Electrochemical determination of the stability of complexes formed by proton-ionizable ligands of 3,5-disubstituted 1H-pyrazole with phenethylamine.
The application of two extreme models for diffusion in two-component systems to electrochemically determine equilibrium constants is discussed. The application of cyclic voltammetric, diferential pulse and rotating-disc electrode voltammetric data to elucidate the stoichiometry and formation constant of complex species by applying a generalization of the molar-ratio method is described. Molar-ratio experiments permit the distinction between the limiting diffusive regimes. The values of the equilibrium stability constants for complexation of phenethylamine and phenethylammonium ions by a 26-membered dioxotetraester crown of 3,5-disubstituted 1H-pyrazole as free ligand 1[L] and as dipyrazolate anion 1'[L(2-)]2Na(+), respectively, were determined.
Sodium Ion-Selective Electrodes Based on Dibenzo-16-crown-5 Compounds with Pendent Amide Groups
Potentiometric selectivities for alkali-metal cations of dibenzo-16-crown-5 compounds with amide-containing side arms attached to the central carbon atom of the three-carbon bridge have been determined in solvent polymeric membrane electrodes. The lariat ethers include N-alkyl- and N,N-dialkyl-sym-(R)-dibenzo-16-crown-5-oxyacetamides with R = hydrogen or an alkyl group. The presence of an alkyl group on the ring carbon which bears the amide-containing side arm markedly increases the Na[sup +]/K[sup +] selectivity of poly(vinyl chloride) matrix membrane electrodes with o-nitrophenyl octyl ether as the membrane solvent. Lariat ethers with a N,N-dipentyloxyacetamide group as the side arm and a geminal alkyl group of two or more carbon atoms exhibit high Na[sup +]K[sup +] selectivities (log K[sub Na,K][sup Pot] = [minus]2.1) with good selectivities for Na[sup +] over the other alkali-metal cations, H[sup +], NH[sub 4][sup +], and alkaline-earth-metal cations. 25 refs., 6 figs., 1 tab.
Synthesis of highly lipophilic crown ether carboxylic acids
Synthetic routes to eight highly lipophilic crown ether carboxylic acids are described. Structural variations within this series of crown ether carboxylic acids include changes in the crown ether cavity size, the lipophilic group attachment site, and the basicity of the crown ether oxygens.