The extractant, methylimino-bis-N,N’-dioctylacetamide (MIDOA), was used for the extraction of soft acid metals. It was found that MIDOA can extract not only Cr(VI), Mo(VI), W(VI), Tc(VII) and Re(VII), whose metals can form oxonium anions due to their high oxidation states, but also other metal cations, like Nb(V), Ta(V) and Pd(II). Analogous compounds, imino-bis-N,N’-dioctylacetamide (IDOA) and methylimino-bis-N,N’-di-2-ethylhexylacetamide (MIDEHA), were synthesized and compared for their extractability. It is clear that these extractants have almost the same or lower D values than those for MIDOA. In order to examine the effect on extractability with different donor atoms, TODGA (N,N,N’,N’-tetraoctyl-diglycolamide) and TDGA (N,N,N’,N’-tetraoctyl-tyiodiglycolamide) having oxygen and sulfur donor were employed. The comparison of their extractabilities suggests that the trend of Pd and Re extraction is N > S > O and N > O > S, respectively. The chemical stability and the structure of MIDOA were also studied and discussed in this paper.
