Portugaliae Electrochimica Acta

Cyclic Voltammetry and RRDE Studies on the Electrochemical Behavior of Azetidinone Ester

Azetidinone ester is the key intermediate during the synthesis of injectable cephalosporin compounds. This intermediate is undergoing electrochemical reaction during the process of conversion from penicillin to cephalosporin. The CV and RRDE studies clearly indicate that electro-reduction of this compound is taking place in three steps under the condition. The first two peaks correspond to the two, one electron transfers and the third one is due to the proton addition from the non-aqueous solvent. And during the process, the cyclisation is also taking place in order to neutralise the charge. Further CV and RRDE studies with the addition of small amount of water to the above system clearly confirm the mechanism. This was very well confirmed by the FTIR analysis of the product obtained from the bulk electrolysis.

Process Optimization Studies on Mediated Electrooxidation

The purpose of optimization consists in establishing suitable values for the operational parameters of a process, in order to achieve the results of that process to the greatest possible advantages. These ideal operating conditions are known as the optimum. The process parameters are current density, temperature, concentration, electrode materials, flow rate, cell voltage, mixing and diaphragm and engineering quantities are like current efficiency, space-time yield, energy consumption, yield and conversion. There are several possible targets in optimization of process and the main aim is to get maximum yield, high current efficiency, high purity and minimum energy consumption for mediated electrochemical oxidation. Mediated electro oxidation or indirect electrosynthesis is a cyclic process involving electrochemical generation of cerium(IV) and uses that agent to effect a chemical reaction. Cerium(IV) has attracted attention in electroorganic synthesis for synthesis of aldehydes and quinones.

Study of the Electrochemical Behaviour of Tolitriazole in Phosphating Bathings of Carbon Steel 1008

The characteristics of corrosion inhibitors of the tolitriazole (TTA) for the carbon steel 1008, covered by zinc or tricationic phosphate (Mn, Zn, Ni), in the means of H2SO4 0.1 mol L-1 and NaCl 0.5 mol L-1, were investigated by physical and electrochemical methods. The results obtained in the absence of the inibidor TTA showed that the corrosion protection properties of the tricationic phosphate (Ptri) are better than those observed for the zinc phosphate (PZn), probably due to the presence of vacancies in the layer of PZn. The curves of anodic polarization presented current densities (j) smaller for the steel phosphatized with Ptri, when compared with the metal substrate without phosphate and with PZn. The results of impedance electrochemistry (IE) showed a polarization resistance (Rp) larger for the electrodes phosphatized with Ptri. The electrochemistry measurements of the samples of steel phosphatized, with PZn and/or Ptri, in the presence of [TTA] = 1x10-3 mol L-1, present smaller j and larger Rp when compared with the absence of TTA. In the process of phosphatization of the carbon steel with PZn + TTA, it was observed similar j and Rp in the samples of steel phosphatized with Ptri without TTA. These results suggest that the bathing of zinc phosphate with [TTA] = 1x10-3 mol L-1 can substitute the well known industrial bathing of tricationic phosphate. Corrosion testing by Salt Spray of steel phosphatized with PZn and PZn + TTA, painted with white polyester ink, confirmed the eletrochemical results.

As características inibidoras de corrosão do tolitriazol (TTA) para o aço de carbono 1008, revestidos por fosfato de zinco ou tricatiônico (Mn, Zn, Ni) nos meios de H2SO4 0.1 mol.L -1 e NaCl 0.5 mol L-1, foram investigadas por métodos físicos e electroquímicos. Os resultados obtidos na ausência do inibidor TTA mostraram que as propriedades de protecção à corrosão do fosfato tricatiônico (Ptri) são melhores do que as observadas para o fosfato de zinco (PZn), provavelmente devido a porosidade existente na camada do PZn. As curvas de polarização anódicas apresentaram densidades de corrente (j) menores para as peças de aço fosfatizadas com Ptri quando comparadas aos dos substratos sem fosfato e com PZn. Os resultados de impedância electroquímica (IE) mostraram uma resistência de polarização (Rp) maior para os electrodos fosfatizados com Ptri. As medidas electroquímicas das amostras de aço fosfatizadas, com PZn e/ou Ptri, na presença de [TTA] = 1.10 -3 mol L-1, apresentaram j menor que Rp maior do que as observadas para as amostras de aço fosfatizadas na ausência do TTA. No processo de fosfatização do açocarbono com PZn + TTA, observou-se j e Rp semelhantes as observadas nas amostras de aço fosfatizadas com Ptri sem TTA. Estes resultados sugerem que o banho de fosfato de zinco contendo [TTA] = 1.10 -3 mol L-1 pode substituir o mundialmente consagrado banho industrial de fosfato tricatiônico. Os ensaios em câmara de Salt Spray de amostras de aço fosfatizadas com PZn e PZn + TTA, pintadas com tinta pó poliéster branca, confirmaram os resultados electroquímicos obtidos.

Development of a Voltammetric Method to Determine Molybdenum in Food Grains

It was developed a very sensitive analytical method to determine molybdenum in water and food grains, using the linear sweep voltammetry technique, with adsorptive preconcentration of a Mo(VI) 8-hydroxyquinoline complex, in an acetate buffer media of pH = 3.5 and KClO3 0.5 mol/L as a support electrolyte. The linear range of the methodology goes from 1.0 hg/L to 10 mg/L, with a limit of detection of 0.3 hg/L and quantification of 1.0 hg/L. The methodology is suitable in the range of mg/L and hg/L. The method was applied to grinded samples of rice, beans, lentil seeds and chickpeas with the following result: 6.2 mg/kg in lentil seeds, 6.0 mg/kg in chickpeas, 3.2 mg/kg in red beans, and 1.7 mg/kg in rice.

Se desarrolló un método analítico muy sensible, para determinar molibdeno en agua y granos, utilizando la técnica de voltamperometría de barrido lineal, con preconcentración adsortiva de un complejo de Mo(VI) con 8 hidroxiquinoleína, en un medio de buffer de acetato de pH = 3.5 y KCIO3 0.5 mol/L como electrolito soporte. El ámbito lineal del método va desde 1.0 ηg/L hasta 10 µg/L, con un límite de detección de 0.3 ηg/L y de cuantificación de 1.0 ηg/L. El método resulta adecuado en el ámbito de µg/L y ηg/L. Se aplicσ el mιtodo en muestras molidas de arroz, frijoles, lentejas y garbanzos y se logró cuantificar las siguientes cantidades: 6.2 mg/kg en lentejas, 6.0 mg/kg en garbanzos, 3.2 mg/kg en frijoles, y 1.7 mg/kg en arroz.

Development and Optimization of a Voltammetry Adsortive Method with Alizarine for Aluminium Determination in Water

Some of the aluminium complexes are electroactive at positive potentials, being necessary a carbon vitreous electrode to their quantitative determination. Nevertheless the aluminium alizarine complex could be measured at negative potential with a mercury hanging electrode, but this complex is not electroactive at negative potential; instead of that, the residual alizarin non complex could be measured. The kinetic complex is very slow, so it is necessary to heat at 80 0C, for five minutes. The study of experimental conditions of complex formation was established at pH 9.25 and is determinant in the complex formation; besides, the buffers employed should be of high regulatory capacity to obtain derivative formation. The optimization of the measurement experimental conditions was done by square wave voltammetry (SWV). Detection limit got using standard deviation of seven blank solutions was 3 mg /L, the variation coefficient was 8%, and the mean recovery for 16 mg /L was 97%. The calibration curves were done in a linear interval of 8 to 64 mg /L. The method application to water samples is possible after previous evaporation.

Algunos complejos de aluminio son electroactivos a potenciales positivos, siendo necesario un electrodo de carbón vítreo, para su determinación cuantitativa. Sin embargo el complejo de aluminio con alizarina se puede medir a potencial negativo, con un electrodo de marcurio de gota suspendida; el complejo de aluminio-alizarina no es electroactivo, y la alternativa es medir la alizarina residual después de la formación del complejo com aluminio, cuya cinética es muy lenta y debe calentarse 5 minutos a 80 º C. Se prodedió al estudio de las condiciones experimentales bajo las cuales se forma el complejo aluminio con alizarina, siendo el pH de 9.25 determinante; asimismo se encontró que el buffer debía ser de alta capacidad reguladora para obtener la formación del derivado. Se realizó la optimización de las condiciones experimentales de medición por la técnica de voltamperometría de onda cuadrada (SWV). El límite de detección obtenido a partir de la desviación estándar de 7 blancos fue 3 µg/L, y el coeficiente de variación 8%, la recuperación promedio para 16 µg/L fue de 97%. Las curvas de calibración se realizaron en un ámbito de 8 a 64 µg/L. La aplicación del método a muestras de agua es posible mediante la previa evaporación de las mismas.

Electrochemical Evaluation on Repairs with Mortars in Structures Affected by Chlorides Contamination

Inside the construction industry, in the area of sea water retention structures, the chlorides contamination is a main cause of the corrosion, because in the concrete they could form macro cells upon repairing and applying a mortar free of this ion, forming anodes in the repaired zones, and thus increasing corrosion. In the reinforcements are commonly formed corrosion products because the concrete is exposed to mechanical, physical, chemical or biological conditions that commit and shorten their performance. As a consequence, it is important to determine their useful life and that of the made repairs, using electrochemical techniques that allow determining the level of protection, the effect of the macro cells in the corrosive process of the reinforcement, and the mechanism of deterioration in the structures. The present work was carried out using six beams with preoxided reinforcements, six precracking and one beam blank. After curing, those beams were exposed to accelerated cycles of deterioration for causing the cracking of the concrete, making possible to observe their electrochemical behaviour. The tests carried out were corrosion potential and corrosion rate, through the resistance to the polarization technique.

Dentro del campo de la construcción, en el área de estructuras para retención de aguas marinas, la contaminación por clorurus es una causa principal de la corrosión, se pueden formar macroceldas al reparar y aplicar un mortero libre de este ión, produciéndose ánodos en las áreas de las zonas reparadas, y provocando con ello la corrosión. En el acero de refuerzo se forman productos de corrosión comúnmente porque el concreto esta expuesto a condiciones mecánicas, físicas, químicas o biológicas que comprometen y acortan su desempeño, por ello es importante determinar su vida útil y la de las reparaciones efectuadas, empleando técnicas electroquímicas que permitan determinar el nivel de protección, el efecto de las macroceldas en el proceso corrosivo del refuerzo, y el mecanismo de deterioro en las estructuras. En el presente trabajo se realizaron seis vigas preagrietadas, seis preoxidadas y una viga testigo, después del curado se expusieron a ciclos acelerados de deterioro para provocar el agrietamiento del concreto y observar su comportamiento electroquímico previo y posterior a su reparación. Las pruebas realizadas son: medición de potenciales de corrosión y velocidad de corrosión, empleando la técnica de resistencia a la polarización.