Sustainable “green” Chemistry


What is an example of how to “green” a chemical process?

At the pharmaceutical giant Pfizer, the synthesis of Viagra® (see “The World Around Us”) originally had an E-factor of 105. However, even before Viagra® was made available to the public, a team of researchers at Pfizer re-examined the entire synthesis step by step. Relatively toxic chlorinated solvents were replaced with less toxic alternatives. The synthesis was also modified to recycle the solvents wherever possible. The use of hydrogen peroxide, which carries some associated health hazards, was removed from the process. Another reagent, oxalyl chloride, is also no longer used; use of this reagent results in the production of carbon monoxide, which is now avoided. In the end, the E-factor for synthesis of Viagra® was reduced to only 8, an over thirteen-fold reduction!

Subsequently, similar changes were made to processes throughout Pfizer. The E-factor for Lyrica®, an anticonvulsant drug, was similarly reduced from an initial value of 86 to now only 9. These sorts of improvements are eliminating millions of tons of chemical waste, while in most cases simultaneously lowering production costs, making safer work conditions, and making products safer for consumers.


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