Abstract--The effect of pipcridine (P), few piperidones [2,6-diphcnylpiperidin-4-onc (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-CI-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 spectrophotomctric measurements of the metal ions in solution and potcntiostatic polarization method. The inhibition efficiency of these compounds has becn found to decrease as follows: cis-2,6-DP-4-THTP (78%) > trans-2,6-DP-4-THTP -3-Me-2,6-DPP --2,6 DPP (68%) > P (60%) > 2,2-DMe-6-PP (55%) > N-CI-2,6-DPP (42%). The inhibitors rctard the corrosion process by blocking anodic reaction sites. The negative frec energy of adsorption, the positive heat of adsorption and the decrease in apparent free energy of activation in the presence of inhibitors arc 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.

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