By Melanie Mastronardi, Chair for the GCI and Laura Reyes, Secretary for the GCI
2. Atom Economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
Atom Economy, the 2nd principle of green chemistry, comes down to preventing waste on a molecular level. It is an example of a green chemistry metric, which helps us understand the efficiency of a reaction. The equation for atom economy, shown below, essentially tells us the percentage of atoms that end up in the desired reaction product compared to how many atoms are put into the reaction. The higher the atom economy the better, since any atoms that are not incorporated into the final product are considered wasted.
In the GCI’s second video, Brian and Melanie outlined the concept of atom economy by comparing two different synthetic methods for making the over-the-counter drug ibuprofen.
As a supplement to the video, here we show how we did the atom economy calculations:
The % atom economy is calculated using the molar mass values indicated for each molecule in the reactions schemes above, excluding catalysts since they can be reused and therefore do not count towards a reaction’s atom economy. The atom economy for Brian’s reaction is determined as follows:
For Melanie’s reaction, the atom economy calculation looks like this:
It’s clear through these two calculations that the new method for making ibuprofen, shown by Melanie, is much more atom economical at 77%, compared to 40% for the old method shown by Brian. Another way to think of this is that previously, 60% of the reagents used in the making of ibuprofen were wasted, but this was improved to only 23% being wasted. On an industrial scale, that’s a huge difference!
In the video, Melanie also explains that in the industrial process for her reaction, the excess acetic acid by-product that is formed ends up getting sold for other purposes, meaning that it doesn’t go to waste, so her % atom economy essentially ends up being 100%.
Be sure to also check out all of the videos in our campaign on our YouTube channel and keep an eye out for those to come!