**4. Conclusions**

The study demonstrates that 3-mercaptoalkyl derivatives of 5-amino-1*H*-1,2,4-triazole are effective corrosion inhibitors for α-brass in chloride environment. Their protective effect increases with the length of the alkyl chain and at higher concentrations of the additive. The maximum protection (>99%) is possible at Cinh > 0.10 mM, when the inhibitors become comparable in degree of protection. This can be accounted for by the similarity of the quantum chemical parameters of the organic molecules responsible for the inhibition. The inhibition effect results from the formation of a passive film on the brass surface. The film includes oxides of the brass components as well as sparingly soluble complex compounds of zinc and copper with molecules of the considered 3-mercaptoalkyl derivatives of 5-amino-1*H*-1,2,4-triazole. The fact that the protective film actually forms on the brass surface is proved by a decrease in the double-layer capacitance, an increase in the polarization resistance of the brass electrode, and a rapid increase in the Warburg impedance upon the introduction of the inhibitor.

**Author Contributions:** Conceptualization, I.Z.; Data curation, Y.K.; Investigation, D.S., A.K., E.K. and A.P.; Methodology, A.K., E.K. and A.P.; Project administration, K.S.; Software, C.P. and A.T.; Writing—original draft, O.K., D.S. and A.K.; Writing—review & editing, K.S., C.P., A.T., I.Z. and Y.K.

**Funding:** The study received financial support from the Ministry of Education and Science of the Russian Federation within the framework of State Contract with universities regarding scientific research in 2017–2019, project No. 4.3633.2017/4.6.

**Conflicts of Interest:** The authors declare no conflict of interest.
