Two PcSn(IV) dicarboxylate molecules were obtained through efficient microwave methodology with the aim to test them as corrosion inhibitors in the oil industry. The compounds were characterized by elemental analysis, IR, UV-vis, (1)H, (13)C NMR, and X-ray diffraction. The relative configuration of the two carboxylates is cis, placing the fatty acid moieties on the same face of the phthalocyanine macrocycle. In the solid-state the tin atoms possess square antiprismatic octacoordinated geometries. Both tin phthalocyanines were tested as corrosion inhibitors for hydrogen sulfide corrosive media showing a chemisorption process of the nanocap motifs on the metallic surface. Apparently, the length of the hydrophobic chain contributes significantly to the inhibition efficiency, in the sense that shorter chains increase the efficiency.
The development of a methodology to predict the performance of a corrosion inhibitor (CI) using specific types of modeled and experimental surfaces and their subsequent estimation is presented. For previously reported imidazoline CIs, the theoretical partition coefficients and molecular volumes were calculated, providing a guide for molecular engineering of new imidazolines. The new CIs, N-[2-(2-alkyl-4,5-dihydroimidazol-1-yl)ethyl]alkylamides and N-[2-(2-alkyloylaminoethylamino)ethyl]alkylamides, were designed, prepared, and their theoretical partition coefficients and molecular volumes calculated. These indexes were correlated between tested and prototype CIs to select the best ones for the corrosion inhibition tests. The inhibition efficiencies were measured through potentiodynamic polarization curves (PPC), linear polarization resistance (LPR), and weight loss measurements (WLM) for SAE-1010 and SAE-1018 steels. The leading molecules were 1-(2-decylaminoethyl)-2-decylimidazoline and 1-(2-dodecylaminoethyl)-2-dodecylimidazoline with WLM efficiencies (steel 1010), of 62.8 and 78.9%, respectively. The efficiencies for the PPC/LPR tests (steel 1018) were 97 and 94%. To understand the mechanism of action of CIs, a simple model is suggested for the growth of self-assembled monolayers of CIs on a crystalline substrate. This model takes into account the amphiphilic nature of the inhibitor molecule on the adsorption process. Despite the simplicity of the model, the Monte Carlo simulations reproduce qualitatively many of the experimentally observed features involved in the formation of monolayers and provide a tentative explanation for the mechanism of corrosion inhibition.
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