摘要:

AbstractWe have performed a product and kinetic study of the hydrolysis of 3,4‐diphenyl‐1,2,5‐thiadiazole‐1,1‐dioxide in aqueous solution. Benzil and sulfamide are the only products of hydrolysis and are formed in equimolar yields.The kinetic results indicate that a first order law is followed up to 90% conversion. The observed rate constant is independent of substrate concentration.Ionic strength and buffer concentration do not affect the rate constant, but the reaction is acid‐base catalyzed. The rate‐pH profile has been determined and a mechanism that fits the experimental data satisfactorily is proposed. Corresponding rate constants and equilibrium constants for the protonation of the substrate

ISSN:0538-8066    

DOI:10.1002/kin.550230302

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe reaction of peroxomonophosphoric acid and hydrazinium ion in acid perchlorate solutions occurs as per stoichiometry (i), and the rate law (ii) at large [N2H5+],where K′dis the first acid dissociation constant of H3PO5andk1andk2are rate constants found to be 2.6 × 10−4s−1and 5.0 × 10−2M−1s−1, respectively, at 35°. The reaction is greatly catalyzed by iodide ions. The mechanism involves a redox cycle I−/I2and the rate is independent of [N2H5+] in the presence of iodide ions. K′dwas found to be 0.55 M−1and indepe

ISSN:0538-8066    

DOI:10.1002/kin.550230303

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractRate constants for the retro‐Diels‐Alder dissociation of 1,2,3,6‐tetrahydropyridine, to 1,3‐butadiene and methanimine, have been measured over 650–1450 K. To cover this range, three separate techniques were used at three laboratories: laser schlieren and single pulse shock tube methods, and a comparative rate flow system technique. The derived rate constants are extrapolated to the high‐pressure limit with an RRKM model parameterized to fit the falloff observed in the laser‐schlieren measurements. The resulting high‐pressure rate constants show a reduction in activation energy of about 10 kcal/mol, comparing the isoelectronic cyclohexene, but little change in A‐factor. There is an apparent increase in activation energy of 4 kcal/mol over the temperature range of these experiments, which is just outside probable error. Such a rise in activation energy is in marked contrast to the drop usually seen in simple bond fission, and may reflect a change from a concerted to a stepwise, biradical mechanism at

ISSN:0538-8066    

DOI:10.1002/kin.550230304

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractBromite, BrO2−, in aqueous carbonate or borate buffers (pH 9–11), reacts rapidly with H3AsO3, with the tartrate complex of Sb(III), and with the EDTA complexes of Sn(II) and U(IV). Each reaction yields Br−, even when BrO2−is taken in excess. Reaction rates with Sb(III) and Sn(II) are independent of pH, but the acidity pattern observed with As(III) points to competing bimolecular reductions by H2AsO3−and H3AsO3having specific rates 3.4 and 1.2 M−1s−1(25°C, μ = 0.5M). Reduction by U(IV) is strongly inhibited by carbonate; data for carbonate buffers are in accord with the operation of two contributing reaction paths (specific rates 0.45 and 6.3 M−1s−1) with the activated complex for the slower featuring one more carbonate than that for the rapid. Reactions of BrO2−with single electron reductants, or with reagents that can undergo both 1e and 2e changes, are generally complicated by variable induction periods, inhibition by O2, catalyzed decomposition of BrO2−, or combinations of these. The much smoother reductions by 2e−reagents must pass through OBr−, which reacts much more rapidly than BrO2−in each case. An inner‐sphere path, operating through an oxygen‐bridged transition state and culminating in oxygen atom transfer, is proposed for the 2e reductants. Hypophosphite, despite its highly negative formal potential, is not oxidized by BrO2−under our conditions. Here it is likely that the substitution‐inert character of the coordinatively saturated P(I) center rules out formatio

ISSN:0538-8066    

DOI:10.1002/kin.550230305

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3→ products (1):k1= (1.5 ± 0.2) × 10−14; IO + CH3SH → products (2):k2= (6.6 ± 1.3) × 10−16; IO + C2H4→products (3):k3<2 × 10−16; IO + C3H6→ products (4):k4<2 × 10−16(units are cm3molecule−1s−1). CH3S(O)CH3and HOI were found as products of reactions (1) and (2), respectively. The present lower value ofk1compared to our previous d

ISSN:0538-8066    

DOI:10.1002/kin.550230306

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of benzoylformic acid into carbon dioxide and benzaldehyde is a unimolecular first‐order reaction which takes place according to the rate equation logk= 15.3–42,500/4.575 K. At 600 K the reaction takes place 18 times faster than the corresponding decomposition of pyruvic acid into carbon dioxide and acetaldehyde. This is consistent with the 4‐center process proposed previously for pyruvic acid, in which a partial negative charge develops on the carbon of the α‐carbonyl group in the transition state. Benzoylformic acid is considerably less reactive towards thermal elimination than is oxalic acid, which also accords with the proposed m

ISSN:0538-8066    

DOI:10.1002/kin.550230307

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractStability and sensitivity analysis are used to examine the ignition/reaction characteristics of dilute hydrogen‐oxygen mixtures. The analysis confirms the existence of two distinct regions of ignition and fast reaction previously labeled “weak” and “strong” ignition, both of which are located in the explosive pressure‐temperature domain and separated by a region related to the “extended” classical second limit. The stability analysis is based on an eigenanalysis of the Green's function matrix of the governing kinetic equations. The magnitudes of the largest (and system controlling) eigenvalue allow the strengths of the two processes to be quantified, giving a clear definition to the terms “weak” and “strong.” The sensitivities of the largest eigenvalue to the reaction rate constants of the mechanism pinpoint the elementary steps controlling the two ignition processes and the subsequent reaction. The associated eigenvectors yield the direction of change in species concentrations and temperature during the course of reaction. These vectors are found to be nearly constant during the induction period of both “weak” and “strong.” ignition, thus producing constant overall stoichiometric reactions. The subsequent reaction of major reactants associated with “weak” ignition also has a constant overall reaction vector, although, different than that during the induction period. However, the vector describing the reaction of major reactants associated with “strong.” ignition is found never to be constant, but continuous

ISSN:0538-8066    

DOI:10.1002/kin.550230308

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550230301

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY