Ddt 1n3g10

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://s.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.