Dr Seemal Jelani
Chem-240
Fall, 2013
1
Nomenclature
Properties
Preparation
Reaction
Dr Seemal Jelani
Chem-240
Spring, 2011
2
 Considered
derivatives of water
OH
SH
OH
alcohol
thiol
phenol
O
thiophenol
S
ether
Dr Seemal Jelani
SH
sulfide
Chem-240
Spring, 2011
3
Pure
phenol is a white
crystalline solid, smelling of
disinfectant
It has to be handled with great
care because it causes
immediate white blistering to
the skin
The crystals are often rather
wet and discolored.
Dr Seemal Jelani
Chem-240
Spring, 2011
4
The
simple monohydric phenols are
either liquid with low melting
crystalline
Some chromophoric group is present
in their molecules but phenols are
generally colorless
Dr Seemal Jelani
Chem-240
Spring, 2011
5
What
is the reason of coloration in
phenols
The colour of many phenols may be
due to the presence of chromophoric
group and also due to the presence
of their oxidation products as
impurities because they are easily
oxidized on exposure to air
Dr Seemal Jelani
Chem-240
Spring, 2011
6
It
is useful to compare phenol's
melting and boiling points with
those of methylbenzene (toluene)
 Both molecules contain the same
number of electrons and are a very
similar shape
That means that the intermolecular
attractions due to Vander Waals
dispersion forces are going to be
very similar.
Dr Seemal Jelani
Chem-240
Spring, 2011
7
The
symmetrical phenols
generally have higher MP than
unsymmetrical isomers
Examples
Among the chlorophenols, the
para isomer has the highest MP,
whereas the ortho isomer is
liquid at ordinary temperature
Dr Seemal Jelani
Chem-240
Spring, 2011
8
Melting point (°C)
C)Boiling point (°C)
40-43 °C
118 °C
-95 °C
111 °C
C6H5OH
Dr Seemal Jelani
C6H5CH3
Chem-240
Spring, 2011
9
The
reason for the higher values for
phenol is in partly due to permanent
dipole-dipole attractions due to the
electronegativity of the oxygen - but
is mainly due to hydrogen bonding.
Hydrogen bonds can form between a
lone pair on an oxygen on one
molecule and the hydrogen on the OH group of one of its neighbors.
Dr Seemal Jelani
Chem-240
Spring, 2011
10
The
O-H bond of phenols is more
polar than that of alcohols
Phenols therefore form stronger
HB than alcohols, resulting in
higher BP and greater solubility
in water
Compare the boiling point and
solubility of phenol with that of
Cyclohexanol ( a comparable
alcohol)
Dr Seemal Jelani
Chem-240
Spring, 2011
11
Cyclohexanol
boils at 161 degree C
and has solubility of 3.6g/100 mL of
water
According to the general rule,
symmetrical molecules should have
lower boiling points than the
unsymmetrical molecules. This is not
the case with phenols, particularly
those having an electronegative
substituent ortho to the -OH group
Dr Seemal Jelani
Chem-240
Spring, 2011
12
Because
it has been seen that in
many such cases the ortho isomers,
despite their lack of symmetry, have
BP much lower than the meta and
para isomers
Compare the BP of o and p
nitrophenols
The lower BP ( higher volatility) of onitrophenol can be attributed to
intramolecular HB ( chelation)
Dr Seemal Jelani
Chem-240
Spring, 2011
13
Chelation
of o-nitrophenol helps
its separation from its m- and p
isomers by steam distillation
Non- chelated m- and pnitrophenols are not steamvolatile due to the
intermolecular HB which
inhibits their steam-volatility by
lowering their vapour pressure
Dr Seemal Jelani
Chem-240
Spring, 2011
14
Phenol
is moderately soluble in
water - about 8 g of phenol will
dissolve in 100 g of water.
If you try to dissolve more than this,
you get two layers of liquid. The top
layer is a solution of phenol in
water, and the bottom one a
solution of water in phenol
Dr Seemal Jelani
Chem-240
Spring, 2011
15
Solubility
of phenols increases
with an increase in the number
of –OH which cause increased
hydrogen bonding
However this effect is
counterbalance by the symmetry
of the molecules which helps
them to stabilize by themselves
Dr Seemal Jelani
Chem-240
Spring, 2011
16
Example
Resorcinol has solubility of
123g/100 mL of water at 250 C,
hydroquinone is soluble only to
the extent of 8g/100 mL of
water 250 C
Dr Seemal Jelani
Chem-240
Spring, 2011
17
OH
OH
OH
H3C
CH3
CH3
p-cresol
m-cresol
o-cresol
OH
OH
OH
HO
OH
OH
catechol
hydroquinone
resorcinol
Dr Seemal Jelani
Chem-240
Spring, 2011
18
 Water
is soluble in phenol to the extent of
29 g /100 mL of phenol
 Phenols and water are miscible in all
proportions above 65 0 C
 A small amount of water lowers the MP of
phenols, thus phenol which has the MP of
420 C often found as semi liquid
because of the presence of small
amount of water; it is completely
liquified by the addition of about 5%
of water
Dr Seemal Jelani
Chem-240
Spring, 2011
19
The
liquid form of phenol,
containing 5% of water is known
as Carbolic acid and it is used as
disinfectant and germicide
Dr Seemal Jelani
Chem-240
Spring, 2011
20
The
solubility behaviour of
phenol and water is complicated
Phenol is somewhat soluble in
water because of its ability to
form hydrogen bonds with the
water.
Dr Seemal Jelani
Chem-240
Spring, 2011
21
Common
natural source – coal tar
Found in many plants
OH
OH
CO2CH3
oil of wintergreen
OH
coal tar
OH
OH
CO2H
R
willow bark
bioactive ingredient
poison ivy and oak
Dr Seemal Jelani
Chem-240
Spring, 2011
22
OH
OH
OMe
OMe
isoeugenol (oil of nutmeg)
eugenol (oil of clove)
OH
OMe
OH
O
O
C5H11
tetrahydrocannabinol
vanillin
Dr Seemal Jelani
Chem-240
Spring, 2011
23
Hydroxybenzene is used as a parent name in
most of its derivatives
 Name substituents on aromatic ring by their
position from OH

OH
OH
H3C
o-chlorophenol
p-methylphenol
Dr Seemal Jelani
OH
Cl
Chem-240
Spring, 2011
O2N
NO2
2,4-dinitrophenol
24
 While
naming the polyfunctional aromatic
compounds the hydroxy function is
generally placed low in the order of
priority
 Only amino and ether functions are
placed lower than the hydroxy function
 Examples:
p-hydroxy benzoic acid
p-Amino phenol
Dr Seemal Jelani
Chem-240
Spring, 2011
25
 Many
common names in use
OH
OH
OH
H3C
CH3
CH3
p-cresol
m-cresol
o-cresol
OH
OH
OH
HO
OH
OH
catechol
hydroquinone
resorcinol
Dr Seemal Jelani
Chem-240
Spring, 2011
26
Ar-OH is more acidic than ROH
 Soluble in dilute NaOH
 Anion is resonance stabilized
 EWG make phenols more acidic than phenol
 EDG make phenols less acidic than phenol

O
O
OH
-
NaOH
Dr Seemal Jelani
Chem-240
Spring, 2011
27
Although
phenols and alcohols
have the same FG –OH, phenols
are much more acidic than
alcohols but weaker acids than
carboxylic acids
The pKa values of alcohols,
phenols and carboxylic acids are
in the vicinity of 18,10 and 5
Dr Seemal Jelani
Chem-240
Spring, 2011
28
 Electron-
 Electron-
releasing
substituent
 Decreases acidity
withdrawing
substituent
 Increases acidity
Methyl group
Halogens
Dr Seemal Jelani
Chem-240
Spring, 2011
29
Strongly
EWG like NO2 have acid-
strengthening effect
It is more acid-strengthening
when it is ortho or para to –OH
group
Additional nitro groups further
increase the acid strength
Dr Seemal Jelani
Chem-240
Spring, 2011
30
Thus
the acidity of
dinitrophenols is comparable to
that of carboxylic acids
The cumulative effect of three
nitro groups makes 2,4,6trinitrophenol nearly as strongly
acidic as a mineral acid and it is
known as picric acid
Dr Seemal Jelani
Chem-240
Spring, 2011
31
In
general phenols are very acidic.
They are caustic towards flesh and
very poisonous
Phenol itself is used as disinfectant
either in solution or mixed with
Ca(OH)2, for toilets, stables, floors
and drains
It is also used as a caustic for
animals bites
Dr Seemal Jelani
Chem-240
Spring, 2011
32
Reactions of
phenols
Dr Seemal Jelani
Chem-240
Spring, 2011
33
They
give two types of reactions
a) The reactions due to the –OH
b) The reactions due to the aromatic
ring
OH-group reactions involve the
cleavage of the O-H bond, as e.g.
In the formation of salts, ethers
and esters, so they resemble
alcohols in this respect
Dr Seemal Jelani
Chem-240
Spring, 2011
34
Most
of the reactions of phenols fall
in the second category in which
phenols distinctly differ from
alcohols
The striking feature
High reactivity of its ring towards
ESR, due to the presence of the
strongly activating -OH
Dr Seemal Jelani
Chem-240
Spring, 2011
35
Thus
phenols undergoes ESR like
nitration, halogenation, Friedel
–Crafts reaction and sulfonation
characteristics of aromatic
compounds
A number of important ESR of
phenols involve phenoxide ions
which are formed under basic
conditions
Dr Seemal Jelani
Chem-240
Spring, 2011
36
O
O
OH
-
NaOH
•This
phenoxide is water soluble
•The –O- of the phenoxide ions is
strongly electron releasing and
thus more strongly activating
than the –OH group
Dr Seemal Jelani
Chem-240
Spring, 2011
37
Phenoxide
ion can therefore
react with even weaker
electrophiles like carbon dioxide
With phenols special care must
be taken to prevent
polysubstitution and oxidation
Dr Seemal Jelani
Chem-240
Spring, 2011
38
Phenols
are stronger acid than
alcohols therefore they can form
salts even with weaker bases
The most phenols can be converted
into their salts by aq. NaOH, a much
weaker base than the sodium metal
which is required to form salts with
alcohols, as alcohols do not react
with NaOH
Dr Seemal Jelani
Chem-240
Spring, 2011
39
Most
phenols can dissolve in aq.
NaOH by forming sodium phenoxides
whereas
Most alcohols having more than five
carbon atoms do not
This provides a convenient method
of distinguishing as well as
separating phenols from alcohols
Dr Seemal Jelani
Chem-240
Spring, 2011
40
Alcohols
with five or fewer carbon
atoms dissolve in aq. NaOH not by
forming sodium salts but because
they are soluble in water
2,4,6-ter-butylphenol does not form
salt even with sodium metal, why?
Due to steric hindrance to approach
of a reagent to the –OH group and to
solvation of the phenoxide ion
Dr Seemal Jelani
Chem-240
Spring, 2011
41
On
treatment with alkyl halides
in the presence of aq. NaOH,
alkyl aryl ethers are formed
With aq. NaOH, a phenol is
converted to a phenoxide ions
which act as a Nu: and displaces
halide ion from the alkyl halide
in an SN2 reaction
Dr Seemal Jelani
Chem-240
Spring, 2011
42
Dialkyl
sulphates ca also be used
as alkylating agents under these
conditions
Dr Seemal Jelani
Chem-240
Spring, 2011
43
Phenols
can be used to form
esters
The reaction is carried out with
an acid chloride or anhydride in
the presence of a base or an
acid
Dr Seemal Jelani
Chem-240
Spring, 2011
44
Acetyl
salicylic acid
commonly known as Aspirin is
prepared by Acetylation of
salicylic acid
Dr Seemal Jelani
Chem-240
Spring, 2011
45
On
treatment with conc.
Nitric acid, phenol is
converted into 2,4,6trinitrophenol (picric acid)
Mononitrophenols are
produced by using dilute
nitric acid
Dr Seemal Jelani
Chem-240
Spring, 2011
46
Reacts
readily with an excess of
chlorine or bromine in aqueous
solution to give 2,4,6-trihalophenols
Phenols have high reactivity
therefore no Lewis acid is required
Monohalogenation of phenol can be
achieved by carrying out the
reactions in a solvent of low polarity
such as chloroform, carbon
tetrachloride or carbon disulfide at
Dr Seemal Jelani
Chem-240
Spring, 2011
47
low temperature
These conditions reduce the
electrophilic reactivity of halogens
Monochlorination gives a mixture of
o and p-chlorophenols
They differ in BP by 410 C and easily
can be separated by fractional
distillation
Dr Seemal Jelani
Chem-240
Spring, 2011
48
Monobromination
yields pbromophenol exclusively
o-Bromophenol can be also prepared
Dr Seemal Jelani
Chem-240
Spring, 2011
49
Friedel
Crafts reactions with phenols
in the presence of aluminium
chloride is complicated by an
reaction of the phenol with the
Lewis acid
Yield is poor
However alkyl and acyl derivatives
of phenols can be prepared by other
methods
Dr Seemal Jelani
Chem-240
Spring, 2011
50
Alkylation
of phenols can be
achieved by using an olefin as an
alkylating agent in the presence of
HF
Dr Seemal Jelani
Chem-240
Spring, 2011
51
Can
be obtained by heating alkyl
phenyl ethers
Catalyst is aluminium chloride
Reaction is intermolecular process
involving substitution of the alkyl
group
Dr Seemal Jelani
Chem-240
Spring, 2011
52
On
treatment with conc. H2SO4
250 C
Product is ortho
However with increased
temperature
i.e.100 0 C para product is mainly
formed
Dr Seemal Jelani
Chem-240
Spring, 2011
53
Introduction
of Formyl group –
CHO into the aromatic ring of
phenols
Generally o-positions
Dr Seemal Jelani
Chem-240
Spring, 2011
54
Reaction
with Br-water gives 2,4,6tri bromophenol
Many phenols when treated with
FeCl3 in dilute aqueous or alcoholic
solution, give characteristics colour
ranging from violet through blue and
green to red
Phenols itself gives violet coloration
and cresols give a blue colour
Dr Seemal Jelani
Chem-240
Spring, 2011
55
The
color develops due to the
formation of ferric phenoxides (
coordination complexes) which
involve an extended delocalization
of pi electrons of the aromatic rings
through the iron atoms and thus
absorb visible light
Phenols show distinct colors with
ferric chloride why ?
Dr Seemal Jelani
Chem-240
Spring, 2011
56
 Industrial
process from readily available cumene
 Forms cumene hydroperoxide with oxygen at
high temperature
 Converted into phenol and acetone by acid
Dr Seemal Jelani
Chem-240
Spring, 2011
57
Cl
OH
NaOH/heat
Dr Seemal Jelani
Chem-240
Spring, 2011
58
 From
aromatic sulfonic acids by melting with
NaOH at high temperature
 Limited to the preparation of alkyl-substituted
phenols
Dr Seemal Jelani
Chem-240
Spring, 2011
59