Transcript Phenol - Macmillan Academy

Phenol
Draw the following structures
Phenol
2. 2-ethylphenol
3. 3,4,4-trichlorobiphenyl
4.
2-phenylethanol
Extension:
Why is no. 4 not a phenol?
1.
Learning Outcomes
Explain what PCBs are
 Describe the reactions of phenol
 Discuss the uses of phenols
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PCB’s (Polychlorinated biphenyls)
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3,4,4-trichlorobiphenyl
Learning Outcomes
Explain what PCBs are
 Describe the reactions of phenol
 Discuss the uses of phenols
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Diploma
Phenol
Phenol cannot be made directly from
benzene, the benzene ring is inert to
attack by the nucleophile OH-.
CH(CH3)2
AlCl3
+CH3CH=CH2
heat
benzene
propene
OH
i)O2
+CH3COCH3
ii)H+
(propan-2-yl) benzene
‘cumene’
This is called the ‘cumene’ process
phenol
propanone
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 55°C
equation
C6H6 + HNO3
——>
C6H5NO2 + H2O
mechanism
electrophilic substitution
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] ——> C6H5NH2
mechanism
reduction
+ 2H2O
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
nitrous acid and hydrochloric acid (use sodium nitrite)
conditions
keep below 10°C
equation
C6H5NH2 + HNO2 + HCl ——> C6H5N2+ Cl¯ + 2H2O
reaction type
diazotisation
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 10°C
equation
C6H5N2+ Cl¯ + H2O ——> C6H5OH
reaction type
hydrolysis / substitution
+
N2 + HCl
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
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
p orbitals in the system
the p orbital on the O overlaps
with the p orbitals in the ring
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
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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
Learning Outcomes
Explain what PCBs are
 Describe the reactions of phenol
 Discuss the uses of phenols

Summary sheet

Phenol summary sheet.doc
Exam questions

benzene and phenols.rtf