Chemical Reactions of 2,5-Dimercapto-1,3,4-thiadiazole (DMTD) with Metallic Copper, Silver, and Mercury

Chemical reactions of DMTD with metallic copper, silver, and mercury have been studied by infrared (IR), surface-enhanced Raman scattering (SERS), UV−vis, and X-ray photoelectron spectrum (XPS) techniques. It is found that DMTD can react readily with metallic copper, silver, and mercury under mild conditions. The reaction product of DMTD with metallic copper shows an IR spectrum slightly different from that of Cu(DMTD)2, suggesting a Cu+ component in the product, which is further confirmed by the XPS result. The reaction products of DMTD with metallic silver and liquid mercury are Ag(DMTD) and Hg(DMTD)2, respectively. A two-step mechanism is proposed for these surface reactions: first DMTD is chemisorbed on the metal surfaces with the formation of the disulfide salt of DMTD as the intermediate product, and then the unstable disulfide salt reacts further with the excessive DMTD in solution, forming the monosulfide salt of DMTD which covers the metal surfaces in the form of a polymer layer or even a monolayer.