The Greening of Science

A philosophy only recently introduced to the chemicals industry, green chemistry promotes the careful design of chemicals manufacturing processes to reduce the use of toxic components and minimize waste and energy use. The sustainable and more benign practices that follow green chemistry’s principles have found support in industry and government and are being researched more and more by universities and government agencies around the world.

When ibuprofen, the popular pain reliever that remedies headaches, stiff muscles, and fevers, was first manufactured in the 1960s, it generated more waste than drug. Chemists were making ibuprofen by adding an excess of aluminum trichloride to isobutyl-benzene and pushing through a six-step reaction with solvents and separation agents. Although the method certainly turned out the drug, it was highly inefficient and produced unwanted by-products at each step of the way: an annual production of 30 million pounds of ibuprofen generated 45 million pounds of waste, mostly tossed for scrap.

But in the early 1990s ibuprofen got a makeover. Using catalysts rather than excess reagents to drive the reactions, chemists halved the number of stages in the ibuprofen manufacturing process and eliminated carbon tetrachloride, a toxic solvent, from the process. In the new process, atom economy—the percentage of raw materials and reagents used in the synthesis that ends up in the final product—hovered between 80% and 99%. Those materials and reagents that didn’t end up in the final product, such as acetic acid, could be reclaimed or recycled. The revamped reaction was not only good for business (in that it reduced clean-up costs and minimized the consumption of raw materials), it was good for the environment.

One doesn’t have to look too far into the past to find examples of chemicals and chemical processes that have had a negative impact on human health and the environment. But more recently a new type of chemistry—green chemistry—is taking hold of academia, industry, and government. Green chemistry rethinks the design of chemical processes and offers environmental benefits by reducing waste, eliminating expensive chemical treatments, and reducing the use of energy and resources. According to the American Chemical Society (ACS) this chemical revolution unleashes scientists’ creativity and inventiveness while increasing the performance and value of chemicals and materials.

Industrial Origins, Nobel Ends

Green chemistry has become fashionable only in the last two decades, but its origins can be traced to 1950s industry. In 1956 chemists in DuPont’s petrochemical department in Wilmington, Delaware, found that passing propene over a molybdenum-on-aluminum catalyst produced a mixture of propene, ethene, and 1-butene. Other chemists were uncovering similar results when they combined olefins (alkenes) with other molybdenum catalysts. The products were the result of breaking and rebuilding the double bonds in the alkenes. The carbon of the double bond of one alkene swapped places with one carbon of the double bond of the other alkene. But chemists lacked a mechanism to explain what was taking place. 

A number of theories were proposed over the next 15 years, but it wasn’t until 1971 that Yves Chauvin of the Institut Français du Pétrole along with student Jean-Louis Hérisson identified the process: a metal carbene was kicking off the reaction. Chauvin called it a molecular dance, in which one partner was cast off for another. Twenty years later, Richard Schrock of the Massachusetts Institute of Technology uncovered which metals could be used as catalysts. One group of molybdenum catalysts was particularly effective at rearranging the compounds’ double bonds. But these were highly reactive and sensitive to both oxygen and moisture. They were far from perfect. In 1992, Robert Grubbs, of the California Institute of Technology, discovered a ruthenium catalyst that was stable in air and more selective than Schrock’s catalysts.

Together these chemists’ contributions explained and developed the olefin metathesis reaction, creating a new tool to shorten the route to a desired molecule and reduce the number of unwanted and often hazardous by-products. Its discovery opened up new opportunities in the industrial production of pharmaceuticals, plastics, and other materials.