Influence of the alkyl chain length of 2 amino 5 alkyl 1,3,4 thiadiazole compounds on the corrosion inhibition of steel immersed in sulfuric acid solutions

► API X52 steel corrosion in H 2SO 4 was evaluated with EIS. ► The corrosion inhibition efficiency of six thiadiazole compounds were evaluated. ► The alkyl chain length of these compounds was related to their corrosion IE. ► 2-Amino-5-undecyl-1,3,4-thiadiazole, IC-11, was the best inhibitor at 100 ppm. ► IC-11 corrosion inhibition lasted over 90% for at least 720 h. The corrosion inhibition efficiency of 2 amino 5 alkyl 1,3,4 thiadiazole compounds with different alkyl chain lengths, namely: 2 ethyl, 3 n propyl, 5 n penthyl, 7 hepthyl, 11 undecyl and 13 tridecyl, was evaluated in the system steel/1 M H 2SO 4. These compounds were synthesized, characterized by FT-IR and NMR spectroscopy analysis and evaluated using electrochemical impedance spectroscopy and SEM analysis. The results showed that the inhibition mechanism involves blockage of the steel surface by the inhibitor molecules by a Langmuir-type adsorption process and that the alkyl chain length plays an important role in the inhibition efficiency of the synthesized inhibitors.