Formation of a copper-butyl ethoxycarbonyl thiourea complex

Butyl ethoxycarbonyl thiourea (BECTU) reacts readily with cupric solution to form an insoluble Cu-BECTU complex in a reaction which increases with pH. The selectivity of BECTU for copper ions was confirmed as no reaction was observed between BECTU and ferrous, ferric or lead ions. The complex was characterised by elemental analysis, nuclear magnetic resonance and fast atom bombardment mass spectroscopies as well as infrared and X-ray photoelectron spectroscopies. These analyses indicate that the complex has an extended structure with an average stoichiometry derived from a mixture of cuprous, CuBECTU, and cupric, CuBECTU2, species. It is suggested that the reaction probably involves an electrochemical mechanism in which cupric ion is reduced to cuprous ion to form a copper chelate in the same way as xanthate collectors form stable, cuprous complexes. Infrared and X-ray photoelectron analyses suggest that BECTU acts as a bidentate ligand bonding with the copper ion through the carbonyl oxygen and the thiol sulfur atoms to form a six membered ring structure. Furthermore, these results support the earlier assertion that a proton is removed from the collector during the reaction with the copper ions.