Studies of Alternative Solvent Systems to Recycle Phase Selectively Soluble Catalysts
MetadataShow full item record
In recent years, the Bergbreiter group has investigated the synthesis and use of recyclable polymer-supported catalysts. If the polymer-supported catalyst has high phase selective solubility in certain solvents, the catalyst can often be separated from products with opposite phase selective solubility by using a biphasic separation. Thermomorphic systems, comprised of two solvents that are initially immiscible but that form one phase at elevated temperature, are used to run a reaction under homogeneous conditions and to separate the catalyst and the product in two phases afterward. This work details the use of polymer-supported dyes as catalyst surrogates to examine the phase selective solubility of catalyst supports in thermomorphic systems and to study how leaching of polymer-supported materials into a product phase can be minimized. These studies include the synthesis of a nonpolar phase selectively soluble PIB-supported naphthol azo dye and its use as a catalyst surrogate to study leaching into the polar phase of a heptane/methanol thermomorphic system. It was found that leaching of the PIB-supported dye into the methanol phase was effectively minimized by the addition of nontoxic and nonvolatile poly(α-olefins) (PAOs) as cosolvents. Furthermore, when PAOs were used as a replacement for heptane, PAOs did not appreciably leach into the polar solvent when DMF or methanol were used. The synthesis of a polar phase selective MPEG-supported dansyl fluorophore and its use as a catalyst surrogate to study the phase selective solubility of PEG supports in a heptane/DMF thermomorphic system is also described. The addition of MPEG as a polymer cosolvent did not affect the leaching of PEG-supported dansyl dyes into heptane when PEG supports with molecular weights of greater than 1000 Da were used. Thus, MPEG could serve as a green cosolvent for this system. Finally, the synthesis of a PIB-supported BINOL ligand is detailed. This ligand was prepared in a few steps and was tested in an N-arylation reaction. Although it showed very low reactivity in comparison with BINOL, similar PIB-supported ligands could be prepared and tested. The previous studies of alternative solvents can then be applied to the design of greener recycling systems for such polymer-supported materials.
Harrell, Mary Layne (2017). Studies of Alternative Solvent Systems to Recycle Phase Selectively Soluble Catalysts. Doctoral dissertation, Texas A&M University. Available electronically from