Complexes of chromium(III) with nitrilotriacetic acid and their extraction by solutions of aliquat-336 in dichloro-ethane |
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Authors: | H. M. N. H. Irving and R. H. Al-Jarrah |
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Affiliation: | Department of Inorganic and Structural Chemistry, University of Leeds, Leeds England |
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Abstract: | It has been shown that chromium(III) and nitrilotriacetic acid (NTA; H3Z) form only a series of 1:1 complexes in solution. The violet uncharged species [CrZ(H2O)2] cannot be extracted by a solution of the long-chain quaternary ammonium chloride, Aliquat-336, in dichloroethane. Its acid dissociation constant (pK1 = 5.87) was determined spectrophotometrically. On increasing the pH of the solution the blue anion CrZ(H2O)(OH)- of pK2=8.74 and its conjugate base the binegative anion CrZ(OH)2-2 of pK3= 11.81 are successively formed. Both of these anionic species are extracted by Aliquat-336 with maximal extraction (ca. 60%) at about pH 9. At still higher pH values the olive-green anion, CrZ(OH)33-of much lower or negligible extractability, is formed. |
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