Inhibitive properties and quantum chemical studies of 1,4-benzothiazine derivatives on mild steel corrosion in acidic medium

4-benzyl-2-substituted-[1,4]-benzothiazin-3-one derivatives (p3 and p4),were synthesized from 2-substituted-[1,4]-benzothiazin-3-one. the structures of all newly synthesized compounds were elucidated by elemental analysis,1h-nmr and 13c-nmr. adsorption of compounds (p3 and p4) on mild steel surface in 1 m hcl solution and its corrosion inhibition properties has been studied by a series of techniques,such as polarization,electrochemical impedance spectroscopy (eis),weight loss and quantum chemical calculation methods. the experimental results suggest that these compounds are an efficient corrosion inhibitors and the inhibition efficiency increases with the increase in inhibitors concentration. adsorption of these compounds on mild steel surface obeys langmuir's isotherm. correlation between quantum chemical calculations and inhibition efficiency of the investigated compounds are discussed using the density functional theory method (dft).