Pyrrolidine-based quaternary ammonium salts containing propargyl and hydrophobic C-12 and C-16 alkyl chains as corrosion inhibitors in aqueous acidic media

Abstract

A new series of industrially relevant pyrrolidine based quaternary ammonium salts containing propargyl motif and hydrophobic C-12, C-16 alkyl chains were synthesized in excellent yields and evaluated for mild steel corrosion in 1 M HCl. FT-IR, NMR, and TGA were analyzed to characterize these corrosion inhibitors. The performance of these corrosion inhibitors was examined by gravimetric weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and theoretical calculations using density functional theory (DFT) methods. The surface morphology of mild steel samples was studied by UV–vis spectroscopy, scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). Results revealed that the inhibition capabilities of corrosion inhibitors N, N-dipropargylpyrrolidium bromide (DPPB), N-dodecyl, N-propargylpyrrolidium bromide (DDPPB), N-hexadecyl, N-propargylpyrrolidium bromide (HDPPB) are concentrations, immersion time and temperature-dependent, and found to be very good inhibitors even at a meager concentration of 60.3 μmol L−1 with an efficiency value 92.6, 93.7, and 96.2%, respectively. The inhibition efficiency order of these corrosion inhibitors, as shown by gravimetric and electrochemical studies, is as follows: HDPPB > DDPPB > DPPB. The inhibition efficiencies obtained from gravimetric weight loss, PDP, and EIS measurements are in good agreement. The thermodynamic parameters such as Ea, Kads, ΔG°mic, and ΔG°ads were determined. As compare to ΔG°mic, the more negative ΔG°ads values suggested favorable adsorption over the micellization. The critical micelle concentration (CMC) values of DPPB, DDPPB, and HDPPB were found to be 35.5, 31.8, and 30.0 mmol L−1. At CMC, the percent surface coverage was ≈90%, revealed that the monolayer formation by the inhibitor molecules at the metal/solution interface is almost complete before the concentrations reach their CMC values. Electrochemical studies suggested that corrosion inhibitors DPPB and DDPPB act as a mixed type with predominantly cathodic inhibitors, while HDPPB serves as a cathodic inhibitor. Surface analysis by UV–vis spectroscopy, SEM, and XPS supported the adsorption of inhibitor molecules on the mild steel surface. The DFT analysis is in good agreement with the experimentally obtained results on the molecular structure and adsorption strength.