by dr. nahed nasser 1. contents structure and classes of halocompounds nomenclature physical...

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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