Polynuclear Aromatics

Phenanthrene

AnthraceneNaphthalene

12

3

45

6

78

9

10

Napthalene

Naphthalene: nomenclature:

Mono substituted: α- 1-β- 2-

Special names:

NO2

2-nitronaphthalene -nitronaphthalene

OH NH2 SO3H

-naphthol -naphthylamine -naphthalenesulfonic acid

also

flat, sp2 4i + 2 = 10 e- aromatic

Heat of hydrogenation is –61 Kcal/mole lower than predicted (resonance stabilization energy).

Benzene is –36 Kcal/mole lower than predicted.

- 61 = - 36 - 25 the second aromatic ring is less stable.

Naphthalene, reactions:

1) oxidation:

O

O

O

O

O

CrO3

HOAc, 25o

O2, V2O5

460-480o

1,4-naphthoquinone

phthalic anhydride

Note: Because naphthalene is sensitive to oxidation, you cannot make naphthoic acids via oxidation of a side chain.

[oxid.]CH3 CH3

O

O

CCH3

O

NaOICOOH

2. Reduction:

Na, EtOH

78o

Na, i-PeOH

132o

(xs) H2, Pt

heat, pressure

1,4-dihydronaphthalene

tetrahydronaphthalene(tetralin)

decalin

3. Electrophilic Aromatic Substitution:

a) nitrationHNO3

NO2

b) sulfonationH2SO4

H2SO4

80o

1600

SO3H

SO3H

c) halogenationBr2

CCl4

Br

nocatalyst required

Electrophilic aromatic substitution (cont.)

d) Friedel-Crafts alkylation

e) Friedel-Crafts acylation

polyalkylation!

CH3COCl, AlCl3

non-polar solvent

CH3COCl, AlCl3

nitrobenzene

C

C

O CH3

CH3

O

Why is EAS in naphthalene mostly to the alpha-position?

EAS in syntheses of substituted naphthalenes:

Alpha-substitution via halogenation or nitration.

Br MgBr

NO2NH2

Br2

CCl4

HNO3

Mg

H2/Ni

Beta-substitution via high temp sulfonation or Friedel-Crafts acylation in nitrobenzene.

SO3H ONa

OHNH2

CCH3

O

COOH

CNH2

ONH2

OH-, 3000

H+

NH3

heat,pressure

OI- SOCl2; then NH3

OBr-

EAS in substituted naphthalenes:

a) With an activating group to EAS

in the alpha position 4- plus a little 2-

in the beta position 1-

b) With a deactivating group to EAS

the other ring, usually alpha ( 5- & 8- )

G

G

G

+ a little 2-

OH OH

OH

NO2

NO2

N

N2

N

+

HNO3

azo dye

polynitration

OH OH

NO2 NO2

NO2

NO2NO2

HNO3

N2

NN

+

+

Haworth Synthesis of naphthalene

O

O

O

O

HO2C

AlCl3+

Zn(Hg)

HClHO2C

HF orPPA

O

Zn(Hg)

HCl

Pd

CO2, heat

Substituted naphthalenes via Haworth synthesis:

CH3

O

O

O

+ AlCl3

CH3

CO

COOH

CH3

beta-

O

+ RMgX

OHR

H+

Pd, CO2

heat

a) use a substituted benzene G = -R, -X, -OCH3

b) Grignard

RR

alpha-

O

HO2C

R'OH, H+

O

R'O2C

RMgX H2OR OH

R'O2C

H+, heat

R

HO2C

R

alpha-

2

34

1

10

9

56

78

anthracene

Heat of hydrogenation is-84 Kcal lower than expected.2 x -36 = -72-86 - (-72) = -12 Kcal/mole toremove the middle ring'saromaticity.

3

21

4

109

8

76

5

3

2

1

4

1098

7

6 5

Phenanthrene

14 pi e-, totalof five resonacestructures

Heat of hydrogenation is -92 Kcal/mole lower thanpredicted.2 x -36 = -72-92 -(-72) = -20 Kcal/mole to remove the aromaticityof the middle ring.

K2Cr2O7

H+

K2Cr2O7

H+

O

O

OO

9,10-antraquinone

9,10-penanthrone

Oxidation:

Na, heat

EtOH

Na,heat

i-PeOH

9,10-dihyroanthracene

9,10-dihydrophenanthrene

Reduction:

EAS in anthracene or phenanthrene yields mixtures and is not generally useful. For example, in sulfonation:

13%

8%

18%

18%0%

Bromination is an exception:

Br2

FeBr3

Br2, CCl4

Br

BrBr

H

Br

Br

H

Br

9-bromoanthracene

OH- or heat

Br2, CCl4

Haworth synthesis of anthracene

O

O

HO2C

O

O

O

O

+AlCl3

H2SO4

Zn(Hg)

HCl

Pd, CO2, heat

phthalic anhydride

Haworth synthesis of phenanthrene

O

O

COOH O

HOOC

+

O

O

+AlCl3

succinic anhydride Zn(Hg), HCl

COOH

HOOC

+HF

O

O

+

Pd, CO2, heatZn(Hg),HCl