1. A guide for A level students KNOCKHARDY PUBLISHING
ROUTES
TO PHENOL
A guide for A level students
KNOCKHARDY PUBLISHING

2. KNOCKHARDY PUBLISHING
PHENOL
INTRODUCTION
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3. 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

4. Before you start it would be helpful to…
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

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

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

7. PHENOL 1 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 55°C
equation C6H HNO ——> C6H5NO H2O
mechanism electrophilic substitution

8. PHENOL 2 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 C6H5NO [H] ——> C6H5NH H2O
mechanism reduction

9. PHENOL 3 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 nitrous acid and hydrochloric acid (use sodium nitrite)
conditions keep below 10°C
equation C6H5NH HNO HCl ——> C6H5N2+ Cl¯ + 2H2O
reaction type diazotisation

10. PHENOL 4 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 10°C
equation C6H5N2+ Cl¯ H2O ——> C6H5OH N HCl
reaction type hydrolysis / substitution

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)

12. 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) ——> C6H5O¯ Na+(aq) + H2O(l)

13. 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) ——> 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) Na(s) ——> 2C6H5O¯ Na+(s) H2(g)

14. 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

15. 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 10°C
equation C6H5NH HNO HCl ——> C6H5N2+ Cl¯ H2O
notes nitrous acid is unstable and is made in situ from sodium nitrite
C6H5NH2 + NaNO HCl ——> C6H5N2+ Cl¯ + NaCl H2O
the solution is kept cold to slow down decomposition
of the diazonium salt
C6H5N2+ Cl¯ H2O ——> C6H5OH HCl N2

16. 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

17. DIAZONIUM SALTS - SUBSTITUTIONOH
reagents water (hydrolysis)
conditions warm above 10°C
equation C6H5N2+ Cl¯ H2O ——> 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 ——> C6H5I KCl N2

18. DIAZONIUM SALTS - COUPLING
reagents phenol and sodium hydroxide
conditions alkaline solution below 10°C
equation
(4-hydroxyphenol)azobenzene YELLOW
use making dyes

19. What should you be able to do?
REVISION CHECK
What should you be able to do?
Recall the structures of phenol and benzene diazonium chloride
Explain and understand the difference in reactivity between phenol and benzene
Recall the reagents and conditions used in the steps to convert benzene into phenol
Recall the different types of reaction undergone by benzene diazonium chloride
CAN YOU DO ALL OF THESE? YES NO

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22. © 2004 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
ROUTES
TO PHENOL
THE END
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23. AMIDES - CHEMICAL PROPERTIES