摘要:

AbstractThe effects of the concentrations of LiCl, NaCl, KCl, CsCl, Na2CO3, BaCl2, and Me4NCl on the rates of reactions of hydroxide ion with ionizedN‐hydroxyphthalimide (NHP) at 30°C and in a H2O–MeCN solvent containing 98%,v/v, H2O reveal a nonlinear increase in observed rate constants with increase in salt concentrations. The observed rate constants are highly sensitive to the valence state of cations and almost insensitive to the valence state of anions of the salts. These observations are explained in terms of ion‐pair formation between cations an

ISSN:0538-8066    

DOI:10.1002/kin.550230702

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe nucleophilic second‐order rate constant (kOH) for the reaction of ŌH with ionizedN‐hydroxyphthalimide (S−) appears to follow a reaction mechanism similar to that for reactions of ŌH with neutral phthalimide and itsN‐substituted derivatives. Kinetically indistinguishable terms,k′w[H2O][S−] andkŌH[ŌH][SH](SH represents nonionizedN‐hydroxyphthalimide), which constitute the pH‐independent rate region of the pH‐rate profile, are resolved qualitatively. It is shown that the termkŌH[ŌH][SH], rather thank′w[H2O][S−], is important in these reactions. The rates of ŌH‐catalyzed cleavage of S−were studied at 32° in the presence of micelles of sodium dodecyl sulphate (SDS). At a constant [ŌH], the observed pseudo first‐order rate constants (kobs) increase linearly with [SDS]T(total SDS concentration). These data are explained in terms of the pseudophase model of micellar effects on reactivity. The linear dependence ofkobswith [SDS]T(within [SDS]Trange of 0.0–0.2 or 0.3 M) is attributed to the occurrence of the reaction between the exterior boundary

ISSN:0538-8066    

DOI:10.1002/kin.550230703

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe kinetics of the reactions of IO, BrO, and ClO with DMS have been investigated at 298 K and total pressures of 0.5–6.8 mbar He using the discharge flow‐mass spectrometry technique to monitor the halogen oxide radicals. Rate coefficients of (8.8 ± 2.1) × 10−15, (2.7 − 0.5) × 10−13and (9.5 ± 2.0) × 10−15cm3molecule−1s−1have been obtained for the reactions of IO, BrO, and ClO with DMS, respectively. The result for IO with DMS is in good agreement with two other recent studies on this reaction but is nearly three orders of magnitude slower than two earlier studies, one of which was from this laboratory. The earlier studies are now thought to be in error because of heterogeneous and secondary chemistry occurring in the systems investigated. The rate coefficient for BrO with DMS is in excellent agreement with a previously reported preliminary value from this laboratory. However, the rate coefficient for ClO with DMS is a factor of 4 lower than our previously determined value. The new data are considered more reliable in view of the much improved experimental technique in the present study. DMSO was detected as a product in all of these reactions. A semi‐quantitative determination of the DMSO yield was only possible in the case of the reaction of IO with DMS where a yield

ISSN:0538-8066    

DOI:10.1002/kin.550230704

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe oxidation of L‐Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first‐order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first‐order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are pro

ISSN:0538-8066    

DOI:10.1002/kin.550230705

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe reaction pathways ofn‐butoxy ands‐butoxy radicals have been investigated by TLC and HPLC analysis of end products, particularly peroxides and carbonyl compounds. The butoxy radicals were produced by the pyrolysis of very low concentrations of the corresponding dibutylperoxide in an atmosphere of oxygen and nitrogen, at atmospheric pressure. The decomposition reaction (3)s‐BuO → C2H5+ CH3CHO and the reaction (2)s‐BuO + O2→ HO2+ CH3COC2H5have been studied, and the ratiok3/k2has been determined in the temperature range 363–503 K by kinetic modeling of the formation of the observed acetaldehyde and methylethylketone. The rate constantk3obtained was:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_3 /{\rm s}^{ - 1} = \left({13.8 \pm _{0.3}^{0.2} } \right) - \left({15.0 \pm 0.9} \right){\rm kcal\,mol}^{ - 1} /2.303\,RT. $$\end{document}A good agreement was observed between experimental data and RRKM theory. The implications of the results for atmospheric chemistry and combustion are discussed. At room temperature, the reaction with O2, yielding HO2radicals and methylethylketone is, by far, the main channel fors‐BuO radicals. In the field of low temperature combustion, the decomposition ofs‐BuO radicals producing C2H5and CH3CHO is the main pathway; the routes‐BuO + O2decreases tremendously in importance as the temperature is

ISSN:0538-8066    

DOI:10.1002/kin.550230706

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractUltrasonic relaxation spectra of LiClO4plus the open chain polyether triglyme (TG) at CLiClO4≃ 0.8 M, molar ratio R = [TG]/[LiClO4] = 1, and at temperatures of 15, 25, 35, and 45°C in dry acetonitrile are reported. Corresponding spectra for LiClO4plus the macrocycle 12‐crown‐4 (12C4) at R = [12C4]/[LiClO4] = 1, at 10, 15, 20, 25, 30, and 40°C, and CLiClO4= 0.32 M in acetonitrile are also reported.Both relaxation envelopes, for the two systems, have been fitted by two Debye relaxation processes and interpreted by the Eigen‐Winkler reaction scheme:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Li}^ + \cdots {\rm PE} \mathop{\rightleftharpoons}\limits^{k_1}_{k_-1}{\rm LiPE}^ + \mathop{\rightleftharpoons}\limits^{k_2}_{k_-2} ({\rm LiPE})^ + $$\end{document}where “PE” symbolizes the polyether, Li+… PE is a solvent separated species and LiPE+and (LiPE)+are two complex species. The temperature dependence of the relaxation spectra permits the calculation of the activation parameters for the forward and reverse processes for the system LiClO4+ TG and for one of the two processes for the LiClO4+ 12C4 system.Comparisons between the two sets of data lead to the conclusion that the much slower second relaxation process, in the case of the macrocycle, is attributable to a combination of an enthalpic and an entropic effect on the energy barrier for the

ISSN:0538-8066    

DOI:10.1002/kin.550230707

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C2H6and N2, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C3H8(3.5 × 10−3), C2H4(3.2 × 10−4), CH4(3 × 10−3), andn‐C4H10(trace). Quantum yields of H2of 4 × 10−5and 2 × 10−5were measured at azomethane pressures of 0.1 and 1.0 torr, respectively.The minor hydrocarbon products can be accounted for by reactions of CH3and C2H5radicals following hydrogen abstraction from azomethane by CH3. The H2product observed represents an upper limit for the H2elimination from vibrationally excited C2H6formed by CH3combination in the system, corresponding to a rate of elimination ca. 5 × 10−5times the competing rate of dissociation to 2CH3. Assuming a frequency factor of 1013s−1for the H2elimination, a lower limit of about 90 kcal mol−1was estimated

ISSN:0538-8066    

DOI:10.1002/kin.550230708

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate of hydrolysis of title schiff bases was studied in the pH range 4–13 in 10% dioxanewater system, CTAB, NaLS micellar solutions. The hydrolysis was found to be due to ‘water’ and ‘hydroxide’ reactions and hence the rate constants in different pH were computed and analyzed with an intermediate involving a water molecule being positioned with the help of 2‐OH group and the thiazolyl C–N pi bond. The ‘hydroxide’ reaction was due to a direct nucleophilic attack of hydroxide ion at the aldimine linkage of the reactant. The influence of cationic and anionic micelles supports the mechanistic picture in th

ISSN:0538-8066    

DOI:10.1002/kin.550230709

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550230701

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY