Association of Tris(acetylacetonato)chromium(III) with Chlorinated Phenols in the Liquid–Liquid Partition System

Abstract

Abstract The liquid–liquid partition behavior of tris(acetylacetonato)chromium(III) ([Cr(acac)3]) between heptane and 0.10 mol dm−3 aqueous sodium perchlorate solutions has been studied in the presence of a series of chlorinated phenols (HA) at 298.2 K. A large enhancement of the partition coefficient of [Cr(acac)3] with HA has been observed, e.g., it rises by about 1000-fold in the presence of 0.02 mol dm−3 3,5-dichlorophenol in the organic phase. This effect is ascribable to the association of [Cr(acac)3] with HA in the organic phase. From a partition-equilibrium analysis, the association complexes have been identified as being [Cr(acac)3]·iHA (i=1,2), and the association constants (βass,i) determined. The βass,i, value increases with an increase of the acid-dissociation constant of HA in the family of HA with the same combination of substituents at the 2,6-positions, i.e., the association is due to hydrogen bonding of the hydroxyl hydrogen atom of HA to [Cr(acac)3]. A linear free-energy relationship has been found between the βass,i, values of [Cr(acac)3] and those of [Co(acac)3] previously reported.