SCH 4U Day 5
Organic Halides
Assignment:
Page 33 # 1, 2;35 #5; 37 #6
Section Page 37 # 1-3
1.4 Organic Halides
P Naming organic halides
P Properties of organic halides
P Cost of Air Conditioning
P Preparing Organic Halides
P Preparing Alkenes from Organic Halides
Naming Organic Halides
P Name as substitutions to main carbon chain
P Replace “ine” ending with “o”
P Fluoro-, chloro-, bromo-, iodoP Number the main chain and use prefixes
Nomenclature of Alkyl Halides
P Name alkyl halides as substituents on the
main carbon chain
Common names of Alkyl Halides
P Common names end with the name of the
halide
Properties of Organic
Halides
P Halogens are more polar than H
P C-X bonds are more polar than C-H bonds
P Dipole-dipole attractions lead to higher BP
P Dipole-dipole attractions lead to higher
solubility in polar solvents (but not water)
P Mixtures are produced during halogenation
of hydrocarbons
The Cost of Air Conditioning
P Chlorofluorocarbons replaced toxic coolants
in 1920's
P CF2Cl2 or CFC-12 is known as Freon
P CFC’s are inert in the lower atmosphere
P CFC’s decompose in the upper atmosphere
P Highly reactive Cl atoms catalyze ozone
decompostion
P Halons (Bromoalkanes) destroy ozone more
effectively than CFC’s
Radical Reactions
The Ozone Layer and CFCs
Halon
Alternatives to CFC’s
P Hydrochlorofluorocarbons HCFC’s
P Hydrofluorocarbons HFC’s
P H atoms react with OH- ions in
atmosphere to decompose HCFC and
HFC
P No threat to ozone but powerful
greenhouse gases
P “Puron”
Industrial uses of Organic
Halides
Cl
P Solvents: CH2Cl2, CHCl3, CCl4
P Refrigerants:
Cl
C
Cl
< CF2Cl2 - Freon-12 (decomposes O3)
< HCF2Cl - Freon-22 (destroyed at lower
altitudes)
P Pesticides: DDT
< introduced 1939
< banned 1972 (Rachael Carson)
CH
Cl
Cl
Industrial Applications of
Organic Halides
P Chlordane -termites
< banned 1995
Cl
Cl
Cl
Cl
H
H
Cl
H
H
Cl
Cl
P Capacitors, etc.
Cl
< PCB (polychlorinated biphenyl)
banned 1985
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Industrial applications of
Organic Halides
P Anaesthetics
< CHCl3 - chloroform carcinogenic
< CH3CH2Cl - ethyl chloride topical use
< CF3CHBr-Cl - halothane - general
P Polymers
< Polyvinylchloride (PVC)
< Teflon
Preparing Organic Halides
P Halogenation of alkanes (slow)
P Addition of halogens or hydrohalogens to
alkenes and alkynes
P Markovnikov’s rule for hydro halogens
P Benzene derivatives are formed by
substitution reaction with halogens (not
addition reactions)
Halogenation
H
H
H
C
C
H
H
H
+
Heat or Light
D or hv
Br2
H
Ethane
C
Heat or Light
D or hv
H
H
Methane
+
H
C
C
H
H
Br
+
HBr
Bromoethane
H
H
H
Cl2
H
H
C
Cl
+
HCl
H
chloromethane
CH2Cl2 and CHCl3
may be observed
Substitution R eaction – a reaction in which part
of a small reacting molecule replaces an atom or a
group of atoms on the organic molecule (usually very slowly)
Preparing Alkenes from
Alkyl Halides
P Eliminate H and adjacent halide to form
alkene
P Hydroxide ions are required
P Elimination reactions are the most
commonly used method of preparing
alkenes
ELIMINATION REACTIONS
An elimination reaction is one where starting
material loses the elements of a small molecule
such as HCl or H 2O or Cl2 during the course of
the reaction to form the product.
C
C
H
Cl
- HCl
C
C
MAKING ALKYNES
“DOUBLE ELIMINATION”
COMPOUNDS WITH TWO HALOGENS
If you have a compound with two halogens it can
react twice (two E2 eliminations).
If both halogens are on the same carbon, an alkyne
is produced.
The second elimination is more difficult than the
first one - it requires a stronger base.
H Cl
H3 C
H3 C C C CH3
H
H Cl
most bases
will work
Cl
C C
H3 C C C CH3
CH3
more difficult, requires a
stronger base like NH 2 -
COMPOUNDS WITH TWO HALOGENS
If you have a compound with two halogens it can
react twice (two E2 eliminations).
If the halogens are on different carbons, a diene is
usually produced.
Cl
Cl
KOH
EtOH
Br
Br 2
CCl4
D
Br
NaOEt
EtOH
D