Portugaliae
Electrochimica Acta

The influence of experimental parameters on the yields and stereochemistry of Wittig reaction was studied. The synthesis of stilbene initiated by different electrogenerated bases was used as a model reaction. Preparative electrolyses were carried out in different conditions including constant potential or constant current with different electrode materials and using solvents of different polarity. Both the yield and the stereochemistry of the reaction are affected by the electrolysis experimental conditions. Hence, the proper selection of experimental conditions in Wittig reactions allows the choice of the stereosselectivity of the reactions and the optimization of yields.

Sb doped tin dioxide films were prepared by thermal decomposition of SnCI4.5H20 and SbCl3 mixtures applied on pre-treated Ti surfaces. Precursor solutions containing 20 % p/v SnCl4.5H20 and 0.1, 0.2 or 0.3%'p/v SbCl3 were used. The influence of Sb on film morphology and on electrochemical activity were assessed by SEM and cyclic voltammetry in solutions containing ferri-ferrocyanide couple, respectively. In general, the films were quite adherent to the substrate, with mud like cracked appearance when observed by SEM. Their conductivity increased with the SbCl3 content in the mixture. Organic oxidation at the Sn02-Sb205 interface was found to be in the same potential domain to that observed on Pt polycrystalline electrodes suggesting a common mechanism. Electrocatalytic performance was evaluated regarding the electroconversion of 3,4-dimetoxibenzoic and 3,4-dihidroxibenzoic acids, for a specific electrolysis condition.

In this paper, the use of digital simulation as a tool to understand electrochemical data is discussed. The various approaches to digital simulation of electrochemical processes will be reviewed, and some applications of these methods to the interpretation of experimental results are presented.

The Ibero-American Map of Atmospheric Corrosiveness (MICAT) project was set up in 1988 sponsored by the International Ibero-American Programme "Science and Technology for Development (CYTED)". Fourteen countries have been involved in the project: Argentina, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Mexico, Panama, Peru, Portugal, Spain, Uruguay and Venezuela. Research has been conducted both at laboratories and in a network of 72 atmospheric exposure test sites throughout the Ibero-American region, thus considering a broad spectrum of climatological and pollution conditions. This paper presents a summary of some of the results obtained in one-year atmospheric exposure testing of carbon steel, zinc, copper and aluminium: corrosion rate, morphology of attack of the base metal and of the corrosion products formed, their nature and electrochemical properties. The Thematic Network "Anti-Corrosion Protection of Metals in the Atmosphere" (PATINA) was constituted in Lisbon in December 1994, upon the finalization of the MICAT project. The network is participated by the fourteen countries mentioned above plus Bolivia. One of the main tasks of this network is to evaluate the corrosion protection behaviour of a wide range of conventional and advanced coatings in typical atmospheres of the Ibero-American region. This paper presents an overview of the organizational structure of the network and of the coating materials being studied.

The addition of tefra-alkylammonium salts, namely fefra-methylammonium, tefra-ethylammonium, tefra-butylammonium and tefra-hexylammonium salts, to the supporting electrolyte, in the presence of different metal ions, does not change the observed cathodic current for shorter carbon chains. However, an important effect is observed when n > 4 (number of carbon atoms of each chain). This is shown through the polarograms which were recorded for different solutions of cadmium, zinc and manganese ions, in the presence and absence of those ions. The interpretation based on electrocapillary curves has shown that electron transfer through the double-layer becomes more difficult as the length of the carbon chain increases. Polarographic and electrocapillary experiments were followed all over.

A comment from a reader of a paper on the definition of electrolyte and the author's reply is presented.

The use of in situ infrared (IR) vibrational spectroscopy on the elucidation at a molecular level of electrochemically induced phenomena, i.e., in situ IR spectroelectrochemistry, has been rapidly developing in the last two decades, since a pioneer work of Bewick et al., by using modulation and synchronous detection of the signal in external reflectance IR spectroscopy. In situ IR spectroelectrochemistry has been proved to be a powerful tool for investigation of the electrode solution interface, namely by providing information on the structural, bonding and dynamical properties of adsorbate species on electrode surfaces, on the behaviour of supporting electrolyte and solvent molecules at the electrochemical interface and also on reaction mechanisms and kinetics of electrocatalytic reactions. An overview of some theoretical aspects of IR reflectance spectroscopy is presented and experimental details of some in situ techniques are described, namely EMIRS (Electrochemically Modulated Infrared Reflectance Spectroscopy), SNIFTIRS (Subtractively Normalised Interfacial Fourier Transform Infrared Reflectance Spectroscopy) and SPAIRS (Single Potential Alteration Infrared Reflectance Spectroscopy). A few selected applications of these techniques to electrocatalysis are also presented.

The polarographic and voltammetric reduction of dithizone (1, 5-diphenylthiocarbazon, H2Dz, thiol form I) has been studied in Britton-Robinson buffers (pH 2.10-12.00) containing 50% ethanol at room temperature. The reduction of the compound takes place in single 2e- transfer, giving a diffusion controlled reversible wave in the entire pH range of the study corresponding to the reduction of the azo group. A mechanism is proposed for the reduction process of the compound.

Increased interest in highly conducting polymer electrolytes is clearly evident from the open literature, particularly on the specific area of energy-related applications. Poly(ethylene oxide), PEO, although well studied, continues to intrigue us and must still be regarded as playing a central role in polymer electrolyte research and development. Ion containing organic polymers involving essentially PEO as the solvent matrix are reviewed here. The greatest technological driving force for its continued study is still, by far, the desire for thin film rechargeable batteries that meet a multitude of ambitious energy, power density and safety requirements, while not being prohibitively expensive.

Using square- wave voltammetry at a static mercury drop electrode, a fast and simple method has been developed for the assay of the water-soluble vitaniins tliiamiiie hydrochloride, riboflavin, folic acid and nicotinamide. In Britton Robinson buffer (pll 9.5) by cathodic scan thiamine hydrochloride give a peak at -1.33 V, riboflavin give two peaks at -0.61 V and -0.73 V, folic acid gives a peak at -0.91V and nicotinamide give a peak at -1.74 V vs. Ag/AgCl reference electrode at the same buffer solution. These four vitamins can be determined by the same voltammogram. The reduction peak currents are linearly dependent on the concentration of the vitamins. The method is successfully applied to determine these four vitamins contents of multivitamin preparations simultaneously. The values found agreed well with those determined by other methods.

The electrochemical behaviour of the cyanometalate complexes [Fe(CN)e]4" [W(CN)8]4\ [Os(CN)6]4-, [Mo(CN)8]4" and [Ru(CN)6]4" is investigated at high concentrations of the corresponding potassium salts (0.6 M) in alkaline solution (pH = 13) by voltammetric measurements with a platinum microdisk electrode. Under these experimental conditions the electrode reactions are reversible and the half-wave potentials are about 130 mV more positive than the standard redox potentials of these couples. The analytical characteristics of voltammetric determinations at high concentrations of electroactive species are studied using K4[W(CN)g] as a model compound.

In the present study the voltammetric behaviours of some phenothiazines namely Promazine hydrochloride, Promethazine hydrochloride and Fluphenazine hydrochloride were investigated. And it was shown that the electro oxidation of the substances was dependent on the nature of the supporting electrolyte, pH, scan rate. The results of the statistical analysis revealed that the quantitative analysis of these substances could be made using glassy carbon electrode, activated by a simple electrochemical procedure, with good accuracy and precision.

Mercury film microelectrodes, prepared by potentiostatic electrodeposition of Hg(II) from an acidic solution onto a gold microdisk electrode, in combination with adsorptive stripping voltammetry in the presence of catechol were used to study the behavior of copper, iron and nickel in aqueous solutions. The voltammetric behavior of hydrogen ion was also investigated by performing cyclic voltammetry and stripping voltammetry with mercury microelectrodes.

The use of some p-substituted benzoic acid derivatives as low cost inhibitors for the corrosion of aluminium in 60% H3PO4 solution was explored by weight loss and galvanostatic polarization measurements. The inhibition efficiency of the compounds increases in the order: p-OH > P-NH2 > benzoic acid > p-Br > p-N02- This order is not affected by the variation in temperature in the range 30-60 °C. Rate of corrosion is affected by both concentration of inhibitors and the temperature of the medium. The reaction rate was found to be proportional to the absolute value of Hammett constant (a). Some thermodynamic functions were computed and are discussed. Key words: Corrosion, aluminium, polarization, weight-loss measurements.

Basic concepts of electrochemistry are not yet properly understood in areas related with technical aspects where this science is fundamental, such as corrosion. Examples of this are given here with the objective of alerting electrochemists for the need to give their collaboration in technical bodies (e.g. ISO, CEN, OIML [1]) where it is useful to complement the very important technical knowledge of applied experts on the relevant field (e.g. corrosion) with fundamental knowledge of electrochemistry.

The effect of some 4-amino-4' -nitroazobenzene derivatives as corrosion inhibitors for copper in nitric acid solution at 30 °C was investigated using thermometric and polarization techniques. The corrosion rate was found to be a function of the nature, of inhibitor and temperature of the medium. The calculated degree of concentration surface coverage was used to evaluate the free energy of adsorption (A G°a) of the process. All the inhibitors follow the Frunkin adsorption isotherm. The mechanism of inhibitor action has been discussed on the basis of adsorption and molecular polarizahility of the inhibitors. The observed experimental data indicate that these compounds act as mixed inhibitors. Some thermodynamic function was calculated and discussed. Key words: Corrosion, inhibitors, acid solution, copper, dyes.

A recent survey of secondary school pupils' attitudes to chemical formulae show interesting similarities with the attitudes of XIX century scientists to the formulae system developed by Berzelius (the basis of the present system). Dalton's opposition to this system, Children's alterations of a Berzelius original when translating it to English, a fact praised by contemporaries, and other objections of the time are compared with today's secondary school pupil’s comments collected in a recent study. These comparisons make it easier to understand the difficulties in teaching formulae at school.

The open-ended capillary cell has been used as a reliable method to measure mutual differential diffusion coefficients of a great variety of aqueous solutions of electrolytes [1, 2]. In the last few years we have been developing, with some success, a capillary cell capable of measuring thermodynamic diffusion coefficients of electrolytes imbibed in polymeric matrices [3-5]. We have developed two different systems, called "manual" and "automatic", to measure diffusion coefficients. In this communication we will present an improvement of the "manual" system that permit us to measure a large range of concentrations, from approximately 10 M until at least 2 M, with very good precision, and accuracy.