3.1 Alternative feedstocks/starting materials
Currently, 98% of all organic chemicals synthesized in the United Sates are made from petroleum feedstocks. Petroleum refining takes up 15% of the total energy used in the US, and its energy usage is rising because the low quality raw petroleum available now requires more energy for refinement. During conversion to useful organic chemicals, petroleum undergoes oxidation, the addition of oxygen or an equivalent; this oxidation step has historically been one of the most environmentally polluting steps in chemical synthesis. As a result of these consideration, it is important to reduce our use of petroleum-based products by using alternative feedstocks….
The exploration of biological sources of alternative feedstocks need not be limited to agricultural products: agricultural waste or biomass, and non-food-related bioproducts, which are often made up of a variety of lignocellulosic materials, may provide important alternative feedstocks.
Other classes of alternative feedstocks are also emerging, such as light. For example, heavy metals, which are often used in petroleum oxidation processes, are also quite toxic and are carcinogens or cause damage to neurological systems. Recently discovered alternative syntheses replace the heavy metal reagents with the use of visible light to carry out the required chemical transformations.
3.3 Alternative Solvents
An important area of green chemistry investigations has centered around the selection of a medium in which to carry out a synthetic transformation. Because the dominant paradigm of chemical synthesis has been around solution chemistry, the question is often phrased as ‘What solvent should be used?’. This phrasing, of course, begs the question, ‘Should a solvent be used at all?’. Many of the solvents commonly used are some of the volatile organic compounds known to cause smog when released to air. These solvents are listed in the United States’ Clean Air Act as substances to be avoided. Research is being is conducted that pursues chemistry that has previously been done in a solvent and discovers a way to do the same chemistry in various solventless systems….
3.4 Alternative product/target molecule
While a synthesis is often driven by the pursuit of a particular target molecule, it is also commonly the case that what is actually being pursued is the ability to make any chemical that can serve a particular function or have a certain performance criterion. For many years the pharmaceutical industry has been doing research into designing safer chemicals. With pharmaceuticals, the object is to maximize the therapeutic benefits of a molecule while minimizing or eliminating the toxic side-effects. These same principles can be applied to the full range of chemical applications.
In the cases where function is the primary motivation, molecular manipulation that preserves efficacy of function while mitigating toxicity or other hazards is the goal of green chemistry. Through these efforts and other toxicological research, it is often possible to identify the part or parts of a molecule that produce toxic effects. Similarly, through chemical research, we are able to identify those parts of a molecule that are required to give the chemical the desired function – to allow it to serve a specific, desired use.
In designing safer chemicals, one identifies the undesirable, toxic portion of a molecule and lessens or eliminates its toxicity, while maintaining the function of the molecule. In many cases, the overlap of the toxic and functional portions creates a worthy challenge for the synthetic chemist….
3.6 Alternative catalysts
Some of the major advances in chemistry, especially industrial chemistry, over the past generation have been in the area of catalysis. Catalysis has not only advanced the level of efficiency but has also brought about concurrent environmental benefits. Through the use of new catalysts, chemists have found ways of removing the need for large quantities of reagents that would otherwise have been needed to carry out the transformations, and would ultimately have contributed to the waste stream. It is true that various classes of catalysts, such as the heavy metal-based catalysts, have been found to be extremely toxic.
excerpts from pages 22 – 27
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