Green Chemistry and the Ten Commandments

Plant-derived insecticides include nicotine from tobacco and rotenone extracted
from the roots of some kinds of plants. Pyrethrins are excellent, biodegradable
insecticides extracted from dried chrysanthemum or pyrethrum flowers. Noted for
their low toxicities to mammals and excellent abilities to “knock down” flying insects,
pyrethrins were probably used to kill insects in China 2000 years ago. The current major
source of these environmentally-friendly insecticides are chrysanthemum varieties grown
in Kenya. Because of the excellent insecticidal properties of pyrethrins, their synthetic
analogs, pyrethroids, have been synthesized and widely produced. These substances are
now insecticides of choice for household applications. Because of their biodegradability,
pyrethrins and pyrethroids are not serious water pollutants.

Herbicides

Herbicides are applied to vast areas of farmland to control weeds that crowd out
corn, soybeans, cotton, and other economically important crops. The manner in which
herbicides must be applied ensures that they are susceptible to being washed off fields by
rainfall with a high potential to become water contaminants. Herbicides are commonly
found in drinking water supplies and some municipalities are required to use activated
carbon filtration to remove herbicides from municipal drinking water.
Herbicides come in an enormous variety of chemical compounds. One of the
most widely produced types consists of the triazines, which have 6-membered rings
in which C atoms alternate with N atoms (“triazine” denotes 3 nitrogent atoms). Three
of these widely used to control weeds on corn and soybeans are atrazine, simazine, and
glyphosate:

Glyphosate

HO C C N C P OH

O H N

H

H

H OH

O

N

C

N

C

N

C

Cl

N C

CH 3

CH 3

N H

H C C

H

H H

H

H

Atrazine

N

C

N

C

N

C

Cl

N N

H C C

H

H H

H

H H

C C H

H H

H H

Simazine

Glyphosate kills weeds by interfering with the synthesis of some kinds of amino
acids essential for plant proteins. It is a postemergence herbicide, which means that
it is applied directly to weeds after they have started to grow. It is effective against
broadleaf weeds, grasses, and perennial plants. Glyphosate is the active ingredient in
Monsanto’s Roundup herbicide. Monsanto has developed genetically modified soybeans
and other crops that are “Roundup ready,” meaning that they are not harmed by the
direct application of this herbicide, which kills competing weeds.

182 Green Chemistry, 2nd ed