Equilibrium studies on lithium(I) transfer into ionic liquid with a water-soluble octabromoporphyrin (H2(OBTMPyP)4+) from aqueous phase

A water-soluble octabromoporphyrin 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (H-2(OBTMPyP)(4+)), H2P4+) and its lithium complex, Li(OBTMPyP)(3+), (LiP3+), transferred quantitatively to an ionic liquid (IL), 1-butyl-3-methylimidazolium hexa-fluorophosphate (BMIM+PF6-) with no addition of other counter ions. The acid- dissociation constants of H-2(OBTMPyP)(4+) between aqueous and BMIM+PF6- phases were determined spectrophotometrically and found to be 10(-7.67) and 10(-11.33) at I = 0.1 for K-a1,K-IL = [H+](aq)[HP3+](IL)/[H2P4+](IL) and K-a2,K-IL = [H+](aq)[P2+](IL)/[HP3+](IL), respectively. Since the acid-dissociation constants involve the partition of H-2(OBTMPyP)(4+) between aqueous and IL phases, the determined values are ten times as low as those observed in aqueous solution. The transfer equilibrium constants of LiP3+ and NaP3+ to IL defined by K-MP,K-IL = [MP3+](IL)/[M+](aq)[P2+](IL) (M = Li+ or Na+) were found to be 10(4.83) and 10(1.31) for K-LiP,K-IL and K-NaP,K-IL, respectively. LiP3+ transferred selectively in the presence of Na+ (K-LiP,K-IL/K-NaP,K-IL = 10(3.52)) to IL phase through an ion-exchange mechanism between BMIM+PF6- and Li(OBTMPyP)(3+).