CONTENTS

1
PHENOL

• CONTENTS
• Prior knowledge
• Synthesis from benzene
• Reactions of the OH group
• Reactions of the ring
• Benzene diazonium chloride - preparation
• Benzene diazonium chloride - reactions
• Revision check

2
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

3
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
4
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
5
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
1
Step 1 - Nitration of benzene reagents conc.
nitric acid and conc. sulphuric acid
(catalyst) conditions reflux at
55C equation C6H6 HNO3 gt
C6H5NO2 H2O mechanism electrophilic
substitution
6
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
2
Step 2 - Reduction of nitrobenzene reagents tin
and conc. hydrochloric acid conditions reflux
equation C6H5NO2 6 H gt
C6H5NH2 2H2O mechanism reduction
7
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
3
Step 3 - Diazotisation of phenylamine reagents ni
trous acid and hydrochloric acid (use sodium
nitrite) conditions keep below 10C equation C6H5
NH2 HNO2 HCl gt C6H5N2 Cl
2H2O reaction type diazotisation
8
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
4
Step 4 - Substitution of diazo group by
OH reagents water conditions warm above
10C equation C6H5N2 Cl H2O gt
C6H5OH N2 HCl reaction
type hydrolysis / substitution
9
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)
10
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) NaOH phenol reacts
with sodium hydroxide to form a salt - sodium
phenoxide it is ionic and water soluble
C6H5OH(aq) NaOH(aq) gt C6H5O Na(aq)
H2O(l)
11
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) NaOH phenol reacts
with sodium hydroxide to form a salt - sodium
phenoxide it is ionic and water soluble
C6H5OH(aq) NaOH(aq) gt 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) gt 2C6H5O
Na(s) H2(g)
12
PHENOL - REACTIONS OF THE AROMATIC RING
ELECTROPHILIC SUBSTITUTION Bromine the OH
group is electron releasing it increases
the electron density of the delocalised system
it makes substitution much easier compared to
benzene the electron density is greatest at
the 2,4 and 6 positions substitution takes
place at the 2,4 and 6 positions 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
13
BENZENE DIAZONIUM CHLORIDE
Structure has the formula C6H5N2 Cl a
diazonium group is attached to the ring the
aromatic ring helps stabilise the
ion PREPARATION reagents phenylamine, nitrous
acid and hydrochloric acid conditions keep below
10C equation C6H5NH2 HNO2 HCl
gt C6H5N2 Cl 2H2O notes nitrous acid is
unstable and is made in situ from sodium
nitrite C6H5NH2 NaNO2 2HCl gt
C6H5N2 Cl NaCl 2H2O the solution
is kept cold to slow down decomposition of the
diazonium salt C6H5N2 Cl H2O gt
C6H5OH HCl N2
14
AMIDES - CHEMICAL PROPERTIES
15
DIAZONIUM SALTS - REACTIONS
Benzene diazonium chloride undergoes two main
types of reaction SUBSTITUTION OF THE
DIAZONIUM GROUP nitrogen expelled COUPLING
REACTIONS nitrogen atoms are retained
16
DIAZONIUM SALTS - SUBSTITUTION
OH reagents water (hydrolysis) conditions warm
above 10C equation C6H5N2 Cl H2O
gt C6H5OH HCl N2
use the only reasonably simple way to substitute
OH phenol is an antiseptic and is used to
make polymers I reagents potassium iodide
solution conditions warm equation C6H5N2 Cl
KI gt C6H5I KCl N2
17
DIAZONIUM SALTS - COUPLING
reagents phenol and sodium hydroxide conditions a
lkaline solution below 10C equation (4
-hydroxyphenol)azobenzene
YELLOW use making dyes