Chromogenic and Fluorogenic Crown Ether Compounds for the Selective Extraction and Determination of Hg(II)

Abstract

Two novel crown ether compounds, N,N`-bis(2-hydroxy-5-nitrobenzyl)-4, 13-diazadibenzo-18-crown-6 (CCE) and N, N`-bis(7-hydroxy-4-methylcoumarin-8-methylene)-4, 13-diazadibenzo-18-crown-6 (FCE), have been synthesized as potential reagents for the selective extraction and determination of heavy metal ions. Characterizations of the acid-base reactivity and the heavy metal ion extraction capabilities are reported. Both CCE and FCE undergo four-step ionization processes with associated tautomeric transformations and form stable complexes with divalent metal cations that can be extracted into 1,2-dichloroethane. Extraction constants for Ba(II), Ca(II), Cd(II), Cu(II), Hg(II), Pb(II), and Sr(II) have been determined for both reagents. For CCE, the extraction order is Hg(II) > Pb(II) > Cu(II) > Cd(II) > Ca(II) > Sr(II) > Ba(II), whereas the order for FCE is Hg(II) > Cu(II) > Pb(II) > Cd(II) > Ca(II) > Sr(II) > Ba(II). The selectivity of CCE for Hg(II) over the next-best-extracted cation, Pb(II), is nearly 2 x 10{sup 7} and that of FCE for Hg(II) over next-best-extracted cation, Cu(II), is nearly 5 x 10{sup 6}. Potential applications to chemical analysis, based on the unprecedented selectivity of both reagents for Hg(II), are briefly examined. 54 refs., 7 figs., 3 tabs.