The Ion Transfer From Aqueous(w), Formamide(fa) or W-Fa Mixtures to Organic Solution Studied by Polarography at the Electrolyte Solution Dropping Electrode

Abstract

Formamide or aqueous-formamide mixture is introduced for the ion transfer voltammetry at a liquid/liquid interface as one phase in place of the aqueous phase. The transfer of I-, BF4-, C104-and CH3(CH2)~(CH3)3N+ (n>_1) was investigated at the interface of aqueous, formamide or the aqueousformamide mixtures and 2-nitro-m-xylene.The transfer of these ions was confirmed to be polarographically reversible. The relations are discussed between the standard Gibbs transfer free energy, L\G°~•, of these ions and the nature of the transferring ions or the properties of solvents based on the halfwave potentials in the polarograms. The AG°a of small anions from formamide to nitroxylene are smaller than those from aqueous. The effect of the addition of CH2 in CH3(CH2)n(CH3)3N+ on AG°~ from formamide to nitroxylene is smaller than that from aqueous.Key words formamide, aqueous-formamide mixture, ion transfer polarography at a liquid/liquid interface Formamide (FA) is a liquid at ordinary temperature in spite of its small molecular weight and has a large dielectric constant (e), dipole moment (it), donor number (DN) and acceptor number (AN). Since FA is a good solvent for inorganic salts, a structured solvent through hydrogen bonding and immiscible with some organic solvents of low [1], FA has been considered to be a solvent which resembles closely to water (W). In detail, however, considerable differences exist between properties of FA and W, which may reflect on the solute-solvent interaction of an ion in the solvents. If we use FA or W-FA as solvents instead of W taking into account the differences, new fields will be developed for the recognition of ions or molecules.In the present paper, the applicability of the ion transfer voltammetry [2] at the interface between FA or W-FA mixture and organic solution (Org) is demonstrated, and the ion-solvent interactions in W, FA and W-FA mixture are discussed based on the results obtained by the ion transfer polarography. EXPERIMENTAL Polarographic measurementThe polarographic cell, potentiostat, galvanostat, function generator, X-Y recorder, and the apparatus for JR drop compensation employed in the present work were identical to those described in the previous paper on the ion transfer at the W/ Org interface [3]. In recording the polarograms, W, FA or W-FA mixture containing 0.1 M Li2SO4 as the supporting electrolyte (SE) was forced upward or downward dropwise into Org containing various salts as SE through a capillary made of Teflon fluororesin. The objective ion was added into W, FA, or W-FA mixture. The mean flow rate of W, FA or W-FA mixture were 0.02 -0.05 ml s-l, and the drop-time were 3 -6 s, at open circuit. Current-scan polarograms were recorded scanning the applied current at a rate of 0.5 µA s-1 with the aid of two silver/silver chloride electrodes, SSE, and measuring the potential difference, AV, between W, FA or W-FA mixture and Org using SSE and a tetraphenylborate, TPhB-, ion selective electrode, TPhBE [3]. Here, w containing 1 M LiCI was used as the electr...