Post on 05-Apr-2018
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Phenols Ar-OH
Phenols are compounds with an OH group
attached to an aromatic carbon. Although they
share the same functional group with alcohols,
where the OH group is attached to an
aliphatic carbon, the chemistry of phenols is
very different from that of alcohols.
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Nomenclature.
Phenols are usually named as substituted phenols. The
methylphenols are given the special name, cresols. Some otherphenols are named as hydroxy compounds.
OH
phenol
OH
Br
m-bromophenol
CH3
OH
o-cresol
OH
COOH
salicylic acid
OH
OH
OH
OH
OH
OH
catechol resorcinol hydroquinone
COOH
OH
p-hydroxybenzoic acid
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phenols, syntheses:
1. From diazonium salts
2. Alkali fusion of sulfonates
N2H2O,H
+
OH
SO3 Na NaOH,H2O
300o
ONaH+ OH
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as acids:
with active metals:
with bases:
CH4 < NH3 < HCCH < ROH < H2O < phenols < H2CO3 < RCOOH < HF
OH
Na
ONa
sodium phenoxide
+ H2(g)
OH
+ NaOH
ONa
+ H2O
SA SB WB WA
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2. ester formation (similar to alcohols)
OH
CH3+ CH3CH2C
O
OH
H+
CH3CH2CO
O
H3C
+ H2O
OH
COOH
salicyclic acid
+ (CH3CO)2O
O
COOH
CH3C
O
aspirin
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3. ether formation (Williamson Synthesis)
Ar-O-Na+ + R-X Ar-O-R + NaX
note: R-X must be 1o or CH3
Because phenols are more acidic than water, it is possible
to generate the phenoxide in situ using NaOH.
OH
CH3
+ CH3CH2Br, NaOH
OCH2CH3
CH3
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4. Electrophilic Aromatic Substitution
TheOH group is a powerful activating group in EAS
and an ortho/para director.
a) nitration
OH OH
NO2
NO2
O2Npolynitration!
OHdilute HNO3
OHOH
NO2
NO2
+
HNO3
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OH
Br2 (aq.)
OH
Br
Br
Br no catalyst required
use polar solvent
polyhalogenation!OH
Br2, CCl4
OH OH
Br
Br
+
non-polar solvent
b) halogenation
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c) sulfonation
OH
H2SO4, 15-20oC
OH
SO3H
H2SO4, 100oC
OH
SO3H
At low temperature the reaction is non-reversible and the lower Eact ortho-
product is formed (rate control).
At high temperature the reaction is reversible and the more stablepara-
product is formed (kinetic control).
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d) Friedel-Crafts alkylation.
OH
+ H3C C CH3
CH3
Cl
AlCl3
OH
C CH3
CH3
H3C
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e) Friedel-Crafts acylation
OH
CH3CH2CH2CO
Cl+
AlCl3
OH
O
Do not confuse FC acylation with esterification:
OH
CH3CH2CH2CO
Cl+ O
O
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OH
O
OH
CH3CH2CH2CO
Cl+ O
O
AlCl3
Fries rearrangement of phenolic esters.
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f) nitrosation
OHHONO
OH
NO
EAS with very weak electrophile NO+
OH
CH3 NaNO2, HCl
OH
CH3
NO
p-nitrosophenol
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g) coupling with diazonium salts
(EAS with the weak electrophile diazonium)
OH
CH3+
N2 Cl
benzenediazoniumchloride
CH3
OH
N
N
an azo dye
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h) Kolbe reaction (carbonation)
ONa
+ CO2125oC, 4-7 atm.
OH
COONa
sodium salicylate
H+
OH
COOH
salicylic acid
EAS by the weaklyelectrophilic CO2
O C O