Synthesis and characterization of novel diphosphonic acids for supercritical carbon dioxide extraction

Past waste management and mismanagement practices from fifty years of weapons development at various government sites have led to large-scale contamination of soil, production facilities, and waste sites. Most of these wastes consist primarily of non-hazardous materials contaminated with relatively small quantities of actinide elements, or with a combination of hazardous and radioactive materials (mixed waste). Separation of these wastes into their non-hazardous, hazardous, and radioactive components so that each can be dealt with separately and egectively would dramatically reduce the cost of stabilization and disposal.; Dialkyl alkylenediphosphonic acids have proven to be powerful complexing agents for the extraction of actinide metal ions from mixed waste. However, the organic solvents traditionally employed in solvent extraction procedures are harmful to the environment. Supercritical carbon dioxide is an environmentally benign alternative to organic solvents. Combining the superior complexing ability of a diphosphonic acid with the unique solvent properties of supercritical carbon dioxide could provide an attractive solvent extraction system for actinide separations.; The diphosphonic acids commonly used in solvent extraction procedures are not soluble in supercritical carbon dioxide. A general synthetic approach to gem-diphosphonates with supercritical carbon dioxide solubilizing groups (i.e., siloxanes) was established in this study. Initially, the synthesis of tetraethyl alkylenediphosphonates was optimized via the Michaelis-Arbuzov reaction. These diphosphonates were hydrolyzed to the corresponding alkylenediphosphonic acids. Both the tetraethyl esters and the free acids are valuable synthetic precursors to the desired diphosphonic acid derivatives. The acids were converted to the symmetric silyl-substituted partial esters via dicyclohexylcarbodiimide-activated esterification with 3-(trimethyisilyl)-1-propanol.; The synthesis of dimethyl di-[3-poly(dimethylsiloxy)-1-propyl] methylenediphosphonates was achieved via the tetrazole-catalyzed esterification of methylenebis(phosphonic dichloride). The necessary 3-poly(dimethylsiloxy)-1-propanol starting materials were prepared via the hydrosilylation of allyl benzyl ether and the requisite removal of the benzyl group via catalytic hydrogenolysis. Methylene bridge-substituted diphosphonates were prepared by alkylation of tetraethyl methylenediphosphonate and dimethyl di-(2-ethylhexyl) methylenediphosphonate with allyl iodide, followed by the hydrosilylation of the allylic functionality. Free acids were prepared by hydrolysis of the ethyl esters with concentrated hydrochloric acid.; All products were characterized by common analytical techniques. Preliminary solubility screenings indicated the most promising ligands for supercritical carbon dioxide extraction.