ALBERT

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.).

Notizen: 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).

Notizen: 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+.

Notizen: 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).

Notizen: 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.

Notizen: 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.

Notizen: 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).

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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).

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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).

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: 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.

Notizen: Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°-328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows:Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10-6 exp { z-(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10-12 cm3/sec independent of temperature, k1a = 1.2 × 10-11 exp {-(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10-13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (-2b), which was found to have a rate coefficient k-2b = 6 × 1017 exp {-26,000/RT} sec-1 based on the value of k1a given above. The intermediate can also decompose via Reaction (10b) is at least partially heterogeneous.

Notizen: Tertiary-amyl amine has been decomposed in single-pulse shock-tube experiments. Rate expressions for several of the important primary steps are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11 - {\rm NH}_2} \to t{\rm C}_5 {\rm H}_{11}\!\!\cdot + {\rm NH}_2\cdot) = 10^{15.9} \exp (-39,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm C}_2 {\rm H}_5- {\rm C}({\rm CH}_3)_2{\rm NH}_2 \to {\rm C}_2 {\rm H}_5 \cdot + \cdot{\rm C}({\rm CH}_3)_2{\rm NH}_2) = 10^{16.5} \exp (- 38,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11} {\rm NH}_2 \to {\rm C}_5 {\rm H}_{10} + {\rm NH}_3) 〈10^{14.5} \exp (- 37,200/T)\sec ^{- 1} $$\end{document}This leads to D(CH3—H) - D(NH2—H) = -10.5 kJ and D[(CH3)3C—H] - D[(CH3)2NH2C—H] = + 6 kJ.The present and earlier comparative rate single-pulse shock-tube data when combined with high-pressure hydrazine decomposition results-(after correcting for fall off effects through RRKM calculations) gives \documentclass{article}\pagestyle{empty}\begin{document}$$ [k_r^2 (t{\rm C}_5 {\rm H}_{11} \cdot,{\rm NH}_2 \cdot)/k_r (t{\rm C}_5 {\rm H}_{11} \cdot,t{\rm C}_5 {\rm H}_{11} \cdot)k_r ({\rm NH}_2 \cdot,{\rm NH}_2 \cdot)]^{1/2} \sim 2\,{\rm at}\,1100^o {\rm K} $$\end{document} where kr(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then \documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty ({\rm N}_2 {\rm H}_4 \to 2{\rm NH}_2 \cdot) = 10^{16.25} \exp (- 32,300/T)\sec ^{- 1} $$\end{document} Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated: \documentclass{article}\pagestyle{empty}\begin{document}$$ D(i{\rm C}_3 {\rm H}_7 {-\!-} {\rm H}) {-\!-} D[{\rm CH}_3 ({\rm NH}_2){\rm CH} {-\!-} {\rm H}] = 14.3\,{\rm kJ} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ D({\rm C}_2 {\rm H}_5 {-\!-} {\rm H}) - D({\rm NH}_2 {\rm CH}_2 {-\!-} {\rm H}) = 15.9\,{\rm kJ} $$\end{document}

Notizen: The thermal decomposition of F5SOOSF5, P, in the presence of CO has been investigated between 130.1° and 161.9°C at total pressures between 50 and 600 torr. The reaction is homogeneous, and the only final products formed are CO2 and S2F10. The rate of reaction is proportional to the pressure of P. The partial pressures of CO and O2 and the total pressure have no influence on the course of reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d\left[P \right]}}{{dt}} = k\left[P \right] $$\end{document}The results are explained by the following mechanism:

Notizen: The unimolecularity of the thermal dehydrogenation of cyclopentene has been confirmed using the technique of very low-pressure pyrolysis (VLPP). Application of RRKM theory shows that the experimental unimolecular rate constants obtained over the temperature range of 942°-1152°K are consistent with the high-pressure Arrhenius parameters given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k/\sec ^{-1}) = 13.35 - 61/\theta $$\end{document} where θ = 2.303 RT kcal/mol. These parameters are in good agreement with static and shock tube studies. No firm evidence could be found for any side reactions or reversibility under the experimental conditions used.

Notizen: The thermal decomposition of isopropyl peroxide in solvents is shownto be a competition between unimolecular homolysis (kr) and an electrocyclic reaction yielding H2 plus acetone (kH). The value of kH increases markedly with increasing solvent polarity: PhCH3 〈 i-PrOH 〈 MeOH 〈 H2O. Log kH correlates linearly with Et (or Z). The effect on kr is similar but less pronounced. Log kr's for both i-Pr2O2 and t-Bu2O2 are shown to correlate with the molar solubility parameter δ. The negligible contribution of the electrocyclic reaction to thermal decompositions of peroxides in the vapor phase is thus not due to peculiar behavior of that reaction, which clearly has a polartransition state. It is argued that the transition state for unimolecular homolysis has no polar character despite the apparent sensitivity of homolysis rates to solvent polarity.

Notizen: The kinetics of the gas-phase decomposition of 1-methylcyclohex-1-ene has been studied over the temperature range of 1000°-1180° K in a single-pulse shock tube using a comparative-rate technique. The retro Diels-Alder reaction to ethylene and isoprene accounts for the bulk of the products with a rate constant given by \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{15.57} \exp \left({- 35,000/T} \right)\sec ^{- 1} $$\end{document}

Notizen: The decomposition of acetonyl bromide, isopropenylmethylether, and hexanedione-2,5 was studied using the very-low-pressure pyrolysis (VLPP) technique. The acetonyl radical is a product of each reaction. Arrhenius parameters determined are or acetonyl bromide ← acetonyl + Br: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 16.0 - 62.5/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document} and for isopropenylmethylether ← acetonyl + CH3: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 15.8 - 66.3/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document} These lead to values of acetonyl stabilization energy (SE) of 0.8 and -4.0 kcal/mol, respectively. Comparison of the pyrolyses of hexanedione-2,5 and 2,5-dimethylhexane indicate a value of SE ∼ 2 kcal/mol. The total of these results is taken, along with previous work, to indicate that 0 ≲ SE ≲ 2 kcal/mol.

Notizen: Relative Arrhenius parameters have been determined for the addition of trifluoromethyl radicals to vinyl chloride (X=Cl), vinyl bromide (X=Br), acrylonitrile (X=CN), methyl vinyl ketone (X=COCH3), 2-methylbut-2-ene, and to iso-butene, taking the rate of addition to ethylene as standard. Addition occurred virtually exclusively at the unsubstituted end of all the olefins. The relative rates of addition at 164°C show very little variation. The preexponential terms for addition to the CH2 ends are constant within experimental error, and the small variations in rate are due principally to the activation energy term. The present results are put on an absolute scale using the previously determined Arrhenius parameters for addition to ethylene and are compared with data for other similar monomers determined previously.

Notizen: The kinetics of the deprotonation of tropaeolin O by OH- ions was investigated between 9° and 30°C, and by OD- ions at 24.7°C. The pH range was 10.7-12.5, and the ionic strength 0.1M throughout. All results were obtained by the temperature jump method. On the basis of a mechanism suggested earlier, rate constants k31 for the reaction between OL- and the internally bonded weak acid and k32 for the opening of the internal hydrogen bond were evaluated. The activation energies in ordinary water were found to be ΔH≠31 = 3.6 kcal/mol, ΔS≠31 = -19 eu, and ΔH≠32 = 27 kcal/mol, ΔS≠32 = 46 eu. The kinetic isotope effect was k31H2O/k31D2O ∼ 1.5 and k32H2O/k32D2O ∼ 0.9. The unusual results for reaction path are discussed in terms of solvent participation.

Notizen: The autoinhibiting reaction of ozone with dimethyl sulfide (DMS), has been studied at 296°K and 1.1 kPa (8 torr) as a function of the concentrations of both reactants. The major products of the reaction are H2CO, H2O, CO, and SO2. The specific rate of primary attack of O3 on DMS is immeasurably slow. It is suggested that the rapid overall rate observed for this reaction is due to a chain reaction initiated by the very slow primary reaction. It is concluded that reaction (1) cannot be important under atmospheric conditions and that the major loss process for DMS in the atmosphere is probably reaction with photochemically generated free radicals.

Notizen: Methyl radical reactions with matrix molecules in glasses C2H5OH, (CH2OH)2, n- and i-C3H7OH, n- and i-C4H9OH, n- and i-C5H11OH, C2D5OH, and i-C3D7OD, and the reactions of Ċ2H5, Ċ3H7, Ċ4H9, Ċ5H11 with methanol glasses have been studied. Alkyl radicals were produced by photolysis of diphenylamine-alkylhalide-alcohol mixtures using ultraviolet light. In all cases the alkyl radical decay follows the law c = c0 exp(-k √t). The √t law should not be associated with alkyl radical diffusion in a matrix. A method of processing the kinetics of those reactions in which one paramagnetic species changes into another with the total concentration being constant and the electron spin resonance spectra of both species overlapping, is described.

Notizen: A kinetic study has been made of the 3130-Å photolysis of CH2O (8 torr) in O2-containing mixtures (0.02-8 torr) and in the presence of added CO2 (0-300 torr) at 25°C. Quantum yields of formation of H2, CO, and CO2 and the loss of O2 were measured. ΦH2 and ΦCO were much above unity. In an explanation of these unexpected results, a new H-atom-forming chain mechanism was postulated involving HO2 and HO addition to CH2O: CH2O + hν → H + HCO (1) H + CH2O → H2 + HCO (3) H + O2 + M → HO2 + M (6) HCO + O2 → HO2 + CO (8) HO2 + CH2O → (HO2CH2O) → HO + HCO2H (15) HO + CH2O → H2O + HCO† (16); HCO† → H + CO (19) HO + CH2O → H2O + HCO (17) and HO + CH2O → HCO2H + H (18). When the results are rationalized in terms of this mechanism, the data suggest k16 ≫ k17 and k16/k18 ≅ 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO2H formation was used as a monitor of the rate of reaction (7) HCO + O2 + M → HCOO2 + M (7). The present data from experiments at PCH2O = 8 torr and PO2 = 1-4 torr give k7[M]/(k7[M] + k8) ≥ 0.049 ± 0.017. These data coupled with the k8 estimates of Washida and coworkers give k7 ≥ (4.4 ± 1.6) × 1011 l2/mol2·sec for M = CH2O. The reaction sequence proposed here is consistent with the observed deterimental effect of O2 addition on the laser-induced isotope enrichment in HDCO. In additional studies of CH2O-O2-isobutene mixtures it was found that ΦH2 was equal to φ2 as estimated in O2-free CH2O-isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O2 addition in CH2O photolysis does not result from perturbations in the fragmentation pattern of the excited CH2O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O2 → HO2 + CO (ν = 1).

Notizen: Using the ECR technique the electron scavenging properties of the halomethanes CHF3, CHClF2, and CHCl2F were investigated. A brief discussion is given on the evaluation of experimental data for inefficient polar scavengers. Absolute attachment rate constants were obtained from the decrease of the cyclotron resonance signal upon addition of the above scavengers. For the molecules CHF3 and CHCl2F the activation energies for the capture processes are given. Possible capture mechanisms are discussed.

Notizen: A nitrogen laser pumped tunable dye laser has been used to observe the three-photon ionization of NO through a two-photon resonance with the C2II state. Fluorescence is also observed from this state. The wavelength dependence of both signals have been measured. A reaction mechanism is postulated, which includes the initial two-photon excitation of the C2II state as the rate-limiting step. This mechanism predicts the observed second-order intensity dependence of the ionization signal and shows that the simple rate equation treatment is valid in this system.

Notizen: It is shown that the activation energies E oF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energies D and the Taft polar and steric substituent constants σ* and Es by the expression: \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta E = \alpha \Delta D + \rho \sigma ^* + \delta E_{\rm s} $$\end{document} where ΔE and ΔD represent the differences between the E and D values of a given substrate and those of a reference compound (CH3 substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical data.

Notizen: The reactions of ozone with propene and isobutene have been studied in the gas phase at 298°K and 530 Pa (4 torr) using a stopped-flow reactor coupled to a photoionization mass spectrometer. Reactant and product concentrations were followed as a function of reaction time. The major reaction products monitored were CH2O, CH3CHO, CO2, and H2O from the propene reaction, and CH2O, (CH3)2CO, CO2, and H2O from the isobutene reaction. The observations were interpreted on the basis of the Criegee mechanism for ozonolysis in solution: for which we find kA≈kB.In the gas phase the carbene peroxy radical is postulated to isomerize and decompose into molecular and free-radical products.

Notizen: Rate constants for the reaction O(3P) + SO2 + M have been determined over the temperature range of 299°-440°K, using a flash photolysis-NO2 chemiluminescence technique. For M=Ar, the Arrhenius expression \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 ^{{\rm Ar}} {\rm = 3}{\rm .1 \times 10}^{{\rm - 32}} e^{{\rm - (2005 \pm 300)/RT}} {\rm cm}^{\rm 6} {\rm /molec}^2 \cdot \sec $$\end{document} was obtained. At room temperature k2Ar = (1.05 ± 0.21) × 10-33 cm6/molec2·sec. In addition, the rate constants k2N2 = (1.37 + 0.27) × 10-33 cm6/molec2·sec, k2SO2 = (9.5 ± 3.0) ± 10-33 cm6/molec2·sec, k3N2 = (1.1 ± 0.2) ± 10-31 cm6/molec2·sec, and k3SO2 = (2.6 - 0.9) ± 10-31 cm6/molec2·sec were obtained at room temperature where k3M is the rate constant for the reaction O + NO + M → NO2 + M. The rate data are compared and discussed with literature values.

Notizen: The addition of ethene to cyclohexa-1,3-diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa-1,3-diene. The reaction is of the “Diels-Alder” type and leads to the formation of bicyclo[2.2.2]oct-2-ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_a = - (25,970 \pm 50)/4.576{\rm T + }(6.66 \pm 0.02) $$\end{document}The retron-Diels-Alder pyrolysis of bicyclo[2.2.2]oct-2-ene has also been studied. In the ranges of 548-632 K and 4-21 torr the reaction is first order, and its rate constant (in sec-1) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_p = - (57,300 \pm 100)/4.576{\rm T + }(15.12 \pm 0.04) $$\end{document}The reaction mechanism is discussed. The heat of formation and the entropy of bicyclo[2.2.2]oct-2-ene are estimated.

Notizen: The kinetics of ethane oxidation was studied at 320, 340, 353 and 380°C, mixture composition 2 C2H6 + 1 O2, and total pressure 609 torr. It was found that at 320°C CH2O and CH3CHO were branching agents. A series of experiments was conducted on 2C2H6 + O2 oxidation in the presence of 0.7% 14C-labeled ethylene. The ethylene oxide was found to form only from C2H4, formaldehyde formed from C2H4 and C2H6; and CH3CHO, C2H5OH, and CH3OH formed only from ethane. The formation rates of C2H4, C2H4O, and CH2O were calculated by the kinetic tracer method. At 320°C the fraction of oxygen-containing products formed from C2H4 was 16-18%, and at 353 and 380°C it was 30-40%.

Notizen: The thermal unimolecular decomposition of bromocyclobutane has been investigated over the temperature range of 791-1224 K using the technique of very low-pressure pyrolysis (VLPP). HBr elimination is the sole mode of decomposition under the experimental conditions. No evidence could be found for the ring-cleavage pathway to ethylene and vinyl bromide. Assuming a four-center transition state and an Arrhenius A factor the same as that for HCl elimination from chlorocyclobutane, RRKM calculations show that the experimental unimolecular rate constants are consistent with the Arrhenius expression \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\,{\rm sec}^{{\rm - 1}} {\rm )}\, = \,(13.6 \pm 0.3) - (52.0 \pm 1.0)/{\rm \theta }\,$$\end{document} where θ = 2.303RT kcal/mol. The activation energy is higher than that for the open-chain analog, 2—bromobutane. This finding is consistent with the results for the corresponding chloro and iodo compounds.

Notizen: The kinetics and mechanism of ascorbic acid (DH2) oxidation have been studied under anaerobic conditions in the presence of Cu2+ ions. At 10-4 ≤ [Cu2+]0 〈 10-3M, 10-3 ≤ [DH2]0 〈 10-2M, 10-2 ≤ [H2O2] ≤ 0.1M, 3 ≤ pH 〈 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ2 (25°C) = (6.5 ± 0.6) × 10-3 sec-1. The effective activation energy is E2 = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu+ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu+ initiation in the Cu2+ reaction with ascorbic acid by the expression where C is a function of pH and of H2O2 concentration. The rate equation where k1(25°C) = (5.3 ± 1) × 103M-1 sec-1 is true for the steady-state catalytic reaction. The Cu+ ion and a species, which undergoes acid-base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu2+-DH2-H2O2 system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu+ with H2O2, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme.Initiation: Propagation: Termination:

Notizen: Using published data on the kinetics of pyrolysis of C2Cl6 and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations:The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction isA reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease.From the analysis, the bond dissociation energy DH0(C2Cl5—Cl) is found to be 70.3 ± 1 kcal/mol and ΔHf3000(·C2Cl5) = 7.7 ± 1 kcal/mol. The resulting π—bond energy in C2Cl4 is 52.5 ± 1 kcal/mol.

Notizen: Spectrophotometric methods were used to investigate the rate of the reaction of Br2 with HCOOH in aqueous, acidic media. The reaction products are Br- and CO2. The kinetics of this reaction are complicated by both the formation of Br3- as Br- is formed and the dissociation of HCOOH into HCOO- and H+. Previous work on this reaction was carried out at acidities lower than the highest used here and led to the conclusion that only HCOO- reacts with Br2. It is agreed that this is by far the principal reaction. However, at the highest acidity experiments, an added small component of reaction was found, and it is suggested that it results from the direct reaction of Br2 with HCOOH itself. On this assumption, values of the rate constants for both reactions are derived here. The rate constant for the reaction of HCOO- with Br2 agrees with values previously reported, within a factor of 2 on the low side. The reaction involving HCOOH is more than 2000 times slower than the reaction involving HCOO-, but it does contribute to the overall rate as [H+] approaches 1M. These derived rate constants are able to simulate quantitatively the authors' absorbance-versus-time data, demonstrating the validity of their data treatment methods, if not mechanistic assignments. Finally, activation parameters were determined for both rate constants. The values obtained are: ΔE

Notizen: The reaction of carbon monoxide with ozone was studied in the range of 75-160°C in the presence of varying amounts of CO2 and, for a few experiments, of O2. At room temperature the reaction was immeasurably slow, but in a flow system it showed chemiluminescence with undamped oscillations. In a static system above 75°C the emission showed damped oscillations when O2 was present. In the absence ofadded O2 the emission showed a slow decay with a half-life of 1 hr. The luminescence consisted of partially resolved bands in the range of 325-600 nm, and the source was identified as CO2(1B2) → CO2(1Σg+) + hv. The kinetics were complex, and the observed rate law could be accounted for bya mechanism involving the chain sequence \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm O(}^{\rm 3} P{\rm ) + CO( + M)}\mathop {{\rm rightarrow}}\limits^{\rm 3} {\rm CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) ( + M), CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) + O}_{\rm 3} {\rm }\mathop {{\rm rightarrow}}\limits^{\rm 7} {\rm CO}_{\rm 2} {\rm (}^{\rm 1} \sum\nolimits_{\rm g}^{\rm + } {} {\rm ) + O}_{\rm 2} {\rm + O} $\end{document}. From measurements of -d[O3]/dtand relative emission, rate constant ratios were obtained and estimates of k3were made.

Notizen: The reaction NO + O3 → NO2 + O2 has been studied in a 220-m3 spherical stainless steel reactor under stopped-flow conditions below 0.1 mtorr total pressure. Under the conditions used, the mixing time of the reactants was negligible compared with the chemical reaction time. The pseudo-first-order decay of the chemiluminescence owing to the reaction of ozone with a large excess of nitric oxide was measured with an infrared sensitive photomultiplier. One hundred twenty-nine decays at 18 different temperatures in the range of 283-443 K were evaluated. A weighted least-squares fit to the Arrhenius equation yielded k = (4.3 ± 0.6) × 10-12 exp[-(1598 ± 50)/T] cm3/molecule sec (two standard deviations in brackets). The Arrhenius plot showed no curvature within experimental accuracy. Comparison with recent results of Birks and co-workers, however, suggests that a nonlinear fit, as proposed by these authors, is more appropriate over an extended temperature range.

Notizen: The gas-phase free radical displacement reaction has been studied in the temperature range of 240-290°C and at 140°C with the thermal decomposition of azomethane (AM) and di-tert-butylperoxide (DTBP), respectively, as methyl radical sources. The reaction products of the CD3 radicals were analyzed by mass spectrometry. Assuming negligible isotope effects, Arrhenius parameters for the elementary radical addition reaction were derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_1 (cm^3 /mol\sec) = (10.5 \pm 0.4) - (11,500 \pm 1100)/4.576T $$\end{document}The data are discussed with respect to the back reaction and general features of elementary addition reactions.

Notizen: The redox potential and iodine concentration behavior of the title reaction and component reactions have been examined. The effect of hydrogen peroxide, potassium iodate, manganese (II) sulfate, sulfuric acid, and acetone concentration on the time period and redox potential behavior is reported. Iodine production and consumption rates for the component reactions are given, and some mechanistic suggestions, involving iodine dioxide as the one electron oxidant, are made.

Notizen: The production of both the b1Σ+ and a1Δ states of NCl has been observed from the reaction of HN3 with flowing streams of Cl and F atoms. The results suggest that a two-step reaction sequence is responsible for the production of excited NCl, as follows: The rate contant (all products) for the first step is k(F + HN3) 〉 1 × 10-11 cm3/molecule sec. Comparison of this value to results obtained in a previous study of the F + HN3 system yields a value k(F + N3) = 2 × 10-12 cm3/molecule sec. The rate constant for the reaction of chlorine atoms with HN3 was determined to be k(Cl + HN3) 1 × 10-12 cm3/molecule sec. The difference between the Cl + HN3 and F + HN3 rates is interpreted in terms of an addition-elimination mechanism.

Notizen: The kinetics of oxidation of benzyl alcohol and substituted benzyl alcohols by sodium N-chloro-p-toluenesulfonamide (chloramine-T, CAT) in HClO4 (0.1-1 mol/dm3) containing Cl- ions, over the temperature range of 30-50°C have been studied. The reaction is of first order each with respect to alcohol and oxidant. The fractional order dependence of the rate on the concentrations of H+ and Cl- suggests a complex formation between RNCl- and HCl. In higher acidic chloride solution the rate of reaction is proportional to the concentrations of both H+ and Cl7hyphen;. The observed solvent isotope effect (kD2O/kH2O) is 1.43 at 30°C. The reaction constant (p = -1.66) and thermodynamic parameters are evaluated. Rate expressions and probable mechanisms for the observed kinetics have been suggested.

Notizen: The kinetics and mechanism of the silver(II) oxidation of methanol, ethanol, 1-propanol, 1-methyl- ethanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, D4-methanol, and D6-methanol have been investigated at 8.0 and 20.0°C in aqueous perchloric acid media (1.00 ≤ [HClO4] ≤ 4.00M; μ = 4.0M). The kinetics were monitored by following the disappearance of Ag(II) with a spectrophotometric stopped-flow technique. The reactions are first order in each reactant and involve both Ag2+ and AgOH+ species. No kinetic or spectroscopic evidence for complex formation between reactants was obtained. The results are discussed with reference to electron density on the —OH or αC-H substrate sites and to the isotopic hydrogen/deuterium rate quotients found for methanol and ethanol.

Notizen: The carbon kinetic isotope effect in the reaction of CH4 with OH has an experimentally measured value of 1.003. The measurement was performed using a static system in which the source of OH was the gas-phase photolysis of H2O2 with ultraviolet light produced by a high-pressure mercury arc lamp. Implications for the tropospheric cycle of CH4 are considered briefly.

Notizen: It was found that the rates of absorption of oxygen by pyridine-aqueous sodium hydroxide emulsions and the same emulsions containing benzil were catalyzed by the addition of quaternary salts and followed the same rate law:\documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{dPo_2}}{{dt}} = k_1 \left[{{\rm Po}_{\rm 2}} \right]\left[{^ -} \right]\left[{{\rm benzil}} \right]^0 + k_2 \left[{{\rm Po}_2} \right]\left[{OH^ -} \right]\left[{{\rm Et}_{\rm 4} {\rm NCl}} \right][benzil]^0 $$\end{document}. It was concluded that the autooxidation of benzil in pyridine-aqeuous sodium hydroxide emulsions has as its rate-determining step a step in the autooxidation of pyridine. Possibly the superoxide formed in the autooxidation of pyridine is the oxidizing agent in the oxidation of benzil.

Notizen: It is shown how electron spin resonance spectroscopy with modulated radical initiation can be used to analyze by purely spectroscopic means the second-order termination kinetics of systems containing two different kinds of radicals. The technique is applied to species generated by photoreduction of acetone in tetraethoxy silane. The bimolecular self- and cross reactions of \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm O)}_{\rm 3} {\rm SiO\dot CHCH}_{\rm 3} (\dot R_1 )\,and\,(CH_3 )_2 \dot COH(\dot R_2 )$\end{document} are found to be encounter-controlled processes. For the cross termination the often used relation k12 = (4 k1k2)1/2 is verified experimentally.

Notizen: The homogeneous gas-phase thermal decomposition kinetics of germane have been measured in a single-pulse shock tube between 950 and 1060 K at pressures around 4000 torr. The initial decomposition is GeH4 → GeH2 + H2 in its pressure-dependent regime, with log kGeH4(4000) = 13.83 ± 0.78 - 50,750 ± 3570 cal/2.303RT. RRKM calculations suggest that the high-pressure Arrhenius parameters are log k GeH4(M → ∞) = 15.5 - 54,300 cal/2.303RT. Extrapolations to static system pyrolysis conditions (T ∼ 600 K, P ∼ 200 torr) give homogeneous reaction rates which are much slower than those observed, hence the static system pyrolysis of germane must be predominantly heterogeneous. Shock-initiated pyrolysis reaction stoichiometry is 2 mol H2 per mole GeH4, suggesting that the subsequent decomposition of germylene is essentially quantitative. Investigations of the hydrogen product yields for pyrolysis of GeD4 in øCH3 further indicate that the germylene decomposition reaction is mainly GeH2 → H2 + Ge, but that a small amount of reaction to H atoms may also occur.

Notizen: The photooxidation of chloral was studied by infrared spectroscopy under steady-state conditions with irradiation of a blackblue fluorescent lamp (300 nm 〈 λ 〈 400 nm, λmax = 360 nm) at 296 ± 2 K. The products were hydrogen chloride, carbon monoxide, carbon dioxide, and phosgen. The kinetic results reveal that the reaction proceeds via chain reaction of the Cl atom:The results lead to the conclusion that mechanism (B) is confirmed to be more likely than mechanism (A), which was favored at one time by Heicklen for the mechanism of the oxidation of trichloromethyl radicals by oxygen molecules: The ratio of the initial rates of CO and CO2 formation gave k7/k6 = 4.23M-1, and the lower limit of reaction (5) was found to be 3.7 × 108M-1 sec-1.

Notizen: The kinetics of bromination of several aromatic compounds (anilides, anisoles, and phenols) was investigated in 80% aqueous acetic acid (v/v) in the temperature range 20-50°C using N-bromosuccinimide (NBS) as the reagent. The reaction was found to be first order in the aromatic substrate (ArH), and zero order in NBS, the overall order being 1. Stoichiometry of the reaction was 1:1. An increase in solvent polarity increased the reaction rate, and chloride ions were found to be specific catalysts for the reaction. Arrhenius activation energy remained almost constant for all the substrates. A probable mechanism explaining all these observed facts was proposed. The mechanism involved an attack by Br+ or more probably by a solvated Br+ ion on the aromatic substrate.

Notizen: The photooxidation of the 1,3-butadiene-NO-air system at 298 ± 2 K was investigated in an environmental chamber under simulated atmospheric conditions. The irradiation gave rise to the formation of acrolein in a 55% yield, based on 1,3-butadiene initial concentration for all the experimental runs.The rate of formation of acrolein was the same as that of 1,3-butadiene consumption, indicating that acrolein is the major product of the 1,3-butadiene oxidation in air.The dependence of acrolein concentration on irradiation time showed thata secondary process, identified as an oxidation of acrolein by ⋅OH radicals, was occurring during the photochemical runs. The rate constant of this secondary process was determined by measuring the relative rates of disappearance of acrolein and n-butane during the irradiation of acrolein-n-butane-NO-air mixtures. The so obtained relative rate constant value was placed on an absolute basis using a reported rate constant for the n-butane + ⋅OH reaction; a value of (1.6 ± 0.2) × 1010 M-1 sec-1 was obtained.

Notizen: The Cl atom-initiated oxidation of CH2Cl2 and CH3Cl was studied using the FTIR method in the photolysis of mixtures typically containing Cl2 and the chlorinated methanes at 1 torr each in 700 torr air. The results obtained from product analysis were in general agreement with those reported by Sanhueza and Heicklen. The relative rate constant for the Cl atom reactions of CH2Cl2 and CH3Cl was determined to be k(Cl +CH3Cl)/k(Cl + CH2Cl2) = 1.31 ± 0.14 (2σ) at 298 ± 2 K.

Notizen: The experimental data on alkane decomposition from shock-tube and radical buffer studies and radical combination from very-low-pressure pyrolysis and modulation spectroscopy are shown to be consistent. They lead to experimental A factors which decrease by factors of 10-2000 from 300° to 1100°K. Heats of formation for ethyl, isopropyl, and t-butyl radicals have been found to be 10, 10 and 20 kJ higher than currently accepted numbers from metathesis reactions.

Notizen: CO laser emission at 5 μm was detected when SO2 and CFBr3 were flash photolyzed in the vacuum ultraviolet above 165 nm. Over 40 vibrational-rotational transitions ranging from Δv = 2 → 1 to 14 → 13, with the exception of those between 8 → 7 and 11 → 10, were identified. The CO emission is believed to result from the O + CF reaction:The vibrational population of the CO has been measured by means of a CO laser resonance absorption method. The CO was found to be vibrationally excited to v = 24 with a vibrational temperature of about 1.4 × 104°K. The “surprisal analysis” of the observed CO distribution showed the possible occurrence of a minor process (presumably O + CFBr) that generated vibrationally colder CO. The effects of various additives on the CO emission were also examined. The addition of CO2 to a D2-SO2-CFBr3-He mixture resulted in a simultaneous osciallation at 3.6, 5, and 10.6 μm due to DF, CO, and CO2, respectively. Additionally, the utilization of the O + CFn (n = 1, 2, 3) reactions as F-atom sources for HF-laser operation in flash-initiated systems were demonstrated.

Notizen: No. Abstract.

Notizen: The kinetics of gamma-radiation-induced free-radical chain reactions in solutions of carbon tetrachloride in mixtures of varying composition of cyclohexane and n-hexane was investigated in the temperature range of 296°-413°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated alkyl radicals with the solute. The kinetics of the following reactions were studied: The following rate expression was obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_4 /k_5 = 0.32 \pm 0.04 - (0.14 \pm 0.07)/\theta $$\end{document} The error limits are the standard deviation from the least mean-square Arrhenius plots. The present results, combined with previously measured activation parameters for hydrogen-atom abstraction from c-C6H12 and n-C6H14 by CCl3 radicals relative to CCl3 combination, afford experimental evidence that the decay of trichloromethyl species in alkane solutions is a diffusion-limited process. The thesis that activation energies of reactions (4) and (5) in the liquid phase are equal to their respective values in the gas phase is confirmed.

Notizen: Permanganate ion rapidly oxidizes the thiol group in 2-thiouracils (2,3-dihydro-2-thioxo-4(1H)-pyrimidinones, 4-hydroxy-2-pyrimidinethiols) to the corresponding uracil-2-sulfonates in phosphate-buffered solutions. The oxidations, which are first order in oxidant and first order in reductants, are characterized by relatively small energies of activation (Ea ≅ 4.3-6.7kcal/mol) and relatively large negative entropies of activation (ΔS

Notizen: The decay kinetics of aryloxy and semiquinone radicals in the presence of copper ions in aqueous solutions has been studied by means of the flash photolysis technique. The radicals are involved in electron transfer reactions and those leading to the formation of intermediate complexes with copper ions. The complexes of p-benzosemiquinone anion radicals and 2-hydroxyphenoxy radicals with cupric ions decay in bimolecular self-reactions at a much slower rate than the original radicals. The increased stability of the complexes compared with the initial radicals is attributed to partial delocalization of the unpaired electron over the electron shell of copper and to steric hindrances in the self-reactions of complexes.