摘要:

AbstractThe rates of gas‐phase elimination reactions ofN‐benzoyl andN‐acetyl‐propanamide andN‐benzoyl andN‐acetyl‐2‐methylpropanamide are measured and discussed. They undergo unimolecular first‐order elimination reactions. The reactivities ofN‐benzoylamides have been compared with each other and with those ofN‐acetylamides. The kinetic data together with the product analysis reveals that, the statistical factor of the availability of β‐hydrogen atoms for elimination as well as steric factor are obscured by polar factor in gas‐phase elimination reactions ofN‐benzoylamides while the statistical factor rather than electronic effect operates in each ofN‐acetylamide

ISSN:0538-8066    

DOI:10.1002/kin.550270102

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of oxidation of ethanol by cerium(IV) in presence of ruthenium(III) (in the order of 10−7mol dm−3) in aqueous sulfuric acid media have been followed at different temperatures (25–40°C). The rate of disappearance of cerium(IV) in the title reaction increases sharply with increasing [C2H5OH] to a value independent of [C2H5OH] over a large range (0.2–1.0 mol dm−3) in which the rate law conforms to:\documentclass{article}\pagestyle{empty}\begin{document}$$ -2.303\frac{{d\log [{\rm Ce}^{{\rm IV}}]}}{{dt}} = k_{obsd} = (k_c + k_d [{\rm H}^{\rm + }]^{ - 1})[{\rm Ru}]_T $$\end{document}where [Ru]Tgives the total ruthenium (III) concentration. The values of 10−3kcand 10−3kdare 3.6 ± 0.1 dm3mol−1s−1and 3.9 ± 0.2 s−1, respectively, at 40°C,I= 3.0 mol dm−3. The proposed mechanism involves the formation of ruthenium(III)−substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)−substrate complex followed by the rapid red‐ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(IV) rapidly. The mechanism is consistent with the existence of the complexes RuIII· (C2H5OH) and RuIII· (C2H5O−) and both are kinetically active. The overall bisulphate dependence conforms to:kobsd=A[Ru]T/{1 + C[HSO4−]} whereA= 2.2 × 104dm3mol−1s−1,C= 1.3 at 40°C, [H+] = 0.5 mol dm−3, andI= 3.0 mol dm−3. The observations are consistent with the Ce(SO4)2as the kinetica

ISSN:0538-8066    

DOI:10.1002/kin.550270103

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of the solvolysis of the hydrophobic ion, Co(4‐t‐Bupy)4Cl2+, have been followed in mixtures of water with co‐solvents having a hydrophilic tendency, ethane‐1,2‐diol and 2‐methoxyethanol. The variation of In(rate constant) with the reciprocal of the dielectric constant is nonlinear for both co‐solvents. The enthalpy and the entropy of activation are rather insensitive to changes in the solvent composition in both mixtures, but low maxima may exist at mol fractions of co‐solvent Ca. 0.10–0.20. The application of a Gibbs energy cycle to the process of the initial state going to the transition state suggest that, in water‐rich conditions, the increase in the stability of the emergent solvated CoIIIion in the transition state relative to the increase in the stability of Co(4‐t‐Bupy)4Cl2+in the initial state as the co‐solvent content rises is greater for 2‐methoxyethanol than for ethane‐1,2‐di

ISSN:0538-8066    

DOI:10.1002/kin.550270104

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe rate constant for the reaction of the hydroxyl radical with 1,2,2‐trifuoroethane has been determined over the temperature range 278–323 K using a relative rate technique. The results provide a value ofk(OH + CH2FCHF2) = 2.65 × 10−12exp(−1542 ± 500/T) cm3molecule−1s−1based onk(OH + CH3CCl3) = 1.2 × 10−12exp(−1400 ± 200/T) cm3molecule−1s−1for the rate constant of the reference reaction. The chlorine atom initiated photooxidation of CH2CHF2was investigated from 255 to 330 K and as a function of O2pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. The major carbon‐containing products were CHFO and CF2O suggesting that the alkoxy radicals CH2FCF2O and CHF2CHFO, formed in the reaction, react predominantly by carbon‐carbon bond cleavage. The results indicate that formation of CHF2CFO from the reaction of CHF2CHFO radicals with O2will be unimportant under all atmospheric conditions.

ISSN:0538-8066    

DOI:10.1002/kin.550270105

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe consecutive reactions of (CH3)2Si(OC2H5)2and CH3Si(OC2H5)3with methoxide ions were investigated in methanol solutions. The reverse transesterification reactions with ethoxide ions could be neglected in both cases since the concentration of ethoxide in methanol solution was assumed to be low due to the fast equilibrium reaction C2H5O−+ CH3OH ⇌ C2H5OH + CH3O−. The progress of the reactions was followed by monitoring the formation of ethanol with a Fourier‐transform infrared spectrometer. All rate constants were determined at 295 K. The reactions between the dialkoxydimethylsilanes and methoxide ions were assumed to consist of two consecutive steps that can be represented by the net reaction; (CH3)2Si(OC2H5)2+ 2CH3O−→ (CH3)2Si(OCH3)2+ 2C2H5O−. The two consecutive rate constants were established as 1.93 ± 0.12M−1s−1and 1.00 ± 0.12M−1s−1, respectively. The consecutive rate constants for the reactions between the trialkoxymethylsilanes and methoxide ions can be written according to the total reaction; CH3Si(OC2H5)3+ 3CH3O−→ CH3Si(OCH3)3+ 3C2H5O−. The three rate constants corresponding to each consecutive step were established as 1.12 ± 0.09 M−1s−1, 0.82 ± 0.10 M−1s−1, and 0.51 ± 0.06 M−1s−

ISSN:0538-8066    

DOI:10.1002/kin.550270106

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reactions of secondary alicyclic amines with the title substrate (PDTC) are subjected to a kinetic study in 44 wt.% aqueous ethanol, 25.0°C, ionic strength 0.2 M (KCl). Pseudo‐first‐order rate coefficients (kobs) are found under amine excess. Linear plots of [N]/kobsagainst 1/[N], whereNis the free amine, are obtained for the reactions with piperidine, piperazine, 1‐(2‐hydroxyethyl)piperazine, and morpholine. The reaction with 1‐formylpiperazine exhibits a linear plot ofkobsagainst [N]2. These results are interpreted through a mechanism consisting of two tetrahedral intermediates: a zwitterionic (T±) and an anionic (T−), where the amine catalyzed proton transfer fromT±toT−is partially rate determining for the four former reactions and is fully rate determining for the reaction of 1‐formylpiperazine. The rate microcoefficients involved in the reaction scheme are either determined experimentally or estimated. Comparison with the corresponding microcoefficients reported for the same reactions in water reveals that the rate coefficient for formation ofT±from reactants (k1) is smaller and that for the reversal of this (k−1) is larger in aqueous ethanol compared to water, in agreement with the expected structure of the corresponding transition state.Bronsted‐type plots are obtained fork1,k−1, and K1(=k1/k−1) with slopes ca. 0.4, −0.6, and 1.0, respectively. Comparison of the present stepwise reactions with the concerted ones found in the same aminolysis ofO‐ethyl 2,4,6,‐(trinitrophenyl) dithiocarbonate indicates thatT±is so destabilized by the change of PhS by the 2,4,6‐trinitrobenzenethio group thatT±no longer exists and becomes a transiti

ISSN:0538-8066    

DOI:10.1002/kin.550270107

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction of S atoms with O2was studied behind reflected shock waves applying atomic resonance absorption spectroscopy (ARAS) for concentration measurements of S and O atoms. S atoms were generated either by laser‐flash photolysis (LFP) of CS2or by the high‐temperature pyrolysis of COS, respectively. The concentrations of O2in the mixtures ranged between 50 ppm and 400 ppm, and those of the S precursors, CS2and COS, between 5 and 25 ppm. The rate coefficient of the reactionwas determined from the observed decay of the S absorption signals for temperatures 1220 K ⩽T⩽ 3460 K. The measured O‐atom concentration profiles in COS/O2/Ar reaction systems were evaluated, using simplified kinetic mechanism, to verify the given rate coefficientk5. In experiments with the highest value of the [O2]/[COS]ratio the measured O‐atom concentrations were found to be sensitive to the reaction:The fitting of the calculated O‐atom profiles to the measured ones results in mean value of:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_6 = 8.0 \times 10^{11} \,{\rm cm}^{\rm 3} \,{\rm mol}^{{\rm - 1}} \,{\rm s}^{{\rm - 1}} $$\end{document}which is to be valid for the temperature range 2570 K ⩽T⩽ 2980 K.A first‐order analysis of the observed S absorption decay in LFP shock wave experiments on CS2/Ar gas mixtures resulted in a rate coefficient of the background reaction (R4):for temperatures 1260 K ⩽T⩽ 1820 K. © 1

ISSN:0538-8066    

DOI:10.1002/kin.550270108

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe isoconversional method was used to elucidate the kinetics of reversible solid‐state reactions occurring under nonisothermal linear heating. The characteristic dependencies of the effective activation energy (E) on the extent of conversion (W) were established for two model processes: a reversible first‐order reaction and a reversible reaction followed by an irreversible one. For the first process,Eis almost independent ofWand varies between the activation energy of the direct and inverse reaction. For the second, process with an endothermic reversible step, the dependence ofEonWis of decreasing shape. The effective activation energy is limited by the sum of the activation energy of the irreversible reaction and the enthalpy of the reversible reaction, at low conversions, and by the activation energy of the irreversible reaction at high conversions. Analyses of the kinetic data for the dehydration of crystalhydrates, as well as other processes proceeding through a reversible step, show the dependencies ofEonWcharacteristic of a reversible reaction followed by an irreversible one. © 1995 John Wiley&Sons,

ISSN:0538-8066    

DOI:10.1002/kin.550270109

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of 2‐bromo‐3‐methylbutyric acid in the gas phase was studied over the temperature range of 309.3–357.0°C and pressure range of 15.5–100.0 torr. This process, in seasoned static reaction vessels and in the presence of the free radical inhibitor cyclohexene, is homogeneous, unimolecular, and follows first‐order rate law. The observed rate coefficients are represented by the following Arrhenius equations: logk1(s−1) = (12.72 ± 0.25) − (181.8 ± 2.9) kJ mol−1(2.303RT)−1. The primary products are isobutyraldehyde, CO, and HBr. The polar five‐membered cyclic transition state type of mechanism appears to be preferred in the dehydrohalogenation process of α‐haloacids in the gas phase.

ISSN:0538-8066    

DOI:10.1002/kin.550270110

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550270101

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY