1. KNOCKHARDY PUBLISHING
AN INTRODUCTION TO
THE CHEMISTRY
OF ALCOHOLS
KNOCKHARDY PUBLISHING

2. THE CHEMISTRY OF ALCOHOLS
CONTENTS
Structure of alcohols
Nomenclature
Isomerism
Physical properties
Chemical properties of alcohols
Identification using infra-red spectroscopy
Industrial preparation and uses of ethanol
Revision check list

3. CLASSIFICATION OF ALCOHOLS
Aliphatic • general formula CnH2n+1OH - provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton

4. CLASSIFICATION OF ALCOHOLS
Aliphatic • general formula CnH2n+1OH - provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton
Aromatic • in aromatic alcohols (or phenols) the OH is attached directly to the ring
• an OH on a side chain of a ring behaves as a typical aliphatic alcohol
The first two compounds are
classified as aromatic alcohols
(phenols) because the OH group
is attached directly to the ring.

5. CLASSIFICATION OF ALCOHOLS
Aliphatic • general formula CnH2n+1OH - provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton
Aromatic • in aromatic alcohols (or phenols) the OH is attached directly to the ring
• an OH on a side chain of a ring behaves as a typical aliphatic alcohol
The first two compounds are
classified as aromatic alcohols
(phenols) because the OH group
is attached directly to the ring.
Structural
differences • alcohols are classified according to the environment of the OH group
• chemical behaviour, eg oxidation, often depends on the structural type
PRIMARY 1° SECONDARY 2° TERTIARY 3°

6. Alcohols are named according to standard IUPAC rules
NAMING ALCOHOLS
Alcohols are named according to standard IUPAC rules
• select the longest chain of C atoms containing the O-H group;
• remove the e and add ol after the basic name
• number the chain starting from the end nearer the O-H group
• the number is placed after the an and before the ol ... e.g butan-2-ol
• as in alkanes, prefix with alkyl substituents
• side chain positions are based on the number allocated to the O-H group
e.g. CH3 - CH(CH3) - CH2 - CH2 - CH(OH) - CH3 is called 5-methylhexan-2-ol

7. STRUCTURAL ISOMERISM IN ALCOHOLS
Different structures are possible due to...
A Different positions for the OH group and
B Branching of the carbon chain
butan-1-ol
butan-2-ol
2-methylpropan-2-ol
2-methylpropan-1-ol

8. CHEMICAL PROPERTIES OF ALCOHOLS
The OXYGEN ATOM HAS TWO LONE PAIRS; this makes alcohols...
BASES Lewis bases are lone pair donors
Bronsted-Lowry bases are proton acceptors
The alcohol uses one of its lone pairs to form a co-ordinate bond
NUCLEOPHILES Alcohols can use the lone pair to attack electron deficient centres

9. ELIMINATION OF WATER (DEHYDRATION)
Reagent/catalyst conc. sulphuric acid (H2SO4) or conc. phosphoric acid (H3PO4)
Conditions reflux at 180°C
Product alkene
Equation e.g. C2H5OH(l) ——> CH2 = CH2(g) + H2O(l)
Mechanism
Step 1 protonation of the alcohol using a lone pair on oxygen
Step 2 loss of a water molecule to generate a carbocation
Step 3 loss of a proton (H+) to give the alkene
Alternative
Method Pass vapour over a heated alumina (aluminium oxide) catalyst

10. All alcohols can be oxidised depending on the conditions
OXIDATION OF ALCOHOLS
All alcohols can be oxidised depending on the conditions
Oxidation is used to differentiate between primary, secondary and tertiary alcohols
The usual reagent is acidified potassium dichromate(VI)
Primary Easily oxidised to aldehydes and then to carboxylic acids.
Secondary Easily oxidised to ketones
Tertiary Not oxidised under normal conditions.
They do break down with very vigorous oxidation
PRIMARY 1° SECONDARY 2° TERTIARY 3°

11. OXIDATION OF PRIMARY ALCOHOLS
Primary alcohols are easily oxidised to aldehydes
e.g. CH3CH2OH(l) [O] ——> CH3CHO(l) H2O(l)
ethanol ethanal
it is essential to distil off the aldehyde before it gets oxidised to the acid
CH3CHO(l) [O] ——> CH3COOH(l)
ethanal ethanoic acid

12. OXIDATION OF PRIMARY ALCOHOLS
Primary alcohols are easily oxidised to aldehydes
e.g. CH3CH2OH(l) [O] ——> CH3CHO(l) H2O(l)
ethanol ethanal
it is essential to distil off the aldehyde before it gets oxidised to the acid
CH3CHO(l) [O] ——> CH3COOH(l)
ethanal ethanoic acid
Practical details
the alcohol is dripped into a warm solution of acidified K2Cr2O7
aldehydes have low boiling points - no hydrogen bonding - they distil off immediately
if it didn’t distil off it would be oxidised to the equivalent carboxylic acid
to oxidise an alcohol straight to the acid, reflux the mixture
compound formula intermolecular bonding boiling point
ETHANOL C2H5OH HYDROGEN BONDING °C
ETHANAL CH3CHO DIPOLE-DIPOLE °C
ETHANOIC ACID CH3COOH HYDROGEN BONDING °C

13. OXIDATION OF PRIMARY ALCOHOLS
Controlling the products
e.g. CH3CH2OH(l) [O] ——> CH3CHO(l) H2O(l)
then CH3CHO(l) [O] ——> CH3COOH(l)
OXIDATION TO ALDEHYDES
DISTILLATION
OXIDATION TO CARBOXYLIC ACIDS
REFLUX
Aldehyde has a lower boiling point so distils off before being oxidised further
Aldehyde condenses back into the mixture and gets oxidised to the acid

14. OXIDATION OF SECONDARY ALCOHOLS
Secondary alcohols are easily oxidised to ketones
e.g CH3CHOHCH3(l) [O] ——> CH3COCH3(l) H2O(l)
propan-2-ol propanone
The alcohol is refluxed with acidified K2Cr2O7. However, on prolonged treatment with a powerful oxidising agent they can be further oxidised to a mixture of acids with fewer carbon atoms than the original alcohol.

15. OXIDATION OF SECONDARY ALCOHOLS
Secondary alcohols are easily oxidised to ketones
e.g CH3CHOHCH3(l) [O] ——> CH3COCH3(l) H2O(l)
propan-2-ol propanone
The alcohol is refluxed with acidified K2Cr2O7. However, on prolonged treatment with a powerful oxidising agent they can be further oxidised to a mixture of acids with fewer carbon atoms than the original alcohol.
OXIDATION OF TERTIARY ALCOHOLS
Tertiary alcohols are resistant to normal oxidation

16. Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
OXIDATION OF ALCOHOLS
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.

17. Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
OXIDATION OF ALCOHOLS
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.
H H
R C O [O] R C O H2O
H H 1°

18. Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
OXIDATION OF ALCOHOLS
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.
H H
R C O [O] R C O H2O
H H 1°
H H
R C O [O] R C O H2O
R R 2°

19. This is possible in 1° and 2° alcohols but not in 3° alcohols.
OXIDATION OF ALCOHOLS
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.
H H
R C O [O] R C O H2O
H H 1°
H H
R C O [O] R C O H2O
R R 2°
This is possible in 1° and 2° alcohols but not in 3° alcohols.

20. 1° 2° 3° OXIDATION OF ALCOHOLS H H R C O + [O] R C O + H2O H H H H
Why 1° and 2° alcohols are easily oxidised and 3° alcohols are not
For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms.
H H
R C O [O] R C O H2O
H H 1° 2° 3°
H H
R C O [O] R C O H2O
R R
This is possible in 1° and 2° alcohols but not in 3° alcohols.
R H
R C O [O] R

21. ESTERIFICATION OF ALCOHOLS
Reagent(s) carboxylic acid + strong acid catalyst (e.g conc. H2SO4 )
Conditions reflux
Product ester
Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) H2O(l)
ethanol ethanoic acid ethyl ethanoate
Notes Concentrated H2SO4 is a dehydrating agent - it removes water
causing the equilibrium to move to the right and increases the yield

22. ESTERIFICATION OF ALCOHOLS
Reagent(s) carboxylic acid + strong acid catalyst (e.g conc. H2SO4 )
Conditions reflux
Product ester
Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) H2O(l)
ethanol ethanoic acid ethyl ethanoate
Notes Concentrated H2SO4 is a dehydrating agent - it removes water
causing the equilibrium to move to the right and increases the yield
Uses of esters Esters are fairly unreactive but that doesn’t make them useless
Used as flavourings
Naming esters Named from the alcohol and carboxylic acid which made them...
CH3OH + CH3COOH CH3COOCH H2O
from ethanoic acid CH3COOCH3 from methanol
METHYL ETHANOATE

23. BROMINATION OF ALCOHOLS
Reagent(s) conc. hydrobromic acid HBr(aq) or
sodium (or potassium) bromide and concentrated sulphuric acid
Conditions reflux
Product haloalkane
Equation C2H5OH(l) conc. HBr(aq) ———> C2H5Br(l) H2O(l)
Mechanism The mechanism starts off similar to that involving dehydration
(protonation of the alcohol and loss of water) but the carbocation
(carbonium ion) is attacked by a nucleophilic bromide ion in step 3
Step 1 protonation of the alcohol using a lone pair on oxygen
Step 2 loss of a water molecule to generate a carbocation (carbonium ion)
Step 3 a bromide ion behaves as a nucleophile and attacks the carbocation

24. INFRA-RED SPECTROSCOPY
Chemical bonds vibrate at different frequencies. When infra red (IR) radiation is passed through a liquid sample of an organic molecule, some frequencies are absorbed. These correspond to the frequencies of the vibrating bonds.
Most spectra are very complex due to the large number of bonds present and each molecule produces a unique spectrum. However the presence of certain absorptions can be used to identify functional groups.
BOND COMPOUND ABSORBANCE RANGE
O-H alcohols broad cm-1 to cm-1
O-H carboxylic acids medium to broad cm-1 to cm-1
C=O ketones, aldehydes strong and sharp cm-1 to cm-1
esters and acids

25. INFRA-RED SPECTROSCOPY
IDENTIFYING ALCOHOLS USING INFRA RED SPECTROSCOPY
Differentiation Compound O-H C=O
ALCOHOL YES NO
ALDEHYDE / KETONE NO YES
CARBOXYLIC ACID YES YES
ESTER NO YES
ALCOHOL CARBOXYLIC ACID ESTER
BUTAN-1-OL PROPANOIC ACID ETHYL ETHANOATE
O-H absorption O-H + C=O absorption C=O absorption

26. LABORATORY PREPARATION OF ALCOHOLS
from haloalkanes - reflux with aqueous sodium or potassium hydroxide
from aldehydes - reduction with sodium tetrahydridoborate(III) - NaBH4
from alkenes - acid catalysed hydration using concentrated sulphuric acid
Details of the reactions may be found in other sections.

27. What should you be able to do?
REVISION CHECK
What should you be able to do?
Recall and explain the physical properties of alcohols
Recall the different structural types of alcohols
Recall the Lewis base properties of alcohols
Recall and explain the chemical reactions of alcohols
Write balanced equations representing any reactions in the section
Understand how oxidation is affected by structure
Recall how conditions and apparatus influence the products of oxidation
Explain how infrared spectroscopy can be used to differentiate between functional groups

28. A guide for A level students KNOCKHARDY PUBLISHING
PHENOL
A guide for A level students
KNOCKHARDY PUBLISHING

29. 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)

30. 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)

31. 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)

32. Test for Phenol
The test for phenol is to add Iron (III) Chloride (greeny-yellow) which then turns a deep purple complex with phenol