The Acidity of the HBr/AlBr3 System: Stabilization of Crystalline Protonated Arenes and Their Acidity in Bromoaluminate Ionic Liquids

Bulk protonated mesitylene, toluene, and benzene bromoaluminate salts were stabilized and characterized in the superacidic system HBr/n AlBr₃ with NMR spectroscopy and X‐ray analysis of [HC₆H₃(CH₃)₃]⁺[AlBr₄]^? ( 1 ), [HC₆H₅(CH₃)]⁺[AlBr₄]^? ( 2 ), and [C₆H₇]⁺[Al₂Br₇]^??C₆H₆ ( 3 ). Protonation attempts in bromoaluminate ILs led to a complete protonation of mesitylene, and a protonation degree of up to 15 % for toluene in the IL BMP⁺[Al₂Br₇]^?. Benzene could only be protonated in the more acidic IL BMP⁺[Al₃Br₁₀]^?, with a degree of 25 %. Protonation attempts on aromatics provide evidence that the bromoaluminate ILs tolerate superacidic environments. On the basis of the absolute Brønsted acidity scale, quantum chemical calculations confirmed the superacidic properties, and rank the acidities in ILs down to a pH_abs value of 164 with an error of less than one pH unit compared with experimental findings. The neat AlBr₃/HBr system even may reach acidities down to pH_abs 163.     

Polyethylene glycol-functionalized polyoctahedral silsesquioxanes as H+-conducting electrolytes

Proton-conducting electrolytes composed of a mixture of MePEG₇SO₃H acid and poly(ethylene) glycol-functionalized polyoctahedral silsesquioxanes (Q₈M₈-MePEG_n) are prepared. Eight MePEG_n (n?=?3, 7, and 12) arms are attached to a (HSiMe₂O)₈Si₈O₁₂ (Q₈M₈ ^H) core in the molecule. These Q₈M₈-MePEG_n compounds show nearly the same fractional free volume (FFV), but show increased volume fractions of PEG (V _f,PEG) and viscosities with longer PEG arms. At low MePEG₇SO₃H acid concentration (0.26 M), V _f,PEG and FFV dominantly affect the ionic conductivity. Q₈M₈-MePEG₁₂ shows the highest conductivity due to the largest V _f,PEG at 0.26 M. At a high acid concentration (1.32 M), the differences of V _f,PEG are much smaller and viscosity becomes more important. Q₈M₈-MePEG₃ reaches the largest conductivity of 1.32?×?10^?4 S cm^?1 at 55 °C at 1.32 M because of the lowest viscosity.     

Determination of electrochemical kinetic parameters by square-wave polarography: Polarographic reduction of Zn(II) in 1 M KCl,KBr, and KNCS solutions

A new method of determining electrochemical kinetic parameters by square-wave polarography was presented, in which the faradaic current at θ/2, θ being the half-period of superimposed square-wave voltage, was used for the analysis. The method gave the following kinetic parameters for the electrode reaction, Zn(II) + 2e(Hg), in aqueous solutions at 25° C: k_c^θ=0.0052 cm s^?1 and α_c=0.36 in 1 M KCl, k_c^θ=0.011 cm s^?1 and α_c=0.30 in 1 M KBr, and k_c^θ=0.020 cm s^?1 and α_c=0.52 in 1 M KNCS. Induced adsorption of Zn(II) on the dropping mercury electrode was suggested in solutions containing thiocyanate ions.     

THE pKa OF DIPROTONATED SEMIMETHYLENE BLUE, IN 5% ETHANOL AND 50% ACETONITRILE AQUEOUS SOLUTIONS

Abstract— Semimethylene blue was generated by reductive quenching of triplet methylene blue, ³MBH²⁺, with diphenylamine at pH 0.62–3.4. A Q-switched ruby laser flash-photolysis-kinetic spectro-photometric apparatus was used to characterize the absorption spectrum of semimethylene blue from 350 to 900 nm and a number of physical constants at 25°C with μ= 0.4 M and Cl^? as the anion. The specific rate of quenching of ³MBH²⁺ by DPA is 2.8 × 10⁹M^?1 s^?1 in 5% EtOH-95% water and 1.2×10⁹M^?1 s^?1 in 50 v/v% aq. CH₃CN. Corresponding efficiencies of net electron transfer are, respectively, 0.15 and 0.62. Spectral characteristics in 5% EtOH are, for MBH²₂±, λ_max= 375 nm, ε₃₇₅= 9000 M^?1 cm^?1; λ_max= 880 nm, ε₈₈₀= 12700 M^?1 cm^?1; for MBH±, λ_max= 410 nm, ε₄₁₀= 9800 M^?1 cm^?1, λ_max= 880 nm, ε₈₈₀= 33000 M^?1 cm^?1; for MBH± in 50 v/v% AN, λ_max= 400 nm, ε₄₀₀= 11000 M^?1 cm^?1 and λ_max= 880 nm,ε₈₈₀= 39000 M^?1 cm^?1. The pK_a of MBH²₂ε calculated from the pH dependence of the absorption spectrum is 1.86 × 0.04 in 5% EtOH and 1.15 in 50 v/v% AN. Rate constants, k_decay, for reaction DPAH±⁺ with MBH²₂ε and MBH± in 5% EtOH are, respectively, 3.9 × 10⁹ and 9.5 × 10⁹M^?1 s^?1. The value of pK_a of MBH²₂ε calculated from the dependence of k_decay on pH is 1.75 in 5% EtOH.     

Kinetic study of the reaction of meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(II) with chloride,bromide, iodide,hexacyanocobaltate(III) and thiocyanate ions in aqueous solution

The reaction of Cl^?, Br^?, I^?, Co(CN)₆^3? and NCS^? with meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(III), [RhTAPP(H₂O)₂]⁵⁺, has been studied at 15, 25 and 35°C in 0.1 M [H⁺] with μ = 1.00 M (NaNO₃). The value of the acidity constant, K_al, at 25°C is 4.39 × 10^?9 M. The reactions are first order in anion concentration up to 0.9 M. The values of the stability constants, K₁, and the second order rate constants, k₁, for the reaction with Cl^?, Br^?, I^?, Co(CN)₆^3? and NCS^? are respectively 0.23 M^?1 and 2.5 × 10^?3 M^?1 s^?1, 1.1 M^?1 and 6.92 × 10^?3 M^?1 s^?1, 40.0 M^?1 and 17.0 × 10^?3 M^?1 s^?1, 550 M^?1 and 20.0 × 10^?3 M^?1 s^?1, 3400 M^?1 and 20.9 × 10^?3 M^?1 s^?1. The porphine greatly labilizes the Rh(III). There has been about a 500-fold increase in the rate constant for substitution compared to that of [Rh(NH₃)₅H₂O]³⁺. The substitution rates are however about the same as for [Rh(TPPS)(H₂O)₂]^3?, indicating that the overall charge on the complex plays only a minor role. The kinetic results indicate that dissociative activation is occurring in these reactions.     

A re-examination of the decay kinetics of pulse radiolytically generated Br-2 radicals in aqueous solution

The decay of Br^-₂ in Ar-purged or N₂O-saturated aqueous solutions of KBr (0.01-1.0 M) in the pH range 1–7 has been re-examined using the techniques of pulse radiolysis and computer simulation. The dependence of the rate constant for the intrinsic decay of Br^-₂ on ionic strength (controlled by KBr) has been established; the values of k (Br^-₂ + Br^-₂) are (1.9 ± 0.1) × 10⁹, (2.2 ± 0.3) × 10⁹ and (2.4 ± 0.3) × 10⁹ M^-1 s^-1 in the presence of 0.01, 0.1 and 1.0 M KBr, respectively, independent of pH between 2 and 7. The computer simulation of the decay of Br^-₂ has also generated, for the latter species, ϵ = 10,000 ± 700 M^-1 cm^-1 at λ_max = 360 nm; this value has been calculated without making any assumption concerning G(Br^-₂). For the reduction of Br^-₂ by H atoms, a value of k (H + Br^-₂) = (1.4 ± 0.3) × 10¹⁰ M^-1 s^-1 has been obtained in the presence of 0.01-1.0 M KBr, independent of pH between 1–4. For the reduction of Br^-₂ by e^-_aq at pH 7 (10^-3 M phosphates) and μ = 0.1, a value of k (Br^-₂ + e^-_aq = (1.1 ± 0.2) × 10¹⁰ M^-1 s^-1 has been obtained.     

Autoionizing rydberg states of. The Li2 molecule: Molecular constants for Li2+

Autoionizing Rydberg series of Li₂ have been observed in the two-step optical cxcitation of a supersonic lithium beam. The series limits are vibrational states of Li₂⁺. In the most probable assignment IP(Li₂) = 41236.4 ± 2.5 cm^?1 and for Li₂⁺ω_e = 263.45 ± 1.3 cm^?1; ω_eχ_e = 1.35 ± O.2 cm^?1; r_e = 3.032 ± 0.01 Å; D_e = 10807 ± 150 cm^?1.     

Electrochemistry of Na2SO4 (I) solid solutions with aliovalent cation substitution

Conductivity data of several Na₂SO₄(I) solid solutions with cation substitutions are presented. The substitution of sodium by bi- and trivalent atoms generates cation vacancy concentrations up to 30% in the structure of Na₂SO₄(I) thus creating high mobility of Na⁺. Electrochemical measurements showed that Na⁺ ion conductivity prevails and that the electronic partial conductivity is negligible. Complex impedance diagrams were used to determine the influence of the vacancy concentration on the ionic conductivity of Na₂SO₄(I) solid solutions. It was found that the conductivity is strongly correlated to the vacancy concentrations, whereas the size and the charge of the substituting ions show no effect within the accuracy of the measurements. The activation energy as function of the vacancy concentration exhibits a minimum of 0.7 eV at a vacancy concentration of 1%. The maximum of conductivity was found to be 1.5 × 10^?2 Ω^?1 cm^?1 at 500°C with 7% vacancies.     

Kinetics of O(1D) interactions with the atmospheric gases N2, N2O,H2O,H2, CO2, and O3

Rate coefficients for collisional removal of O(¹D) by six atmospheric gases have been measured by monitoring the appearance of O(³P) following photolytic production of O(¹D). The measured values, k_M±2σ, in units of 10^?11 cm^?3 molecule ^?1 s^?1 are k_O3 = 22.8±2.3, k_N2 = 2.52 ± 0.25, k_CO2 = 10.4 ± 1.0,k_H2O 195± 2.0, k_N2O = 11.7 ± 1.2, and k_H2, = 11.8±1.2.     

Analytical applications of picolinealdehyde salicyloylhydrazone: Spectrophotometric determination of nickel and zinc

With a view to the use of picolinealdehyde salicyloylhydrazone as analytical reagent, a study of the physical properties and chemical reactions of this substance has been carried out. It reacts with nickel (λ_max = 375 nm, ? = 3.9 × 10⁴M^?1cm^?1) or zinc (λ_max = 365 nm, ? = 4.8 × 10⁴M^?1cm^?1) to produce a yellow 1:2 complex in both cases. Spectrophotometric determinations of trace amounts of nickel and zinc have been established.     

Solid potassium-conducting electrolytes in the K2 − 2x Ga2 − x V x O4 system

New potassium-conducting solid electrolytes based on potassium monogallate in the K_2?2x Ga_2?x V _x O₄ system are synthesized and studied. It is found that an introduction of V⁵⁺ ions leads to a considerable increase in the KGaO₂ conductivity due to the formation of vacancies in the potassium sublattice. The conductivity for optimal compositions is approximately 10^?3 S cm^?1 at 400°C and above 10^?2 S cm^?1 at 700°C. The results are compared with early obtained data for potassium monogallate dopped with four-charged cations.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

The potential energy curve for the B1IIu state of Li2

Multiconfiguration self-consistent field calculations of the potential curve for the B¹Π_u state of Li₂ show a 700 cm^?1 high hump at 5.365 Å in good agreement with experimental estimates of 930 ± 300 cm^?1 and 523 ± 50 cm^?1.     

Determination of ruthenium as ruthenate by stripping voltammetry

Stripping voltammetric analysis of ruthenium with a platinum RDE was studied in the concentration range from 5×10^?7 to 1.2×10^?5M RuO₄^2?, where linear dependence of the anodic peak height on the ruthenate concentration was obtained. Special attention has been paid to a simple preparation of the sample for analysis. Ruthenate can be prepared directly in the electrolytic vessel from the ruthenium compounds by oxidation with potassium persulphate in alkaline medium. As a supporting electrolyte 10^?2 to 5×10^?2M K₂S₂O₈ with 10^?1 to 1 M KOH was used.     

Proton conductivity and structural properties of precursors mixed PVA/PWA-based hybrid composite membranes

A new class of hybrid nanocomposite membranes containing poly(vinyl alcohol) (PVA), phosphotungstic acid (PWA), 3-glycidyloxypropyltrimethoxysilane (GPTMS), 3-mercaptopropyltrimethoxysilane (MPTMS) and glutaraldehyde (GA) were prepared by a sol–gel method. The aim of this research study was to investigate these novel and highly proton-conducting membranes including their properties, and performances for proton exchange membrane fuel cells (PEMFCs) operating at low temperature. 'Swelling' was observed at room temperature for all the composites. The manner in which the conductivity depended on temperature and humidity was determined and a maximum conductivity value of 2.5?×?10^?2 S cm^?1 was found at a 140°C and 30 % relative humidity (RH) for the PVA/PWA/GPTMS/MPTMS/P₂O₅/GA (50/5/15/10/10/10 wt.%) hybrid composite membrane. It was suggested that the conductivity depended strongly on the nature of the organic/inorganic components as well as on the acid concentration. X-ray diffraction (XRD) results demonstrated that this membrane had an amorphous phase, and Fourier transform infrared spectroscopy (FTIR) results confirmed the composite formation. Finally, membrane-electrode assemblies with a loading of 0.1 mg cm^?2 of Pt/C on a prepared electrode gave rise to a current density of 309 mA cm^?2 at 0.5 V.     

Solid electrolytes with cesium cation conductivity in the Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Cs<Subscript>2</Subscript>O system

Solid solutions based on cesium monogallate CsGaO₂ are synthesized in the Ga₂O₃-TiO₂-Cs₂O system. Their crystalline structure and also temperature and concentration conductivity dependences are studied. The cesium cation character of conductivity is confirmed. The most conducting samples contain an excess of cesium oxide and have the structure of high-temperature γ-modification of KAlO₂. Their specific conductivity is (5.0–6.7) × 10^?3 S cm^?1 at 400 °C, (2.5–5.0) × 10^?2 S cm^?1 at 700°C at the activation energy of 33–35 kJ/mol^?1.     

Composition-controlled metal-insulator transitions and minimum metallic conductivity in the oxide systems LaNi1−xMxO3 (M = Cr,Mn, Fe,or Co)

The composition-controlled metal-insulator transition in the perovskite systems LaNi_1?xM_xO₃ (M = Cr, Mn, Fe, and Co) has been investigated by transport measurements over the temperature range 12–300 K. These systems, which have critical electron densities (n_c) in the range (1–2) × 10²⁰ electrons cm^?3, exhibit sharp metal-insulator transitions at the base temperature. The corresponding minimum metallic conductivity (σ_min), separating the localized and itinerant electronic regimes, is of the order of 10² ohm^?1 cm^?1. Particular attention is paid to the idea of σ_min scaling with n_c, and our present results are compared with earlier studies of the metal-insulator transition in low (e.g., Ge:Sb) and high (e.g., metal-ammonia, supercritical Hg) electron-density systems. A link is established between the transport and magnetic properties of the title systems at the metal-insulator transition.     

Analytical applications of mixed-ligand complexes: II. Determination of hydrogen peroxide in the presence of perioxide derivatives

The mixed ligand complex TiXOH₂O₂ was found suitable for the determination of small amounts of hydrogen peroxide in the presence of peroxy acids of sulfur. The pH optimum for the determination depends on the concentrations of the reagents [titanium (IV) and xylenol orange]: for 2 × 10^?4M titanium (IV) and XO the optimum pH is 1.25. ?⁵²⁰ = 13,200 M^?1 cm^?1. The method is suitable for determination of 4–40 μM H₂O₂. Mention is made of the possible causes of the contradictions to be found in the literature concerning the ternary complex.     

Li+ ion conductivity in the system Li4SiO4Li3VO4

Two ranges of solid solutions were prepared in the system Li₄SiO₄Li₃VO₄: Li_4?xSi_1?xV_xO₄, 0 < x ? 0.37 with the Li₄SiO₄ structure and Li_3+yV_1?ySi_yO₄, 0.18 ? y ? 0.53 with a γ structure. The conductivity of both solid solutions is much higher than that of the end members and passes through a maximum at ～40Li₄SiO₄ · 60Li₃VO₄ with values of ～1 × 10^?5 ohm^?1 cm^?1 at 20°C, rising to ～4 × 10^?2 ohm^?1 cm^?1 at 300°C. These conductivities are several times higher than in the corresponding Li₄SiO₄Li₃(P,As)O₄ systems, especially at room temperature. The solid solutions are easy to prepare, are stable in air, and maintain their conductivity with time. The mechanism of conduction is discussed in terms of the random-walk equation for conductivity and the significance of the term c(1 ? c) in the preexponential factor is assessed. Data for the three systems Li₄SiO₄Li₃YO₄ (Y = P, As. V) are compared.     

A study of the gold/aqueous electrolyte interphase by modulated reflection spectroscopy

The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO₄, 0.01 M Na₂SO₄ and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO₄ evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm^?2), is 3% at +8 μC cm^?2 and at?17 μC cm^?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl^? interaction and the covalent character of the bond at the most positive charges.