Synthesis and metal ion complexation of synthetic ionophores

Abstract

The use of synthetic ionophores in both academic and industrial settings continues to increase. Growth in this field of chemistry has created a need for ionophores with pendant groups which allow for further chemical elaboration. This dissertation treats the synthesis of such ionophores.

Crown ethers (macrocyclic polyethers) and cryptands (macrobicyclic polyethers) which bear hydroxymethyl functions are prepared from benzyl-protected and allyl-protected precursors, respectively. Crown ethers containing ionizable chromogenic subunits are synthesized from benzocrown ether and hydroxymethylcrown ether starting materials in high yields. Neutral fluorogenic crown ethers are obtained in two steps from commercially-available starting materials. A series of novel bis-crown ethers results from condensation of diacid chlorides with hydroxy-16-crown-5 compounds.

Several bis-crown ethers are tested for their ability to complex the alkali metal cations by the picrate extraction method. Results indicate that the formation of 2:1 (crown:cation) complexes with potassium ion may be promoted by linking two oxymethyl-15-crown-5 units ortho on an aryl ring. A broad spectrum of small-ring four-oxygen crown ethers are tested by the same method for their ability to extract lithium ion. Results indicate that the 14-crown-4 ring size is the best suited in extraction capacity and selectivity for the complexation of lithium. Chloroform solutions of the ionizable chromogenic crown ethers are tested for their response upon contact with aqueous solutions of the alkali metal hydroxides. It is determined that the l-amino-2,4-dinitro-6-trifluoromethylbenzene chromophore is the best suited for incorporation into chromogenic crown ethers because of its acidity, high extinction coefficient and well-resolved spectral shift upon ionization.