New Kemp's diacid derivatives give efficient transport and modifiable selectivity for alkaline earth and transition metal ions

New derivatives of 1,3,5-trimethyl-r-1, c-3, c-5-cyclohexanetricarboxylic acid (Kemp's triacid) showed high efficiency for alkaline earth and transition metal ion transport through a chloroform liquid membrane. Simple syntheses from Kemp's triacid or its geometric isomer provided chelating agents with a tripodal binding site for metal cations. The tripodal binding site consisted of r-1, c-3-diaxial carboxyl group and a c-5-amide, ester, or C-methyl group. Alkaline earth metal transport was quite variable and sensitive to c-5-group changes. For transition metal transport, c-5-amide diacids gave high total transport efficiency. For c-5-ester or C-methyl diacids, complexation of smaller divalent cations was decreased, resulting in increased selectivity for large cations.