Atom efficiency and catalysis in organic synthesis*

The key to waste minimization in fine chemicals manufacture is the widespread substitution of classical organic syntheses employing stoichiometric amounts of inorganic reagents with cleaner, catalytic alternatives. The E factors (by waste per kg product) of chemical processes increase dramatically on going downstream from bulk to fine chemicals and pharmaceuticals, mainly owing to the use of “stoichiometric” methods. The concept of atom efficiency is a useful tool for rapid evaluation of the amount of waste generated by alternative processes. The general theme of atom-efficient, catalytic processes is illustrated with industrially relevant examples. These include catalysis by solid acids and bases, catalytic reductions and oxidations, catalytic C–C bond formation, asymmetric catalysis, biocatalysis, and catalysis in novel media (aqueous and fluorous biphasic systems, supercritical fluids, and ionic liquids).