Water-dichloroethane , interface between

By using cyclic voltammetry, Schiffrin and coworkers [26, 186, 187, 189] studied electron transfer across the water-1,2-dichloroethane interface between the redox couple FefCNls /Fe(CN)6 in water, and lutetium(III) [186] and tin(IV) [26, 187] diphthalocyanines and bis(pyridine)-me50-tetraphenylporphyrinato-iron(II) or ru-thenium(III) [189] in the organic solvent. An essential advantage of these systems is that none of the reactants or products can cross the interface and interfere with the electron transfer reaction, which could be clearly demonstrated. Owing to a much higher concentration of the aqueous redox couple, the pseudo-first order electron transfer reactions could be analyzed with the help of the Nicholson-Shain theory. However, though they have all appeared to be quasireversible, kinetic analysis was restricted to an evaluation of the apparent standard rate constant o. which was found to be of the order of 10 cm s [186, 189]. Marcus [199] has derived a relationship between the pseudo-first-order rate constant for the reaction (8) and the rate... 

FIGURE 32.4 Potential dependence of the interfacial tension J and the capacity C for the interface between solutions of 5mM tetrabutylammonium tetraphenylborate in 1,2-dichloroethane and lOOmM LiCl in water. The potential scale E represents the Galvani potential difference relative to the standard ion transfer potential for tetraethylammonium ion, cP o EA+ = 0.02 V. 

FIGURE 32.5 Cyclic voltammogram for the interface between solntions of 5mM tetra-butylammoninm tetraphenylborate in 1,2-dichloroethane and 5mM NaCl in water in the absence (dashed bne) and the presence (sohd bne) of 0.5 mM tetraethylammoninm in the aqneons phase. Sweep rate lOmV/s, interfacial area 0.02 cm. ... 

Heterogeneous electron reactions at liquid liquid interfaces occur in many chemical and biological systems. The interfaces between two immiscible solutions in water-nitrobenzene and water 1,2-dichloroethane are broadly used for modeling studies of kinetics of electron transfer between redox couples present in both media. The basic scheme of such a reaction is... 

In a closely related study, Marecek et al. [46] used the pendant drop video-image method to investigate the adsorption and surface reactions of calix[4]arene ligands at the ideally polarized water-1,2-dichloroethane interface. The difference between the surface tensions in acidic and alkaline media was ascribed to a difference in the charge on the... 

Following the early studies on the pure interface, chemical and electrochemical processes at the interface between two immiscible liquids have been studied using the molecular dynamics method. The most important processes for electrochemical research involve charge transfer reactions. Molecular dynamics computer simulations have been used to study the rate and the mechanism of ion transfer across the water/1,2-dichloroethane interface and of ion transfer across a simple model of a liquid/liquid interface, where a direct comparison of the rate with the prediction of simple diffusion models has been made. ° ° Charge transfer of several types has also been studied, including the calculations of free energy curves for electron transfer reactions at a model liquid/liquid... 

The electrodes used in conventional polarography and voltammetry are electronic conductors such as metals, carbons or semiconductors. In an electrode reaction, an electron transfer occurs at the electrode/solution interface. Recently, however, it has become possible to measure both ion transfer and electron transfer at the interface between two immiscible electrolyte solutions (ITIES) by means of polarography and voltammetry [16]. Typical examples of the immiscible liquid-liquid interface are water/nitrobenzene (NB) and water/l,2-dichloroethane (DCE). 

Monte Carlo and molecular dynamics calculations of the density profile of model system of benzene-water [70], 1,2-dichloroethane-water [71], and decane-water [72] interfaces show that the thickness of the transition region at the interface is molecu-larly sharp, typically within 0.5 nm, rather than diffuse (Fig. 4). A similar sharp density profile has been reported also at several liquid-vapor interfaces [73, 74]. The sharpness of interfaces thus seems to be a general characteristic of the boundary between two stable phases and it is likely that the presence of supporting electrolytes would not significantly alter the thickness of the transition region at an ITIES. The interfacial mixed solvent layer [54, 55], if any, would probably have a thickness comparable with this thin inner layer. 

Liquid-liquid interfacial tensions can in principle also be obtained by simulations, but for the time being, the technical problems are prohibitive. Benjamin studied the dynamics of the water-1,2-dichloroethane interface in connection with a study of transfer rates across the interface, but gave no interfacial tensions. In a subsequent study the interface between nonane and water was simulated by MD, with some emphasis on the dynamics. Nonane appears to orient relatively flat towards water. The same trend, but weaker, was found with respect to vapour. Water dipoles adjacent to nonane adsorb about flat, with a broad distribution the ordering is a few molecular layers deep. Fukunishi et al. studied the octane-water Interface, but with a very low number of molecules. Their approach differed somewhat from that taken in the simulations described previously they computed the potential of mean force for transferring a solute molecule to the interface. The interfacial tension was 57 11 mN m", which is in the proper range (experimental value 50.8) but of course not yet discriminative (for all hydrocarbons the interfacial tension with water is very similar). In an earlier study Linse investigated the benzene-water interface by MC Simulation S He found that the water-benzene orientation in the interface was similar to that in dilute solution of benzene in water. At the interface the water dipoles tend to assume a parallel orientation. The author did not compute a x -potential. Obviously, there is much room for further developments. 

There is considerable interest in ion and electron transfer processes at the interface between two immiscible electrolyte solutions (ITIES), e.g., water and 1,2-dichloroethane. SECM can be used to monitor such processes (Chapter 8). It allows one to separate ion transport from electron transfer... 

Potential-modulated fluorescence spectroscopy at liquid/liquid interfaces between immiscible liquids has been reported and a cell design has been provided [78], The dependence of the adsorption of the free, bare or the water-soluble porphyrins at the polarized water/l,2-dichloroethane interface has been studied [79], Observed spectral differences suggest a solvation structure at the interface that is different from that inside the bulk of the respective solution phases. For further studies with related porphyrins at the same interface, see [79]. Details of the transfer mechanism of the rose bengal dianion across the water/l,2-dichloroethane interface have been elucidated [80],... 

Ohde, H., Maeda, K., Yoshida, Y. and Kihara, S. (2000) Redox reactions between molecular oxygen and tetrachlorohydroquinone at the water I 1,2-dichloroethane interface. Journal of Electroanalytical Chemistry, 483, 108-116. 

We now return to the example introduced in Section 20.1.1, where two electrolyte solutions a and P were placed in contact and a hypothetical barrier was invoked that prevented the transfer of one of the ions between the phases. Although this example may have seemed obscure, such a system may readily be constructed for the interface between two immiscible electrolyte solutions (ITIES). Such a system can be formed by contacting water with an immiscible organic solvent such as nitrobenzene or 1,2-dichloroethane, as discussed in Section 17.3 in Chapter 17 of this handbook. The two solvents possess a slight mutual solubility. Once the two phases are equilibrated, the system is composed of an organic saturated aqueous phase in contact with a water saturated organic phase. For this reason, measmement of any transport property should always be performed on mutually pre-saturated solutions. 

Shao, Y. and H. H. Girault, Kinetics of the transfer of acetylcholine across the water-i-sucrose/l-2-dichloroethane interface. A comparison between ion transport and ion transfer, J Electroanal Chem, Vol. 282, (1990) p. 59. 

How sharp is the interfacial region between water and an organic liquid and what is its molecular structure Broadly, three possibilities should be considered (1) the interface is sharp and flat, as assumed in continuum models (2) the interfacial region is a mixture of the two liquids and (3) the interface is a locally sharp but rough surface that fluctuates in time. Recent computer simulations of interfaces between water and benzene, " decane, nonane, hexane, dodecane, 1,2-dichloroethane (DCE), CCU, and octanol have dealt with this issue. 

---