Journal of the Taiwan Institute of Chemical Engineers 49 (2015) 229–239 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice 2-Aminobenzene-1,3-dicarbonitriles as green corrosion inhibitor for mild steel in 1 M HCl: Electrochemical, thermodynamic, surface and quantum chemical investigation Chandra Bhan Verma a , M.A. Quraishi a,∗ , Ambrish Singh b a Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India b State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China article info Article history: Received 13 August 2014 Revised 27 October 2014 Accepted 30 November 2014 Available online 23 December 2014 Keywords: Mild steel Acid corrosion EIS SEM/EDX Quantum chemical calculation abstract The three 2-aminobenzene-1,3-dicarbonitriles derivatives (ABDNs) namely 5 ′ -amino-2,4-dihydroxy-4 ′′ - methyl-1,1 ′ :3 ′ ,1 ′′ -terphenyl-4 ′ ,6-dicarbonitrile (ABDN-1), 5 ′ -amino-2,2 ′′ ,4-trihydroxy-1,1 ′ :3 ′ ,1 ′′ -terphenyl- 4 ′ ,6 ′ -dicarbonitrile (ABDN-2) and 5 ′ -amino-2,3 ′′ ,4-trihydroxy-1,3-methoxy,1 ′ :3 ′ ,1 ′′ -terphenyl-4 ′ ,6 ′ - dicarbonitrile (ABDN-3) were synthesized and their corrosion inhibition properties on mild steel in 1 M HCl were investigated using weight loss and electrochemical techniques. Among the compounds investigated, ABDN-3 exhibited the best inhibition efficiency of 97.83% at 100 mg/L. Scanning electron microscopy (SEM) and dispersive X-ray spectroscopy (EDX) examinations was performed on inhibited and uninhibited mild steel samples to show the presence of ABDNs on mild steel surface. The potentiodynamic polarization studies reveal that all three studied inhibitors were of mixed type and their adsorption on the mild steel surface in 1 M HCl follows the Langmuir adsorption isotherm. Quantum chemical calculations studied were also performed to support weight loss and electrochemical experimental observations. © 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Mild steel and its alloys are commonly used for construction ma- terial in the petroleum, food, power production, chemical and elec- trochemical industries. However, mild steel is a reactive material and very sensitive to corrosion in acid media [1]. Because of the destruc- tive and corrosive nature of acid solutions, the use of inhibitors to control the destructive attack of acid environment was found to have widespread applications in many industries [2]. Most of the well known inhibitors are organic compounds containing heteroatoms in- cluding nitrogen, sulfur, and/or oxygen atoms and heterocyclic com- pounds in polar groups such as carbonyl, sulfur, nitrogen, amino, ni- trile group and conjugated double bonds [3–5]. The selection of such compounds based on the fact that these compounds contain a better π electron conjugation and heteroatoms (N, O), responsible for effec- tive adsorption properties. The adsorb inhibitor film blocks the active sites present on mild steel surface, thereby isolates the mild steel from corrosive attack. The literature survey revealed that only few ∗ Corresponding author. Tel.: +91 9307025126; fax: +91 542 2368428. E-mail address: maquraishi.apc@itbhu.ac.in, maquraishi@rediffmail.com (M. Quraishi). carbonitriles and similar compounds [6–9] were utilized as corrosion inhibitors. Recently quantum chemical calculations based on DFT theory have been developed to study the structural properties of inhibitor molecules and their reactivity toward metal surface [10]. The struc- tural parameters, such as the frontier molecular orbital, the energy of highest occupied molecular orbital (E HOMO ), the energy of lowest un- occupied molecular orbital (E LUMO ), energy gap E (E HOMO – E LUMO ) and dipole moment (μ) are the common parameters which affect the molecular (electronic) interaction between inhibitor and metal surface. The microwave irradiation has gained a powerful rapid tool for transformation of verities of compounds including etherifica- tion, hydrolysis, addition, and rearrangement [11]. The application of microwave irradiation has several advantages over convention synthesis such as: uniform heating occurs throughout the mate- rial, reaction rate is increased, high reaction yield, higher atom economy, higher purity of product, improve reproducibility, envi- ronmental heat loss can be reduced, reduce wastage of heating reaction vessel and low operating cost [12]. We herein describe the synthesis of three novel 2-aminobenzene-1,3-dicarbonitrile derivatives namely 5 ′ -amino-2,4-dihydroxy-4 ′′ -methyl-1,1 ′ :3 ′ ,1 ′′ - terphenyl-4 ′ ,6 ′ -dicarbonitrile (ABDN-1), 5 ′ -amino-2,2 ′′ ,4-trihydroxy- 1,1 ′ :3 ′ ,1 ′′ -terphenyl-4 ′ ,6 ′ -dicarbonitrile (ABDN-2) and 5 ′ -amino-2, 3 ′′ , http://dx.doi.org/10.1016/j.jtice.2014.11.029 1876-1070/© 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.