Atom economy

The atom economy ( atom efficiency also ) is the percentage of convicted in a chemical reaction of the starting materials in the products atoms.

Examples

• An example of a completely atom-economical reaction is the [ 4 2 ] cycloaddition ( Diels -Alder reaction), in which all atoms of the starting materials can be found again in the product.
• The Cope rearrangement is an atom- efficient reaction which incurs no waste. This applies analogously to the Claisen rearrangement.
• The Fries rearrangement proceeds atom-efficient, there are no low-molecular waste.
• The addition of bromine to an alkene to form a dibromoalkane is an efficient nuclear reaction; however, the catalytic bromination of benzene is less atom-efficient, since in addition to bromobenzene one equivalent hydrogen bromide produced, not to mention the fate of the catalyst.
• The hydroformylation is an atom- efficient reaction when the regioselectivity is high.
• In the industrial synthesis of phenol after Cumolhydroperoxidverfahren acetone is produced as a by-product in a stoichiometric amount, the atom efficiency is mediocre.
• A little atom-economical reaction is the Grignard reaction, resulting from the significant salt waste.
• The production of thionamides of amides with Lawesson's reagent or phosphorus pentasulfide is little atom-efficient, waste volumes are significantly usually.
• The Gabriel synthesis is an example of a synthesis with a markedly poor atom economy; even at high yields caused significantly greater amounts of waste than the desired product ( primary amine).
• In a resolution can at best an atom economy of 50 % can be achieved, unless the undesired enantiomer is racemized continuously or it can be externally racemized and recycled.
• The Cannizzaro reaction yields, at best, with 50 % atom economy the desired reduction product - alcohol - the remaining aldehyde is oxidized to the carboxylic acid.

Meaning and application

A viable method has been described for the determination of atom economy multistage syntheses.

In the chemical industry, the atom economy is playing an increasingly important role. Modern syntheses are designed so that they operate with high atom efficiency, which is also almost always the most economical method. This disposal is often minimized in stoichiometric amounts of undesired emergent by-products or even completely unnecessary.

Large chemical companies such as BASF AG (keyword: Verbund site ), have been practicing for decades successfully applied in large-scale atom economy. In this case, not only the maximum efficiency of a production process considered, but the efficiency of the complex as a unit location. Putative waste in the manufacturing process A can be valuable starting materials for the production process B represent.

This concept is also pursued energetic point of view. The energy released in an exothermic chemical reaction energy is used in an establishment other than heating.

Systematic approaches to a " sustainable " chemistry and the involvement of other factors that go beyond the atom economy are described in the literature. This involves the use of renewable raw materials, the inclusion of life cycle assessments, social accounting, product life cycles, etc.