Exercício de Química Sintética e Organica Mista (699)

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24.24 The driving force for this reaction is the stabilization that results from formation of the aromatic
ring. A reasonable series of steps begins with protonation of the carbonyl oxygen.
24.25 Bromination of p-hydroxybenzoic acid takes place in the normal fashion at both positions ortho to
the hydroxy group.
A third bromination step, this time at the para position, leads to the intermediate shown.
Aromatization of this intermediate occurs by decarboxylation.
� �CO2 H
�
2,4,6-Tribromophenol
OH
Br
Br
Br
OH
Br C
O
O
H
�
� Br2 � Br
�
OH
BrBr
CO2H
OH
BrBr
Br CO2H
�
Br2
OH
BrBr
CO2H
3,5-Dibromo-4-
hydroxybenzoic acid
OH
CO2H
p-Hydroxybenzoic
acid
�H�
Protonated ketone
can rearrange by
alkyl migration.
OH
H
H
H
H
�
OH
HH
H
Aromatization of this
intermediate occurs 
by loss of a proton.
OH
H
H
H
H
�
H�
O
H
H
H
H
�OH
H
H
H
H
OH
H
H
H
H
�
Resonance forms of protonated ketone
694 PHENOLS