UBC Theses and Dissertations
Development of mechanistic tools for understanding organic reactions: from manual to automated sampling Yu, Diana
Kinetic studies were conducted on three unrelated reaction types using traditional and modified reaction monitoring tools. The Aza-Piancatelli rearrangement was studied through ReactIR and HPLC-MS to obtain a better understanding of why the substrate scope was limited. It was found that the Lewis acid catalyzed reaction is often zero-order, dependent on the lanthanide metal used. Off-cycle binding of the nucleophile to the Lewis acid was proposed to help explain the zero-order profile. Differences between Lewis and Brønsted acid catalysts were found through subsequent experiments assessing catalyst deactivation and the chemoselectivity of the products in the Aza-Piancatelli rearrangement. An automated sampling system was created for hands-free reaction monitoring and offline analysis by HPLC-MS to provide detailed information about more complicated reactions. The automated sampling system was modified for the study of microwave assisted reactions. This application allowed for more information to be derived from the field of poorly-understood microwave chemistry than allowed by previous technology. Comparisons were made between microwave-assisted and conventionally heated reactions, using a Claisen rearrangement as a model reaction. As expected, it was found that the Claisen rearrangement of allylphenyl ethers displayed similar kinetics between the two heating modes. The technology was also used briefly to search for the existence of non-thermal effects. It was shown that the sampling apparatus could be useful for collecting data observed from microwave-specific effects. Mechanistic studies were also conducted on the Kinugasa reaction to obtain a better understanding of why the reaction generally behaves poorly in regards to the formation of β-lactam product. To study the reaction, samples for HPLC-MS analysis were taken manually, then by a liquid handler, and then through direct-injection to the HPLC. It was found that its side-product formation was directly coupled to the desired product formation, suggesting that both the product and imine side-product stem from a common intermediate. Another little-known side-product was isolated, suggesting the common intermediate could be intercepted by select nucleophiles to form an amide. This finding will direct future attempts to find conditions to favor either β-lactam or amide formation.
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