Green Chemistry Metrics - Atom Economy

Atom Economy

Atom economy was designed in a different way to all the other metrics; most of these were designed to measure the improvement that had been made. Barry Trost conversely, designed atom economy as a method by which organic chemists would pursue “greener” chemistry. The simple definition of atom economy is a calculation of how much of the reactants remain in the final product. This is shown below:

For a generic multi-stage reaction: A + B → C C + D → E E + F → G

Atom economy = m.w. of G × 100 Σ (m.w. A,B,D,F)

The drawback of atom economy is that assumptions have to be made. For example, inorganic reagents (such as potassium carbonate in a Williamson ether synthesis) are ignored as they are not incorporated into the final product. Also, solvents are ignored, as is the stoichiometry of the reagents.

The atom economy calculation is a very simple representation of the “green-ness” of a reaction as it can be carried out without the need for experimental results. However, it is useful as a low atom economy at the design stage of a reaction prior to entering the laboratory can drive a cleaner synthetic strategy to be formulated.