Hidekazu Doe

Voltammetric study of protonated 1,10-phenanthroline cation transfer across the water/nitrobenzene interface

Abstract The ion transfer of 1,10-phenanthroline (phen) across the water/nitrobenzene interface has been studied in the pH range 1–7 by electrochemical methods, adding phen to the aqueous phase or to the organic (nitrobenzene) phase. Current-scan polarography at an ascending water electrode and potential-scan cyclic voltammetry at a stationary plane electrode were used. With each addition, an anodic wave caused by the transfer of a protonated phen (Hphen + ) from the aqueous to the organic phase was observed. Here a detailed mechanism of the ion transfer is proposed by considering branch diffusions of phen species from the interface to either bulk phase by which the Hphen + transfer producing the anodic wave is depressed. With the addition of phen to the aqueous phase, the wave became deformed, noisy and steep, and finally separated into two waves as the phen concentration was increased and the pH was decreased. This is probably caused by the interfacial adsorption of Hphen + . The adsorption phenomenon is also discussed with the aid of electrocapillary curves.

Interaction and Stability of Mixed Micelle and Monolayer of Nonionic and Cationic Surfactant Mixtures

Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmcs were analyzed with the pseudophase separation model, the regular solution theory, and the Maedas approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants.

Ion transfer of tetraalkylammonium cations at an interface between frozen aqueous solution and 1,2-dichloroethane

Abstract Cyclic voltammetry with a frozen electrode has been used to investigate the ion transfer of tetramethylammonium (TMA + ), tetraethylammonium (TEA + ), and tetrapropylammonium (TPrA + ) across the water/1,2-dichloroethane (DCE) interface at −15°C and to compare these results with the liquid/liquid system at 25°C. All the half-wave potentials of these ion transfers shift to negative potential in the frozen system, and the ion transfers exhibit less reversibility comparing transfers in the liquid system with the same composition at 25°C. These negative shifts indicate that the ionic solvations are unstable in the frozen phase. The degree of negative shifts increases in the order TMA + + + . This order has been discussed in terms of the aqueous solvation of these ions. The diffusion coefficients of ions in the aqueous phase have been evaluated, and a very slow transport process found in the frozen system. In both frozen and liquid systems these values decrease in the order TMA + > TEA + > TPrA + . The apparent standard rate constants have also been evaluated for both systems. The values in the liquid system are larger than those in the frozen system, and both increase in the order TMA + + + . That is, the ion transfer rate increases but the ion transport rate decreases with the Stokes radius of the ion in both systems.

Voltammetric and electrospray ionization mass spectrometric studies of the facilitated ion transfer of sodium and potassium cations by naphtho-15-crown-5 across the water | 1,2-dichloroethane interface

Abstract The transfer Na + and K + cations, facilitated by naphtho-15-crown-5, N15C5, from an aqueous phase to a 1,2-dichloroethane (DCE) phase were studied by cyclic voltammetry under two following conditions, the metal ion concentration in the aqueous phase was much higher than the N15C5 concentration in the organic phase (N15C5 diffusion controlled process) and the N15C5 concentration was much higher than metal ion concentration in the aqueous phase (metal ion diffusion controlled process). In both conditions, diffusion controlled waves were observed and the diffusion coefficients of Na + and K + in the aqueous phase and that of N15C5 in the organic phase were evaluated to be 1.03×10 −5 , 1.28×10 −5 and 5.4×10 −6 cm 2 s −1 , respectively. The stoichiometries of the complexes were determined to be 1:1 (cation to ligand) for Na + -N15C5 and 1:2 for K + -N15C5. Under the both conditions, the stability constants, β 1 , of the Na(N15C5) + complex, in the organic phase were evaluated to be 3.9×10 8 M −1 and 2.3×10 5 M −1 because two reference standard potentials were reported elsewhere. The β 2 values of the K(N15C5) 2 + complex were 2.5×10 11 M −2 and 1.2×10 11 M −2 under the conditions of N15C5 and K + diffusion controlled processes, respectively. The stoichiometries of the complexes were also studied by electrospray ionization mass spectrometry. The complexes of Na(N15C5) + and Na(N15C5) 2 + were observed and their stabilities were almost similar to each other in the gas phase. On the other hand, the K(N15C5) + complex was very unstable and the K(N15C5) 2 + complex was only observed in the gas phase. This result is very consistent with the electrochemical results. Comparing the intensities in the ESI-MS spectra, the K(N15C5) 2 + was more stable than Na(N15C5) 2 + in the gas phase.

On-line electrospray mass analysis of photoallylation reactions of dicyanobenzenes by allylic silanes via photoinduced electron transfer

Abstract Photoinduced electron transfer reaction of 1,4-dicyanobenzene with allyltrimethylsilane in acetonitrile was analyzed by on-line electrospray mass spectrometry. A reductive allylation product of 1,4-dicyanobenzene was detected for the first time as a key intermediate in the photoinduced electron transfer reaction. The electrospray technique, combined with a flowing photoreaction cell, was shown to be a useful tool for detecting and identifying unstable intermediates or primary products in organic photochemical reactions.

Characterization of ice electrodes

In order to investigate the mechanism of ion transfer across an interface between frozen aqueous and organic phases, a novel ice electrode which consists of the frozen aqueous electrolyte solution has been developed and characterized in 1,2-dichloroethane (DCE) containing various electrolytes. The transfer of tetraethylammonium (TEA+), potassium (K+) and protonated piperidine (Hpip+) cations was studied by cyclic voltammetry at −15.0°C. All the half-wave potentials of these ion transfers shift in the negative direction in the frozen electrolyte system compared with the transfers from the liquid aqueous solution with the same composition at 25.0°C, and some transfers from the frozen phase exhibit slight irreversibility. The degree of the negative shift increases in the order TEA+ < Hpip+ < K+. An interfacial redox reaction between the Fe(III)(CN)3−6Fe(II)(CN)4−6 couple in the frozen aqueous phase and the ferrocene/ferricenium cation couple in the DCE phase was studied at −15.0°C, and the half-wave potential of this reaction (the electron transfer across the interface from the aqueous to the organic DCE phase) was also more negative than that of the liquid aqueous system at 25.0°C. The size of this shift is between those of TEA+ and Hpip+. The shifts in the half-wave potential are discussed in detail, considering a microscopic structure of water molecules near an ion and a network structure of bulk water associated through hydrogen bonds.

Electrospray mass analysis of chemical oxidation of 1,2-diarylcyclopropanes by Cu(II) salt

Electrospray ionization mass spectrometry was used to study chemical electron-transfer reactions of 1,2-diarylcyclopropanes by Cu(II) salt in acetonitrile. The ion [M − H]+ with a hydrogen atom loss and the solvent adduct ions, [M+42]+, etc., were detected as the initial reaction products, where [M+42]+ represents the ion whose mass is 42 u greater than the parent molecule M. From the study of deuterated derivatives, the hydrogen abstraction was revealed to occur at the 3 position of the cyclopropanes, and the mechanism of the hydrogen abstraction reaction and of the solvent addition were discussed.

Mass transfer of acetylacetone, ethylene glycol mono-n-butyl ether and ethylene glycol monophenyl ether across water-carbon tetrachloride and water-chloroform interfaces

Abstract The interfacial mass transfer kinetics of acetylacetone (acac), ethylene glycol mono- n -butyl ether (EGBE) and ethylene glycol monophenyl ether (EGPE) across water-carbon tetrachloride (Ccl 4 ) and water-chloroform (CHCl 3 ) interfaces were studied by stirring the two phases at various speeds, maintaining a quiescent interface with a constant area. In the analysis of data, two rate-determining steps consisting of a diffusion toward the interface and a mass exchange between the interface and bulk phases are considered. It is shown that the transfer of EGBE and EGPE in both CHCl 3 and Ccl 4 systems is controlled by the diffusion step even at high stirring speeds, whereas the transfer of acac in Ccl 4 is controlled by the interfacial exchange step at high stirring speeds. An irreversible transfer has been also observed in the EGBE and EGPE systems at low stirring speeds.

Transfer of trifluoroacetylacetone across a water/1,2-dichloroethane interface

Abstract The ion transfer of 1,1,1-trifluoroacetylacetone (HTAA) across a water/1,2-dichloroethane interface has been studied at various pH values, using current-scan polarography at the ascending water electrode, and a cathodic wave caused by the transfer of TAA − from the aqueous to the organic phase has been observed. Experiments have been carried out with two different types of addition of HTAA; one is the addition to the organic phase and the other to the aqueous phase. Although the anodic wave appears with both additions, the limiting current and the half-wave potential depend on the pH differently. Their dependences have been ascribed to the following: (1) the slow keto-enol tautomerization rate of HTAA; (2) the existence of TAA 2− hydrate anion; (3) some branch diffusions from the interfacial region to the bulk phase. The p K a2 value of HTAA has been determined to be 9.2.

Mixed Monolayer and Micelle Formation of Cationic and Zwitterionic Surfactant of Identical Hydrocarbon Tail in an Aqueous Medium: Interfacial Tension, Fluorescence Probe, Dynamic Light Scattering, and Viscosity Studies

We have studied the properties of the mixed monolayers and the mixed micelles formed from the mixture of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and the zwitterionic surfactant dimethyldodecylammoniopropanesulfonate (DPS), that have the identical hydrocarbon tail but different polar head groups, by measuring interfacial tension, fluorescence, dynamic light scattering (DLS), and viscosity. From the results of interfacial tension measurements, the various interfacial and bulk parameters such as the maximum surface excess, the surface pressure at the critical micellar concentration, and the standard free energies of interfacial adsorption and of micellization have been evaluated. The deviation from the ideal of the mixed micelles has been discussed on the basis of Clint theory. The interaction parameters in the mixed micelles and in the mixed monolayers, and also the compositions of the mixed micelles and the mixed monolayers were obtained with the help of regular solution theory. From a static fluorescence quenching method, the mean micellar aggregation number of pure and mixed micelles was obtained. Microviscosity in the pure and mixed micelles was monitored by fluorescence polarization measurements using Rhodamine B (RB) as a fluorescence probe. The hydrodynamic radii of the micelles were obtained in the mixtures at different mole fractions of surfactant from DLS measurements. The change of viscosity with α of DTAB revealed a minimum, and it was shifted to a higher αvalue in the mixture of high concentration of surfactant. This minima suggested a structural change in the mixed micelles.