Environmental questions, benign

For a given desired product, there are typically numerous reaction alternatives that should be identified and screened. The identification of these reactions is not a straightforward task. The problem is further compounded when the search is limited to environmentally benign cost-effective chemistry. In this context, the following questions should be answered ... 

Environmentally benign hydrogen is clearly the ideal fuel for use with fuel cells. The question is whether to store the hydrogen nn-bnard or to generate it on board from liquid fuels that are easier to store and distribute. 

Other metrics have also been proposed for measuring the environmental acceptability of processes. Hudlicky and coworkers [19], for example, proposed the effective mass yield (EMY), which is defined as the percentage of product of all the materials used in its preparation. As proposed, it does not include so-called environmentally benign compounds, such as NaCl, acetic acid, etc. As we shall see later, this is questionable as the environmental impact of such substances is very volume-dependent. Constable and coworkers of GlaxoSmithKline [20] proposed the use of mass intensity (MI), defined as the total mass used in a process divided by the mass of product, i.e. MI = E factor+1 and the ideal MI is 1 compared with zero for the E factor. These authors also suggest the use of so-called mass productivity which is the reciprocal of the MI and, hence, is effectively the same as EMY. 

Environmentally benign synthetic processes may also favor water as a solvent [...] though this question is not completely free of ambiguity. ... 

Since the second edition appeared, much of the interest in soil chemistry has been on the fate of so-called toxic chemicals and elements in soils. This edition points out that (1) all of the chemical elements—toxic and beneficial—were always in the soil, (2) the soil is the safest part of the environment in which to deposit our wastes, (3) there are wise and unwise ways to utilize soil for waste disposal, (4) soil chemistry degrades wastes and converts them into benign or useful substances, (5) environmental activists and the popular media usually ignore the dose-response concept that is central to toxicology and to soil fertility, and (6) how much is in the soil, how fast it is changing, and how easily it transfers to plants and water are more important than what is there. Soil chemistry can answer those important questions. A goal for the future is to answer them better. 

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