Time-resolved,Gas-phase Kinetic and Quantum Chemical Studies of the Reaction of Germylene with Hydrogen Chloride

Time-resolved studies of germylene, GeH₂, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene at 193 nm and monitored by laser absorption, have been carried out to obtain rate constants for its bimolecular reaction with HCl. The reaction was studied in the gas phase, mainly at a total pressure of 10 Torr (in SF₆ bath gas) at five temperatures in the range 295–558 K. Experiments at other pressures showed that these rate constants were unaffected by pressure. The second-order rate constants at 10 Torr (SF₆ bath gas) fitted the Arrhenius equation: log(k/cm³ molecule⁻¹ s⁻¹)=(−12.06±0.14)+(2.58±1.03 kJ mol⁻¹)/RTln10 where the uncertainties are single standard deviations. Quantum chemical calculations at G4 level support a mechanism in which an initial weakly bound donor-acceptor complex is formed. This can then rearrange and decompose to give H₂ and HGeCl (chlorogermylene). The enthalpy barrier (36 kJ mol⁻¹) is too high to allow rearrangement of the complex to GeH₃Cl (chlorogermane).     

Gold Nanoparticles Formation via Au(III) Complex Ions Reduction with l‐Ascorbic Acid

In this paper, the kinetics and mechanism of gold nanoparticles formation during the redox reaction between [AuCl₄]− complex and l ‐ascorbic acid under different conditions were described. It was also shown that reagent concentration, chloride ions, and pH influence kinetics of nucleation and growth. To establish rate constants of these stages, the model of Finke and Watzky was applied. From Arrhenius and Eyring dependencies, the values of activation energy (22.5 kJ mol⁻¹ for the nucleation step and 30.3 kJ mol⁻¹ for the growth step), entropy (about −228 J K⁻¹ mol⁻¹ for the nucleation step and −128 J K⁻¹ mol⁻¹ for the growth step), and enthalpy (19.8 kJ mol⁻¹ for nucleation and 27.8 kJ mol⁻¹ for particles growth) were determined. It was also shown that the disproporationation reaction had influence on the rate of nanoparticles formation and may have impact on final particles morphology.     

Kinetic studies of cyclohexane hydrogenation catalyzed by the Rh(I) compounds with 2-aminopyridine

The kinetics of homogeneous hydrogenation of cyclohexene in the presence of the catalytic Rh₂Cl₂(C₈H₁₄)₄ + 2-aminopyridine has been investigated (C₈H₁₄ = cyclooctene). The rate of reaction may be expressed as

At 30 °C the equilibrium constants are: K₁ = 862 mol⁻¹ l, K₂ = 4.9 mol⁻¹ l and rate constant k = 14.0 mol⁻¹ l s⁻¹. The activation parameters are: E_a = 26.9 kJ mol⁻¹, ΔH^≠ = 24.4 kJ mol⁻¹, ΔS^≠ = − 135.9 J K⁻¹ mol⁻¹. The catalyst is about 10 times more active in the hydrogenation of cyclohexene than RhCl (PPh₃)₃.     

Communication: The insertion of silylene in C?H bonds; rate constant limits and the energy barrier

The technique of laser flash photolysis has been used to set limits on the rate constants for the bimolecular reactions of SiH₂ with methane (CH₄) and tetramethylsilane (SiMe₄) at both ambient and elevated temperatures (ca 600 K). These limits show that the energy barriers to insertion reactions of SiH₂ in the C H bonds of CH₄ are at least 45(±6) kJ mol⁻¹ and in the C H and/or Si C bonds of SiMe₄ are at least 23(±6) kJ mol⁻¹. The best thermochemical estimate of the activation energy for SiH₂+CH₄ is 59(±12) kJ mol⁻¹. Reasons for the greatly diminished reactivity of SiH₂ with C H as compared with Si H bonds are discussed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 393–395, 1999     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

Complexation and abstraction channels in the Al + CO2 reaction

The AI + CO₂ reaction is studied in the gas phase at 296 K by laser-induced fluorescence monitoring of Al and AlO. Pressure dependence of the effective bimolecular rate constant in the range 10–600 Torr (Ar+CO₂) indicates a complex formation channel yielding a stable Al·CO₂ adduct. Observation of AlO confirms the presence of an abstraction channel. A simple chemical activation mechanism is used to interpret the pressure dependence of the effective bimolecular rate constant. The activation energy for Al·CO₂ complex formation is estimated at ⪢ 1.0 kcal mol⁻¹, and the binding energy is estimated at ⪢ 9 kcal mol⁻¹.     

Kinetic studies of the reaction between dihalodicarbonylrhodate(I) anions and 2-aminopyridine

The kinetic behavior of the reaction between dihalodicarbonylrhodate(I) anions, [RhX₂(CO)₂]⁻¹, where X = Cl, Br, and the chelating agent 2-aminopyridine was investigated spectrophotometrically. The reaction for both halo analogues was found to obey third order kinetics, first order in the complex anion and second order in the 2-aminopyridine concentrations. The third order rate constants for the chloro and bromo complex anions had the values, at 25°C, of 779 and 156 l² mol⁻² min⁻¹, respectively, and the corresponding activation energies were 3.00 and 5.50 Kcal mol⁻¹. A mechanism is proposed to account for these observations.     

The kinetics and mechanisms of gas phase elimination of primary,secondary, and tertiary 2‐hydroxyalkylbenzenes

2‐Phenylethanol, racemic 1‐phenyl‐2‐propanol, and 2‐methyl‐1‐phenyl‐2‐propanol have been pyrolyzed in a static system over the temperature range 449.3–490.6°C and pressure range 65–198 torr. The decomposition reactions of these alcohols in seasoned vessels are homogeneous, unimolecular, and follow a first‐order rate law. The Arrhenius equations for the overall decomposition and partial rates of products formation were found as follows: for 2‐phenylethanol, overall rate log k₁(s⁻¹)=12.43−228.1 kJ mol⁻¹ (2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=12.97−249.2 kJ mol⁻¹ (2.303 RT)⁻¹, styrene formation log k₁(s⁻¹)=12.40−229.2 kJ mol⁻¹(2.303 RT)⁻¹, ethylbenzene formation log k₁(s⁻¹)=12.96−253.2 kJ mol⁻¹(2.303 RT)⁻¹; for 1‐phenyl‐2‐propanol, overall rate log k₁(s⁻¹)=13.03−233.5 kJ mol⁻¹(2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=13.04−240.1 kJ mol⁻¹(2.303 RT)⁻¹, unsaturated hydrocarbons+indene formation log k₁(s⁻¹)=12.19−224.3 kJ mol⁻¹(2.303 RT)⁻¹; for 2‐methyl‐1‐phenyl‐2‐propanol, overall rate log k₁(s⁻¹)=12.68−222.1 kJ mol⁻¹(2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=12.65−222.9 kJ mol⁻¹(2.303 RT)⁻¹, phenylpropenes formation log k₁(s⁻¹)=12.27−226.2 kJ mol⁻¹(2.303 RT)⁻¹. The overall decomposition rates of the 2‐hydroxyalkylbenzenes show a small but significant increase from primary to tertiary alcohol reactant. Two competitive eliminations are shown by each of the substrates: the dehydration process tends to decrease in relative importance from the primary to the tertiary alcohol substrate, while toluene formation increases. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 401–407, 1999     

Dimerization of electrogenerated Mo(V) in sulphuric acid solutions

The electrochemical behaviour of molybdenum(VI) in sulphuric acid solutions was investigated by cyclic voltammetry. In the reduction of Mo(VI) to Mo(III) a dimerization reaction of Mo(V) is involved; the rate constant for the reaction was estimated to be 2.79×10² M⁻¹ s⁻¹ and the activation energy was ca. 35 kJ mol⁻¹ in 0.1 M H₂O₄. Oxidation of the monomer and dimer Mo(V) species take place at −0.31 and +0.18 V (vs. SCE), respectively.     

The solid state chemistry of uranium: Part IV. The thermal decomposition and kinetics of tetrachlorobis(N,N, N1, N1-tetramethylurea) uranium(IV)

The thermal decomposition of UCl₄2tmu in an oxygen atmosphere was studied. Decomposition of single crystals begins around 180° C and approximates to UCl₄2tmu_(s) + O_2(g) → UO₂Cl₂tmu_(s) + tmu_(g) + gases and is exothermic (ΔH = −270 ± 5 kJ mol⁻¹). The apparent activation energy for the initial stages (nucleation process) of the reaction was estimated as 362 kJ mol⁻¹. The growth period is described by a one-dimensional diffusion process and the decay period by the contracting-area model.     

Rate constants and transition‐state geometry of reactions of alkyl,alkoxyl, and peroxyl radicals with thiols

Enthalpy, activation energy, and rate constant of 9 alkyl, 3 acyl, 3 alkoxyl, and 9 peroxyl radicals with alkanethiols, benzenethiol, and L ‐cysteine are calculated. The intersection parabolas model is used for activation energy calculations. Depending on the structure of attacking radical, the activation energy of reactions with alkylthiols varies from 3 to 43 kJ mol^?1 for alkyl radicals, from 7 to 9 kJ mol^?1 for alkoxyl, and from 18 to 35 kJ mol^?1 for peroxyl radicals. The influence of adjacent π‐bonds on activation energy is estimated. The polar effect is found in reactions of hydroxyalkyl and acyl radicals with alkylthiols. The steric effect is observed in reactions of alkyl radicals with tert‐alkylthiols. All these factors are characterized via increments of activation energy. Quantum chemical calculations of activation energy and geometry of transition state were performed for model reactions: C^?H₃ + CH₃SH, CH₃O^? + CH₃SH, and HO₂^? + CH₃SH with using density functional theory and Gaussian‐98. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 284–293, 2009     

Evaluation of propagation rate constants for the free radical polymerization of methacrylonitrile by pulsed laser photolysis

Propagation rate constants for the free radical polymerization of methacrylonitrile (MAN) have been obtained by pulsed laser photolysis (PLP). The temperature dependence of the propagation rate constants indicates a frequency factor of 10^{(6,43 ± 0,26)} L · mol⁻¹ · s⁻¹ and an activation energy of 29,7 ± 1,5 kJ · mol⁻¹. These parameters suggest that the relatively slow rate of propagation in MAN polymerization in relation to other common monomers (methyl methacrylate, styrene) can be attributed to the relative steric bulk and stability of the propagation species.     

Evaluation of the 3-hydroxy pyridine antioxidant effect on the thermal-oxidative degradation of HTPB

The effect of the mixture of two antioxidants has been evaluated on the thermal-oxidant degradation of the hydroxyl-terminated polybutadiene (HTPB) because of its importance in the coatings and adhesives industries. 2,2-Methylene bis(4-methyl-6-tertiarybutylphenol) or A.O.2246 and 3-hydroxy pyridine have been considered as antioxidants in this study as a common HTPB antioxidant and an active antioxidant, respectively. The thermal-oxidant degradation behavior of the HTPB has been investigated in the presence of a mixture of two antioxidants by TGA and DTG tests, and, subsequently, the results of these tests have been interpreted by two model-free methods, e.g., Kissinger–Akahira–Sunose and Friedman methods. The results revealed that the mixture of two antioxidants affected the activation energy of the thermal-oxidant degradation reaction of the HTPB. The calculated activation energy value obtained from the Kissinger–Akahira–Sunose method was about 199 ± 1 kJ⋅mol⁻¹. In addition, the E_a value at various conversion rates has also been calculated by using the Friedman method. This method showed that the highest E_a value in the thermal-oxidant degradation reaction belonged to the initiation step of the reaction (about 299 kJ⋅mol⁻¹). Moreover, the lowest activation energy value was correlated to the second step of the degradation reaction at a conversion rate of 0.6 (about 184 kJ⋅mol⁻¹).     

Halogenation and amination dual properties of haloamines in Raschig environment: A chlorine transfer reaction between chloramine and 3-azabicyclo[3,3,0]octane

The chlorine transfer reaction between 3-azabicyclo[3,3,0]octane “AZA” and chloramine was studied over pH 8–13 in order to follow both the amination and halogenation properties of NH₂Cl. The results show the existence of two competitive reactions which lead to the simultaneous formation of N-amino- and N-chloro- 3-azabicyclo[3,3,0]octane by bimolecular kinetics. The halogenation reaction is reversible and the chlorine derivative obtained, which is thermolabile and unstable in the pure state, was identified by electrospray mass spectrometry. These phenomena were quantified by a reaction between neutral species according to an apparent S_N2-type mechanism for the amination process and a ionic mechanism involving a reaction between chloramine and protonated amine for the halogenation process. Amination occurs only in strongly basic solutions (pH ≥ 13) while chlorination occurs at lower pH's (pH ≤ 8). At intermediate pH's, a mixture of these two compounds is obtained. The relative proportions of the products are a function of intrinsic rate constants, pH and pK_a of the reactants. The rate constants and thermodynamic activation parameters are the following: k₁ = 45.5 × 10⁻³ M⁻¹ s⁻¹; ΔH₁^0# = 59.8 kJ mol⁻¹; ΔS₁^0# = − 86.5 J mol⁻¹ K⁻¹ for amination; k₂ = 114 × 10⁻³ M⁻¹ s⁻¹; ΔH₂^0# = 63.9 kJ mol⁻¹; and ΔS₂^0# = − 48.3 J mol⁻¹ K⁻¹ for chlorination. The ability of an interaction corresponding to a specific (NH₃Cl⁺/RR′NH) or general (NH₂Cl/RR′NH) acid catalysis has been also discussed. © 1997 John Wiley & Sons, Inc.     

Kinetics of the acid-catalyzed hydrolysis of tetraethoxysilane (TEOS) by <Superscript>29</Superscript>Si NMR spectroscopy and mathematical modeling

Tetraethoxysilane (TEOS) is widely used to synthesize siliceous material by the sol–gel process. However, there is still some disagreement about the nature of the limiting step in the hydrolysis and condensation reactions. The goal of this research was to measure the variation in the concentration of intermediates formed in the acid-catalyzed hydrolysis by ²⁹Si NMR spectroscopy, to model the reactions, and to obtain the rate constants and the activation energy for the hydrolysis and early condensation steps. We studied the kinetics of TEOS between pH 3.8 and 4.4, and four temperature values in the range of 277.2–313.2?K, with a TEOS:ethanol:water molar ratio of 1:30:20. Both hydrolysis and the condensation rate speeded up with the temperature and the concentration of oxonium ions. The kinetic constants for hydrolysis reactions increased in each step k_h1?<?k_h2?<?k_h3?<?k_h4, but the condensation rate was lower for dimer formation than for the formation of the fully hydrolyzed Si(OH)₄. The system was described according to 13 parameters: six of them for the kinetic constants estimated at 298.2?K, six to the activation energies, and one to the equilibrium constant for the fourth hydrolysis. The mathematical model shows a steady increase in the activation energy from 34.5?kJ?mol^?1 for the first hydrolysis to 39.2?kJ?mol^?1 in the last step. The activation energy for the condensation reaction from Si(OH)₄ was ca. 10?kJ?mol^?1 higher than the largest activation energy in the hydrolytic reactions. The decrease in the net positive charge on the Si atom contributes to the protonation of the ethoxy group and makes it a better leaving group.

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Kinetics and Mechanism Study of the Substitution Reactions of the Chloride Ligand in Dichloro(5,10,15,20)‐tetraphenyl‐21H,23H‐porphinato)tin(IV) by Organic Bases in Dimethylformamide Solvent

Substitution reactions of a Cl⁻ ligand in [SnCl₂(tpp)] (tpp=5,10,15,20‐tetraphenyl‐21H,23H‐porphinato(2−)) by five organic bases i.e., butylamine (BuNH₂), sec‐butylamine (^sBuNH₂), tert‐butylamine (^tBuNH₂), dibutylamine (Bu₂NH), and tributylamine (Bu₃N), as entering nucleophile in dimethylformamide at I=0.1M (NaNO₃) and 30–55° were studied. The second‐order rate constants for the substitution of a Cl⁻ ligand were found to be (36.86±1.14)⋅10⁻³, (32.91±0.79)⋅10⁻³, (22.21±0.58)⋅10⁻³, (19.09±0.66)⋅10⁻³, and (1.36±0.08)⋅10⁻³ M ⁻¹s⁻¹ at 40° for BuNH₂, ^tBuNH₂, ^sBuNH₂, Bu₂NH, and Bu₃N, respectively. In a temperature‐dependence study, the activation parameters ΔH^≠ and ΔS^≠ for the reaction of [SnCl₂(tpp)] with the organic bases were determined as 38.61±4.79 kJ mol⁻¹ and −150.40±15.46 J K⁻¹mol⁻¹ for BuNH₂, 40.95±4.79 kJ mol⁻¹ and −143.75±15.46 J K⁻¹mol⁻¹ for ^tBuNH₂, 30.88±2.43 kJ mol⁻¹ and −179.00±7.82 J K⁻¹mol⁻¹ for ^sBuNH₂, 26.56±2.97 kJ mol⁻¹ and −194.05±9.39 J K⁻¹mol⁻¹ for Bu₂NH, and 39.37±2.25 kJ mol⁻¹ and −174.68±7.07 J K⁻¹ mol⁻¹ for Bu₃N. From the linear rate dependence on the concentration of the bases, the span of k₂ values, and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the ligand substitution.     

Optical resolution of tris (acetylacetonato) aluminium(III) by low temperature chromatography

Al(acac)₃ was resolved into optical isomers with a high yield by chromatography on D-lactose/Al₂O₃ at 210 K and the circular dichroism (CD) spectra of the enantiomers were measured.The absolute configuration was established both by using a locally excited transition in the ligand and by correlating the retention order due to the adsorption with that of an equivalent complex with known configuration. The nomenclature (CD+)₃₀₃-Al(acac)₃ is suggested for the enantiomer exhibiting positive CD at 303 nm. This enantiomer has the absolute configuration

From the observed racemisation rate constants at elevated temperatures activation parameters were estimated: E_α = 131 ± 5 kJ mol⁻¹, ΔH = 130 ± 5 kJ mol⁻¹, ΔS = 220 ± 16 J K⁻¹ mol⁻¹.Al(acac)₃ is the first example of a compound that has been optically resolved by low temperature chromatography (LTC).     

Direct kinetic parameters for the reaction of Br atoms with neopentane

Laser flash photolysis coupled with resonance fluorescence detection of Br atoms was employed to investigate the temperature dependence of the reaction Br + neo‐C₅H₁₂ (1) between 688 and 775 K. The following Arrhenius preexponential factor and activation energy were determined (±1 σ): A₁ = (6.89 ± 2.27) 10¹⁴ cm³ mol⁻¹ s⁻¹ and E_A,1 = 57.61 ± 2.05 kJ mol⁻−¹ The only other kinetic parameters reported for the reaction of Br atoms with neo‐C₅H₁₂ were obtained from competitive kinetic experiments relative to Br + C₂H₆. Comparison with our direct results is hampered by uncertainties in the kinetic data for the reference reaction that may need reinvestigation. The standard enthalpy of formation for the neo‐C₅H₁₁ radical was estimated to be 34.7 and 41.6 kJ mol⁻¹, depending on the value of the activation energy assumed for the reverse reaction neo‐C₅H₁₁ + HBr (−1). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 49–55, 2001     

Solid state mechanism of the thermal dehydration of [Rh(NH3)5(H2O)]X3 (X = Cl−, Br−, I−)

The solid phase thermal deaquation-anation of [Rh(NH₃)₅(H₂O)]X₃ (X = Cl⁻, Br⁻, I⁻) has been investigated by means of isothermal TG measurements applying all the principal g(α) expressions (0.8 ⩾ α ⩾ 0.2). The values found for the activation energy are low: ≈ 95 kJ mol⁻¹ for the Cl⁻ compound; ~105 kJ mol⁻ for the Br⁻ compound and ≈110 kJ mol⁻¹ for the I⁻ compound. These data permit the assignment of the deaquation-anation mechanism of the S_N1 dissociative type, involving a square-based pyramid activated complex and elimination of water as Frenkel defects. These values are similar to those reported for the Co(III) and Ir(III) analogues, indicating that the D_q parameter is not the principal contribution to the activation energy of the dehydration-anation process.     

Kinetic study of the ligand substitution on the trimethylplatinum(iv) complexes with unidentate ligands

Ligand substitution kinetics for the reaction [Pt^IVMe₃(X)(NN)]+NaY=[Pt^IVMe₃(Y)(NN)]+NaX, where NN=bipy or phen, X=MeO⁻, CH₃COO⁻, or HCOO⁻, and Y=SCN⁻ or N₃⁻, has been studied in methanol at various temperatures. The kinetic parameters for the reaction are as follows. The reaction of [PtMe₃(OMe)(phen)] with NaSCN: k₁=36.1±10.0 s⁻¹; ΔH₁^≠=65.9±14.2 kJ mol⁻¹; ΔS₁^≠=6±47 J mol⁻¹ K⁻¹; k₋₂=0.0355±0.0034 s⁻¹; ΔH₋₂^≠=63.8±1.1 kJ mol⁻¹; ΔS₋₂^≠=−58.8±3.6 J mol⁻¹ K⁻¹; and k₋₁/k₂=148±19. The reaction of [PtMe₃(OAc)(bipy)] with NaN₃: k₁=26.2±0.1 s⁻¹; ΔH₁^≠=60.5±6.6 kJ mol⁻¹; ΔS₁^≠=−14±22 J mol⁻¹K⁻¹; k₋₂=0.134±0.081 s⁻¹; ΔH₋₂^≠=74.1±24.3 kJ mol⁻¹; ΔS₋₂^≠=−10±82 J mol⁻¹K⁻¹; and k₋₁/k₂=0.479±0.012. The reaction of [PtMe₃(OAc)(bipy)] with NaSCN: k₁=26.4±0.3 s⁻¹; ΔH₁^≠=59.6±6.7 kJ mol⁻¹; ΔS₁^≠=−17±23 J mol⁻¹K⁻¹; k₋₂=0.174±0.200 s⁻¹; ΔH₋₂^≠=62.7±10.3 kJ mol⁻¹; ΔS₋₂^≠=−48±35 J mol⁻¹K⁻¹; and k₋₁/k₂=1.01±0.08. The reaction of [PtMe₃(OOCH)(bipy)] with NaN₃: k₁=36.8±0.3 s⁻¹; ΔH₁^≠=66.4±4.7 kJ mol⁻¹; ΔS₁^≠=7±16 J mol⁻¹K⁻¹; k₋₂=0.164±0.076 s⁻¹; ΔH₋₂^≠=47.0±18.1 kJ mol⁻¹; ΔS₋₂^≠=−101±61 J mol⁻¹ K⁻¹; and k₋₁/k₂=5.90±0.18. The reaction of [PtMe₃(OOCH)(bipy)] with NaSCN: k₁ =33.5±0.2 s⁻¹; ΔH₁^≠=58.0±0.4 kJ mol⁻¹; ΔS₁^≠=−20.5±1.6 J mol⁻¹ K⁻¹; k₋₂=0.222±0.083 s⁻¹; ΔH₋₂^≠=54.9±6.3 kJ mol⁻¹; ΔS₋₂^≠=−73.0±21.3 J mol⁻¹ K⁻¹; and k₋₁/k₂=12.0±0.3. Conditional pseudo-first-order rate constant k₀ increased linearly with the concentration of NaY, while it decreased drastically with the concentration of NaX. Some plausible mechanisms were examined, and the following mechanism was proposed. [Note to reader: Please see article pdf to view this scheme.] © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 523–532, 1998