Nonaqueous Conductometric Titration of β-Diketone Metal-chelates with EDTA

Abstract

The ligand substitution reaction between the metal acetylacetonates and EDTA was utilized to estimate the amount of metal acetylacetonates by nonaqueous conductometry. DMF or DMSO was used as a solvent because the metal acetylacetonates readily dissolved in the organic solvents, such as DMF, DMSO, pyridine, etc, while EDTA could dissolve in DMF and DMSO only.
The sample solutions were prepared by dissolving the dried metal acetylacetonates in DMF or DMSO. The used metal acetylacetonates were cobalt copper (II), manganese( II), iron (III) and chromiu m (III) acetylacetonates.
The preparation of EDTA solution has been already described in detail. By conductometric titration of metal acetylacetonate with EDTA, the combination ratios between the metal acetylacetonate and EDTA were obtained at the molar ratios of 4: 1, 2: 1, and 1: 1.
These combination ratios were characteristic of the used metal acetylacetonates. These reactivities between the metal acetylacetonates and EDTA were different by the kind of metal acetylacetonate.
The mixture of metal acetylacetonates could be titrated by taking advantage of these differences of reactivity.
Less than 1% of water, inorganic acids and organic solvents such as benzene and chloroform gave no influence on the inflection points in the conductometric titration curves. The determination limits were from 1 x10-4 moledm-3 to 5 ×10^-4 mol·dm^-3 of the metal acetylacetonate. By using these results, determination of Fe (III) after the extraction with acetylacetone was investigated. The results were in close agreement with the those of the extraction photometry.