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What exactly is “Green Chemistry?”

Green chemistry is more of a philosophy than a set of rules. It is a “cradle to grave” approach when dealing with chemicals.

In 1942 nylon went to war. American paratroopers dropped from the sky with nylon parachutes and hunkered down in nylon tents. Soldiers on leave hoped to seduce European women with gifts of nylon stockings. Bristles for toothbrushes, strings for tennis racquets, insulation for wires, bearings for machinery, catheters, sutures, umbrellas, undergarments, shower curtains and numerous items of clothing all made of nylon soon hit the market. Consumers were absolutely taken with this miraculous new material. Nobody asked where the raw materials to make nylon came from, or whether nylon production had any impact on the environment. The benefits of DuPont’s nylon were clear, and the company’s slogan of “better living through chemistry” struck a chord with the public. Other products of chemistry were duly welcomed. Antibiotics battled disease-causing bacteria, pesticides and synthetic fertilizers increased agricultural yields, preservatives cut food costs, polychlorinated biphenyls improved electrical transformer performance and chlorofluorocarbons introduced a new era in refrigeration and air conditioning. Life was good, chemistry basked in the limelight.

And then in 1962 Rachel Carson’s “Silent Spring” cast a pallor over the burgeoning chemical industry. Synthetic pesticides, she claimed, may increase crop yields, but there would be fewer birds flying over those crops. Pesticides, DDT in particular, interfered with the ability of birds to lay healthy eggs, Carson maintained. And if birds were affected, could humans be far behind? Other revelations further tarnished the image of chemicals. There was the tragedy of thalidomide and dioxin contamination of Agent Orange in Viet Nam. The entire town of Love Canal in upper New York State was abandoned because of waste oozing from a chemical company landfill. Then came the disaster in Bhopal, India, with thousands being killed by the accidental release of methyl isocyanate from a pesticide manufacturing plant. Little wonder that in national surveys people began to link “chemistry” with terms like “pollution,” “nuclear winter,” “toxins,” and “poisons.” Extreme views, to be sure, but not totally dismissible. In the headlong rush for new products and increased profits, pollution control and safety concerns sometimes took a back seat. This made environmentalists and regulators see red! We better start seeing some green, they told the chemical industry. And the industry took heed. The concept of “green chemistry” was born.

Traditionally, chemical manufacturers identified commercial needs and produced products based on maximizing yields while minimizing ingredient and processing costs. Wastes were disposed of in the cheapest possible way with little forethought. Dilution was regarded as the solution to pollution. General Electric, for example, dumped its PCB waste into the Hudson River for years. Now the company is spending millions and millions dredging the river to abide by new pollution laws. Industry mentality was “do what it takes to make a profit, and fix any problems that arise when forced to do so.” But that was then. Today, industrial chemists, with help from academia, are rethinking the entire way that chemicals are brought to the marketplace. Fouling your nest eventually comes back to haunt you, the industry has learned. Furthermore, preventing problems is cheaper than fixing them, and looking for sustainable alternatives to petroleum feedstocks is likely to reap benefits in the long run.

Green chemistry is more of a philosophy than a set of rules. It is a “cradle to grave” approach when dealing with chemicals. Raw materials from renewable sources are preferred and chemical reactions are designed so as to minimize waste by maximizing the incorporation of raw materials into the desired final product. Toxicity of all reagents and products are considered. Biodegradation and environmental persistence issues are taken into account and energy requirements for all processes are minimized. Sounds like motherhood and apple pie, sounds like what we should have been doing all along. But we weren’t. At least not until the U.S. passed the Pollution Prevention Act in 1990 and followed it up by establishing the coveted Presidential Green Chemistry Challenge awards.

In 1998 one of these awards went to the husband-and-wife research team of John W. Frost and Karen M. Draths of Michigan State University for their development of new strains of genetically engineered bacteria that allow petroleum based feedstocks to be replaced by glucose from plants. These bacteria can be used to make adipic acid, a key chemical in nylon manufacture. So what’s the big deal? The usual synthesis of adipic acid starts with benzene, a petrochemical. Beside it being nonrenewable, benzene is carcinogenic and its industrial use is subject to stringent and costly regulations. And one of the steps involved in converting it to adipic acid results in the release of large amounts of nitrous oxide, a greenhouse gas.

Using glucose as the starting material eliminates the need for benzene, as well as the step that generates nitrous oxide. Glucose is of course a renewable resource, available from starch or cellulose in plants. Developing large scale processes based on glucose technology is still a challenge and it is unlikely that benzene for nylon production can be totally displaced, but a 20% replacement is viable. Catechol is another industrial chemical produced from benzene. It is used to make vanillin, the main component of artificial vanilla flavouring. And if you consider that the world demand for vanillin is roughly 15,000 metric tons a year, well, that’s a lot of benzene.


@JoeSchwarcz

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