Design, synthesis, and characterization of allyl- and propargyl-functionalized phenolphthalein derivatives as corrosion inhibitors for carbon steel in 1 M HCl: electrochemical, surface, and theoretical studies.

The objective of this work is to synthesise new dipolarophiles derived from phenolphthalein and to evaluate their inhibitory effect on the corrosion of carbon steel in an acidic environment. These compounds were obtained by reacting phenolphthalein with various halogenated groups containing multiple bonds, such as propargyl bromide, allyl bromide and allyl metabromide. The structures of the synthesized products: 3,3-bis(4-(allyloxy)phényl)benzofuranone (PHA), 3,3-bis(4-((2-méthylallyl)oxy)phényl)benzofuranone (PHMA) and 3,3-bis(4-(prop-2-yn-1-yloxy)phényl)benzofuranone (PHP) were confirmed by IR, 1H NMR, 13C NMR and mass spectrometry. To evaluate their anticorrosive effectiveness, electrochemical techniques, including potentiodynamic polarization and electrochemical impedance spectroscopy, were used, in addition to SEM/EDX surface analyses. In addition, density functional theory (DFT) was used to better understand the mechanisms of interaction between the inhibitors and the metal surface. The results obtained show that the synthesized dipolarophiles significantly reduce the corrosion rate, reaching 91.71%, 91.22% and 88.84% at 10-4 M for PHMA, PHA and PHP, respectively. The adsorption of these inhibitors follows the Langmuir isotherm and involves a chemisorption mechanism. Finally, the study of the effect of temperature reveals that the inhibitory performance of these compounds is maintained at high temperatures.