NEW FLUORINATED HYDROXAMIC ACID REAGENTS FOR THE EXTRACTION OF METAL-IONS WITH SUPERCRITICAL CO2

Research to date on the supercritical fluid extraction (SFE) of metal ions has focused on the use of dithiocarbamates and beta-diketones. Hy droxamic acids are well known as effective chelating agents for a broa d range of transition metal ions. Much attention has centred in inorga nic chemistry on the effect of N-substitution on metal chelate stabili ty and selectivity, and in analytical chemistry on the immobilisation of the chelating agents to the chosen solid supports such as silica. I n this paper, the synthesis of selected fluorinated mono hydroxamic ac ids and their N-substituted derivatives is reported. The new reagents are applied in the SFE of metal ions in particular Fe(III) using unmod ified supercritical CO2. Metal extraction is monitored using atomic ab sorption spectroscopy and visible spectrophotometry. The extraction ef ficiencies were determined as a function of pressure and temperature. The new ligands synthesised and applied were perfluorooctanohydroxamic acid (PFOHA), heptafluorobutyrichydroxamic acid (HFBHA) and their N-m ethylhydroxamic acid derivatives. Of the synthesised reagents, PFOHA w as the most soluble and effective extractant of Fe(III) from spiked fi lter paper, reaching 97% extraction of the metal ion under optimised c onditions. The selectivity of this ligand for Fe(III) in the presence of Cu(II), NI(II), Pb(II) and Zn(II) is also demonstrated.