An Exemplar Imidazoline Surfactant for Corrosion Inhibitor Studies: Synthesis, Characterization, and Physicochemical Properties

Abstract

An optimized one‐pot recipe has been developed to synthesize a surfactant molecule, referred to as OMID, consisting of an imidazoline head group and aliphatic tail, which is an exemplar corrosion inhibitor for carbon steel in acidic solutions. As evidenced by gas chromatography, 1H and 13C nuclear magnetic resonance, and Fourier‐transform infrared data, a high‐purity product was achieved without the use of either a solvent or catalyst. Critical micelle concentration values and corrosion inhibition efficiencies ( η%) were determined in aqueous solutions of hydrochloric acid and sulfuric acid using surface tensiometry and linear polarization resistance measurements, respectively. Hydrolysis of the imidazoline head group as a function of pH (0–11) was explored with ultraviolet–visible absorption spectroscopy. In addition, N 1s and C 1s X‐ray photoelectron spectroscopy data were acquired from both surface‐adsorbed OMID and a multilayer of the imidazoline head group of OMID. These latter data are highly relevant to those attempting to understand OMID inhibition chemistry.

Corrosion inhibition in acidic environments: key interfacial insights with photoelectron spectroscopy

“…5 GL(30) functions, each having a full width at half maximum (FWHM) of ∼1.2 eV, were required to achieve a satisfactory fit to the data. As discussed previously 8,9 and illustrated in Fig. 5, this fit can be reconciled with the adsorption of OMID in two different singly protonated (OMIDH + ) forms, where either the primary amine (–NH 2 → –NH 3 + ) or imine (CN– → CNH + –) is protonated.…”

“…5, this fit can be reconciled with the adsorption of OMID in two different singly protonated (OMIDH + ) forms, where either the primary amine (–NH 2 → –NH 3 + ) or imine (CN– → CNH + –) is protonated. We note that OMID is expected to be doubly protonated, –NH 3 + plus CNH + –, in bulk solution in both 1 M HCl and 0.01 M H 2 SO 4 ; 8 the tertiary amine group (–N) remains unprotonated. Hence, adsorption results in a reduction in the degree of protonation, i.e.…”

“…OMID (97.7% purity) was synthesised in our laboratories; see ref. 8 for details of the synthetic route. The CMC of OMID in each acidic solution was determined through pendant drop surface tensiometry, using a Krüss GmbH Drop Shape Analyzer, DSA100.…”

“…Previous studies have demonstrated that OMID is a very efficient corrosion inhibitor for carbon steel in acidic solution. 5–8 Moreover, we have already applied XPS to characterise the interaction of OMID with carbon steel in 1 M HCl, concluding that the well-inhibited interface comprises OMID bound to film-free substrate, i.e. , there is no surface oxide/salt phase.…”

“…Previous studies have demonstrated that OMID is a very efficient corrosion inhibitor for carbon steel in acidic solution. [5][6][7][8] Moreover, we have already applied XPS to characterise the interaction of OMID with carbon steel in 1 M HCl, concluding that the well-inhibited interface comprises OMID bound to lm-free substrate, i.e., there is no surface oxide/salt phase. 9 Furthering this work, in the following sections we present a study exploring the impact of varying the composition of the acidic solution (see Table 1 for a list of the solutions) on both the corrosion inhibition performance of OMID at the critical micelle concentration (CMC), † and the nature of the interface derived from XPS data; we focus on measurements at the CMC, as it is expected that OMID should perform optimally at this concentration.…”