Protecting the Environment with Green Chemistry

“Green chemistry is not just a mere catch phrase: it is the key to the survival of mankind”
Professor Ryoji Noyori – Nobel Laureate

Green chemistry aims to reduce the negative impact of the chemical industry on human health and the environment. Chemists do this by developing alternative processes and reaction media, such as solvents, which are environmentally friendly.

Greener solvents

The manufacture of chemicals, such as drugs, can involve huge volumes of harmful solvents. So selecting greener solvents is a key target of many green chemistry programmes. Progress is being made towards identifying solvents that can be used in much smaller quantities, and careful selection can also increase reaction rates and lower reaction temperatures.

Making the most of nature’s catalysts

Pregabalin, also known as Lyrica, is a medicine used to control epileptic seizures and pain caused by nerve damage. It is thought to act by decreasing the number of nerve signals firing and hence reducing the pain experienced.

Organic chemists developed a method of producing pregabalin which relied on a natural lipase as a catalyst, and water as a solvent. This meant that previous environmentally harmful solvents could be eliminated. In addition, it is estimated that this greener process will produce three million fewer tonnes of CO₂ than before. That is the equivalent of taking more than one million cars European cars off the road for a year!

Getting rid of dangerous heavy metals

It’s not just solvents that chemists are trying to eliminate from manufacturing processes– there are many other chemicals used in manufacture which can be damaging to the environment. For example, scientists at Pfizer faced a major challenge in improving the manufacture of sildenafil citrate¹, the active ingredient in Viagra^TM and Revatio^TM, a drug used to treat pulmonary hypertension.

The traditional process for manufacturing sildenafil citrate relied on a tin chloride catalyst, as well as chlorinated and volatile solvents. Tin is a heavy metal and a major environmental polluter. Chemists cleaned up the process by replacing the tin reaction with a catalytic hydrogenation. With only water as a by-product, catalytic hydrogenation is one of the cleanest possible chemical reaction steps.

But chemists went even further than this, and eventually created an entirely new synthetic route to make sildenafil citrate, built around a very efficient final step. This new route is predicted to have eliminated 30,000 tonnes of chemical waste between 1997 and 2013.

Advances in Green chemistry will continue to offer opportunities to discover and apply new chemistry, to improve the economics of chemical manufacturing and reduce the chemical related environmental impact.