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

2. KNOCKHARDY PUBLISHING THE CHEMISTRY OF ALCOHOLS
INTRODUCTION
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3. 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

4. THE CHEMISTRY OF ALCOHOLS Before you start it would be helpful to…
Recall the definition of a covalent bond
Recall the difference types of physical bonding
Be able to balance simple equations
Be able to write out structures for simple organic molecules
Understand the IUPAC nomenclature rules for simple organic compounds
Recall the chemical properties of alkanes and alkenes

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

6. 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.

7. 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°

8. 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

9. 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

10. BOILING POINTS OF ALCOHOLS
Increases with molecular size due to increased van der Waals’ forces.
Alcohols have higher boiling points than
similar molecular mass alkanes
This is due to the added presence of
inter-molecular hydrogen bonding.
More energy is required to separate the molecules.
Mr bp / °C
propane C3H just van der Waals’ forces
ethanol C2H5OH van der Waals’ forces + hydrogen bonding

11. BOILING POINTS OF ALCOHOLS
Increases with molecular size due to increased van der Waals’ forces.
Alcohols have higher boiling points than
similar molecular mass alkanes
This is due to the added presence of
inter-molecular hydrogen bonding.
More energy is required to separate the molecules.
Mr bp / °C
propane C3H just van der Waals’ forces
ethanol C2H5OH van der Waals’ forces + hydrogen bonding
Boiling point is higher for “straight” chain isomers.
bp / °C
butan-1-ol CH3CH2CH2CH2OH 118
butan-2-ol CH3CH2CH(OH)CH3 100
2-methylbutan-2-ol (CH3)3COH
Greater branching =
lower inter-molecular forces

12. SOLVENT PROPERTIES OF ALCOHOLS
Solubility Low molecular mass alcohols are miscible with water
Due to hydrogen bonding between the two molecules
Heavier alcohols are less miscible
Solvent
properties Alcohols are themselves very good solvents
They dissolve a large number of organic molecules

13. 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

14. 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

15. ELIMINATION OF WATER (DEHYDRATION)
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
Note 1 There must be an H on a carbon atom adjacent the carbon with the OH
Note 2 Alcohols with the OH in the middle of a chain
can have two ways of losing water.
In Step 3 of the mechanism, a proton can be lost
from either side of the carbocation. This gives a
mixture of alkenes from unsymmetrical alcohols...

16. 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°

17. 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

18. 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

19. 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

20. 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

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. OTHER REACTIONS OF ALCOHOLS
OXYGEN Alcohols make useful fuels
C2H5OH(l) O2(g) ———> 2CO2(g) H2O(l)
Advantages have high enthalpies of combustion
do not contain sulphur so there is less pollution
can be obtained from renewable resources

24. OTHER REACTIONS OF ALCOHOLS
OXYGEN Alcohols make useful fuels
C2H5OH(l) O2(g) ———> 2CO2(g) H2O(l)
Advantages have high enthalpies of combustion
do not contain sulphur so there is less pollution
can be obtained from renewable resources
SODIUM
Conditions room temperature
Product sodium alkoxide and hydrogen
Equation 2CH3CH2OH(l) Na(s) ——> 2CH3CH2O¯ Na H2(g) sodium ethoxide
Notes alcohols are organic chemistry’s equivalent of water
water reacts with sodium to produce hydrogen and so do alcohols
the reaction is slower with alcohols than with water.
Alkoxides are white, ionic crystalline solids e.g. CH3CH2O¯ Na+

25. 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

26. 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

27. 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

28. INDUSTRIAL PREPARATION OF ALCOHOLS
FERMENTATION
Reagent(s) GLUCOSE - produced by the hydrolysis of starch
Conditions yeast
warm, but no higher than 37°C
Equation C6H12O6 ——> 2 C2H5OH CO2
Advantages LOW ENERGY PROCESS
USES RENEWABLE RESOURCES - PLANT MATERIAL
SIMPLE EQUIPMENT
Disadvantages SLOW
PRODUCES IMPURE ETHANOL
BATCH PROCESS

29. INDUSTRIAL PREPARATION OF ALCOHOLS
HYDRATION OF ETHENE
Reagent(s) ETHENE - from cracking of fractions from distilled crude oil
Conditions catalyst - phosphoric acid
high temperature and pressure
Equation C2H H2O ——> 2 C2H5OH

30. INDUSTRIAL PREPARATION OF ALCOHOLS
HYDRATION OF ETHENE
Reagent(s) ETHENE - from cracking of fractions from distilled crude oil
Conditions catalyst - phosphoric acid
high temperature and pressure
Equation C2H H2O ——> 2 C2H5OH
Advantages FAST
PURE ETHANOL PRODUCED
CONTINUOUS PROCESS
Disadvantages HIGH ENERGY PROCESS
EXPENSIVE PLANT REQUIRED
USES NON-RENEWABLE FOSSIL FUELS TO MAKE ETHENE
Uses of ethanol ALCOHOLIC DRINKS
SOLVENT - industrial alcohol / methylated spirits
FUEL - petrol substitute in countries with limited oil reserves

31. USES OF ALCOHOLS ETHANOL DRINKS
SOLVENT industrial alcohol / methylated spirits (methanol is added)
FUEL used as a petrol substitute in countries with limited oil reserves
METHANOL
PETROL ADDITIVE improves combustion properties of unleaded petrol
SOLVENT
RAW MATERIAL used as a feedstock for important industrial processes
FUEL
Health warning Methanol is highly toxic

32. 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.

33. 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
CAN YOU DO ALL OF THESE? YES NO

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36. © JONATHAN HOPTON & KNOCKHARDY PUBLISHING
AN INTRODUCTION TO
THE CHEMISTRY
OF ALCOHOLS
THE END
© JONATHAN HOPTON & KNOCKHARDY PUBLISHING