Chemistry Innovations to Reduce Byproduct Waste

Posted on Thursday, April 28th, 2022

woman holding a pipette and filling beakers with a solution
Organic synthesis can be used to make everything from pharmaceuticals and fragrances to food dyes and herbicides.

Undesirable byproducts can be reduced through innovative chemistry transformations.

If you have ever taken aspirin to relieve a fever or headache, then you have used a product that was developed by organic synthesis. Organic synthesis is the process of creating a substance, such as aspirin, from readily available, naturally occurring carbon-rich materials. However, undesirable byproducts are often created during the process, causing less of the desired product outcome (the aspirin) to be produced.

Within the field of organic synthesis, there has been a shift towards using transition metal catalysts, such as iridium, to create a favourable chemical reaction. These catalysts open innovative avenues for chemical functionalization – the process that can introduce new features, properties, and functionality to a molecule. For example, the functionalization of inactive carbon-hydrogen bonds.

Of particular interest in organic synthesis is the intermediate oxabenzonorbornadiene (OBD). In a multi-step chemical reaction, an intermediate is a temporary substance that is produced, but then is used up in a later step. OBD is of interest because it has multiple points of reactivity that allow for diverse functionalizations—important for creating all kinds of materials—making it a desirable and versatile starting material in organic synthesis. However, its specific transformation depends on the preferred functionalization between different reaction sites with the resulting product being favoured over another, otherwise known as regioselectivity.

Currently, the regioselectivity of OBD functionalizations are not fully understood. Further understanding is needed to optimize production of the target molecule (the aspirin), over other less desirable byproducts. These initial studies can improve our understanding of these reaction mechanisms.

Understanding the pathway to the structure of chemical systems

University of Guelph chemistry professors, Drs. Leanne Chen and William Tam, along with chemistry PhD student Austin Pounder, recently used density functional theory, a model used to study the structure of chemical systems such as molecules and atoms derived from quantum mechanics – looking at the behaviours of matter and light at the scale of atoms and electrons – to develop a deeper understanding of iridium-catalyzed reactions of OBD. Their goal was to confirm the origin of regioselectivity. The team proposed a catalytic cycle that utilized iridium with a major step where the oxidization process, forming a new carbon-to-carbon bond, is reversed (reductive elimination).

Based on their analysis, Chen and Tam predicted that reductive elimination and the creation of the carbon-to-carbon bond is the origin of regioselectivity because this step is irreversible due to the energy required for converting one molecule into another. Ultimately, these findings will help reduce toxic byproducts resulting during the process and increase the output of the desired products.

“This research will impact the fields of chemistry, agriculture and medicine, which all use organic synthesis to develop important products we use everyday. Understanding the origin of regioselectivity will enable us to produce products like shampoo and plastics while reducing toxic byproducts and improving yields, resulting in a more environmentally friendly and cost-effective production process,” says Tam.

Dr. Leanne Chen headshot
Dr. Leanne Chen is an Assistant Professor in the Department of Chemistry

Dr. William Tam headshot
Dr. William Tam is a Professor in the Department of Chemistry

This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants and an NSERC Postgraduate Scholarship – Doctoral program.

Ho A, Pounder A, Valluru K, Chen L, Tam W. Iridium-catalyzed hydroacylation reactions of C1-substituted oxabenzonorbornadienes with salicylaldehyde: an experimental and computational study. Beilstein J. Org. Chem. 2022 Mar 2. doi: 10.3762/bjoc.18.30.

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