Atom economy describes the conversion efficiency of a chemical process in terms of all atoms involved. In an ideal chemical process the amount of starting materials or reactants equals the amount of all products generated (see stoichiometry) and no atom is wasted. Recent developments like the advent of Green chemistry and high raw material (oil) prices increasingly demand high atom economy.
Atom economy can be written as:
% atom economy = Molecular weight (desired products) / Molecular weight (all reactants)* 100%
Note that atom economy can be poor even when chemical yield is 100%, see for instance the Cannizzaro reaction. A Diels-Alder reaction is an example of a potentially very atom efficient reaction.On the other hand ff the desired product is an enantiomer the reaction needs to be sufficiently stereoselective even when atom economy is 100%.
Atom economy can be improved upon by carefull selection of starting materials and catalyst system. Atom economy is just one way of looking at a chemical process, other criteria are for instance energy consumption, levels of pollution or price.
references
- Atom Economy. A Challenge for Organic Synthesis", B.M. Trost, Angew.Chem. Int. Ed. Engl. 1995, 34, 259.
- Atom Economy: A Green Chemistry Module www.chemsoc.org [1]