ALBERT

Notes: The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391-432°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm DMP}} & \stackrel{1}{\longrightarrow} & {2{\rm MeO}} \\ {{\rm MeO + DMP}} & \stackrel{2}{\longrightarrow} & {{\rm MeOH + CH}_{\rm 2} {\rm O} + {\rm MeO}} \\ \end{array} $$\end{document} The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec-1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M-1· sec-1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm MeO} + {\rm NO}_2 (+ {\rm M})} \stackrel{7a}{\longrightarrow} & {{\rm MeONO}_{\rm 2} (+ {\rm M})} \\ {{\rm MeO} + {\rm NO}_2} \stackrel{7b}{\longrightarrow} & {{\rm CH}_{\rm 2} {\rm O} + {\rm HONO}} \\ \end{array} $$\end{document}When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396-442°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm CH}_{\rm 3} {\rm O} + {\rm O}_2} \stackrel{12}{\longrightarrow} & {{\rm CH}_2 {\rm O} + {\rm HO}_{\rm 2}} \\ \end{array} $$\end{document} A review of literature data produced k7a = 109.8±0.5M-1·sec-1, giving log k12(M-1·sec-1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.

Notes: By means of the technique of laser-induced fluorescence, the room-temperature vibrational relaxation of DF(v = 1) has been studied in the presence of several polyatomic chaperones. The rate coefficients obtained [in units of (μ;sec·torr)-1] are CH4, 0.22; C2H6, 0.61; C4H10, 1.26; C2H2, 4.0 × 10-2; C2H2F2, 1.86 × 10-2; C2H4, 0.175; CH3F, 0.36; CF3H, 1.95 × 10-2; CF4, 1.0 × 10-3; CBrF3, 5.6 × 10-4; NF3, 5.1 × 10-4; SO2, 1.27 × 10-2; and BF3, 7.1 × 10-3. Results are also reported for vibrational relaxation rate coefficients for HF(v = 1) in the presence of the following chaperones: CH4, 2.6 × 10-2; C2H6, 5.9 × 10-2; C3H8, 8.4 × 10-2; and C4H10, 0.128. A comparison of DF and HF results indicates that for deactivation by CnHn+2, rate coefficients for DF are approximately an order of magnitude larger than for HF. The deactivation rate coefficient of DF(v = 1) by CH4 was found to decrease with increasing temperature between 300 and 740°K.

Notes: The reactions between alizarin yellow G and six different bases B (including OH-) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature-jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion-controlled reaction between the base and that fraction which is present in the “open” non-hydrogen-bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge.The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method.

Notes: The reaction of 1,3-cyclopentadiene (CPD) with ground-state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3-methylcyclopropene, 1,3-butadiene, 1,2-butadiene, and 1-butyne. The yield of carbon monoxide over oxygen atoms produced (φCO) was equal to the sum of the yields of C4H6 isomers in any experiment. φCO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers.It was found that 3-methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1-butyne. The excess energy was estimated to be about 50 kcal/mol.The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans-2-butene and 1-butene. The ratios kCPD+O/ktrans-2-butene+O= 2.34 and kCPD+O/k1-butene+O = 11.3 were obtained.Probable reaction mechanisms and intermediates are suggested.

Notes: The kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2-C2Cl3H3, 1,1-C2Cl2H4, and 1,2-C2Cl2H4 by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4. The following Arrhenius parameters were obtained: TextE(EClH)-TemperatureA(ECLH)E(CCl4)log A(EClH)E(EClH)RangelogEClHA(C2Cl4)(kcal/mol)(1.mol·sec)(kcal/mol)(°C)CHCL2CH2Cl0.03 ± 0.083.87 ± 0.178.98 ± 0.1411.17 ± 0.27150 - 250CHCL2CH30.13 ± 0.134.63 ± 0.278.18 ± 0.1911.93 ± 0.37130 - 250CHCL2CH2Cl0.50 ± 0.177.57 ± 0.359.18 ± 0.2314.87 ± 0.45150 - 250The error limits are the standard deviations from least mean square Arrhenius plots.The α and ß activation effects on the kinetics of Cl atom abstraction from chloroalkanes are discussed. From the linear relation between the relative reactivities of cyclohexyl radicals toward the XCCl3 and XCHCl2 series, ECl(c-C6H11· + CHCl2CHCl2) = 10.2 ± 1 kcal/mol and ECl(c-C6H11· + CHCl22CCl3) = 9.7 ± 1 kcal is derived.

Notes: Reactions of OH(v = 1) with HBr, O, and CO have been studied at 295°K using a fast discharge flow apparatus: The reaction O + HBr → OH(v = 1) + Br was used as a source of OH(v = 1), and subsequent chemical reactions of the excited radical were followed using EPR spectroscopy. Rate constants for reactions (2b), (3b), and (6b) were measured as (4.5 ± 1.3) × 10-11, (10.5 ± 5.3) × 10-11, and 〈5 × 10-12 cm3/molec·sec, respectively. The rate constant for physical deactivation of OH(v = 1) by CO was determined as 〈4 × 10-13 cm3/molec·sec.

Notes: The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived: TextTemperatureElog ArangeReaction(kcal/mol)(1./mol·sec)(°K)ĊH3 + C2H4 → Ċ3H77.3 ± 1.08.32 ± 0.5350 - 500ĊH3 + C2H2 → Ċ3H57.7 ± 1.58.79 ± 0.8379 - 487ĊH3 + C6H6 → C7H97.6 ± 1.08.79 ± 0.5372 - 484The results for methyl addition to ethylene are based on previous determinations by other techniques as well as the present studies. The results for methyl addition to acetylene and benzene are derived solely from the present experiments and are calculated relative to a rate constant of log k2(l./mol·sec) = 7.42 - (7.1/θ) for the reference reaction (2), ·H3 + (CH3)3CH → CH4 + ·4H9.

Notes: The thermal decomposition of propene in the presence of D2 was studied in a single-pulse shock tube in the temperature range of 1200-1400°K. The main decomposition products were methane, ethylene, allene, and propyne. Furthermore, deuterated species were observed of each product and of propene, with characteristic compositions that were dependent on propene conversion. Geometrical isomers of monodeuterated propene, as the result of H-D exchange, were analyzed by microwave spectroscopy. From these observations, the reactivities of n- and isopropyl radicals at high temperatures were determined. The former was found to be an intermediate of methane and ethylene and the latter was found to be responsible for the formation of the deuterated propene as follows: The rate constant ratio kn/ki was estimated to be 0.5-0.8, which was more than ten times greater than that obtained at room temperature. It was also found that allene or propyne was produced from allyl radicals and that acetylene was produced from vinyl radicals. In addition, the rate constant of the hydrogen abstraction by the hydrogen atom from C3H6 was found to be six times greater than that by the hydrogen atom from D2.

Notes: The oxidation of cerous ions by bromate ions in sulfuric acid medium was followed spectrophotometrically under various experimental conditions. The results were compared to the calculated predictions on the basis of a mechanism suggested by R. M. Noyes and collaborators. The computations were done by solving the complete set of the kinetic differential equations. The results of the computations show that the proposed mechanism explains adequately most of our and previous experimental data. In particular, the mechanism predicts the main features of the reaction, namely, the induction and the fast and slow reaction periods which occur during the oxidation.

Notes: The thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 → antisymmetric-NO3 + NO. The results on the reaction, NO2 + SO2 → NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low-temperature data and provides a modification of the rate-constant expression that is applicable over a wide temperature range.

Notes: The kinetics of the reaction of cis-(NO)2 with solid oxygen to form iso-N2O4 have been studied between 13 and 29 K. The overall reaction is pseudo first order in cis-(NO)2, and solid oxygen serves both as a reactant and the matrix. The pseudo-first-order rate constants are calculated to be k(14N) = 4.25 × 10-2 exp(-103/RT), and k(15N) = 3.00 × 10-2 exp(-105/RT) sec-1, based on temperature measurements from a thermocouple junction which may be at most three degrees lower than the actual reacting film. Most significantly, however, 14k/15k = 1.55 at∼13 K. The condensed phase reaction has been compared to that observed in the gas phase, and the extremely small pre-exponential factors and large isotope effects have been discussed in terms of tunneling corrections and orientational constraints. It is suggested that the form of the crystal plays an integral role in the observed process.

Notes: The flash photolysis-vacuum ultraviolet kinetic absorption spectroscopy technique has been used to measure the absolute rate constant for the reaction of ground state S(3P) atoms withnitric oxide,\documentclass{article}\pagestyle{empty}\begin{document}${\rm S}\left({^{\rm 3} P} \right) + {\rm NO}\mathop {\longrightarrow}\limits^{\rm M} {\rm SNO}\left({{\rm M} = {\rm CO}_2} \right)$\end{document} as a function of nitric oxide concentration and total pressure. The rateconstant was determined to be 1.9±0.1 × 1011 12/mol2.sec at 298°K, with a high-pressure limit of 9.3 ± 2.1×109 l/mol·sec-1. The observed kinetics are consistent with a termolecular energy transfer mechanism.

Notes: The title reaction has been investigated in the temperature range 667-715K. The only reaction products were trifluorosilyl iodide and hydrogen iodide. The rate law \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d\left[{{\rm I}_2} \right]}}{{dt}} = \frac{{k\left[{{\rm I}_2} \right]^{1/2} \left[{{\rm F}_3 {\rm SiH}} \right]}}{{1 + k\prime \left[{{\rm HI}} \right]/\left[{{\rm I}_2} \right]}} $$\end{document} was obeyed over a wide range of iodine and trifluorosilane pressures. This expression is consistent with an iodine atom abstraction mechanism and for the step \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm F}_3 {\rm SiH}\mathop {\longrightarrow}\limits^1 {\rm F}_3 {\rm Si}^\cdot + {\rm HI} $$\end{document} log k1(dm3/mol·sec) = (11.54 ± 0.17) - (130.5 ± 2.2 kJ/mol)/RT In 10 has been deduced. From this the bond dissociation energy D(F3Si—H) = (419 ± 5) kJ/mol (100.1 kcal/mol) is obtained. The kinetic andthermochemical implications of this value are discussed.

Notes: The recombination of bromine atoms at room temperature has been studied by flash photolysis in the range of 1-100 atm of the inert diluent He, leading to a value for the third-order rate constant of (1.5 ± 0.2) × 1015 cm6/mol2.sec. In the presence of NO the recombination is considerably accelerated. The falloff curve of the recombination Br + NO (+He) → BrNO (+He) was also measured resulting in a value for the limiting low-pressure rate constant of (3.4 ± 1.3) × 1015 cm6/mol2.sec. In experiments with excess NO, rate constants of (2.2 ± 1) × 1014 cm3/mol·sec for the reaction Br + BrNO → Br2 + NO, and (6.1 ± 0.4) × 109 cm6/mol2.sec for the reaction Br2 + 2NO → 2BrNO were obtained.

Notes: A previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction at the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first-order decay constants of H at room temperature in various pressures (10-1500 torr) of six heat bath gases. The atomic concentration is monitored by Lyman-α absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to ∼400 torr and depend only on one parameter,γ, the recombi-nation coefficient. This should be contrasted with the earlier work where slight variation in γ was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.

Notes: Atomic resonance absorption spectrometry with a nonreversed fluorine resonance lamp (∼95 nm) has been used to study the kinetics of elementary reactions of ground state F2PJ atoms in a discharge-flow system. The following rate constants (in cm3/molec·sec)All rate constants are given with 1.5 σ. were determined at 298° K: The reaction F 2PJ + HCl(1) was found to give J-excited Cl 2P1/2 atoms with a product branching ratio [Cl 2P1/2]/[Cl 2P3/2] = 0.10.

Notes: Equations for the average energy of chemically activated species are developed, and uncertainties in the various energy quantities involved are discussed. Various approaches to the energy distribution function of chemically activated species are discussed. Trial calculations on methylcyclobutane are presented.

Notes: The hydrogen-atom recombination reaction has been simulated using a molecular dynamics technique recently formulated by the authors [1]. The rate of recombination has been calculated over a range of temperatures and inert gas concentrations (He and Ar) and agrees well with available experimental data. The calculations reproduce the negative activation energy characteristic of an atom recombination process. Over the range of conditions studied recombination was found to proceed via the energy transfer mechanism only, no evidence of bound HAr or HHe species was observed. Recombination was found to occur through an intermediate metastable diatomic molecule which is in equilibrium with its environment and from which there is a bottleneck to the formation of a stable molecule. The initial formation of a metastable species is sensitive to the hydrogen-inert gas potential, but relaxation of the total energy is primary determined by the mass of the third-body and the collision frequency.

Notes: The title reaction, displaying peculiar characteristics as to relative rates and isomer distributions, has been studied in detail. Prior to this study, different mechanisms had been advanced by several groups. Kinetic features (isomer patterns, relative and absolute rates, reaction orders, influences of additives, H/D isotope effects) strongly point to a free-radical (chain) process, in which (1) is a crucial step. This abstraction reaction, endothermal by about 6 kcal/mol, apparently proceeds via a transition state closely resembling the free aryl radical. Relative rates and isomer distributions therefore reflect differences in stabilization energies, or in DH°(Ar - H). With high arene-Cl2 intake ratios or, more pronounced, with CCl4 as the reagent, aryl radicals also lead to biaryl, where arene successfully competes with the halogenating agent. This interpretation is quantitatively supported by our observation that “added,˝” recognizable aryl radicals yield the same chlorination-arylation product ratio, and by the results of competitive chlorination of benzene and chloroform over a temperature range of 200°C, where the latter study substantiates the value DH0(C6H5 - H) ≈ 109 kcal/mol.

Notes: The pyrolysis of ethylene-butene-2 mixtures has been studied in a static system over the temperature range of 689°-754°k and for initial pressures of each olefin of 20-200 torr. The two main addition products were cyclopentene and 3-methylpentene-1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3-methylpentene-1 was formed by the molecular “ene¨” addition of ethylene to butene-2 through a six-center transition state. The following rate constants were obtained: The pyrolysis of 3-methylpentene-1 has been studied over the same temperature range and for initial pressures of 20-100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k-1t and k-1c were, however, in reasonable agreement with the measurements of k1t and k1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.

Notes: The pyrolysis of ethylene-propylene and ethylene-isobutene mixtures has been studied in a static system over the temperature range of 682°-754° K and for initial pressures of each olefin of 33-300 torr. The following molecular ene reactions were observed and the rate constants measured: Using thermodynamic data, rate constants for the corresponding retro-ene decomposition reactions were calculated and compared to kinetic data reported for similar compounds. Other products were formed by radical chain processes, the main higher molecular weight ones being cyclopentene and 1-methylcyclopentene. A mechanism involving addition of allyl radicals is suggested for the formation of these products.

Notes: A program system is described for the integration of the rate equations resulting from large systems of elementary reactions. The Gear integration method is used for this problem, which frequently may exhibit stiffness instability when other integration methds are employed. No usage of the quasi-steady-state approximation is necessary. Ease in varying the reaction mechanism and simplicity of input structure are coupled with efficient execution and minimal demands for program storage as key features. The input-output structure, method of operation, and implementation are summarized, along with core storage requirements and execution times for trials using an IBM 360/44 computer.

Notes: The thermal reaction of 2-pentene (cis or trans) has been performed in a static system over the temperature range of 470°-535°C at low extent of reaction and for initial pressures of 20-100 torr. The main products of decomposition are methane and 1,3-butadiene. Other minor primary products have been monitored: trans-2-pentene, trans- and cis-2-butenes, ethane, 1,3-pentadienes, 3-methyl-1-butene, propylene, 1-butene, hydrogen, ethylene, and 1-pentene. The initial orders of formation, 0.8-1.1 for most of the products and 1.5-1.8 for 1-pentene, increase with temperature. The formation of the products and the influence of temperature on their orders can be essentially explained by a free radical chain mechanism. But cis-trans or trans-cis isomerization and hydrogen elimination from cis-2-pentene certainly involve both molecular and free radical processes. The formation of 1-pentene mainly occurs from the abstraction of the hydrogen atom of 2-pentene by resonance stabilized free radicals (C5H9.).

Notes: The kinetics of the thermal bromination reaction have been studied in the range of 261°-391°C. The observed rate law is compatible with initiation by the step for which we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_6 (cm^3 /mol - \sec) = (13.41 \pm 0.26) - (11700 \pm 700)/\theta $$\end{document} where Θ = 2.303RT cal/mol. Using the above value of E6, we have \documentclass{article}\pagestyle{empty}\begin{document}$$ {D(C}_{\rm 6} {\rm F}_{{\rm 5}^{\rm -}} {\rm I)} \to {\rm 53.5}\ {\rm kcal/mol} $$\end{document}This result disagrees with values of D(C6F5-I) obtained in other ways and we conclude that reaction (3) probably does not involve initiation by reaction (6). Instead, initiation may involve an addition of Br to the ring in C6F5I followed by decomposition of the adduct to give C6F5Br. If correct, this implies that the Arrhenius parameters above refer to the addition reaction rather than to reaction (6).

Notes: The rate constants and modes of reaction of NO2+ and C2H5ONO2NO2+ with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and substitution reactions (NO2+ + M → MO+ + NO; C2H5ONO2NO2+ + M → MNO2+ + C2H5ONO2) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C2H5ONO2NO2+ ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO2+ and C2H5ONO2. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C2H5ONO2NO2+ ions, on the energetics of the competing charge transfer process. Both NO2+ and C2H5ONO2NO2+ undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k (collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO2+.

Notes: A general competitive method is described for the study of the kinetics of the reactions of radicals with halogens and interhalogen compounds in the gas phase. The method is applied to the reactions over the temperature range of 48°-199°C. It is found that \documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k_6 /k_5) = \log (k_\varepsilon /k_7) = (- 0.042 \pm 0.060) - (8700 \pm 1300)/\theta $$\end{document} where Θ=2.303RT J/mol. Also \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} A_7 = 1/2A_{5,} \,\,\,\,\,\,\,\,\,\,\,\,E_7 = E_5 \\ A_8 = 1/2A_{6,} \,\,\,\,\,\,\,\,\,\,\,\,E_8 = E_6 \\ \end{array} $$\end{document}There is no correlation between differences in activation energies and differences in enthalpy changes for these reactions, but polar effects may be important in reactions (7) and (8).

Notes: 4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}s {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + s{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{15.9} \exp (- 35,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + n{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.9} \exp (- 28,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.1} \exp (- 36,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{2.3} \exp (- 27,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + n{\rm C}_{\rm 3} {\rm H}_{\rm 7} \cdot) = 10^{15.9} \exp (- 36,300/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm allene} + n{\rm C}_{\rm 3} {\rm H}_{\rm 6}) = 10^{12.7} \exp (- 28,400/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to {\rm CH}_3 {\rm C}) \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.2} \exp (- 36,800/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to 1,2-butadiene + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.3} \exp (- 28,700/T)\sec ^{- 1} $$\end{document} In combination with previous results, rate expressions for propargyl C—C bond cleavage are related to that for the alkanes by the expression \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm B} (alkyne) = \frac{1}{{3 \pm 1.5}}\exp (+ 4.25/T)k_{\rm B} (alkane) $$\end{document} These results yield a propargyl resonance energy of D(nC3H7-H) - D(C3H3-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH3C≡CCH2-H) - D(C3H3-H) = 0.6 ± 3 kJ, D(sC4H9-H) - D(iC3H7-H) = 0 ± 3 kJ, D(iC4H9-H) - D(nC3H7-H) = 2 ± 3 kJ, and D(nC3H7-H) - D(iC3H7-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.

Notes: The reactions of hydroxyl radicals with eight substituted aromatic hydrocarbons and four olefins were studied utilizing the flash photolysis-resonance fluorescence technique. The rate constants were measured at 298°K using either Ar or He as the diluent gas. The values of the rate constants (k × 1012) in the units of cm3/molec. sec are (a) OH + o-xylene → products: (12.9±3.8), 20 torr He; (13.0±0.3), 20 torr Ar; (12.4±0.1), 200 torr He;(b) OH + m-xylene → products: (15.6±1.4), 3 torr Ar; (19.4±0.8), 20 torr Ar; (21.4±0.2), 20 torr He; (20.3±1.9), 200 torr Ar; (20.6±1.3), 200 Torr He;(c) OH + p-xylene → products: (8.8±1.2), 3 torr Ar; (10.1±1.0), 20 torr He; (10.5±0.6), 200 torr He;(d) OH + ethyl benzene → products: (7.50±0.38), 3 torr He; (7.06±0.26), 20 torr He; (7.95±0.28), 200 torr He;(e) OH + n-propylbenzene → products: (6.40±0.36), 20 torr He; (5.86±0.16), 200 torr He;(f) OH + isopropylbenzene → products: (7.79±0.40), 200 torr He;(g) OH + hexafluorobenzene → products: (0.221±0.020), 20 torr He; (0.219±0.016) 200 torr He;(h) OH + n-propyl pentafluorobenzene → products: (2.52±0.54), 3 torr He; (3.01±0.76), 20 torr He; (3.06±0.24), 200 torr He;(i) OH + propylene → products: (25.6±1.2), 20 torr He; (26.3±1.2), 200 torr He;(j) OH + 1-butene → products: (29.6±1.9), 3 torr He; (29.4±1.4), 20 torr He;(k) OH + cis-2-butene → products: (43.2±4.1), 3 torr He; (42.6±2.5), 20 torr He;(l) OH + tetramethylethylene → products: (56.9±1.3), 20 torr He.

Notes: The first-order kinetics and hydrogen kinetic isotope effect of the decarboxylation of oxalic acid in acetophenone were studied in the temperature range of 109.6°-150.0°C. The rate constants, activation parameters, and hydrogen kinetic isotope effect were calculated. Detailed comparison and discussion of the results were made with the data reported in the literature. Kinetic isotope effects and solvent effects on rates should be considered similar in mechanistic and/or theoretical studies in the sense that kinetic isotope effects result from a small perturbation of the reaction coordinate, while the solvent effect causes a general overall variation on the potential energy surface (thereby resulting in a change in the reaction coordinate).

Notes: The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1-12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O + hν → H + HCO (1): CH2O + hν → H2 + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCO and ΦH2. The ratio ΦCO/ΦH2 was found to be 1.01 ± 0.09(2σ) and (ΦH2 + ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced ΦH2 to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/ΦH2 reached a limiting value of 2.3; with NO addition ΦCO exceeded unity. The addition of small amounts of Me3SiH reduced ΦH2 to 1.02 ± 0.08 and lowered ΦCO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with φ2 = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with φ1 = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)-(5): H + CH2O → H2 + HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2 + 2CO (5). The data suggest k4/k5 ≅ 5.8. Isobutene reduced ΦH2 by the reaction H + iso-C4H8 → C4H9 (20), and the results give k20/k3 ≅ 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k3 and k20.

Notes: The oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20-40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H+], ionic strength, temperature, etc. The reactions were found to be totally second order-first order with respect to each reactant. The second-order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one-electron oxidation to the iminoxy radical followed by an another one-electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.

Notes: The rate of disappearance of C2N2 in the presence of a large excess of H atoms has been measured in a discharge-flow system at pressures near 1 torr and temperatures in the range of 282-338 K. Under these conditions the reaction has a small negative temperature coefficient. A transition from second-order to third-order kinetics with decreasing pressure occurs at pressures near 1 torr. The results are discussed in terms of the mechanism where k7 = (1.5 ± 0.2) × 10-15 cm3/molec1·sec is found for the forward rate of reaction (7). The results also give k7k8/k-7 = 3.7 × 10-31 cm6/molec2·sec and k7k9/k-7 = 3.0 × 10-32 cm6/molec2·sec, the first being probably an upper limit and the second probably a lower limit; hence k8/k9 = 12 is found as an upper limit.

Notes: Oxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by using N-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 the reaction.

Notes: Vinylacetylene was pyrolyzed at 300-450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half-suppressed by the addition of the free-radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(-79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5—dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free-radical processes in a second-order process with an overall k ≃ 3 × 108 exp(-122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (-118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(-77 kJ/mol RT), 1.7 × 105 exp(-89 kJ/mol RT), and 3.1 × 109 exp(- 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free-radical process and by isomerization of COT.

Notes: The product quantum yields in the photolysis of 2,2,4,4-tetramethyl-3-pentanone have been measured in homogeneous solvents of different viscosities, in micellar solutions of cetyltrimethylammonium chloride and sodium dodecyl sulfate, and in dioctadecyl ammonium chloride vesicles.The product quantum yield in n-heptane was found to be 1. This value decreases to 0.5 in paraffin oil as a consequence of geminate recombination. In the presence of free radical scavengers, the extent of geminate disproportionation can be evaluated from the yields of isobutene and 2,2-dimethyl propionaldehyde. From these yields and the geminate recombination yields the total amount of geminate processes and the disproportionation-to-combination ratio for caged radicals are estimated. It is found that micelles provide the most efficient cages. In these media only about 10% of the radicals avoid cage processes. The disproportionation-to-combination ratio of tert-butyl and pivaloyl radicals was found to be extremely media dependent. The measured values ranged from about 0.2 in paraffin oil to 0.8 in cetyltrimethylammonium chloride micelles.

Notes: Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300-1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.

Notes: The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8-94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:The temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 /k_2 = (1.099 \pm 0.015)\exp [(429 \pm 2)/T] $$ $$ k_1 /k_r = (1.422 \pm 0.026)\exp [(1113 \pm 3)/T] $$ $$ k_2 /k_r = (1.295 \pm 0.029)\exp [(684 \pm 3)/T] $$ $$ k_3 /k_r = (1.177 \pm 0.025)\exp [(717 \pm 4)/T] $$ $$ k_4 /k_r = (1.115 \pm 0.023)\exp [(732 \pm 2)/T] $$ $$ k_5 /k_r = (0.978 \pm 0.020)\exp [(985 \pm 2)/T] $$\end{document} and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.

Notes: The reaction between ozone and carbon monoxide was reinvestigated in the range of 80-160°C. The previously reported rate law -d[O3]/dt = ka[O3][CO] + kb[O3]2 was confirmed and simulated using a mechanism based on an impurity-initiated chain reaction. When the CO was sufficiently purified, kb tended to zero and ka reduced to the value expected for the thermal decomposition of O3. Subsequent reactions of O atoms with CO produced chemiluminescence which was used to measure k3 for \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm O}\,\, + \,\,{\rm CO}\,\,\mathop {\longrightarrow}\limits^{\rm 3} \,\,{\rm CO}_{\rm 2} \left( {^3 B_2 } \right) $$\end{document} as 10-14.0±0.3 exp[-(1630 ± 325)/T] cm3 molecule-1 s-1. The implications of this are discussed.

Notes: The thermal decomposition of azoisopropane (AIP) was studied by detailed product analysis in the temperature and pressure intervals 498-563 K and 0.67-5.33 kPa. Besides the predominant termination and hydrogen-abstraction reaction of the 2-propyl radical, the decomposition is characterized by a very short chain process. The following rate constants were determined from the measurements\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{rcl} \log (k_1 {\rm /s}^{ - 1} ) &=& (16.3 \pm 0.2) - (199.9 \pm 1.6){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_4 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (4.1 \pm 0.3) - (52.5 \pm 3.0){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_5 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (2.4 \pm 0.1) - (27.6 \pm 1.3){\rm kJ mol}^{ - 1} /2.3RT \\ k_2 /k_3 &=& 0.51 \pm 0.02 \end{array}$$\end{document} for the following reactions:

Notes: Chlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3-chloropropene, cis- and trans-1-chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.

Notes: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254-425 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule-1 S-1): k1 = (1.33 ± 0.29) × 10-11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10-12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10-11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.

Notes: The reactions of ground-state S(3PJ) atoms with thiirane, methylthiirane, and trans-2,3-dimethylthiirane have been studied by flash photolysis-VUV kinetic absorption spectroscopy. From the analysis of the S(3PJ) decay plots the following rate constants were determined: (1.4 ± 0.2) × 1013, (2.7 ± 0.3) × 1013 and (4.0 ± 0.2) × 1013 (in cm3 mol-1 s-1 units) for thiirane, methylthiirane and trans-2,3-dimethylthiirane, respectively, showing an upward trend with increasing methylation.

Notes: NO Abstract.

Notes: An examination of the results of measurements of the forward and reverse rate constants for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm H} + {\rm C}_{\rm 2} {\rm H}_{\rm 6} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {\rm H}_{\rm 2} + {\rm C}_{\rm 2} {\rm H}_{\rm 5} $$\end{document} shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol-1. This system therefore provides further support for the recent measurement of this quantity.

Notes: The very low pressure reactor (VLPR) technique has been used to measure the bimolecular rate constant of the title reaction at 300 K. The rate constant is given by log k1 (1/mol s) = (11.6 ± 0.4) - (5.9 ± 0.6)/θ the equilibrium constant has also been measured at the same temperature and is given by K1 = (5.6 ± 1) × 10-3 and hence log k-1 (1/mol s) = 9.5 ± 0.1. The results show that the reaction Br + t—C4H9 → HBr + i—C4H8 is unimportant under the present experimental conditions. Assigning the entropy of t-butyl radical to be 74 ± 2 eu which is in the possible range, the value of K1 gives ΔH°f (t-butyl) = 9.1 ± 0.6 kcal/mol-1. This yields for the bond dissociation, DH° (t-butyl-H) = 93.4 ± 0.6 kcal/mol. Both of these values are found to be in good agreement with recent VLPP studies.

Notes: Kinetics of the basic hydrolysis of glyceryl trinitrate (TNG) were investigated in CO2-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. TNG hydrolyzed via second-order reaction at 25°C, 18°C, and 10°C. The activation energy of the hydrolysis reaction of TNG was calculated from the kinetic data and found to be equal to 27.53 kcal/mol. The major products of the hydrolysis of TNG in solution of calcium hydroxide were calcium nitrate and calcium nitrite, accounting for approximately 50% of the degradation products. The minor identified products such as calcium oxalate and nitrate esters amounted to approximatey 6% of the products. The remaining 30% of the isolated products was a mixture of calcium formate, a nitrate ester, and unidentified volatiles, polymerlike substances, and other organic residue.

Notes: Results obtained from the photolysis of ketene with acetylene strongly support the formation of C3H3 radicals in the title reaction. Stationary state studies are interpreted in terms of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_3 {\rm H}_{\rm 4}^{\rm *} \buildrel3\over\rightarrow{\rm C}_3 {\rm H}_3^ \cdot + {\rm H}^ \cdot$$\end{document} with a rate constant (109.8 s-1) which is compared to RRKM predictions. In pulsed laser induced decomposition experiments, recombination products involving C3H3 have been detected (some for the first time) and their formation modeled using step (3) with the same rate constant.

Notes: A readily applicable empirical formula is obtained for the collisional efficiency for energy transfer between a highly vibrationally excited reactant and a seasoned (usually quartz) wall, in terms of the molecular weight, potential well depth and dipole moment of the reactant. This expression is used to examine corrections due to nonunit wall collision efficiency in the high-pressure rate parameters obtained from very low-pressure pyrolysis experiments. It is found that these corrections are up to ca. ±5 kJ/mol in the high-pressure activation energy and a factor of ca. 2 in the high-pressure frequency factor, for molecules with molecular weight less than ca. 100 and where experiments are carried out at temperatures exceeding 1000 K.

Notes: The rate constants for reactions (4) and (5) were determined at room temperature by pulsed laser photolysis and time resolved mass spectrometry. A description of the experimental setup is given. CFCl2O2 radicals were generated by photolysis of CFCl3 at 193 nm in the presence of an excess of oxygen, using an excimer laser. The rate constant for reaction (4), determined under different experimental conditions is: \documentclass{article}\pagestyle{empty}\begin{document}$$k_4 = 1.6{\rm }(\pm 0.2) \times 10^{ - 11} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1}$$\end{document} The rate constant of reaction (5) was determined in the pressure range of 1-12 torr, using oxygen as the buffer gas. The reaction is in its fall-off region and the parameters determined by using the semiempirical method of Troe, taking Fc = 0.6 are: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k(0) = 3.5{\rm }(\pm 0.5) \times 10^{ - 29} {\rm cm}^{\rm 6} \cdot {\rm molecule}^{ - 2} \cdot {\rm s}^{ - 1} \\ k(\infty) = 6.0{\rm }(\pm 1.0) \times 10^{ - 12} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1} \\ \end{array}$$\end{document} The value of k(∞) is obtained from the low-pressure measurements and therefore the uncertainty on the actual high-pressure limit is higher than the error limits quoted above. The results are compared with those reported for similar reactions.

Notes: Potassium persulfate oxidizes triphenylphosphine to triphenylphosphine oxide in 60% aqueous acetonitrile. It has been suggested that the oxygen of the product, triphenylphosphine oxide, might originate from solvent water, following nucleophilic attack on an intermediate phosphonium ion. We have investigated the origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate in 60% aqueous acetonitrile containing 20% [18O]water. The product was analyzed by using the 18O isotope effect in 31P NMR spectroscopy. The magnitude of the 18O isotope-induced shift was determined by synthesizing triphenylphosphine [18O]oxide and was found to be 0.038 ppm upfield. The product of the oxidation reaction in 20% [18O]water displayed no 18O isotope effect. The origin of the oxygen in the oxidation reaction is the persulfate ion, consistent with an alternative mechanism involving nucleophilic attack by water at the sulfur atom of a phosphonium peroxysulfate intermediate.

Notes: It is shown how kinetic electron spin resonance spectroscopy with intermittent radical generation can be used to obtain rate constants of various simultaneous reactions in systems containing more than one kind of transient radicals. The technique is applied to reactions of tert-butyl [(CH3)3Ċ] and isopropylol [(CH3)2ĊOH] radicals generated by photolysis of di-tert-butyl ketone and acetone in 2-propanol/acetone mixtures. It yields the rates of generation of the two radicals, the rate constants for their self- and crossterminations and for the reaction of tert-butyl with 2-propanol. The extent of diffusion control of the termination constants is discussed.

Notes: Trifluoro-t-butoxy radicals have been generated by reacting fluorine with 2-trifluoromethyl propan-2-ol: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \dot F} + {\rm CF}_3 {\rm C}({\rm OH})({\rm CH}_3)_2 \to {\rm HF} + {\rm CF}_3 {\rm C}({\rm \dot O})({\rm CH}_3)_2 $$\end{document} Over the temperature range 361-600 K the trifluoro-t-butoxy radical decomposes exclusively by loss of the —CF3 group [reaction (-2)] rather than by loss of —CH3 group [reaction (-1)]: The limits of detectability of the product CF3COCH3, by gas-chromatographic analysis, place a lower limit on the ratio k-2/k-1 of ca. 75. The implications of these results in relation to the reverse radical addition reactions to the carbonyl group are discussed along with the thermochemistry of the reactions.

Notes: The gas-phase reaction of CF3 with HCN has been examined over a wide conversion range using CF3I as a thermal and photolytic source of radicals. Quantitative and qualitative results show a significant increase of the specific rate constant for the hydrogen abstraction reaction relative to CF3 recombination when reaction is carried out under ultraviolet irradiation. This “extra” formation of the reaction product, CF3H, has been assigned to the participation of iodine in this system through the formation of a (I-HCN) intermediate. Arrhenius parameters obtained for the addition mechanism of I to HCN do not seem to conform to a single reaction step, on the contrary, they correspond to a more complex reaction scheme.

Notes: Small low residence time flow tube reactors made of alumina and used as molecular beam sources are described. In these reactors, gas mixtures are rapidly heated and brought to reaction. The composition of the gas leaving the reactor is analyzed by molecular beam mass spectroscopy. For quantitative simulation of the reacting gas flow, the theory of one-dimensional compressible flow with friction, heat transfer, and chemical reaction is brought into a form suitable for practical computation. The system has been applied to study the thermal decompositions of O3 and N2O. The experimental results on both reactions can be well modeled by homogeneous reaction mechanisms with accepted rate constants. Heterogeneous reaction steps are shown to be unimportant.

Notes: The yield of benzene in the reaction of 1,4- and 1,3-cyclohexadiene with OH radicals in the presence of oxygen was determined using H2O2 and CH3ONO as OH radical sources. Both in the H2O2 and the CH3ONO systems, the yield of benzene from 1,4-cyclohexadiene was 15.3% and the yield from 1,3-cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per C—H in cyclohexadiene was determined to be 3.8 × 10-12 cm3 molecule-1 s-1. The branching ratio of the hydrogen abstraction to overall reaction for 1-butene and 1-pentene was estimated to be (25-14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts [4].

Notes: The photolysis of carbon tetrachloride in the presence of a number of organosilicon compounds has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the organosilane. Arrhenius parameters for hydrogen atom transfer were determined relative to those for trichloromethyl radical combination. The activation energies for the reaction of methyl, trifluoromethyl, and trichloromethyl radicals with organosilicon compounds are compared and the results rationalized in terms of polar effects.

Notes: Calculations of low-pressure limit, third-order rate constants are presented for the association reactions A + O2 + N2 and A + OH + N2 (A = Li, Na, K) over the temperature range 200-2000 K and a comparison is made with the available experimental data.

Notes: The photooxidation of formaldehyde in CH2O—O2, oxygen-lean mixtures was studied in the temperature range 298-378 K. H2 and CO formation and the loss of O2 proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO2 + CH2O ⇄ HO2CH2O (5) is now assumed to be reversible and ΔH5° is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H2 and CO and of the consumed O2 remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH2O → H2O HCO† (7), HO + CH2O → H2O + HCO (8) and HO + CH2O → HOCH2O (9) are temperature independent.

Notes: The kinetics of OH reactions with 1-4 carbon aliphatic thiols have been investigated over the temperature range 252-430 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2-4.6 × 10-11 cm3 molecule-1 s-1, -Eact = 0.6-1.0 kcal/mol, A = 0.6-1.2 × 10-11 cm3 molecule-1 s-1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.

Notes: The oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Charton's triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 9-16, 1997.

Notes: By conducting an excimer laser photolysis (193 and 248 nm) behind shock waves, three elementary reactions important in the oxidation of H2S have been examined, where, H, O, and S atoms have been monitored by the atomic resonance absorption spectrometry. For HS + O2 → products (1), the rate constants evaluated by numerical simulations are summarized as: k1 = 3.1 × 10-11exp|-75 kJ mol-1/RT| cm3molecule-1s-1 (T = 1400-1850 K) with an uncertainty factor of about 2. Direct measurements of the rate constants for S + O2 → SO + O (2), and SO + O2 → SO2 + O (3) yield k2 = (2.5 ± 0.6) × 10-11 exp|-(15.3 ± 2.5) kJ mol-1/RT| cm3molecule-1s-1 (T = 980-1610 K) and, k3 = (1.7 ± 0.9) × 10-12 exp|-(34 ± 11) kJ mol-1/RT| cm3molecule-1s-1 (T = 1130-1640 K), respectively. By summarizing these data together with the recent experimental results on the H(SINGLE BOND)S(SINGLE BOND)O reaction systems, a new kinetic model for the H2S oxidation process is constructed. It is found that this simple reaction scheme is consistent with the experimental result on the induction time of SO2 formation obtained by Bradley and Dobson. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 57-66, 1997.

Notes: Rate constants have been measured for the reaction of OH radicals with four amides, R1N(CH3) - C(O)R2 (R1 = H or Methyl, R2 = Methyl or Ethyl), at 300 and 384 K using flash photolysis/resonance fluorescence. Reactants are introduced under slow flow conditions and are controlled by two independent methods, gas saturation and continuous injection. It turns out that the reactivities of the amides are considerably lower than those of the corresponding amines. The pattern of rate constants obtained at 300 K: 14, 21, 5.2, and 7.6 · 10-12 cm3/s for N,N-Dimethylacetamide (dmaa), N,N-Dimethylpropionamide (dmpa), N-Methylacetamide (maa), and N-Methylpropionamide (mpa), respectively, indicates a single, dominating reaction center and strong electronic effects of the substituents at both sides of the amide function. Correspondingly, the observed negative temperature dependence (E/R = - 400 to - 600 K) excludes a direct abstraction mechanism. © 1997 John Wiley & Sons, Inc.

Notes: The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5-5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH 〉 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO+/NO2H2+ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol 〉 phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH# against ΔS# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO+/NO2H2+. © 1997 John Wiley & Sons, Inc.

Notes: For a number of hydrofluorocarbons (HFCs), EHez has been found to have a linear correlation with each of the following: (i) log (k/n); (ii) A/n; and (iii) Ea/R, where EH = HOMO energy of the molecule, z = average fractional positive charge on the abstractable hydrogen atom in the molecule, k = rate constant of the gas-phase H abstraction reaction of the molecule with OH radical at 298 K, n = number of abstractable H atoms in the molecule, A = preexponential factor, and Ea/R = activation temperature of the said reaction. These correlations have been used to estimate the temperature dependent rate constants for the reactions of OH radical with CF3CF2CH2CH2CF2CF3, CF3CH2CF2CH2CF3, CF3CF2CH2CH2F, CF3CH2CH3, CF3CH2CHF2, CF3CHFCH2F, and CHF2CHFCHF2 as {6.97 × 10-13 exp(1481/T)}, {5.43 × 10-13 exp(1754/T)}, {7.95 × 10-13 exp(l308/T)}, {8.0 × 10-13 exp(1300/T)}, {7.03 × 10-13 exp(1470/T)}, {7.33 × 10-13 exp(1417/T)}, and {8.09 × 10-13 exp(1285/T)}, respectively. These have not yet been measured experimentally. Linear correlation between EHez and log (k/n) has also been observed for nine halogen substituted acetaldehydes. On the other hand, EH is found to have a better linear correlation with log (k/n) than EHez in the case of fluorinated ethers and alcohols where the available experimental data are at present limited. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 187-194, 1997.

Notes: The reaction between the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and phenols follows a kinetic law given by \documentclass{article}\pagestyle{empty}\begin{document}$$ d[ABTS^{\buildrel{+}\over{\cdot}}]/dt=k [ABTS^{\buildrel{+}\over{\cdot}}]^2[PhOH]/[ABTS] $$\end{document} with stoichiometric coefficients between one and two. The rate constant is almost unrelated to the structure of the phenol, while the number of ABTS radicals scavenged by each phenol molecule increases with para-substitution. These results are explained in terms of a fast, reversible electron transfer \documentclass{article}\pagestyle{empty}\begin{document}$$ ABTS^{\buildrel{+}\over{\cdot}}\,+PhOH {\buildrel{\longrightarrow}\over{\longleftarrow}} ABTS + PhO\bullet+H^{+} $$\end{document} followed by the self-combination of the phenoxy radicals and/or their reaction with another ABTS derived radical action. The relative rate of these processes determine the value of the stoichiometric coefficient. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 219-224, 1997.

Notes: A continuous flow-through reactor with a thin layer of solid particles (size ranging from 100 to 300 μm) was used to obtain a deeper knowledge on the mechanism of dissolution of UO2 under oxidizing conditions. Using this methodology the dissolution rate of uranium dioxide was determined at three different oxygen partial pressures (5, 21, and 100% in nitrogen) and as a function of pH (between 3 and 12) in a noncomplexing medium.From the results of these experiments the following rate equation was derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ (3 〈 pH 〈 6.7)\,r\,(mol\cdot s^{-1}\cdot m^{-2})\,=\,(3.5 \pm 0.8) \cdot 10^{-8} \cdot [H^{+}]^{0.37\pm 0.01}\cdot[O_2]^{0.31\pm 0.02} $$\end{document} In addition, XPS characterizations were performed to determine the U(IV)/U(VI) ratio on the solid surface at different experimental times and conditions. These results showed that at acidic conditions (pH below 6.7) the final solid surface presents a stoichiometry close to UO2, while at alkaline conditions the final solid surface average composition is close to UO2.25. This information was integrated with the results of the leaching experiments to present a model for the mechanism of dissolution of uranium dioxide under the experimental conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 261-267, 1997.

Notes: The kinetics of the gas-phase reactions of OH radicals, NO3 radicals, and O3 with indan, indene, fluorene, and 9,10-dihydroanthracene have been studied at 297 ± 2 K and atmospheric pressure of air. The rate constants, or upper limits thereof, for the O3 reactions were (in cm3 molecule-1 s-1 units): indan, 〈 3 × 10-19; indene, (1.7 ± 0.5) × 10-16, fluorene, 〈 2 × 10-19; and 9,10-dihydroanthracene, (9.0 ± 2.0) × 10-19. Using a relative rate method, the rate constants for the OH radical and NO3 radical reactions, respectively, were (in cm3 molecule-1 s-1 units): indan, (1.9 ± 0.5) × 10-11 and (6.6 ± 2.0) × 10-15; indene, (7.8 ± 2.0) × 10-11 and (4.1 ± 1.5) × 10-12; fluorene, (1.6 ± 0.5) × 10-11 and (3.5 ± 1.2) × 10-14; and 9,10-dihydroanthracene, (2.3 ± 0.6) × 10-11 and (1.2 ± 0.4) × 10-12. These kinetic data were used to assess the relative contributions of the various reaction pathways. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 299-309, 1997.

Notes: A laser-flash photolysis/UV absorption technique has been used to study the temperature dependence (from T = 300 - 470 K) of the self-reaction kinetics of representative primary secondary and tertiary β-hydroxyperoxy radicals \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{lclr} 2\,\rm{HOCH}_2\rm{CH}_2\rm{O}_2 & \longrightarrow & 2\,\rm{HOCH}_2\rm{CH}_2\rm{O}\,+\,\rm{O}_2 & (1\rm{a})\\ & \longrightarrow & \rm{HOCH}_2\rm{CH}_2\rm{OH}\,+\rm{HOCH}_2\rm{CH}_2\rm{O}\,+\,\rm{O}_2 & (1\rm{b})\\ 2\,\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}_2 & \longrightarrow & 2\,\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}\,+\,\rm{O}_2 & (2\rm{a})\\ & \longrightarrow & \rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{OH} & \\ & &+\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}+\rm{O}_2 & (2\rm{b})\\ 2\,\rm{HOC}(\rm{CH}_3)_2\rm{C}(\rm{CH}_3)_2\rm{O}_2 & \longrightarrow & 2\,\rm{HOC}(\rm{CH}_3)_2 \rm{C}(\rm{CH}_3)_2\rm{O}\,+\,\rm{O}_2 & (3)\\ \end{array} $$\end{document} The following Arrhenius expressions were derived for the rate coefficients of reactions (1)-(3) (in cm3 molecule -1s-1) and for the product branching ratios of reactions (1) and (2) as a function of temperature (all errors 1σ) \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l}k_1=(6.9_{+2.1}^{-1.5})\times 10 ^{-14}\,\exp[(1040\pm 100)/\rm{T}]\\ \beta_1=(3100_{+3700}^{-1700})\,\exp[(-2400\pm 280)/\rm{T}] (\hbox{ where } \beta_1=k_{1a}/k{1\rm{b}})\\ k_2=(7.7_{+12.8}^{-4.8})\times 10 ^{-15}\,\exp[(1330\pm 350)/\rm{T}]\\ \beta_2=(4.0_{+0.2}^{-0.1})\times 10 ^{4}\,\exp[(-3600\pm 100)/\rm{T}]\\ k_3=(4.7_{+6.5}^{-2.7})\times 10 ^{-13}\,\exp[(-1420\pm 320)/\rm{T}]\\ \end{array} $$\end{document} The calculated rate coefficients for reactions (1)-(3) at 298 K are therefore (in 10-13 cm3molecule -1s -1 23 ± 2, 6.7 ± 1.3, and 0.040 ± 0.012, respectively which compare well with the values measured elsewhere at this temperature using a similar technique. The product branching ratios and the Arrhenius parameters are compared with those for other substituted and unsubstituted peroxy radical self reactions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 323-331, 1997

Notes: The gas-phase reactivities of W(a5DJ, a7S3) with N2O, SO2, and NO in the temperature range of 295-573 K are reported. Tungsten atoms produced by the photodissociation of W(CO)6. The tungsten atoms were detected by a laser-induced fluorescence technique. The removal rate constants for the 6s25d4 a5Dl states were found to be pressure dependent for all of the reactants. Removal rate constants for the 6s15d5 a7S3 state were found to be fast compared to the a5DJ states and often approached the gas kinetic rate constant. The reaction rates for all the states were found to be pressure independent with respect to the total pressure. Results are discussed in terms of the different electronic configurations of the states of tungsten © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 367-375 1997

Notes: Real-time kinetic measurements are reported for the Cl + CH3CO → CH2CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10-200 torr and a temperature range of 215-353 K. Within experimental error the rate constant under these conditions is k5a = (1.8 ± 0.5) × 10-10 cm3 s-1. We have also examined the Cl + CH2CO reaction and found it to have a rate constant of k6 = (2.5 ± 0.5) × 10-10 cm3 s-1 independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421-429, 1997.

Notes: The kinetics of oxidation of indigo carmine (IC) by N-sodio-N-bromotoluenesulfonamide or bromamine-T (BAT) in pH 5 buffer medium has been investigated at 30°C using spectrophotometry at 610 nm. The reaction rate shows dependencies of first-order on [IC]0 second-order on [BAT]0, fractional order on [H+], and inverse first-order on [ρ-toluenesulfonamide]. The addition of chloride and bromide ions, and the variation of ionic strength of the medium have no influence on the reaction rate. There is a negative effect of the dielectric constant of the solvent. Activation parameters have been calculated. A single-pathway mechanism for the reaction, consistent with the kinetic data, has been proposed. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 453-459, 1997

Notes: The Cl- and Br- initiated oxidations of CHCl(DOUBLEBOND)CCl2 in 700 torr of air at 296 K have been studied using a Fourier transform infrared spectrometer. Rate constants k(Cl+CHCl(DOUBLEBOND)CCl2)=(7.2±0.8)×10-11 and k(Br+CHCl(DOUBLEBOND)CCl2)=(1.1±0.4)×10-13 cm3 molecule-1 s-1 were determined using a relative rate technique with ethane and ethylene as references, respectively. The major products observed were CHXClC(O)Cl, (X=Cl or Br), CHClO, and CCl2O. Combining results obtained for the Cl-initiated oxidation of CHCl2(SINGLEBOND)CHCl2, we deduced that Cl-addition on trichloroethylene occurs via channel 1a, Cl+CHCl(DOUBLEBOND)CCl2→ CHCl2(SINGLEBOND)CCl2, (100±12)%. Self-reaction of the subsequently generated peroxy radicals CHCl2(SINGLEBOND)CCl2O2 leads to CHCl2CCl2O radicals which were found to decompose via channel 8a, CHCl2C(O)Cl+Cl, (91±11)% of the time, and channel 8b, CHCl2+CCl2O, (9±2)%. The reaction Br+CHCl(DOUBLEBOND)CCl2→CHBrCl(SINGLEBOND)CCl2 (17a) accounted for ≥(96±11)% of the total reaction. Decomposition of the CHBrCl(SINGLEBOND)CCl2O radicals proceeds (≥93±11)% via CHBrClC(O)Cl+Cl. As part of this work, k(Cl+CHCl2C(O)Cl)=(3.6±0.6)×10-14 and k(Cl+CHCl2(SINGLEBOND)CHCl2)=(1.9±0.2)×10-13 cm3 molecule-1 s-1 were measured. Errors reported above include statistical uncertainties (2σ) and estimated systematic uncertainties. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 695-704, 1997.

Notes: The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35°C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate=k[BAB][OsO4][OH-]x, which in the absence of the catalyst changes to the form, rate=k[BAB][S][OH-]y, where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO2NBr-, and the catalyst, OsO4, in the rate determining step. This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO2NBr-, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80×103 at 35°C. The average value for the same constant for the uncatalyzed reactions is 1.02×104 at 35°C. © 1997 John Wiley & Sons, Inc.

Notes: Relative rate coefficients for the reaction of acetyl (CH3CO) radicals with O2 (k4) and Cl2 (k7) have been obtained at 298 K and 228 K as a function of total pressure, using FTIR/environmental chamber techniques. Measured values of k4/k7 were placed on an absolute basis using k7=2.8×10-11 exp(-47/T) cm3 molec-1 s-1. At 298 K, the value of k4 is constant ((7±2)×10-13 cm3 molec-1 s-1) at pressures from 0.1 to 2 torr, then increases to a high pressure limiting value of (3.2±0.6)×10-12 cm3 molec-1 s-1, which is approached at pressures above 300 torr. At 228 K, the low-pressure value of k4 increases by about 20-30%, while the high pressure value remains unchanged. Experiments designed to elucidate the products of reaction (4) as a function of pressure at 298 K indicate that the reaction occurs via a concerted mechanism in which CH3CO radicals combine with O2 to give an excited acetylperoxy radical (CH3COO2*) which is increasingly stabilized at high pressure at the expense of a low pressure decomposition channel. The yield of acetylperoxy radicals from reaction (4) decreases from 〉95% at pressures above 100 torr, to about 90% at 60 torr, and 50% at 6 torr. Indirect evidence for formation of OH radicals from the low pressure decomposition is presented, although the carbon-containing coproduct(s) of this channel could not be identified. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 655-663, 1997.

Notes: The sodium-hydrogen ion exchange constant for the system sodium 1-dodecanesulfonate-hydrochloric acid in aqueous acetonitrile has been determined from the pseudo-phase ion exchange model for surfactant catalytic effects. The results indicate that the micellar system behaves similarly for the aqueous and the aqueous acetonitrile (2.106 M) solvent systems.The influence of substrate molecular structure on micellar catalysis by perfluorooctanoic acid of the hydrolysis of hydroxamic acids (R - CO - NHOH) in aqueous acetonitrile has been explored. Data for substrate structures of fifteen compounds with R=alkyl, aralkyl, alicyclylalkyl, phenylalkyl, alkyl-substituted phenylalkyl, and with chain branching at the α, β, and γ positions are compared. Relative binding constant values indicate that substrates with aromatic groups are less well solubilized in the perfluoro micellar environment than are substrates with saturated groups.There is now evidence for specific micellar effects on the reaction rate as well as general micellar catalysis. © 1997 John Wiley & Sons, Inc.

Notes: It is shown experimentally that pentafluoroethane undergoes rapid protium-deuterium exchange with water in the presence of hydroxide ion. Addition of dimethylsulfoxide enhances the rate at least by a factor of 100. The first measured fractionation factor data are presented for the temperature range of 50-120°C. These values are compared with the theoretical estimations calculated by using isotopic reduced partition function ratios based on molecular vibrational frequencies. Although catalytic exchange is slow at ambient temperature, the reaction rate becomes measureable above around 60°C because of large activation energy (92 kJ/mole). Comparisons are made with similar data available for various halomethane and haloethane systems. © 1997 John Wiley & Sons, Inc.

Notes: Experimental kineticists are always faced with the problem of reducing kinetic data to extract physically meaningful information. A particularly vexing problem arises when different models reproduce the data but yield different values for the physical parameters. For over forty-five years Monte Carlo simulation techniques have been used to study the statistical behavior of parameters extracted from data. Not only do these simulations provide realistic uncertainties, correlation coefficients, and confidence envelopes, but they also provide insight into the nature of the model. These insights may be obtained by viewing two-dimensional scatter plots of the fractional changes of the parameters and one-dimensional histograms of the distributions of the changes in the parameters. Monte Carlo simulations are illustrated with examples from OH+CH4 → CH3+H2O and the high-pressure rate coefficient for methyl-methyl association. A more complex problem involves models for pressure-dependent rate coefficients in the falloff region. We have modeled methyl-methyl association with five of the most current analytic approximations for behavior in the falloff region. All of these reproduce the data to within their uncertainties. However, when Monte Carlo techniques are applied the correlations between the parameters and the nonlinear nature of their behavior become evident. We postulate that the statistical behavior of the parameters of a model may be used to distinguish one model from another and, thereby, identify those analytic approximations that hold promise for further investigation and utilization. Finally, the recent advent of high-speed workstations implies that Monte Carlo simulations should become a routine part of the analysis of kinetic data. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 803-817, 1997

Notes: Rate constants for three dimethylbenzaldehydes and two trimethylphenols have been determined for the OH reactions at 298±2 K and atmospheric pressure using a relative rate method. The OH reaction rate constants were placed on an absolute basis using the literature rate constant for 1,2,4-trimethylbenzene of (3.25±0.5)×10-11 cm3 molecule-1s-1). The measured rate constants were (in units of cm3 molecule-1 s-1) 2,4-dimethyl-benzaldehyde, (4.32±0.67)×10-11; 2,5-dimethylbenzaldehyde, (4.37±0.68)×10-11; 3,4-dimethylbenzaldehyde, (2.14±0.34)×10-11; and 2,3,5- trimethylphenol, (12.5±1.9)×10-11, 2,3,6-trimethylphenol, (11.8±1.8)×10-11. Using an average OH concentration of 8.7×105 molecule cm-3, the estimated atmospheric lifetimes are ca. 7.5 h for 2,4- and 2,5-dimethylbenzaldehydes, ca. 15 h for 3,4-dimethylbenzaldehyde, ca. 2.5 h for 2,3,5- and 2,3,6-trimethylphenols. The reactivities of the trimethylphenols exceed those of the dimethyl-benzaldehydes by more than a factor of 3. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 523-525, 1997.

Notes: The kinetics of the oxidation of formate, oxalate, and malonate by |NiIII(L1)|2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0-5.75, 2.80-5.50, and 2.50-7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|NiIII(L1)2+| = kobs|NiIII(L1)2+| = (kd + nks |R|)|NiIII(L1)2+|, where kd is the auto-decomposition rate constant of the complex, ks is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: kHCOOH 〉 kHCOO-; kH2ox 〉 kHox- 〉 kox2-, and kH2mal 〉 kHmal- 〈 kmal2- for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225-230, 1997.

Notes: Na2(Mo2vO4EDTA).4H2O crystals have been prepared in pure form. Kinetics for the oxidation of the compound by S2O82- have been studied spectrophotometrically in dilute sulphuric acid medium. The effects of hydrogen ion concentration, metal ion concentration, S2O82- ion concentration, and temperature on the process have been studied. Rate equations have been derived to explain the experimental observations. On the basis of the observations, suitable mechanisms have been suggested. The kinetic parameters E*, ΔH≠, and ΔS≠ of the process have also been determined. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 269-274, 1997

Notes: The rates of gas-phase elimination reactions of methyl benzoylformate (1) and 3-hydroxy-3-methyl-2-butanone (2) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 - 53270/(4.574 × 600) for (1) and log k = 12.4 - 53060/(4.574 × 600) for (2). The products of pyrolysis of (1) are benzaldehyde, formaldehyde and CO, while those of (2) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 106-fold more reactive than (1), and pyruvic acid ca. 105-fold more reactive relative to (2); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 295-298, 1997.

Notes: A differential method for analyzing first-order kinetic data is presented. While the essence of this approach has been known for almost a century, the use of computers to collect, store, and manipulate data has reenergized this innovative idea. Based on the equation ln |dA1/dt| = ln |k(Ao - A(infinity))| - kt, plots of ln |dAt/dt| vs. t were found to be lienar for both simulated kinetic data and data collected for the reaction of [(en)2Co(SCH2CH2NH2)]2+ with acrylamide. The rate constants for the reaction obtained by this method are identical to those obtained by the infinite-time method of analysis but do not require infinite-time measurements in their evaluation. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 333-338, 1997

Notes: Relative rate constant measurements have been carried out on the Cl-atom reactions with benzene, chlorobenzene, toluene, xylene, and styrene in 740 torr of air at room temperature (295 K), using the photochemical reactor-FTIR spectroscopy technique. The Cl atoms were generated by the UV photolysis of Cl2, and the reference compounds were CHF, Cl for benzene and chlorobenzene and isobutane for toluene xylene and styrene. Using the absolute rate constant for these two reference compounds reported in the literature, the following kinetic data were obtained for the study compounds (in units of cm3s-1). \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{ll} {\rm Benzene} & (1.3\pm 0.3)\times 10 ^{-15}\\ {\rm Chlorobenzen} & (9.8\pm 2.4)\times 10 ^{-16}\\ {\rm Toluene} & (5.9\pm 0.5)\times 10 ^{-11}\\ o-{\rm Xylene} & (1.5\pm 0.1)\times 10 ^{-10}\\ m-{\rm Xylene} & (1.4\pm 0.1)\times 10 ^{-10}\\ p-{\rm Xylene} & (1.5\pm 0.1)\times 10 ^{-10}\\ {\rm Styrene} & (3.6\pm 0.3)\times 10 ^{-10}\end{array} $$\end{document} The quoted error bars are for ± 2σ. The present kinetic results are compared with available literature data to update and expand the kinetics database for Cl-atom reactions of organic compounds. The results are also analyzed to provide insights into the reaction mechanism for the Cl-atom initiated oxidation of benzene under atmospheric conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 349-358, 1997

Notes: The initiation reaction of the thermal decomposition of silicon tetrachloride \documentclass{article}\pagestyle{empty}\begin{document}$$ SiCl_4\,+\,M\,{\buildrel{k_1}\over{\longrightarrow}} SiCl_3\,+Cl\,+M \eqno(R1) $$\end{document} was studied behind reflected shock waves at temperatures between 1550 K and 2370 K and pressures between 1 and 1.5 bar. Atomic resonance absorption spectrometry (ARAS) was applied for time-resolved measurements of H atoms at the Lα-line in SiCl4/H2/Ar systems. Additional experiments were performed in the SiCl4/Ar system following the absorption of SiCl4 at the Lα-line. Rate coefficients for the reaction (RI) were determined to be: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1=4.8\times 10^{16}\exp(-40954 K/T) cm^3 mol^{-1} s^{-1}. $$\end{document} The choice between two possible alternatives of the first decomposition step, namely elimination of either Cl2 or Cl, has been made in favor of the second reaction on the basis of kinetic and energetic considerations. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 415-420, 1997.

Notes: Mixtures of cyclopentadiene diluted with argon were used to investigate its decomposition pattern in a single pulse shock tube. The temperatures ranged from 1080 to 1550 K and pressures behind the shock were between 1.7-9.6 atm. The cyclopentadiene concentrations ranged from 0.5 to 2%. Gas-chromatographic analysis was used to determine the product distribution. The main products in order of abundance were acetylene, ethylene, methane, allene, propyne, butadiene, propylene, and benzene. The decomposition of cyclopentadiene was simulated with a kinetic scheme containing 44 species and 144 elementary reactions. This was later reduced to only 36 reactions. The ring opening process of the cyclopentadienyl radical was found to be the crucial step in the mechanism. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 505-514, 1997.

Notes: Rate constants for the reactions of OH, NO3, and O3 with pinonaldehyde and the structurally related compounds 3-methylbutanal, 3-methylbutan-2-one, cyclobutyl-methylketone, and 2,2,3-trimethyl-cyclobutyl-1-ethanone have been measured at 300±5 K using on-line Fourier transform infrared spectroscopy. The rate constants obtained for the reactions with pinonaldehyde were: kOH=(9.1±1.8)×10-11 cm3 molecule-1 s-1, kNO3=(5.4±1.8)×10-14 cm3 molecule-1 s-1, and kO3=(8.9±1.4)×10-20 cm3 molecule-1 s-1. The results obtained indicate a chemical lifetime of pinonaldehyde in the troposphere of about two hours under typical daytime conditions, [OH]=1.6×106 molecule cm-3. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 527-533, 1997.

Notes: CF3O2CF3 was photolyzed at 254 nm in the presence of CO in 760 torr N2 or air at 296 K in a static reactor. In N2, the products CF3OC(O)C(O)OCF3 and CF3OC(O)O2C(O)OCF3 were detected by FTIR spectroscopy. In air, the only observed products were CF2O and CO2 and a chain process, initiated by CF3O, was invoked for the conversion of CO to CO2. From both product studies, a mechanism for the CF3O initiated oxidation of CO was derived, involving the addition reaction CF3O2 + CO → CF3OC(O). The rate constant for the reaction CF3O + CO at 296 K at a total pressure of 760 torr air was determined to be k(CF3O + CO) = (5.0 ± 0.9) × 10-14 cm3 molecule-1 s-1. © 1997 John Wiley & Sons, Inc.

Notes: The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of ethyl 3-ethoxypropionate (EEP, CH3CH2(SINGLE BOND)O(SINGLE BOND)CH2CH2C(O)O(SINGLE BOND)CH2CH3). EEP reacts with OH with a bimolecular rate constant of (22.9±7.4)×10-12 cm3 molecule-1s-1 at 297±3 K and 1 atmosphere total pressure. In order to more clearly define EEP's atmospheric reaction mechanism, an investigation into the OH+EEP reaction products was also conducted. The OH+EEP reaction products and yields observed were: ethyl glyoxate (EG, 25±1% HC((DOUBLE BOND)O)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl (2-formyl) acetate (EFA, 4.86±0.2%, HC((DOUBLE BOND)O)(SINGLE BOND)CH2(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl (3-formyloxy) propionate (EFP, 30±1%, HC((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH2(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl formate (EF, 37±1%, HC((DOUBLE BOND)O)O(SINGLE BOND)CH2CH3), and acetaldehyde (4.9±0.2%, HC((DOUBLE BOND)O)CH3). Neither the EEP's OH rate constant nor the OH/EEP reaction products have been previously reported. The products' formation pathways are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. © 1997 John Wiley & Sons, Inc.

Notes: Pseudo-first-order rate constants (k1 obs) for the reaction of MeNHOH with NCPH obey the relationship: k1 obs=k′b[MeNHOH]T2 where [MeNHOH]T represents total concentration of N-methylhydroxylamine buffer. The rate constants, k1 obs obtained at different total concentration of acetate buffer ([Buf]T) in the presence of 0.004 mol dm-3 MeNHOH follow the relationship: k1 obs=kb[Buf]T. The values of acetate buffer-catalyzed rate constant (kb) at different pH reveal the occurrence of both general base- and general acid- or general base-specific acid-catalysis in the reaction of MeNHOH with NCPH. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 647-654, 1997.

Notes: The temperature dependence of the rate coefficients for the OH radical reactions with iso-propyl acetate (k1), iso-butyl acetate (k2), sec-butyl acetate (k3), and tert-butyl acetate (k4) have been determined over the temperature range 253-372 K. The Arrhenius expressions obtained are: k1=(0.30±0.03)×10-12 exp[(770±52)/T]; k2=(109±0.14)×10-12 exp[(534±79)/T]; k3=(0.73±0.08)×10-12 exp[(640±62)/T]; and k4=(22.2±0.34)×10-12 exp[-(395±92)/T] (in units of cm3 molecule-1 s-1). At room temperature, the rate constants obtained (in units of 10-12 cm3 molecule-1 s-1) were as follows: iso-propyl acetate (3.77±0.29); iso-butyl acetate (6.33±0.52); sec-butyl acetate (6.04±0.58); and tert-butyl acetate (0.56±0.05). Our results are compared with the previous determinations and discussed in terms of structure-activity relationships. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 683-688, 1997.

Notes: The processes of vibrational relaxation and unimolecular dissociation of the perfluoromethyl halides CF3Cl, CF3Br, and CF3I have been studied in the shock tube with the laser-schlieren technique. Vibrational relaxation was resolved in pure CF3Cl and CF3Br (400-484 K and 400-500 K, respectively), and in the mixtures; 2% CF3Cl/Kr (500-1000 K), 10% CF3Cl/Kr (440-670 K), 4% CF3Br/Kr (450-850 K), and 2% CF3I/Kr (620-860 K). Relaxation in the pure gases is extremely rapid, but shows a well-resolved, accurately exponential decay which provides very precise relaxation times in close agreement with ultrasonic results. Relaxation times as short as 0.1 μs-atm can be resolved, showing the method has a resolution within a factor 2-3 of the best ultrasonic methods. Relaxation dilute in rare gas shows a complex double exponential behavior consistent with a two-stage series process. Rates of CF3(SINGLEBOND)X fission in these mixtures were measured over 1800-3000 K, P〈0.55 atm, for CF3Cl; 1600-2500 K, P〈0.55 atm, in CF3Br; and 1260-2100 K, P〈0.34 atm, in CF3I. Rates for dissociation were derived from a full profile modeling using a secondary mechanism of six CF3 reactions. RRKM analysis showed all dissociations to lie near the low pressure limit. Using literature barriers, these rates are best fit with (ΔE)all=-270 cm-1 for CF3Cl, 〈ΔE〉down=0.3 T for CF3Br, and 〈ΔE〉down=800 cm-1 for CF3F. All these transfers are on the large side, similar to those found in other halogenated methanes. © 1997 John Wiley & Sons, Inc.