Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl₂^˙? radicals with 2-propen-1-o1 and 2-buten-1-o1 as a function of temperature and with 2, 3-dimethyl-2-butene at room temperature. The rate constants were in the range of 10⁶–10⁹ L mol^?1 s^?1, the activation energies were relatively low (1–10 kJ mol^?1), and the pre-exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, E_T(30), and the hydrogen-bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO₄^˙? with 2-propen-1-o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.     

Solid‐Liquid Equilibria in the Quinary Na+, K+//Cl−, SO2−4, B4O2−7‐H2O System at 298 K

The solid‐liquid equilibria in the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K had been studied experimentally using the method of isothermal solution saturation. Solubilities and densities of the solution of the quinary system were measured experimentally. Based on the experimental data, the dry‐salt phase diagram and water content diagram of the quinary system were constructed, respectively. In the equilibrium diagram of the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K, there are five invariant points F1, F2, F3, F4 and F5; eleven univariant curves E1F1, E2F2, E3F3, E4F5, E5F2, E6F4, E7F5, F1F4, F2F4 F1F3 and F3F5, and seven fields of crystallization saturated with Na₂B₄O₇ corresponding to Na₂SO₄, Na₂SO₄·10H₂O, Na₂SO₄·3K₂SO₄ (Gla), K₂SO₄, K₂B₄O₇·4H₂O, NaCl and KCl. The experimental results show that Na₂SO₄·3K₂SO₄ (Gla), K₂SO₄ and K₂B₄O₇·4H₂O have bigger crystallization fields than other salts in the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K.     

[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines

The N₂ negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [M + 11]^?˙. This addition is also observed in the N₂ positive chemical ionization (PCI) mass spectra. An ion at [M – 15]^? is found in the NICI spectra of aminoaromatics such as aniline, 1- and 2-aminonaphthalene and 1- and 2-aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [M + 11]^?˙, [M – 15]^?˙ and [M + 11]^+˙ ions result from the ionization of analytes altered by surface-assisted reactions. Experiments with ¹⁵N₂, [¹⁵N] aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆] aniline show that the [M + 11]^?˙ ion corresponds to [M + N – 3H]^?˙. The added nitrogen originates from the N₂ buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N₂ PCI mass spectrum of aniline suggest that the neutral product of the surface-assisted reaction is 1,4-dicyanobuta-1,3-diene. Experiments with diamino-substituted aromatics show analogous reactions resulting in the formation of [M – 4H]^?˙ ions for aromatics with ortho-amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.     

Rate constants for the elementary reactions between CN radicals and CH4, C2H6, C2H4, C3H6, and C2H2 in the range: 295 ⩽ T/K ⩽ 700

Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH₄, C₂H₆, C₂H₄, C₃H₆, and C₂H₂. They have yielded rate constants for these five reactions at temperatures between 295 and 700 K. The data for the reactions with methane and ethane have been combined with other recent results and fitted to modified Arrhenius expressions, k(T) = A′(298) (T/298)ⁿ exp(?θ/T), yielding: for CH₄, A′(298) = 7.0 × 10^?13 cm³ molecule^?1 s^?1, n = 2.3, and θ = ?16 K; and for C₂H₆, A′(298) = 5.6 × 10^?12 cm³ molecule^?1 s^?1, n = 1.8, and θ = ?500 K. The rate constants for the reactions with C₂H₄, C₃H₆, and C₂H₂ all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)ⁿ with k(298) = 2.5 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.24 for CN + C₂H₄; k(298) = 3.4 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.19 for CN + C₃H₆; and k(298) = 2.9 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.53 for CN + C₂H₂. These reactions almost certainly proceed via addition-elimination yielding an unsaturated cyanide and an H-atom. Our kinetic results for reactions of CN are compared with those for reactions of the same hydrocarbons with other simple free radical species. © John Wiley & Sons, Inc.     

High-pressure range of the recombination O + O2 → O3

The recombination reaction O + O₂ → O₃ was studied by laser flash photolysis of pure O₂ in the pressure range 3–20 atm, and of N₂O? O₂ mixtures in the bath gases Ar, N₂, (CO₂, and SF₆) in the pressure range 3–200 atm. Fall-off curves of the reaction have been derived. Low-pressure rate coefficients were found to agree well with literature data. A high-pressure rate coefficient of k_∞ = (2.8 ± 1.0) × 10^?12 cm³ molecule^?1 s^?1 was obtained by extrapolation.     

A study of the reaction NO3 + NO2 + M → N2O5 + M(M = N2, O2)

The gas-phase reaction of the NO₃ radical with NO₂ was investigated, using a flash photolysis-visible absorption technique, over the total pressure range 25–400 Torr of nitrogen or oxygen diluent at 298 ± 2 K. The absolute rate constants determined (in units of 10^?13 cm³ molecule^?1 s^?1) at 25, 100, and 400 Torr total pressure were, respectively, (4.0 ± 0.5), (7.0 ± 0.7), and (10 ± 2) for M = N₂ and (4.5 ± 0.5), (8.0 ± 0.4), and (8.8 ± 2.0) for M = O₂. These data show that the third-body efficiencies of N₂ and O₂ are identical, within the error limits, and that previous evaluations for M = N₂ are applicable to the atmosphere. In addition, upper limits were determined for the rate constants of the reactions of the NO₃ radical with methanol, ethanol, and propan-2-ol of ?6 × 10^?16, ?9 × 10^?16, and ?2.3 × 10^?15 cm³ molecule^?1 s^?1, respectively, at 298 ± 2 K.     

Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

Rate constants for reactions of SO4˙− radicals in acetonitrile

Rate constants have been measured for the reactions of the sulfate radical, SO₄^˙?, with alkanes, alkenes, alcohols, ethers, and amines in 95% acetonitrile solution. The rate constants were in the range of 10⁶ L mol^?1 s^?1 for the abstraction reactions and 10⁷?10⁹ L mol^?1 s^?1 for the addition and electron transfer reactions. These values are 20 to 80 times lower than those measured in aqueous solutions. Furthermore, the rate constants for the reactions of SO₄^˙? with the primary alcohols increase with the number of carbon atoms and then level off, in contrast to the behavior observed in aqueous solution, where the rate constant increases more sharply for the larger alcohols. © 1993 John Wiley & Sons, Inc.     

Loss of methyl from [H2CC(OH)?CH3]+˙ ions prepared by electron impact ionization of unstable 2-hydroxypropene

Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10^?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C₂H₃O]⁺ and [CH₃]⁺ ions originating from different parts of the parent ion was examined by means of ¹³C and deuterium labelling. Threshold-energy [H₂C?C(OH)? CH₃]^+˙ ions decompose to CH₃CO⁺+CH₃^˙ with appearance energy AE(CH₃CO⁺) = 11.03 ± 0.03 eV. Higher energy ions also form CH₂?C?OH⁺ + CH₃ with appearance energy AE(CH₂?C?OH⁺) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C₂H₃O]⁺ ions containing the original methyl group and [CH₃]⁺ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H₂C?C(OH)? CH₃]^+˙ →[CH₃COCH₃]^+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.     

The Dependence on H2O and on NH3 of the Kinetics of the self-reaction of HO2 in the gas-phase formation of HO2·H2O and HO2·NH3 complexes

Electron pulse radiolysis at ?298°K of 2 atm H₂ containing 5 torr O₂ produces HO₂ free radical whose disappearance by reaction (1), HO₂ + HO₂ →H₂O₂ + O₂, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO₂ absorption cross section, the values k₁ = 2.5×10^?12 cm³/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO₂) ?13 are obtained. In the presence of small amounts of added H₂O or NH₃, the observed second-order decay rate of the HO₂ signal is found to increase by up to a factor of ?2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO₂ + H₂O ? HO₂·H₂O (4a) and HO₂ + NH₃? HO₂·NH₃ (4b), which are more reactive than uncomplexed HO₂ toward a second uncomplexed HO₂ radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10^?20?K_4a?6.3 × 10^?19 cm³/molec at 295°K and K_4b = 3.4 × 10^?18 cm³/molec at 298°K. Several deuterium isotope effects are also reported, including k_H/k_D = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.     

Deactivation of O2(A3Σ) by O2, O,and Ar

O₂ in the A³Σ_u⁺ 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(A³Σ_u⁺) by O, O₂, and Ar, respectively.     

The distonic ions HO+CHCH2C˙H2 and CH3C(O+H)CH2C˙H2

The distonic ions HO⁺?CHCH₂C^˙H₂ (1) and CH₃C(?O⁺H)CH₂C^˙H₂ (2) were directly generated, their decompositions characterized and their appearance energies determined by photoionization. Heats of formation derived from the appearance energies were 757 kJ mol^?1 for 1 and 692 kJ mol^?1 for 2. Deuterium labeling demonstrates that both ions decompose at low energies in the same ways as their isomers with the same skeletal structures, consistent with proposals that 1 and 2 are intermediates in the decompositions of those systems. Surprisingly, the values of the translational energy releases accompanying the formation of CH₃CO⁺ and C₂H₅CO⁺ from 2 appear to be inversely proportional to the available excess energy. The 1,2-H-shift RC(?O⁺H)CH₂C˙H₂ → RC(?O₊H)C˙HCH₃ is compared to the corresponding, non-occurring 1,2-H-shift in alkyl free radicals.     

An FTIR study of the Cl-atom-initiated reaction of glyoxal

The kinetics and mechanism of Cl-atom-initiated reactions of CHO? CHO were studied using the FTIR detection method to monitor the photolysis of Cl₂–CHO? CHO mixtures in 700 torr of N₂–O₂ diluent at 298 ± 2 K. The observed product distribution in the [O₂] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHO? CHO → HCl + CHO? CO with a rate constant of [3.8 ± 0.3(σ)] × 10^?11 cm³ molecule^?1 s^?1; (2) the primary product CHO? CO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10^?7 s; (3) alternatively, the CHO? CO reacts with O₂ leading to the formation of CO, CO₂, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO₂ radical, formed in the secondary reaction CHO + O₂ → HO₂ + CO, reacts with the CHO? CHO with a rate constant ca. 5 × 10^?16 cm³ molecule^?1 s^?1 to form HCOOH and a new transient product resembling that detected previously in the HO₂ reaction with HCHO.     

Darstellung von μ-Schwefeldisulfoniumsalzen [(CH3)2S?Sx?S(CH3)2]2+2A− (x = 1–3, A− = AsF6−, SbF6−, SbCl6−). Über die Analogie im Reaktionsverhalten zwischen Sulfanen und Sulfoniumsalzen

Preparation of μ-Sulfurdisulfonium Salts [(CH₃)₂S? S_x? S(CH₃)₂]²⁺2A^? (x = 1–3, A^? = AsF₆^?, SbF₆^?, SbCl₆^?). On the Analogy of the Reactivity of Sulfanes and Sulfonium Salts The preparation of the μ-sulfurdisulfonium salts [(CH₃)₂S? S_x? S(CH₃)₂]²⁺(A^?)₂ with x = 1–3 and A^? = AsF₆^?, SbF₆^?, SbCl₆^? is reported. The salts are formed by reaction of (CH₃)₂SH⁺A^? and (CH₃)₂SSH⁺A^? with SCl₂ and S₂Cl₂, resp. They are characterized by vibrational spectroscopic measurements. [(CH₃)₂S? S₂? S(CH₃)₂]²⁺(SbF₆^?)₂ crystallizes in the space group C2/c with a = 1 884.5(7) pm, b = 1 302.8(5) pm, c = 1 477.2(5) pm, β = 98.62(3)° und Z = 8.     

Comparison of the Plasma Temperature and Electron Number Density of the Pulsed Electrolyte Cathode Atmospheric Pressure Discharge and the Direct Current Solution Cathode Glow Discharge

A novel-pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) plasma source driven by an alternating current (AC) power supply coupled with a high-voltage diode was generated under normal atmospheric pressure between a metal electrode and a small-sized flowing liquid cathode. The spatial distributions of the excitation, vibrational, and rotational plasma temperatures of the pulsed-ECAD were investigated. The electron excitation temperature of H T_exc(H), vibrational temperature of N₂ T_vib(N₂), and rotational temperature of OH T_rot(OH) were from 4900?±?36 to 6800?±?108 K, from 4600?±?86 to 5800?±?100 K, and from 1050?±?20 to 1140?±?10 K, respectively. The temperature characteristics of the dc solution cathode glow discharge (dc-SCGD) were also studied for the comparison with the pulsed-ECAD. The effects of operating parameters, including the discharge voltage and discharge frequency, on the plasma temperatures were investigated. The electron number densities determined in the discharge system and dc-SCGD were 3.8–18.9?×?10¹⁴?cm^–3 and 2.6?×?10¹⁴ to 17.2?×?10¹⁴?cm^–3, respectively.     

Classical dynamics of the O + ClO → Cl + O2 and Cl + O3 → ClO + O2 reactions

An explicit function has been derived for the potential-energy surface of the ground state of ClO₃ with the six interatomic distances as variables. This surface is valid over all configurations of the atoms. The surface has been used to calculate classical trajectories for the reactions R₁: O(³P₂)+ClO(²Π_3/2)→ O₂(³∑)+Cl(²)P_3/2 and R₂: Cl(²P_3/2)+O₃(¹A₁)→ClO(²Π_3/2)+O₂(³∑). An appreciable fraction (～1/3) of the reactive trajectories for R₁ go through a long-lived complex ClOO(²A″). The cross section decreases with increasing rotational state of the ClO; and 37% of the energy release is vibrational. The calculated rate constant at 298°K is 2.6 × 10^?11 cm³/molecule sec. For reaction R₂ there is no evidence of long-lived complexes. The product ClO is predominantly found in the backward-scattering direction. Most of the internal energy is carries off by ClO but O₂ carried off most translational energy. An Arrhenius expression has been deduced from calculations at 220 and 300°K to give an A factor of 2.488 × 10^?11 cm³/molecule sec and an activation energy of 1.543 kJ/mol.     

The spin delocalization substituent parameter σ˙. 7. Meta-substituent effects on the cyclodimerization of trifluorostyrenes. A test for the σ˙JJ approach

Rate constants (k's) of the thermal cyclodimerization of ten meta-substituted trifluorostyrenes (m-Y-TFS's) have been measured in the temperature range 110–160°C. On the basis of these k's and the σ_mb values derived from ¹⁹F NMR data the spin-delocalization substituent constant σ^˙_m values of these ten meta-substituents have been calculated. The averaged σ^˙_m values are: m-Et, 0.09; m-t-Bu, 0.11; m-F, 0.03; m-Cl,?0.05; m-Br, 0.12: m-CF₃, ?0.07; m-OMe, 0.10; m-NO₂, ?0.002; m-CN, 0.11 and m-CO₂Me, 0.08. Both the smallness of these values and the nonexistence of correlation between Hammett-Type polar σ^X and these σ^˙_m values support our belief that the σ_j?J approach is reliable and trustworthy.     

The potential energy surface for the [C2H2O]+˙ system: The ketene radical cation [CH2CO]+˙ and its isomers

Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C₂H₂O]^+˙ potential energy surface. Four [C₂H₂O]^+˙ isomers have been identified as potentially stable, observable ions. These are the experimentally well-known ketene radical cation, [CH₂?C?O]^+˙ (a), and the presently unknown ethynol radical cation, [CH₂?C? OH]^+˙ (b), the oxirene radical cation (c) and an ion resembling a complex of CO with [CH₂]^+˙, (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol^?1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.     

Gas‐phase ozonolysis: Rate coefficients for a series of terpenes and rate coefficients and OH yields for 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene

The kinetics of the gas‐phase reactions of O₃ with a series of selected terpenes has been investigated under flow‐tube conditions at a pressure of 100 mbar synthetic air at 295 ± 0.5 K. In the presence of a large excess of m‐xylene as an OH radical scavenger, rate coefficients k(O₃+terpene) were obtained with a relative rate technique, (unit: cm³ molecule^?1 s^?1, errors represent 2σ): α‐pinene: (1.1 ± 0.2) × 10^?16, ³Δ‐carene: (5.9 ± 1.0) × 10^?17, limonene: (2.5 ± 0.3) × 10^?16, myrcene: (4.8 ± 0.6) × 10^?16, trans‐ocimene: (5.5 ± 0.8) × 10^?16, terpinolene: (1.6 ± 0.4) × 10^?15 and α‐terpinene: (1.5 ± 0.4) × 10^?14. Absolute rate coefficients for the reaction of O₃ with the used reference substances (2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene) were measured in a stopped‐flow system at a pressure of 500 mbar synthetic air at 295 ± 2 K using FT‐IR spectroscopy, (unit: cm³ molecule^?1 s^?1, errors represent 2σ ): 2‐methyl‐2‐butene: (4.1 ± 0.5) × 10^?16 and 2,3‐dimethyl‐2‐butene: (1.0 ± 0.2) × 10^?15. In addition, OH radical yields were found to be 0.47 ± 0.04 for 2‐methyl‐2‐butene and 0.77 ± 0.04 for 2,3‐dimethyl‐2‐butene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 394–403, 2002