Green metrics

Barry Trost of Stanford University published the first formal green metric in 1991 in Science. Trost s idea, atom economy, measures the percentage ratio of the total mass of the products to starting materials (Equation 13.2).26 

Atom economy is strictly a theoretical number. The calculation considers only reagents from the balanced chemical reaction. The calculation does not include practical factors such as yield or excess reagents. A given reaction has the same atom economy whether its yield is 90% or 10%. Regardless, atom economy was the first accepted attempt at quantifying the greenness of a reaction. 

SCHEME 13.16 Atom economy information for Boots synthesis of ibuprofen 

The Boots patent on ibuprofen expired in the 1980s, and other manufacturers became able to manufacture and sell ibuprofen. In 1991, the Boots and Hoechst Celanese 

SCHEME 13.18 Atom economy information for BHC synthesis of ibuprofen 

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Application of Green Metrics Analysis to Chemical Reactions and Synthesis Plans... 

Over the last decade there has been a vigorous attempt to answer quantitatively the simple question is a given reaction or synthesis plan green using the so-called green metrics . 

One can see that the forms of equations (4.4) and (4.5) are identical. It is clear that RME (AE) and Em (Emw) describe material efficiency from different points of view, the former with respect to the target product and the latter with respect to the waste products. Figure 4.1 shows the interconnections between the key material green metrics presented above. 

A Microsoft Excel (Version 5.0 or higher) spreadsheet template form has been developed which allows the calculation of the complete reaction mass efficiency (RME) according to equation (4.1) and raw material cost (RMC) for any chemical transformation. Lines are numbered and line instructions are embedded in the same manner as a personal income tax form. Green metrics are evaluated to determine the greermess of the experiment in a rigorous quantitative way and to determine the bottom line cost of carrying out the experiment. Formula entries are inserted in appropriate cells to facilitate computation. Any... 

Figure 4.2 Microsoft Excel spreadsheet output of green metrics analysis for the synthesis of diphenyl-methanol using the Crignard methodology.

For material green metrics calculation for each reaction beginning with the last step (j = N) and working toward the first step (j = 1) ... 

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