Examples of Organic Halides
2,3-dichloro-2,3-difluoro-1,1-diiodobutane
H Cl Cl
I I I
H-C-C-CI I I
H F F
I
I
C-I
I
H
Ozone Depletion
• An environmental concern has been raised by
this type of reaction, which ends up producing
products known as chlorofluorocarbons (CFC’s).
• These molecules have been used widely in foam
products, as aerosol propellants and
refrigerator/air conditioning coolants.
• Their use has been banned in the last 10 years
or so but they are still present in many older
refrigerators and AC units.
• Proper disposal of these appliances is essential
to prevent further release of CFC’s.
• CFC’s react in the atmosphere to destroy
ozone molecules.
• As a result of this destruction, deadly UV
radiation passes through our atmosphere and
causes skin cancer.
• CFC’s have also been identified as a
greenhouse gas and are so contributing to
global warming.
Answers to Activity
1.
2.
3.
4.
bromobenzene
chloroethane
3-chlorobut-1-ene
1,4-dichlorobenzene (p-dichlorobenzene)
Organic Halide Reactions
• Halocarbons are chemically reactive.
• They are involved in a number of different
reactions such as addition, substitution and
elimination.
• We will look at elimination reactions after
looking at alcohols.
Addition Reactions
• These occur when a substance is added to
double or triple bonds in alkenes or alkynes,
since these bonds are reactive.
• Addition reactions add a new functional group
to a compound.
Addition
• When water is added, this is called a
hydration reaction. This can occur when an
alkene and water are heated to 100oC in the
presence of a trace amount of a catalyst,
such as nickel metal.
H - C = C – H + HOH(l)
I I
H H
ethene + water
Ni

H OH
I I
H-C-C-H
I I
H H
ethanol
Test for Unsaturation
• The addition of bromine to the carboncarbon double or triple bonds is often used
as a test for unsaturated organic molecules.
• Bromine has a brownish-orange colour.
• The loss of this colour when bromine is
added to an organic compound is a positive
test for unsaturation.
• Although benzene has double bonds, it is
stable and does not give a positive test for
unsaturation with bromine.
Example-Reaction 1
Pt
H-C ≡C-H
ethyne
+
+ Br2(l)
bromine

Br
I
H-C=C-H
I
Br
1,2 - dibromoethene
The addition of halogens to alkynes results in alkenes
or alkanes.
Example-Reaction 2
Br
Br Br
l
Pt
I I
H - C = C - H + Br2(l)

H-C-C-H
I
I I
Br
Br Br
1,2-dibromoethene + bromine  1,1,2,2 -tetrabromoethane
Since addition reactions are very fast, the alkene
produced, can undergo a second addition reaction.
Substitution Reactions
• Under the right conditions alkanes will
undergo chemical reactions with halogens,
such as chlorine:
UV light
• Eg:
CH4 (g) + Cl2 (g)

CH3Cl (g)
+ HCl (g)
chloromethane
• Note that in situations such as this,
ultraviolet light (UV light) is included as a
catalyst.
Substitution Reactions
• A chemical reaction in which an atom or a
group of atoms replace another atom or group
of atoms is called a substitution reaction.
• In these reactions, the product of the
previous reaction is reacted with chlorine
again.
• We continue this process to end up with
products such as chlorinated solvents, paint
removers and degreasing agent.
Substitution Reactions
• This involves the replacement of an atom or
group of atoms by another atom or group of
atoms.
• For example: a halogen substituting hydrogen
on an alkane to give a halocarbon:
H H
I I
H-C-C-H
I I
H H
ethane
UV
+ Cl2(g) 
+
chlorine
Cl H
I I
H - C - C - H + HCl(g)
I I
H H
chloroethane
Substitution
Example 2:
This reaction is so slow that it requires both light
and a catalyst.
Substitution
• Example 3: Alcohols may be produced by
the substitution of a halogen by
hydroxide ions:
water & heat
CH3CH2Cl (l) + NaOH(s)
chloroethane

CH3CH2OH (l) + NaCl(aq)
ethanol
Activity
• Section 10.2 Questions 2-5 & 7.