摘要:

AbstractExplosions occur when O3and H2CO are mixed in a fresh vessel, even in the presence of several hundred torr of N2or O2. However, in an aged vessel the reaction is well behaved. The reaction between O3and H2CO was studied at room temperature in an aged vessel in the presence of about 400 torr of either N2or O2. The initial rate of O3decay in the presence of N2is about 103times faster than in the presence of O2, and very small amounts of O2quickly reduce the initial rate of O3decay in the N2case. A chain mechanism is postulated to account for the results in which chain initiation can occur both by thermal decomposition of O3, followed by reaction of O(3P) with H2CO to produce HO and HCO, as well as bywhich may occur both homogeneously and heterogeneously. The rate coefficientk1≃ 2.1 × 10−24cm3/molec · sec represents an upper limit (to within a factor of 2 uncertainty) to the direct gas‐phase reaction between O3a

ISSN:0538-8066    

DOI:10.1002/kin.550080602

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe kinetics of gas‐phase reaction of CH3CF2I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism:A least squares treatment of the data gave\documentclass{article}\pagestyle{empty}\begin{document}$$\log k_1 (M^{- 1} \cdot \sec ^{- 1}) = (11.4 \pm 0.3) - \frac{{(15.7 \pm 0.8)}}{\theta}$$\end{document}where θ = 2.303RTkcal/mole. The observed activation energyE1was combined withE2= 0 ± 1 kcal/mole to yield\documentclass{article}\pagestyle{empty}\begin{document}$$DH^ \circ ({\rm CH}_{\rm 3} {\rm CF}_2 - {\rm I}) = 52.1 \pm 1.0{\rm kcal}/{\rm mole}$$\end{document}The result, combined with data for several CI bond dissociation energies, leads us to conclude that the C(sp3)I bond is relatively insensitive to F for H substitution and that the C(sp2)–I bond has considerable double‐bon

ISSN:0538-8066    

DOI:10.1002/kin.550080603

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractA combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br2−in the surrounding aqueous medium. The reaction3Pmic+ Br→ P mic++ 2 Br−was followed by optical absorption measurements in the 10−8−10−4–sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 106sec−1and 1 × 109M−1· sec−1.The fast component is related to the probability of a Br2−radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br2−radical–micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br2−radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this elect

ISSN:0538-8066    

DOI:10.1002/kin.550080604

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractNew experimental data have been obtained for H + C2H2, D + C2H2, H + C2D2, and D + C2D2at room temperature. Two previously described apparatus were used in order to measure the pressure dependence of the reactions. The absolute rate constants are compared to results from other laboratories. The present results and those of Payne and Stief are used to obtain the high‐pressure limiting rate constant at room temperature. When the activation energy from the work of Payne and Stief is considered, it is shown that theAfactor for H + C2H2is too low by a factor of ∼20. If a transmission coefficient is introduced which is constant for all isotopic variations, the pressure dependence can be explained in terms of the randomly energized radicals. RRKM theory is then invoked to explain the observed statistical nonequilibrium kinetic isotope effe

ISSN:0538-8066    

DOI:10.1002/kin.550080605

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractPhotolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2‐difluoro‐2,3‐dihydro‐5‐trifluoromethylfuran‐3‐one:The HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF2radicals which, if HFAA is present, undergo an insertion into the enolic OH bond,(9)The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both ϕ1and ϕ5depend on pressure and the ratio ϕ1/ϕ5increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio ϕ1/ϕ5increases as the vibrational energy of electronically exc

ISSN:0538-8066    

DOI:10.1002/kin.550080606

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractTandem chemical laser techniques have been used to detect HF formed through photoelimination from 1,1,1,5,5,5‐hexafluoroacetylacetone, HFAA. Information about the HF vibrational population ratios is deduced:N2/N1<0.37 andN1/N0<0.45. This work supports the deduction by Bassett and Whittle that photodecomposition of the enol form of HFAA results mainly in HF elimination and ring closure to a dihydrofuranone, a new type of reactio

ISSN:0538-8066    

DOI:10.1002/kin.550080607

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe flash photolysis of azomethane in a quartz reaction vessel produces mainly ethane (>75%) plus smaller quantities of methane, ethylene, and acetylene. The minor products are interpreted quantitatively in terms of methyl radical photolysis at 216 nm to give CH2and H. This interpretation is substantiated by the dependence of the minor products on flash intensity. The reduction of the ethane yield on adding NO is employed to obtain a rate constant for CH3+ NO as a function of total pressure, based on a value for methyl radical recombination of 4.2 × 10−11cm3/molec · sec. An RRKM analysis is used to extrapolate the data to give a limiting high‐pressure rate constant for CH3+ NO of (1.2 ± 0.1) × 10−11cm3/molec · se

ISSN:0538-8066    

DOI:10.1002/kin.550080608

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe decomposition of ethane sensitized by isopropyl radicals was studied in the temperature range of 496–548°K. The rate of formation ofn‐butane, isopentane, and 2,3‐dimethylbutane were measured. The expressionk1/k2½was found to be\documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_1 /k_2 ^{1/2} ({\rm dm}^{{\rm 3/2}} /{\rm mol}^{{\rm 1/2}} \cdot \sec ^{1/2}) = (3.2 \pm 0.4) - (54 \pm 3{\rm kJ/mol})/2.3RT$$\end{document}wherek1andk2are rate constants ofThe decomposition of propylene sensitized by isopropyl radicals was studied between 494 and 580°K by determination of the initial rates of formation of the main products. The ratio ofk13/k21/2was evaluated to be\documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_{13} /k_2 ^{1/2} ({\rm dm}^{{\rm 3/2}} /{\rm mol}^{{\rm 1/2}} \cdot \sec ^{1/2}) = (1.9 \pm 0.7) - (32 \pm 7{\rm kJ/mol})/2.3RT$$\end{document}wherek13is the rate constant forThe isomerization of the isopropyl radical was investigated by studying the decomposition of azoisopropane. The decomposition of the iso‐C3H7radical into C2H4and CH3was followed by measuring the rate of formation of C2H4. On the basis of the experimental data, obtained in the range of 538–666° K,k15/k2½was found:\documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_{15} /k_2 ^{1/2} ({\rm mol}^{{\rm 1/2}} /{\rm dm}^{{\rm 3/2}} \cdot \sec ^{1/2}) = (9.3 \pm 0.8) - (152 \pm 9{\rm kJ/mol})/2.3RT$$\end{document}wherek15is the r

ISSN:0538-8066    

DOI:10.1002/kin.550080609

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe rate of decomposition ofs‐butyl nitrite (SBN) has been studied in the absence (130–160°C) and presence (160–200°C) of NO. Under the former conditions, for low concentrations of SBN (6 × 10−5− 10−4M) and small extents of reaction (∼1.5%), the first‐order homogeneous rates of acetaldehyde (AcH) formation are a direct measure of reaction (1) sincek3c»k2(NO): . Unliket‐butyl nitrite (TBN),d(AcH)/dtis independent of added CF4(∼0.9 atm). Thusk3cis always »k2(NO) over this pressure range. Large amounts of NO (∼0.9 atm) (130–160°C) completely suppress AcH formation.k1= 1016.2–40.9/θ sec−1. Since (E1+RT) and ΔH°1are identical, within experimental error, both may be equated withD(s‐BuO‐NO) = 41.5 ± 0.8 kcal/mol andE2= 0 ± 0.8 kcal/mol. The thermochemistry leads to the result ΔH°f(s‐\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}) = − 16.6 ± 0.8 kcal/mol. From ΔS°1andA1,k2is calculated to be 1010.4M−1· sec−1, identical to that for TBN. From an independent observation thatk6/k2= 0.26 ± 0.01 independent of temperature,\documentclass{article}\pagestyle{empty}\begin{document}${\rm s - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}, we findE6= 0 ± 1 kcal/mol andk6= 109.8M−1· sec−1. Under the conditions first cited, methyl ethyl ketone (MEK) is also a product of the reaction, the rate of which becomes measurable at extents of conversion>2%. However, this rate is ∼0.1 that of AcH formation. Although MEK formation is affected by the ratioS/Vfor different reaction vessels, in a spherical reaction vessel, this MEK arises as the result of an essentially homogeneous first‐order 4‐centre elimination of HNO.\documentclass{article}\pagestyle{empty}\begin{document}${\rm SBN}\mathop \to \limits^{\rm 5} {\rm MEK} + {\rm HNO}$\end{document};k5= 1012.8–35.8/θ sec−1.Sec‐butyl alcohol (SBA), formed at a rate comparable to MEK, is thought to arise via the hydrolysis of SBN, the water being formed from HNO. The rate of disappearance of SBN, that is,d(MEK + SBA + AcH)/dt, is given bykglobal= 1015.7–39.6/θ sec−1. In NO (∼1 atm) the rate of formation of MEK was about twice that in the absence of NO, whereas the SBA was greatly reduced. This reaction was also affected by the ratioS/Vof different reaction vessels. It was again concluded that in a spherical reaction vessel, the rate of MEK formation was essentially homogeneous and first order. This rate is given bykobs= 1012.9–35.4/θ sec−1, very similar tok5. However, although it is clear that the rate of formation of MEK is doubled in the presence of NO, the value forkobsmakes it difficult to associate this extra MEK with the disproportionation ofs‐\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}and NO:s‐\documentclass{article}\pagestyle{empty}\begin{document}$s{\rm - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}. NO at temperatures of 130–160°C completely suppresses AcH formation. AcH reappears at higher temperatures (165–200°C), enablingk3cto be determined. Ignoring reaction (6),d(AcH)/dt=k1k3(SBN)/[k3c+k2(NO)];k3c= 1014.8–15.3/θ sec−1. Inclusion of reaction (6) into the mechanism m

ISSN:0538-8066    

DOI:10.1002/kin.550080610

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe photolysis of SO2in the presence ofcis‐ andtrans‐2‐pentene has been investigated at 3660 Å and 22°C. Quantum yield measurements of the SO2photosensitized conversion of one isomer into the other are consistent with a mechanism in which the only participating excited electronic state of SO2is the SO2(3B1) state. Quantum yield measurements were made for a variation inPSO2/Pisomerreactant ratios of 4.01–283 and 57.5–351 for thecisandtransisomers, respectively. The data are consistent with a mechanism in which a (SO2‐olefin)3collision intermediate is the precursor to the photosensitized isomeric products. The intermediate undergoes unimolecular decay to yield thecisandtransisomers with probabilities of 0.26 ± 0.05 and 0.69 ± 0.04, respectively. Estimates of the quenching rate constants at 22°C for removal of SO2(3B1) molecules bycis‐ andtrans‐2‐pentene are (0.633 ± 0.125) × 1011l./mole/sec and (1.00 ± 0.27) × 1011l./mole/sec, respectively. An experimentally determined photostationary composition, [trans‐2‐pentene]/[cis‐2‐pentene] = 2.3 ± 0.1 was in fair agreement with that of 1.7 ± 0.7 as predicted fro

ISSN:0538-8066    

DOI:10.1002/kin.550080611

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY