Products from the Oxidation of n-Butane from 298 to 735 K Using Either Cl Atom or Thermal Initiation: Formation of Acetone and Acetic Acid-Possible Roaming Reactions?

The oxidation of 2-butyl radicals (and to a lesser extent 1-butyl radicals) has been studied over the temperature range of 298-735 K. The reaction of Cl atoms (formed by 360 nm irradiation of Cl2) with n-butane generated the 2-butyl radicals in mixtures of n-C4H10, O2, and Cl2 at temperatures below 600 K. Above 600 K, 2-butyl radicals were produced by thermal combustion reactions in the absence of chlorine. The yields of the products were measured by gas chromatography using a flame ionization detector. Major products quantified include acetone, acetic acid, acetaldehyde, butanone, 2-butanol, butanal, 1- and 2- chlorobutane, 1-butene, trans-2-butene, and cis-2-butene. At 298 K, the major oxygenated products are those expected from bimolecular reactions of 2-butylperoxy radicals (butanone, 2-butanol, and acetaldehyde). As the temperature rises to 390 K, the butanone decreases while acetaldehyde increases because of the increased rate of 2-butoxy radical decomposition. Acetone and acetic acid first appear in significant yield near 400 K, and these species rise slowly at first and then sharply, peaking near 525 K at yields of ∼25 and ∼20 mol %, respectively. In the same temperature range (400-525 K), butanone, acetaldehyde, and 2-butanol decrease rapidly. This suggests that acetone and acetic acid may be formed by previously unknown reaction channels of the 2-butylperoxy radical, which are in competition with those that lead to butanone, acetaldehyde, and 2-butanol. Above 570 K, the yields of acetone and acetic acid fall rapidly as the yields of the butenes rise. Experiments varying the Cl atom density, which in turn controls the entire radical pool density, were performed in the temperature range of 410-440 K. Decreasing the Cl atom density increased the yields of acetone and acetic acid while the yields of butanone, acetaldehyde, and 2-butanol decreased. This is consistent with the formation of acetone and acetic acid by unimolecular decomposition channels of the 2-butylperoxy radical, which are in competition with the bimolecular channels that form butanone, acetaldehyde, and 2-butanol. Such unimolecular decomposition channels would be unlikely to proceed through conventional transition states because those states would be very constrained. Therefore, the possibility that these decomposition channels proceed via roaming should be considered. In addition, we investigated and were unable to fit our data trends by a simplified ketohydroperoxide mechanism.

Study of the Reaction Cl + Ethyl Formate at 700-950 Torr and 297 to 435 K: Product Distribution and the Kinetics of the Reaction C2H5OC(═O) → CO2 + C2H5.

The kinetics and mechanism of the reaction of atomic chlorine with ethyl formate [Cl + CH3CH2O(C═O)H, reaction 1] have been examined. These experiments were performed at pressures of 760-950 Torr and temperatures from 297 to 435 K. Reactants and products were quantified by gas chromatography-flame ionization detector (GC/FID) analysis. The initial mixture contained ethyl formate, Cl2, and N2. Cl atoms were generated by UV photolysis of this initial mixture at 360 nm, which dissociates Cl2. The rate constant of reaction 1 was measured at 297 K relative to that of the reaction Cl + C2H5Cl (reaction 2), yielding the rate constant ratio k1/k2 = 1.09 ± 0.05. The final products formed from reaction 1 are ethyl chloroformate, 1-chloroethyl formate, and 2-chloroethyl formate. These products result from the reactions with Cl2 of the three free radicals formed by H atom abstraction from ethylformate in reaction 1. Based on the molar yields of these three chlorinated products, the yields of the three radicals formed from reaction 1 at 297 K are (25 ± 3) mole percent of CH3CH2O(C═O); (67 ± 5) mole percent of CH3CHO(C═O)H; and (8 ± 2) mole percent of CH2CH2O(C═O)H. A second phase of this experiment measured the rate constant of the decarboxylation of the ethoxy carbonyl radical [CH3CH2O(C═O) → CO2 + C2H5, reaction 4] relative to the rate constant of its reaction with Cl2 [CH3CH2O(C═O) + Cl2 → CH3CH2O(C═O)Cl + Cl, reaction 3a]. Over the temperature range 297 to 404 K at 1 atm total pressure, this ratio can be expressed by k4/k3a = 10(23.56±0.22) e(-(12700±375)/RT) molecules cm(-3). Estimating the value of k3a (which has not been measured) based on similar reactions, the expression k4 = 5.8 × 10(12) e(-(12700)/RT) s(-1) is obtained. The estimated error of this rate constant is ± a factor of 2 over the experimental temperature range. This rate expression is compared with recent ab initio calculations of the decarboxylation of the analogous methoxy carbonyl radical.

Study of the Thermodynamics (Thermal and Cl Catalyzed) and Kinetics of the Cis and Trans Isomerizations of CF3CF═CHF, CF3CH═CHCF3, and CH3CH═CHCH3 in 100-950 Torr of N2 Diluent at 296-875 K: Effect of F and CF3 Substitution on the Isomerization Process Including the Fluorine "Cis Effect".

The equilibrium constants for the Z to E isomerizations of CF3CF═CHF (K1) and CF3CH═CHCF3 (K2) have been measured using GC/FID analysis over the temperature ranges 360­850 and 297­850 K, respectively. At lower temperature, K was determined using Cl atom catalysis. At higher temperature, K was measured without a catalyst. The temperature-dependent expressions are K1 (Z to E) = 1.45(±0.15)e(­[2845(±100)/RT]) and K2 (Z to E) = 1.9(±0.22)e(+[4330(±120)/RT]) (where the gas constant R ≡ 1.986 cal mol(­1) K(­1)). For isomerization 1, the Z (fluorine cis) isomer is 2.85 kcal mol(­1) lower in energy than the E (fluorine trans) isomer, providing another example of the fluorine "cis effect" in olefins. For isomerization 2, the E(trans) isomer is 4.3 kcal mol(­1) lower in energy than the corresponding Z(cis) isomer as is normal for olefins. The isomerization rate constant in a single direction was also measured for each fluorinated compound: k­1(E to Z) = 10(13.87±0.24)e(­59530(±887)/RT) s(­1); and k2(Z to E) = 10(13.89±0.23)e(­58845(±675)/RT) s(­1). To verify the experimental method, cis to trans (k3) and trans to cis (k­3) isomerization rate constants were also measured for cis- and trans-2-butene for comparison to several previous studies. The rate constants determined herein are k3 (cis to trans) = 10(13.95±0.23)e(­63245(±815)/RT) s(­1); and k­3 (trans to cis) = 10(14.32±0.28)e(­64993(±1132)/RT) s(­1). k3 agrees well with four previous measurements and represents the best available rate constant for 2-butene. All errors quoted here are 2σ. The typical total pressure for these experiments was 760 ± 100 Torr. Limited experiments performed at 100 Torr showed no pressure dependence for any of the compounds above 100 Torr. Thus, all isomerization rate constants represent high-pressure limits. The rates of the addition reactions of Cl to the double bonds of CF3CF═CHF (k4) and CF3CH═CHCF3 (k7) (used in Cl catalysis) were also measured in pure N2 and in pure O2. In O2, the rate constants expressions are k4 = 1.56 (±0.22) × 10(­11) e(+(643/RT)) cm3 molecule(­1) s(­1); and k7 = 1.05 × 10(­12) e(+(1874/RT)) cm(3) molecule(­1) s(­1). In N2, k4 and k7 decrease several orders of magnitude as the temperature increases because of the increasing reversibility of the Cl addition reaction, which produces the catalytic effect.

Rate constant and mechanism of the reaction Cl + CFCl2H → CFCl2 + HCl over the temperature range 298-670 K in N2 or N2/O2 diluent.

The rate constant of the reaction Cl + CFCl2H (k1) has been measured relative to the established rate constant for the reaction Cl + CH4 (k2) at 760 Torr. The measurements were carried out in Pyrex reactors using a mixture of CFCl2H, CH4, and Cl2 in either N2 or N2/O2 diluent. Reactants and products were quantified by GC/FID analysis. Cl atoms were generated by irradiation of the mixture with 360 nm light to dissociate the Cl2 for temperatures up to ~550 K. At higher temperature, the Cl2 dissociated thermally, and no irradiation was used. Over the temperature range 298-670 K, k1 is consistently a factor of ~5 smaller than that of k2 with a nearly identical temperature dependence. The optimum non-Arrhenius rate constant is represented by the expression k1 = 1.14 × 10(-22) T(3.49) e(-241/T) cm(3) molecule(-1) s(-1) with an estimated uncertainty of ±15% including uncertainty in the reference reaction. CFCl3 formed from the reaction CFCl2 + Cl2 (k3) is the sole product in N2 diluent. In ~20% O2 at 298 K, the CFCl3 product is suppressed. The rate constant of reaction 3 was measured relative to that of reaction 4 [CFCl2 + O2 (k4)] giving the result k3/k4 = 0.0031 ± 0.0005 at 298 K. An earlier experiment by others observed C(O)FCl to be the major product of reaction channel 4 [formed via the sequence, CFCl2(O2) → CFCl2O → C(O)FCl + Cl]. Our current experiments verified that there is a Cl atom chain reaction in the presence of O2 as required by this mechanism.

Relative rate study of the kinetics, mechanism, and thermodynamics of the reaction of chlorine atoms with CF3CF═CH2 (HFO-1234yf) in 650-950 Torr of N2 or N2/O2 diluent at 296-462 K.

The rate constant of the reaction Cl + CF(3)CF═CH(2) (k(1)) has been measured relative to several reference species using the relative rate technique with either gas chromatographic analysis with flame-ionization detection (GC/FID) or Fourier transform infrared (FTIR) analysis. Cl atoms were generated by UV irradiation of Cl(2)/CF(3)CF═CH(2)/reference/N(2)/O(2) mixtures. At 300-400 K in the presence of >20 Torr O(2), k(1) = 1.2 × 10(-11) e((+1100/RT)) cm(3) molecule(-1) s(-1). In N(2) diluent, k(1) has a sharp negative temperature coefficient resulting from the relatively small exothermicity of the following reactions: (1a) Cl + CF(3)CF═CH(2) ↔ CF(3)CFClCH(2)(•); (1b) Cl + CF(3)CF═CH(2) ↔ CF(3)CF(•)CH(2)Cl (reaction 1), which were determined in these experiments to be ∼16.5 (±2.0) kcal mol(-1). This low exothermicity causes reaction 1 to become significantly reversible even at ambient temperature. The rate constant ratio for the reaction of the chloroalkyl radicals formed in reaction 1 with Cl(2) (k(2)) or O(2) (k(3)) was measured to be k(2)/k(3) = 0.4 e(-(3000/RT)) for 300-400 K. At 300 K, k(2)/k(3) = 0.0026. The reversibility of reaction 1 combined with the small value of k(2)/k(3) leads to a sensitive dependence of k(1) on the O(2) concentration. Products measured by GC/FID as a function of temperature are CF(3)CFClCH(2)Cl, CF(3)COF, and CH(2)Cl(2). The mechanism leading to these products is discussed. The rate constant for the reaction Cl + CF(3)CFClCH(2)Cl (k(11)) was measured as a function of temperature (300-462 K) at 760 Torr to be k(11) = 8.2 × 10(-12) e(-(4065/RT)) cm(3) molecule(-1) s(-1). Rate constants relative to CH(4) for the reactions of Cl with the reference compounds CH(3)Cl, CH(2)Cl(2), and CHCl(3) were measured at 470 K to resolve a literature discrepancy. (R = 1.986 cal K(-1) mol(-1)).

Kinetics and mechanism of the reaction of methacrolein with chlorine atoms in 1-950 Torr of N2 or N2/O2 diluent at 297 K.

The rate constant of the reaction of Cl atoms with methacrolein (k(1)) has been measured relative to that of Cl with propane (k(2)) or cyclohexane (k(6)) at ambient temperature and pressures varying from 1-950 Torr. The experiments were carried out by irradiation (350 nm) of Cl(2)/methacrolein/propane or cyclohexane mixtures in N(2) or N(2)/O(2) diluent at ambient temperature in a spherical (500 cm(3)) Pyrex reactor (GC/FID analyses) or a 140 L FTIR smog chamber. The measured relative rate constant ratios in the GC/FID experiments were k(1)/k(2) = 1.464 +/- 0.015(2sigma) in N(2) and k(1)/k(2) = 1.68 +/- 0.03(2sigma) in N(2)/O(2) diluent (O(2) > 20,000 ppm). No pressure dependence was observed over the range studied in N(2) (120-950 Torr) using the GC/FID. In the FTIR/smog chamber experiments values of k(1)/k(6) = 0.645 +/- 0.032, 0.626 +/- 0.037, 0.586 +/- 0.026, and 0.479 +/- 0.024 were measured in 700, 100, 10, and 1 Torr, respectively, of N(2) diluent. Using k(2) = (1.4 +/- 0.2) x 10(-10) and k(6) = (3.3 +/- 0.5) x 10(-10) high pressure limiting rate constants of k(1) = (2.05 +/- 0.3) x 10(-10) [GC/FID] and (2.13 +/- 0.34) x 10(-10) [FTIR] cm(3) molecule(-1) s(-1) were determined. In experiments using the GC/FID reactor with N(2) diluent the following products (molar yields) were observed: 2,3-dichloro-2-methylpropanal [(47.2 +/- 8)% excluding error in calibration]; methacryloyl chloride [(22.9 +/- 2)%]; and 2-chloromethylacrolein [(2.3 +/- 0.8)%]. Addition of 200 ppm O(2) (with Cl(2) = 5000 ppm) resulted in a sharp reduction of the 2,3-dichloro-2-methylpropanal yield (to approximately 2%) with an accompanying appearance of chloroacetone [yield = (55 +/- 7)% decreasing to (44 +/- 7)% in air diluent]. The methacryloyl chloride yield was 23% for [O(2)]/[Cl(2)] ratios from 0 to 0.2 but decreased to near zero as the O(2)/Cl(2) ratio was increased to approximately 400. The variation in methacryloyl chloride yield with the O(2)/Cl(2) ratio in the initial mixture allowed an approximate measurement of the rate constant for the reaction of the methacryloyl radical with O(2) relative to that with Cl(2) (k(O(2))/k(Cl(2)) = 0.066 +/- 0.02). In experiments using the FTIR reactor in 700 Torr of N(2) diluent, methacryloyl chloride [(26 +/- 3)%] and HCl [(27 +/- 3)%] were observed as products. In 700 Torr of air diluent, the observed products were: chloroacetone [(44 +/- 5)%], CO(2) [(27 +/- 3)%], HCl [(21 +/- 3)%], and HCHO [(14 +/- 2)%], and CH(3)C(O)CH(2)OH (3-4%). The observation of CH(3)C(O)CH(2)OH indicates the presence of OH radicals in the system. At atmospheric pressure and 297 K, the title reaction proceeds [(24.5 +/- 5)%] via abstraction of the aldehydic hydrogen atom, [(2.3 +/- 0.8)%] via abstraction from the -CH(3) group, and approximately [(47 +/- 8) %] via addition to the CH(2)=C < double bond with most of the addition occurring at the terminal carbon atom (uncertainties represent statistical 2sigma). The results are discussed with respect to the literature data.

Products and mechanism of the reaction of chlorine atoms with 3-pentanone in 700-950 torr of N(2)/O(2) diluent at 297-515 K.

The products, kinetics, and mechanism of the reaction Cl + 3-pentanone have been measured by UV irradiation of Cl(2)/3-pentanone/N(2) (O(2)) mixtures using primarily GC analysis with selected cross checks by FTIR. In the absence of O(2), the products are 1- and 2-chloro-3-pentanone with yields of 21 and 78%, respectively. As the temperature is increased, the yield of 1-chloro-3-pentanone increases modestly relative to the 2-chloro-3-pentanone yield. On the basis of this increase, the activation energy for hydrogen abstraction at the 1 position is determined to be 500 (+/-500) cal mole(-1) relative to abstraction at the 2 position. In the presence of 500 ppm of O(2) with 900-1000 ppm of Cl(2) at 297 K, the yield of 2-chloro-3-pentanone decreases dramatically from 78 to 2.5%, while the 1-chloro-3-pentanone decreases only modestly from 21 to 17%. The observed oxygenated species are acetaldehyde (59%), 2,3-pentanedione (9%), and propionyl chloride (56%). Increasing the temperature to 420 K (O(2) = 500 ppm) suppresses these oxygenated products, and 2-chloro-3-pentanone again becomes the primary product, indicating that the O(2) addition reaction to the 2-pentanonyl radical has become reversible. At 500 K and 10 000 ppm O(2), a new product channel opens which forms a small yield ( approximately 4%) of ethylvinylketone. Computer modeling of the product yields has been performed to gain an understanding of the overall reaction mechanism in the presence and absence of O(2). The reaction of chlorine atoms with 3-pentanone proceeds with a rate constant of 8.1 (+/-0.8) x 10(-11) cm(3) molecule(-1) s(-1) independent of temperature over the range of 297-490 K (E(a) = 0 +/- 200 cal mole(-1)). Rate constant ratios of k(C(2)H(5)C(O)CHCH(3) + Cl(2))/k(C(2)H(5)C(O)CHCH(3) + O(2)) = 0.0185 +/- 0.0037 and k(C(2)H(5)C(O)CH(2)CH(2) + Cl(2))/k(C(2)H(5)CH(2)C(O)CH(2)CH(2) + O(2)) = 2.7 +/- 0.4 were determined at 297 K in 800-950 Torr of N(2)/O(2) diluent. In 800-950 Torr of N(2)/O(2) diluent, the major fate of the alkoxy radical CH(3)CH(O)C(O)C(2)H(5) is decomposition to give C(2)H(5)C(O) radicals and CH(3)CHO. These results show that the chemical mechanisms of the 3-pentanone reactions are very similar to those observed for butanone. In addition, the rate constants of the reactions of chlorine atoms with 1-chloro-3-pentanone [3 (+/-0.6) x 10(-11) over the range of 297-460 K], 2,3-pentanedione [1.4 (+/-0.3) x 10(-11) at 297 K], and ethylvinylketone [1.9 (+/-0.4) x 10(-10) over the range of 297-400 K, decreasing rapidly above 400 K] were measured at ambient pressure.

Products and mechanism of the reaction of Cl with butanone in N2/O2 diluent at 297-526 K.

The products, kinetics, and mechanism of the reaction Cl + butanone have been measured by UV irradiation of Cl(2)/butanone/N(2) (O(2)) mixtures using either GC or FTIR analysis. In the absence of O(2), the products are 1-, 3-, and 4-chlorobutanone with yields of 3.1%, 76%, and 22.5%, respectively. As the temperature is increased, the yields of 1- and 4-chlorobutanone increase relative to the 3-chlorobutanone yield. On the basis of these increases, the activation energies for hydrogen abstraction at the 1 and 4 positions are determined to be 1800 (+/-300) and 470 (+300, -150) cal mol(-1) relative to abstraction at the 3 position. In the presence of 400 ppm of O(2) with 700-900 ppm of Cl(2) at 297 K, the yields of 1- and 3-chlorobutanone decrease dramatically from 3.1% to 0.25% and from 76% to 2%, respectively, while the 4-chlorobutanone decreases only slightly from 22.5% to 18.5%. The observed oxygenated species are acetaldehyde (52%), butanedione (11%), and propionyl chloride (2.5%). Increasing the temperature to 400 K (O(2) = 500 ppm) suppresses these oxygenated products and 1- and 3-chlorobutanone again become the primary products, indicating that the O(2) addition reaction to the 1- and 3-butanonyl radicals is becoming reversible. At 500 K and very high O(2) mole fraction (170,000 ppm), a new product channel opens which forms a substantial yield (approximately 20%) of methylvinylketone. Computer modeling of the product yields has been performed to gain an understanding of the overall reaction mechanism in the presence and absence of O(2). The reaction of chlorine atoms with butanone proceeds with a rate constant of 4.0 (+/-0.4) x 10(-11) cm(3) molecule(-1) s(-1) independent of temperature over the range 297-475 K (E(a) = 0 +/- 200 cal mol(-1)). Rate constant ratios of k(CH(2)C(O)C(2)H(5) + Cl(2))/k(CH(2)C(O)C(2)H(5) + O(2)) = 0.027 +/- 0.008, k(CH(3)C(O)CHCH(3) + Cl(2))/ k(CH(3)C(O)CHCH(3) + O(2)) = 0.0113 +/- 0.0011, and k(CH(3)C(O)CH(2)CH(2) + Cl(2))/k(CH(3)C(O)CH(2)CH(2) + O(2)) = 1.52 +/- 0.32 were determined at 297 K in 800-950 Torr of N(2) diluent. In 700-900 Torr of N(2)/O(2) diluent, the major fate of the alkoxy radicals CH(3)C(O)CH(O)CH(3) and OCH(2)C(O)C(2)H(5) is decomposition to give CH(3)C(O) radicals and CH(3)CHO and HCHO and C(O)C(2)H(5) radicals, respectively.

Kinetics and mechanism of the reaction of chlorine atoms with n-pentanal.

The kinetics and mechanism of the reaction Cl + CH3(CH2)3CHO was investigated using absolute (PLP-LIF) and relative rate techniques in 8 Torr of argon or 800-950 Torr of N2 at 295 +/- 2 K. The absolute rate experiments gave k[Cl+CH3(CH2)3CHO] = (2.31 +/- 0.35) x 10(-10) in 8 Torr of argon, while relative rate experiments gave k[Cl+CH3(CH2)3CHO] = (2.24 +/- 0.20) x 10(-10) cm3 molecule(-1) s(-1) in 800-950 Torr of N2. Additional relative rate experiments gave k[Cl+CH3(CH2)3C(O)Cl] = (8.74 +/- 1.38) x 10(-11) cm3 molecule-1 s(-1) in 700 Torr of N2. Smog chamber Fourier transform infrared (FTIR) techniques indicated that the acyl-forming channel accounts for 42 +/- 3% of the reaction. The results are discussed with respect to the literature data and the importance of long range (greater than or equal to two carbon atoms along the aliphatic chain) effects in determining the reactivity of organic molecules toward chlorine atoms.

Rate constants for the reaction of cl with a series of C4 to C6 ketones using the relative rate method.

Rate constants for the reaction of Cl with eight ketones were measured relative to the rate constant of propane in approximately 900 Torr of N2 at ambient temperature. Experiments were carried out in a Pyrex reactor with GC analysis of the consumption of the ketones and propane. Chlorine atoms were generated by irradiation of Cl2 in the initial mixture using a black-light-blue fluorescent lamp. The rate constants determined in these experiments (10-11 cm3 molecule-1 s-1) are: butanone (3.8 +/- 0.3); 2-pentanone (11.6 +/- 1.0); 3-pentanone (8.3 +/- 0.7); 2-hexanone (19.4 +/- 1.9); 3-hexanone (15.3 +/- 1.1); cyclopentanone (10.4 +/- 0.9); 3-methyl-2-butanone (6.2 +/- 0.5); and 4-methyl-2-pentanone (12.8 +/- 1.0). The results for 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, 3-methyl-2-butanone, and 4-methyl-2-pentanone are significantly higher (by a factor of 3 for 2-hexanone) than reported in two previous absolute rate studies. The likely explanation for this discrepancy is discussed.

Kinetics, products, and stereochemistry of the reaction of chlorine atoms with cis- and trans-2-butene in 10-700 Torr of N2 or N2/O2 diluent at 297 K.

The reactions of Cl atoms with cis- and trans-2-butene have been studied using FTIR and GC analyses. The rate constant of the reaction was measured using the relative rate technique. Rate constants for the cis and trans isomers are indistinguishable over the pressure range 10-900 Torr of N2 or air and agree well with previous measurements at 760 Torr. Product yields for the reaction of cis-2-butene with Cl in N2 at 700 Torr are meso-2,3-dichlorobutane (47%), DL-2,3-dichlorobutane (18%), 3-chloro-1-butene (13%), cis-1-chloro-2-butene (13%), trans-1-chloro-2-butene (2%), and trans-2-butene (8%). The yields of these products depend on the total pressure. For trans-2-butene, the product yields are as follows: meso-2,3-dichlorobutane (48%), dl-2,3-dichlorobutane (17%), 3-chloro-1-butene (12%), cis-1-chloro-2-butene (2%), trans-1-chloro-2-butene (16%), and cis-2-butene (2%). The products are formed via addition, addition-elimination from a chemically activated adduct, and abstraction reactions. These reactions form (1) the stabilized 3-chloro-2-butyl radical, (2) the chemically activated 3-chloro-2-butyl radical, and (3) the methylallyl radical. These radicals subsequently react with Cl2 to form the products via a proposed chemical mechanism, which is discussed herein. This is the first detailed study of stereochemical effects on the products of a gas-phase Cl+olefin reaction. FTIR spectra (0.25 cm(-1) resolution) of meso- and DL-2,3-dichlorobutane are presented. The relative rate technique was used (at 900 Torr and 297 K) to measure: k(Cl + 3-chloro-1-butene) = (2.1 +/- 0.4) x 10(-10), k(Cl + 1-chloro-2-butene) = (2.2 +/- 0.4) x 10(-10), and k(Cl + 2,3-dichlorobutane) = (1.1 +/- 0.2) x 10(-11) cm3 molecule(-1) s(-1).

Automotive fuels and internal combustion engines: a chemical perspective.

Commercial transportation fuels are complex mixtures containing hundreds or thousands of chemical components, whose composition has evolved considerably during the past 100 years. In conjunction with concurrent engine advancements, automotive fuel composition has been fine-tuned to balance efficiency and power demands while minimizing emissions. Pollutant emissions from internal combustion engines (ICE), which arise from non-ideal combustion, have been dramatically reduced in the past four decades. Emissions depend both on the engine operating parameters (e.g. engine temperature, speed, load, A/F ratio, and spark timing) and the fuel. These emissions result from complex processes involving interactions between the fuel and engine parameters. Vehicle emissions are comprised of volatile organic compounds (VOCs), CO, nitrogen oxides (NO(x)), and particulate matter (PM). VOCs and NO(x) form photochemical smog in urban atmospheres, and CO and PM may have adverse health impacts. Engine hardware and operating conditions, after-treatment catalysts, and fuel composition all affect the amount and composition of emissions leaving the vehicle tailpipe. While engine and after-treatment effects are generally larger than fuel effects, engine and after-treatment hardware can require specific fuel properties. Consequently, the best prospects for achieving the highest efficiency and lowest emissions lie with optimizing the entire fuel-engine-after-treatment system. This review provides a chemical perspective on the production, combustion, and environmental aspects of automotive fuels. We hope this review will be of interest to workers in the fields of chemical kinetics, fluid dynamics of reacting flows, atmospheric chemistry, automotive catalysts, fuel science, and governmental regulations.

The relationship between gasoline composition and vehicle hydrocarbon emissions: a review of current studies and future research needs.

The purpose of this paper is to review current studies concerning the relationship of fuel composition to vehicle engine-out and tail-pipe emissions and to outline future research needed in this area. A number of recent combustion experiments and vehicle studies demonstrated that reformulated gasoline can reduce vehicle engine-out, tail-pipe, running-loss, and evaporative emissions. Some of these studies were extended to understand the fundamental relationships between fuel composition and emissions. To further establish these relationships, it was necessary to develop advanced analytical methods for the qualitative and quantitative analysis of hydrocarbons in fuels and vehicle emissions. The development of real-time techniques such as Fourier transform infrared spectroscopy, laser diode spectroscopy, and atmospheric pressure ionization mass spectrometry were useful in studying the transient behavior of exhaust emissions under various engine operating conditions. Laboratory studies using specific fuels and fuel blends were carried out using pulse flame combustors, single- and multicylinder engines, and vehicle fleets. Chemometric statistical methods were used to analyze the large volumes of emissions data generated from these studies. Models were developed that were able to accurately predict tail-pipe emissions from fuel chemical and physical compositional data. Some of the primary fuel precursors for benzene, 1,3-butadiene, formaldehyde, acetaldehyde and C2-C4 alkene emissions are described. These studies demonstrated that there is a strong relationship between gasoline composition and tail-pipe emissions.

Application of time-resolved infrared spectral photography to chemical kinetics.

We discuss the application of time-resolved infrared spectral photography to the determination of the time-dependent reactant and product concentrations in the simple chain reaction of chlorine atoms, generated by pulsed photolysis, with ethane-Cl(2) mixtures. The technique and experimental results are discussed in terms of the limitations and advantages of the method for general kinetic studies in the microsecond and submicrosecond time domain.