NEO - JEE - 12 - P1 - CHE - E - Haloalkanes and Haloarenes. - S5 - 209
NEO - JEE - 12 - P1 - CHE - E - Haloalkanes and Haloarenes. - S5 - 209
NEO - JEE - 12 - P1 - CHE - E - Haloalkanes and Haloarenes. - S5 - 209
-H
CH4 CH3X
+X
Haloalkanes/haloarenes are
compounds in which at least
one halogen atom replaces
hydrogen atom of an -H
alkane/aromatic compound.
+X
Haloalkanes and Haloarenes in Daily Life
Bromochlorodifluoromethane is
used in fire extinguishers.
Dichlorodiphenyltrichloroethane
(DDT) is used as pesticides.
Medicinal Uses of Haloalkanes and Haloarenes
Mono-haloalkanes Mono-haloarenes
Example
Dihaloalkane
H2C CH2
X X
Polyhaloalkane/ Polyhaloarene
Polyhalogen compounds
can be named as tri, tetra, etc.
Trihaloalkane Trihaloarene
Polyhaloalkanes and Polyhaloarene
Polyhaloarene
Polyhaloalkanes
1° 2° 3°
Types of Alkyl Halides
Alkyl halides
Primary (1°)
Secondary Alkyl Halide
Secondary (2°)
Tertiary Alkyl Halide
Tertiary (3°)
Allylic Halides
δ+ δ- More
C X electronegative
Less
electronegative
Generally,
Electronegativity Polarisation
difference of C-X bond
Bond Length
Dipole moment of
a bond depends on
Chemical
Preparation
Properties
Halo
Compounds
R-OH R-X
Hydrohalic acid,
Reagents
phosphorus halides
used
and thionyl chloride
Preparation from Alcohols and HX
General reaction
CH3 CH3
CH3 CH3
ZnCl2
CH3CH2CH2OH + HCl CH3CH2CH2Cl + H2O
Δ
Preparation from Alcohols and HCl
R-OH + HCl
When When
ROH = 3° ROH = 1°, 2°
Can react
ZnCl2 is used
without ZnCl2
R-Cl + H2O
A mixture of concentrated
hydrochloric acid and
anhydrous zinc chloride is
called the Lucas reagent.
Preparation from Alcohols and HX
Δ
CH3CH2CH2OH + HI CH3CH2CH2I + H2O
X Cl, Br, I
3R Cl + H3PO3
Preparation from Alcohols and PX5
+ POCl3 + HCl
Preparation from Alcohols and SOCl2
General reaction
Pyridine, Δ
ROH + SOCl2 RCl + SO2 + HCl
By-products are
gaseous in nature
Preparation from Alcohols and SOCl2
Pyridine, Δ
ROH + SOCl2 RCl + SO2 + HCl
+ SO2 + HCl
Preparation of Alkyl Halides
From Hydrocarbons
Halogenation of alkanes
by free radical mechanism
Generates a mixture of
mono/poly haloalkanes
Mono Halogenation
Cl2
UV light
Mono
Dihaloalkanes
haloalkanes
Addition of HX Addition of X2
Addition of Hydrogen Halides (HX)
Example
Major product
Addition of Halogens
Br
Finkelstein Swarts
reaction reaction
Finkelstein Reaction
Acetone
RX + NaI RI + NaX When RCl or RBr is treated with
a solution of NaI in acetone
X : Cl, Br
General reaction
R-Br/R-Cl R-F
Reagents
AgF, CoF2, Hg2F2
used
Example
Cl
FeCl3
+ Cl2 + HCl
25 ℃
Reactivity of Halogens in ESR
Electrophilic Substitution
F2 Cl2, Br2 I2
Fluorination is Iodination is
highly reactive very slow
Preparation of Diazonium Salt
+ _
+ _ CuCl
+ N2
Treatment of diazonium
salts with cuprous chloride
or bromide leads to aryl
chlorides or bromides,
respectively. It follows free CuBr
radical mechanism. + N2
Formation of Iodobenzene
+ _
I
+ KI + N2 + KCI
Formation of Fluorobenzene
Heat
+ HBF4 + N2 + BF3
ppt
Physical
Properties
Chemical
Preparation
Properties
Halo
Compounds
Boiling point
Physical
Melting point
Properties
Solubility
Density
Colour and Odour
Polarity and
Branching of
molar mass of
parent chain
the compound
Boiling Points of Haloalkanes
Polarity of C X bond
Polarity of Dipole-dipole
C X bond attraction
Order of B.P.
300
B.P. (K)
200
Here boiling point is
shown on the graph:
For the same halogen, 100
as the length of
hydrocarbon chain
0
increase, b.p. increases.
CH3Cl CH3CH2Cl CH3CH2CH2Cl
400
300
B.P. (K)
200
Here boiling point is
shown on the graph:
For same hydrocarbon 100
chain, as the size of
halogen increase, b.p.
0
increases. CH3Cl CH3Br CH3I
400
300
B.P. (K)
200
G G G
a a a
100
s s s
0
CH3X CH3CH2X CH3CH2CH2X
Chlorides
Bromides
Iodides
Boiling Points of Haloalkanes
1
Boiling point ∝ Branching
> >
B.P. of haloalkanes is
greater than their parent
hydrocarbon due to
Cl
Cl
Cl
Molecules with better packing
Cl
have higher melting point. Cl
Cl
Cl
Cl
is greater than
Hence, solubility
of haloalkanes
in water is low.
Solubility of Haloalkanes in Organic Solvents
is nearly same as
Density
2.0
1.5
Density
1.0
For same hydrocarbon (g/mL)
chain, as the size of
halogen increase, density 0.5
increases.
0.0 n-C3H7Br n-C3H7I
n-C3H7Cl
2.0
1.5
0.0
CH2Cl2 CHCl3 CCl4
Physical
Properties
Chemical
Preparation
Properties
Halo
Compounds
Reaction with
Substitution Elimination
metals
–
OH
–
RO
–
SH
–
CN
R = Me, 1 o,
or 2o
X = Cl, Br, or I
-
Dehydrohalogenation
General reaction
EtONa
EtOH
Example
EtONa
+
EtOH
81% 19%
Synthesis of Alkynes
2NaNH2
+ 2NH3 + 2NaBr
Mechanism
Step 1
+ + +
Step 2
+ + +
Reactions with Metals
Grignard
Wurtz reaction
reagent
Preparation of Grignard Reagent
Et2O
ArX + Mg ArMgX
Structure and Reaction of Grignard Reagent
δ- δ+ δ+ δ-
–
:
: :
:
Reaction of Grignard Reagent with Alcohol
δ- δ+ δ+ δ-
–
:
:
R — MgX + H — O — R’ R — H + R’ O + Mg2+ + X‒
:
:
Wurtz Reaction
Na
R—X + 2Na + X—R R—R + 2NaX
Ether (dry)
Wurtz Reaction
Na
+
Ether (dry)
Reactions of Haloarenes
General reaction
+ Nu– + X–
X = Halogen
Nucleophilic Aromatic Substance (SNAr)
General reaction
+ + HA
X = F, Cl, Br, I
X
Dry ether
2 + 2Na + 2NaX
90
Corey-House
Synthesis
Corey-House Synthesis
General Reaction
Gilman reagent
92
Structure of Gilman’s Reagent
_
δ
Preferably
covalent bond
_
+ δ+
Preferably _ Preferably
δ
ionic bond covalent bond
93
Corey House Synthesis
_
δ+ δ_ δ_ δ+ δ_ +
+
+ RCu + LiX
94
Corey House Synthesis
Example
CH3CH2CH2CH2Br + (CH3)2CuLi
Example
CH3CH2Br + (CH3CH2)2CuLi
Dichloromethane
Trichloromethane
Triiodomethane
Tetrachloromethane
Freons
DDT
Dichloromethane
Dichloromethane
(Methylene chloride)
Structure Uses Harmful effects
Uses
Paint remover
Propellent in aerosol
Dichloromethane
Metal cleansing
As a solvent
Harmful Effects of Dichloromethane
Slight hearing
Direct contact can cause
and vision
impairment
26-04-2021 102
Uses
Click to edit Master title style
Solvent for fats,
• Click to edit Master text styles alkaloids and iodine
• Second level
• Third level
• Fourth level Production of freon
Trichloromethane
• Fifth level
refrigerants (R-22)
Anesthetic in surgery
26-04-2021 103
Harmful Effects of Trichloromethane
Click to edit Master title style
Dizziness, fatigue,
Chloroform exposure causes and headache
• Click to edit Master text styles
• Second level
• Third level Damage to liver
• Fourth level and kidneys
• Fifth level
light
2CHCl3 + O2 2COCl2 + 2HCl
(Iodoform)
• Fifth level
Has antiseptic
properties due
to the liberation
of free iodine.
26-04-2021 105
Tetrachloromethane
Click to edit Master title style
• Click to edit Master text styles
Tetrachloromethane
• Second level
(Carbon tetrachloride)
• Third level
• Fourth level
Structure Uses Harmful Effects
• Fifth level
26-04-2021 106
Uses
Click to edit Master title style
Manufacture of
• Click to edit Master text styles refrigerants and propellants
• Second level for aerosol cans
• Third level
• Fourth level
• Fifth level
Feedstock in the synthesis
Tetrachloromethane
of chlorofluorocarbons
Pharmaceuticals
manufacturing
26-04-2021 107
Uses
Click to edit Master title style
Cleaning fluid
• Click to edit Master text styles
• Second level
• Third level
•Tetrachloromethane
Fourth level Degreasing agent
• Fifth level
Fire extinguisher
26-04-2021 108
Harmful Effects of Tetrachloromethane
Click to edit Master title style
• Click
CCl to edit Master text styles
4 exposure causes
CCl4 exposure causes
• Second level
• Third level
• Fourth level Dizziness & light
• FifthNerve
level cell damage headedness
Liver cancer
26-04-2021 109
Freons
Click to edit Master title style
Chlorofluorocarbon
• Click to edit Master text styles
compounds of methane
• Second level & ethane are collectively
• Third level known as freons.
• Fourth level
• Fifth level
Freons
Uses and
Structure Harmful Effects
26-04-2021
characteristics 110
Uses
Click to edit Master title style
Usesstyles
• Click to edit Master text of Freon-12
• Second level
• Third level
• Fourth level
Aerosol
• Fifth level Propellants
Refrigerators
Air-conditioners
26-04-2021 111
Characteristics of Freons
Click to edit Master title style
Freons are
• Click to edit Master text styles
• Second level
• Third level Stable In stratosphere, freon is able
• Fourth level
• Fifth level
to initiate radical chain
reactions that can upset
Non-reactive the natural ozone balance.
Non-toxic
Liquefiable gases
26-04-2021 112
DDT
Click to edit Master title style
DDT
• Click to edit Master text styles
• Second level
• Third level
• Fourth level
• Fifth level
Structure Uses Harmful Effects
26-04-2021 113
Structure
Click to edit Master title style
• Click to edit Master text styles
• Second level
• Third level
• Fourth level
• Fifth level
26-04-2021 114
Harmful Effect of DDT
Click to edit Master title style
• Click to edit Master text styles
• Second level DDT is not metabolised
• Third level very rapidly by animals
• Fourth level
• Fifth level
26-04-2021 115