Determination of Acid/Base Equilibrium Constants for the Protonation of Triaryl Phosphines in Acetonitrile/Water Mixtures. ANDREW SHUFF (Texas A&M University College Station, TX 77844) ANDREJA BAKAC (Ames Laboratory, Ames, IA, 50011)

There have been questionable and contradicting values for K_H's of different phosphines in literature. Clarification of these values will relieve some of the confusion and aid those seeking to use the values as a vital part of their experiment. The goal of this project was to determine the protonation constants for triphenylphosphine, tri-p-tolylphosphine, tris(p-methoxyphenyl)phosphine, tris(p-trifluoromethylphenyl)phosphine, and tris(p-fluorophenyl)phosphine by UV-Vis and NMR spectroscopies. This was done by measuring the UV absorption or chemical shift of the phosphine in different concentrations of acid with the same ionic strength. The constants were also measured at different solvent mixtures between 50:50 acetonitrile (AN)/H₂O (v/v) and 90:10 AN/H₂O (v/v), then tested for a dependence on the fraction of water in the solvent. It was shown that UV-Vis and NMR spectroscopies give results that are identical within the experimental error. Both tris(p-trifluoromethylphenyl)phosphine and tris(p-fluorophenyl)phosphine were determined to not protonate. The protonation constants of the other three phosphines were found to be proportional to the fraction of water in the solvent. For example, the protonation constants for tri-p-tolylphosphine are 32.3 at 90:10 AN/H₂O (v/v), 11.7 at 80:20 AN/H₂O (v/v), and 4.33 at 67:33 AN/H₂O (v/v).

Preparation of Alkamides for Evaluation as Insecticides. AMANDA DEVRIES (Buena Vista University Storm Lake, IA 50588) GEORGE KRAUS (Ames Laboratory, Ames, IA, 50011)

The idea of a biorefinery is modeled after the highly successful oil refinery wherein petroleum is converted into gasoline, oil, and monomers such as ethylene and propylene. Unlike petroleum refineries, corn grain and soy biorefineries are in their first stages of development. For biorefineries to be successful on a long-term basis, they must produce: 1) high volume fuels such as ethanol or biodiesel; and, 2) a portfolio of high value products and chemicals. One such chemical is 1,3-propanediol, which can be polymerized for use in textiles and fabrics, such as in DuPont's Sorona. Another high value product would be an insecticide or herbicide based on alkyl amides derived from natural oils. Some alkamides have been shown to inhibit the hatching of larvae. Alkamides can be synthesized by using a Wittig reaction with the amide portion coming from the phosphonium ylide and the alkyl chain coming from the aldehyde. To synthesize the phosphonium salts needed for the production of the alkamides, a variety of organic synthesis techniques were used. Synthesizing the first phosphonium salt required initial reflux of chloroacetyl chloride with isobutylamine in ethyl ether. In a bimolecular nucleophilic substitution reaction (S_N2) the resulting amide was then added to triphenylphosphine in toluene and boiled to produce the phosphonium salt. The preparation of the second phosphonium salt began with crotonic acid and a bromination reaction. The bromoacid then underwent halogen substitution with thionyl chloride under reflux conditions. The resulting acid chloride was added to a solution of isobutylamine in ethyl ether with stirring. An S_N2 reaction was used by adding the amide to triphenylphosphine in toluene to produce the second phosphonium salt. To synthesize the seven-carbon aldehyde, 5-hydroxy-1-pentyne in methanol and potassium hydroxide reacted with iodine. The product of this reaction then underwent a coupling reaction with trimethylsilylacetylene, and the resulting alcohol was oxidized to create the aldehyde. Each product synthesized was confirmed using nuclear magnetic resonance (NMR). Future work will include carrying out the Wittig reaction to synthesize the desired alkamides. The alkamides will be evaluated as insecticides. The biological studies will be conducted by DuPont.

Synthesis and Characterization of Gd5-xYxSiyGe4-y. ERIC POWELEIT (University of Wisconsin Madison, WI 53715) GORDON MILLER (Ames Laboratory, Ames, IA, 50011)

The system of Gd₅Si_xGe_4-x , while previously studied for it's rather unique ability to break and form covalent bonds upon temperature change, is still only partially understood. This work seeks to further the understanding of this system by exploring similar RE₅Tt₄ systems of Gd_5-xY_xSi_yGe_4-y and Nd_zEr_5-zGe₄ and observing how their structure and properties differ from those of Gd₅Si_xGe_4-x. Samples were prepared by repeatedly arc melting stoichiometric mixtures of constituent elements in an argon atmosphere, reaching temperatures of approximately 3500 ºC. The structure of each sample was characterized by x-ray powder diffraction. In the Gd_5-xY_xSi_yGe_4-y system, two structural transitions were observed, the first occurring between y = 2.5 and y = 3.0 from a Sm₅Ge₄ - type structure to a monoclinic Gd₅Si₂Ge₂ - type structure and the second between y = 3.5 and y = 4.0 leading to an orthorhombic Gd₅Si₄ - type structure. Comparatively, the monoclinic phase in Gd₅Si_xGe_4-x has been reported in the region between x = 2.012 and x =1.72. This shift in composition suggests that by reducing the volume of the rare earth sites, the formation of covalent bonds between the two-dimensional slabs that define the crystal becomes more favorable. In the Nd_zEr_5-zGe₄ system, a structural transition was observed occurring between z = 1.8 and z = 2.0 from a Sm₅Ge₄ - type structure to a monoclinic Zr_3.9Ta_1.1Ge₄ - type structure. These results provide some novel insight into how the RE₅Tt₄ systems function and suggest that further characterization of these systems may produce a better understanding of their unique structural characteristics.