Jamshedpur Cooperative College Jamshedpur B Sc Chem Hons Semester III Outline Nomenclature Structure Synthesis Physical and Chemical Properties Nomenclature Phenols are defined as compounds having hydroxyl group attached directly to a benzene nucleus Its general formula is ID: 935928
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Slide1
Phenols
Dr. Neeta Sinha
Jamshedpur Cooperative College Jamshedpur
B. Sc. (
Chem
Hons
) Semester III
Slide2Outline
NomenclatureStructureSynthesisPhysical and Chemical Properties
Slide3Nomenclature
Phenols are defined as compounds having hydroxyl group attached directly to a benzene nucleus. Its general formula is ArOH, where Ar is aryl group and - OH is functional group.
OH
Phenol
Or,
Benzenol
Or,
Hydroxybenzene
Slide4Nomenclature continued …..
OH
OH
OH
OH
CH3
2-Methylphenol
OH
1,2-
Benzenediol
Cl
2-Chlorophenol
NO2
4-Nitrophenol
Slide5Structure
OH
In phenol, C-O bond is formed by the overlapping of sp2 orbital of carbon of the benzene nucleus and sp3 orbital of oxygen whereas O-H bond is formed by the overlapping of sp3 orbital of oxygen and 1s orbital of hydrogen . The C-O-H bond angle in phenol is 109 degree. The c-o bond length is slightly less than single covalent bond because of the resonating structure in which C-O bond acquires some double bond character.
The oxygen atom is more electronegative than carbon and hydrogen and hence
aquires
slight negative charge where as carbon and hydrogen
aquires
slight positive charge. As a result phenol has a dipole moment of 1.54 D.
C6H5 – O – H
Angle C-O-H = 109 degree
Slide61. From Chlorobenzene
( Dow’s process ) - When chlorobenzene is treated with 10% NaOH
solution at 3550 C
and
300
atm
pressure
using
Cu as catalyst to produce phenol after acidification
.
10%NaOH/ 3550/Cu
HCl
C6H5Cl
C6H5ONa C6H5OH
Chlorobenzene
Sodium
phenoxide
Phenol
2. From
sulphonic
acid – Phenols can be prepared by heating benzene
sulphonic
acid or their salts with
NaOH at
3000 C followed by acidification
.
NaOH fuse/300 deg.C
Dil. HCl
C6H5SO3Na C6H5ONa C6H5OH
Phenol
3. From the hydrolysis of diazonium salt - In this method
diazinium salt solution is added to boiling dilute sulphuric
acid, phenol is obtained.
H2SO4
/ Heat
C6H5N2Cl C6H5OH
4
Synthesis
Phenol
+ -
Slide74. From Grignard reagent – Phenols are prepared by bubbling oxygen through etherial solution of Grignard reagent followed by acidification.
O2 H+ /H2O C6H5MgBr C6H5OMgBr C6H5OH
Phenol5. From aniline –
In this process aniline is first
diazotised
and then
hydrolised
to get phenol.
Diazotised
Dil. H2SO4
C6H5NH2 C6H5N2Cl C6H5OH
Synthesis continued
…….
+ -
Slide8Properties
Boiling points – Like alcohols, boiling point of phenol is also higher than the corresponding aromatic hydrocarbon. This is because like alcohols , phenols also form intermolecular hydrogen bond.
2. Solubility – Phenols are soluble in water, again here because of the formation of intermolecular hydrogen bond with water molecule
.
H – O ………..H –O ……….H-O
…….
I
I
I
C6H5 H C6H5
H – O ………..H –O ……….H-O ………
I
I
I
C6H5
C6H5
C6H5
Slide9Properties continued …..
3. Acidic nature - Phenols are weakly acidic because it
ionises
to give
phenoxide
ion and hydrogen ion. Because of the formation of H+ ion , this is acidic and also the
phenoxide
ion is resonance
stabilised
.
C6H5OH
C6H5O
-
+
H
+
Phenoxide
ion
Alcohols are weaker acid than phenol. Alcohol
ionises as R – O – H RO- + H+
Alkoxide ionDue to + I effect of alkyl gr. , the electron density increases around oxygen and hence tendency of ionisation of alcohol decreases to release H+ ion . Secondly the
alkoxide ion formed is not stabilised by resonance like phenoxide ion.
The acidic strength of phenol is also affected by the presence of substituent. The electron withdrawing groups like nitro, cyano
, chloro increases the acidic strength because of the further dispersal of negative charge in phenoxide ion and further stabilises it whereas electron releasing groups like alkyl,
alkoxy, decreases the acidity because these grs. Intensify the negative charge and destabilises
the phenoxide ion.
Slide104. Acylation ( Fries rearrangement) - Phenol when reacts with acid chloride or acid anhydride corresponding esters are formed. C6H5OH + CH3COCl C6H5OCOCH3 +
HCl C6H5OH + ( CH3CO)2O C6H5OCOCH3 + CH3COOH5. Electrophilic
subtitution
reaction – Phenol is
ortho
,
para
directing because –OH group increases the electron density at these position.
i
) Nitration - Nitration of phenol with dilute nitric acid gives the mixture of ortho &
para nitrophenol.
C6H5OH
Halogenation
-
Halogenation
of phenol gives 2,4,6-
trisubstituted
product.
Br2/H2O C6H5OH
Properties
continued …..
OH
OH
OH
+
NO2
NO2
Br
Br
Br
If solvent is non-polar then 2-bromo & 4-bromophenol is obtained.
Slide11Properties continued ……….
iii) Sulphonation - At low temperature phenol gives ortho product whereas at higher temperature it gives para product with H2SO4. C6H5OH
C6H5OH
OH
OH
H2SO4
H2SO4
L
ow temp
High temp
SO3H
SO3H
Slide12Properties continued…….
iv) Friedel craft alkylation – Alkylation of phenol gives the mixture of o- & p- products with poor yield. CH3Cl /anhy AlCl3 C6H5OH
v) Kolbe’s reaction – When sodium salts of phenol is treated with carbon dioxide at 125 degree c under pressure followed by acidification gives salicylic acid. C6H5OHvi) Reimer – Tiemann
reaction – When phenol is treated with chloroform and
NaOH
, mixture of
ortho
and
para
hydroxy
benzaldehyde are formed.
OH
OH
OH
OH
OH
+
CH3
CH3
COOH
C6H5OH
CHO
CHO
+
Slide13Properties continued ….…
vii)
Gattermann
synthesis - Phenol on treatment with HCN/
HCl
in presence of
anhy
. AlCl3 produce
parahydroxybenzaldehyde
.
C6H5OH
viii)
Laderer
–
Manasse
reaction - In acidic or alkaline medium , phenol
condences
with aromatic or aliphatic
aldehyde
to produce
ortho
&
para
hydroxybenzyl
alcohol. HCHO / H+ or OH-
C6H5OHHauben –
Hoesch reaction – It involves acylation of highly reactive triphenol in presence of CH3CN,
HCl and anhy. AlCl3.
C6H5(OH)3
OH
CHO
OH
OH
OH
OH
OH
+
CH2OH
CH2OH
COCH3
Slide14x) Williamson’s synthesis - In Williamson’s synthesis ether is prepared by heating sodium or potassium salts of phenol with alkyl halide.
C6H5ONa + CH3I C6H5OCH3 + NaI Methylphenyl
etherC6H5OK + C2H5Br C6H5OC2H5 +
KBr
Ethylphenyl
ether
Properties
continued ..…..
Slide15Thank You