126 Green Chemistry, 2nd ed
C H
H
H H
H
H
H
H
H H
H
H
C C C C C
C
C
O
O
O
O
C C C C C
H
H H
H
H
H
H
H
H H
H
C H
H C H
H C H
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C
C
H H
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Di(2-ethylhexyl) phthalateAlternative means of making monomers by green processes have consumed
significant effort in the practice of green chemistry. Progress has been made in the green
synthesis of adipic acid, one of the two monomeric molecules used to make nylon 66
(see Reaction 5.5.1). The conventional synthesis of adipic acid as it has been practiced
since the 1940s begins with the addition of H 2 to benzene (see discussion of aromatic
compounds in Section 5.2) to produce cyclohexane, (Figure 5.1). Air oxidation over metal
catalysts attaches an -OH group to the cyclohexane to make the alcohol, cyclohexanol.
This compound is then oxidized with 60% nitric acid, a very severe oxidizing agent, to
adipic acid in a process that releases air pollutant nitrous oxide. As a green alternative
to the severe chemical conditions required by this synthesis, laboratory studies have
shown that genetically engineered Escherichia coli bacteria can convert glucose sugar
to cis,cis-muconic acid, which requires only mild treatment with hydrogen gas to give
adipic acid.
5.6. Life Chemicals
As noted at the beginning of this chapter, living organisms produce a variety of
organic chemicals or biochemicals. These are considered under the topic of biochemistry,
the chemistry of life processes. The topic of biochemistry and its relationship to green
chemistry is addressed in more detail in later chapters, especially Chapters 9 and 13. At
this point, however, it is useful to introduce several classes of the most important kinds
of chemicals produced by organisms.
Biochemicals are governed by the same laws of chemistry as are other kinds of organic
chemicals. For example, many fats, oils, and waxes produced by organisms are esters, a
class of organooxygen compounds described in Section 5.4 and shown in Reaction 5.4.1.