Wednesday, May 19, 2010

Click chemistry and green chemistry

Click chemistry, in a broader sense, is about using easier reactions to make compounds for certain functions, drugs or materials or anything else. Let us say it is almost purely a scientific term. Green chemistry has been in place for long as a scientific term without much significane until reacent times when everything wants or needs to be "green". To be scientific, not fancy here, I try to connect and compare these two, using the "Twelve Principles of Green Chemistry", by Anastas and Warner.

1.Prevention - It is better to prevent waste than to treat or clean up waste after it has been created.
Click chemistry can do a good job in here since the reaction is addition and high-yielding.
2.Atom Economy - Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
Click chemistry is particularly good at this.
3.Less Hazardous Chemical Syntheses - Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
Azide and Copper(1+) do not fit the bill but there are other good reactions in click chemistry - and the reactions are growing.
4.Designing Safer Chemicals- Chemical products should be designed to effect their desired function while minimizing their toxicity.
EPA recently launched ToxRefDB (Toxicity Reference Database) but obviously this type of testing takes time. 
5.Safer Solvents and Auxiliaries - The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
Click chemistry is good for this, especially the tolerance of water as the solvent.
6.Design for Energy Efficiency - Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.
Click chemistry is good here - a lot of reactions can be done without much heating.
7.Use of Renewable Feedstocks - A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
Yet to see the relevance.
8.Reduce Derivatives - Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.
Click chemistry wins big for its superior selectivity and tolerance of most functional groups.
9.Catalysis - Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
Click chemistry does well, either by chemical or light catalysts.
10.Design for Degradation - Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
Yet to establish the relevance.
11.Real-time analysis for Pollution Prevention - Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
Yet to establish the relevance.
12.Inherently Safer Chemistry for Accident Prevention - Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.
Azides do not play well but there are other types of click reactions such as ene - thiol etc.

Well, green chemistry right now is as big as one can imagine, although many doubts exist among chemists. Let us wait and see.

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