Synthesis of mono- and dibenzocrown ethers with fluorinated or chromogenic substituents
Campbell, Martin J
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Macrocyclic polyethers (crown ethers) are known for their ability to bind metal cations within their central cavities. This allows crown ethers to be utilized in the separation and determination of metal ion species. Since their discovery in 1967, a number of structural modifications have been evaluated to enhance the performance of crown ethers in solvent extraction systems requiring high organic phase solubility coupled with low aqueous phase solubility to ensure extraction efficiency. In addition, the attachment of chromogenic side arms has enhanced their utility in the spectroscopic determination of metal ions. The advent of new extraction technologies, such as supercritical fluid extraction, and fluorous biphasic extraction systems, has brought about the need for crown ethers with enhanced solubility in these nontraditional solvents. Unrelated research has proven the high solubility of highly fluorinated compounds in these systems. Therefore, the synthesis of crown ethers with highly fluorinated side arms has been explored. The use of suitable protected and derivatized benzenes as starting materials made possible the development of a new series of dibenzocrown ethers which are ideally suited for incorporation of perfluoroalkyl groups and, potentially, for use in many other organic transformations. Substituted benzene moieties incorporating polyfluorinated tails were developed as precursors for the construction of other crown ethers. Methods for attaching highly fluorinated alkyl and aromatic groups directly to the polyether macroring were explored. Novel crown ethers with perfluorinated benzene side arms were prepared. Several mono- and dialcohols were prepared which contained both a traditional hydrocarbon alcohol unit and a perfluorocarbon chain remote from the alcohol functionality. These alcohols are expected to be useful building blocks for the construction of additional crown ethers in which partially fluorinated side groups are attached directly to the macroring. A new series of proton-ionizable lariat ethers with chromogenic side groups was developed. In these chromoionophores, the proton-ionizable chromogenic groups were attached to the macroring in a way previously unexplored. The interesting solution-phase and solid state geometries which resulted from this rigid, planar attachment were explored. These lariat ethers exhibited significant color changes under basic conditions.