摘要:

AbstractThis article describes the first direct determination of the rate coefficient for the self‐reaction between two NO3radicals. A laser photolysis technique was used to generate NO3, and time‐resolved decays of NO3were followed after stopping the photolysis. The products of the reaction are inferred to be NO2and O2. The derived rate coefficient at room temperature for the self‐reaction of (2.3 ± 0.8) ×10−16cm3molecule−1s−1is in excellent agreement with the only other data, which were obtained in an indirect study. Consideration is given to the magnitude and influence of secondary chemistry and to the participation of FO in the chemistry of the NO3buildup phase. The studies were conducted over a pressure range of 8 to 100 torr in helium. No clear pressure dependence was observed, and some tentative inferences are drawn both from this result and from the absolute magnitude of the rate coefficient about the mechanism of the reaction. There is apparently no role for the reaction in the chemistry of the atmosphere. © 1993 John W

ISSN:0538-8066    

DOI:10.1002/kin.550251002

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractUsing a relative rate technique the reactions of chlorine and fluorine atoms with CF3CHO have been determined to proceed with rate constants of (1.8 ± 0.4) × 10−12and (2.7 ± 0.1)×10−11cm3molecule−1s−1, respectively. Experiments were performed at 295 ± 2 K and 700 torr total pressure of nitrogen. The results are discussed with respect to the design and interpretation of laboratory studies of the atmospheric chemistry of CFC replacements. © 1993 John Wi

ISSN:0538-8066    

DOI:10.1002/kin.550251003

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractSynthesis of methyl tert‐butyl ether (abbreviated as MTBE) from methanol (MeOH) and tert‐butyl alcohol (TBA) in the liquid phase was studied by using Amberlyst 15 in the H+form as an acid catalyst. Experiments were carried out in a stirred batch reactor at different temperatures (313, 318, and 323 K) under atmospheric pressure.It was found that catalyst sizes and rotation speeds had no significant effects on reaction rates. Mechanism studies showed that three reactions took place simultaneously. It was also found that dehydration of TBA could not be neglected. The experimental concentration profiles with time could be simulated well by simple kinetics. Finally, rate constants could be expressed by Arrhenius equations. © 1993 John Wiley&Sons,

ISSN:0538-8066    

DOI:10.1002/kin.550251004

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rate coefficients for the removal of Cl atoms by reaction with three HCFCs, CF3CHCl2(HCFC‐123), CF3CHFCl (HCFC‐124), and CH3CFCl2(HCFC 141b), were measured as a function of temperature between 276 and 397 K. CH3CF2Cl (HCFC‐142b) was studied only at 298 K. The Arrhenius expressions obtained are:k1= (3.94 ± 0.84)× 10−12exp[−(1740 ± 100)/T] cm3molecule−1s−1for CF3CHCl2(HCFC 123);k2= (1.16 ± 0.41) × 10−12exp[−(1800 ± 150)/T] cm3molecule−1s−1for CF3CHFCl (HCFC 124); andk3= (1.6 ± 1.1) × 10−12exp[−(1800 ± 500)/T] cm3molecule−1s−1for CH3CFCl2(HCFC 141b). In case of HCFC 141b, non‐Arrhenius behavior was observed at temperatures above ca. 350 K and is attributed to the thermal decomposition of CH2CFCl2product into Cl + CH2CFCl. In case of HCFC‐142b, only an upper limit for the 298 K value of the rate coefficient was obtained. The atmospheric significance of these results

ISSN:0538-8066    

DOI:10.1002/kin.550251005

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe thermal reaction of HNCO with NO2has been studied in the temperature range of 623 to 773 K by FTIR spectrometry. Major products measured are CO2and NO with a small amount of N2O. Kinetic modeling of the time resolved concentration profiles of the reactants and products, aided by the thermochemical data of various likely reactive intermediates computed by means of the BAC‐MP4 method, allows us to conclude that the reaction is initiated exclusively by a new bimolecular process:with a rate constant,k1= 2.5 × 1012e−13,100/Tcm3/mols. The well‐known bimolecular reactionis the only strong competitive process in this important reactive system throughout the temperature range studied. Kinetic modeling of NO formation and NO2decay rates gave rise to values ofk10which were in close agreement with literature data. © 1993 John Wiley&So

ISSN:0538-8066    

DOI:10.1002/kin.550251006

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA kinetic study on the basic hydrolysis of cephaloridine atpD= 10.5 was carried out by using the1HNMR technique. Epimerization at H7, a nucleophilic attack of hydroxyl ion on the β‐lactam carbonyl group followed by the release of the pyridine molecule, and isomerization of the double bond at position 3 in the dihydrothiazine ring were the major reactions observed.Based on the results obtained, it should be emphasized that the presence of a pyridine group at 3′ results in a slightly increased formation constant for the exo methylene compound relative to other cephalosporins with different substituents at that position.The activation energy for the epimerization constant and the cleavage of the β‐lactam ring atpD10.5 was 21.2 kcal/mol. © 1993 John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550251007

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rate constant for the reaction of phenyl radical with hydrogen bromide has been measured with the cavity‐ring‐down method at six temperatures between 297 and 523 K. The Arrhenius expression for the H abstraction reaction can be effectively given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_\phi = 10^{ - 10.39 \pm 0.10} {\rm exp[-(551} \pm {\rm 19 +)/T]cm}^{\rm 3} /{\rm s} $$\end{document}. The values of these parameters are similar to those for the H + HBr reaction, but are in sharp contrast to those for alkyl radical reactions. The gross difference between the alkyl radical reactions and the phenyl and H‐atom reactions could be rationalized in terms of the inductive effects of these radicals as measured by Taft's σ* (polar) constants. © 1993 John Wiley&So

ISSN:0538-8066    

DOI:10.1002/kin.550251008

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550251001

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY