QUANTUM CHEMICAL STUDY ON RELATIONSHIP BETWEEN STRUCTURE OF SOME THISEMICARBAZIDE AND TETRAZOLE DERIVATIVES AND THEIR INHIBITION PERFORMANCE

Semicarbazide, known as carbohydrazide, is the chemical compound with the formula OC(NH2)(N2H3). It is a water-soluble white solid. It is a derivative of urea prepared by treating urea with hydrazine. A thiosemicarbazide is the analog with sulfur atom in place of oxygen atom. Semicarbazones are derived by the condensation reaction between a ketone (or aldehyde) and a semicarbazide. Thiosemicarbazide derivatives were tested as corrosion inhibitors for steel in HCl, HNO3 environments, however, very little work was published on copper in chloride environments. In the present work, relationships between corrosion inhibition efficiency of two thiosemicarbazide and based compounds namely; 4-phenyl thiosemicarbazide (PTSC), Salicylaldehyde thiosemicarbazone (STSC) and one tetrazole derivative; 5-phenyl-1-H-tetrazole (PTAH), and their molecular electronic properties have been theoretically studied at the level of DFT/B3LYP with 6- 31+G (2d, 2p) base sets. These compounds are also tested as corrosion inhibitors for copper in sea water using polarization techmiques. The structural parameters, such as energy, highest occupied molecular orbital (HOMO) energy and lowest unoccupied molecular orbital (LUMO) energy, the charge distribution of the studied inhibitors, the absolute electronegativity (????) values were calculated and discussed using linear regression analysis to determine the most effective parameters to establish inhibition efficiency. The calculated and experimentally measured inhibition efficiencies (Table 1) show that PTAH posses the highest inhibition efficiency (93%), followed by TSCS (81%), while PTSC gives very low inhibition efficiency (16%). The table shows an agreement between the theoretical and experimentally measured inhibition efficiencies.