The progress of green chemistry so far has been partly a matter of technical feasibility, as researchers have developed less toxic alternatives to conventional methods. A prime example is supercritical carbon dioxide: ordinary, non-toxic carbon dioxide that has been heated and pressurized above its ‘critical point’ of 31.1 °C and 7.39 megapascals, beyond which it behaves like both a gas and a liquid, and readily serves as a solvent for a wide range of organic and inorganic reactions. Other non-toxic replacements for solvents have been found among the ionic liquids: exotic cousins to ordinary table salt that happen to be liquid at or near room temperature.
Other roadblocks to the adoption of green chemistry are technical. For example, even after decades of research, green solvents are not always more efficient than the widely used chlorinated solvents. Nor have chemists completely eliminated the need for catalysts containing precious or toxic metals — although Dunn, for one, is optimistic that this may eventually be possible through advances in enzyme technology. And how to make bulk chemicals from biomass and other renewable feedstocks, rather than from crude oil, is still an open challenge. “It’s a different way of looking at a chemical synthesis,” says Leitner, who points out that the conventional problem gets turned on its head. Instead of starting out with a relatively simple hydrocarbon extracted from oil, and then adding side groups to the molecule to give it the desired properties, chemists have to start with the incredibly complex mixture of biomolecules typical of most renewable feedstocks, and get to what they want by snipping off pieces in a controlled manner.
Green Chemistry in the Redesign of the Sertraline Process ..
It moves because of economic incentives.” The pharmaceutical industry is striving to become more cost competitive through process intensification and other efforts, and minimizing waste and negative environmental impacts are now serious considerations even at the stage of early route selection. As the world sees increases in the cost of waste disposal and the price of petrochemicals, green chemistry considerations come to the forefront.
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Nor is Pfizer alone; the pharmaceutical sector is so competitive that no company can afford to ignore green chemistry’s potential savings. The Pharmaceutical Roundtable, first convened in 2005 by the American Chemical Society’s Green Chemistry Institute, now has 14 member companies that jointly fund academic research in the field and share pre-competitive information.
Sertraline-Active Ingredient in Zoloft ..
After that success, Peter Dunn, the leader of the Viagra synthesis team, became head of the more systematic green-chemistry drive started by Pfizer in 2001. Dunn says he is not free to talk about specific cash savings, but can point to sweeping changes made across the company. Pfizer has reduced the E-factor of the anticonvulsant pregabalin (Lyrica) from 86 to 9, he says, and has made similar improvements for the antidepressant sertraline and the non-steroidal anti-inflammatory celecoxib. “These three products alone have eliminated more than half a million metric tons of chemical waste,” says Dunn.
The Impact of Process Chemists and Engineers on Green Chemistry
Nor does it always pay to be green in the speciality chemicals sector — as Thomas Swan and Company in Consett, UK, learned the hard way. In 2001, building on the work of chemist Martyn Poliakoff at Nottingham University, it opened the world’s first continuous-flow reactor using supercritical carbon dioxide as a solvent. “It looked as if it could have been game-changing within the industry,” says managing director Harry Swan. But when no government subsidies were forthcoming, the plant could not provide chemicals more cheaply than those made by the standard non-green methods, he says. So the facility was mothballed, and may soon be decommissioned and dismantled.
The Impact of Process Chemists and Engineers on ..
Scepticism hasn’t gone away entirely; a mention of green chemistry in a gathering of chemists can still provoke sighs and eye-rolling, says Warner. But scepticism has lessened as research has improved. The EPA, for example, has made notable progress in lifting one barrier to effective green chemistry, which is that researchers trying to create a new, non-toxic manufacturing process often don’t know if a given compound is ‘green’ or not. No one has had the time or money to gather the toxicity data, which typically requires expensive animal testing.