Green chemistry

From The Book of THoTH (Leaves of Wisdom)

Green chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature, green chemistry seeks to reduce and prevent pollution at its source[1]. In 1990 the Pollution Prevention Act was passed in the United States. This act helped create a modus operandi for dealing with pollution in an original and innovative way.

In 2005 Ryoji Noyori identified three key developments in green chemistry: use of supercritical carbon dioxide as green solvent, aqueous hydrogen peroxide for clean oxidations and the use of hydrogen in asymmetric synthesis. Examples of applied green chemistry are supercritical water oxidation, on water reactions and dry media reactions.

Bioengineering is also seen as a promising technique for achieving green chemistry goals. A number of important process chemicals can be synthesized in engineered organisms, such as shikimate, a Tamiflu precursor which is fermented by Roche in bacteria.

Contents 1 The 12 principles of green chemistry 2 Green chemistry trends 3 Examples 3.1 Supramolecular Chemistry 4 See also 5 External links 6 References

The 12 principles of green chemistry

Paul Anastas, then of the EPA, and John C Warner developed 12 principles to green chemistry[2], which go some way in explaining what the definition means in practice. The principles cover such concepts as:

• the design of processes to maximise the amount of raw material that ends up in the product;
• the use of safe, environment-benign solvents where possible;
• the design of energy efficient processes;
• the best form of waste disposal, aiming not to create it in the first place.

The 12 principles are:

1. Prevent waste: Design chemical syntheses to prevent waste, leaving no waste to treat or clean up.
2. Design safer chemicals and products: Design chemical products to be fully effective, yet have little or no toxicity.
3. Design less hazardous chemical syntheses: Design syntheses to use and generate substances with little or no toxicity to humans and the environment.
4. Use renewable feedstock: Use raw materials and feedstock that are renewable rather than depleting. Renewable feedstock are often made from agricultural products or are the wastes of other processes; depleting feedstock are made from fossil fuels (petroleum, natural gas, or coal) or are mined.
5. Use catalysts, not stoichiometric reagents: Minimize waste by using catalytic reactions. Catalysts are used in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and work only once.
6. Avoid chemical derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste.
7. Maximize atom economy: Design syntheses so that the final product contains the maximum proportion of the starting materials. There should be few, if any, wasted atoms.
8. Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals. If these chemicals are necessary, use innocuous chemicals. If a solvent is necessary, water is usually the best medium.
9. Increase energy efficiency: Run chemical reactions at ambient temperature and pressure whenever possible.
10. Design chemicals and products to degrade after use: Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.
11. Analyze in real time to prevent pollution: Include in-process real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts.
12. Minimize the potential for accidents: Design chemicals and their forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires, and releases to the environment.

Green chemistry trends

Attempts are being made not only to quantify the greenness of a chemical process but also to factor in other variables such as chemical yield, the price of reaction components, safety in handling chemicals, hardware demands, energy profile and ease of product workup and purification. In one quantitative study[3], the reduction of nitrobenzene to aniline receives 64 points out of a 100 marking it as an acceptable synthesis overall whereas a synthesis of an amide using HMDS is only described as adequate with a combined 32 points.

Examples

Supramolecular Chemistry

Research is currently ongoing in the area of supramolecular chemistry to develop reactions which can proceed in the solid state without the use of solvents. The cycloaddition of trans-1,2-bis(4-pyridyl)ethylene is directed by resorcinol in the solid state. This solid-state reaction proceeds in the presence of UV light in 100% yield.

See also

Green computing - a similar initiative in the area of computing

External links

• EPA Green Chemistry Website
• EPA Green Chemistry Fact Sheet
• Green Chemistry Institute
• Green chemistry takes root (USA Today)
• Green Chemistry PhD Program at University of Massachusetts Lowell
• Green Chemistry Experiments for Education, University of Oregon
• Green Chemistry at the University of Scranton
• Green Chemistry Journal Published by the Royal Society of Chemistry, UK

References

1. Pursuing practical elegance in chemical synthesis Ryoji Noyori Chemical Communications, 2005, (14), 1807 - 1811 Abstract
2. www.epa.gov online Link
3. EcoScale, a semi-quantitative tool to select an organic preparation based on economical and ecological parameters. Van Aken K, Strekowski L, Patiny L Beilstein Journal of Organic Chemistry, 2006 2:3 ( 3 March 2006 ) Article

• The MacGillivray Research Group

--Angel 15:58, 13 June 2006 (CDT)