Download Synthesis of DDT Mechanism

Nature’s Nightmare: A study of the chemistry
of DDT and its effects on the environment.
Scott Zeglin
Synthesis of DDT
Abstract
Dichlorodiphenyltrichloroethane,
commonly known as DDT, is a powerful
insecticide that combats the vectors of human
disease and crop pests. DDT was first used in
World War II to combat infectious disease in
humans, but its main use was as a pesticide
until the EPA banned it in 1973. Problems
with DDT arose when it was discovered that
the compound is stable and fat soluble, which
means that it accumulates in animal fat tissue
and becomes more and more concentrated in
the offspring of infected species. It is useful to
understand why DDT is such a powerful
insecticide, but also why it’s half-life in animals
is so long (8 years). By analyzing the
chemical make-up of this compound,
improvements might be possible to make the
compound non-soluble in fat or accumulating
in animals, while still maintaining its lethal
effects towards pests.
Introduction
After World War II, DDT was the most
commonly used pesticide in the world, since it
seemed to eradicate all unwanted insects, and
left all other organisms alone. DDT is an
organochlorine that undergoes biomagnification
as it accumulates through the food chain, which
means that higher concentrations of the chemical
will be found in animals at the top of the food
chain, but there is no evidence that DDT harms
humans in any way. The mechanism and
synthesis of DDT was studied to understand why
it is such a good insecticide, but what properties
allow it to be so harmful to non-target organisms.
DDT Biomagnification
Cl
Cl
H
Cl
Cl
Cl
O
OH
H
+
Cl
O S O
+ H
Cl
OH
O
OH
+
-
O
S
Cl
Cl
O
OH
+
H
Chlorobenzene
-HSO4-
O
Cl
Cl
Cl
Cl
H
+ H
Cl O
+
H
Cl
Cl
H
Cl
H
Cl
O
Cl
H+
H
Cl
H
Cl
O
Cl
H
Cl
H
Conclusion
+
-H2O
Cl
Cl
Cl
Cl
Cl
Cl
+
Cl
H
Cl
Cl
Cl
H
-H
Cl
Cl
+
The main reason DDT accumulates as
it moves up the food chain is because it is
hardly metabolized or excreted. This is
because DDT is a lipophile, meaning that
DDT binds to lipids, such as fat in animals.
This solubility in fat, coupled with the stability
provided by the anchoring of chlorobenzene
groups at each end of the compound give a
highly stable compound almost incapable of
being metabolized in the animal body.
H
Cl
Cl
Mechanism
DDT can be synthesized from two starting products,
Trichloroacetaldehyde and chlorobenzene. The reaction between
these two starting materials occurs primarily in the para position
of chlorobenzene, yielding an intermediate alcohol, which in the
presence of acid, readily forms a second carbocation with another
chlorobenzene.
DDT poses a great risk to animals at
the top of the food chain. However, by
understanding the chemistry behind why
DDT is such an effective insecticide allowed
chemists to develop alternatives such as
dieldrin and methoxychlor. These
alternatives are typically more expensive
than DDT and are not typically as effective.
However, some of the better alternatives
are more environmentally friendly,
eliminating this nightmare from nature.
Acknowledgements
Kimball, John. (2003). [online], available HTTP:
http://users.rcn.com/jkimball.ma.ultranet/Biol
ogyP ages/I/Insecticides.html
Wikipedia, The Free Online Dictionary. (2000 or
later). [online], available HTTP:
http://en.wikipedia.org/wiki/DDT
Williamson, K.L. Macroscale and Microscale
Organic
Experiments, 2nd edition. 1994:
Houghton Mifflin,
Boston.