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The methyl 2-(1,3-dithietan-2-ylidene)-3-oxobutanoate (MDYO) and 2-(1,3-dithietan-2-ylidene) cyclohexane-1,3-dione (DYCD) were synthesized and tested at various concentrations as corrosion inhibitors for 316L stainless steel in 1 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface analysis techniques (SEM/EDX and Raman spectroscopy) and Functional Density Theory (DFT) was also used to calculate quantum parameters. The obtained results indicated that the inhibition efficiency of MDYO and DYCD increases with their concentration, and the highest value of corrosion inhibition efficiency was determined in the range of concentrations investigated (0.01 × 10−3 – 10−3 M). Polarization curves (Tafel extrapolation) showed that both compounds act as mixed-type inhibitors in 1M HCl solutions. Electrochemical impedance spectra (Nyquist plots) are characterized by a capacitive loop observed at high frequencies, and another small inductive loop near low frequencies. The thermodynamic data of adsorption of the two compounds on the stainless steel surface and the activation energies were determined and then discussed. Analysis of experimental results shows that MDYO and DYCD inhibitors adsorb to the metal surface according to the Langmuir model and the mechanism of adsorption of both inhibitors involves physisorption. SEM-EDX results confirm the existence of an inhibitor protective film on the stainless steel surface. The results derived from theoretical calculations supported the experimental observation.

The adsorption behaviour of Ethyl 2-cyano-2-(1,3-dithian-2-ylidene) acetate (ECDYA) on carbon steel and its inhibitive action on corrosion in 1 M HCl and 0.5 M H2SO4 aqueous solutions were examined using different corrosion evaluation methods, such as weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopy. The results obtained showed that the inhibitory character of this product increases with the concentration but this character is inversely related to the temperature. Tafel curves have revealed that this compound (ECDYA) possesses the indices of a mixed inhibitor. The inhibiting effect of this compound was interpreted through its adsorption on the metal surface. The Langmuir isotherm adequately describes the process of adsorption of the ECDYA molecules on the surface of the steel in this medium. The experimental results revealed that ECDYA restrains the corrosion reaction in both acidic environments, the inhibition efficiency being stronger in H2SO4 than in HCl. The discussion of kinetic and thermodynamic parameters such as activation energy, enthalpy, entropy and adsorption free energy has also been the subject of this work. Quantum chemical parameters were calculated and discussed.