296 Green Chemistry, 2nd ed
4C 3 H 5 N 3 O 9 → 12CO 2 + 10H 2 O + 6N 2 + O 2 (11.8.2)
This reaction shows that the nitroglycerin molecule actually contains an excess of
oxygen because elemental oxygen is released when the nitroglycerin explodes. Some
structural features of molecules are known to be associated with reactivity. One example
is the close presence of oxygen and nitrogen on the same molecule, particularly where
multiple nitrogen atoms are bonded together. A final category of hazardous chemical
substances consists of those that are corrosive. In general, a corrosive substance is one
that attacks materials, including even human flesh. A more specific definition is that a
corrosive substance is one that produces high concentrations of either H+ ion or OH- ion,
that is, a strong acid or a strong base.
Often hazardous chemicals belong to two or even more of the categories outlined
above. An example of such a substance is concentrated nitric acid, HNO 3. In addition to
its being a strong acid, this material acts as a source of oxygen, represented as ^O` in
the reaction below:
2HNO 3 Heat 3^O` + H 2 O + 2NO (11.8.3)Hazardous concentrated nitric acid is used in some chemical synthesis reactions in
which an acidic oxidant is needed. Among the many other potentially hazardous strong
oxidants used are permanganate (MnO 4 -^ ) and oxygen-containing compounds such as
potassium dichromate, K 2 Cr 2 O 7.
The ideal way to deal with hazardous substances in the practice of green chemistry is
to totally avoid making or using them. A laudable goal in principle, it is often impossible to
completely avoid hazardous materials in practice. In cases where dealing with hazardous
substances is necessary, every effort must be made to prevent their release, exposure to
humans, or circumstances in which their hazards may be manifested.
11.9. Feedstocks, Reagents, Media, and Catalysts
The main components of a chemical process can be divided into the four categories
of feedstocks, reagents, media, and catalysts, all of which are important in the practice
of green chemistry. These four aspects of chemical production are addressed in this
section.
Feedstocks
Feedstocks are the main ingredients that go into the production of chemical products.
As discussed below, feedstocks may be acted upon by reagents, and often there is some
overlap between the two categories of materials. Feedstocks are addressed briefly here
and in greater detail in Chapter 12.
There are three major components of the process by which raw materials from a
source are obtained in a form that can be utilized in a chemical synthesis, then converted
to a product. The first of these is the source of the feedstock, an aspect that has a