ByBy
Dr. Nahed NasserDr. Nahed Nasser
1
CONTENTSCONTENTS
• Structure and classes of halocompounds
• Nomenclature
• Physical properties
• Preparation of halocompounds
• Reactions of halocompounds
• Uses of haloalkanes
THE CHEMISTRY OF Organic THE CHEMISTRY OF Organic halide compoundshalide compounds
2
I
C
CH3
CH3
BrCH3
ClCH3
Halocompounds:Halocompounds: contain the functional group C-X where X is 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:Classes of haloalkanes: Halogenoalkanes are classified according to the type of carbon atom bearing the halogen into:
• Primary alkyl halide CH3-X and R-CH2-X
• Secondary alkyl halide (R)2-CH-X
• Tertiary alkyl halide (R)3-C-X
STRUCTURE OF HALOGENOCOMPOUNDSSTRUCTURE OF HALOGENOCOMPOUNDS
• IUPAC namesIUPAC 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 CH3-CH2-Br (CH3)2-CH-F
CommonCommon Methyl Chloride Ethyl bromide Isopropyl fluoride
IUPAC IUPAC Chloromethane Bromoethane 2-Fluoropropane
Class Class 1° 1° 2°
CommonCommon Cyclohexyl Iodide t-Butyl bromide Methylcyclopentyl chloride
IUPACIUPAC Iodocyclohexane 2-Bromo-2- 1-Chloro-1-methyl
methylpropane cyclopentane
Class Class 2° 3 ° 3 °
I
C
CH3
CH3
BrCH3
ClCH3
Nomeclature OF HALOGENOALKANESNomeclature OF HALOGENOALKANES
Physical PropertiesPhysical Properties
5
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
• 2-bromo -2-methylpropane (CH3)3CBr 73
PREPARATION OF HALOGEN COMPOUNDSPREPARATION OF HALOGEN COMPOUNDS
1- Direct halogenation of hydrocarbons1- Direct halogenation of hydrocarbons
a) Halogenation of alkanesa) Halogenation of alkanes
b) Halogenation of alkenesb) Halogenation of alkenes
R H + X2 R XUV or heat + HX (X=Cl, Br)
CH2 CH CH2R + X2
UV or heatCH2 CH CHR
X
+ HX
CH2 CH CH2R X2 CH CH2RCH2
X X
CCl4+
CH2 CH CH2R CH CH2RCH3
X
CCl4HX+
d) Halogenation of alkyl benzene and d) Halogenation of alkyl benzene and aromatic aromatic
compoundscompounds
c) Halogenation of alkynesc) Halogenation of alkynesCH C CH2R + X2
UV or heatCH C CHR
X
+ HX
CH C CH2R X2 C CH2RCH
X X
X XCCl4+
CH C CH2R C CH2RCH3
X
XCCl4
HX+
CH2R
+ X2UV or heat
CHXR
+ HX
CH2RCH2RFeX3
+
XX
p-Isomer o-Isomer
2- Halogenation of alcohols2- Halogenation of alcohols
H3C
OHPCl3 / heat
H3C
Cl
- (HO PCl2)OH
SOCl2 + SO2 + HCl
Cl
CH3
OH
PBr3
CH3
Br- (HO PBr2)
CH3
OHH3C
CH3
conc. HCl
CH3
ClH3C
CH3
- H2O
R OH + HX ZnCl2 R X + H2O
R OH + SOX2 R X + SO2 + HCl
R OH + PX3 R X + HOPX2
R OH + PX5 R X + HOPX4
(X= Br, Cl)
Reactions of Organic HalidesReactions of Organic Halides
1- Nucleophilic Subtitution1- Nucleophilic Subtitution ReactionsReactions
NuNu- - = OH, OR, OCOR, NH= OH, OR, OCOR, NH22, RNH, SH, SR, RC=C, CN, , RNH, SH, SR, RC=C, CN,
acytilide anion, Iacytilide anion, I--
R X + Nu-
R Nu + X-
CH3 Brdil KOH CH3 OH (primary and secondary)
ClNaCN CN
ClPhO
-Na
+OPh
Br CH C-Na
+
CH
Cl
O
NaNH2 NH2
O
Br I
NaIAcetone
2- Elimination2- Elimination Reactions:Reactions:Alkyl halides can lose HX molecule to give an alkene.e.g.1e.g.1
e.g.2e.g.2
If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2-bromopentane) a mixture of isomeric alkene products is obtained.
C3H7Br + NaOH(alc) ——> C3H6 + H2O + NaBr
Br
Conc. KOH Or C2H5O Na Or PhO Na
EtOH / Heat+
2-Butene Major
1-Butene Minor
CH3
C ClH3C
CH3
C2H5O Na / EtOH / HeatCH2
H3C
H3C-HCl
3- Reactions of Grignared reagent3- Reactions of Grignared reagent
a) Formation of Grignard reagenta) Formation of Grignard reagent
b) Reactions of Grignard reagentb) Reactions of Grignard reagent
R X + Mg Dry ether
R MgX (X=Cl, Br, I)
Ar X Mg Dry ether
Ar MgX (X=Cl, Br, I)+
R MgX
H2O
R'OH
HC CH
R H
R H
R H
+
+
+
Mg(OH)X
Mg(OR')X
Mg(HC C)X
4- Reduction of alkyl halides4- Reduction of alkyl halidesa- Reduction by Znic metal and acids or by metal hydrides a- Reduction by Znic metal and acids or by metal hydrides
b- Reduction by sodium metal (coupling reaction)b- Reduction by sodium metal (coupling reaction)
c- Reduction using lithium dialkyl cupratec- Reduction using lithium dialkyl cuprate
CH3 Br2 + 2 Na CH3 CH3 + 2 NaBr
(CH3CH2)2CuLi + CH3Br CH3CH2CH3
CH3CH2CH2Br + Zn H CH3CH2CH3 + ZnBr2
CH3CH2CH2CH2Br1) LiAlH4 / ether
2) H3O
CH3CH2CH2CH3
USES OF HALOALKANESUSES OF HALOALKANES
SyntheticThe reactivity of the C-X bond means that halogenoalkanes play animportant part in synthetic organic chemistry. The halogen can be
replaced by a variety of groups via nucleophilic substitution.
PolymersMany useful polymers are formed from halogeno hydrocarbons
Monomer Polymer Repeating unit
chloroethene poly(chloroethene) PVC - (CH2 - CHCl)n –
USED FOR PACKAGING
tetrafluoroethene poly(tetrafluoroethene) PTFE - (CF2 - CF2)n -
USED FOR NON-STICK SURFACES
Chlorofluorocarbons - CFC’sdichlorofluoromethane CHFCl2 refrigerant
trichlorofluoromethane CF3Cl aerosol propellant, blowing agent
bromochlorodifluoromethane CBrClF2 fire extinguishers
CCl2FCClF2 dry cleaning solvent, degreasing agent
All are/were chosen because of their LOW REACTIVITY, VOLATILITY, NON-TOXICITY