Synthesis and anticorrosion properties of N-aryl-N1-pyridylthioureas and their benzylated products

N-Phenyl-, 1- and 2-naphthyl-N1-2- and 4-pyridylthioureas were synthesized via the reaction of phenyl-, 1- and 2-naphthylisothiocyanates with 2- and 4-aminopyridines, and the corresponding pyridine salts were prepared by benzylation of the latter. The anticorrosive properties of the synthesized compounds were studied by the gravimetric method in 3 M HCl at 800C using the 08 kp steel samples. The introduction of a benzyl fragment into the structure of N-aryl-N1-pyridylthioureas led to the emergence of a new adsorption ammonium center, which increased the overall anti-corrosion efficiency of the obtained compounds. When using N-aryl-N1-pyridylthioureas, the corrosion inhibition coefficient had the values of 4.5 to 59.0, whereas it increased to 90.8-629.0 for their salts. To explain the different anti-corrosion activity of N-aryl-N1-pyridylthioureas and their pyridine salts, quantum-chemical calculations of the energy parameters ЕНОМО, ЕLUMO and Е=ЕLUMO–EHOMO were carried out and the dependences of the corrosion inhibition coefficients on EHOMO and E, eE were obtained. A correlation was established between the inhibitory efficiency and energy parameters of the studied compounds.