摘要:

AbstractPermanganate ion rapidly oxidizes the thiol group in 2‐thiouracils (2,3‐dihydro‐2‐thioxo‐4(1H)‐pyrimidinones, 4‐hydroxy‐2‐pyrimidinethiols) to the corresponding uracil‐2‐sulfonates in phosphate‐buffered solutions. The oxidations, which are first order in oxidant and first order in reductants, are characterized by relatively small energies of activation (Ea≅ 4.3–6.7kcal/mol) and relatively large negative entropies of activation (ΔS‡ = −24.9–−34.4 eu). The relative rates of oxidation of 2‐thiouracil (2), 6‐methyl‐ (4), 6‐n‐propyl‐ (6), 1,6‐dimethyl‐(8), and 3,6‐dimethyl‐2‐thiouracil (9) are 1.00:1.23:0.98:7.32:2.54. The rate of oxidation of 1,3,6‐trimethyl‐2‐thiouracil (12) is several orders of magnitude slower than that of the other thiouracils. Although the thiol group or thiolate anion is probably involved in the rate‐deter

ISSN:0538-8066    

DOI:10.1002/kin.550100902

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe gas‐phase pyrolysis of 2‐chloroethylbenzene andp‐methoxy‐2‐chloroethylbenzene was studied in a static system over the temperature range of 411°–471°C and a pressure range of 39–202 mm Hg. The reactions in seasoned vessels, with the propene inhibitor always present, were homogeneous, first‐order, and unimolecular. The rate constants are given by the Arrhenius equation for 2‐chloroethylbenzene:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{- 1}) = (13.07 \pm 0.35) - (220.9 \pm 4.6){\rm kJ/mol/2}{\rm .303}RT $$\end{document}and forp‐methoxy‐2‐chloroethylbenzene:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{- 1}) = (13.81 \pm 0.34) - (228.4 \pm 4.6){\rm kJ/mol/2}{\rm .303}RT $$\end{document}The presence of phenyl substituents in the β position of ethyl chloride has been found to provide anchimeric assistance in t

ISSN:0538-8066    

DOI:10.1002/kin.550100903

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe rate of decomposition oftert‐amyl nitrite (t‐AmONO) has been studied in the absence (120°–155°C) and presence (160°–190°C) of nitric oxide. In the absence of nitric oxide for low concentrations oftert‐amyl nitrite (∼10−4M) and small extents of reaction (∼1%), the first‐order homogeneous rates of acetone formation are a direct measure of reaction (1) sincek3a≫k2(NO):The rate of acetone formation is unaffected by the addition of large amounts of carbon tetrafluoride or isobutane (∼1 atm) but is completely suppressed by large amounts of nitric oxide (1 atm 120°–155°C).The rate of reaction (1) is given byk1= 1016.3±0.110−40.3±0.1/θ sec−1. Since (E1+RT) and ΔH°1are identical, both may be equated withD(t‐AmO – NO) = 40.9 ± 0.1 kcal/mol andE2= 0 ± 0.1 kcal/mol. The thermochemistry leads to the result that ΔH°f(t‐AmO) = −26.6 ± 1 kcal/mol. From ΔS°1andA1,k2is calculated to be 1010.5±0.2M−1·sec−1.Although the addition of nitric oxide completely suppresses acetone formation at lower temperatures, it reappears at higher temperatures. This is a result of reaction (3a) now competing with reaction (2), thus allowingk3ato be determined. The rate constant for reaction (3a) is given byk3a= 1014.7 ± 0.210−14.3 ± 1/θ sec−1. There are two possible routes for the decomposition of thetert‐amyloxyl radical:The dominating process is (3a). From the result at 160°C thatk3a/k3b= 80, we arrive at the resultk3b= 1015.0–18.7/θ sec−1.In addition to the products accounted for by the radical split (1), methyl‐2‐but‐1‐ene and methyl‐2‐but‐2‐ene are produced as a result of the six‐centre elimination of nitrous acid (5):The ratiok5a/k5bwas 0.35. Unliketert‐butyl where the rates of the two paths were comparable [(l) and (5)], here the total rate of the eli

ISSN:0538-8066    

DOI:10.1002/kin.550100904

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA nitrogen laser pumped tunable dye laser has been used to observe the three‐photon ionization of NO through a two‐photon resonance with theC2II state. Fluorescence is also observed from this state. The wavelength dependence of both signals have been measured. A reaction mechanism is postulated, which includes the initial two‐photon excitation of theC2II state as the rate‐limiting step. This mechanism predicts the observed second‐order intensity dependence of the ionization signal and shows that the simple rate equation treatment is valid in th

ISSN:0538-8066    

DOI:10.1002/kin.550100905

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractIt is shown that the activation energiesEoF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energiesDand the Taft polar and steric substituent constants σ* andEsby the expression:\documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta E = \alpha \Delta D + \rho \sigma ^* + \delta E_{\rm s} $$\end{document}where ΔEand ΔDrepresent the differences between theEandDvalues of a given substrate and those of a reference compound (CH3substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical

ISSN:0538-8066    

DOI:10.1002/kin.550100906

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA numerical method to solve the set of differential equations which describes the chemical development in polluted air is presented. The photochemical lifetimes, continuously monitored for all compounds, determine how the integrations are performed at all times. Components with lifetimes less than 10% of the time step, which is taken as 30 sec, are assumed to be in photochemical equilibrium, while compounds with photochemical lifetimes greater than 100 times the time step are computed according to Euler's method. All other components are calculated from the exponential solution of the continuity equation. The computational accuracy may be improved by iteration on components assumed to be determined by the instant values of other components. The convergence of the iteration is speeded up by ordering the short‐lived compounds in a hierarchical sequence. Since computational errors connected with QSSA methods are difficult to assess, comparison with an automatic scheme is necessary. Our method has been compared with Gear's method for a range of model mixtures of hydrocarbons, nitrogen oxides, and air, thought to cover most conceivable situations of atmospheric pollution. The agreement with Gear's method is within a few percent for all components all the time, in most cases even within 1%. No accumulation of deviations occur during long‐term integrations (e.g., 48 hr with day and night shiftings), and differences which appear during periods with strong concentration gradients (e.g., after sunrise) vanish when the activity has culminated. The method presented here is considerably more efficient than Gear's method, with respect to both computer time and stor

ISSN:0538-8066    

DOI:10.1002/kin.550100907

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractOxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by usingN‐bromosuccinimide (NBS) as oxidant in the temperature range of 25°‐50°C. It has been found that the order with respect to NBS is zero while with respect to diethyl ketone and [H+], it is unity. Succinimide, sodium perchlorate, and mercuric acetate have an insignificant effect on the reaction rate, while the dielectric effect was negative. A solvent isotope effect (k0D2O/k0H2O= 1.6–1.8) at 35°C has been observed. On the basis of the available evidences a suitable mechanism consistent with the experimental results has been proposed in which it is suggested that the mechanistic route for NBS oxidation in an acidic medium is through the enol form of the ketone. The magnitude of the solvent effect also supports the mechanism. Various activation parameters have been calculated, and the 1,2‐dicarbonyl compound has been identified as the end product of th

ISSN:0538-8066    

DOI:10.1002/kin.550100908

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550100901

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY