1. Phenol

2. Draw the following structures
Phenol
2-ethylphenol
3,4,4-trichlorobiphenyl
2-phenylethanol
Extension:
Why is no. 4 not a phenol?

3. Learning Outcomes Explain what PCBs are
Describe the reactions of phenol
Discuss the uses of phenols

4. PCB’s (Polychlorinated biphenyls)
3,4,4-trichlorobiphenyl

5. Learning Outcomes Explain what PCBs are
Describe the reactions of phenol
Discuss the uses of phenols

6. Diploma
Phenol
Phenol cannot be made directly from benzene, the benzene ring is inert to attack by the nucleophile OH-.
CH(CH3)2 OH
AlCl3
i)O2
+CH3CH=CH2
+CH3COCH3
ii)H+
heat
benzene
propene
(propan-2-yl) benzene
‘cumene’
propanone
phenol
This is called the ‘cumene’ 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)
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)

12. ELECTROPHILIC SUBSTITUTION
PHENOL - REACTIONS OF THE AROMATIC RING
ELECTROPHILIC SUBSTITUTION
Ease the OH group is electron releasing
it increases the electron density of the delocalised system
it makes substitution much easier compared to benzene
a p orbital on the oxygen overlaps with the p orbitals in benzene
the p orbital on the O overlaps with the p orbitals in the ring
p orbitals in the system

13. ELECTROPHILIC SUBSTITUTION
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

14. The OH group is electron releasing
Electron pair donation takes place from a p orbital on oxygen
It increases the electron density of the delocalised system
It makes substitution much easier compared to benzene
The electron density is the 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. Learning Outcomes Explain what PCBs are
Describe the reactions of phenol
Discuss the uses of phenols

16. Summary sheet
Phenol summary sheet.doc

17. Exam questions
benzene and phenols.rtf