Green Chemistry
Green Chemistry, the quest for clean and efficient chemical transformations under conditions which minimize environmental impact, is a socially responsible field that is growing rapidly both in terms of acceptance and importance.
Also known as sustainable chemistry, the Environmental Protection Agency (EPA) states that green chemistry refers to “environmentally friendly chemicals and processes that result in: reduced waste, eliminating costly end-of-the-pipe treatments; safer products; and reduced use of energy and resources—all improving the competitiveness of chemical manufacturers and their customers.” Green chemistry is a preventative philosophy looking to stop pollution at its source, instead of cleaning up afterwards, by encouraging the design of chemical products and processes that reduce or eliminate the use and generation of environmentally hazardous substances according to the 12 principles of Paul Anastas (Anastas, P.T.; Warner, J.C. Green Chemistry Theory and Practice 1998, p 30) which are:
1. Prevent waste
2. Design safer chemicals and products
3. Design less hazardous chemical syntheses
4. Use renewable feedstock
5. Use catalysts, not stoichiometric reagents
6. Avoid chemical derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible.
7. Maximize atom economy
8. Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals.
9. Increase energy efficiency: Run chemical reactions at ambient temperature and pressure whenever possible.
10. Design chemicals and products to degrade after use
11. Analyze in real time to prevent pollution
12. Minimize the potential for accidents
Many of the incompatibilities between classical chemical methods and green chemistry are related to the use of organic solvents as reaction media. In fact, some estimates claim that up to 80% of the waste generated during the manufacture of a typical pharmaceutical ingredient is related to use of an organic solvent (Jiminez-Gonzales, C.; Cursons, A. D.; Constable, D. J. C.; Cunningaham, V. L. Int. J. LCA 2004, 114. Eissen, M.; Hungerbuhler, K.; Dirks, S.; Metzger, J. Green Chem, 2003, G25).
Water, the most abundant solvent on the planet, has numerous advantages as an alternative reaction solvent: it is inexpensive, readily available, and non-toxic. There are no issues with electrostatic discharge or flammability, no noxious fumes are released, and it is environmentally friendly. In short, water is the ideal solvent for chemical reactions!
Nevertheless, water is rarely the solvent of choice because most compounds used in manufacturing are organic, and as such, do not dissolve in water. Therefore, organic solvents are more commonly used to manufacture everyday products including: dyes, polymers, plastics, textiles, rubber, printing inks, agricultural products, and pharmaceuticals. Organic solvents are also effective in extracting and purifying compounds from a mixture. They are easily removed by evaporation or distillation, leaving the dissolved substance behind unchanged. Unfortunately, this also generates tons of waste solvents daily, many of which are recognized by the National Institute for Occupational Safety as carcinogens, reproductive hazards, and neurotoxins http://www.cdc.gov/niosh/topics/organsolv/. If these solvents spill or leak from industrial sites and reach the underlying soil and/or water supply, they can cause health problems in affected populations.
The Ubisol-Aqua™ technology enables the unprecedented use of water as a reaction solvent for such commercially relevant chemical processes as the Suzuki coupling, the Heck reaction, the Sonagashira coupling, and both cross- and ring closing metathesis (published research). With Ubisol-Aqua™, these processes can be run in pure water at room temperature while delivering excellent yields and (where applicable) stereoselectivities. This provides a technology platform that can truly be described as “green”. In fact, many of the reactions conducted with the aid of Ubisol-Aqua™ outperform similar processes typically employed under classical conditions using organic solvents and heat. The basis behind the success of this process lies in the micelle-forming properties of PTS; i.e., the “micellar effect”. In these important cases of transition metal-catalyzed processes, the switch to green enables environmental responsibility and real enhancements in synthetic efficiency!