LAUSR

Abstract Two secondary amide compounds with and without fluorine atoms, N-(2-ethylhexyl)-2,2,2-trifluoroacetamide (TFAA) and N-(2-ethylhexyl)acetamide (AA), respectively, were synthesised in high yield under different reaction conditions. Both extraction reagents exhibited selectivity for Ga(III) over other metals in competitive solutions from hydrochloric acid media. Comparatively, the extraction selectivity of TFAA was superior to that of AA because of the electron-withdrawing nature of fluorine atoms, which increased the charge density on the N-H hydrogen atom and decreased electron density on the carbonyl oxygen atom of TFAA. The stoichiometries for both extraction reagents to Ga(III) were determined by slope analysis for concentrations of extractants, protons, and chloride ions. FT-IR, 1H-NMR, and 19F-NMR spectroscopic analyses were conducted to elucidate the extraction mechanism. At high HCl concentrations, AA was protonated; consequently, GaCl–4 was extracted with assistance from the O-bound hydronium ion, while at low HCl concentrations, AA was not protonated and GaCl–4 and a hydronium ion as a counter cation were extracted via the N-H hydrogen atom. On the contrary, TFAA was not protonated over the entire tested HCl concentration range and extraction of GaCl–4 occurred only via the N-H hydrogen atom and a hydronium ion as a counter cation. One proton of the hydronium ion bonded to GaCl–4 and one to an electron-withdrawing fluorine atom; consequently, the remaining hydrogen atom is partially positively charged and extracts a second GaCl–4 accompanied by a second hydronium ion. Overall, the mechanism involves an allosteric extraction of a second GaCl–4 assisted by an already TFAA-bound Ga(III) and hydronium ion. Exhaustive stripping of Ga(III) from the organic phase after forward extraction with either amide can be achieved using distilled water.