Green Chemistry and the Ten Commandments

Chap. 11. Toward a Greener Anthrosphere through Industrial Ecology 303

material (increased percent yield) and decreases the amount of waste byproducts from
undesired side reactions.
Another important attribute of a good catalyst is related to the basic way in which
a catalyst works, which is by lowering the activation energy that is required to make a
reaction proceed at a significant rate. As a consequence, catalysts lower the total amount
of energy that must be put into a chemical process to get it to occur. Lowered energy
requirements are a basic part of the practice of green chemistry and in this respect good
catalysts can be extremely beneficial in lowering costs and environmental impact.
Nature’s catalysts, the enzymes in organisms, are experts in carrying out chemical
processes efficiently under mild conditions. In consideration of this fact, a great deal of
attention is being devoted to using organisms, especially bacteria, to carry out chemical
processes. By splicing desired genes for making specific enzymes into bacteria so that
they will carry out desired reactions, genetic engineering has the potential of making
an enormous contribution to the development of enzyme-catalyzed green chemical
processes.
Chemists are trying to use enzymes as models for synthetic catalysts that have
performance characteristics of enzymes, but which are much simpler and work under
conditions that would destroy enzymatic catalysts. A promising area in which this
might be accomplished is the use of iron-containing catalysts to oxidize alkene (C=C)
groups in organic compounds using relatively mild hydrogen peroxide reagent, H 2 O 2.
Organisms accomplish this task using catalysts in which the Fe^2 + ion is bonded by four
N atoms in relatively large heme porphyrin molecules. The same oxidation has now
been accomplished with a catalyst in which Fe2+ is bound by four N atoms by an organic
molecule with the formidable name of N,N’-dimethyl-N,N’bis(2-pyridylmethyl)-
ethylenediamine as shown in Figure 11.4. A big advantage of this catalyst that is shared
with enzyme catalysts that enable peroxide oxidations is that it does not cause the
decomposition of hydrogen peroxide as do a number of synthetic catalysts.

+ H 2 O 2

N N

N Fe N

C

H

H R

C

O

H

Alkene  (R  is  an  unspecified

organic group

Catalyst    of  N,N'-dimethyl-N,N'bis(2-pyridyl-

methyl)ethylenediamine  bonded  to  Fe 2+   ion

Epoxide group   attached    by

oxidation   at  C=C bond

C

H

H R

H

C

Figure 11.4. Action of an iron-containing compound modelled after iron-based enzymes as a catalyst to
bring about the oxidation of an alkene hydrocarbon group with hydrogen peroxide.

SUPPLEMENTARY REFERENCES

McDonough, William, and Michael Braungart, Cradle to Cradle: Remaking The Way
We Make Things, North Point Press, 2002.