Synthesis, electrochemical and quantum chemical studies of new pyrido[2,3-d]pyrimidine derivatives incorporating sulfonamide moiety

7-Thioxopyrido[2,3-d]pyrimidine derivative 5 bearing sulfonamide moiety was synthesized from the reaction of 2-amino-4-(4-chlorophenyl)-5-cyano-N-(4-sulfamoyl phenyl)-6-thioxo-1,6-dihydropyridine-3-carboxamide (3) with either dimethyl-formamide dimethylacetal (DMF-DMA) or triethyl orthoformate. The reaction of 5 with different halo-compounds afforded 7-thioalkylpyrido[2,3-d]-pyrimidine derivatives 8a-e. Potentiodynamic polarization and scanning electron microscopy techniques were used to examine the efficacy of pyridopyrimidine derivatives (5, 8A, 8B, 8C, 8D, and 8E) on mild steel corrosion in 1.0M H₂SO₄. The current density increases without inhibitors (blank solution) than the presence. Among the compounds tested, compound 5 had the highest inhibitory effectiveness, with a value of 94.15% at 200 ppm. Adsorption of the inhibitors onto the surface of the mild steel was governed by physical electro forces according to the Langmuir adsorption isotherm. The electrochemical descriptors emphasize that all the tested compounds act as mixed-type inhibitors. The activity of the inhibitors used in this study was discussed according to quantum chemical calculations of the pyridopyrimidine derivatives. From the results, the experimental data are in agreement with theoretical parameters. The scanning electron microscope was examined for the morphology of mild steel in the absence and presence of the best compound (5) that has high inhibition efficiency.