Synthesis of lipophilic acyclic polyether dicarboxylic acids and lipophilic, chromogenic, and fluorogenic crown ethers
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Abstract
The unique properties of podand and crown ether compounds which enable selective metal ion complexation provides a unique opportunity for the determination of metal ions, separation of desired metal ions via bulk solvent extraction from aqueous solution and selective metal ion separation via ion transport through bulk solvent membranes comprised of such compounds. Synthetic routes to proton-ionizable podands and various crown ether compounds for application in each of these areas is described. The influence of structural changes in the organic complexing agent on the selectivity and efficiency of metal ion complexation, extraction and transport are discussed. A series of twenty-one novel lipophilic, dicarboxylic acid podands for use in selective divalent metal ion extraction are conveniently synthesized from two equivalents of a corresponding lipophilic a-bromocarboxylic acid and various commercially available diols, dithiols and diamines. Structural variations within this series of podands include changes in the overall lipophilicity, the rigidity and number of carbon atoms in the linking unit and also the number and type of donor atoms in the structure. In addition, a lipophilic tricarboxylic acid di-podand with potential use in trivalent metal ion extraction is also synthesized. An efficient synthesis of crown ethers with two pendant lipophilic groups for use in selective metal ion transport is discovered and developed. Reaction of lipophilic diols with sodium hydride in tetrahydrofuran followed by cyclization of the lipophilic dialkoxide with a ditosylate produces superior yields of the corresponding lipophilic crown ethers. In all, nineteen crown ethers are synthesized in which incremental changes in the crown ether lipophilicity, polyether ring size, relative lipophilic group attachment site and type of donor atom produce a homologous series of lipophilic crown ether compounds. Unusual features in the iH NMR spectra are discussed and explained with the aid of a deuterated analog. A highly lipophilic crown ether with four pendant lipophilic groups is also prepared. An improved synthesis of a versatile dibenzodiaza-18-crown-6 intermediate is presented followed by its conversion into a chromogenic crown ether which has recently demonstrated remarkable mercury selective extraction and determination properties. The syntheses of a structurally similar chromogenic monobenzodiaza-18-crown-6 compound is also described. The preparation of two fluorogenic crown ethers, similar to the previous chromogenic analogs, are also prepared. Finally, two lipophilic, monobenzo diamino acid crown ethers are also prepared for use in divalent metal ion complexation studies.