Exercício de Química Sintética e Organica Mista (671)

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nucleophilic aromatic substitution of both chlorines is possible but leads to a compound with
the wrong molecular formula (C6H7N3O2).
To obtain a final product with the correct molecular formula, the original nitration reaction
must lead not to a mononitro but to a dinitro derivative. This is reasonable in view of the fact
that this reaction is carried out at elevated temperature (120°C).
This two-step sequence has been carried out with product yields of 70–71% in the first step
and 88–95% in the second step.
(d ) This problem also involves two transformations, nitration and nucleophilic aromatic substitu-
tion. Nitration will take place ortho to chlorine (meta to trifluoromethyl).
(e) The primary alkyl halide is more reactive toward nucleophilic substitution than the aryl
halide. A phosphonium salt forms by an SN2 process.
( f ) N-Bromosuccinimide (NBS) is a reagent used to substitute benzylic and allylic hydrogens
with bromine. The benzylic bromide undergoes SN2 substitution with the nucleophile,
methanethiolate. As in part (e), the alkyl halide is more reactive toward substitution than the
aryl halide.
NBS
benzoyl peroxide,
CCl4, heat
NaSCH3
OCH3
H3C
Br
2-Bromo-5-
methoxytoluene
OCH3
CH2Br
Br
2-Bromo-5-methoxy-
benzyl bromide
OCH3
CH3SCH2
Br
2-Bromo-5-methoxybenzyl
methyl sulfide
�I CH2Br
p-Iodobenzyl bromide
I CH2P(C6H5)3 Br
�
(p-Iodobenzyl)triphenyl-
phosphonium bromide (86%)
(C6H5)3P
Triphenyl
phosphine
�
HNO3
H2SO4
NaOCH3
CH3OH
1-Chloro-4-
(trifluoromethyl)-
benzene
CF3
Cl
1-Chloro-2-nitro-4-
(trifluoromethyl)-
benzene
NO2
CF3
Cl
2-Nitro-4-
(trifluoromethyl)-
anisole
NO2
CF3
OCH3
Cl
NO2O2N
Cl NH2
NO2O2N
H2N
1,5-Diamino-2,4-dinitrobenzene
(C6H6N4O4)
ClCl
m-Dichlorobenzene
NH3
ethylene
glycol, 140�C
HNO3, H2SO4
120�C
Cl
NO2
Cl
2,4-Dichloro-1-
nitrobenzene
NH2
NO2
H2N
2,4-Diamino-1-
nitrobenzene
NH3
666 ARYL HALIDES