Continuing on the trend of adding green chemistry features to apps, which started with a previous train of thought, a useful reference value for reactions is the Process Mass Intensity. As it happens, the Yield101 app is very well positioned to be the recipient of this upgrade.
The app has the same input fields as before, except now there’s some extra information at the bottom. The image below shows a very non-green reaction: mercuration of naphthalene by boiling it in acetic acid for a low yielding product:
Zooming in a little further, we can see that this contains information regarding the process mass intensity (PMI), which is calculated by adding up the mass of all the ingredients on the left hand side, divided by the total mass of the products on the right hand side:
The PMI value is 135.197, which means that the quantity of product recovered is less than 1% of the mass that was dumped in. It doesn’t take into account the unpleasantness of the byproduct, but it does tell us that there is a lot of waste. If the yield was higher, or less solvent was used, or if an exactly stoichiometric amount of reagent was used, or if some of the unused ingredients were recovered, then the PMI would be more favourable.
Also, for each reaction component, the percentage of the total mass, on that side of the reaction, is shown as a percentage bar.
The PMI calculation is supposed to include all of the inputs, which means that solvents, catalysts, reagents, etc., should be included in the scheme. For the calculation to be meaningful, the products section should only contain the substances you are keeping, i.e. typically just the products, and solvents or reagents that are retained.
For convenience, the new version of Yield101 (1.0.3) also has an Add Solvent button, which brings up a list of common solvents (which are, totally coincidently, the same entries used for Green Solvents!), which can be added as non-stoichiometric reactants.
At the time of writing, the new version of Yield101 had just been submitted for review on the iTunes AppStore. With any luck, it will be available in a few days.