ORGANIC HALOGEN COMPOUNDS
By
Dr. Nahed Nasser
1
THE CHEMISTRY OF Organic
halide compounds
CONTENTS
• Structure
and classes of halocompounds
• Nomenclature
• Physical properties
• Preparation of halocompounds
• Reactions of halocompounds
• Uses of haloalkanes
2
STRUCTURE OF HALOGENOCOMPOUNDS
Halocompounds: contain the functional group C-X where X
s a halogen (F,Cl,Br or I)
The halogen atom may be attached to an aliphatic skeleton alkyl group; Halogenoalkanes or to a benzene (aromatic) ring
Classes of haloalkanes: Halogenoalkanes are classified
according to the type of carbon atom bearing the halogen
nto:
I
Primary alkyl halide
Secondary alkyl halide
Tertiary alkyl halide
CH
CH33-X and
H3C C
Br
(R)
-CH-X
CH2
3
(R)3-C-X
H C
R-CH23-X
Cl
Nomeclature OF HALOGENOALKANES
•
IUPAC names derived from original alkane with a prefix indicating halogens and
their positions. While common names derived from the corresponding alkyl group
followed by the name of halogen atom
CH3-Cl
Common Methyl Chloride
IUPAC
Chloromethane
Class
1°
CH3-CH2-Br
Ethyl bromide
Bromoethane
1°
(CH3)2-CH-F
Isopropyl fluoride
2-Fluoropropane
2°
I
CH3
H3C
C
H3C
Cl
Br
CH3
Common Cyclohexyl Iodide
t-Butyl bromide
IUPAC
2-Bromo-2methylpropane
3°
Class
Iodocyclohexane
2°
Methylcyclopentyl
chloride
1-Chloro-1-methyl
cyclopentane
3°
Physical Properties
Solubility : All organic halides are insoluble in water and soluble
in common organic solvents.
Boiling point : The boiling points increases with increasing in
molecular weights.
Therefore, the boiling points increases in the order F<Cl<Br<I.
M.W
bp / °C
1- Chloropropane
78.5
47
1- Bromopropane
124
71
• Boiling point also increases for “straight” chain isomers.
i.e. Greater branching = lower boiling points
bp / °C
•
1-bromobutane
CH3CH2CH2CH2Br
101
•
2-bromobutane
CH3CH2CHBrCH3
91
•
5
2-bromo -2-methylpropane (CH ) CBr
73
PREPARATION OF HALOGEN COMPOUNDS
1- Direct halogenation of hydrocarbons
a) Halogenation of alkanes
R
H
+
X2
UV or heat
R X
+
HX
(X=Cl, Br)
b) Halogenation of alkenes
H2C
CH
CH 2R
+
UV or heat
H2C
X2
CH CHR
+
X
H2C
H2C
CH
CH
CH 2R
CH 2R
+
+
X2
HX
CCl 4
CCl 4
H2C
HC
X
X
H3C
HC
X
CH 2R
CH 2R
HX
c) Halogenation of alkynes
HC
HC
C
C
CH 2R
CH 2R
+
+
UV or heat
HC
X2
CCl 4
X2
C
X
X
X
HC
C
X
X
C
CH 2R
+
HX
+
CH 2R
X
CCl 4
HC
CHR
HX
H3C
C
CH 2R
X
d) Halogenation of alkyl benzene and aromatic
compounds
CHXR
CH2R
+
X2
UV or heat
+
HX
FeX3
CH2R
CH2R
+
X
X
p-Isomer
o-Isomer
2- Halogenation of alcohols
ZnCl2
R
OH
+ HX
R
OH
+ SOX2
(X= Br, Cl)
R
OH
R
OH + PX
5
+ PX3
R
X
+ H2O
R
X
+ SO2 + HCl
R
+ HOPX2
X
R
+ HOPX4
X
OH
PCl3 / heat
H3C
- (HO PCl2)
Cl
H3C
OH
Cl
SOCl2
+ SO2 + HCl
CH3
CH3
PBr3
OH
- (HO PBr2)
Br
CH3
CH3
conc. HCl
H3C
H3C
OH
Cl
- H2O
CH
CH3
Reactions of Organic Halides
1- Nucleophilic Subtitution Reactions
R
+
X
Nu
-
R
+
Nu
-
X
Nu- = OH, OR, OCOR, NH2, RNH, SH, SR, RC=C, CN,
acytilide anion, Idil KOH
H3C
H3C
Br
Cl
Cl
NaCN
-
OH
CN
PhO Na
OPh
+
CH
Br
HC
-
C Na
+
(primary and secondary)
O
O
Cl
NaNH 2
NH2
Br
I
NaI
Acetone
2- Elimination Reactions:
Alkyl halides can lose HX molecule to give an alkene.
e.g.1
e.g.2
C3H7Br + NaOH(alc) ——> C3H6 + H2O + NaBr
CH3
H3C
C
H3C
Cl
C2H5O Na / EtOH / Heat
CH2
-HCl
CH3
H3C
If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2bromopentane) a mixture of isomeric alkene products is obtained.
Br
Conc. KOH Or C2H5O Na Or PhO Na
+
EtOH / Heat
2-Butene
Major
1-Butene
Minor
3- Reactions of Grignared reagent
a) Formation of Grignard reagent
R
Ar
X
X
+
+
Mg
Mg
Dry ether
R
Dry ether
Ar
(X=Cl, Br, I)
MgX
MgX
b) Reactions of Grignard reagent
H2O
R
MgX
R'OH
HC
R
H
+
Mg(OH)X
R
H
+
Mg(OR')X
CH
R
H + Mg(HC
C)X
(X=Cl, Br, I)
4- Reduction of alkyl halides
a- Reduction by Znic metal and acids or by metal hydrides
H
+ Zn
CH3CH2CH2Br
1) LiAlH4 / ether
CH3CH2CH2CH2Br
CH3CH2CH3
+ ZnBr2
CH3CH2CH2CH3
2) H3O
b- Reduction by sodium metal (coupling reaction)
2 H3C
Br
+
2 Na
H3C
CH3
+
2 NaBr
c- Reduction using lithium dialkyl cuprate
(CH3CH2)2CuLi
+
CH3Br
CH3CH2CH3
USES OF HALOALKANES
Synthetic
The reactivity of the C-X bond means that halogenoalkanes play an
important part in synthetic organic chemistry. The halogen can be
replaced by a variety of groups via nucleophilic substitution.
Polymers
Many useful polymers are formed from halogeno hydrocarbons
Monomer
chloroethene
Polymer
poly(chloroethene) PVC
Repeating unit
- (CH2 - CHCl)n –
USED FOR PACKAGING
tetrafluoroethene
poly(tetrafluoroethene) PTFE
- (CF2 - CF2)n -
USED FOR NON-STICK SURFACES
Chlorofluorocarbons - CFC’s
dichlorofluoromethane
trichlorofluoromethane
bromochlorodifluoromethane
CHFCl2
CF3Cl
CBrClF2
CCl2FCClF2
All are/were chosen because of their
refrigerant
aerosol propellant, blowing agent
fire extinguishers
dry cleaning solvent, degreasing agent
LOW REACTIVITY, VOLATILITY, NON-TOXICITY