Síntese de (Tio)semicarbazonas e avaliação experimental e teórica da atividade anti-corrosão

Abstract

In this dissertation 30 compounds were synthesized, 15 of them belonging to the class of semicarbazones and 15 others belonging to the class of thiosemicarbazones, in order to assess their efficiency as corrosion inhibitors. Previously, the compounds were analyzed by Molecular Modeling, yielding information about structural properties that affect the efficiency of inhibition. All compounds were obtained with satisfactory purity and good yields, ranging between 44 and 96% (semicarbazones) and 53 and 95% (thiosemicarbazones). All compounds were characterized by IR, and most were also characterized by 1H and /or 13C NMR. Seventeen compounds, 10 thiosemicarbazones and 7 semicarbazones, were tested by spectrophotometric assay with ferrozine to assess their potential chelation. The results showed that all compounds can act as corrosion inhibitors, since all competed with ferrozine for complexation of Fe2+ ion. Eight compounds were tested against the corrosion of carbon steel AISI 1020 in 0.5% HCl solution. For this assessment the electrochemical technique Potentiodynamic Polarization was used. The results showed excellent percentages of corrosion inhibition, reaching a rate of 96.4% efficiency at the highest concentration, obtained for the compound p-hydroxy-m-methoxybenzaldehyde thiosemicarbazone. All assessment methodologies used (Molecular Modeling, potential chelating and Potentiodynamic Polarization) indicated the thiosemicarbazones as corrosion inhibitors more potent in comparison with the similar structure of semicarbazones. The experimental results, in all cases, confirmed the theoretical results previously obtained.