Kinetics of the reactions of OH radicals with 2‐methoxy‐6‐(trifluoromethyl)pyridine,diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol at 298 ± 2 K

Rate constants for the reactions of 2‐methoxy‐6‐(trifluoromethyl)pyridine, diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with OH radicals have been measured at 298 ± 2 K using a relative rate method. The measured rate constants (cm³ molecule^?1 s^?1) are (1.54 ± 0.21) × 10^?12 for 2‐methoxy‐6‐(trifluoromethyl)pyridine, (1.19 ± 0.25) × 10^?10 for diethylamine, and (1.76 ± 0.38) × 10^?12 for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol, where the indicated errors are the estimated overall uncertainties including those in the rate constants for the reference compounds. No reaction of 2‐methoxy‐6‐(trifluoromethyl)pyridine with gaseous nitric acid was observed, and an upper limit to the rate constant for the reaction of 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with O₃ of <7 × 10^{? 20} cm³ molecule^?1 s^?1 was determined. Using a 12‐h average daytime OH radical concentration of 2 × 10⁶ molecule cm^?3, the lifetimes of the volatile organic compounds studied here with respect to reaction with OH radicals are 7.5 days for 2‐methoxy‐6‐(trifluoromethyl)pyridine, 1.2 h for diethylamine, and 6.6 days for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol. Likely reaction mechanisms are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 631–638, 2011     

Reactions of naphthalene in N2O5?NO3?NO2? air mixtures

The reactions of naphthalene in N₂O₅? NO₃? NO₂? N₂? O₂ reactant mixtures have been investigated over the temperature range 272–297 K at ca. 745 torr total pressure and at 272 K and ca. 65 torr total pressure using long pathlength Fourier transform infrared absorption spectroscopy. 2,3-Dimethyl-2-butene was added to the reactant mixtures at 272 K to rapidly scavenge the NO₃ radicals both initially present in the added N₂O₅ and formed from the thermal decomposition of N₂O₅ during the reactions. The data obtained in the presence and absence of added 2,3-dimethyl-2-butene showed that napthalene undergoes initial reaction with the NO₃ radical to form an NO₃-naphthalene adduct, which either rapidly decomposes back to the reactants (at a rate of ca. 5 × 10⁵ s^?1 at 298 K) or reacts exclusively with NO₂ to form products. When NO₃ radicals, N₂O₅ and NO₂ are in equilibrium, this overall process is kinetically equivalent to reaction of naphthalene with N₂O₅, and previous kinetic and product studies have indeed assumed the reactions of naphthalene and alkyl-substituted naphthalenes in N₂O₅? NO₃? NO₂? air mixtures to be with N₂O₅, and not with NO₃ radicals.     

The gas-phase reaction of hydrazine and ozone: A nonphotolytic source of OH radicals for measurement of relative OH radical rate constants

The homogeneous gas-phase reaction of N₂H₄ with O₃ in air atmospheric pressure has been used to generate OH radicals in the dark, allowing the determination of relative OH radical rate constants for compounds which photolyze rapidly. This technique was first validated by determining the OH radical rate constant ratios for n-butane/cyclohexane and methanol/dimethyl ether, both of which are in excellent agreement with the literature values. The rate constant for the reaction of OH radicals with methyl nitrite at 300 ± 3 K was then determined relative to those for the reaction of OH radicals with n-hexane and dimethyl ether. The resulting rate constant of 1.8 × 10^?13 cm³/molecule·s is about seven times lower than those of previous measurements which employed a different nonphotolytic relative rate method.     

A product study of the gas-phase reaction of Methacrolein with the OH radical in the presence of NOx

The gas-phase reaction of methacrolein with the OH radical, in the presence of NO_x, was investigated at 298 ± 2 K and atmospheric pressure of air. Hydroxyacetone, methylglyoxal, a peroxyacyl nitrate identified as CH₂ ? C(CH₃)C(O)OONO₂ (peroxymethacryloyl nitrate), formaldehyde, CO, and CO₂ were observed to be the major products. The product yield data for these compounds show that OH radical addition to the >C ? C< bond accounts for ca. 50% of the overall reaction, with the remaining ca. 50% proceeding via H—atom abstraction from the ? CHO group. The data suggest that the alkoxy radical formed following the addition of OH to the terminal carbon atom, decomposes primarily to give the formyl radical plus hydroxyacetone. A lower limit ratio of 5: 1 has been estimated for OH radical addition to the terminal carbon atom of the double bond relative to addition on the inner carbon atom.     

Ion trap mass spectrometry affords advances in the analytical and atmospheric chemistry of 2-hydroxy-2-methylpropanal,a proposed photooxidation product of 2-methyl-3-buten-2-Ol

In the western United States, in areas where emissions of the biogenic hydrocarbon, 2-methyl-3-buten-2-ol (MBO) are high, MBO contributes significantly to the oxidative capacity of the atmosphere. Hydroxyl radical oxidation of MBO can play an important role in forming tropospheric ozone, and MBO reaction products may contribute to the formation of secondary organic aerosols [1-3]. Although 2-hdyroxy-2-methylpropanal was tentatively identified as a product from the reaction of MBO with .OH in indoor chamber studies, the identity of the compound was not confirmed due to the lack of an authentic standard. Further, no data exists on the atmospheric generation and fate of 2-hydroxy-2-methylpropanal in the ambient environment. Herein, we provide further evidence that 2-hydroxy-2-methylpropanal is generated by .OH reaction with MBO by identifying 2-hydroxy-2-methylpropanal in an indoor chamber experiment and in ambient air sampled in the Blodgett Forest, where MBO emissions are high. We analyzed 2-hydroxy-2-methylpropanal by using a method that relies on O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and bis-(trimethylsilyl) trifluoroacetamide (BSTFA) derivatization along with ion-trap mass spectrometry. Tentative identification of 2-hydroxy-2-methylpropanal was possible by using knowledge gained in this study regarding the mass spectrometry of PFBHA-BSTFA derivatives of carbonyls with primary, secondary, and tertiary -OH groups, and ado- and keto-acids. The identification was confirmed by comparing the methane CI mass spectra and relative gas chromatographic retention time obtained by analyzing 2-hydroxy-2-methylpropanal in a sample extract and a synthesized authentic standard. Since the standard became available at the end of this study (after all samples were analyzed), we also developed a method for semi-quantification of 2-hydroxy-2-methylpropanal, with a detection limit of 27 pptv in air. We used the method to provide the first ambient air measurements of 2-hydroxy-2-methylpropanal. The analyte is not commercially available, and hence other researchers who have not synthesized an authentic standard can employ the method.     

Reactions of NO3-naphthalene adducts with O2 and NO2

The kinetics of the gas-phase reaction of the NO₃ radical with naphthalene have been investigated at 150 torr O₂ + 590 torr N₂ and 600 torr O₂ + 140 torr N₂ at 298 ± 2 K. Relative rate measurements were carried out in reacting NO₃? N₂O₅-naphthalene-propene-O₂? N₂ mixtures by longpath Fourier transform infrared absorption spectroscopy. A rate constant ratio for the reactions of O₂ and NO₂ with the NO₃-naphthalene adduct of k/k < 4 × 10^?7 was obtained from the competition between O₂ and NO₂ for reaction with the NO₃-naphthalene adduct and thermal decomposition of the adduct back to reactants. Atmospheric pressure ionization MS/MS measurements of the nitronaphthalene products of the NO₃ radical-initiated reaction of naphthalene are consistent with the proposed reaction mechanism, and the atmospheric implications of the data are discussed. © 1994 John Wiley & Sons, Inc.     

Atmospheric chemistry of dimethyl phosphonate, dimethyl methylphosphonate, and dimethyl ethylphosphonate

Rate constants for the reactions of OH radicals and NO3 radicals with dimethyl phosphonate [DMHP, (CH3O)2P(O)H], dimethyl methylphosphonate [DMMP, (CH3O)2P(O)CH3], and dimethyl ethylphosphonate [DMEP, (CH3O)2P(O)C2H5] have been measured at 296 +/- 2 K and atmospheric pressure using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10(-12) cm3 molecule(-1) s(-1)) were as follows: DMHP, 4.83 +/- 0.25; DMMP, 10.4 +/- 0.6; and DMEP, 17.0 +/- 1.0, with a deuterium isotope effect of k(OH + DMMP)/k(OH + DMMP-d9) = 4.8 +/- 1.2. The rate constants obtained for the NO3 radical reactions (in units of 10(-16) cm3 molecule(-1) s(-1)) were as follows: DMHP, < 1.4; DMMP, 2.0 +/- 1.0; and DMEP, 3.4 +/- 1.4. Upper limits to the rate constants for the O3 reactions of < 8 x 10(-20) cm3 molecule(-1) s(-1) for DMHP and < 6 x 10(-20) cm3 molecule(-1) s(-1) for DMMP and DMEP were determined. Products of the reactions of OH radicals with DMHP, DMMP, and DMEP were investigated in situ using atmospheric pressure ionization mass spectrometry (API-MS) and, for the DMMP and DMEP reactions, Fourier transform infrared (FT-IR) spectroscopy. API-MS analyses showed the formation of products of molecular weight 96 and 126, attributed to CH3OP(O)(H)OH and (CH3O)2P(O)OH, respectively, from DMHP; of molecular weight 110, attributed to CH3OP(O)(CH3)OH, from DMMP; and of molecular weight 124 and 126, attributed to CH3OP(O)(C2H5)OH and (CH3O)2P(O)OH, respectively, from DMEP. FT-IR analyses showed formation (values given are % molar yields) of the following: from DMMP, CO, 54 +/- 6; CO2, 5 +/- 1 in dry air; HCHO, 3.9 +/- 0.7; HC(O)OH, < 1.4 in dry air; RONO2, approximately 4; and formate ester, approximately 8; and from DMEP, CO, 50 +/- 7; CO2, 11 +/- 4; CH3CHO, 18 +/- 8; HCHO, < 7; HC(O)OH, < 6; RONO2, < or = 5; and formate ester, 5.0 +/- 1.5. Possible reaction mechanisms are discussed.     

Atmospheric reactions of chloroethenes with the OH radical

The kinetics and products of the homogeneous gas-phase reactions of the OH radical with the chloroethenes were investigated at 298 ± 2 K and atmospheric pressure. Using a relative rate technique and ethane as a scavenger for the chlorine atoms produced in these OH radical reactions, rate constants (in units of 10^?12 cm³ molecule^?1s^?1) of 8.11 ± 0.24, 2.38 ± 0.14, and 1.80 ± 0.03 were obtained for 1,1-dichloroethene, cis-1, 2-dichloroethene and trans-1,2-dichloroethene, respectively. Under these conditions, the major products observed by long pathlength FT-IR absorption spectroscopy were HCHO and HC(O)Cl from vinyl chloride; HC(O)Cl from cis- and trans-1,2-dichloroethene; HCHO and COCl₂ from 1,1-dichloroethene; HC(O)Cl and COCl₂ from trichloroethene; and COCl₂ from tetrachloroethene. In the absence of a Cl atom scavenger, significant yields of the chloroacetyl chlorides, CH_xCl_3?xC(O)Cl, were observed from 1,1-dichloro-, trichloro- and tetrachloroethene, indicating that these products resulted from reactions involving chlorine atoms. The yields of all of these products are reported and the mechanisms of these gas-phase reactions discussed. In addition, OH radical reaction rate constants were redetermined, in the presence of a Cl atom scavenger, for cis- and trans-1,3-dichloropropene and 3-chloro-2-chloromethyl-1-propene, being (in units of 10^?12 cm³ molecule^?1 s^?1) 8.45 ± 0.41, 14.4 ± 0.8, and 33.5 ± 3.0, respectively.     

Extent of H-atom abstraction from the reaction of the OH radical with 1-butene under atmospheric conditions

Products of the reaction of OH radicals with 1-butene have been investigated in the presence of NO in one atmosphere of air at room temperature using gas chromatography and in situ long pathlength Fourier transform infrared absorption spectroscopy. The major product observed was propionaldehyde, with a formation yield (after allowing for its subsequent loss processes) of 0.94 ± 0.12. Minor yields of organic nitrates (RONO₂) and of peroxypropionyl nitrate, a secondary product arising from propionaldehyde, were also observed. However, none of the products expected from the reactions subsequent to H-atom abstraction from 1-butene by OH radicals were observed, allowing an upper limit of 10% for this process to be derived. These data are compared with the available literature results and the implications are discussed.     

H‐atom abstraction from selected C?H bonds in 2,3‐dimethylpentanal, 1,4‐cyclohexadiene,and 1,3,5‐cycloheptatriene

The gas‐phase reactions of OH radicals with 1,4‐cyclohexadiene, 1,3,5‐cycloheptatriene, and 2,3‐dimethylpentanal have been investigated to determine the importance of H‐atom abstraction at specific positions in these molecules. Benzene was observed as a product of the reaction of OH radicals with 1,4‐cyclohexadiene in 12.5 ± 1.2% yield, in good agreement with a previous study and indicating that this is the fraction of the reaction proceeding by H‐atom abstraction from the allylic C? H bonds. In contrast, no formation of tropone from 1,3,5‐cycloheptatriene was observed, suggesting that in this case H‐atom abstraction is not important. For the reaction of OH radicals with 2,3‐dimethylpentanal, formation of 3‐methyl‐2‐pentanone was observed in 5.4 ± 1.0% yield (after correction for reaction of 3‐methyl‐2‐pentanone with OH radicals), and this product is predicted to be formed after initial H‐atom abstraction from the 2‐position CH group. Acetaldehyde and 2‐butanone were also observed as products, with initial yields of ～90% and ～26%, respectively, and their formation appeared to involve, at least in part, an intermediary acyl peroxy radical. Using a relative rate method, the measured rate constants for the reactions of OH radicals with 2,3‐dimethylpentanal, 3‐methyl‐2‐pentanone, and tropone are (in units of 10^?12 cm³ molecule^?1 s^?1) 2,3‐dimethylpentanal, 42 ± 7; 3‐methyl‐2‐pentanone, 6.87 ± 0.08; and tropone, 42 ± 6. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 415–426, 2003