Benzene and Its Derivatives Chapter 4

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Benzene and Its DerivativesChapter 4

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AROMATIC HYDROCARBONS
-very "aromatic," hence the name. -benzene the
most common. Toxic, industrially
important. -hybrid ring structure, since 3
double bonds not always in the same location.
so, C-6 H-6 formula. -Nomenclature involves both
the use of benzene suffix as well as common
names. (see examples below) -important
application Fused Aromatics and Carcinogens,
such as Benzo-a-pyrene and smoke
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Kekules Structure of Benzene

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• (A)The bonds in C6H6 are something between single
  and double, which gives it different chemical
  properties than double-bonded hydrocarbons. (B)
  The six-sided symbol with a circle represents the
  benzene ring. Organic compounds based on the
  benzene ring are called aromatic hydrocarbons
  because of their aromatic character.

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Benzene
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• Benzene
• Benzene is one of the most fascinating molecules.
  The structure of this molecule eluded chemists
  until 1865 when Friedrich August Kekulé proposed
  that it consisted of a hexagonal ring with a
  carbon atom at each vertex. Every student of
  Organic Chemistry has heard the story of how the
  structure appeared to Kekulé in a dream in which
  he saw chains of carbon atoms dancing in circles
  like a snake chasing its own tail. Alas,
  benzene is both toxic and carcinogenic. In fact,
  it might be considered "the mother of all
  carcinogens," as a large number of carcinogens
  have structures that include benzene rings. (See
  the link below for the explanation of this.) I
  recall my Organic Chemistry professor joking
  about how he used to "practically bathe in
  benzene up to the elbows" when he would use it in
  his research (presumably before it was identified
  as a carcinogen). He predicted that this would
  probably lead to his demise. He was right--he
  died due to leukemia several years ago.

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Aromatic Compounds and Benzene

• Aromatic compounds contain benzene.
• Benzene, C6H6 , is represented as a six carbon
  ring with 3 double bonds.
• Two possible can be drawn to show benzene in
  this form.

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Aromatic Compounds and the Structure of Benzene

• In the early days the word aromatics was used to
  described many fragrant molecules isolated from
  natural sources. Today the term aromatic is
  used to describe benzene like molecules.
• Benzene is a flat, symmetrical molecule with the
  molecular formula C6H6.
• It has alternating three carbon-carbon double and
  three single bonds.

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• Benzenes relatively lack of chemical reactivity
  is due to its structure.
• There are two possible structures with
  alternating double and single bonds.

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• Experimental evidence suggest that all six
  carbon-carbon bonds in benzene are identical.
• The properties, including the above one, of
  benzene can only be explained by assuming that
  the actual structure of benzene is an average of
  the above two possible equivalent
  structures-known as resonance.
• Simple aromatic compounds like benzene are
  non-polar, insoluble in water, volatile, and
  flammable.
• Unlike alkenes, several aromatic hydrocarbons are
  toxic. Benzene itself is implicated as a cancer
  causing chemical.

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Aromatic Compounds in Nature and Health

• Many aromatic compounds are common in nature and
  in medicine.

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Naming Aromatic Compounds

• Aromatic compounds are named with benzene as the
  parent chain. One side group is named in front of
  the name benzene.
• - No number is needed for mono-substituted
  benzene since all the ring positions are
  identical.
• methylbenzene chlorobenzene
• (toluene)

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Naming Aromatic Compounds

• When two groups are attached to benzene, the
  ring is numbered to give the lower numbers to the
  side groups. The prefixes ortho (1,2), meta
  (1,3-) and para (1,4-) are also used.

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Some Common Names

• Some substituted benzene rings also use a common
  name. Then naming with additional more side
  groups uses the ortho-, meta-, para- system.

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• Many substituted aromatic compounds have common
  names in addition to their systematic names.

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Learning Check

• Select the names for each structure
• a. Chlorocyclohexane
• b. Chlorobenzene
• c. 1-chlorobenzene
• a. Meta-xylene
• b. Meta-dimethylbenzene
• c. 1,3-dimethylbenzene

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Learning Check

• Write the structural formulas for each of the
  following
• A. 1,3-dichlorobenzene
• B. Ortho-chlorotoluene

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New Attached Groups

• Phenyl
• Benzyl
• Nitro -NO2

4-phenyl-1-butene
Benzyl alcohol
Refer to your chart for order of priority!
2,4,6-trinitrotoluene
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DDT and Benzene website
DDT the first of the chlorinated organic
insecticides, was originally prepared in 1873,
but it was not until 1939 that Paul Muller of
Geigy Pharmaceutical in Switzerland discovered
the effectiveness of DDT as an insecticide he was
awarded the Nobel Prize in medicine and
physiology in 1948 for this discovery). The use
of DDT increased enormously on a worldwide basis
after World War II, primarily because of its
effectiveness against the mosquito that spreads
malaria and lice that carry typhus. The World
Health Organization estimates that during the
period of its use approximately 25 million lives
were saved. DDT seemed to be the ideal
insecticideit is cheap and of relatively low
toxicity to mammals (oral LD50 is 300 to 500
mg/kg). However, problems related to extensive
use of DDT began to appear in the late 1940s.
Many species of insects developed resistance to
DDT, and DDT was also discovered to have a high
toxicity toward fish. The chemical stability of
DDT and its fat solubility compounded the
problem. DDT is not metabolized very rapidly by
animals instead, it is deposited and stored in
the fatty tissues. The biological half-life of
DDT is about eight years that is, it takes about
eight years for an animal to metabolize half of
the amount it assimilates. If ingestion continues
at a steady rate, DDT builds up within the animal
over time. The use of DDT was banned in the
United States in 1973, although it is still in
use in some other parts of the world. The buildup
of DDT in natural waters is a reverisble process
the EPA reported a 90 reduction of DDT in Lake
Michigan fish by 1978 as a result of the ban

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DDT/Benzene continued

• Benzene rings have two important properties
• 1. Two or more benzene rings can themselves bind
  together and,2. Chlorine can replace hydrogen
  on the outside of the ring.
• These principles explain the formation of the
  very toxic families of PCBs, furans and dioxins.
  A pair of benzene rings joined together forms
  biphenyl
• If chlorine is present when benzene is burned
  (and there is plenty of chlorine in plastics),
  hydrogen atoms can be released and chlorine atoms
  can replace them. The result is poly-chlorinated
  biphenyls, knows as PCBs. Their production was
  banned in the 1970's.
• If oxygen (abbreviated "O") forms another link
  between the two benzene rings the result is
  furans. If chlorine replaces hydrogen atoms, the
  furans are also very toxic
• Sometimes benzene molecules bind together with
  two oxygen atoms, with the resulting name of
  dioxin. Unlike furans, dioxins are symmetrical
  (the same at the top and bottom).

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Estrogen and aromatics
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Reproductive Hormones and Benzene-like
carcinogenswebsite

• The importance of other possible factors such as
  breast-feeding history and exposure to
  environmental toxins, however, have been more
  difficult to establish. A review of the
  literature on these two possible factors, with
  commonly used organochlorine pesticides as the
  environmental toxins being examined reveals
  linkage between the two, with far-reaching
  implications for women to consider.

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Estrogen and Chemicals

• Too Much Estrogen...
• Excessive levels of estrogen can also increase
  the risk of breast cancer. The female hormone
  signals cells to proliferate, which is necessary
  and normal during conception and fetal attachment
  to the womb. At other times, however, estrogen
  may tell normal cells to grow uncontrollably.
• Twenty years ago, nutrition educator Carlton
  Fredericks, Ph.D., noted that some women produced
  five more estrogen than did other women,
  increasing their risk of breast cancer. Other
  women may increase their risk through
  estrogen-replacement therapy.
• But several years ago, researchers stumbled
  across something completely unexpected many
  common pesticides and plastics contain chemicals
  that mimic estrogen in the body. These estrogenic
  chemicals, called xenoestrogens, end up in the
  food and can greatly increase the risk of breast
  cancer. Four years ago, Mary Wolff, Ph.D., of the
  Mt. Sinai School of Medicine in New York City,
  found that high levels of estrogen-mimicking
  pesticides increased breast cancer risk in women
  by four times.

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Estrogen continued

• Because hormones are so powerful, only small
  quantities can do a lot of damage. In one
  experiment, researchers found that 2 to 5 parts
  per billion of bisphenol-A (BPA), one type of
  xenoestrogen, are enough to trigger hormonal
  changes.
• Combinations of pesticides magnify the risk, and
  such combinations are common in foods and the
  environment. Last year, John McLachan, Ph.D., an
  expert on pesticides and hormones at Tulane
  University, New Orleans, reported in the journal
  Science that combinations of just two
  estrogen-like pesticides were 1,000 times more
  potent than they were by themselves. What happens
  when you mix together dozens of common
  estrogen-mimicking chemicals? It's anyone's guess
  - but it doesn't bode well.
• According to Malins, these xenoestrogens, along
  with the estrogen a woman normally produces,
  could add to the free radical burden on breast
  cancer cells. Additional free radicals, he
  pointed out, might also be generated when the
  body breaks down estrogens and xenoestrogens. All
  these free radicals would greatly increase a
  person's "oxidative stress" - and the need for
  compensatory antioxidant vitamins.

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The connection between Hormones in the Human
Body and Organic Aromatics
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PCBs(Polychlorinated Biphenyls)

• There are 209 varieties of PCBs, known
  individually as congeners. A congener may have
  between 1 and 10 chlorine atoms, which may be
  located at various positions on the PCB molecule.

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PCBs

• PCBs are mixtures of man-made chemicals with
  similar chemical structures. PCBs can range from
  oily liquids to waxy solids. Due to their
  non-flammability, chemical stability, high
  boiling point and electrical insulating
  properties, PCBs were used in hundreds of
  industrial and commercial applications including
  electrical, heat transfer, and hydraulic
  equipment as plasticizers in paints, plastics
  and rubber products in pigments, dyes and
  carbonless copy paper and many other
  applications. More than 1.5 billion pounds of
  PCBs were manufactured in the United States prior
  to cessation of production in 1977.

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Food Dyes

• Food dye website
• Food dye website from manufacturer

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Phenols
-contain OH directly attached to aromatic
ring -initially used as antispectics -since this
is burning to healthy tissue, replacements have
been found to be used in mouthwashes, etc.