Synthesis of lariat ethers with proton-ionizable and non-ionizable side arms and their acyclic analogues
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Lariat ethers are crown ethers (macrocychc polyethers) which have one or more donor-group-bearing side arms. Functionalization of crown ethers by addition of a pendent ann(s) substituted v^th a proton-ionizable group(s) or non-ionizable donor group(s) is an effective method to improve the metal ion binding ability and selectivity of crown ethers due to the extra coordination sites. To study the nature of the polyether unit (i.e., acychc or cychc) upon the efiSciency and selectivity of metal ion complexation, the synthesis of acyclic polyethers which have two proton-ionizable side arms was performed. Several series of proton-ionizable lariat ethers with structural variations which include the crown ether ring size, length of the linkage which joins the acidic fimction to the crown ether ring, and the identity of the proton-ionizable group were prepared. For the lariat ether carboxyhc acids, dibenzo-16-crown-5, dibenzo-19-crown-6, tribenzo-19-crown-6, and benzo-18-crown-6 compounds were synthesized. Investigations of metal ion complexation behavior of these lariat ether carboxyhc acids and their polymers, which were prepared by their reaction with formaldehyde condensation in formic acid, have been undertaken.