STABILIZATION OF COPPER(I) WITH ORGANIC LIGANDS FOR TRACE LEVEL ANALYSIS IN AQUEOUS SOLUTIONS (KINETICS, CORROSION, CYANIDE, DETERMINATION).
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PublisherThe University of Arizona.
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AbstractThe dissolution of copper metal in the presence of copper(II) ions and allyl alcohol in aqueous solution is found to be pseudo-first order with respect to both copper(II) ions and allyl alcohol. The reaction is inhibited by acid. The rate determining step is not the formation of copper(I) but the transfer of electrons from the surface of copper metal to the copper(II) ions in solution. The reaction rate has been monitored spectrophotometrically by complexing the copper(I) formed with 2,9-dimethylphenanthroline (neocuproin) and measuring the absorbance of the solution at the wavelength of maximum absorption of the complex, 450 nm. Other factors that affect the reaction are the presence of anions, the solvent composition, the nature of the unsaturated ligand used to stabilize the copper(I) and the rate of stirring. The reduction of copper(II)-neocuproin by allylamine and allyl alcohol has been studied in basic solution. A method has been developed for the rapid, sensitive determination of CN⁻ based on a spectrophotometric technique using copper(I)-neocuproin as a reagent. SCN⁻ does not interfere but S²⁻ appears to be a very powerful source of interference. By appropriate choice of the concentration of copper(I)-neocuproin reagent the range of response can be adjusted to be in the range 1-10 ppm. The theoretical detection limit of the method is as low as 19 ppb at the 95% confidence limit and the precision, measured as the relative standard deviation, is better than 1.5%. The disturbance of the equilibrium between the bis ligand and mono ligand complexes of copper(I) appears to be the reason for the observed decrease in absorbance on the addition of cyanide to a solution of copper(II)-neocuproin. The problems associated with using the commercially available ion selective electrode for cupric determination have been highlighted. The possibility of developing a PVC matrix membrane electrode for the determination of CN⁻ has been explored. The main difficulty is the instability of the copper(I)-neocuproin complex at pH values as high as 11 that are required to stabilize CN⁻.