for glutaraldehyde were especially difficult because the dialdehyde has no sharp spectral features to aid in determining the concentrations from the infrared spectra; consequently, it was necessary to determine many points for the plot of eq 3 to reduce the uncertainties in the fit to the data. An additional problem was that the spectrum of the acetaldehyde product from the reaction of trans-2-butene and propene with OH overlapped the strongest glutaraldehyde absorption band at 2715 cm-', making the spectral subtractions more uncertain. This accounts to a large extent for the scatter seen in Figure 3. In any case, an average value of (2.38 f 0.60) X lo-'' cm3 molecule-' s-' was measured for the rate constant for the reaction of OH with glutaraldehyde. This number is the average of the independent determinations using trans-2-butene and propene as the reference organic compounds. These results for glutaraldehyde are the first measurements of the rate constant for the reaction of OH with a dialdehyde, and it is thus interesting to compare these results with literature values for monoaldehydes. The reaction preferentially proceeds by the abstraction of the aldehydic H atom by OH to yield water and an acyl radical as products (28). The recommended (22) rate constant for cm3 molecule-' s-'; acetaldehyde is (1.62 f 0.32) X two recent absolute measurements of this rate constant are (1.22 f 0.25) X 10-l' cm3 molecule-' s-' reported by Semmes et al. (29) and (1.55 f 0.22) X lo-'' cm3molecule-' s-l reported by Michael et al. (30). The rate constant for the reaction of glutaraldehyde with OH thus seems to be less than twice that for acetaldehyde. Atkinson and Lloyd (31) estimated an OH rate constant of 1.5 X lo-'' cm3 molecule-' s-l per CHO group; this estimate predicts a rate constant of 3.0 X lo-'' cm3 molecule-' s-l for glutaraldehyde, assuming that the CH2groups do not contribute to the total rate constant. The more elaborate treatment of OH group rate constants by Atkinson (22) predicts a rate constant of 5.94 x 10-1' cm3 molecule-1 s-l for glutaraldehyde, consisting of contributions of (in units of lo-'' cm3 molecule-l s-l) 4.15 from the two CHO groups, 1.62 from the P-CH2 group, and 0.16 from the two a-CH2 groups. This predicted rate constant for glutaraldehyde is 2.5 times larger that the experimental rate constant. Part of the reason for this difference could be that the contribution calculated for the P-CH2 group in glutaraldehyde is too large. Indeed, in the refinements of the group rate constants made by Atkinson (22) to data for various organic species, rate data were not available for a CH, group in a P position relative to more than one CHO group as is the case with glutaraldehyde. The results for glutaraldehyde can be used to estimate a rate constant for the reaction of OH with adipaldehyde,
the product formed initially in the reaction of OH with cyclohexene. If the overall rate constant for the reaction of OH with dialdehydes is largely due to reaction of OH with the CHO groups and very little contribution from the aliphatic chain, the present results suggest, then the OH rate constant for small aldehydes is largely determined by the number of CHO groups. This suggests that the rate constant for the reaction of OH with adipaldehyde will be cm3 similar to glutaraldehyde and thus be -2.4 X molecule-l s-l. The rate constants reported herein for the reactions of OH with cyclohexene, cyclopentene, and glutaraldehyde and the estimate for adipaldehyde provide important rate data for input to models of atmospheric chemistry. Our measurement of the rate constant for the OH-glutaraldehyde reaction is the first such measurement for a dialdehyde and is thus important in establishing the expected magnitude of rate constants for this class of OH reactions. Further work is necessary to identify the detailed product distributions from the reactions of OH with cyclic alkenes and with dialdehydes and to understand how these species contribute to aerosol formation in the atmosphere.
Acknowledgments The assistance of Linda A. Rhead in performing the measurements is gratefully acknowledged. Registry No. HO, 3352-57-6; cyclohexene, 110-83-8; cyclopentene, 142-29-0; glutaraldehyde, 111-30-8.
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Received for review July 30, 1987. Accepted August 22, 1988.
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