Single scale for ion activities and electrode potentials in ethanol-water solvents based on the triisoamylbutylammonium tetraphenylborate assumption

Ruthenium complexes of 3-hydroxy-4-pyranones and of 3-hydroxy-4-pyridinones

“…Chloride loss from chlororuthenates is slow, for Ru II , Ru III and Ru IV , with the rate constant for chloride loss decreasing sharply as the number of chloride ligands decreases in the series [Ru III Cl n (H 2 O) 6-n ] x [41]. Chloride will be more reluctant to leave from ruthenium in the mixed solvent medium than in water, as the transfer chemical potential of chloride from water into 60% ethanol is + 9 kJ mol -1 [42]. Indeed, rate constants for aquation of [Ru(NH 3 ) 5 Cl] 2+ and of cis-[Ru(en) 2 Cl 2 ] + decrease markedly as the proportion of organic co-solvent increases in water-methanol, -ethanol, or -acetone mixtures [43].…”

Solvation of Ions

“…Extrathermodynamic assumptions for the estimation of single-ion medium effects have been summarized and evaluated [344]. These assumptions are divided into two groups: (1) those which presume the liquid-junction potential at an aqueous-nonaqueous boundary can be suppressed by interposition of a salt bridge and (2) those based on proposed quantitative relationships between the size of ions or molecules and their energy of solvation.…”

“…The assumption that an uncharged species and the corresponding ion of unit charge have equal medium effects in a given medium in inherent in the use of the ferrocene-ferricenium and cobaltocene-cobaltocinium redox couples [344,361], the Hammett acidity functions, the iodine-triodide couple, and the reactant-transition state pair in aromatic nucleophile substitution [344,346]. Several reviews have led to a possibly balanced perspective with reference to the first two couples.…”

Estimation of Medium Effects for Single Ions in Non-Aqueous Solvents

“…measurements on the hydrogen-silver chloride cell without transference: Pt(s); H 2 (g), HC1, AgCl(s); Ag(s) (9) If the standard potential of the above cell in a given non-aqueous solvent is S E°, values of pa,1| = -log (m H s y,,) in that solvent can be calculated from: pa,1 = (E-s E°)/A:+log/» c l + log s y cl (10) In Equation 10, E is the measured e.m.f., s y,, and s y C | are the salt-effect activity coefficients, m u and m Ci the molalities of hydrogen and chloride ions, respectively, and k = (RT In 10)/F. Unfortunately, the paf, scales established in the above manner are different for each solvent composition, so that equal numerical values of paf, in different media do not, as a rule, reflect equal acidities.…”

“…For example, from such scales, it is impossible to tell whether a pa,1| of 4 in ethanol represents a greater or a lesser acidity (proton activity) than a pa H of 4 in water, e t c In order to express pH measurements in different media on a single scale, it is best to refer all of them to the aqueous standard state. According to Equation 4, the paf, of a non-aqueous solution can be expressed on the (aqueous) pa H scale with the aid of the medium effect for the proton, m y H , characteristic of the solvent: (11) Alternatively, if in Equation 10 we use the aqueous standard potential for cell 9, ^E 0 , the pa H (aqueous standard state) can be calculated directly from the cell e.m.f., E, measured in the non-aqueous solvent, provided the medium effect for the chloride ion, m y a , is known. 21 In either case, it is the medium effect for a single ion that enables us to correlate pH measurements in different solvents by translating them into a single scale referred to the aqueous standard state.…”