Download Phenol_structure, properties and reactions File

methylbenzene
ethylbenzene
NO2
HO
O
benzoic acid
NO2
Phenol
L.O. To explore the effect of an OH group on the reactivity of
the benzene ring.
To be able to describe and explain the key reactions of
phenol.
OH
Phenol
Structure: Phenol is an aromatic alcohol with formula C6H5OH
- OH group is attached directly to the benzene ring
- Almost colourless crystalline solid
Properties: The OH group changes the reactivity of the benzene ring and the
benzene ring changes the reactivity of the OH group.
•
Hydrogen bonding from OH group = stronger intermolecular forces
resulting in phenol being solid at room temperature.
•
Acting as an ACID: OH group also hydrogen bonds with water.
Therefore phenol dissolves in water and alkalis (forming soluble ionic
salts).
•
Weak acid so does not fully ionise in water and so does not react with
carbonates to produce CO2.
What are the products when phenol reacts with
the following?
Water
NaOH
Na
Phenol – reactions of the OH group
Water -Phenol is a weak acid and dissolves only slightly in water forming a weakly
acidic solution
-Stronger acid than aliphatic alcohols
-Ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq)
NaOH
C6H5O¯(aq)
+
H+(aq)
-Phenol reacts with sodium hydroxide to form a salt - sodium phenoxide
-Ionic and water soluble
C6H5OH(aq) + NaOH(aq)
C6H5O¯ Na+(aq) + H2O(l)
Sodium -Phenol reacts with sodium to form an ionic salt - sodium phenoxide
-Hydrogen is also produced (similar to sodium reacting with aliphatic alcohols
such as ethanol)
2C6H5OH(s)
+
2Na(s)
2C6H5O¯ Na+(s)
+
H2(g)
Phenol
Preparation: An OH group cannot be directly added to a benzene ring by
electrophilic substitution.
- Instead, phenol is synthesised in a multi-stage process
1
Step 1 - Nitration
reagents
conditions
equation
mechanism
of benzene
conc. nitric acid and conc. sulphuric acid (catalyst)
reflux at 55°C
C6H6 + HNO3
C6H5NO2 +
electrophilic substitution
H2O
Phenol
2
Step 2 - Reduction of nitrobenzene
reagents
tin and conc. hydrochloric acid
conditions
reflux
equation
C6H5NO2 + 6 [H]
mechanism
reduction
C6H5NH2
+ 2H2O
3
Step 3 - Diazotisation of phenylamine
reagents
nitrous acid and hydrochloric acid (use sodium nitrite)
conditions
keep below 10°C
equation
C6H5NH2 + HNO2 + HCl
C6H5N2+ Cl¯ + 2H2O
reaction type
diazotisation
Phenol
4
Step 4 - Substitution of diazo group by OH
reagents
water
conditions
warm above 10°C
equation
C6H5N2+ Cl¯ + H2O
reaction type
hydrolysis / substitution
C6H5OH
Naming
derivatives of
phenol
+
N2 + HCl
What does the OH group do to the reactivity of
the benzene group?
The OH groups ACTIVATES the benzene ring.
Group
ELECTRON DONATING
Example(s)
Electron density of ring
Ease of substitution
Position of substitution
OH, CH3
Increases
Easier
2,4,and 6
ONE LONE PAIR of electrons on the oxygen of OH interacts with the delocalised
electrons of the benzene ring, aiding E+ attack. This results in MILDER CONDITIONS for
phenol reactions compared to the corresponding benzene reactions.
Phenol - reactions of the aromatic ring
Electrophilic substitution
Bromine
- OH group is electron releasing
- Increases the electron density of the delocalised system, so making
substitution much easier compared to benzene
- Electron density is greatest at the 2,4 and 6 positions, so substitution
takes place at the 2,4 and 6 positions
- Phenol reacts readily with bromine water WITHOUT A CATALYST
- In fact so easy, multiple substitution takes place
Nitric acid - Dilute HNO3 reacts rapidly with phenol at room temperature.
- Resulting product is a BROWN MIXTURE.
- Main products are 2 and 4-nitrophenol.
Compare this to the conditions required for nitration of a benzene ring when the ring is
NOT activated.
Uses of phenol
•
Production of antiseptics and disinfectants
•
Antiseptics – chemicals that kill microorganisms, but can be used
safely on the skin.
•
Disinfectants – chemicals that kill microorganisms. Very powerful
reagent and as such is now not used on skin or living tissue as too
dangerous.
•
Phenol not used as an antiseptic as it burns the skin.
•
Substituted phenols can however be used as an antiseptic – TCP,
Dettol.
•
Thermosetting plastics (resins)
•
Thermoplastic polymers – soften on heating and can be moulded into
different shapes. These shapes remain on cooling (e.g. polyethene,
pvc)
•
Thermosetting polymers – set hard on formation and CAN NOT be
softened or moulded (BAKELITE)
Polyethene and pvc
Thermoplastic polymers
Bakelite
Thermosetting polymer
N.B: Phenol is only partially soluble and forms 2 layers
with water at r.t.
OH
OH
Br
Br
O-
NaOH (aq)
3Br2 (aq)
Colourless solution
+ H20
+ 3HBr (aq)
Br
CH3COCl
White ppt formed
(NO catalyst needed)
O
O
Ester formation
=
phenylethanoate
+ HCl