August 2, 2011 | 1
Like other scientific disciplines, chemistry is in the business of building knowledge. In addition to knowledge, chemistry sometimes also builds stuff — molecules which didn’t exist until people figured out ways to make them.
Scientists (among others) tend to assume that knowledge is a good thing. There are instances where you might question this assumption — maybe when the knowledge is being used for some evil purpose, or when the knowledge has been built on your dime without giving you much practical benefit, or when the knowledge could give you practical benefit except that it’s priced out of your reach.
Even setting these worries aside, we should recognize that there are real costs involved in building knowledge. These costs mean that it’s not a sure thing that more knowledge is always better. Rather, we may want to evaluate whether building a particular piece of knowledge (or a particular new compound) is worth the cost.
In chemistry, these costs aren’t just a matter of the chemist’s time, or of the costs of the lab facilities and equipment. Some of these costs are directly connected to the chemical reagents being brought together in reactions that transform the starting materials into something new. These chemical reagents (in solid, liquid, or gas phase, pure or in mixtures or in solutions) all come from somewhere. The “somewhere” could be a source in nature, or a reaction conducted in the laboratory, or a reaction process conducted on a large scale in a factory.
Getting a reasonably pure chemical substance in the jar means sorting out the other stuff hanging around with that substance — impurities, leftover reactants from the reaction that makes the desired substance, “side-products” of the reaction that makes the desired substance. (A side-product is a lot like a side-effect, in that it’s produced by the reaction but it’s not the thing you’re actually trying to produce.) When you’re isolating the substance you’re after, that other stuff has to go somewhere. If there’s not a particular way to collect the other stuff and put it to some other use, that other stuff becomes chemical waste.
There’s a sense in which all waste is chemical waste, since everything in our world is made up of chemicals. The thing to watch with waste products from chemical reactions is whether these waste products will engage in further chemical reactions wherever you end up storing them. Or, if you’re not careful about how you store them, they might get into our air or water, or into plants and animals, where they might have undesired or unforeseen effects.
In recent years, chemists have been working harder to recognize that the chemicals they work with come from someplace, that the ones they generate in the course of their experiments need to end up someplace, and to think about more sustainable ways to build chemical compounds and chemical knowledge. A good place to see this thinking is in The Twelve Principles of Green Chemistry (here as set out by Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice, Oxford University Press: New York, 1998, p.30.):
It is better to prevent waste than to treat or clean up waste after it has been created.
- Atom Economy Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
- Less Hazardous Chemical Syntheses Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
- Designing Safer Chemicals Chemical products should be designed to effect their desired function while minimizing their toxicity.
- Safer Solvents and Auxiliaries The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
- Design for Energy Efficiency Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.
- Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
- Reduce Derivatives Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.
- Catalysis Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
- Design for Degradation Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
- Real-time analysis for Pollution Prevention Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
- Inherently Safer Chemistry for Accident Prevention Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.
At first blush, these might look like principles developed by a group of chemists who just returned from an Earth Day celebration, what with their focus on avoiding hazardous waste and toxicity, favoring renewable resources over non-renewable ones, and striving for energy efficiency. Certainly, thoroughgoing embrace of “Green Chemistry” principles might result in less environmental impact due to extraction of starting materials, storage (or escape) of wastes, and so forth.
But these principles can also do a lot to serve the interests of chemists themselves.
For example, a reaction that can be conducted at ambient temperature and pressure requires less fancy equipment (i.e., equipment to maintain temperature and/or pressure at non-ambient conditions). It’s not just more energy efficient, it’s less of a hassle for the experimenter. Safer solvents are better for the environment and the public at large, but it’s usually the chemists working with the solvents who are at immediate risk when solvents are extremely flammable or corrosive or carcinogenic. And generating less hazardous waste means paying for the disposal of less hazardous waste — which means that there’s also an economic benefit to being more environmentally friendly.
What I find really striking about these principles of “Green Chemistry” is the optimism they convey that chemists are smart enough to figure out new and better ways to produce the compounds they want to produce. The challenge is to rethink the old strategies for making the compound of interest, strategies that might have relied on large amounts of non-renewable starting materials and generated lots of waste products at each intermediate step. Chemistry is a science that focuses on transformations, but part of its beauty is that there are multiple paths that might get us from staring materials to a particular product. “Green Chemistry” challenges its practitioners to use the existing knowledge base to find out what is possible, and to build new knowledge about these possibilities as chemists build new molecules.
And, to the extent that chemistry is in the business of finding new knowledge (rather than relying on established chemical knowledge as a master cook book), these twelve principles seem almost obvious. Given the choice, would you ever want to make a new compound for an application that had the desired function but maximized toxicity? Would you choose a synthetic strategy that generated more waste rather than less (and whose waste was less likely to break down into innocuous compounds rather than more)? Would you opt to perform the separation with a solvent that was more likely to explode if a less explosive solvent would do the trick? Probably not. Of course, you’d be on the lookout for a better way to solve the chemical problem — where “better” takes into account things like cost, experimental tractability, risks to the experimenter, and risks to the broader public (including our shared environment).
This is not to say that adhering to the principles of “Green Chemistry” would be sufficient to be an ethical chemist. Conceivable, one could follow all these principles and still fabricate, falsify, or plagiarize, for example. But in explicitly recognizing some of the costs associated with building chemical knowledge, and pushing chemists to minimize those costs, the principles of “Green Chemistry” do seem to honor chemists’ obligations to the welfare of the people with whom they are sharing a world.