Synthesis of Substituted Pyrazoles and Imidazolium Salts

This summer research was based in organic chemistry. It consisted of pyrazole and imidazolium chloride salt synthesis. Heterocyclic molecules, pyrazoles and imidazolium salts contain three carbon atoms and two nitrogen atoms in their 5-membered rings. In pyrazoles, the nitrogen atoms are adjacent to one another. On the contrary, imidazolium salts have non-adjacent nitrogen atoms, one being positively charged. These salts also contain an acidic hydrogen atom that can be removed by a base. The resulting product is a resonance-stabilized carbene species that can be used in ligand synthesis and other reactions. This project focuses on producing substituted pyrazoles and imidazolium chloride salts as precursors to desired ligands. The ligands can then be used in lactide polymerization to generate poly-lactic acid, a promising biodegradable alternative to polyethylene. Two substituted pyrazoles have been synthesized in moderate to high yield. Both compounds were characterized by infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Imidazolium salts can be synthesized in two-step reactions. The first step involves a reaction between an amine and glyoxal to create a diimine, a molecule with two carbon-nitrogen double bonds. In the second step, the diimine reacts with paraformaldehyde and trimethylsilyl chloride (TMSCl) to produce the imidazolium salt. Two substituted diimines have been synthesized in low to high yield. The molecules were analyzed using NMR spectroscopy. The diimines were employed in the second reaction step but resulted in impure product. Future work will include improving the imidazolium salt synthesis reactions and making other pyrazoles and diimines with different substituents.