Transcript Phenol
Phenols (Ar-OH)
I. Structure and nomenclature:
Phenols are compounds of the general formula Ar-OH, where Ar- is phenyl, substituted phenyl, or one of the other aryl groups.
G G
Phenols differ from alcohols in having the -OH group attached directly to an aromatic ring.
Hydroxybenzene, the simplest member of the phenols, is generally referred to as phenol.
Dr. Talat R. Al-Ramadhany
OH CH 2 OH
Phenol Benzylalcohol
−OH is directly linked −OH is not directly linked to the aromatic ring carbon to the aromatic ring carbon
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OH OH OH Cl CH 3
o-
Chlorophenol
o
-cresol COOH
m
-Cresol CH 3 COOH OH
o
-Hydroxybenzoic acid
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OH
p-
Hydroxybenzoic acid
II. Physical properties:
The simplest Phenols are liquid or low-melting solids.
Phenols have high boiling points.
Phenol itself is somewhat soluble in water
most other Phenols are essentially insoluble in water.
Phenols are colorless, but they easily oxidized by atmospheric air and become colored compounds.
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m- and p- isomers have higher boiling point because of the intermolecular hydrogen bonding and their solubility in water is due to the hydrogen bonding with water.
Dr. Talat R. Al-Ramadhany
For o-nitrophenol, the each other and they form –NO 2 and –OH groups are closed to intramolecular hydrogen bonding (within a single molecule). Therefore o-nitrophenol does not have the low volatility of an associated liquid, cannot form hydrogen bonding with water , therefore it have lower solubility in water.
Dr. Talat R. Al-Ramadhany
III. Acidity of Phenols:
Phenols are fairly acidic compounds, and in this respect differ markedly from alcohols, which are even more weakly acidic than water.
Carboxylic acid > Phenol > Water > Alcohol
Aqueous hydroxides convert Phenols into their salts; aqueous mineral acids convert salts back into the free Phenols.
Dr. Talat R. Al-Ramadhany OH Ar-OH ArO H +
A Phenol A Phenoxide ion (acid) (salt)
Insoluble Soluble in water in water
The acidity of phenols is mainly due to an electrical charge distribution in phenols that causes the -OH oxygen to be more positive. As a result, the proton is held less strongly, and phenols can easily give this loosely held proton away to form a phenoxide ion as outlined below.
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Industrial sours of Phenols:
Conc.
i.
ii. Dow process
, in which
Chlorobenzene
is allowed to react the
aqueous sodium hydroxide
at a temperature of about
360ºC
. Cl O Na + Chlorobenzene NaOH, 360 o 4500 lb/in.
2 Sodium phenoxide HCl OH Phenol
Dr. Talat R. Al-Ramadhany
iii. Oxidation of Cumene
:
Cumene
is converted by
air oxidation
into
cumene hydroperoxide
, which is converted by
acid
into
Phenol
and
acetone
.
aqueous
O 2 H 2 O, H + H 3 C C H CH 3
Cumene
H 3 C C OOH CH 3
Cumene hydroperoxide
OH Phenol + H 3 C C CH 3 O Acetone
Preparation of Phenols in the laboratory i.
Hydrolysis of diazonium salts
ArN
2 +
+ H
2
O ArOH + H
+
+ N
2 N 2 + HSO 4 Cl H 2 O, H +
heat
OH Cl + N 2
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ii. Oxidation of arylthallium compounds This method has two advantages over the diazonium route: A.The speed and high yield.
B.Orientation control in the thallation step.
Tl(O O C CF 3 ) 2 O O C CF 3 Tl(OOCCF 3 ) 3 Pb(OAc) 4 Ph 3 P Arylthallium trifluoroacetate H 2 Aryltrifluoroacetate O, OH
heat
O H + OH
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iii. Alkaline hydrolysis of aryl halides
Cl OH NaOH (10%) 350 o 10% Cl NO 2 NaOH (15%) 160 o OH NO 2 15%
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Cl NO 2 NO 2 NaOH
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O Na + NO 2 H + NO 2 OH NO 2 OH NO 2 HNO 3 O 2 N H 2 SO 4 NO 2 Picric acid NO 2 O 2 N Cl NO 2 H 2 O O 2 N OH NO 2 NO 2 NO 90% 2
Reaction of Phenols There are two type of reaction: A. Reaction of ( O–H ) bond.
O H B. Reaction of aromatic ring ( Electrophilic Aromatic Substitution ).
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A. Reaction of ( O–H ) bond.
1) Acidity, salt formation.
O a N H 3 C 3
2) Ether formation (Williamson Synthesis) Phenols are converted into solution with alkyl halides .
ethers by reaction in alkaline OH
O O R aqueous NaOH
heat
R X + X OH OC 2 H 5 + C 2 H 5 I aqueous NaOH
heat
OH aq.NaOH
heat
Cl + phCH 2 O O phCH 2 Br X OCH 2 ph
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Aryl halide must be containing strong electron-withdrawing group to form corresponding ether.
Cl NO 2 + CH 3 O Na + NO 2 OCH 3 NO 2 NO 2
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3) Ester formation Phenols are usually converted into their esters by the reaction with carboxylic acids , acid chlorides or anhydrides .
Phenol
OH NaOH + COCl O C O
Benzoyl chloride Phenyl benzoate
O 2 N
p-Nitrophenol
OH + (CH 3 CO) 2 O CH 3 COONa
Acetic anhydride
O 2 N O C O
p-Nitrophenyl acetate
CH 3
(Fries rearrangement) When esters of Phenols are heated with aluminum chloride , the acyl group migrates from the Phenolic oxygen to an
ortho
or
para
position of the ring and yield a ketone.
This reaction is called the Fries rearrangement , is often used to prepare phenolic ketones.
OH Phenol O O C C 2 H 5 OH OH O C 2 H 5 COCl AlCl 3 CS 2 Phenyl propionate C o-Hydroxyphenyl ethyl ketone C 2 H 5 + C C 2 H 5 O p-Hydroxyphenyl ethyl ketone
B. Reaction of aromatic ring (Electrophilic Aromatic Substitution) .
1. Halogenation ( Bromination )
Treatment of
Phenols
with aqueous solution of
bromine
results in replacement of every hydrogen
–OH
group
ortho
or
para
to the
OH OH + 3 Br 2 H 2 O Br Br + 3HBr Br 2,4,6-tribromophenol
If halogenation is carried out in a solvent of low polarity: OH + 2 Br 2 CHCl 3 nonpolar solvent OH Br + OH + 2HBr Br + 2 2 C 2 0 C
OH OH CH 3
+ 2 Br 2 (aq)
Br CH 3
+ 2HBr
o
-Cresol
Br
2,4-Dibromo-6-methylphenol
Some group can replace by bromine OH OH Br
+ 3 Br 2 (aq)
Br
+ 3HBr + H 2 SO 4
SO 3 H
p
-Phenolsulfonic acid
Br
2,4,6-Tribromophenol
2) Sulfonation: OH H 2 SO 4 Conc.
OH SO 3 H
15-20 o C
o
-Phenolsulfonic acid
Conc.
H 2 SO 4 , 100 o C OH
100 o C
SO 3 H
p
-Phenolsulfonic acid
3) Nitration: OH dilute
HNO 3 20 o C
OH OH NO 2
+
OH
o
-Nitrophenol
p
NO 2
-Nitrophenol
40% yield 13% yield
OH Conc.
HNO 3
20 o C O 2 N NO 2 NO 2
Picric acid
4) Friedel-Crafts alkylation Alkyl phenols can be prepared by alkylation of Phenols, but the yields are often poor.
Friedel-Crafts
OH + H 3 C CH 3 C CH 3 Cl
tert
-Butyl chloride HF HO CH 3 C CH 3 CH 3
p-tert
-Butylphenol
Phenolic ketones acylation of Phenols can be made by direct Friedel-Crafts , they are more often prepared in two steps by means of the Fries rearrangement .
OH 25 o C OH (CH 3 CO) 2 O CH 3
m
-Cresol O O C CH 3 CH 3
m
-Cresyl acetate AlCl 3 CH 3 O C CH 3 2-Methyl-4-hydroxyacetophenone 160 o C H 3 C O C OH CH 3 4-Methyl-2-hydroxyacetophenone
5) Nitrosation: Nitrous acid converts Phenols into nitrosophenols
OH OH NaNO 2 , H 2 SO 4 7 - 8 o C NO
p-
Nitrosophenol
80% yield
Dr. Talat R. Al-Ramadhany
6) Synthesis of Phenolic acids (Kolbe reaction) : Treatment of the salts of a Phenol with carbon dioxide brings about substitution of the carboxyl group, -COOH, for hydrogen of the ring. This reaction is known as the Kolbe reaction ; its most important application is in the conversion of Phenol into o-Hydroxybenzoic acid , known as
salicylic acid
.
ONa O + C O Dr. Talat R. Al-Ramadhany OH COONa 125 o C 4-7 atm.
Sodium salicylate
(Chief product)
H + OH COO
Salicylic acid
H
7) Synthesis of Phenolic aldehydes (Reimer-Tiemann reaction): Treatment of hydroxide Phenol introduces an with chloroform aldehyde group , and aqueous –CHO , into the aromatic ring, generally
ortho
to the –OH. This reaction is known as the Reimer-Tiemann reaction
.
OH CHCl 3 , aq.NaOH
70 o C O CHCl 2 O CHO HCl O H CHO Salicyladehyde
(Chief product)
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