How to Practice Green Chemistry – Wheel of Green Chemistry
Green chemistry is focused on the design of products and processes that minimize or eliminate the use and generation of hazardous materials (HazMat).
There exist two related terms, viz.,
atom economy (AE) and environmental factor (E-factor).
% AE = [(Stoichiometric
mass of the desired product) / (Mass of a stoichiometric mixture of reactants)]
x 100
Simply put, a large AE
means a little waste and reduces raw material costs and environmental impact.
E-factor = (Mass of waste
produced) / (Mass of product obtained)
The mass of the water is excluded
if the reaction or process produces waste water. However, the masses of
substances dissolved in the water are included.
A small E-factor is wanted.
For real-time monitoring of the
impact of modifications to a synthesis or industrial process, the E-factor
is chiefly valuable. Most laboratory and industrial processes also utilize a
solvent and an excess of one or more of the reagents in the reaction, which
increase the amount of waste; and therefore, the E-factor.
Examples of green
chemistry
Hydrogenation of Ethene (100%
AE): To form Ethane only via catalytic addition (addition reactions generally
more efficient than substitution or elimination reactions)
Hydrogenation of esters:
Catalytic hydrogenolysis of an ester to an alcohol
Diels-Alder
reactions (100% AE): To combine a diene and a dienophile into a
single ring structure (adduct) without producing by-products via cycloaddition
Rearrangement reactions (100%
AE): e.g., Claisen rearrangement
Improved Ibuprofen synthesis (77.4%
AE): Modern three steps Hoechst-Celanese method
(compared to the earlier method having 40% AE) to make this non-steroidal
anti-inflammatory drug (NSAID)
Semaglutide synthesis (current bioprocess):
An anti-diabetic medication for the treatment of type 2 diabetes, and an
anti-obesity medication for long-term weight management and to reduce the risk
of major adverse cardiovascular events
Wheel of green chemistry: Click/tap to enlarge the image
The twelve principles of green chemistry
- Better to avoid waste than to treat or clean up waste after its generation
- Synthesis to be designed to maximize the incorporation of all starting materials (SMs) used in the process into the final product
- To use and create substances that possess little or no toxicity to human health and the environment
- To provide their desired function while minimizing their toxicity
- Use of auxiliary substances (e.g., solvents, isolation agents, etc.) to be made unnecessary and innocuous wherever possible
- Environmental and economic impacts to be evaluated and minimized (if possible, to be conducted at ambient temperature and pressure)
- Whenever technically and economically feasible
- Use of protecting/deprotecting groups to be minimized
- Catalysts to be reused
- At the end of their function chemicals to break down into safe products and not to persist in the environment (eco-friendly or biodegradable)
- Analytical methodologies to be developed for in-process monitoring and control for pollution prevention
- Potential for chemical accidents, including releases, explosions, and fires to be minimized by rationally choosing substances and their forms
Glamorous green chemistry ❓What other wheel(s) 🎡 of organics would you like to see❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗
References:
(1) Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.
(2) Graham, T. W.; Fryhle, C. B.; Snyder, S. A. Organic Chemistry.; Hoboken, Nj John Wiley Et Sons, Inc, 2016.
(3) Anastas, P. T.; John Charles Warner. Green Chemistry : Theory and Practice; Oxford University Press: Oxford ; New York, 2000.
(4) Wikipedia. Semaglutide. Wikipedia. https://en.wikipedia.org/wiki/Semaglutide.
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