www.scholarsresearchlibrary.com t Available online a Scholars Research Library Der Pharmacia Lettre, 2016, 8 (4):96-107 (http://scholarsresearchlibrary.com/archive.html) ISSN 0975-5071 USA CODEN: DPLEB4 96 Scholar Research Library Evaluation of corrosion inhibition of mild steel in 1.0 M HCl by Sulfathiazole: Experimental and theoretical studies M. Saadouni 1 , M. Larouj 2 , R. Salghi 3* , H. Lgaz 2,3 , S. Jodeh 4* , M. Zougagh 5,6 and A. Souizi 1 1 Laboratory of Organic, Organometallic and Theoretical Chemistry, Faculty of Science, Ibn Tofaïl University, 14000 Kenitra, Morocco 2 Laboratory Separation Processes, Faculty of Science, University IbnTofail PO Box 242, Kenitra, Morocco 3 Laboratory of Applied Chemistry and Environment, ENSA, Université Ibn Zohr, PO Box 1136, 80000 Agadir, Morocco 4 Department of Chemistry, An-Najah National University, P. O. Box 7, Nablus, Palestine 5 Regional Institute for Applied Chemistry Research, IRICA, E-13004, Ciudad Real, Spain 6 Castilla-La Mancha Science and Technology Park, E-02006, Albacete, Spain _____________________________________________________________________________________________ ABSTRACT The inhibition effect of sulfathiazole (STZ) on the corrosion inhibition of mild steel in 1.0 M HCl solution was studied by polarization, EIS, weight loss measurements and quantum chemical calculation. It was found that the inhibitor was effective and the inhibition efficiency was significantly increased with increasing concentration. Polarization curves revealed that the used inhibitor represent mixed-type inhibitor. Adsorption of the inhibitor led to a reduction in the double layer capacitance and an increase in the charge transfer resistance, and was found also to obey Langmuir isotherm. A good correlation between theoretical data and experimental data has been obtained. Keywords: Corrosion inhibition; DFT; Sulfathiazole; HCl; EIS, Polarization _____________________________________________________________________________________________ INTRODUCTION Corrosion inhibitors are of great practical importance, being extensively employed in minimizing metallic waste in engineering materials. The wide spread use of mild steel in a variety of petroleum applications, such as down hole tubular, flow lines and transmission pipelines are well known[1–[6]. Hydrochloric acid solutions are widely used in petroleum fields, for cleaning and descaling of iron and steel alloys[7–10]. The use of inhibitors is one of the best- known methods of corrosion protection[11, 12]. Organic compounds used as inhibitors act through a process of surface adsorption, so the efficiency of an inhibitor depends not only on the characteristics of the environment in which it acts, the nature of the metal surface and electrochemical potential at the interface, but also on the structure of the inhibitor itself, which includes the number of adsorption active centers in the molecule, their charge density, the molecule size, the mode of adsorption, the formation of metallic complexes and the projected area of the inhibitor on the metal surface[13–19]. The use of theoretical parameters presents two main advantages: firstly, the compounds and their various fragments and substituents can be directly characterized based on their molecular structure only; and secondly, the proposed mechanism of action can be directly accounted for in terms of the chemical reactivity of the compounds under study[20-23]. In the present paper, in order to obtain as effective inhibitor, sulfathiazole have been studied by electrochemical techniques to investigate electrochemical behaviour of mild steel in 1.0 M HCl solution. Theoretical investigation of studied compound were also described by DFT method. Fig. 1 show the molecular structure of studied inhibitor: