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Lehigh Researcher Presents Study On Greener Chemistry

Kimberly Choquette, a graduate researcher in the department of chemistry, has been chosen as one of 50 in the nation to present her work at the American Chemical Society’s annual research symposium at the University of Colorado, Boulder on July 26. Choquette will present a series of organic chemistry studies published in the Journal of the American Chemical Society on the use of samarium diiodide.

For chemical novices, samarium diiodide, serves many industries for its power to donate single electrons to other chemical compounds. Scale this chemical compound up a few trillion times and it becomes a powerful single electron reductant that carries out reactions important for the production of pharmaceutically relevant compounds—and at room temperatures.

Choquette and Robert Flowers, chair of the chemistry department, explored the speed and efficiency of SmI2 in a common chemical reaction called the Barbier reaction. Barbier reactions are a focus of chemists in the Flowers Lab because they combine relatively inexpensive metal compounds, chemicals and water to form a desired end compound, making them part of the green chemistry movement. This transformation is routinely used when putting together the pieces to synthesize pharmaceuticals.

Searching for more efficient chemical reactions, the team focused on hexamethylphosphoramide, or HMPA, a chemical commonly added to samarium reactions to improve the yield of the target product and increase the rate of the reaction.  Surprisingly, chemists use this catalyst but had no idea why the addition of HMPA seemed to be critical for success. HMPA is suspected to be a toxic substance, so the team believed that by determining how it works in the reaction, they were contributing to the search for a less harmful replacement.

Through a series of kinetic studies and computational work, Choquette, Flowers and Dhandapani V. Sadasivam determined that HMPA interacts with the alkyl halide starting material, activating the alkyl halide bond and making it more susceptible to reduction by SmI2.

Their finding demonstrates how HMPA accelerates the samarium Barbier reaction, and with this information alternatives for the toxic additive can start to be designed.  By replacing HMPA, this reaction can be adapted more broadly in important industrial chemical processes. 

Choquette is beginning her 5th year as a graduate student and has worked in the Flowers Lab since arriving at Lehigh. Her work focuses on the kinetics of organic reactions—the natural transformations brought on by the pairing of electrons that are the catalyst for many chemical reactions.

“I was always intrigued by the chemistry of nature, even back in high school,” said Choquette. “Think of all the areas it impacts. Organic chemistry is everywhere. It is all around us, from laundry detergent to drug development.”

Story by Jordan Reese

Posted on Tuesday, July 17, 2012

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