S. A. Kashtanov

Effect of the humidity on the uptake of NO3 on coatings composed of MgCl2 · 6H2O and MgBr2 · 6H2O and mixtures thereof with NaCl

The reactive uptake of NO3 radicals on the surface of wetted individual X salts and of wetted X-NaCl salts (X = MgCl2 · 6H2O and MgBr2 · 6H2O) at [H2O] = 2 × 1012−2 × 1015 cm−3 and NO3 (4.8 × 1012 cm−3) was studied using a reactor with a movable insert covered with a salt coating in combination with a mass spectrometer for monitoring the initial reactant and products. The probabilities of NO3 uptake γ on X-NaCl binary salts as functions of the content of doping salt were determined. A parametric approximation of the experimental data was proposed, which makes it possible to quantitatively predict the extent of surface enrichment of a wetted binary salt coating in doping salt and its dependence on the humidity and the content of this salt in the binary mixture. It was established that the relative surface density σX of X doping salt depends on its mole fraction μX in the X-NaCl binary salt as σX = aμX (a = 2.2 for MgBr2 and 13.1 for MgCl2) over the entire humidity range covered. The contributions of the X salts to the overall uptake of NO3 at NO3 concentration typical of the tropospheric conditions ([NO3] ∼ 107 cm−3 and relative humidities of RH ≤ 20%) were estimated.

Synthesis of aryl perfluoroalkyl sulfides from aromatic disulfides

Thermolysis of xenon(ii) bis(perfluoroalkanecarboxylates) in the presence of diaryl disulfides occurs through the S—S bond cleavage to form dihalo-, halonitro-, and halodinitrophenyl perfluoroalkyl sulfides. The latter type of compounds was obtained for the first time. The main side process is the perfluoroalkylation of the aromatic ring.

Initial uptake of NO2 on methane flame soot

A thermostated flow reactor with a movable soot-coated insert coupled to a high-resolution mass spectrometer with low-energy electron ionization is used to study the uptake of NO2 reagent gas at [NO2] = 1 × 1012−2 × 1013 cm−3 and a humidity of [H2O] = 5 × 1012−1.8 × 1015 cm−3. The BET (Brunnauer-Emmett-Teller) method is used to determine the specific surface area of the soot coating: (40 ± 10 (2σ)) m2/g. A set of time-dependent uptake coefficients of NO2 on fresh soot coatings in this range of reactant gas concentrations is determined. An analysis of the experimental data shows that the uptake coefficient depends on the time as 1/γ(t) = 1/γ0 + c1t and yields the dependences of the parameters γ0 and c1 on the NO2 concentration: 1/γ0 = c2 + c3[NO2] and c1 = k[NO2] with constants c2 = (6.5 ± 1.3) × 103, c3 = (5.6 ± 1.3) × 10−10 cm3 molecule−1, and k = (2.4 ± 0.2) × 10−10 cm3 molecule−1 s−1. The gas-phase products of NO2 uptake on soot are NO and HONO, with the NO yield constituting ∼50% of the reacted NO2. It is experimentally demonstrated that an increase in the humidity causes no changes in the uptake coefficient and in the composition and ratio of the products. The initial stage of NO2 uptake on a methane soot coating is described using the Langmuir adsorption model, according to which the process of uptake consists of a sequence of elementary steps, such as reversible adsorption, surface complex formation, and its subsequent unimolecular decomposition to form products. Interpretation of the experimental dependence γ0 = f([NO2]) enables to estimate the Langmuir constant for the NO2-methane soot pair, KL = (8.6 ± 2.6) × 10−14 cm3 molecule−1, the rate constant for NO2 desorption from the soot coating, kd = (530 ± 160) s−1, and the rate constant for the monomolecular decomposition of the surface complex, kr = (8.2 ± 2.5) × 10−2 s−1.

Mass Spectrometric Studies of Physical, Thermochemical and Reactive Properties of Xenon Fluorides, Xenon Oxides and Xenon Oxyfluorides

Using a reactor with a flowing diffusion cloud coupled to a high-resolution, low-energy electron-impact ionization mass spectrometer, mechanistic, kinetic and thermochemical characteristics of gas-phase reactions with the participation of charged and neutral xenon oxides, xenon fluorides and xenon oxyfluorides have been investigated. Ionization energies for XeF, XeF2, XeF4, XeO3, XeO4, XeOF4 molecules and appearance energies for the ions formed from these molecules were obtained. Based on experimental and reference data, the enthalpies of XeO3 and XeOF4 formation were refined and a number of binding energies in the parent and fragment ions were calculated. For electron-impact ionization, the ionization cross-sections for Xe, XeF2, XeF4 and XeOF4 proved to correlate with a semi-empirical principle of full ionization. Based on the temperature dependencies of saturated vapor pressures for XeO4, XeOF4 and XeO2F2, their enthalpies of evaporation, sublimation and melting were determined. The mechanisms of gas-phase reactions between H atoms and neutral XeF2, XeF4, XeF6, XeO4 and XeOF4 were studied.

1-Chloro-2,6-dinitro-4-perfluoroalkylthiobenzenes in the Synthesis of Heterocycles

Abstract1-Chloro-2,6-dinitro-4-perfluoroalkylthiobenzenes was obtained in first time by perfluoroalkylation of bis(4-chloro-3,5-dinitrophenyl)disulfide in the presence of xenon bisperfluoroalkylcarboxylates. At the interaction of these compounds with potassium ethylxanthogenate only substitution of chlorine atom occurred. The reaction with sodium N,N-dimethyldithiocarbamate leads to the nucleophilic substitution of nitro group with formation of 1,3-benzodithiol-2-one, but on action of ethyl thioglycolate the intramolecular condensation occurs with formation of benzothiazoles N-oxides.

Kinetic mechanisms of the uptake of atmospheric gases on the surface of sea salts. ClNO3 uptake on MgCl2 · 6H2O/NaCl

The uptake coefficients γ of chlorine nitrate on MgCl2 · 6H2O crystallites and a MgCl2 · 6H2O-NaCl mixture deposited from an aqueous solution are measured using a flow reactor with a movable salt-substrate-coated insert equipped in combination with a mass spectrometer at 295–428 K, [ClNO3] = (0.2−12) × 1012 cm−3, and [H2O] = 1.0 × 1012 − 4.3 × 1015 cm−3. Immediately after the exposure of the salt substrate to a ClNO3 flow, γ(t) decreases exponentially with time, γ(t) = γ0 × exp(−t/τ) + γs, to a steady-state level, γs, which depends on the temperature and the ClNO3 and H2O concentrations. The main gas-phase product is Cl2, HOCl appears only when water vapor is admitted into the reactor. The coefficient of steady-state uptake on wetted MgCl2 · 6H2O at 295 K can be described by the approximation γ = a + b [H2O] with a = 3.5 × 10−3 cm3 and b = 3.2 × 10−18 cm3. The mechanism of the uptake of ClNO3 on MgCl2 · 6H2O is discussed. The experimental data are treated within the framework of a steady-state uptake model to estimate the heat of adsorption of ClNO3 on MgCl2 · 6H2O (Qad = 62 kJ/mol) and the activation energy of the bimolecular heterogeneous reaction ClNO3 + Zs = 2Cl2 + Mg(NO3)2 · 6H2O (Ea = 21.8 kJ/mol; Zs denotes a ClNO3-MgCl2 · 6H2O surface complex). When the MgCl2 · 6H2O: NaCl is varied from 0 to ∼3 wt %, the steady-state uptake coefficient changes from the value corresponding to uptake on pure NaCl to that characteristic of uptake on pure MgCl2 · 6H2O.

Kinetics of NO2 uptake on methane flame soot

The dependences of the initial NO2 uptake coefficient γ on a methane soot coating at 255 K on the NO2 concentration (1.3 × 1012–3.3 × 1013 cm–3) and time t were studied using a flow reactor with a mobile insert and mass spectrometric recording of gaseous reagents and products: 1/γ(t) = 1/γ0 + at, where γ0 and a are the parameters that depend on the NO2 concentration; γ0 = γ0ini/(1 + kL [NO2], a= k [NO2], with the constants γ0ini = (4.8 ± 2) × 10–4, KL = (8.2 ± 3) × 10–13 cm3, and k = (2.3 ± 0.1) × 10–10 cm3 s–1. The elementary parameters that determine the uptake were evaluated on the basis of the Langmuir adsorption model: desorption rate constant kd = (52 ± 20) s–1, adsorption heat Qad = (38 ± 8) kJ mol–1, rate constant of the unimolecular heterogeneous conversion of NO2 into the product kr = (2.5 ± 1.3) × 10–2 s–1, and its activation energy Ea = (19 ± 10) kJ mol–1. The laboratory data were extrapolated, based on the uptake coefficient, to the limiting tropospheric NO2 concentrations in remote marine (1 ppb) and polluted industrial regions (40 ppb).

10. Perfluoroalkylation of bis(tetrafluoro-4-pyridyl) disulfide

In the previous communication, we described tile perfluoroalkylation of 4-mercaptotetrafluoropyridine by xenon bisperfluoroalkylcarboxylates to 4-perfluoroalkylthiotetrafluoropyridines with yields of 25-52%. The process is accompanied by transformation of the initial thiol into bis(tetrafluoro-4-pyridyl) disulfide (I). In the present work, by varying the conditions for the thermolysis of xenon bistrifluoromethylcarboxylate (II) in the presence of compound (I) we were able to detect its transformation into the required 4-trifluoromethylthiotetrafluoropyridine (III). The highest yield (41%) was obtained with simultaneous generation of the xenonates in situ and their thermolysis (method B [2]) at 50-60°C. It was also determined that the optimum molar ratios of the reagents were: Disulfide (I):XeF2:CF3COOtt = 1:2:(34)

Rate measurements for the reaction of H-atoms with the xenon and krypton fluoride molecules.

Abstract Elementary strongly exothermic reactions of H-atoms with the F 2 , KrF 2 , XeF 2 , XeF 4 , XeF 6 molecules useful for chemical lasers have been investigated by mass-spectrometric probing of the diffusion cloud in flow [1] . Some ionisation and appearance potentials were defined [2] from experimental ionization efficiency curves. Arrhenius expressions were obtained for the rate constants between 298–505 K. They correspond to an activation energy of 8.9± 0.6; 11.3±0.2; 21.8±2; 22.6±5; 28.5±3.8 kj/mol for the H + F 2 , KrF 2 , XeF 2 , XeF 4 , XeF 6 reactions respectively, with the preexponential factor near 10 −10 cc/molec-c for all rate constants. It was established that HF product of the H+F 2 “model” reaction is excited up to 8-th vibrational level while such one of the H+ KrF 2 reaction is not vibrationally excited. Thus a second product of H+KrF 2 reaction may be eximer KrF(B 2 Σ) with the energy excitation 481.3 kJ/mol which corresponds to sum of the reaction heat and activation energy.

Kinetics of N2O5 uptake on a methane soot coating

The uptake of N2O5 on a soot coating at Т = 255 and 298 K was studied by low-voltage electron ionization using a thermostatted flow reactor with a mobile insert with soot deposited on it and a mass spectrometer while varying the N2O5 concentration in the range 1.3 × 1012–3.3 × 1013 cm–3. A series of timedependent N2O5 uptake coefficients on fresh soot coatings were recorded in the indicated range of reactant gas concentrations. The uptake coefficient is described by the equation l/γ(t) = l/γ0 + at. The dependences of the γ0 and а parameters of this equation on the N2O5 concentration were determined: l/γ0 = 1/γ0ini (1 + KL[N2O5]), a = k[N2O5] with the constants k, γ0ini, and KL equal to (0.8 ± 0.1) × 10–10 cm3 s–1, (4.2 ± 1.9) × 10–4, and (2.3 ± 0.8) × 10–13 cm3 (255 K) and (1.1 ± 0.1) × 10–10 cm3 s–1, (5.5 ± 0.2) × 10–5, and (7.4 ± 1.4) × 10–15 cm3 (298 K), respectively. The uptake is the result of the joint action of physical sorption and chemical reaction. NO was recorded as the only gas-phase product of uptake. The quantity of NO corresponds to ~60% of consumed N2O5. A description of the initial uptake of N2O5 was suggested based on the Langmuir concept of adsorption. It follows from the model description of the experimental dependences that KL is the Langmuir constant. Other constants were evaluated: the rate constant of desorption kd = 108 ± 17 (255 K) and 4030 ± 320 s–1 (298 K) and its adsorption heat Qad = (52.4 ± 2.6) kJ mol–1; the rate constant of the monomolecular heterogeneous reaction kr = 0.2 ± 0.01 (255 K) and 0.8 ± 0.05 s–1 (298 K) and its activation energy Ea = (21.9 ± 1) kJ mol–1.