Photometric determination of copper(II) in nickel alloys using azoderivatives of ethyl acetoacetate

1-Ethoxy-2-(2-hydroxy-3-sulfo-5-chlorophenylazo)butane-1,3-dion (L-1), 1-ethoxy-2-(2-hydroxy-3,5-disulfophenylazo)butane-1,3-dion (L-2), 1-ethoxy-2-(2-hydroxy-4-nitrophenylazo)butane-1,3-dion (L-3), and 1-ethoxy-2-(2-hydroxyphenylazo)butane-1,3-dion (L-4) were synthesized on the basis of ethyl acetoacetate, and their analytical characteristics were studied. The following dissociation constants of the reagents were determined by potentiometric titration: pK (1) = 5.94 +/- 0.04 and pK (2) = 9.75 +/- 0.04 (L-1), pK (1) = 5.78 +/- 0.02 and pK (2) = 9.55 +/- 0.03 (L-2), pK (1) = 6.03 +/- 0.03 and pK (2) = 9.86 +/- 0.05 (L-3), and pK (1) = 6.19 +/- 0.05 and pK (2) = 9.98 +/- 0.06 (L-4). The chemical analytical characteristics of copper(II) complexes of L-1-L-4 were determined by spectrophotometry. It was found that, with an increase in the elecrophilic properties of the substituents introduced into the aromatic ring of the molecule, the sensitivity of the reaction increased; the substituents had no effect on the ratio of Cu : L = 1 : 2. A photometric procedure was developed for determining copper in nickel-based alloys.