aryl halides

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Aryl halides Dr. Talat R. Al- Ramadhany

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Aryl halides. Dr. Talat R. Al- Ramadhany. Aryl halides ( Ar -x ). Aryl halides are organic compounds containing halogen atom attached to an aromatic ring. They have the general formula ArX , where ( Ar -) is phenyl or substituted phenyl and (x) is F, Cl, Br, I. m - Bromonitrobenzene. - PowerPoint PPT Presentation

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Page 1: Aryl halides

Aryl halides

Dr. Talat R. Al-Ramadhany

Page 2: Aryl halides

Aryl halides (Ar-x)

Aryl halides are organic compounds containing halogen atom attached to an aromatic ring. They have the general formula ArX, where (Ar-) is phenyl or substituted phenyl and (x) is F, Cl, Br, I.

X

Page 3: Aryl halides

Dr. Talat R.Al-Ramadhany

Cl Br

NO2

I

OH

COOHCl

Chlorobenzene m-Bromonitrobenzene p-Iodophenol

o-Chlorobenzoic acid

Page 4: Aryl halides

Dr. Talat R.Al-Ramadhany

An aryl halide is not just any halogen compound containing an aromatic ring. Benzyl chloride, for example, is not an aryl halide; its halogen is not attached to the aromatic ring, in structure and properties it is simply a substituted alkyl halide.

CH2 Cl C C X

Benzyl chloride A vinyl halide

Page 5: Aryl halides

Dr. Talat R.Al-Ramadhany

Physical properties:

1. Aryl halides are insoluble in water but soluble in organic solvents.

2. Para-isomer has a melting point about (70-100ºC) degree higher than ortho- or meta- isomers.

3. Para- isomer is more symmetrical which fits better into a crystalline lattice and the higher m.p.

4. Because of the strong intracrystalline forces, p- Isomer is less soluble in a given solvent than ortho-isomer.

Page 6: Aryl halides

Dr. Talat R.Al-Ramadhany

Preparation of aryl halide compounds:

1. Direct halogenations of aromatic compounds:

ArH + X2 ArX + HX

X2 = Cl2, Br2

Lewis acid = FeCl3, AlCl3, BFe3, ....etc

Lewis acid

NO2 NO2

Cl2 , AlCl3

Cl

Example:

Page 7: Aryl halides

Dr. Talat R.Al-Ramadhany

2. From aryl diazonium salts

ArH HNO3H2SO4

ArNO2reduction ArNH2

HONO0

ArN2+

Diazniumsalt

BF4-

ArF

KI ArI

ArCl

ArBr

CuCl

CuBr+ N2ArN2

+

Diazniumsalt

Page 8: Aryl halides

Dr. Talat R.Al-Ramadhany

Sandmeyer reaction

Replacement of the diazonium group by Cl, or Br is carried out by mixing the solution of the freshly prepared diazonium salt with cuprous chloride or cuprous bromide at room temperature.

ArN2+X- CuX

ArX + N2

Page 9: Aryl halides

Dr. Talat R.Al-Ramadhany

3. From arylthallium compoundsAryl iodides can be prepared by simple treatment of

arylthallium with iodine. The thallation route has the advantages of speed, high yield, and orientation control.

[ArH + Tl(OOCCF3)3 ] ArTl(OOCCF3)2 + I2 ArIArylthallium

triflouroacetate

CH3

Tl(OOCCF3)3 I2

CH3

I

CH3

Tl(OOCCF3)2

For iodides only

Page 10: Aryl halides

Dr. Talat R.Al-Ramadhany

The preparation of aryl halides from diazonium salts is more important than direct halogenation for several reasons:

First of all, fluorides and iodides, which can seldom be prepared by direct halogenation, can be obtained from the diazonium salts.

Second, where direct halogenation yields a mixture of ortho- and para- isomers; the ortho isomer, at least, is difficult to obtain pure. On the other hand, the ortho and para isomers of corresponding nitro compounds, from which the diazonium salts ultimately come, can often be separated by fractional distillation.

Page 11: Aryl halides

Dr. Talat R.Al-Ramadhany

Low reactivity of aryl and vinyl halides:

Br

alcoholic AgNO3

Dry /N. R.

alcoholic AgNO3

Dry /N. R.H2C CHBr

Page 12: Aryl halides

Dr. Talat R.Al-Ramadhany

X

Aryl halide

or

C C X

Vinyl halide

Ag+

OH

OR

NH3

CN

ArH,

AlCl3

No Reaction

Page 13: Aryl halides

Dr. Talat R.Al-Ramadhany

The low reactivity attributed to two factors:

A. Delocalization of electrons by resonance.

B. Differences in σ bond energies due to differences in hybridization of carbon.

Cl Cl

H

Cl

H

Cl

H

I II III IV

Page 14: Aryl halides

Dr. Talat R.Al-Ramadhany

Reactions of aryl halides:

1. Formation of Grignard reagents

Br MgBr

Mg

anhyd.Et2O

Cl MgCl

Mg

THF

Page 15: Aryl halides

Dr. Talat R.Al-Ramadhany

Br

G

MgBr

G

Mg

ether

G may not be:

COOH C O

OH COOR

NH2 C N

SO3H NO2

and many others....

G may be:

R OR

Ar Cl

Page 16: Aryl halides

Dr. Talat R.Al-Ramadhany

Br

HNO3, H2SO4

Br

NO2Br NO2+

H2SO4 , SO3

Br

SO3HBr SO3H+

Br

BrBrBr+

Br2, Fe

Br

CH2CH3 Br CH2CH3+CH3CH2Br

AlCl3

2 .Electrophilic Aromatic Substitution (EAS)

Page 17: Aryl halides

Dr. Talat R.Al-Ramadhany

3. Nucleophilic aromatic substitution:

Ar:X + :Z Ar:Z + :X-

(Ar-) must contain strongly electron withdrawing groups ortho and/or para to the X.

H+

Cl

+ NaOH

N.R

350oC4500 psi

ONa OH

Page 18: Aryl halides

Dr. Talat R.Al-Ramadhany

Cl

NO2

15% NaOH160oC

ONa

NO2

H+

OH

NO2

Cl

NO2

NO2

boiling aq.Na2CO3130oC

OH

NO2

NO2

Page 19: Aryl halides

Dr. Talat R.Al-Ramadhany

Cl

NO2

NO2

O2Nwarm water

OH

NO2

NO2

O2N

Cl

NO2

NO2

+ NaOH

ONa

NO2

NO2

OH

NO2

NO2

H+

2,4-Dinitrophenol2,4-Dinitrochlorobenzene

Page 20: Aryl halides

Dr. Talat R.Al-Ramadhany

4. Nucleophilic aromatic substitution.

When the ring is not activated toward bimolecular displacement

Ar:X + :Z Ar:Z + :X-

Br

+ NaNH2

NH2

NH3

Bromobenzene Aniline

Page 21: Aryl halides

Dr. Talat R.Al-Ramadhany

F

+

Li

PhenyllithiumFluorobenzene

Li

H2O

Biphenyl

OCH3

Br3-Bromo-4-methoxybiphenyl

NaNH2 , NH3OCH3

NH2

2-Amino-4-methoxybiphenyl

Page 22: Aryl halides

Dr. Talat R.Al-Ramadhany

Analysis of aryl halides

►Insoluble in cold sulfuric acid.

►Inertness toward bromine in carbon tetrachloride) CCl4 (and toward permanganate solution (KMnO4).

►Formation of orange to red colors when treated with chloroform and aluminum chloride.

►dissolution in cold fuming sulfuric acid, but at a slower rate than that of benzene.