Synthèse de nouveaux précurseurs de porphyrines et application des dérivés substitués de phosphonium.

Abstract

In this work, two parts have been developed. The first is devoted to the synthesis, characterization and theoretical study of new meso-substituted dipyrromethanes. These compounds have been synthesized by a double Friedel-Crafts reaction from substituted pyrrole and aromatic aldehydes using iodine as a catalyst. The reaction is carried out in dichloromethane under stirring at room temperature. Ten novel substituted dipyrromethanes have been prepared with good yields in most cases within 21-98% and were characterized using 1H, 13C NMR, two-dimensional methods (HMBC, HSQC and COSY), UV, IR and mass spectrometry. Compound 2c has been structurally characterized by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, where supramolecular self-assembly of the compound is dominated by a variety of intermolecular interactions such as C–HO and C– Hπ. The role of weak intermolecular interactions in the crystal packing has been analyzed and quantified using Hirshfeld surface analysis. The geometric parameters, electronic transitions and theoretical frequencies for compound 2c were estimated at the DFT/B3LYP level of theory and compared to the experimental data. The second part was devoted to studying the effectiveness efficacy of two phosphonium salts in preventing corrosion on steel in a 0.5M H2SO4 solution. Two types of techniques were used: gravimetric and electrochemical methodes (potentiodynamic polarization analysis and electrochemical impedance spectroscopy). A series of experiments at various temperatures and inhibitor concentrations were conducted. For both compounds, the inhibition efficiency (%IE) increases steadily with the concentration of inhibitors. Both investigated inhibitors are mixed-type inhibitors, according to the PDP analysis. Additionally, according to the Langmuir adsorption isotherm model, the inhibitor molecules are reliably adsorbed on the steel surface, and the inhibitory effectiveness decreases slightly with temperature. The order of IE determined from experimental measurements is successfully supported by surfaces analysis. Interactions between inhibitors and the metallic surface was further studied using DFT method that give several computational parameters such as EHOMO, ELUMO, ΔE, χ, η, σ and ΔN.