Aug 072011
 
Cover of "Green Chemistry: Theory and Pra...

Cover of Green Chemistry: Theory and Practice

Building knowledge (and stuff) ethically

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.):

  1. Prevention
    It is better to prevent waste than to treat or clean up waste after it has been created.
  2. Atom Economy Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
  3. 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.
  4. Designing Safer Chemicals Chemical products should be designed to effect their desired function while minimizing their toxicity.
  5. 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.
  6. 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.
  7. Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
  8. 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.
  9. Catalysis Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
  10. 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.
  11. 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.
  12. 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.

Read more . . .

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