(known as dioxin) is a contaminant formed during the manufacture of Agent Orange.
TCDD has been implicated as the causative agent behind various symptoms suffered
by those exposed to Agent Orange during the war.
Because of the known physiological activities of adrenaline and mescaline,
chemists have synthesized compounds with similar structures. One such compound is
amphetamine, a central nervous system stimulant. Amphetamine and a close relative,
methamphetamine, are used clinically as appetite suppressants. Methamphetamine is
the street drug known as “speed”because of its rapid and intense psychological ef-
fects. Two other synthetic substituted benzenes, BHA and BHT, are preservatives (see
Section 9.8) found in a wide variety of packaged foods. These compounds represent
just a few of the many substituted benzenes that have been synthesized for commercial
use by the chemical and pharmaceutical industries.
In Chapter 15, we looked at the reactions benzene undergoes and we saw how
monosubstituted benzenes are named. Now we will see how disubstituted and
polysubstituted benzenes are named, and then we will look at the reactions of
substituted benzenes. The physical properties of several substituted benzenes are given
in Appendix I.
Introduction 623
CH 2 CHNHCH 2 CH 3
CF 3
fenfluramine
CH 3
CH 2 CNH 2
CH 3
phentermine
CH 3
saccharin
C(CH 3 ) 3
OCH 3
butylated
hydroxyanisole
BHA
a food antioxidant
O
O O
OH
Cl
p-dichlorobenzene
mothballs and
air fresheners
Cl
(CH 3 ) 3 C C(CH 3 ) 3
CH 3
butylated
hydroxytoluene
BHT
a food antioxidant
C
NH
S
OH
MEASURING TOXICITY
The toxicity of a compound is indicated by its
value—the quantity needed to kill 50% of
the test animals exposed to the compound. Dioxin, with an
value of for guinea pigs, is an extremely
toxic compound. Compare this with the LD 50 values of
LD 50 0.0006 mg>kg
LD 50
for strychnine and for sodium cyanide—
far less toxic compounds. One of the most toxic agents known
is the botulism toxin, with an value of about
1 * 10 -^8 mg>kg.
LD 50
0.96 mg>kg 15 mg>kg
OCH 2 COH
Cl Cl
2,4-dichlorophenoxyacetic acid
2,4-D
O
OCH 2 COH
Cl Cl
Cl
2,4,5-trichlorophenoxyacetic acid
2,4,5-T
O
O Cl
O Cl
Cl
Cl
2,3,7,8-tetrachlorodibenzo[b,e][1,4]dioxin
TCDD
CH 2 CHNH 2
amphetamine
CH 3 CH 3
CH 2 CHNHCH 3
methamphetamine
“speed”
COH
OCCH 3
acetylsalicylic acid
aspirin
hexachlorophene
a disinfectant
O
O
Cl Cl Cl Cl
Cl OH HO Cl
CH 2