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 pyrolysis of 2-dimethylaminoethyl chloride in the temperature range of 360-400°C and the pressure range of 60-271 mmHg is a homogeneous, unimolecular, first-order reaction giving dimethylvinyl amine and hydrogen chloride. 2-Methoxyethyl chloride pyrolysis in the temperature range of 450-490°C and the pressure range of 53-110 mmHg by a similar unimolecular, first-order reaction yields methylvinyl ether and hydrogen chloride. These reactions were carried out in a seasoned reaction vessel and in the presence of a propene inhibitor. The methylvinyl ether decomposes slowly into other products at the temperature of pyrolysis. The rate constants are given by the Arrhenius equations(a) 2-dimethylaminoethyl chloride: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{ - 1}) = (13.22 \pm 0.17) - (203.7 \pm 2.1)kJ/mol/2.303RT $$\end{document}(b) 2-methoxyethyl chloride: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{ - 1}) = (14.06 \pm 0.53) - (244.7 \pm 7.1)kJ/mol/2.303RT $$\end{document}The effects of polar β substituents in the 2 position of ethyl chloride are discussed in terms of anchimeric assistance and electron-withdrawing deactivation in these elimination reactions. The present results are consistent with the heterolytic nature of the four-centered cyclic transition state for the gas-phase pyrolysis of alkyl halides.

Notes: The reaction\documentclass{article}\pagestyle{empty}\begin{document}$ CH\left({CH_3 } \right)\left({COOH} \right)_2 + I_2 \rightleftharpoons CI(CH_3)\left({COOH} \right)_2 + H^ + + I^ - $\end{document} was followed spectrophotometrically at 353 nm and 470 nm at 25°C under various conditions of pH and methylmalonic acid concentration. The equilibrium constant for the reaction is 0.11 ± 0.02. An iterative technique was used to integrate postulated rate equations. Agreement between experimental and calculated absorbance versus time curves was generally better than 0.005 A (approximately 5% of maximum) at both wavelengths for a mechanism where the rate-determining step is formation of an enolate (k = 1.63 Θ 10-4 ± 0.03 Θ 10-4 sec-1). The enolate may be rapidly transformed to the enol or enol carboxylate anion depending on the pH. All three forms are rapidly iodinated. The mechanism of general base catalysis is supported by rate increases proportional to base concentration in buffer solutions. The bases, acetate ion, chloracetate ion, sulfate ion, dichloracetate ion, and water, follow a Brønsted relationship with β = 0.7.

Notes: The kinetics of oxidation of glycine, alanine, phenylalanine, serine threonine, aspartic, and glutamic acid by acid permanganate were investigated to elucidate the mechanism of the reactions. The rate law was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{ - d[Mn\left({VII} \right)]}}{{dt}} = k_0 [a\min oacid][Mn\left({VII} \right)] $$\end{document} The reactions were found to be acid catalyzed, and the kinetic data indicate the participation of the water molecules in the rate-determining step as a proton-abstracting agent from the substrate, as per Bunnett's hypothesis. As Ag+ was found to catalyze these reactions, the oxidation of glycine and glutamic acid was studied, and the rate law was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{ - d\ln [Mn\left({VII} \right)]}}{{dt}} = \frac{{Kk_c^{''} [a\min oacid][Ag^ +]}}{{1 + K[a\min oacid] = K[Ag^ +]}}$$\end{document} A probable mechanism consistent with the observed results is discussed.

Notes: The competitive photochlorination and chlorine photosensitized dehydrochlorination of 1,1,1,2-C2H2Cl4 have been studied over the temperature range of 349.4-404.5 K after less than 1% conversion. The results are discussed and a value of \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_{4A} (\sec ^{ - 1}) = (11.6\pm 0.6) - (16,400\pm 1000)/4.58T $$\end{document} is proposed for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CCl}_{\rm 3} {\rm CHCl}\mathop \to \limits^{(4{\rm A)}} {\rm CCl}_{\rm 2} {\rm CHCl + Cl} $$\end{document} This result, combined with existing thermochemical data, indicates that there is no evidence of an activation energy for the addition of a Cl atom on the most chlorinated carbon in trichloroethylene: in that case the selectivity of the addition of Cl on the less chlorinated carbon should not depend on temperature.

Notes: Lifetime data have been obtained for the decay of SO2(3B1 0,0,0) at 25°C over the pressure range of 1-762 torr. The 3B1 state was populated by direct absorption to eliminate any possible complications in interpretation due to the participation of excited-singlet manifolds. At pressures greater than about 10 torr, the measured lifetimes are longer than predicted from low-pressure Stern-Volmer parameters. This deviation can be interpreted in terms of Freed's theory on collisionally induced intersystem crossing and provides unequivocal evidence to support earlier speculations that the lengthening of the lifetimes at high pressures is due to saturation in depopulation of the 3B1 state.

Notes: Our previous mechanistic model for the Belousov-Zhabotinsky reaction has been revised to include a more realistic set of reactions for the oxidation pathways of the organic intermediates. A few other rate constants have also been modified to include new information. The revised mechanism reproduces the essential experimental observations, although the periods of oscillation are somewhat too long and oscillations cease at malonic acid concentrations about ten times greater than the observed lower limit. However, the essential features of the mechanism are clearly understood.

Notes: The photolysis was investigated at 313 nm wavelength, 253-529 K temperatures, and 4 × 10-11-2 × 10-9 mol·photon/cm2·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.

Notes: The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) is studied in HClO4 and NaOH media with OsO4 as a catalyst in the latter medium. In acid medium, the rate law is -d [CAT]/dt = k [CAT][DMSO][H+]. Alkali retards the reaction and the rate law takes the form -d [CAT]/dt = k [CAT][DMSO][OsO4]/[NaOH], but is reduced to -d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied.The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO4 which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine-T and the substrate.

Notes: The rate constant for the bimolecular combination of trichloromethyl radicals in methanol is determined as a function of temperature by steady-state kinetics and electron-spin resonance with modulated radical initiation. The rate constant is in accord with the Smoluchowski equation and indicates a diffusion-controlled radical termination. The temperature dependence of the rate constant for the electron-transfer reaction between hydroxymethyl radicals and carbon tetrachloride in methanol is determined, and is found to disagree with predictions of the Marcus theory. This disagreement is tentatively ascribed to the structure of the transition state.

Notes: During the oxidation of carbon monoxide containing a trace of water, ten well-known atomic and molecular species can be identified as of potential significance. All conceivable reactions of these species in their ground electronic states were considered, and rate constants for all those that are of potential importance are either known or can be estimated with considerable confidence. For compositions and temperatures of experimental interest an isothermal system goes to a single steady state that is stable to perturbation and will neither explode nor oscillate. These steady-state computations also predict that as the temperature is raised above about 1000 K most of the water is converted to H, OH, and HO2 radicals. Under such conditions, exothermic reactions would be so rapid that strong thermal gradients would develop in any real system of plausible dimensions. A simple model based on these calculations predicts explosion limits consistent with those observed experimentally. Simultaneous behavior in time and in space must be calculated in detail before it is clear whether or not this model based on ground electronic states can model the oscillations that are sometimes observed in this system.

Notes: A procedure is suggested to estimate the positions of a transition state (TS) along the reaction coordinate in reaction series involving several radical reactions. It is based on the dependence between experimental activation energies U± and heat effects Q. Taking into account the shift of a TS position, the following relation between these quantities is obtained: U± -; U0± = A (Q - Q0)2 + B(Q - Q0). The subscript 0 indicates the standard reference reaction. For three series, namely, the hydrogen abstraction from hydrocarbon substrates by radicals CH3·, CF·3, and Br·, the bond lengths characterizing the TS reaction center are evaluated. The TS positions appear to vary significantly in the reaction series, which accounts for significant changes in the experimentally observed activation volumes. The derivation of the Hammond rule and the range of its validity for the series with polar and steric substituent effects are discussed.

Notes: The kinetics of chlorine transfer from CH2Cl2, CHCl3, CCl4, and CCl3CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1-bromopentane was used as a reference. The following Arrhenius parameters were determined:where the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et3Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.

Notes: The mutual combination reaction is proposed as the rate-limiting step in the removal of ClO radicals at moderate pressures. The third--order rate constants measured at room temperature were k1(Ar) = 3.51 ± 0.14 × 109 l2/mol2·ec; k1(He) ≈ 2.8 × 109 l2/mol2·sec, and k1(O2) ≈ 7.9 × 109 l2/mol2·sec. There is also an independent second-order reaction for which k3 ≈ 8 × 106 l/mol·sec. A new absorption spectrum has been observed in the ultraviolet and attributed to Cl2O2. The extinction coefficient for Cl2O2 has been measured at six wavelengths, and, between 292 and 232 nm, it increases from 0.4 × 103 to 2.9 × 103 l/mol·cm. In the presence of the chlorine atom scavengers OClO or Cl2O, Cl2O2 exists in equilibrium with ClO. The equilibrium constant Ke1 = 3.1 ± 0.1 × 106 l/mol at 298 K, and, with ΔS10 estimated to be -133 ± 11 J/K·mol, ΔH10 = -69 ± 3 kJ/mol and ΔHf0(Cl2O2) = 136 ± 3 kJ/mol.

Notes: The relations of quantum and kinetic isotope effects are investigated using the exact quantum corrections to the collision and activated complex theories. The latter are computed for the collinear three-atomic reaction H2 + H → H + H2 and the related isotopic reactions using realistic potential energy surfaces. Taking into account the bent configurations of the collision complex H-H-H gives a very good agreement between the quantum collision theory and the experimental data for the absolute values and the isotopic ratios of rate constants. Classical trajectory calculations yield considerably lower results.

Notes: The reactions of ground-state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro-1,3-dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast-flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants arek(O + C2CS) =(3.09 ± 0.54) × 10-11 exp(+115 ± 106 cal/mol/RT),k(O + F2CS) = (1.22 ± 0.19) × 10-11 exp(-747 ± 95 cal/mol/RT), andk(O + F4C2S2) = (2.36 ± 0.52) × 10-11 exp(-1700 ± 128 cal/mol/RT) cm3/molec·sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy-rich adduct which then decomposes by C-S bond cleavage.

Notes: The reaction of methyl radicals with CCl4 and CCl3Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH3CCl3, formed via the combination of methyl and trichloromethyl radicals.From these investigations Arrhenius parameters for the reactions have been determined: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = 10^{8.8 \pm 0.3} {\rm exp - }\left({\frac{{{\rm 10}{\rm .1} \pm {\rm 0}{\rm .5}\,{\rm kcal}}}{{RT}}} \right)1/{\rm mol} \cdot {\rm sec} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{15} { } = { 10}^{8.1 \pm {0}{.3}} { exp - }\left({\frac{{{3}{.5 } \pm { 0}{.5 kcal}}}{{RT}}} \right){ 1/mol} \cdot {sec} $$\end{document}Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl4 and CCl3Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C2Cl6, and the HCl precursor CH3CCl3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl3Br and a chloromethane. Arrhenius parameters were obtained for the reactions and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.

Notes: The products of the heterogeneous reactions of chlorine atoms and chlorine oxide radicals with acid coated Pyrex walls have been directly determined for the first time. Contrary to the usual assumption that chlorine atoms recombine to form Cl2, we find that the major product is HCl, with small amounts of perchlorate also formed. Similarly, ClO radicals form HCl rather than Cl2. The source of hydrogen for these reactions is probably the water always found in this type of vacuum system. These results may change the interpretation of flow tube experiments with chlorine atoms. Application to the H + HCl reaction is discussed as an example.

Notes: The kinetics of gas-phase elimination of 3-methyl-1-butyl acetate and 3,3-dimethyl-1-butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360-420°C and the pressure range of 63-250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first-order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation3-methyl-1-butyl acetate: \documentclass{article}\pagestyle{empty}\begin{document}$$ {log k(sec}^{{ - 1}} {) = (12}{.73 } \pm { 0}{.29) - (202}{.5 } \pm { 3}{.8) kJ/mol/2}{.303}RT $$\end{document}3,3-dimethyl-1-butyl acetate: \documentclass{article}\pagestyle{empty}\begin{document}$$ {log k(sec}^{{ - 1}} {) = (12}{.34 } \pm { 0}{.35) - (194}{.1 } \pm { 4}{.2) kJ/mol/2}{.303}RT $$\end{document} The points in a plot of log (k/k0) of β-alkyl and several β-substituted ethyl acetates against Es values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.

Notes: Using the technique of CO2 laser photosensitized decomposition, ethane and propane decomposition was investigated in relation to energy transfer from an SF6 photosensitizer to the hydrocarbon. The end products appearing in the course of irradiation are similar to those formed during classical thermal pyrolysis. The energy transfer from SF6 to the hydrocarbon is closely related to hydrocarbon decomposition. A similar overall kinetic behavior for the two alcanes allows the use of a general diffusional kinetic treatment, provided pressure, intensity, and duration of irradiation are well defined.

Notes: Rate constants for the reaction HO2 + NO2(+ M) = HO2NO2(+ M) have been obtained from direct observations of the HO2 radical using the technique of molecular modulation ultraviolet spectrometry. HO2 was generated by periodic photolysis of Cl2 in the presence of excess H2 and O2, and k1 was determined from the measured concentrations and lifetime of HO2 with NO2 present. k1 increased with pressure in the range of 40-600 Torr, and a simple energy transfer model gave the following limiting second- and third-order rate constants at 283 K: k1∞ = 1.5 ± 0.5 × 10-12 cm3/molec·sec and k1III = 2.5 ± 0.5 × 10-31 cm6/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195-265 nm; it showed a broad feature with a maximum at 200 nm, σmax = 4.4 × 10-18 cm2.

Notes: The thermal decomposition of SF5O3SF5 has been investigated between 5 and 25°C. In the presence of sufficient high pressures of O2 the only products formed are SF5O2SF5 and O2: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm SF}_5 {\rm O}_3 {\rm SF}_5 { } \to { SF}_{5} {O}_{2} {SF}_{5} { + (}{\raise0.5ex\hbox{$\scriptstyle {1}$} \kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle {2}$}}{) O}_{2} {, }\Delta n{ = }{\raise0.5ex\hbox{$\scriptstyle {1}$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 2$}} $$\end{document} The reaction is homogeneous. Its rate is strictly first order with respect to the trioxide pressure and independent of the total pressure of the reaction products and of oxygen above a certain limiting pressure: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{{\rm d}[{\rm SF}_5 {\rm O}_3 {\rm SF}_5 ]}}{{{\rm dt}}}{ = + }\frac{{{\rm d}[{\rm SF}_5 {\rm O}_2 {\rm SF}_5 ]}}{{{\rm dt}}}{ = 2}\frac{{{dp}}}{{{\rm dt}}}{ = k[SF}_{5} {O}_{3} {SF}_{5} {]} $$\end{document} The experimental results can be explained with the following mechanism: In the presence of O2 〉 100 Torr the concentration of SF5 is insignificantly small. Therefore reactions (5) and (6) do not have to be considered any more, and steps (2) and (2′) will be of no importance. From reactions (1)-(4) it follows: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm SF}_{\rm 5} {\rm O}_{\rm 3} {\rm SF}_{\rm 5} ]}}{{dt}} = + \frac{{d[{\rm SF}_{\rm 5} {\rm O}_{\rm 2} {\rm SF}_{\rm 5} ]}}{{dt}} = k_1 \frac{{[{\rm SF}_{\rm 5} {\rm O}_{\rm 3} {\rm SF}_{\rm 5} ]}}{{1 + k'_1 (1/2k_3 k_4 )^{1/2} }}k({\rm sec}^{{\rm - 1}}) = k_1 /\left[ {1 + k'_1 \left({\frac{1}{{2k_3 k_4 }}} \right)^{1/2} } \right] = 10^{16.06 \pm 0.37} {\rm exp( - 26,000} \pm {\rm 500}\,{\rm cal)/1}{\rm .987 }T $$\end{document}The numerical value of the factor [1 + (k′12/2k3k4)1/2] is small. It can be estimated that E3 ≃ 2 ± 1 kcal; therefore, E - E1 ≤ 1 kcal, and D (SF5O—O2SF5) = (26 - 1) ± 1.0 kcal.

Notes: Pyrolytic decay of carbon diselenide was monitored by ultraviolet absorption spectroscopy in reflected shock waves in the temperature range of 1600-2600°K. The temperature dependence of the absorption coefficient of CSe2 at 2308 Å was determined and was used to provide kinetic information along with a deconvolution procedure which accounted for and removed systematic distortions of the fast time-resolved absorbance profile. For temperatures of 1600-2600°K and argon densities of 1.5-7.0 × 10-5 mol/cm3 dilute (1.0-9.0 × 10-9 mol/cm3) CSe2 pyrolyzed with measured first-order decay rates in the range of log10 k1 (sec-1) = 3.0-5.7; at midrange (2100°K and 4.3 × 10-5 mol/cm3 in Ar) k1 ≈ 3 × 104 sec-1. The decay probably occurs via a unimolecular low-pressure process, first order in both CSe2 and Ar, for which k2 ± 109 cm3/mol·sec at 2100°K. The deconvoluted data yield Arrhenius activation energies of 53.2 kcal/mol under second-order treatment, but the activation energy is less reliable than the general magnitude of the rate constant. A comparison of CSe2 with other molecules which are isoelectronic in their valence shells (CO2, CS2, OCS, and N2O) is made.

Notes: A sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO2, O3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies.

Notes: The electron transfer step of the reduction of Mn(acac)3 and Co(acac)3 by Fe(II) in acetonitrile is preceded by the one-ended dissociation of an acac ligand and the formation of a binuclear bridged complex. After the electron transfer has taken place through the bridging ligand, the complex dissociates into the products M(acac)2 (M = Mn, Co) and Fe(acac)2+. These primary reaction products could not be identified, since the transfer of acac from M(acac)2 to Fe(acac)2+ is too rapid, producing ultimately Fe(acac)3 and M2+. The M(III)-oxygen cleavage is accelerated by M(acac)2. Furthermore, the dissociation of the binuclear intermediate is catalyzed by the M(acac)3 reactant. Mn(acac)3 is reduced more than a thousand times faster than Co(acac)3.

Notes: The gamma-radiation-induced free-radical chain reactions in liquid CCl4—C2Cl4—c—C6H12 mixtures were studied in the temperature range of 363-448°K. The main products in this system are chloroform, hexachloropropene and chlorocyclohexane. These products are formed via reactions (1)-(5): with G values (molec/100 eV) of the order of magnitude of 102 and 103 at the lowest and highest temperatures, respectively. Values of k2/k1 were determined from the product distribution. In turn, these values gave the following Arrhenius expression for k2/k1 (θ = 2.303RT, in kcal/mol): \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\,k_2 /k_1 = ( - 1.21 + 0.10) + (1.59 \pm 0.27)/\theta $$\end{document} From this result and the previously determined Arrhenius parameters of reaction (1), k2 is found to be given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\,k_2 (1/{\rm mol} \cdot {\rm sec) = 7}{\rm .58 - 9}{\rm .49/}\theta $$\end{document}.

Notes: Flash photolysis technique has been used to obtain the rate and thermodynamic parameters of the reversible dimerization reactions of a range of ten phenoxy radicals (I-X) in a toluene-dibutylphthalate mixture (0.6 cP ≤η≤18.4 cP): \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R}^{.} + {\rm R}^{.} {\mathop{{\buildrel{-\!\!\longrightarrow}\over{\longleftarrow}}}\limits_{k_{-1}}^{k_1}}{\rm D} $$\end{document} The main reason for the difference in the k1 values are the different steric hindrances in radicals. It has been found that the values of k1 for 2,6-diphenyl-4-methoxy- (I), 2-phenyl-(III), and 2-methoxyphenoxy (IV) radicals are 3-5 times smaller than the respective diffusion constants calculated according to the Debye formula with regard to the spin-statistical factor: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{diff} = \sigma \frac{{8{\rm RT}}}{{3000{\rm \eta }}} $$\end{document} The resultant ΔH1≠values for these radicals in toluene and dibutylphthalate are close to the activation energies of the viscous flow of the solvents B. Linear relationships with a slope equal to unity are observed between log k1 and log(T/η). The recombination of radicals I, III, and IV is limited by translational diffusion. The k1 values for 2,6-diphenyl- (VII), 2,6-di-tert-butyl- (IX), and 2,6-di-tert-butyl-4-methylphenoxy (X) radicals are 10-60 times smaller than kdiff and Δ H≠ B. In the case of radical X in toluene ΔH1≠ 0. The recombination of these three radicals includes an intermediate step of complex formation: \documentclass{article}\pagestyle{empty}\begin{document}$${{\rm R}^\cdot+{\rm R}^\cdot}{\mathop {{\scriptstyle\longleftarrow}^{\hskip-13pt\longrightarrow}}}{\rm R^\cdot}\ldots {\rm R}^\cdot \rightarrow {\rm D}$$ \end{document} For 4-phenyl- (II), 2,6- dimethoxy- (V), 2,4-diphenyl- (VI), and radicals VII, IX, and X the linear relationships between log k1 and log (T/η) have a slope of from 0.5 ± 0.05 to 0.8 ± 0.05. The k1-1 versus η relationships for these radicals are not straight lines. The recombination of these six radicals is limited by translational and rotational diffusion. With the aid of theoretical models, the k1 versus η relationships have been used to derive the steric factor f in radical recombination and the angle θ between the axis and the solid angle generatrix. The solid angle defines the reaction spot on the radical-sphere surface. The recombination of the 2,6-diphenyl-4-diphenylmethylphenoxy radical (VIII) takes place in the region intermediate between the diffusion and the kinetic ones, and the relationship between log k1 and log (T/η) for this radical has a plateau portion. The log k-1 versus log (T/η) relationships have precisely the same form as the corresponding k1 relationships, which is quite in line with the theory of diffusion-controlled reversible recombination reactions.

Notes: The decomposition of CH3CD2CH3 was studied from 713 to 853 K at pressures of 98-466 torr. The values of k1/k2 = 2.08 ± 0.05 and k3/k4 = 2.04 ± 0.66 were found independent of temperature by measuring the ratios of CH4/CH3D and CH3CHD2/CH3CD3, respectively, for the following reactions:. Isomerization of CH3CDCH3 was detected by measuring CHDCH2 formed from the isomerized radical. The expression of k21/k22 was found to be where k21 and k22 are the rate constants of. The results and conclusions are discussed and compared with previous works.

Notes: A detailed investigation of the mechanism of cyanogen oxidation is presented. Recent induction time measurements of ignition in cyanogen-oxygen-argon mixtures behind reflected shocks are computer modeled to obtain an agreement between the experimental and calculated values. A 15-step reaction scheme is suggested to reproduce the parameters E and βi in the experimental parametric relation: τ = 10αexp(E/RT)IICiβi. An explanation is offered to the very strong dependence of the induction time on the cyanogen concentration and the very weak dependence on the oxygen concentration. The sensitivity spectrum shows that the induction time is highly dependent on the O + C2N2 → NCO + CN and NCO + M → N + CO + M reactions (shortened) and the O + NCO → CO + NO and N + NCO → N2 + CO reactions (increased).

Notes: Atmospheric photodissociation rate coefficients and photodissociation lifetimes for nitromethane, methyl nitrite, and methyl nitrate were calculated as a function of altitude from their measured visible and near ultraviolet photoabsorption cross sections at 298 K. The lifetime of methyl nitrite is nearly independent of altitude and is approximately 2 min. From 0 to 50 km the lifetime of nitromethane varies from 10 to 0.5 hr, while that of methyl nitrate changes from 5.3 to 0.09 days, respectively.

Notes: Ethyl N—methylcarbamate decomposes thermally over the temperature range of 600-650 K by competing first-order reactions, one forming methylamine, carbon dioxide, and ethylene, the other forming methyl isocyanate and ethanol. The first-order rate constants are described in S—1 units by the equations where R = 1.986 cal/deg mol. The appareance of sym—dimethylurea among the products raised the possibility of gas-phase transesterifications. These were ruled out by the study of the reactions of sym-dimethylurea at 604 K which showed its behavior to be well explained by the rapid decomposition in the gas phase which is reversed in the condensation stage in the analysis.

Notes: The law c = c0 exp(—K √t) in the alkyl radical abstraction reaction is affected by neither the matrix annealing nor the way of the radical generation. If the reaction runs at varying temperature, a dimensionless time τ which does determine unambiguously the degree of conversion can be introduced.

Notes: The kinetics of the gamma-radiation induced free radical reactions in carbon tetrachloride solutions of 2,3-dimethylbutane (DMB) were studied in the temperature range 32-118 °C. The kinetics of the following reactions were measured:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm CCl}_3 + {\rm RH} \to {\rm CHCl}_3 + {\rm R} \\ {\rm CCl}_{\rm 3} + {\rm CCl}_{\rm 3} \to {\rm C}_2 {\rm Cl}_6 \\ \end{array} $$\end{document} and the following rate constants expression was obtained:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 /k_3^{1/2} (M^{ - 1/2} \sec ^{ - 1/2} )\, = \,(2.40 \pm 0.17) - (6.96 \pm 0.26)/{\rm \theta } $$\end{document}. The activation energy and the A factor obtained are in good agreement with the values obtained at the gaseous phase, considering the activation energy for self-diffusion of CCl4.

Notes: Measurement of the rate of the reaction is reported. The measurements were made in a flow tube apparatus. The result is based on data for the absolute density of OH(v = 0) obtained from laser-induced fluorescence measurements in the (0-0) band of the OH(A2Σ+ → X2II) system. The density of oxygen atoms was varied by changing the flow rate of NO which is consumed in the reaction N + NO → O + N2. We find that k1 (298 K) = (5.5 ± 3.0) × 106 cm3/mol sec. This result was obtained with consideration and control of the effect of reaction (2): for which vibrationally excited hydrogen is created by energy transfer in the presence of active nitrogen. It was found that the addition of N2 or CO2 effectively suppressed the excitation of H2(v = 1). Measurements of the density of H2(v = 1) were made by VUV absorption in the Lyman band system of H2. All of the reports of low-temperature measurements and some recent theoretical calculations for k1 are discussed. The present result confirms and extends the growingevidence for significant curvature in the low-temperature end of a modified Arrhenius plot of k1 (T).

Notes: The thermal decomposition of ammonia was studied by means of the shock-tube and vacuum ultraviolet absorption spectroscopy monitoring the concentration of atomic hydrogen. The rate constants of both the initiation reaction and the consecutive reaction were determined directly as \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = 10^{16.14} \exp (- 90.6{\rm kcal}/RT){\rm cm}^{\rm 3} /{\rm molsec} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{II} = 10^{14.30} \exp (- 23.29{\rm kcal}/RT){\rm cm}^{\rm 3} /{\rm molsec} $$\end{document} respectively.

Notes: O2 in the A3Σu+ state has been prepared in a discharge flow system by recombining oxygen atoms on a nickel surface. The decay of this excited state was followed by observing the emission between 280 and 400 nm. The wall deactivation was observed to approach unit efficiency. Rate constants were determined to be 0.9 × 10-11, 2.9 × 10-13, and 8.6 × 10-16 cm3/molecule sec for the quenching of O2(A3Σu+) by O, O2, and Ar, respectively.

Notes: The rate constant for the reaction CH3O2 + NO2 → (products) has been measured directly by flash photolysis and kinetic spectroscopy. At room temperature and at total pressures between 53 and 580 Torr, k3 = (9.2 ± 0.4) × 108 liter/mole sec so that the rate of formation of the probable primary product peroxymethyl nitrate (CH3O2NO2) may be significant in urban atmospheres.

Notes: Existing data on the self-reactions of tertiary peroxy radicals RO2 has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths. For R = t-Butyl, these are logkt(M-1sec-1) = 7.1 - (7.0/θ) and logknt(M-1sec-1) = 9.4 - (9.0/θ), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1-diphenylethyl have been discussed in terms of a much greater cage recombination of cumyloxy radicals as contrasted with t-butoxy radicals. It is shown that for benzyl peroxy radicals, the R - O·2 bond dissociation energy is sufficiently low (18-20 kcal) that reversible dissociation into R· + O2 opens a competing second-order path to fast recombination R· + RO·22 → ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,1-diphenyl ethyl peroxy radicals at (O2) 〈 10-3M. At very low RO·2 concentrations (〈10-5M), in the absence of added O2, an apparent first-order disappearance of RO·2 can occur reflecting the rate determining breaking of the cumyl - O·2 bond followed by the second step above. The thermochemistry of RO·n is used to show that the reaction of R2O4 → 2RO + O2 must be concerted and cannot proceed via RO·3 which is too unstable and cannot form even from RO· + O2.

Notes: Demetallation rates of α,β,γ,δ-tetrakis(p-sulfophenyl)porphiniron(III) in hydrochloric acid-ethanol-water, perchloric acid-ethanol-water, and sulfuric acid-alcohol-water media were determined. For a given acidity value H0 the order of the rates for the three acids was HCl 〉 H2SO4 〉 HClO4. This is also the order for complex formation between acid anion and iron(III). Consequently ligands as well as protons are involved in the breaking of bonds between the metal and the porphyrin leading to the formation of the activated complex. The log k values for HCl and HClO4 media were not linearly related to the Hammett acidity function as they were for sulfuric acid-ethanol-water media. The average ΔH

Notes: A method is presented for the prediction of rate coefficients and Arrhenius parameters for bimolecular hydrogen atom transfer reactions A + BC → AB + C. The treatment sets out from structural considerations of the complex A ⃛ B ⃛ C and calculates the energy of the complex along the reaction path from empirical functions for a bonding energy term and an endgroup contribution. The treatment proceeds by assuming ultrasimple transition state models and assigning the force constants and vibrational frequencies. Finally the rate coefficient and Arrhenius parameters are obtained on the basis of separable activated complex theory. Application of the method requires known properties of reactant and product molecules and does not demand the use of adjustable parameters. The relation and differences between this method and the BEBO treatment as well as Zavitsas' method are dealt with.

Notes: The rate of the reaction was determined in an isothermal discharge flow reactor with a combined ESR-LMR detection under pseudo-first-order conditions in HO2. The rate constant was identical in experiments with two different HO2 sources: F + H2O2 and H + O2 + M. The absolute rate constant at T = 293 K was measured as \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 (293K) = (4.6 \pm 1)10^{12} cm^3 /mol\sec $$\end{document} In the range 2 ≤ p mbar ≤ 17 no pressure dependence for k1 was found.

Notes: The addition reactions of CCl3 radicals with cis-C2Cl2H2, trans-C2Cl2H2, and C2Cl3H in liquid cyclohexane-CCl4 mixtures were studied between 323 and 448 K. The Arrhenius parameters of these reactions were competitively determined versus H-atom transfer from cyclohexane and addition to C2Cl4. The present data and the data obtained in previous liquid and gas phase studies show that the reactivities displayed in addition reactions of different radicals with chloroethylenes reflect primarily variations in activation energies rather than in A factors. The activation energies for the addition of CCl3, CF3, and CH3 radicals to chloroethylenes appear, to a large extent, to be determinedby the stability of the adduct radicals. Comparison of the reactivity trends in the addition reactions of chloro- and fluoro-substitutedethylenes indicates that these two electron-withdrawing substituentshave a converse effect on the reactivity of electrophilic radicals. This behavior is ascribed to the strong mesomeric effect of vinylic chlorosubstituents.

Notes: The titration of chemisorbed oxygen by carbon monoxide to form carbon dioxide has been studied from 373 to 673 K over polycrystalline platinum. The pressure transients for CO and CO2 have been measured and simulated numerically. A complex Langmuir-Hinshelwood mechanism is found which fits all the data, and it is not necessary to invoke Eley-Rideal kinetics. The results fall into two temperature regimes, above and below 473 K, which are characterized by different Arrhenius parameters. A change in activation energy with oxygen coverage is also found below 473 K.

Notes: The kinetics of dimethyl sulfoxide (DMSO) oxidation by peroxomonophosphoric acid (PMPA) in aqueous medium at 308 K and I = 0.4 mol/dm3 follow the rate expressions In the pH range from 0 to 2, where k1 and k2 are 5.092 × 10-1 dm3/mol sec and ≃ 0, respectively; in the pH range from 4 to 7, where k2 = 8.127 × 10-3 and k3 = 2.90 × 10-3 dm3/mol sec; and in the pH range from 10 to 13.6, where k4 ≃ 0, and k5 = 3.08 × 10-2 dm3/mol sec.The reaction is interpreted in terms of mechanisms involving an electrophilic and a nucleophilic attack of the peroxomonophosphoric acid species, respectively, in acid and alkaline regions, on the sulfur atom of the sulfoxide molecule giving rise to SN2-type transition states followed by oxygen-oxygen bond fission to form the products.

Notes: The oxidations of ferrocene (FcH) and n-butylferrocene (FcBu) by ferric salts (nitrate or bromide) are strongly inhibited by aqueous cetyltrimethylammonium bromide and nitrate (CTABr and CTANO3, respectively). The kinetics of inhibition fit a model in which the substrates are distributed between water, and the micelles and binding constants Ks to the micelle can be estimated. The oxidations are strongly catalyzed by micelles of sodium lauryl sulfate (NaLS), and the kinetics can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase and the rate constants in that pseudophase, which for both substrates are very similar to those in water. Some added salts reduce the micellar catalysis by excluding ferric ions from the micelle. The oxidations of FcH and FcBu by ferricyanide ions are too fast to be followed in water, but they are inhibited by anionic micelles of NaLS. By analyzing the rate surfactant profiles using independently measured values of Ks the second-order rate constants in water have been estimated.

Notes: The rate of the cerium (IV) oxidation of p-chloromandelic acid has been studied in perchlorate media at an ionic strength of 1.50 mol/dm3 by the stopped-flow technique and in H2SO4—MHSO4 (M+ = Li+, Na+, K+) and H2SO4—MClO4 (M+ = H+, Li+, Na+) mixtures at constant total electrolyte concentrations of 1.00 and 2.00 mol/dm3 using the conventional spectrophotometric method. In perchlorate media the kinetic data indicate the formation of two intermediate complexes between cerium (IV) and the organic substrate, but only one is significantly involved in the intramolecular electron-transfer process. The oxidation rate is markedly lower in sulfate media, where two reaction paths have been found to contribute to the overall redox reaction. The univalent cations examined exhibit negative specific effects upon the overall oxidation rate increasing in the order H+ 〈 Li+ 〈 Na+ 〈 K+. Activation parameters have been also estimated.

Notes: The spectrum of the intermediate product ascribed to nitrosopentane has been detected in the photolysis of the SO2-pentane (RH)-NO mixture. This result has been interpreted in terms of the radical mechanism by assuming the H-atom abstraction from RH by the excited SO2 molecules to be the primary act. The contribution of the singlet and triplet SO2 states to the product formation rate and the ratio of the singlet-to-triplet rate constants have been evaluated. At NO pressures above 5 torr, the product formation rate significantly deviates from the Stern-Volmer dependence.

Notes: The reaction Cl + H2CO → HCl + HCO has been studied at 295 K. Chlorine atoms were produced via the infrared laser induced dissociation of CCl3F, using a pulsed CO2 TEA laser. Using HCl infrared chemiluminescence as the diagnostic, we find the rate constant to be 7.4 ± 0.7 × 10-11 cm3/molecule sec, in good agreement with several recent studies. An evaluation of TEA laser photolysis as a technique for the generation of chlorine atoms is made, and the relationship of this experiment to recent theories of infrared laser induced chemistry is discussed.

Notes: The kinetics of the reaction have been investigated in H2SO4 medium under different conditions. The observed bimolecular rate constant kobs, has been found to depend on [H+]-0.55 and to increase with the initial concentration ratio of the reactants R0 = [H2O2]0/[U (IV)]0 above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R0 = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate-controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved: A kinetic expression has been derived from which a graphical evaluation of (kK4)-1 and k-1 has been made at R0 = 1 as (12.30 ± 0.09) × 10-3 M min, (6.23 ± 2.19) × 10-4 M min; and at R0 = 0.35 as (12.63 ± 2.13) × 10-3 M min, (8.32 ± 6.62) × 10-4 M min, respectively. Indications of some participation of a chain reactionat R0 = 1 have been obtained without affecting thesecond-order kinetics as observed.

Notes: No reliable rate constant is available for the self-reaction of tert-;butoxy radicals. We have set up a competition between hydrogen abstraction and self-reaction of tert-butoxy radicals in a flash photolysis electron spin resonance study to extract this information. Experimental values of hydrogen abstraction product radical concentrations under various hydrogen donor concentrations were then compared with theoretically calculated values with different values of 2k4 to obtain the best fit. Hydrogen donors such as cyclopentane, anisole, methyl tert-butyl ether, and methanol were chosen for the study. A value of (1.3 ± 0.5) × 109M-1 sec-1 for the rate constant of the self-reaction of tert-butoxy radicals has been determined at 293°K.

Notes: The thermal decomposition of ethane has been reinvestigated using the single pulse, reflected shock technique. Reflected shock temperatures were corrected for boundary layer-induced nonidealities using the thermal decomposition of cyclohexene as a kinetic standard. The rate constant for the reaction was calculated from the rate of formation of methane under conditions of very low extent of reaction, over a temperature range of 1000-1241 K. Ethane compositions of 1% and 3% in argon at total reaction pressures of 3 and 9 atm were used, and a small pressure dependence of k1 was observed.An RRKM model is described which gives excellent agreement with this and other recent dissociation and recombination rate constant data in light of a recent revision to the thermochemistry of the methyl radical. In the range of 1000-1300 K an RRKM extrapolated k1∞ is given by the expression, log k1∞ = 17.2 - 91,000/2.3RT, while at 298 K the calculation gives log k-1∞ (l/mol sec) = 10.44, where k-1∞ is calculated from k1∞ and the equilibrium constant.

Notes: The title reaction has been investigated in the temperature range of 494-545 K. During the early stages of reaction the only observed products were silyl iodide and hydrogen iodide. Initial rates were found to obey the rate law over a wide range of initial iodine and monosilane pressures. Secondary reactions, most probably of SiH3I with I2, became more important as the reaction progressed. However, provided [SiH4]0/[I2]0 〉 20, these secondary processes had a negligible effect on the kinetics, and an integrated rate expression could be used. These kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step has been deduced. From this the bond dissociation energy D(SiH3—H) = 378 ± 5 kJ/mol (90 kcal/mol) is obtained. The kinetic and thermochemical implications of this value, especially to the pyrolysis of monosilane, are discussed.

Notes: It is shown that A factors for atom fissions in polyatomics can be reliably estimated by an improved version of the restricted free rotor model (RFRM). No adjustable parameters are used in the evaluation of A factors for the dissociation of the RO—F bond (R: NO2, SF5, CF3, FSO2), and the authors' predictions are compared with high-pressure kinetic data for these reactions. In the case of O2NOF, for which full spectroscopic information is available, RFRM reproduces the observed value Am well within a factor of 2. Similar agreement is reached for F5SOF and FO2SOF, assigning reasonable limits to their —OF torsional frequencies. For F3COF, Am and the calculated back reaction rate constant, which is independent of the model, are both much too small to be plausible, suggesting falloff effects rather than a failure of RFRM.

Notes: Bis(trifluoromethyl) peroxide is readily dissociated by multiple infrared photon excitation at CO2 laser wavelengths. The primary dissociation product is CF3O; approximately 85% of the nascent radicals are further dissociated in the laser field to form CF2O and F. The F atoms then react with the remaining CF3O to produce CF3OF. The formation of CF3OF is strongly inhibited by addition of HI, which reacts preferentially with the F atoms.

Notes: The acid-catalyzed enolization of acetone in the presence of bromine is found to be catalyzed by the anionic micelles of sodium dodecyl sulfate. The rate acceleration expected on the basis of lowering of activation energy is largely nullified by the decrease in the entropy of activation, leading to a very small rate enhancement, i.e., kψ/k0 = 1.2 at 30°C. The binding constant for the micelle-substrate complex is determined. The micellar rate enhancement is the same, irrespective of the halogen used, chlorine, bromine, or iodine.

Notes: With a continuous jet-stirred tank reactor operating at small space time (0.05-1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene-1, 2,3-dimethyl-butane, 4-methylpentene-1, and 1,5-hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600-780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are The measured rates of formation of the minor products are consistent with the quasi-identical values estimated by Jezequel and co-workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A1 ≃ 1016.65 s-1 and E1 ≃ 84.7 kcal/mole) of the chain initiation process

Notes: Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H2O2 by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe3+ and H2O2 becomes stabilized.

Notes: The unimolecular decomposition of chemically activated methylallylether (MAE) formed by the cross combination of methoxymethyl and vinyl radicals was studied in the gas phase. The experimentally determined rate constant was found to be 1.11 × 108 sec-1 at 9.6°C for the decomposition of MAE into propene and formaldehyde. The decomposition of MAE via the six-center retro-“ene” type transition state is analyzed by using the RRKM unimolecular reaction theory. For the molecular parameter assignments of energized MAE, a model which contains one internal rotational mode is supported, and MAE decomposition is characterized by a tight complex model. The best agreement between experimental and theoretical results was found when a critical energy of 40.1 kcal/mol was used.

Notes: The reaction H + CH3OOH was investigated under conditions of excess atomic hydrogen concentration using a flow reactor attached to a photoionization mass spectrometer. The rate coefficient of the reaction was determined as \documentclass{article}\pagestyle{empty}\begin{document}$$ k = (2.8 \pm 0.9) \times 10^{- 13} {\rm exp\,}[- (1860 \pm 190){\rm cal}/RT \cdot {\rm mol\,}]\,{\rm cm}^3 /{\rm molec} \cdot {\rm sec} $$\end{document} The three important reaction channels were found to be with the individual contributions determined as indicated. The product methoxy and methylperoxy radicals react mainly with atomic hydrogen under the employed experimental conditions according to where the estimates for the percentage contributions of the various channels were derived from the measured product yields.

Notes: The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant-reactant and reactant-inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock-tube measurements, may be greater than has been believed hitherto.The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock-tube conditions the apparent first-order rate coefficient may be at least ten times less than the high-pressure limiting value.

Notes: The kinetics of the gamma radiation induced free radical chain decomposition of BrCH2CN in liquid cyclohexane (RH) was investigated over the temperature range of 60-170°C. In addition competitive experiments in the presence of CCl4 were carried out between 80 and 180°C. For the reactions the following Arrhenius expressions were derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm log}k_3 /(2k_4)^{1/2} ({\rm l}^{{\rm 1/2}} /({\rm mol} \cdot {\rm sec})^{1/2}) = 4.07 \pm 0.35 - (11.96 \pm 0.63)/\theta \\ {\rm log}k_2 /k_5 = - 0.699 \pm 0.167) + (2.69 \pm 0.31)/\theta \\ \end{array} $$\end{document} where θ = 2.303RT in kcal/mol.The effect of CN substitution on the activation energies of reactions (2) and (3) was evaluated based on the present and previously published results. The CN group effect on halogen atom abstraction [reaction (2)] is discussed in terms of inductive and enthalpic factors.The differences E3 - E(CH3 + RH) and E(CCl2CN + RH) - E(CCl3 + RH), which yield a value of about 5.5 kcal/mol, are considered to reflect the cyano stabilization effect at the radical center confirming D(CH2(CN)-H) ∼ 93 kcal/mol.

Notes: Nanosecond flash photolysis of 1,2- and 1,8-dinitronaphthalenes (1,2-DNO2N; 1,8-DNO2N) in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n-hexane the absorption maxima and lifetimes (1/K) are 490 nm and 1.0 μsec for 1,2-DNO2N and 550 nm and 2.5 μsec for 1,8-DNO2N. In deaerated ethanol the corresponding values are 550 nm and 4.3 μsec for 1,2-DNO2N and 590 nm and 5.3 μsec for 1,8-DNO2N. The transient absorptions are attributed to the lowest triplet excited states T1 of the 1,2- and 1,8-DNO2N. The observed red shifts in the absorption maxima of the T1 states are indicative of the extent to which electronic charge is transferred intramolecularly during the T1 → Tn transitions. Furthermore, the increased lifetime of the T1 states with increasing solvent polarity indicates the intramolecular charge transfer character of the T1 states. Changes of dipole moments accompanying the T1 → Tn transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the T1 states of 1,2- and 1,8-DNO2N and tributyl tin hydride (Bu3SnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the case of 1,2-DNO2N. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2- and 1,8-DNO2N behave like n → π* states in nonpolar media while in polar solvents the n → π* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.

Notes: Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k1 is in the fall-off pressure regime at our experimental pressures (20-760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10-12 cm3/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10-31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10-30 with neopentane; we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10-13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10-13 cm3/molec · sec; k3 = (6.0 ± 1.0) × 10-11 cm3/molec · sec.

Notes: The reactions between SO2 and O2 were carried out in the presence of TiO2 and NiO under various partial pressures of SO2 and O2 at temperatures from 240 to 330°C. TiO2 and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO2 pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10-4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first-order kinetics for TiO2 and NiO, respectively. A reaction mechanism to explain the data was suggested.The quantities of anionic vacancies in TiO2 surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics.

Notes: The general problem of eliciting reliable rate constants from experimental data is considered in detail for consecutive reactions. Practical aspects are emphasized.

Notes: The room temperature photolysis of 1,1-dichloroethane at 147 nm in the pressure range of 1.34-196.2 torr is characterized almost entirely by the molecular elimination of HCl, Cl2, and small quantities of H2. Acetylene is also produced. While it is possible that the C2H2 arises, in part, from the decomposition of vibrationally excited ground states of C2H3Cl and/or C2H4, in this particlar case serious consideration has to be given to alternative explanations where the products of the primary processes are formed in electronically excited states. The ±, elimination of molecular chlorine is not inconsistent with an increased degree of Cl—Cl interaction predicted for a «Rydberg «state of 1,1-C2H4Cl2. Varying small yields of CH4 are observed in the presence and absence of NO. The effect of large pressures of CF4 on the quantum yields of the major products is extremely small. The extinction coefficient for 1,1-C2H4Cl2 at 147 nm and 296°K is 246 ± 29 cm-1 ± atm-1.

Notes: NO Abstract.

Notes: 1,2-Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8-20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm-1 · cm-1.The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10-10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbon—halogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.

Notes: Electron pulse radiolysis at ⋍298°K of 2 atm H2 containing 5 torr O2 produces HO2 free radical whose disappearance by reaction (1), HO2 + HO2 →H2O2 + O2, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO2 absorption cross section, the values k1 = 2.5×10-12 cm3/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO2) ⋍13 are obtained. In the presence of small amounts of added H2O or NH3, the observed second-order decay rate of the HO2 signal is found to increase by up to a factor of ⋍2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO2 + H2O ⇋ HO2·H2O (4a) and HO2 + NH3⇋ HO2·NH3 (4b), which are more reactive than uncomplexed HO2 toward a second uncomplexed HO2 radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10-20≲K4a≲6.3 × 10-19 cm3/molec at 295°K and K4b = 3.4 × 10-18 cm3/molec at 298°K. Several deuterium isotope effects are also reported, including kH/kD = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.

Notes: Rate constants have been estimated as a function of temperature for seven reactions of the type W + XYZ = WX + YZ, where W, X, Y, and Z are H and O atoms. From transition state theory and estimates of the heat capacities of activation, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm int\, k/[cm}^{\rm 3} {\rm (mol} \cdot {\rm sec)] = 10}^{{\rm 15}{\rm .87}} \exp (\Delta S_{298}^{\circ _ \ne} /R)T^{0.75} \exp [- (\Delta H_{298}^{\circ _ \ne} + 0.74)/RT] $$\end{document} where int k is the rate constant per transferable atom for the forward and reverse reactions in the exothermic direction, and where ΔH°≠298 is in kcal/mol. Values of ΔS°≠298 and ΔH°≠298 were obtained from the above equation and previously measured and evaluated rate constants at 298°K. The results are summarized in a table. Rate constants were calculated at temperature from 250 to 2000 K. The estimated rate constants were compared with recommended values. The results for ΔH°≠298 for reactions (15), (16), (17), and (19), in which a stable intermediate may precede the transition state, together with similar results previously found for reactions X + YZ = XY + Z, suggests that many such reactions may have values of ΔH°≠298 that are close to zero. The result for the reaction O + O3 = O2 + O2 is however, an exception to the foregoing perhaps because it is the reaction of a singlet with a triplet.ΔS°≠298 for the same reaction is unexpectedly low.

Notes: No Absract.

Notes: Rate, equilibrium, and thermodynamic data for reaction (1) of 2,6-diphenyl-4R-phenoxyl radicals, where R==OCH3 (I), Ph (II), OC2H5 (III), O-n-C18H37 (IV), and 2,6-dicyclohexyl-4-phenylphenoxyl radical (V), in various solvents are obtained. The k1 values of radicals I to V are within (5.5 ± 1.0) × 107-(1.4 ± 0.3) × 109M-1·sec-1 in propanol. The solvent effect on k1 for radicals I and II was studied. The dimerization of radical I is diffusion-controlled in all solvent studies. The dimerization of radical II is viscosity-dependent but not diffusion-controlled. Plots of k1 against ET have a V shape. Specific solvent-solute interactions are seeming to be responsible for numerical k1 values of radicals I and II. The solvent effect is more pronounced for “slow” dimerization of radicals II than for “fast” dimerization of radicals I. The minimum k1 values correspond to pyridine and chloroform. The reaction (1) rate strongly depends upon the composition of a chloroform (S)-cosolvent binary mixture. Besides reaction (1) the following reactions proceed in binary mixture: \documentclass{article}\pagestyle{empty}\begin{document}$$ K_{14} = 0.18 \pm 0.05M^{ - 1},k_{15} = (2.0 \pm 1.0) \times 10^8 M^{ - 1} \cdot \sec ^{ - 1} $$\end{document} (radical I, S-CCL4 mixture) \documentclass{article}\pagestyle{empty}\begin{document}$$ K_{14} = 0.9 \pm 0.2M^{ - 1},k_{15} = (1.2 \pm 0.5) \times 10^7 M^{ - 1} \cdot \sec ^{ - 1} $$\end{document}(radical II, S-C6H14 mixture) \documentclass{article}\pagestyle{empty}\begin{document}$$ K_{14} = 0.45 \pm 0.10M^{ - 1},k_{15} = (9.0 \pm 2.0) \times 10^6 M^{ - 1} \cdot \sec ^{ - 1} $$\end{document}(radical II, S-CCL4 mixture)In all cases k16 ≪ k15. Factors influencing dimerization rates in strongly nonideal mixtures CH3OH-CCL4 and CH3OH-CHCl3 are discussed.

Notes: The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H2SO4—MClO4 (M+ = H+, Li+, Na+) and H2SO4—MHSO4 (M+ = Li+, Na+, K+) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k1 + k2/(1 + a)2[HSO4-]2 = k1 + k2/(1 + 1/a)2[SO42-]2, a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H+ ≤ Li+ 〈 Na+ 〈 K+. The observed negative cation effects on the rate constant k1 are in the order Na+ 〈 Li+ 〈 H+, whereas the order is in reverse for k2, namely, H+ ≤ Li+ 〈 Na+. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters.

Notes: Formic acid molecules highly diluted in argon were passed through a clean platinum screen at 420-730 K and condensed onto an 8-K CsI window. The well-known decomposition products, CO2, CO, and H2O, were observed in the infrared spectra of the resulting matrices. In addition, new absorptions which are attributed to the OCOH free radical were also observed. Experiments with partially deuterated formic acids confirmed that the carbon-hydrogen bond of the formic acid was lost in the formation of the new intermediate species. The activation energy for CO2 production, Ea = 3.5 ± 0.2 kcal/mol, was determined by monitoring its appearance rate at several different catalyst temperatures.

Notes: In the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70-200°C), total pressures (50-2400 torr), and total doses (0.15-2.0 Mrad). The disproportionation-combination ratio kdH/kcH for c-C6H11 radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c-C6D12, the ratio kdD/kcD for c-C6D11 radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C6H11 and C6D11 radicals leads to (kdH)/(kcH)/(kdD/kcD) = 1.47 ± 0.02. The corresponding values for the reactions of c-C6H11 with c-C6D11 were also determined.