Again developed by GSK,iv the reaction mass efficiency takes into account atom economy, chemical yield and stoichiometry. The formula can take one of the two forms shown below:
From a generic reaction where A + B → C Reaction mass efficiency = molecular weight of product C × yield m.w. A + (m.w. B × molar ratio B/A)
Or more simply Reaction mass efficiency = mass of product C × 100 / mass of A + mass of B
Like carbon efficiency, this measure shows the “clean-ness” of a reaction but not of a process, for example, neither metric takes into account waste produced. For example, these metrics could present a rearrangement as “very green” but they would fail to address any solvent, work-up and energy issues arising.
Read more about this topic: Green Chemistry Metrics
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