Dissociation Constants Of Salts Research Articles

Ionic equilibrium in mixtures of polar protophobic and protophilic non-hydrogen bond donor solvents: Acids, salts, and indicators in acetonitrile with 4 mass % dimethylsulfoxide

Acetonitrile (AN) and dimethylsulfoxide (DMSO) belong to the so-called polar non-hydrogen bond donor solvents, in accordance with Bordwell's classification. At that, according to Kolthoff, AN is a protophobic, and DMSO is an expressed protophilic solvent. This article presents a study of the acid-base and related equilibria in a binary AN – DMSO solvent system with mass ratio 96: 4, which corresponds to the molar fraction xDMSO = 0.021. Owing to the aforesaid property of DMSO, the utilization of this binary mixture makes it possible to neglect the interfering influence of water traces, which is difficult to overcome in pure AN. As result, in the solvent under study, the proton is solvated first of all by DMSO despite predominance of AN. The solvent composition was chosen basing on the pKa values of the picric acid, which were determined via UV–visible spectroscopy at different AN – DMSO ratios. The interfering influence of water traces was checked. An operational paH+∗ scale was developed using a quinhydrone electrode in a concentration cell with liquid junction, basing on a picrate buffer solution with paH+∗ = 3.27. The cation-anion association constants of a set of salts were determined using the conductance method, the pKa values of the buffer acids (benzoic, salicylic, 2,4- and 2,6-dinitrophenols) were calculated, and the constants KAHA−f of homoassociation (A− + HA ⇄ AHA−) were estimated. The response of the glass electrode to the acidity of the solutions was proved within the range of 2.5 ≤ paH+∗ ≤ 15.5 (slope = 59.69), the paH+∗ values of 16 picrates of organic bases were determined, and the pKas of 7 indicators, nitrophenols and sulfonephthaleins, were obtained spectroscopically in the solvent under study. The dissociation constants of salts, acids, and indicators in AN–DMSO (96:4) mixed solvents were compared with those in other non-hydrogen bond donor solvents. Basing on some reliable assumptions, the values of the Gibbs energy of the H+ transfer from the binary solvent to AN and DMSO were estimated as ΔGtro = +44 ± 3 and −22.6 ± 3 kJ mol−1, respectively.

Effect of different anions of lithium salt and MMT nanofiller on ion conduction in melt-compounded PEO–LiX–MMT electrolytes

Polymer nanocomposite electrolyte (PNCE) films composed of poly(ethylene oxide) (PEO), lithium salt (\( {\text{LiX}};\;{\text{X}} = ClO_4^{ - },\;BF_4^{ - },\;C{F_3}SO_3^{ - } \)) and montmorillonite (MMT) clay as nanofiller were prepared by melt-compounded hot-pressed technique at 70 °C under 3 tons of pressure. The ionic conductivity and relaxation behaviour of the films were investigated by dielectric relaxation spectroscopy in the frequency range of 20 Hz to 1 MHz at ambient temperature. The results revealed that the ionic conductivity of the PNCE films having 20:1 stoichiometric ratio of ethylene oxide monomer units to the lithium cation are governed by the size of different anions and the dissociation constant of salt, and also MMT concentration. It was found that PEO–LiBF4 film has comparative high dc ionic conductivity, whereas both the LiBF4 and LiClO4 containing PNCE films exhibit anomalous conductivity behaviour with varying MMT concentration. The PEO–LiCF3SO3 film has two orders of magnitude low value of dc ionic conductivity as compared to that of the other salts electrolyte films, but its conductivity enhances by one order of magnitude when 2 wt.% MMT is added as filler. A correlation between the values of ionic conductivity, conductivity relaxation time and the real part of permittivity at 1 MHz were found and the same was discussed in relation to the transient ion-dipolar type cross-linked structural behaviour of the polymeric nanocomposite electrolytes.

Ion and Ion-Pair Contributions to the Polymerization of Tetrahydrofuran

Abstract The cationic polymerization of tetrahydrofuran is generally considered to be effected by an oxonium chain end in the form of an ion pair. Consideration of expected ionic dissociation constants of salts in typical solvents for these reactions suggests that appreciable concentration of free oxonium ions would be present under polymerization conditions. The dissociation constants of such salts have been measured in methylene chloride solution and shown to be near 4 × 10−6, sufficiently high that a contribution to the polymerization by free ions could be expected. Rate constants for the propagation reaction of the polymerization initiated by triethylox-onium tetrafluoroborate have been measured, in both the presence and absence of the common-ion salt tetrabutylam-monium tetrafluoroborate. From the dependence of the rate constant on the initiator concentration and from its reduction by varying concentration of the free common ions, it is possible to calculate the ion-pair rate constant to be 1.4 × 10−...