Search

Aging of soybean biodiesel at an elevated temperature (90 °C) with aeration, simulating diesel engine fuel system conditions, yielded higher molecular weight materials and increased kinematic visco...

Fuels in modern diesel engine fuel systems are exposed to highly oxidizing conditions, thus it is important to understand their degradation mechanisms. A range of chemical and physical properties was monitored during the oxidation and polymerization of soybean methyl ester biodiesel (B100), a diesel fuel (B0), and their blends (B10, B30) at 90 °C with aeration. The initial rapid oxidation of polyunsaturated fatty acid methyl esters (FAMEs) provided a transient pool of peroxides that led to the formation of aldehydes, ketones, and acids as secondary products. Monounsaturated and saturated FAMEs were oxidized concurrently with polyunsaturated FAMEs in B10, B30, and B100, but only B100 showed significant oxidation reactions continuing after the polyunsaturated FAMEs were depleted. New esters were a major oxidation product, eventually comprising 40–60% of the incorporated oxygen. Carboxylic acids and alcohols react to form esters and water, with vaporization of water driving the equilibrium toward ester forma...

Although significant amounts of polymers associated with adverse health effects in oils are produced during frying, the chemical bonds forming these polymers are not well understood. This study revealed that ester bonds are responsible for the polymerization of soybean oil during frying and heating at 175 °C. The ester value of soybean oil increased during frying up to day 3 of the experiment and slightly decreased on day 4 of the experiment indicating that esterification and hydrolysis concomitantly occurred. The 13C NMR spectra showed further evidence of the formation of ester bonds. This study also examined unidentified chemical bonds in the polymer products, other than ester bonds, with NMR spectroscopy. No NMR signals indicating ether bonds were observed. The NMR study after the reaction of oxidized soybean oil with acetyl chloride clarified assignments of proton signals, confirming some previous assignments, and assigning a new proton signal as an alcohol.

Summary Dual Use Research of Concern (DURC) deals with the unintended consequences of research and development and is particularly acute in the area of drug development. The United States National Science Advisory Board for Biosecurity (NSABB) has defined DURC as "research that, based on current understanding, can be reasonably anticipated to provide knowledge, products, or technologies that could be directly misapplied by others to pose a threat to public health, agriculture, plants, animals, the environment, or materiel” (1). One particular receptor antagonist and glycolate anticholinergic compound (BZ, QNB or 3 -quinuclidinyl benzilate) was stockpiled by the United States as a non-lethal chemical weapon that incapacitates and severely degrades the capability of exposed individuals (2). Given time and medical treatment, combatants and non-combatants exposed to such incapacitating agents could recover without any long-term effects. The purpose of this review is to identify potential new and more potent incapacitating agents based on the structures of BZ or atropine using peer reviewed publications of new pharmaceutical agents. A number of peer reviewed studies have reported on compounds with effects observed at lower concentrations than or comparable to BZ suggesting that these compounds could also be developed as potential chemical incapacitating chemical warfare agents and represent good examples of the principal of Dual Use Research of Concern.

The UV absorption spectra of CF(3)CHO, C(2)F(5)CHO, C(3)F(7)CHO, C(4)F(9)CHO, CF(3)CH(2)CHO, and C(6)F(13)CH(2)CHO were recorded over the range 225-400 nm at 249-297 K. C(x)F(2)(x)(+1)CHO and C(x)F(2)(x)(+1)CH(2)CHO have broad absorption features centered at 300-310 and 290-300 nm, respectively. The strength of the absorption increases with the size of the C(x)F(2)(x)(+1) group. There was no discernible (

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with CF(3)CH(2)C(O)H and CF(3)CH(2)CH(2)OH in 700 Torr of N(2) or air diluent at 296 +/- 2 K. The rate constants determined were k(Cl+CF(3)CH(2)C(O)H) = (1.81 +/- 0.27) x 10(-11), k(OH+CF(3)CH(2)C(O)H) = (2.57 +/- 0.44) x 10(-12), k(Cl+CF(3)CH(2)CH(2)OH) = (1.59 +/- 0.20) x 10(-11), and k(OH+CF(3)CH(2)CH(2)OH) = (6.91 +/- 0.91) x 10(-13) cm(3) molecule(-1) s(-1). Product studies of the chlorine initiated oxidation of CF(3)CH(2)CH(2)OH in the absence of NO show the sole primary product to be CF(3)CH(2)C(O)H. Product studies of the chlorine initiated oxidation of CF(3)CH(2)CH(2)OH in the presence of NO show the primary products to be CF(3)CH(2)C(O)H (81%), HC(O)OH (10%), and CF(3)C(O)H. Product studies of the chlorine initiated oxidation of CF(3)CH(2)C(O)H in the absence of NO show the primary products to be CF(3)C(O)H (76%), CF(3)CH(2)C(O)OH (14%), and CF(3)CH(2)C(O)OOH (or =10%). As part of this work, an upper limit of k(O(3)+CF(3)CH(2)CH(2)OH)2 x 10(-21) cm(3) molecule(-1) s(-1) was established. Results are discussed with respect to the atmospheric chemistry of fluorinated alcohols.

Smog chamber/FTIR techniques were used to study the products and mechanism of the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (CF3(CF2)3CH2CH2OH) in 700 Torr of N2/O2 diluent at 296 K....

Smog chamber/FTIR techniques were used to measure (Cl + n-CxF2x+1CHO, x = 1, 3, 4) = (2.1 ± 0.5) × 10-12 and k(OH + n-CxF2x+1CHO, x = 1, 3, 4) = (6.5 ± 1.2) × 10-13 cm3 molecule-1 s-1 in 700 Torr o...

FTIR smog chamber techniques have been used to show that reaction of CF 3 O 2 radicals with NO proceeds via two channels giving either CF 3 O + NO 2 (5a) or CF 3 ONO 2 (5b) as products. In 700 Torr of N 2 /O 2 diluent at 296 K the branching ratio for CF 3 ONO 2 formation is k 5b /( k 5a + k 5b )=(1.67±0.27)×10 −2 . The CF 3 ONO 2 forming channel is in the fall off regime at pressures of 50 Torr and below, while for pressures above 100 Torr the reaction approaches the high-pressure limit. This behavior is consistent with the predictions of recent master equation calculations [Chem. Rev. 103 (2003) 4577].

The first shed skins from the same clutch of neonate Corn Snakes (Elaphe gutatta gutatta) and the shed skin of conspecific adults were extracted sequentially with hexane, dichloromethane, and methanol. These solvents extracted more mass from neonate shed skins compared to adults. Gas chromatography of the hexane extract, after saponification of the lipids, showed that the percent of cholesterol was greater in shed skins from neonates, whereas many of the fatty acids were found in greater amounts from adults shed skins. These data show that the first shed skin of Corn Snakes is biochemically different from adults.

The UVand IR spectra of CxF2x+1CHO (x = 1–4) were investigated using computational and experimental techniques. CxF2x+1CHO (x =1 – 4) have broad UV absorption features centered at 300–310 nm. The maximum absorption cross-section increases significantly and shifts slightly to the red with increased length of the CxF2x+1 group: CF3CHO, 3.10 � 10 � 20 (300 nm); C2F5CHO, 6.25 � 10 � 20 (308 nm); C3F7CHO, 8.96 � 10 � 20 (309 nm); and C4F9CHO, 10.9 � 10 � 20 (309 nm). IR spectra for CxF2x+1CHO were recorded, calculated, and assigned. Results are discussed with respect to the literature data and to the atmospheric fate of CxF2x+1CHO. # 2004 Elsevier B.V. All rights reserved.

Smog chamber/FTIR techniques were used to study the gas-phase reaction of C2F5C(O)O2 with HO2 radicals in 100–700 Torr of air, or O2, diluent at 296 K. The reaction proceeds by two pathways leading to formation of C2F5C(O)OH and O3 in a yield of 24 ± 4% and C2F5C(O)O radicals, OH radicals and O2 in a yield of 76 ± 4%. The gas phase reaction of CnF2n + 1C(O)O2 with HO2 radicals offers a potential explanation for at least part of the observed environmental burden of fluorinated carboxylic acids, CnF2n + 1C(O)OH. As part of this work an upper limit for the rate constant of reaction of Cl atoms with C2F5C(O)OH at 296 K was determined; k(Cl + C2F5C(O)OH)

Smog chamber/FTIR techniques were used to measure k (Cl + C 2 F 5 CHO)=(1.96 ± 0.28) × 10 −12 and k (OH + C 2 F 5 CHO)=(5.26 ± 0.80) × 10 −13 cm 3 molecule −1 s −1 in 700 Torr of N 2 or air at 296 ± 2 K. The Cl initiated oxidation of C 2 F 5 CHO in the presence of NO in air diluent gave COF 2 , CF 3 ONO 2 , and C 2 F 5 C(O)O 2 NO 2 in molar yields of 180 ± 19%, 6.1 ± 0.6%, and 1.0 ± 0.3%, respectively. The IR spectrum for C 2 F 5 C(O)O 2 NO 2 is reported. Results are discussed with respect to the potential for the atmospheric degradation of fluorinated aldehydes, C n F 2 n +1 CHO, to contribute to the observed environmental burden of fluorinated carboxylic acids, C n F 2 n +1 C(O)OH.

The synthesis, IR spectrum, and first-principles characterization of CF3CH(ONO)CF3 as well as its use as an OH radical source in kinetic and mechanistic studies are reported. CF3CH(ONO)CF3 exists in two conformers corresponding to rotation about the RCONO bond. The more prevalent trans conformer accounts for the prominent IR absorption features at frequencies (cm−1) of 1766 (NO stretch), 1302, 1210, and 1119 (CF stretches), and 761 (ONO bend); the cis conformer contributes a number of distinct weaker features. CF3CH(ONO)CF3 was readily photolyzed using fluorescent blacklamps to generate CF3C(O)CF3 and, by implication, OH radicals in 100% yield. CF3CH(ONO)CF3 photolysis is a convenient source of OH radicals in the studies of the yields of CO, CO2, HCHO, and HC(O)OH products which can be difficult to measure using more conventional OH radical sources (e.g., CH3ONO photolysis). CF3CH(ONO)CF3 photolysis was used to measure k(OH + C2H4)/k(OH + C3H6) = 0.29 ± 0.01 and to establish upper limits of 16 and 6% for the molar yields of CO and HC(O)OH from the reaction of OH radicals with benzene in 700 Torr of air at 296 K. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 159–165, 2003

The photolysis of Cl2 molecules in the presence of toluene and oxygen, at levels of ∼1014 radicals/cm-3, initiates a sequence of chemical reactions that rapidly produce an aerosol. Size distributions of the aerosol particles are examined, using a scanning mobility particle sizer, as a function of time, photolysis energy, the initial concentrations of toluene and chlorine, and of added NO and HO2. The number of particles and the volume of aerosol both exhibit a steep nonlinear increase as the initial chlorine atom level is raised. Surprisingly, the number of particles displays a strong inverse dependence on the initial toluene concentration, whereas the aerosol volume remains nearly unaffected by toluene level. Kinetic measurements of particle formation made using a flow reactor reveal an incubation period after initiation of the Cl + C6H5CH3 reaction, followed by steep increases in particle number and volume. The particle number rapidly reaches a plateau, whereas the aerosol volume continues to increase w...

There is growing interest in the use of a nonthermal plasma combined with a catalyst for NO x removal from diesel engine exhaust streams. Such exhaust streams contain excess oxygen (typically 6-10%), low concentrations of hydrocarbons (typically 100-1000 ppm), and significant concentrations of water (typically 5-12%). Conversion of NO x to environmentally acceptable compounds, without requiring a scrubber or an added reductant, is the desired end result. In our research we observe the formation of substantial amounts of methyl nitrate (CH 3 ONO 2 ) by the plasma discharge. Since similar compounds have been proposed as reaction intermediates in NO x removal, tests were performed to elucidate the effect of CH 3 ONO 2 in the plasma-catalyst system. CH 3 ONO 2 was prepared and added to the gas blend on test equipment simulating a diesel exhaust gas. A dielectric barrier plasma discharge was followed by a zeolite-based catalyst. Methyl nitrate introduced upstream of the plasma discharge is largely unreacted upon passing through the plasma. CH 3 ONO 2 arriving at the catalyst is converted to methanol and NO 2 . While methyl nitrate was shown to be formed in this system, it is not a significant intermediate in the mechanism of conversion of NO x to nitrogen.

In recent years there have been numerous reports of an association between daily increases in particle air pollution (PM{sub 10}) and daily increases in mortality and morbidity. Despite these reports, there continue to be unresolved issues with these studies, including the issue of a plausible biological mechanism by which small increases in daily particle levels could cause adverse human health effects. Chemical characterization of particles is a critical step in testing any biological mechanism. The authors have characterized gas-phase material associated with particles from various sources and found that measurable amounts of nitric oxide (NO) can be thermally released from these particles. NO is well-known to be an effective vasodilating agent at very low concentrations. In this work, release of NO from four NIST reference materials, two ambient air particulate samples, and two diesel particulate samples was quantified after heating the samples for 1 hr. The amount of NO originating from particles depends on the temperature used to evolve this gas. NO levels ranged from 0.005 ng of NO/mg of sample at 37 C to 1900 ng of NO/mg of sample at 140 C. These experiments demonstrate that nitric oxide can be released from some particles at physiological temperatures (37more » C).« less

Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(•) radicals. Pulse radiolysis experiments gave σ(C6H5O(•))235 nm = (3.82 ± 0.48) × 10-17 cm2 molecule-1, k(C6H5O(•) + NO) = (1.88 ± 0.16) × 10-12, and k(C6H5O(•) + NO2) = (2.08 ± 0.15) × 10-12 cm3 molecule-1 s-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(•) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(•) + O2) < 5 × 10-21 cm3 molecule-1 s-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NOx. Density functional calculations and gas chromatography−mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(•) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10-10], several chlorophenols [k(Cl + 2-c...

The products of the self-reaction of methylperoxy radicals have been determined at 296 K in a 140-L chamber using continuous ultraviolet photolysis with FTIR detection. The branching fraction for the reaction channel giving methoxy radicals is found to be (41 ± 4)%, in good agreement with two earlier studies but somewhat higher than the most recent investigations. No evidence was found for the production of CH3OOCH3 (yield

About 15 × 106 lbs of paint sludge, produced every year at Ford plants, is disposed of in landfills. An economical alternative to this disposal method, which reclaims or recycles components of paint sludge, is highly desirable to preserve valuable natural resources. Here, we describe an alternative to landfill disposal whereby paint sludge is converted into ceramic composites that can be used as reinforcing materials. The conversion of paint sludge to ceramic composite, I/N2/600, is achieved by pyrolysis under a nitrogen atmosphere. Two additional composites, labeled I/N2/1000 and I/NH3/1000, respectively, are prepared by sintering I/600 at 1000 °C under N2 and NH3. All three composites contain crystalline CaTiO3, BaTiO3, TiO2, amorphous alumina, and carbon. I/NH3/1000 contains an additional crystalline phase of titanium nitride. The application of these composites as reinforcing materials is demonstrated in the fabrication of representative metal matrix composites (MMC's) and reinforced plastic components.

One hundred and three in-use vehicles, identified as high hydrocarbon and/or carbon monoxide emitters by remote sensing and roadside visual, underhood checks during a 1995 South Coast Air Quality Management District program, were tested on the IM240 cycle using a transportable dynamometer. Seventy-one of these vehicles were repaired as part of the program and were retested. Seventeen vehicles in the fleet initially emitted visible smoke from the tailpipe and were classified as "smokers". The fleet ranged in age from 6 to 22 years, with a median age of 12.3 years. Exhaust HC, CO, NOx, and particulate emissions (PM-10) were measured. PM-10 mass and the elemental and carbonaceous composition of the particulate matter were determined. The average fleet PM-10 emission rate was 0.138 g/mi, while the average emission rate for smokers was 0.395 g/mi. It was concluded that the casual observation of smoking vehicles was not very successful in identifying high PM-10 emitting vehicles. The particulate matter composition was primarily carbonaceous, with a variable distribution between the elemental and organic carbon fractions, and showed no significant difference in the percent organic carbon fraction between smokers and non-smokers. The PM composition differed, on average, between pre-repair and post-repair samples. The effect of the California Smog Check repair program on PM emission rates could not be evaluated due to concerns regarding the effect of vehicle conditioning on these measurements.

Real-time kinetic measurements are reported for the Cl + CH3CO CH2CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10–200 torr and a temperature range of 215–353 K. Within experimental error the rate constant under these conditions is k5a = (1.8 ± 0.5) × 10−10 cm3 s−1. We have also examined the Cl + CH2CO reaction and found it to have a rate constant of k6 = (2.5 ± 0.5) × 10−10 cm3 s−1 independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421–429, 1997.

A relative rate technique has been used to study the title reaction over the pressure range 100–700 Torr of air at 296 ± 2 K. Four different reference compounds (13CO, CH4, CH2FCl, and CD4) were used. Using k(CF3O + CH4) = (2.2 ± 0.2) × 10−14 cm3 molecule−1 s−1 a rate constant of k(CF3O + O3) = (1.5 ± 0.5) × 10−14 cm3 molecule−1 s−1 was derived, quoted errors reflect statistical and potential systematic errors. There was no observable effect of diluent pressure over the range 100–700 Torr. As part of the present work the rate constant for reaction of CF3O radicals with CH2FCl was determined to be (1.2 ± 0.2) × 10−14 cm3 molecule−1 s−1. Implications for the atmospheric chemistry of CF3O radicals are discussed.

The interactions between paint/adhesive polymers and metal surfaces that are critical for adhesion have been studied theoretically. This study used zinc oxide as a model of a galvanized steel surface, and ammonia, water, and ethylene as models for amino, hydroxy, and unsaturated functionalities in paint/adhesive polymers. Ab initio molecular orbital calculations were carried out on zinc oxide and zinc oxide dimer. Geometries were optimized at the HF/3-21G level and relative energies were calculated by CASSCF/3-21G and by MP2 with the DZP basis set of Wachters and Hay. Ethylene forms a stable complex with zinc oxide dimer that has a stabilization energy of 24.9 kcal/mol. Insertion of ethylene into zinc oxide dimer to form a stable six-membered ring adduct occurs with a surprisingly low activation energy of 8.8 kcal/mol. The binding energy of ammonia with zinc oxide dimer is 38.5 kcal/mol and the activation energy for insertion of ammonia forming covalent Zn-NH2 and O-H bonds is calculated to be 9.6 kcal/mo...

The UV absorption spectrum and kinetics of the self reaction of CH 3 OCH 2 O 2 at 298 K have been studied using both the modulated photolysis of Cl 2 /CH 3 OCH 3 /O 2 /N 2 mixtures and the pulse radiolysis of SF 6 /CH 3 OCH 3 /O 2 mixtures. The spectrum, characterized in the range 200-290 nm, is in good agreement with the single published determinations. The observed second-order removal kinetics of CH 3 OCH 2 O 2 , k 5obs , were found to be sensitive to both the variation of total pressure (17-760 Torr) and the composition of the reaction mixtures: 2CH 3 OCH 2 O 2 →2CH 3 OCH 2 O+O 2 (5a); →CH 3 OCHO+CH 3 OCH 2 OH+O 2 (5b)

Fourier transform infrared spectroscopy, was used to identify CH 3 OCHO and CH 3 OCH 2 OOH as products of the gas-phase reaction of CH 3 OCH 2 O 2 radicals with HO 2 radicals. At 700 Torr and 295 ± 2 K, branching ratios of k 1a / k 1 = 0.53 ± 0.08 and k 1b / k 1 = 0.40 ± 0.04 were established. Quoted errors are 2 standard deviations together with our estimate of systematic uncertainties. (CH 3 OCH 2 O 2 +HO 2 →CH 3 OCH 2 OOH+O 2 (1a), CH 3 OCH 2 O 2 +HO 2 →CH 3 OCHO+O 2 +H 2 O (1b).) This result is discussed with respect to previous literature data and to computer models of atmospheric chemistry. As part of this work, the rate constants for the reaction of Cl atoms with CH 3 OCH 2 OOH and CH 3 OCHO were determined to be (6.1 ± 0.3) × 10 −11 and (1.4 ± 0.1) × 10 −12 cm 3 molecule −1 s −1 , respectively.

Substantial concentrations (typically 10–100 ng/l) of trifluoroacetic acid (TFA) have been reported in contemporary saltwater and freshwater. It is well established that TFA is produced as the result of industrial activities. It is unclear whether there are any significant natural sources of this compound. To provide insight into the likely magnitude of possible natural sources of TFA we collected five samples of pre-industrial (>2000 year old) freshwater from Greenland and Denmark; there was no detectable TFA (

Particles from the exhaust of diesel-powdered vehicles are of concern because these particles contain carcinogenic compounds. Organic solvent extracts of these particles are mutagenic in the Ames ansay using strains TA98 and TA100. We wanted to know whether TA102, a strain that a sensitive to oxidative mutagens, could detect these types of compounds in methylene chloride extracts of diesel particles Approximately 47% of the mutagenicity applied to the column was recovered

The ultraviolet absorption spectrum of CH 2 FO 2 radicals and the kinetics and mechanism of their self-reaction have been studied in the gas phase at 298 K. Two techniques have been used: pulse radiolysis UV absorption to measure the spectrum and kinetics and long path length Fourier transform infrared spectroscopy (FTIR) to identify and quantify the reaction products. Absorption cross sections were quantified over the wavelenght range 220-300 nm

Effective bacterial control in cooling-tower systems requires accurate and timely methods to count bacteria. Plate-count methods are difficult to implement on-site, because they are time- and labor-intensive and require sterile techniques. Several field-applicable methods (dipslides, Petrifilm, and adenosine triphosphate [ATP] bioluminescence) were compared with the plate count for two sample matrices--phosphate-buffered saline solution containing a pure culture of Pseudomonas fluorescens and cooling-tower water containing an undefined mixed bacterial culture. For the pure culture, (1) counts determined on nutrient agar and plate-count agar (PCA) media and expressed as colony-forming units (CFU) per milliliter were equivalent to those on R2A medium (p = 1.0 and p = 1.0, respectively); (2) Petrifilm counts were not significantly different from R2A plate counts (p = 0.99); (3) the dipslide counts were up to 2 log units higher than R2A plate counts, but this discrepancy was not statistically significant (p = 0.06); and (4) a discernable correlation (r2 = 0.67) existed between ATP readings and plate counts. For cooling-tower water samples (n = 62), (1) bacterial counts using R2A medium were higher (but not significant; p = 0.63) than nutrient agar and significantly higher than tryptone-glucose yeast extract (TGE; p = 0.03) and PCA (p < 0.001); (2) Petrifilm counts were significantly lower than nutrient agar or R2A (p = 0.02 and p < 0.001, respectively), but not statistically different from TGE, PCA, and dipslides (p = 0.55, p = 0.69, and p = 0.91, respectively); (3) the dipslide method yielded bacteria counts 1 to 3 log units lower than nutrient agar and R2A (p < 0.001), but was not significantly different from Petrifilm (p = 0.91), PCA (p = 1.00) or TGE (p = 0.07); (4) the differences between dipslides and the other methods became greater with a 6-day incubation time; and (5) the correlation between ATP readings and plate counts varied from system to system, was poor (r2 values ranged from < 0.01 to 0.47), and the ATP method was not sufficiently sensitive to measure counts below approximately 10(4) CFU/mL.

Ab initio MO methods have been used to study the structures and energetics of dicyandiamide, [(NH2)2CNCN], its isomers, protonated species, radical anions, transition structures for internal conformational change and transition structures for isomerization. Structures were optimized at the HF/STO-3G, HF/3–21G and HF/6–31G* levels; selected barrier heights for smaller analogues were also computed at the MP4SDTQ/6–31G* level. The most stable isomer of dicyandiamide has the cyano group on the imine nitrogen [1, (NH2)2CNCN]; the other isomer [2, HNC(NH2)NHCN] lies 12.8 kcal mol−1 higher. Inversion at the imino nitrogen proceeds by a linear, in plane process with a barrier of 32.5 kcal mol−1. The amino rotation barriers are 19 kcal mol−1 (single NH2) and 40 kcal mol−1 (both NH2 in a conrotaory or a disrotatory fashion; if the NH2 groups are allowed to pyramidalize the disrotatory barrier drops to 20 kcal mol)−1. Protonation occurs preferentially on the imine nitrogen (PA = 219.7 kcal mol−1 for 1); the proton affinities PA of the amino nitrogens are 25–30 kcal mol−1 lower. Isomerization between 2 and 1 would go via a 1,3-sigmatropic hydrogen shift, but the barrier is high (48.3 kcal mol−1); protonation reduces the hydrogen shift barrier by ca 15 kcal mol−1. However, the most likely mechanism for isomerization involves protonation of the imine nitrogen in 2 followed by deprotonation of the cyano-substituted nitrogen to form 1, circumventing the energetically costly 1,3-sigmatropic hydrogen shift. When an electron is transferred to dicyandiamide, a sizeable fraction of the resonance stabilization of the guanidine moiety is lost.

The kinetics of the reactions of Cl atoms with CH3ONO and CH3ONO2 have been studied using relative rate techniques. In 700 Torr of nitrogen diluent at 295 ± 2K, k(Cl + CH3ONO) = (2.1 ± 0.2) × 10−12 and k(Cl + CH3ONO2) = (2.4 ± 0.2) × 10−13 cm3 molecule−1 s−1. The result for k(Cl + CH3ONO2) is in good agreement with the literature data. The result for k(Cl + CH3ONO) is a factor of 4.5 lower than that reported previously. It seems likely that in the previous study most of the loss of CH3ONO which was attributed to reaction with Cl atoms was actually caused by photolysis leading to an overestimate of k(Cl + CH3ONO). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 357–359, 1999

The mechanisms for the Cl-initiated and OH-initiated atmospheric oxidation of t-butyl alcohol (TBA), methyl t-butyl ether (MTBE), and dimethyl ether (DME) have been determined. For TBA the only products observed are equimolar amounts of H 2 CO and acetone, and its atmospheric oxidation can be represented by (7), (CH 3 ) 3 COH+NP+OH→H 2 CO+((CH 3 ) 2 CO+HO 2 +NO 2 (7). The mechanism for the atmospheric oxidation of DME is also straight forward, with the only observable product being methyl formate, (CH 3 )OCH 3 +NO+OH→HCOOCH 3 +NO 2 +HO 2 (8). The mechanism for the atmospheric oxidation of MTBE is more complex, with observable products being t-butyl formate (TBF) and H 2 CO. Evidence is presented also for the formation of 2-methoxy-2-methyl propanal (MMP), which is highly reactive and presumably oxidized to products. The atmospheric oxidation of MTBE can be represented by (9) and (10), CH 3 OC(CH 3 ) 3 +NO+OH→0.6HCOOC((CH 3 ) 3 +0.4CH 3 OC(CH 3 ) 2 CHO+HO 2 +NO 2 (9); CH 3 OC(CH 3 ) 2 CHO+OH+2NO→CO 2 +H 2 CO+(CH 3 ) 2 HO 2 +2NO 2 (10). In terms of atmospheric reactivity, DME, TBA and MTBE all compare favorably with methanol. In terms of rate of reaction in the atmosphere, DME, MTBE, and TBA are 1.4, 0.40 and 0.28 times as reactive as CH 3 OH towards OH on a per carbon basis. With regard to chemistry, atmospheric oxidation of CH 3 OH yields highly reactive H 2 CO as the sole carbon-containing products. In contrast, only 25% of the carbon in TBA is converted to H 2 CO, with the balance yielding unreactive acetone. For DME, all the carbon is converted to methyl formate which is unreactive. Finally, for MTBE, 60% is converted to unreactive TBF while the remaining 40% produces highly reactive MMP. Final assessment of the impact of these materials on the atmopheric reactivity of vehicle emissions requires the determination of their emissions rates under realistic operating conditions

The authors sought to detect S9-activated mutagens in diesel-exhaust particle extracts by fractionating extracts using high-performance liquid chromatography (HPLC) and carrying out Ames assays (strains TA98 and TA100) with and without S9 mix on the eight fractions obtained thereby. S9 activation of the fraction containing unsubstituted and alkyl-substituted polycyclic aromatic hydrocarbons (PAH) was at the limits of detectability for strain TA100 and undetectable for TA98. There was only one fraction that showed S9 activation; it was 20-fold more active with S9 mix. Six other fractions were strongly direct-acting and showed no enhancement of activity with S9 mix. The S9-activated mutagens detected when concentrated in a chromatographic fraction could not be detected in unfractionated extracts because the direct-acting mutagenicity of the other components dominated. They were unable to identify the indirect-acting mutagens from GC-MS data.

The atmospheric reactivity of diethyl sulfate (DES) has been investigated. Upper limits to the rate constants (in cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}) for the homogeneous gas-phase reactions of DES with O{sub 3}, NH{sub 3}, and H{sub 2}O have been determined by FTIR spectroscopy and are 12 years with respect to ozone. With the possible exception of its reaction with water, these results indicate that the atmospheric fate of DES within an urban air parcel is not determined by its homogeneous gas-phase reactions with any of the atmospheric species studied. No evidence has been found for the formation of DES or related compounds during the ozonolysis of olefins in the presence of SO{sub 2} and ethanol.

The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with peroxyacetylnitrate (PAN), peroxypropionylnitrate (PPN), methylhydroperoxide, formic acid, acetone and butanone. Decay rates of these organic species were measured relative to one or more of the following reference compounds; ethene, ethane, chloroethane, chloromethane, and methane. Using rate constants of 9.29×10−11, 5.7×10−11, 8.04×10−12, 4.9×10−13, and 1.0×10−13 cm3 molecule−1 sec−1 for the reaction of Cl atoms with ethene, ethane, chloroethane, chloromethane, and methane respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: PAN

Molecular orbital calculations have been used to model the interfacial reactions that occur during bond formation of epoxy adhesives to galvanized steel. The theoretical calculations were applied to interfacial reactions of generic dicyandiamide-crosslinked epoxy adhesives on zinc surfaces. Semi-empirical MNDO molecular orbital calculations were used to model the reduction reactions. The calculations were used to predict the most stable tautomer of dicyandiamide as well as to suggest the structure of the most likely zinc-dicyandiamide reduction products. The results of the calculations are consistent with infrared spectroscopic studies of dicyandiamide reduction on zinc surfaces that suggest the formation of carbon-nitrogen multiply bonded moieties. An MNDO geometry optimization of dicyandiamide suggests that one tautomeric form of dicyandiamide, the diamino form, is the most stable structure by about 9.3 kcal/mol. The optimized geometry of the diamino form of dicyandiamide is nearly planar, suggesting th...

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the Z and E isomers of CF3CF=CHF, which we refer to as CF3CF=CHF(Z) and CF3CF=CHF(E). The rate constants k(Cl + CF3CF=CHF(Z)) = (4.36 +/- 0.48) x 10-11, k(OH + CF3CF=CHF(Z)) = (1.22 +/- 0.14) x 10-12, and k(O3 + CF3CF=CHF(Z)) = (1.45 +/- 0.15) x 10-21 cm3 molecule-1 s-1 were determined for the Z isomer of CF3CF=CHF in 700 Torr air diluent at 296 +/- 2 K. The rate constants k(Cl + CF3CF=CHF(E)) = (5.00 +/- 0.56) x 10-11, k(OH + CF3CF=CHF(E)) = (2.15 +/- 0.23) x 10-12, and k(O3 + CF3CF=CHF(E)) = (1.98 +/- 0.15) x 10-20 cm3 molecule-1 s-1 were determined for the E isomer of CF3CF=CHF in 700 Torr air diluent at 296 +/- 2 K. Both the Cl-atom and OH-radical-initiated atmospheric oxidation of CF3CF=CHF give CF3C(O)F and HC(O)F in molar yields indistinguishable from 100% for both the Z and E isomer. CF3CF=CHF(Z) has an atmospheric lifetime of approximately 18 days and a global warming potential (100 year time horizon) of approximately 6. CF3CF=CHF(E) has an atmospheric lifetime of approximately 10 days and a global warming potential (100 year time horizon) of approximately 3. CF3CF=CHF has a negligible global warming potential and will not make any significant contribution to radiative forcing of climate change.

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with ethylene glycol diacetate, CH3C(O)O(CH2)2OC(O)CH3, in 700 Torr of N2/O2 diluent at 296 K. The rate constants measured were k(Cl + CH3C(O)O(CH2)2OC(O)CH3) = (5.7 +/- 1.1) x 10(-12) and k(OH + CH3C(O)O(CH2)2OC(O)CH3) = (2.36 +/- 0.34) x 10(-12) cm3 molecule-1 s-1. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the absence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)CH2OC(O)CH3, CH3C(O)OC(O)H, and CH3C(O)OH. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the presence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)H and CH3C(O)OH. The CH3C(O)OCH2O* radical is formed during the Cl atom initiated oxidation of ethylene glycol diacetate, and two loss mechanisms were identified: reaction with O2 to give CH3C(O)OC(O)H and alpha-ester rearrangement to give CH3C(O)OH and HC(O) radicals. The reaction of CH3C(O)OCH2O2* with NO gives chemically activated CH3C(O)OCH2O* radicals which are more likely to undergo decomposition via the alpha-ester rearrangement than CH3C(O)OCH2O* radicals produced in the peroxy radical self-reaction.

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C(x)F(2)(x)(+1)C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O(2)/N(2) diluent at 298 +/- 3 K. A competition is observed between reaction with O(2) to form n-C(x)()F(2)(x)()(+1)C(O)O(2) radicals and decomposition to form n-C(x)F(2)(x)(+1) radicals and CO. In 700 Torr O(2)/N(2) diluent at 298 +/- 3 K, the rate constant ratio, k(n-C(x)F(2)(x)(+1)C(O) + O(2) --> n-C(x)F(2)(x)(+1)C(O)O(2))/k(n-C(x)F(2)(x)(+1)C(O) --> n-C(x)F(2)(x)(+1) + CO) = (1.30 +/- 0.05) x 10(-17), (1.90 +/- 0.17) x 10(-19), (5.04 +/- 0.40) x 10(-20), and (2.67 +/- 0.42) x 10(-20) cm(3) molecule(-1) for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O(2) accounts for 99%, 50%, 21%, and 12% of the loss of n-C(x)F(2)(x)(+1)C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C(x)F(2)(x)(+1)C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.