Atom economy / E factor

Tom Squire
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Atom economy / E factor are important concepts when designing chemical reactions to ensure sustainability, with atom economy in particular a common measure of how “green” a reaction is. For example, a reaction may have 100% yield, but still generate more waste than product. 


Atom economy is defined as the conversion efficiency of a chemical process, in terms of all atoms involved and the desired products produced. 

atom economy equation. Molecular weight of desired product over the sum of all molecular weights of the materials produced multiplied by 100.

E factor (environmental factor) is another simple metric of how “green” a reaction is. It is defined as the ratio of the mass of waste per mass of product. 

Task 1; Can you calculate the approximate E-factor for each industrial sector. 

Industry sector Approx. Annual production (t) Approx. Waste produced (t) E-factor
Oil refining 1×106 – 1×108 1×105 – 1×107  
Bulk chemicals 1×104 – 1×106 1×104 – 5×106  
Fine chemicals 1×102 – 1×104 5×102 – 5×105  
Pharmaceuticals 10 – 1×103 2.5×102 – 1×105  

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Synthesis of Phenol

Old synthetic route (formation of sodium phenolate which is then hydrolysed to phenol);

Even at 100% yield, the reaction generates more waste than product by weight.

Task 2; Calculate the atom economy and E factor for the old synthetic route to make phenol.

New synthetic route (The Cumene route);

Here, the ‘by-product’ is a desirable compound; acetone.  Therefore, can you determine the atom economy and E factor without doing the calculations?


Atom economy and E factor should not replace consideration of yield, ease of product isolation and purity requirements when designing a chemical synthesis. But it should be an additional consideration and it is something that has been widely implemented by the chemical industry with big impacts on sustainability and also economics.

Learn more about designing sustainable synthesis here.

Download a printable version with answers to tasks here

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