1-Alkyl-4-ethoxythiocarbonyl-5-hydroxy-3-methylpyrazole, HETCP, (alkyl = n-octyl; n-dodecyl) were prepared in high yield by the reaction of 1-alkyl-3-methyl-2-pyrazolin-5-one with bis (ethoxythiocarbonyl)sulfide and sodium acetate in dimethylformamide. These reagents act as O, S bidentate ligands in solvent extraction/reextraction studies of Cu (II) from acid aqueous solutions and the extracted specie resulted to be Cu(ETCP)(2).