摘要:

AbstractIn earlier work on the room temperature oxidation of C2H2by O atoms, two distinct sources of methylene radicals have been identified: (i) direct, primary production via channel 1b of the C2H2+ O reaction, and (ii) delayed formation via the secondary reaction 3 involving the products HCCO and H of the other primary channel 1a:Presently, it was confirmed by a detailed sensitivity analysis that the precise shapes of the resulting total methylene concentration‐versus‐time profiles in C2H2/O systems depend strongly on thek1a/k1bbranching ratio. Along that line, the important parameterk1a/k1bwas determined from relative CH2concentration‐versus‐time profiles measured in a variety of C2H2/O/H systems using Discharge Flow‐Molecular Beam sampling Mass Spectrometry techniques (DF‐MBMS). The data analysis was carried out by deductive kinetic modelling; the method, as applied to profile shapes, is discussed at length. Via this novel, independent approach, the CH2(3B1) yield of the two‐channel C2H2+ O reaction was determined to bek1b/k1= 0.17 ± 0.08. The indicated 2σ error includes possible systematic errors due to uncertainties in the rate constants of other reactions that influence the shapes of the CH2profiles. The present result, which translates to an HCCO yieldk1a/k1= 0.83 ± 0.08, is in excellent agreement with other recent determinations. The above mechanism, with the subsequent reactions that it initiates, also reproduces the measured absolute [C2H2], [O], and [H] profiles with an average accuracy of 5%, thus validating the consistency of the C2H2/O/H reaction model put forward here. © 1994 Joh

ISSN:0538-8066    

DOI:10.1002/kin.550260902

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe kinetics of the reaction of CH3O with NO and the branching ratio for HCHO product formation, obtained as ΓHCHO= (Rate of HCHO formation) / (Rate of CH3O decay), have been studied using a discharge flow reactor. Laser induced fluorescence has been used to monitor the decay of the CH3O radical and the build‐up of the HCHO product. Overall rate constants and product branching ratios were measured at room temperature over the pressure range of 0.72–8.5 torr He. Three reaction mechanisms were considered which differed in the routes of HCHO formation: (i) direct disproportionation; (ii) via an energized collision complex; or (iii) both reaction routes. It has been shown that data on the pressure dependence of the overall rate constant are not sufficient to distinguish between these mechanisms. In addition, an accurate value of Γ HCHO∞is required. Analysis of the available experimental data provided 0.0 and about 0.1 as the lower and upper limit for Γ HCHO∞, respectively. Since the rate constants derived for CH3ONO formation were not sensitive to the value assumed for Γ HCHO∞,k CH 3ONO°= (1.69 ± 0.69) × 10−29cm6molecule−2s−1andk CH 3ONO∞= (2.45 ± 0.31) × 10−11cm3molecule−1s−1could be derived. The rate constant obtained for formaldehyde formation when extrapolated to zero pressure isk HCHO0= (3.15 ± 0.92) ×

ISSN:0538-8066    

DOI:10.1002/kin.550260903

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe reaction of CO 2˙−with bilirubin which is not detectable in homogeneous aqueous medium proceeds almost with diffusion controlled rate in CTAB micellar system. This could be explained on the basis of catalysis caused by the possible electrostatic surface potential of cationic CTAB Micelles. The rate constant for the oxidation of bilirubin by haloperoxyl radicals have been shown to increase with increasing solvent polarity. Although the polarity effect was small, it followed a trend in the expected direction. Micellar effect was not observed in the oxidation reactions when alcohol was present in high concentration. But a small increase in the rate constant was observed when alcohol concentration was lower. © 1994 John Wiley&Sons

ISSN:0538-8066    

DOI:10.1002/kin.550260904

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA regression based model was developed to determine whether highest occupied molecular orbital (HOMO) energies, calculated using Kohn‐Sham orbital density functional theory (DFT), could be used to estimate the OH rate constants of hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs), proposed substitutes for stratospheric O3depleting chlorofluorocarbons. The goodness of fit of the DFT model was compared with a second regression model, derived using recently reported HOMO energies obtained from Hartree Fock theory (HFT). Both models were employed to predict OH rate constants for a number of HFCs and HFEs whose OH rate constants have not been measured, thus providing data on the types of chemical structures that may increase the OH reactivity of the substitute and hence decrease its contribution to global warming. The estimated percent standard errors in the OH rate constant HFT and DFT regression models were 72% and 78%, respectively. The goodness of fits were such that the models can differentiate between two rate constants only when their ratio exceeds about a factor of four. Model results suggest that (1) only a limited number of HFEs will have OH rate constants that are more than an order of magnitude greater than the value for their corresponding HFCs and (2) the strategy of introducing an ether linkage into an HFC to dramatically enhance its reactivity will be most effective for the least fluorinated HFCs. © 1994 John Wiley&Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of Ameri

ISSN:0538-8066    

DOI:10.1002/kin.550260905

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe addition of water vapor has a strong positive effect on the rate of ethane oxidation at 575°C. This effect is attributed to the role of H2O as a third body in the decomposition of H2O2to OH radicals. Carbon tetrafluoride likewise enhances the rate of ethane conversion, although not to the extent realized with H2O. A kinetic model, based on known elementary reactions, adequately accounts for the conversions and selectivities observed as a function of H2O pressure, temperature, contact time, and O2pressure. © 1994 John Wiley&Sons, In

ISSN:0538-8066    

DOI:10.1002/kin.550260906

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe formation yields of selected products of the OH radical‐initiated reactions of toluene,o‐xylene, and 1,2,3,‐trimethylbenzene have been measured in the absence of NOxand in the presence of varying concentrations of NO and NO2. The formation yield ofo‐cresol from toluene increased from 0.123 ± 0.022 in the absence of NOxto 0.160 ± 0.008 for an average NO2concentration of 1.7 × 1014molecule cm3. The formation yield of 2,3‐butanedione fromo‐xylene was 0.092 ± 0.013 in the absence of NOx, and in the presence of NOxdecreased from 0.16 at an average NO2concentration of (7–8) × 1012molecule cm−3to 0.09 at an average NO2concentration of ca. 7 × 1013molecule cm−3. The formation yield of 2,3‐butanedione from 1,2,3‐trimethylbenzene increased from 0.18 in the absence of NOxto 0.444 ± 0.053 in the presence of ca. (0.16–3.6) × 1013molecule cm−3of NO2. These product data are consistent with literature kinetic data showing that the hydroxycyclohexadienyl radicals formed by OH radical addition to the aromatic ring react with both O2and NO2and with the NO2reaction rate constants being ca. 105higher than the O2reaction rate constants at room temperature. Under typical tropospheric conditions the reactions of the hydroxycyclohexadienyl radicals with O2will dominate over their reactions with

ISSN:0538-8066    

DOI:10.1002/kin.550260907

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractReactions of ozone with propene, 1‐butene,cis‐2‐butene,trans‐2‐butene, 2,3‐dimethyl‐2‐butene, and 1,3‐butadiene were carried out in N2and air diluent at atmospheric pressure and room temperature and, by monitoring the formation of the epoxides and/or a carbonyl compound formed from the reactions of O(3P) atoms with these alkenes, the formation yields of O(3P) atoms from the O3reactions were investigated. No evidence for O(3P) atom formation was obtained, and upper limits to O(3P) atom formation yields of<4% for propene,<5% for 1.3‐butadiene, and<2% for the other four alkenes were derived. The reaction of O3with 1,3‐butadiene led to the direct formation of 3,4‐epoxy‐1‐butene in (2.3 ± 0.4)% yield. These data are in agreement with the majority of the literature data and show that O(3P) atom formation is not a significant pathway in O3—alkene reactions, and that epoxide formation only occurs to any significant extent from conjugated diene

ISSN:0538-8066    

DOI:10.1002/kin.550260908

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractGas‐phase elimination reactions of number ofN‐substituted diacetamides have been studied. The rates ofN‐phenyl, 4‐methoxyphenyl, 4‐nitrophenyl, and benzyl diacetamide have been measured between 643–683, 642–693, 673–725, and 555–610 K, respectively. They undergo unimolecular first‐order elimination reactions, for which logA= 12.8, 12.9, 12.8, and 11.0 s−1and Ea= 185.7, 191.4, 193.4, and 143.6 kJ mol−1, respectively. The reactivity of these compounds has been compared with the unsubstituted diacetamide at 600 K. The kinetic data reveals that each of theN‐aryldiacetamides is less reactive than the parent molecule. We attribute this observation to the resonance of the lone pair of electrons on the nitrogen with either the two carbonyl oxygen atoms or with the 6π electrons in the aromatic ring which will result in the stabilization of theN‐aryldiacetamides related to the parent molecules.

ISSN:0538-8066    

DOI:10.1002/kin.550260909

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe tetradentate Schiff‐base ligands,N,N′‐bis(salicylidene)‐ethylenediamine (Salen),N,N′‐bis(salicylidene) butylenediamine (Salbut), andN,N′‐bis(salicylidene)‐o–phenylenediamine, (sal‐o‐phen) are very strongly sorbed by cation exchange resin (Dowex‐50W) with Fe2+ions as a counter ion, forming stable complexes. The kinetics of the catalytic decomposition of H2O2using these complexes was studied in ethanolic medium. The reaction was first‐order with salen and sal‐o‐phen and second‐order with salbut with respect to [H2O2]. The rate of the H2O2decomposition increased either from salen to salbut or from salen to sal‐o‐phen. Also, thek(per g dry resin) values decreased with increasing both the particle size and the degree of resin cross‐linkage. The active species formed at the beginning of the reaction, had an inhibiting effect on the reaction rate. The corresponding activation parameters were calculated from a least‐squares fit of the temperature dependence of the rate constant. A reaction mechanism

ISSN:0538-8066    

DOI:10.1002/kin.550260910

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550260901

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY