PIPERIDINE, PIPERIDONES AND TETRAHYDROTHIOPYRONES AS INHIBITORS FOR THE CORROSION OF COPPER IN H2SO4

The effect of piperidine (P), few piperidones [2,6-diphenylpiperidin-4-one (2,6-DPP); 3-methyl-2,6-diphenylpiperidin-4-one (3-Me-2,6-DPP); 2,2-dimethyl-6-phenylpiperidin-4-one (2,2-DMe-6-PP); N-chloro-2-6-diphenylpiperidin-4-one (N-Cl-2,6-DPP)] and the cis and trans forms of 2,6-diphenyltetrahydrothiopyran-4-one(cis-2,6-DP-4-THTP and trans-2,6-DP-4-THTP) on the corrosion of copper in sulphuric acid has been investigated by means of spectrophotometric measurements of the metal ions in solution and potentiostatic polarization method. The inhibition efficiency of these compounds has been found to decrease as follows: cis-2,6-DP-4-THTP (78%) > trans-2,6-DP-4-THTP approximately 3-Me-2,6-DPP approximately 2,6 DPP (68%) > P (60%) > 2,2-DMe-6-PP (55%) > N-Cl-2,6-DPP (42%). The inhibitors retard the corrosion process by blocking anodic reaction sites. The negative free energy of adsorption, the positive heat of adsorption and the decrease in apparent free energy of activation in the presence of inhibitors are suggestive of chemisorption of inhibitors on the surface. The inhibition efficiency of these compounds has been explained on the basis of structure dependent electron donor properties, mode of adsorption and stability of conformers in the cis and trans forms of 2,6-DP-4-THTP.