1,2,5-Thiadiazoline S,S-dioxide derivatives as corrosion inhibitors for mild steel in sulphuric acid solution. Electrochemical studies and cytotoxic effect evaluation

The corrosion inhibitory ability and the possible toxicity on mammalian cells of 3-(4-methoxyphenyl)-3,4-diphenyl-2,3-dihydro-1,2,5-thiadiazole 1,1-dioxide (TANIS) and 4-(1,1-dioxido-3,4-diphenyl-2,3-dihydro-1,2,5-thiadiazol-3-yl)-N,N-dimethylaniline (TDMA), compounds previously synthesized in our laboratory which are stable in acid media, have a high melting point and melt without decomposition (capillary tube method), are reported for the first time. Corrosion tests and biological assays were performed by carrying out electrochemical tests, SEM surface morphological examination and in vitro short-term tests, respectively. The experimental results reveal that TANIS and TDMA at very low concentrations could be used as mild steel corrosion inhibitors in 0.5 M H2SO4 solution. The inhibition efficiency increases with the inhibitor concentration, reaching the values of 82% for TDMA and 76% for TANIS for the highest inhibitor concentration (60 μM) to date. The surface morphology is in accordance with the electrochemical results. Both inhibitors are of mixed-type. The possible mechanistic pathways for the inhibition process are proposed. Cytotoxic effects were observed for both inhibitors; however, this effect is not seen on treatment with the minimum TANIS concentration (60 μM). TANIS cytotoxicity is dose-dependent, whereas that of TDMA is not. These inhibitors should be handled with certain precautions both in plant management and in their disposal as waste according to current environmental regulations. The biological assay results show the necessity to perform cytotoxicity tests for the new corrosion inhibitors to proceed accordingly, considering cost-benefit in each case. It is necessary to establish a strategy that prioritizes dialogue between the use of chemicals by industry and academics that provides information on both the compound and its toxicity, in communion with the regulatory authority.