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Theoretical Study of Chloro-N-(4-methoxybenzylidene)aniline Derivatives as Corrosion Inhibitors for Zinc in Hydrochloric Acid

DOI: 10.1155/2013/819643

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The density functional theory (DFT) was used to investigate the corrosion inhibition of three inhibitors on zinc. Quantum chemical parameters such as the energy of highest occupied molecular orbital ( ), the energy of lowest unoccupied molecular orbital ( ), energy gap , hardness , softness , electrophilicity index , the fraction of electrons transferred from inhibitor molecule to the metal surface, energy change when both processes occur, namely, charge transfer to the molecule and backdonation from the molecule ( ), natural charge , and Fukui functions have been calculated by using B3LYP/6-31+G(d) basis set. The relation between the inhibition efficiency and quantum chemical parameters has been discussed in order to elucidate the inhibition mechanism of the chloro-N-(4-methoxybenzylidene)aniline derivatives. 1. Introduction Quantitative structure activity relationship (QSAR) has been a subject of intense interest in many disciplines of chemistry. In addition, the results of quantum chemical calculations are obtained without laboratory measurements, thus saving time and equipment and alleviating safety and disposal concerns [1, 2]. Density functional theory (DFT) has a potential application towards the design and development of organic corrosion inhibitors in corrosion field [3]. These facts have made quantum calculations to be very powerful tool for studying corrosion inhibition mechanism. Zinc is one of the most vital nonferrous metals having extensive use in metallic coating [4]. The use of zinc sheets as roofing materials and in galvanization of steel makes the study of its corrosion an important theme [5]. Zinc is often attacked by aggressive media, such as acids, bases, and salt solutions [6–8]. In acidic solutions, zinc has high solubility and dissolves with the formation of Zn2+ ions. Since the solubility of zinc decreases with increasing pH in acidic solutions, precipitation of Zn(OH)2 occurs when a certain pH value is reached. In alkaline solutions, with , the solubility of zinc increases with increasing pH, and in the high pH range, zinc oxide and hydroxides tend to dissolve with the formation of zincate ions. Zinc oxide is a common corrosion product in diluted solutions of salts such as NaCl or Na2SO4 with zinc hydroxide present in various amounts as a minor component. For scale removal and cleaning of zinc surface with acid solutions, the use of organic inhibitors is one of the most practical methods for protection against corrosion, especially in acidic media [9–13]. The aim of this work is to study the effect of quantum chemical

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