Green chemistry

 

Green chemistry, also called sustainable chemistry, an approach to chemistry that endeavours to prevent or reduce pollution. This discipline also strives to improve the yield efficiency of chemical products by modifying how chemicals are designed, manufactured, and used.

Green chemistry dates from 1991, when the U.S. Environmental Protection Agency (EPA) launched the Alternative Synthetic Pathways for Pollution Prevention research program under the auspices of the Pollution Prevention Act of 1990. This program marked a radical departure from previous EPA initiatives in emphasizing the reduction or elimination of the production of hazardous substances, as opposed to managing these chemicals after they were manufactured and released into the environment. This research program later expanded to include the development of greener solvents and safer chemicals. The name green chemistry was officially adopted in 1996.

The goal of the Pollution Prevention Act of 1990 was not simply to regulate the quantity and type of emissions but to place limits on the industry in order to reduce the amount of pollution it generated. American chemist Paul Anastas, one of the principal founders of green chemistry, claimed that by improving how chemicals are synthesized, it might be possible to prevent the production of pollutants.

Green chemistry’s 12 principles

To help define a more specific research agenda, the 12 principles of green chemistry were formulated by Anastas and American chemist John Warner in 1998:

1. Prevent waste wherever possible.

2. Promote “atom economy” (that is, maximize the efficiency of production so that fewer by-products are made during the manufacture of the final product).

3. Synthesize less-hazardous chemical by-products.

4. Design safer, less-toxic chemical products.

5. Use safer solvents and auxiliaries in chemical processes.

6. Design energy-efficient chemical-manufacturing processes.

7. Use renewable feedstocks.

8. Reduce or avoid the production of derivatives.

9. Use catalysts (most of which require fewer materials to carry out a chemical reaction).

10. Design chemicals that break down into harmless products after they are used.

11. Promote the development of real-time analysis of chemical products before hazardous substances can form.

12. Promote inherently safer chemistry (such as the use of safer forms of various substances) to prevent accidents from occurring.

Atom economy

Of these principles, “atom economy,” originally suggested by American chemist Barry Trost in 1973, became a central concept among green chemistry researchers. Atom economy was designed to overcome the limitations of the traditional concept of “yield,” the amount of final products, which was used for calculating the efficiency of chemical reactions. To calculate the yield, chemists traditionally considered only the amount of the main chemical product they intended to produce (“target molecules”) and not by-products, which might include environmentally hazardous materials. In contrast, atom economy takes into account all reactants and products and hence provides a more-reliable indicator of whether the reaction produces undesirable by-products—that is, pollutants. Green chemistry has since demonstrated that high-efficiency atom economy is indeed achievable through such processes as hydrogenation, metathesis, and cycloaddition.