TEMA 6. Reactions of Aromatics Compounds

8/9/2019 TEMA 6. Reactions of Aromatics Compounds

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Reactions ofAromatic Compounds

TEMA 6

Qumica Orgnica 2014


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Chapter 17 2

Eectrop!iic

Aromatic "u#stitutionEectrop!iesubstitutes for a !$drogen

on the benzene ring.

=>


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Chapter 17 3

%nusua "ta#iit$Hydrogenation of just one double

bond in benzene is endot!ermic!

=>


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4

Mec!anism

=>


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&romination of &en'ene

"e#uires a stronger ele$trophile than %r2.

&se a strong 'e(is a$id $atalyst) *e%r3.

Br Br FeBr3 Br Br FeBr 3

Br Br FeBr 3

H

H

H

H

H

H

H

H

H

H

H H

Br+ + FeBr4

_

Br

HBr+=>


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Chapter 17 +

Energ$ (iagram for

&romination

=>


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7

C!orination

and )odination Chlorination is si,ilar to bro,ination.

&se -lCl3as the 'e(is a$id $atalyst.

odination re#uires an a$idi$ o/idizing

agent) li0e nitri$ a$id) (hi$h o/idizes the

iodine to an iodoniu, ion.

H+

HNO3 I21/2 I+

NO2 H2O+ ++ +

=>


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*itration of &en'ene&se sulfuri$ a$id (ith nitri$ a$id to for,

the nitroniu, ion ele$trophile.

H O N

O

O

H O S O H

O

O

+ HSO4_

H O N

OH

O+

H O N

OH

O+

H2O + N

O

O

+2then for,s asig,a $o,ple/ (ith

benzene) loses Hto

for, nitrobenzene. =>


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5

"ufonation

6ulfur trio/ide) 63) in fu,ing sulfuri$ a$id

is the ele$trophile.

S

O

O OS

O

O OSO

O OSO

O O

+ + +

_

_ _

S

O

O O

H

SO

O

OH

+

_

S

HOO

O

benzenesulfonic ac

=>


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1

(esufonation

-ll steps are re8ersible) so sulfoni$ a$id

group $an be re,o8ed by heating in

dilute sulfuri$ a$id.

9his pro$ess is used to pla$e deuteriu,

in pla$e of hydrogen on benzene ring.

%enzene:d+

=>

2SO4/2O

lar!e e"cess

H

H

H

H

H

H


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11

*itration of Touene

9oluene rea$ts 2 ti,es faster than benzene.

9he ,ethyl group is an a$ti8ator.

9he produ$t ,i/ $ontains ,ostly ortho and

para substituted ,ole$ules.

=>


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12

"igma Compe+

nter,ediate

is ,ore

stable if

nitrationo$$urs at

the ortho

orpara

position.

=>


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13

Energ$ (iagram

=>


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14

-$ti8ating) O:) P:

;ire$ting 6ubstituents -l0yl groups stabilize the sig,a $o,ple/ by

indu$tion) donating ele$tron density through

the sig,a bond. 6ubstituents ,it! a one pair of eectrons

stabilize the sig,a $o,ple/ by resonan$e.

O#H3

H

NO2

+

O#H3

H

NO2

+

=>


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1+

6u,,ary of

-$ti8ators

=>


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17

;ea$ti8ating ?eta:

;ire$ting 6ubstituents

@le$trophili$ substitution rea$tions fornitrobenzeneare 1) ti,es slo(erthan for benzene.

9he produ$t ,i/ $ontains ,ostly themeta isomer) only s,all a,ounts of theorthoand para iso,ers.

?eta:dire$tors dea$ti8ate all positionson the ring) but the ,eta position is lessdea$ti8ated.

=>


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1

rtho 6ubstitution

on itrobenzene

=>


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15

Aara 6ubstitution

on itrobenzene

=>


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2

?eta 6ubstitution

on itrobenzene

=>


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22

6tru$ture of ?eta:

;ire$ting ;ea$ti8ators

9he ato, atta$hed to the aro,ati$ ring

(ill ha8e a partial positi8e $harge. @le$tron density is (ithdra(n indu$ti8ely

along the sig,a bond) so the ring is less

ele$tron:ri$h thanbenzene.

=>


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23

6u,,ary of ;ea$ti8ators

=>


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24

?ore ;ea$ti8ators

=>


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2

.ao#en'enes

Halogens are deactivating toward

electrophilic substitution) but are ortho)

para:dire$ting!

6in$e halogens are 8ery ele$tronegati8e)

they (ithdra( ele$tron density fro, the

ring indu$ti8ely along the sig,a bond.

%ut halogens ha8e lone pairs of ele$trons

that $an stabilize the sig,a $o,ple/ by

resonan$e. =>


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2+

6ig,a Co,ple/

for %ro,obenzene

Br

%+

Br

H

%

&+'

&+'&+'

Ortho attack

+ Br

%+

Br

H %

+

&+'

&+'&+'

Para attack

rtho and para atta$0s produ$e a bro,oniu, ion

and other resonan$e stru$tures.

=>

Meta attack

Br

%+

Br

H

H

%

+

&+'

&+' o bro,oniu, ionpossible (ith ,eta atta$0.


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27

@nergy ;iagra,

=>


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2

6u,,ary of

;ire$ting @ffe$ts

=>


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25

Mutipe "u#stituents

The most strongly activating substituentThe most strongly activating substituent

will determine the position of the nextwill determine theposition of the next

substitutionsubstitution. ?ay ha8e ,i/tures.O#H3

O2N

SO3

H2SO

4

O#H3

O2N

SO3H

O#H3

O2N

SO3H

+

=>A:iso,er B


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3

*riedel:Crafts -l0ylation

6ynthesis of al0yl benzenes fro, al0yl

halides and a 'e(is a$id) usually -lCl3.

"ea$tions of al0yl halide (ith 'e(is a$idprodu$es a $arbo$ation (hi$h is the

ele$trophile.

ther sour$es of $arbo$ationsal0enes H* or al$ohols %*3.

=>


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31

@/a,ples of

Carbo$ation *or,ation

#H3 #H #H3

#l

+ (l#l3

#H3#

H3# H

#l (l#l3+ _

H2# #H #H3HF

H3# #H #H3

F+

_

H3# #H #H3

OHBF3

H3# #H #H3

OH BF3+

H3# #H #H3+

+ HOBF3

_

=>


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32

*or,ation of

-l0yl %enzene

#

#H3

#H3

H+

H

H

#HH3'2+

H

H

#HH3'2

B

F

F

F

OH

#H

#H3

#H3

+

HF

BF

OHF

=>

:


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33

/imitations of

riedeCrafts "ea$tion failsif benzene has a substituent

that is more deactivating than halogenmore deactivating than halogen.

Carbo$ations rearrange. "ea$tion ofbenzene (ith n:propyl $hloride and -lCl3

produ$es isopropylbenzene.

9he al0ylbenzene produ$t is ,ore rea$ti8ethan benzene) so polyal0ylation o$$urs.

=>


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34

riedeCraftsriedeCrafts

Ac$ationAc$ation -$yl $hloride is used in pla$e of al0yl

$hloride.

9he a$yliu, ion inter,ediate isresonan$e stabilized and does not

rearrange li0e a $arbo$ation.

9he produ$t is a p!en$ etonethat isess reacti3ethan benzene.

=>


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3

?e$hanis, of -$ylation

) #

O

#l (l#l3 ) #

O

(l#l3#l+ _

) #

O

(l#l3#l+ _ (l#l4 +

_ +) # O ) # O

+

#

O

)+

H

#

H

O

)

+#l (l#l3

_#

O

) +

H#l

(l#l3

=>


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3+

Cemmensen Reduction

-$ylbenzenes $an be $on8erted to

al0ylbenzenes by treat,ent (ith

a#ueous HCl and a,alga,ated zin$.

+ #H3#H2#

O

#l1'(l#l3

2'H2O

#

O

#H2#H3*n&H!'

a, H#l

#H2#H2#H3

=>


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37

ArenesArenes

A$#en'enes

Aen$#en'enes A$n$#en'enes


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3

6ide:Chain /idation

A$#en'enes are o+idi'ed to #en'oic

a$id by hot D?n4or a2Cr27EH264.

#HH3'2

#H #H2

-.nO4$ OH

H2O$ 0ea1

#OO

#OO

_

_

=>*ot t#ut$#en'ene


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35

6ide:Chain Halogenation

%enzyli$ position is the ,ost rea$ti8e.

Chlorination is not as sele$ti8e as

bro,ination) results in ,i/tures.

&r2reacts on$ at t!e #en'$ic position.

=>

#H#H2#H3

Br

hBr2$

#H2#H2#H3

B lRdi l


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4

Benzyl Radical

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TEMA 6. Reactions of Aromatics Compounds

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