Portugaliae
Electrochimica Acta

The behaviour of ions in organic and mixed solvents is illustrated by a number of examples. Systematic study of the effect of solvent on potentials of cells with ion-selective electrodes led to the development by Kakabadse and co-workers of a new technique in direct potentiometry, viz. the ion isoconcentration technique (IICT). In IICT, concentration of solvent is varied and that of indicator ion is kept constant. Many simple mixtures show under ion isoconcentration conditions a systematic change of cell potential with variation in the concentration of organic solvent, providing a graphical method for the rapid determination of, (a) individual organic solvents in simple mixtures, and (b) residual water in organic solvents. A laboratory prototype monitor for the continuous determination of ethanol in cider and sherry, using the fluoride isoconcentration technique (FICT), is described.

An electrochemical study on the mesoionic heterocycle mentioned above is carried out, using dc polarography, cyclic voltammetry and controlled potential electrolysis . A reduction mechanism with a consumption of four electrons in each polarographic wave is proposed. On the other hand, we detect a kinetic response of CE type caused by an equilibrium between hydrolysis products ot the heterocycle.

The polarographic reduction of Zn(II> and Co(II) complexes with paludrine has been studied in moderated acid media. The Zn(II) 2:1 complex shows two well defined waves. The Co(II) 2:1 complex shows only one wave. Arrhenius activation energies, obtained from diffusion currents of np, dp, aci , aca, KT and K-L- polarograms, show that all cathodic and anodic processes are controlled by diffusion. The mechanism of these processes is proposed.

Cyclic voltammetric studies were performed for six redox couples at a Pt electrode, in the absence and in the presence of Bi, Pb and Cd adatoms. Standard rate constants were evaluated for all the systems in the absence and in the presence of adatoms. Whenever a catalytic effect was obtained the effect of coverage was studied in a quantitative way.It was found that the rate constant increases initially rapidly and then passes through a maximum or reaches a constant value, at coverages of the order of a monolayer. For all the systems the influence of the adatoms decreases in the order Bi > Pb > Cd.

Within our broad interest on the study of the redox and electronic (1) properties of coordination compounds by electrochemical methods, we embarked upon the investigation of the redox behaviour of series of ferrocene derivatives, FcX [where Fc stands for FeCn^-Cj-H) (n5-C H)]f with different types of (2) substituents (X); the latter may ligate an aromatic ring through, for instance, a sp or an unsaturated sp hybridized C atom, and some homo- and hetero-annular disubstituted ferrocenes have also been investigated. However, in this preliminary communication, we wish to report the results we have obtained with a type of substituents we are particularly interested from a coordination point of view: that with the isocyan functional group. In the ferrocene derivatives under study, CNR [J_; R=Fc (a), CH2FC (b)or CH(Men)Fc (c) where Men=(lR,2S,5R)-2-isopropyl-5-methylcyclohexyl], the isocyan group is prone to coordination to a metal centre and the derived ferrocenyl--isocyanide complexes [Cr(CO)^(CNR)] (2) can be prepared by reaction of the former with [Cr(CO) (thf)].

It has been shown that in the presence of adenine copper (II) ions in 0.25M F^SO^ are reduced at the mercury electrode in two distinct stages; this is a consequence of the interaction of adenine with copper (I) ions. In attempt to clarify which are the reactions involved, the nature of the complexes formed and the respective formation constants a series of experiments using polarographic techniques (sampled DC and DP Polarography) was carried out.