The Green Age of Chemistry
by Mark Shainblum
McGill researchers are at the forefront of a whole new kind of environmentally friendly chemistry. Replacing toxic solvents with water, turning CO2 into biodegradable plastic—you might say they’re saving the world one molecule at a time.
The word organic has become shorthand for Earth-friendly, health-conscious awareness of everything from cotton to coffee. Organic chemistry, however, is an entirely different beast. It focuses on reactions using what scientists call organic compounds, composed primarily of carbon and hydrogen. A far cry from the popular consumer denotation, the name stems from the erroneous 19th-century belief that organic compounds could only be synthesized in living organisms through the vis vitalis. Although it has nothing to do with this life force, organic chemistry most certainly now informs almost every aspect of our lives. Pharmaceuticals, food flavouring, microchips: there’s nary an industrial process or product that isn’t the end result of an organic chemical reaction. Unfortunately, the same processes that engender our computer-loving, fuel-guzzling, antibiotics-popping lifestyles are also poisoning the planet with persistent organic pollutants like polychlorinated biphenyls (PCBs). But all that is about to change.
“Chemistry is the only field whose primary mandate is to make new forms of matter,” says Bruce Lennox, Chair of McGill’s Department of Chemistry. “In order to invent new molecules, you need to have a chemical reaction that you can implement.” In organic chemistry, this means dissolving the solid, liquid or gaseous starting materials in a solvent. These solvents, however, are often highly toxic. That’s why McGill researchers are heading a revolution that hopes to change how we do chemistry. In the research lab and on the shop floor, these pioneers of zero-emission green chemistry aim to replace traditional chemistry processes with cleaner means to the same ends—thus reducing, and even preventing, pollution at the source.
Tak-Hang “Bill” Chan, now Emeritus Professor of Chemistry, is widely credited as the father of green chemistry research in Canada. Chan saw the writing on the wall for organic solvent-based chemistry in 1989, when almost 200 nations ratified the UN-sponsored Montreal Protocol on Substances that Deplete the Ozone Layer. “It was actually the first international agreement which controlled the release of any kind of chemical into the environment,” he says. “This made it clear to me that volatile organic chemicals would not be feasible in the long run.”
Chan hit upon the idea of replacing toxic solvents with a widely available, non-toxic substance: water. The ubiquitous wet stuff was one of chemistry’s first solvents, but it fell out of favour with the introduction of organic molecule upstarts (such as acetone), which were believed to be non-water-soluble. In fact, just 15 years ago water was an unthinkable solvent alternative—but that didn’t stop Chan from giving to his then-new doctoral student, Chao-Jun (C.J.) Li, an outrageous research project: to carry out organic reactions in water.
“People have rarely looked at using water in organic chemistry at all,” says C.J. Li, now Canada Research Chair in Green Chemistry and one of the pre-eminent researchers in the field. “Some industries are still using chemical reactions that were discovered over a century ago.” Li broke with this tradition when he developed ways to use metal catalysts, submerged in water, to get many of the same chemical results that normally require organic solvents; these reactions have numerous industrial applications. Li’s processes “maximize atom economy” (read: they create little waste) and are more energy efficient—making them not only environmentally friendly, but more cost-effective.
Professor Marcus Lindström, recently arrived from Sweden’s University of Lund, is also working toward the long-term goal of replacing organic solvents with water. Lindström and his team have discovered what they believe to be one of the most stable and efficient catalysts for use in aqueous biphasic catalysis, which completely eliminates the use of organic solvents. The results of recent experiments, performed in collaboration with DuPont Chemoswed in Sweden, could very well revolutionize industrial chemical production.
“What’s so exciting about this research area,” Lindström says, “is that we’re creating new strategies and concepts that will have a lasting impact on how efficient we will be at making chemicals, and not waste, in the future.”
Such improved efficiency is a tenet of the green chemistry philosophy. Using current chemistry techniques, the production of fine chemicals (such as those used to make fragrances) and pharmaceuticals entails numerous steps; because organic solvents will not dissolve organic molecules like amino acids or glucose, other substances must be added to the mix, and later separated from the final product. The process is tremendously complicated. “I use the analogy of trying to build a modern city using the techniques of the ancient Egyptians,” explains Chan. “When they built the pyramids, they built a ramp first and then removed it when they were done. You cannot build a modern city that way, it’s impossible. However, when you’re currently making fine chemicals or pharmaceuticals, that’s exactly what you’re doing.”
“Green chemistry is really about innovation,” suggests Lindström. “It’s not just about replacing one solvent with a less hazardous alternative, or one catalyst with a similar, less toxic one—although that type of activity has its place, of course. Our generation needs to rediscover chemistry by thinking outside the tool box handed to us by chemists from the last century, when being green was not always a priority.”
Audrey Moores is part of that generation. The most recent member of McGill’s green team, the professor is on a quest to find new, more efficient catalysts for use in chemical reactions. “We’re working to find new reactions that make the same thing in a shorter time,” she says, “or with less heating, or less waste, or less toxic reagents.” Moores is particularly interested in the green potential of heterogeneous catalysis. In heterogeneous catalysis, the reactant (starting substance) and catalyst are in a different form; one may be a solid, for example, the other a gas. This means that, unlike homogeneous catalysis, it doesn’t require separating the catalyst from the finished product. Saving that extra step, such as evaporation or distillation, saves money.
“That’s green in itself,” says Moores, who came to McGill in January 2007 after completing postdoctoral studies at Yale, “because you’re reducing the energy cost of the process. You don’t have to do the reaction in a batch, stop the batch, then take it elsewhere to do the distillation. All those steps are really energy demanding. With heterogeneous catalysis, you can even do several steps at the same time, which is a great way to reduce costs and waste. And you don’t risk damaging the catalyst, which means you can reuse it, which you often can’t do with homogeneous catalysis.”
Green chemistry isn’t just concerned with streamlining a product’s chemical birth—it’s also striving for a cleaner burial by creating products that will innocuously break down after they’ve been discarded. Li is currently working on a process that would make it possible to recycle existing CO2 into polymer plastics. “This new plastic has extremely good properties, like durability and strength,” he explains, “and it’s biodegradable.
Of course, it’s better to recycle it, but if it does get thrown out, it decomposes and becomes CO2 again. It’s CO2 neutral, meaning it doesn’t add any new CO2 to the environment.”
Li’s work doesn’t just improve on the final act of a product’s life: His innovation would also eliminate petrochemicals and toxic solvents from the plastic-making process itself. Producing less harmful waste from the get-go is a huge step toward reducing future toxic clean-up problems—and that’s green chemistry’s ultimate goal.
“Preventing a problem,” notes Lennox, “is far more satisfactory than trying to fix one.”
This research is funded in part by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation and the Fonds québécois de la recherche sur la nature et les technologies.