Anticorrosive properties of 1,3-thiazolothiadiazin-S,S-dioxides during corrosion of copper and zinc in NaH2PO4 · 2H2O solution

Anticorrosion activity of isomeric 1,3-thiazolothiadiazine-S,S-dioxides was studied by electrochemical and gravimetric methods in a model corrosion-inducing environment (in 0,5 M solution of NaH2PO4·2H2O at pH = 9,5 ÷ 11,5 and t = 25 °C). Analysis of the obtained results showed that the derivatives of 2,6-diaryl-2H,4H-[1,3]-thiazolo[3,2-c][1,3,5]thiadiazine-3,3-dioxides (R-(TD-3,3), where R = H; 4-Me; 4-Et; 4-NH2; 4-NMe2; 4-OMe; 4-OEt; 4-Br; 4-Cl; 4-NO2) provide corrosion inhibition for zinc and copper. Moreover, the nature of a substituent in 1,3-thiazolothiadiazine-S,S-dioxides has little effect on the isomer ratio, but significantly affects their anti-corrosion efficiency. Introduction of substituents of different nature into the R-(TD-3,3) molecule can result in the effect on the efficiency of protection being opposite for zinc and copper. Electrophilic groups in the molecule can increase protective effect for copper, but decrease it for zinc. On the contrary, nucleophilic groups are beneficial for protection of zinc, but less effective for copper. Considering that derivatives of 1,3-thiazolothiadiazine-S,S-dioxides are noticeably hydrophobic and are capable of forming hardly soluble coordination complexes with metal ions, it is advisable to use them for anti-corrosion protection of copper and zinc surfaces in phosphate solutions.