Transcript PHENOL - REACTIONS OF THE AROMATIC RING

PHENOL
PHENOL
Before you start it would be helpful to…
• know the functional groups found in organic chemistry
• know the arrangement of bonds around atoms
• recall and explain electrophilic substitution of aromatic rings
PHENOL
Structure
phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ring
it is an almost colourless crystalline solid
PHENOL
Structure
phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ring
it is an almost colourless crystalline solid
Preparation
You cannot put an OH group directly onto a benzene ring by
electrophilic substitution, so phenol has to be synthesised in
a multi-stage process
PHENOL - REACTIONS OF THE OH GROUP
Water
phenol is a weak acid
it dissolves very slightly in water to form a weak acidic solution
it is a stronger acid than aliphatic alcohols
the ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq)
C6H5O¯(aq)
+
H+(aq)
PHENOL - REACTIONS OF THE OH GROUP
Water
phenol is a weak acid (does not react with carbonates)
it dissolves very slightly in water to form a weak acidic solution
it is a stronger acid than aliphatic alcohols
the 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
it is ionic and water soluble
C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l)
PHENOL - REACTIONS OF THE OH GROUP
Water
phenol is a weak acid
it dissolves very slightly in water to form a weak acidic solution
it is a stronger acid than aliphatic alcohols
the 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
it is 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
this reaction is similar to that with aliphatic alcohols such as ethanol
2C6H5OH(s)
+
2Na(s)
——>
2C6H5O¯ Na+(s)
+
H2(g)
PHENOL - REACTIONS OF THE AROMATIC RING
We previously looked at methylbenzene and
chlorobenzene.
What did you discover about the effects of these
groups on the benzene ring?
PHENOL - REACTIONS OF THE AROMATIC RING
We previously looked at methylbenzene and
chlorobenzene.
What did you discover about the effects of these
groups on the benzene ring?
PHENOL - REACTIONS OF THE AROMATIC RING
ELECTROPHILIC SUBSTITUTION
Bromine
the OH group is electron releasing due to non-bonding pair donation
it increases the electron density of the delocalised system
it makes substitution much easier compared to benzene
phenol reacts readily with bromine water WITHOUT A CATALYST
it is so easy that multiple substitution takes place
other electrophiles such as NO2+ react in a similar way
PHENOL - REACTIONS OF THE AROMATIC RING
ELECTROPHILIC
SUBSTITUTION
With dilute nitric acid
Phenol reacts with dilute nitric acid
at room temperature to give a
mixture of 2-nitrophenol and 4nitrophenol.
PHENOL - REACTIONS OF THE AROMATIC RING
ELECTROPHILIC
SUBSTITUTION
With conc. nitric acid
With concentrated nitric acid, more
nitro groups substitute around the
ring to give 2,4,6-trinitrophenol
(old name: picric acid).
Phenol-methanal plastics
These are amongst the oldest plastics, Backland
patenting the process in 1910. They are prepared
from phenol and methanal on the addition of acid
or alkali.
Substitution
Condensation
The linear polymers linked via 2,6 positions then
react further with more methanal molecules to form
links through the 4 position also.