www.derpharmachemica.com t Available online a Scholars Research Library Der Pharma Chemica, 2015, 7(9):354-367 (http://derpharmachemica.com/archive.html) ISSN 0975-413X CODEN (USA): PCHHAX 354 www.scholarsresearchlibrary.com Effect of 1,5-dibenzyl-1H-pyrazolo[3,4-d]pyrimidine-4(5H)-thioneoninhibition of mild steel corrosion in 1M HCl Y. El Ouadi 1 , M. Elfal 2 , A. Bouyanzer 1 , H. Elmsellem 1* , Y. Ramli 3 , E.M. Essassi 2 , N. Lahhit 1 , A. Aouniti 1 , A. Chetouani 1,4 and B. Hammouti 1 1 Laboratoire de Chimie Appliquée et environnement (LCAE-URAC18), Faculté des Sciences, 60000 Oujda, Morocco 2 Laboratoire de Chimie Organique Hétérocyclique, URAC 21, Pôle de Compétences Pharmacochimie, Université Mohammed V, Faculté des Sciences, Av. IbnBattouta, Rabat, Morocco 3 Medicinal Chemistry Laboratory, Faculty of Medicine and Pharmacy, Mohammed V, University-Rabat, Morocco 4 Laboratoire de chimie physique, Centre Régionale des Métiers de l'Education et de Formation ''CRMEF'', Région de l'Orientale, Oujda, Morocco _____________________________________________________________________________________________ ABSTRACT The inhibition effect of 1,5-dibenzyl-1H-pyrazolo[3,4-d]pyrimidine-4(5H)-thione‘‘MF1’’was estimated on the corrosion of mild steel in 1.0 M HCl solution using weight loss, Electrochemical Impedance Spectroscopy (EIS), Tafel polarization curves and theoretical calculation methods. The results of the polarization curves show that the corrosion current density decreases 577.9 µA/cm 2 to 38.5 µA/cm 2 after addition of the inhibitor. The charge transfer resistance increases 21.08 ohm.cm 2 to 402.2 ohm.cm 2 in the electrochemical impedance spectrum after addition of oil of the inhibotor.Potentiodynamic polarization curves show that 1,5-dibenzyl-1H-pyrazolo[3,4-d]pyrimidine- 4(5H)-thione act as mixed type inhibitor. The adsorption of inhibitors obeys the Langmuir adsorption isotherm, and the thermodynamic parameters (E a , K ads , ∆G 0 ads) were calculated and discussed. Quantum chemical calculations showed that the inhibitor has the tendency to be protonated in the acid and the results agree with experimental observations. Key words: corrosion, inhibition, mild steel,1,5-dibenzyl-1H-pyrazolo[3,4-d]pyrimidine-4(5H)-thione, electrochemical system, HCl 1M, DFT. _____________________________________________________________________________________________ INTRODUCTION Acid solutions are generally used for removal of undesirablescale and rust on the metals, cleaning of boilers and heat exchangers, oil-well acidizing in oil recovery, and so on. [1–4]. HCl solution is one of the most widely used agents for these goals. However, iron and its alloys could be corroded during these applications which result in a waste of resources. Corrosion prevention systems favor the use of chemicals with low or no environmental impacts. The reduction in the corrosion rate of metals has numerous advantages such as saving of resources, economic benefits during theindustrial applications, increasing the lifetime of equipment and decreasing the dissolution of toxic metals from the components into the environment. Therefore, the prevention of metals againstcorrosion is vital and must be dealt with. Commercial inhibitors are generally inorganic and some kind of organic compounds. However, the usage of some of them has been restricted due to the toxicity of their insufficient inhibitory efficiencies at low dosages [5–7]. In recent years, considerable amount of efforts have been devoted to find novel, healthy and efficient corrosion inhibitors. The use of organic inhibitors is one of the most practical methods for protection of metals against corrosion, and is becoming increasingly popular according to recent studies.