Exercício de Química Sintética e Organica Mista (670)

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23.17 Reaction of a nitro-substituted aryl halide with a good nucleophile leads to nucleophilic aromatic
substitution. Methoxide will displace fluoride from the ring, preferentially at the positions ortho and
para to the nitro group.
23.18 (a) This reaction is nucleophilic aromatic substitution by the addition–elimination mechanism.
The nucleophile, , displaces chloride directly from the aromatic ring. The product
in this case was isolated in 57% yield.
(b) The nucleophile, hydrazine, will react with 1-chloro-2,4-dinitrobenzene by an addition–
elimination mechanism as shown.
The nitrogen atoms of hydrazine each has an unshared electron pair and hydrazine is fairly
nucleophilic. The product, 2,4-dinitrophenylhydrazine, is formed in quantitative yield.
(c) The problem requires you to track the starting material through two transformations. The first
of these is nitration of m-dichlorobenzene, an electrophilic aromatic substitution reaction.
Because the final product of the sequence has four nitrogen atoms (C6H6N4O4), 2,4-dichloro-
1-nitrobenzene is an unlikely starting material for the second transformation. Stepwise
Cl
NO2
Cl
2,4-Dichloro-1-
nitrobenzene
ClCl
m-Dichlorobenzene
HNO3
H2SO4
�
Cl
NO2
NO2
1-Chloro-2,4-
dinitrobenzene
H2NNH2
Hydrazine 2,4-Dinitrophenyl-
hydrazine
H2N
NO2
NO2
NH
�H�
�Cl�
Cl
NO2
N�
�O O�
H2N NH2
�
C6H5CH2SS
�
� C6H5CH2SK
Cl
NO2
CH3
4-Chloro-3-
nitrotoluene
SCH2C6H5
NO2
CH3
4-(Benzylthio)-3-
nitrotoluene
NaOCH3
CH3OH
�
NO2
F
F
F
F
F
1,2,3,4,5-Pentafluoro-
6-nitrobenzene
NO2
OCH3
F
F
F
F
2,3,4,5-Tetrafluoro-
6-nitroanisole
NO2
F
F
OCH3
F
F
2,3,5,6-Tetrafluoro-
4-nitroanisole
ARYL HALIDES 665