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| '''Atom economy''' ('''atom efficiency''') describes the [[conversion (chemistry)|conversion]] efficiency of a chemical process in terms of all [[atom]]s involved (desired products produced). In an ideal chemical process, the amount of starting materials or [[reactant]]s equals the amount of all products generated (see [[stoichiometry]]) and no atom is wasted. Recent developments like high raw material (such as [[petroleum|petrochemicals]]) costs and increased sensitivity to environmental concerns have made atom economical approaches more popular. Atom economy is an important concept of [[green chemistry]] philosophy,<ref>{{cite journal
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| | title = Atom Economy. A Challenge for Organic Synthesis
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| | author = [[Barry Trost|Trost B. M.]]
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| | journal = [[Angew. Chem. Int. Ed. Engl.]]
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| | volume = 34
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| | issue = 3
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| | pages = 259–281
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| | year = 1995
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| | doi = 10.1002/anie.199502591}}</ref><ref>{{cite journal
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| | title = Atom efficiency and catalysis in organic synthesis
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| | author = Sheldon R. A.
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| | journal = Pure and Applied Chemistry
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| | volume = 72
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| | issue = 7
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| | pages = 1233–1246
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| | year = 2000
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| | url = http://www.iupac.org/publications/pac/2000/7207/7207pdf/7207sheldon_1233.pdf
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| | doi = 10.1351/pac200072071233}}</ref><ref>[http://www.chemsoc.org/pdf/gcn/atomeff.ppt Atom Economy: A Green Chemistry Module].</ref> and one of the most widely used [[Green chemistry metrics|ways to measure the "greenness" of a process or synthesis]].
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| Atom economy can be written as:
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| <math>\text{atom economy} = \frac{\text{molecular mass of desired product}}{\text{molecular mass of all reactants}} \times 100%</math>
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| noting that [[conservation of mass|the total molecular mass of the reactants is the same as the total molecular mass of the products]].
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| Note that atom economy can be poor even when [[chemical yield]] is near 100%, see for instance the [[Cannizzaro reaction]] or the [[Wittig reaction]]. If the desired product has an [[enantiomer]] the reaction needs to be sufficiently [[stereoselective]] even when atom economy is 100%. A [[Diels-Alder reaction]] is an example of a potentially very atom efficient reaction that also can be chemo-, regio-, diastereo- and enantioselective. Catalytic hydrogenation comes the closest to being an ideal reaction that is extensively practiced both industrially and academically.<ref>{{cite journal
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| | doi = 10.1016/S0040-4020(01)87670-5
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| | title = The Synthesis of (+/-)Isoptychanolide by Application of the a-Alkynone Cycilsation
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| | author = Solaza, B.; Huguet, J.; Karpf, M. and [[André Dreiding|Dreiding, A. S.]]
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| | journal = Tetrahedron
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| | volume = 43
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| | issue = 21
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| | pages = 4875–4886
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| | year = 1987}}</ref>
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| The [[Gabriel synthesis]] of amines is an example of extremely low atom economy, as [[stochiometry|stochiometric]] quantities of [[phthalic acid]] derivatives are formed. In most cases, the atom economy of the Gabriel synthesis is <<50%.
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| Atom economy can also be adjusted if a pendant group is recoverable, for example [[Evans auxiliary]] groups. However, if this can be avoided it is more desirable, as recovery processes will never be 100%. Atom economy can be improved upon by careful selection of starting materials and a [[catalyst]] system.
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| Atom economy is just one way to evaluate a chemical process. Other criteria can include energy consumption, pollutants released and price.
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| Poor atom economy is common in [[fine chemicals]] or [[pharmaceuticals]] synthesis, and especially in research, where the aim to readily and reliably produce a wide range of complex compounds leads to the use of versatile and dependable, but poorly atom-economical reactions. For example, synthesis of an alcohol is readily accomplished by reduction of an ester with [[lithium aluminum hydride]], but the reaction necessarily produces a voluminous floc of aluminum salts, which have to be separated from the product alcohol and disposed of. The cost of such hazardous material disposal can be considerable. Catalytic hydrogenolysis of an ester is the analogous reaction with a high atom economy, but it requires catalyst optimization, is a much slower reaction and is not applicable universally.
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| == Creating reactions utilizing atom economy ==
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| It is fundamental in chemical reactions of the form A+B→ C+D that two products are necessarily generated though product C may have been the desired one. That being the case, D is considered a byproduct. As it is a significant goal of green chemistry to maximize the efficiency of the reactants and minimize the production of waste, D must either be found to have use, be eliminated or be as insignificant and innocuous as possible. With the new equation of the form A+B→C, the first step in making chemical manufacturing more efficient is the use of reactions that resemble simple addition reactions with the only other additions being catalytic materials.
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| == References ==
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| {{Reflist}}
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| [[Category:Stoichiometry]] | |
| [[Category:Green chemistry]]
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