phenols stucture, properties, acidity, synthsis,uses

1. Phenols

2.  Introduction
 Shape
 Nomenclature
 Sources
 Preparation of phenols
 Physical properties
 Chemical properties
 Structure and uses
 Qualitative tests
Contents

3. Compounds in which —OH group is directly attached with
benzene ring are called as Phenols.

4. Phenols
 Phenol is also called as carbolic acid.
 Phenol is discovered by Runge
 Hofmann, another scientist, prepared it first from ‘coal tar’.

5. Shape

6. sp2
- sp2
(C-C σ bond)
sp3
- s
(O-H σ bond)
sp2
– sp3
(C-O σ bond)
sp2
- s
(C-H σ bond)
Formation of sigma (σ ) bonds in Phenol
All ring carbon atoms also have a p orbital and these are perpendicular to the plane
of the σ bonds of the ring. The lateral overlap of these p orbitals produces a
delocalized π molecular orbital.
O
H H
H
H H
H

7. O
H
Adjacent p orbitals overlap to form the delocalized π molecular orbital.one
of the lone pair electrons on the oxygen atom resides in sp3
orbital and
interacts with the delocalized π molecular orbital to form an extended π
molecular orbital containing 8 electrons.

8. Nomenclature

9. 9
Phenols
Examples are:

10. Sources

11. Sources
Phenols occur widely in nature and have many industrial, pharmaceutical, and biological
applications. phenol is a general disinfectant, commonly called carbolic acid.
Poison ivy, which
produces the phenol
urushiol.
Cloves contain the
phenol eugenol.

12. Sources
Peppers, a
source of
capsaicin,
which is a
phenol.
Polyphenols
are found in
olive oil.
Salicylic acid is a
phenol that is
used to treat
acne.

13. Anthocyanins and
flavonoids provide
the bright colors in
certain fruits and
vegetables.

14. Physical properties
● Have higher boiling points than hydrocarbons of the same molecular weight
● Modest solubility in water
● Form strong intermolecular hydrogen bonds

15. Physical properties
Figure : Hydrogen bonding in phenols. The weak
attraction between a positively polarized _
OH hydrogen
and a negatively polarized oxygen holds molecules
 Phenols and alcohols have unusually high boiling points because, like water, they
form hydrogen bonds.
 These forces must be overcome for a molecule to break free from the liquid and
enter the vapor, so the boiling temperature is raised.

17. Preparation of phenols

18. a) Dow process
b) From diazonium salt
c) From benzene sulphonate
d) From salicylic acid
e) from oxidation of cumene
f) From benzene
Preparation of phenols

22. C
H3C
CH3
O O H
H
C
H3C
CH3
O O H
H
C
H3C
CH3
O
H2O
O C
CH3
CH3
H2O
O C
CH3
O
CH3
H
H
O C
CH3
OH
CH3
H
O C
CH3
OH
CH3
H
OH
H3C C CH3
O
Rearrangement
-H2O
-H
World wide production

24. Reaction of phenols

25. Reactions of Phenols
Reactions of OH group Reactions of Benzene ring
 Nitration
 Halogenation
 Sulfonation
 Kolbe’s Reaction
 Claisen Rearrangement
 Fries Rearrangement
 Reimer - Tiemann Reaction
 Reaction with Neutral FeCl3
 Oxidation
 Reaction with Benzene diazonium chloride
 Reaction with Formaldehyde
 Reaction with Phthalic aanhydride
 Formation of salt
 FormationofEther
 FormationofEster
OH

26. Reactions of Phenols
Formation of salt
Phenols are weak acids and react with strong bases, such as NaOH, to form water-
soluble salts.
Most phenols do not react with weaker bases, such as sodium bicarbonate, and do
not dissolve in aqueous sodium bicarbonate.

27. Formation of Ether (Williamson’s Ether Synthesis)
Phenols reacts with alkyl halides in alkali solution to form phenyl
ethers. the alkali first forms phenoxide ion which then reacts with
alky halide
OH
NaOH
ONa
H2O
ONa
(CH3)2SO4
O
NaCl
CH3
Anisole
(Methyl phenyl ether)
ONa
Cl
O
NaCl

28. Formation of Ester
O
NaCl
O
Phenyl acetate
ONa
Cl
O
OH
Na2CO3
ONa
H2O
Phenols reacts with acyl halides in alkali solution to form phenyl esters. the
alkali first forms phenoxide ion which then reacts with alky halide

29. Formation of Ester
OH
R O
O
R
O
phenol Anhydride
O R
O
Ester
OH
R
O
Phenols reacts with anhydrides in alkali solution to form phenyl esters. the
alkali first forms phenoxide ion which then reacts with alky halide

30. Resonance in phenol and phenoxide ion:
 It is evident from the above structures that — OH group of phenol is o- and
p-directing, as these are electron richer places; so electrophiles attack at
these positions.
 Phenoxide ion is resonance stabilized. That is why phenol shows acidic
Reactions of Benzene ring of Phenols

31. Electrophilic aromatic substitution

32. The hydroxyl group is a powerful activating group—and an ortho–para director in
electrophilic aromatic substitutions.
Monobromination of phenol can be achieved by carrying out the reaction in CS2 at a
low temperature, conditions that reduce the electrophilic reactivity of bromine. The
major product is the para isomer
OH
Br
Br
Br
Halogenation

33. Nitration
Phenol reacts with dilute nitric acid to yield a mixture of o- and p-
nitrophenol.
Although the yield is relatively low (because of oxidation of the ring),
the ortho and para isomers can be separated by steam distillation.

34. o- nitrophenol and p - nitrophenol can be separated by steam
distillation
More
Volatile
Less
Volatile
Due to
intramolecular
H -
bonding
Due to
intermolecular
H - bonding
Low B.P. High B.P.
Nitration

35. With concentrated HNO3 , phenol is converted to 2,4,6 – trinitrophenol ( Picric
acid ). The yield of reaction product is poor.
Nitration
Nowadays picric acid is prepared by treating phenol first with concentrated
sulphuric acid which converts it to phenol-2,4-disulphonic acid, and then with
concentrated nitric acid to get 2,4,6-trinitrophenol.
OH OH
NO2
O2N
NO2
Conc.HNO3
Oxidative cleavage of the ring
phenol picric acid

36. Sulfonation
Phenol reacts with concentrated sulfuric acid to yield mainly the ortho-sulfonated product
if the reaction is carried out at 25 o
C and mainly the para- sulfonated product at 100 oC.

37. Kolbe’s Reaction
Phenoxide ion is even more susceptible to SEAr than phenol. The Kolbe–Schmitt reaction
or Kolbe process is a carboxylation chemical reaction that proceeds by heating sodium
phenoxide with carbon dioxide under pressure, then treating the product with sulfuric
acid.

38. Kolbe’s Reaction
Mechanism
OH
OH- O-
C O
O
+
-
O
H
C O
O-
OH
CO2
-
H+
OH
CO2H

39. Claisen Rearrangement
Heating allyl phenyl ether to 2000c effects an intramolecular reaction to
generate o - allylphenol.
Mechanism:

40. Claisen Rearrangement
When the ortho position is occupied, attack take place on para position.
H3C
O
CH3
CH2
H3C
O
CH3
CH2
H3C
O
CH3
H3C
OH
CH3

41. Fries Rearrangement
O R
O
Phenolic esters of aliphatic and aromatic carboxylic acids, when treated with a Lewis acid
as catalyst, do undergo a rearrangement reaction to yield ortho- and para-acylphenols
respectively.

42. Reimer-Tiemann reaction
On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is
introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann
reaction.The intermediate substituted benzal chloride is hydrolysed in the presence of
alkali to produce salicylaldehyde.
H

43. H

44. Reaction with Benzene diazonium chloride
N
2
Cl
OH
1.
NaOH
2.
H
N
N
OH
Benzene
diazonium
chloride
Phenol p-Hydroxyazobenzene
Phenols couples with Benzene diazonium chloride in an alkaline solution to
form p-Hydroxyazobenzene

45. Reaction with Phthalic anhydride
HO
H
OH
H Conc. H2SO4
C
C
O
O
O C
C
O
O
HO OH
Phenols reacts with phthalic anhydride in the presence of sulfuric acid to
fom phenolphthalein.
Phthalic anhydride phenolphthalein
Phenol Phenol

46. Reaction with Formaldehyde
Phenol o and p-Hydroxyazobenzyl alcohol
Phenols is treated with an alkaline solution of formaldehyde, a mixture of o-
and p-Hydroxybenzyl alcohol is formed.
OH
H
C
O
H
Aq. NaOH
OH
OH
H2
C
H2C
OH
OH

47. Reaction with Formaldehyde
If the reaction is carried at high temperature and in
excess of formaldehyde, hard thermosetting plastic
Bakelite is formed.

48. Oxidation
OH
CrO3 or O2
O
O
p-Benzoquinone
Phenols undergoes oxidation with air or chromic acid to form p-
Benzoquinone

50. Structure and uses

53. BHT (Butylated
Hydroxytoluene)
Antioxidant
Disinfect
ant

56. Qualitative tests for Phenols

59. DIFFERENCE BETWEEN ALCOHOLS AND PHENOLS
ALCOHOL
 OH group is attached to an alkyl group
 Hydroxyl derivatives of alkane
 The compounds in which one hydrogen of
water is replaced by an alkyl group
 General formula ROH
 Lower alcohols are colorless liquids
 They characteristics sweet smell and
burning taste
 pKa
≈ 16 - 20
 Readily soluble in water but solubility
PHENOL
 OH group is attached to an aryl group
 Hydroxyl derivatives of benzene
 The compounds in which one hydrogen of
water is replaced by an aryl group
 General formula C6H5OH
 Colorless crystalline deliquescent solids (M.P
41oC)
 They have a characteristics phenolic odor
 pKa ≈ 10
 Sparingly soluble in water forming a pink
o
solution but completely soluble above 68.5 C
 Phenolate ions have resonance structures
but alcohols do not have resonance
structures
decreases in higher alcohols
 Alcohols react in two ways:
 Reaction in C-O bond
breaks
 React
P
i
re
o
p
n
ared
in
By:
O
Sid
-
r
H
a

60. 60
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