摘要:

AbstractA 480 L evacuable reaction chamber, equipped with FT‐IR spectroscopy on‐line and ion chromatography off‐line, has been used to study the gas phase reaction between the nitrate radical, NO3, and the reduced organic sulphur compounds CH3CH2SH, (CH3CH2)2S, (CH3CH2)2S2, and CH3CH2SCH3in air. The products CH3CH2SO3H, SO2, H2SO4, CH3CHO, and CH3CH2ONO2were identified and quantified in the reactions of the first three compounds, CH3CH2SH, (CH3CH2)2S, and (CH3CH2)2S2. The reaction products were CH3CH2SO3H, CH3SO3H, SO2, H2SO4, CH3CHO, and CH2O in the reaction of CH3CH2SCH3. On the basis of identified reaction products and intermediates observed in the infrared spectra, mechanisms are proposed for the reactions between the NO3radical and the four reduced organic sulphur compounds. The results of this study, together with those from previous experiments performed in this laboratory on CH3SCH3, CH3SH, and CH3SSCH3lead to the conclusion that all these species, in the reaction with the NO3radical, follow a similar degradation mechanism producing SO2, H2SO4, RSO3H, RCHO, and RCH2ONO2, as the main reaction products. The inital step of the reaction of NO3with RSR and RSH type (R = CH3, CH2CH3) reduced organic sulphur compounds was found to be H‐atom abstraction, probably after the formation of an initial adduct. For the reaction between NO3and RSSR type compounds, evidence for an addition‐decomposition reaction, as the initial steps, was obtained. RS·, RS(O)·, and RS(O)2· appear to be formed as intermediates in all

ISSN:0538-8066    

DOI:10.1002/kin.550241002

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate‐determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley&Sons, I

ISSN:0538-8066    

DOI:10.1002/kin.550241003

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractData from previous articles on the initial polymerization rates of a series of monoalkyl substituted phenyl methacrylates were found to depend strongly on the size and position of the monoalkyl substituent in the phenyl ring. In order to investigate the possibility of correlation of all the rate data obtained, all those for phenyl methacrylate and ten other alkylphenyl substituted methacrylate monomers were fitted into empirical linear free energy relationships (LFER). Assuming steady‐state kinetics and separating out the initiator decomposition contribution to the initial overall rateRp, it was demonstrated thatk′ =kp/kt½can be successfully correlated with LFER equations containing predominantly steric parameters. The steric influence is more pronounced in theo‐ than in thep‐substitution, due to the proximity of theo‐substituent to the reaction propagation site. The results are corroborated by the existence of an isokinetic relationship of ΔH‡ vs. ΔS‡, providing the proportionality of electronic effects, however small, and the predominating steric effects. The treatment is based on the assumption that the initiator efficiency ƒ equals 1 and that the termination rate constantsktare equal for monomers of similar structure, what might represent an approximation of the true situation in the system investigated. © Jo

ISSN:0538-8066    

DOI:10.1002/kin.550241004

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of vinylacetylene (C4H4) was studied behind reflected shock waves using both a single‐pulse method (reaction time between 0.8 and 3.3 ms) and a time‐resolved UV‐absorption method (230 nm). The studies were done over the temperature range of 1170–1690 K at the total pressure range of 1.3–2.3 atm. The mechanism was used to interpret both the early and late stages of vinylacetylene decomposition at the high temperatures. It was confirmed that C4H4dissociation proceeded through the following three channels.The rate constant expression of reaction (1) was determined ask1= 6.3 × 1013exp(−87.1 kcal/RT) s−1. The rate constants of the succeeding reactions (chain reaction, C4H4+ H →i‐C4H3+ H2and C4H4+ H → C2H2+ C2H3and decomposition reactions of free radicals,i‐C4H3+ M → C4H2+ H + M) were confirmed or estimated

ISSN:0538-8066    

DOI:10.1002/kin.550241005

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe acid‐catalyzed hydrolyses of triacetyl‐glycerol and of tributyryl‐glycerol take place following a simple monoexponential kinetic scheme. The result can be interpreted as all three ester groups reacting with approximately the same specific rate. This observation reported in 1920 is unusual, because the intrinsic reactivities of primary and secondary esters are different, and because as far as the reaction proceeds, the remaining ester groups have neighboring hydroxyl groups, which undoubtly alter the reactivity of the reaction centers, relative to the situation in the initial reactant structure. The phenomenom can be explained by considering that local solvation effects due to neighboring hydrophylic groups remain unchanged as the transition‐state complex is formed in all three stages of the reaction. © John Wiley&S

ISSN:0538-8066    

DOI:10.1002/kin.550241006

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA general expression is derived for the approach to a new equilibrium when a monomer/dimer solution is diluted by a factor ofn. The error introduced by a simple exponential treatment is analyzed. The response of a trityl monomer/dimer equilibrium to dilution by a factor of two in a stopped‐flow apparatus has been used to measure the rate constantk11. The results fall on the same Eyring plot with those obtained at lower temperatures, by another method, in the early 1930's by Ziegler and co‐workers. © John Wiley&Sons,

ISSN:0538-8066    

DOI:10.1002/kin.550241007

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of the permanganate‐sulfite redox reaction has been studied in the alkaline medium using a stopped‐flow technique. In the pH range 10 to 12 the reaction was found to obey the rate expression: −½d[MnO4−]/dt= (k1+k2[OH−]) [MnO4−] [SO32−]. Mechanisms for the two paths involving the formation of a (O3MnOSO3)3−complex prior to the rate‐determining step are consistent with the data. © J

ISSN:0538-8066    

DOI:10.1002/kin.550241008

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe pyrolysis kinetics of primary, secondary, and tertiary β‐hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21–152 torr and the temperature range of 190°–260°C. These eliminations are homogeneous, unimolecular, and follow a first‐order rate law. The rate coefficients are expressed by the following equations: for 1‐hydroxy‐3‐butanone, logk1(s−1) = (12.18 ± 0.39) − (150.0 ± 3.9) kJ mol−1(2.303RT)−1; for 4‐hydroxy‐2‐pentanone, logk1(s−1) = (11.64 ± 0.28) − (142.1 ± 2.7) kJ mol−1(2.303RT)−1; and for 4‐hydroxy‐4‐methyl‐2‐pentanone, logk1(s−1) = (11.36 ± 0.52) − (133.4 ± 4.9) kJ mol−1(2.303RT)−1. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol typ

ISSN:0538-8066    

DOI:10.1002/kin.550241009

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550241010

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550241001

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY