KNOCKHARDY PUBLISHING
2015
SPECIFICATIONS

KNOCKHARDY PUBLISHING
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be used for classroom teaching.
Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

•
Structure and classification of alcohols
•
Nomenclature
•
Isomerism
•
Physical properties
•
Chemical properties of alcohols
•
Identification using infra-red spectroscopy
•
Industrial preparation and uses of ethanol
•
Revision check list

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

CLASSIFICATION OF ALCOHOLS
Aliphatic
• general formula C n
H
2n+1
OH provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton

CLASSIFICATION OF ALCOHOLS
Aliphatic
• general formula C n
H
2n+1
OH 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.

CLASSIFICATION OF ALCOHOLS
Aliphatic
• general formula C n
H
2n+1
OH 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 °

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. CH
3
- CH(CH
3
) - CH
2
- CH
2
- CH(OH) - CH
3 is called 5-methylhexan-2-ol

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

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. propane C ethanol C
3
H
2
H
8
5
OH
M
44
46 r bp / °C
-42
+78 permanent dipole-dipole interactions permanent forces + hydrogen bonding

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. propane C ethanol C
3
H
2
H
8
5
OH
M
44
46 r bp / °C
-42
+78 permanent dipole-dipole interactions permanent forces + hydrogen bonding
Boiling point is higher for “straight” chain isomers.
butan-1-ol butan-2-ol
CH
3
CH
2
CH
2
CH
2
OH
CH
3
CH
2
CH(OH)CH
3
2-methylpropan-2-ol (CH
3
)
3
COH bp / °C
118
100
83
Greater branching = lower inter-molecular forces

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. propane C ethanol C
3
H
2
H
8
5
OH
M
44
46 r bp / °C
-42
+78 just van der Waals’ forces van der Waals’ forces
+ hydrogen bonding
Boiling point is higher for “straight” chain isomers.
butan-1-ol butan-2-ol
CH
3
CH
2
CH
2
CH
2
OH
CH
3
CH
2
CH(OH)CH
3
2-methylpropan-2-ol (CH
3
)
3
COH bp / °C
118
100
83
Greater branching = lower inter-molecular forces

Solubility
SOLVENT PROPERTIES OF ALCOHOLS
Low molecular mass alcohols are miscible with water
Due to hydrogen bonding between the two molecules
Heavier alcohols are less miscible
Solvent properties
Show the relevant lone pair(s) when drawing hydrogen bonding
Alcohols are themselves very good solvents
They dissolve a large number of organic molecules

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

ELIMINATION OF WATER (DEHYDRATION)
Reagent/catalyst conc. sulphuric acid (H
2
SO
4
) or conc. phosphoric acid (H
3
PO
4
)
Conditions reflux at 180 °C
Product
Equation alkene e.g. C
2
H
5
OH(l) ——> CH
2
= CH
2
(g) + H
2
O(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

MECHANISM
ELIMINATION OF WATER (DEHYDRATION)
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...

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
Secondary
Tertiary
Easily oxidised to aldehydes and then to carboxylic acids.
Easily oxidised to ketones
Not oxidised under normal conditions .
They do break down with very vigorous oxidation
PRIMARY 1 ° SECONDARY 2 ° TERTIARY 3 °

OXIDATION OF PRIMARY ALCOHOLS
Primary alcohols are easily oxidised to aldehydes e.g. CH
3
CH
2
OH(l) + [O]
——> CH
3
CHO(l) + H
2
O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid
CH
3
CHO(l) + [O]
——> CH
3
COOH(l) ethanal ethanoic acid

OXIDATION OF PRIMARY ALCOHOLS
Primary alcohols are easily oxidised to aldehydes e.g. CH
3
CH
2
OH(l) + [O]
——> CH
3
CHO(l) + H
2
O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid
CH
3
CHO(l) + [O]
——> CH
3
COOH(l) ethanal ethanoic acid
Practical details
• the alcohol is dripped into a warm solution of acidified K
2
Cr
2
O
7
• 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
ETHANOL
ETHANAL
C
2
H
5
OH
CH
3
CHO
ETHANOIC ACID CH
3
COOH intermolecular bonding
HYDROGEN BONDING
DIPOLE-DIPOLE
HYDROGEN BONDING boiling point
78 °C
23 °C
118
°C

OXIDATION OF PRIMARY ALCOHOLS
Controlling the products e.g. CH
3
CH
2
OH(l) + [O]
——> CH
3
CHO(l) + H
2
O(l) then CH
3
CHO(l) + [O]
——> CH
3
COOH(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

OXIDATION OF SECONDARY ALCOHOLS
Secondary alcohols are easily oxidised to ketones e.g. CH
3
CHOHCH
3
(l) + [O]
——> CH
3
COCH
3
(l) + H
2
O(l) propan-2-ol propanone
The alcohol is refluxed with acidified K
2
Cr
2
O
7
. 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 SECONDARY ALCOHOLS
Secondary alcohols are easily oxidised to ketones e.g. CH
3
CHOHCH
3
(l) + [O]
——> CH
3
COCH
3
(l) + H
2
O(l) propan-2-ol propanone
The alcohol is refluxed with acidified K
2
Cr
2
O
7
. 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

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.

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]
H
R C O + H
H
2
O

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

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

ESTERIFICATION OF ALCOHOLS
Reagent(s)
Conditions
Product
Equation carboxylic acid + strong acid catalyst (e.g conc. H
2
SO
4
) reflux ester e.g.
CH
3
CH
2
OH(l) + CH
3
COOH(l) ethanol ethanoic acid
CH
3
COOC
2
H
5
(l) + H
2 ethyl ethanoate
O(l)
Notes Concentrated H
2
SO
4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and increases the yield

ESTERIFICATION OF ALCOHOLS
Reagent(s)
Conditions
Product
Equation carboxylic acid + strong acid catalyst (e.g conc. H
2
SO
4
) reflux ester e.g.
CH
3
CH
2
OH(l) + CH
3
COOH(l) ethanol ethanoic acid
CH
3
COOC
2
H
5
(l) + H
2 ethyl ethanoate
O(l)
Notes Concentrated H
2
SO
4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and increases the yield
Uses of esters
Naming esters
Esters are fairly unreactive but that doesn’t make them useless
Used as flavourings
Named from the alcohol and carboxylic acid which made them...
CH
3
OH + CH
3
COOH CH
3
COO CH
3
+ H
2
O from ethanoic acid
3
CH
3
METHYL ETHANOATE from methanol

OXYGEN
OTHER REACTIONS OF ALCOHOLS
Alcohols make useful fuels
C
2
H
5
OH(l) + 3O
2
(g) ———> 2CO
2
(g) + 3H
2
O(l)
Advantages have high enthalpies of combustion do not contain sulphur so there is less pollution can be obtained from renewable resources

OXYGEN
OTHER REACTIONS OF ALCOHOLS
Alcohols make useful fuels
C
2
H
5
OH(l) + 3O
2
(g) ———> 2CO
2
(g) + 3H
2
O(l)
Advantages have high enthalpies of combustion do not contain sulphur so there is less pollution can be obtained from renewable resources
SODIUM
Conditions
Product
Equation
Notes room temperature sodium alkoxide and hydrogen
2CH
3
CH
2
OH(l) + 2Na(s) ——> 2CH
3
CH
2
O¯ Na + + H
2
(g) sodium ethoxide 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. CH
3
CH
2
O¯ Na +

Reagent(s)
Conditions
Product
Equation
Mechanism
BROMINATION OF ALCOHOLS conc. hydrobromic acid HBr(aq) or sodium (or potassium) bromide and concentrated sulphuric acid reflux haloalkane
C
2
H
5
OH(l) + conc. HBr(aq) ———> C
2
H
5
Br(l) + H
2
O(l)
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

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
O-H
O-H
COMPOUND alcohols
ABSORBANCE broad carboxylic acids medium to broad
C=O ketones, aldehydes strong and sharp esters and acids
RANGE
3200 cm -1 to 3600 cm -1
2500 cm -1 to 3500 cm -1
1600 cm -1 to 1750 cm -1

INFRA-RED SPECTROSCOPY
IDENTIFYING ALCOHOLS USING INFRA RED SPECTROSCOPY
Differentiation Compound
ALCOHOL
ALDEHYDE / KETONE
CARBOXYLIC ACID
ESTER
O-H
YES
NO
YES
NO
C=O
NO
YES
YES
YES
ALCOHOL
PROPAN-1-OL
O-H absorption
ALDEHYDE
PROPANAL
C=O absorption
CARBOXYLIC ACID
PROPANOIC ACID
O-H + C=O absorption

Reagent(s)
INDUSTRIAL PREPARATION OF ALCOHOLS
FERMENTATION
GLUCOSE - produced by the hydrolysis of starch
Conditions
Equation yeast warm, but no higher than 37 °C
C
6
H
12
O
6
——> 2 C
2
H
5
OH + 2 CO
2

Reagent(s)
INDUSTRIAL PREPARATION OF ALCOHOLS
FERMENTATION
GLUCOSE - produced by the hydrolysis of starch
Conditions
Equation yeast warm, but no higher than 37 °C
C
6
H
12
O
6
——> 2 C
2
H
5
OH + 2 CO
2
Advantages
Disadvantages
LOW ENERGY PROCESS
USES RENEWABLE RESOURCES - PLANT MATERIAL
SIMPLE EQUIPMENT
SLOW
PRODUCES IMPURE ETHANOL
BATCH PROCESS

Reagent(s)
INDUSTRIAL PREPARATION OF ALCOHOLS
HYDRATION OF ETHENE
ETHENE - from cracking of fractions from distilled crude oil
Conditions
Equation catalyst - phosphoric acid high temperature and pressure
C
2
H
4
+ H
2
O
——> C
2
H
5
OH

Reagent(s)
INDUSTRIAL PREPARATION OF ALCOHOLS
HYDRATION OF ETHENE
ETHENE - from cracking of fractions from distilled crude oil
Conditions
Equation
Advantages catalyst - phosphoric acid high temperature and pressure
C
2
H
4
+ H
2
O
——> C
2
H
5
OH
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

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

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

REVISION CHECK
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
YES
NO

© 2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

BIOFUELS
What are they?
Liquid fuels made from plant material and recycled elements of the food chain
Biodiesel
An alternative fuel which can be made from waste vegetable oil or from oil produced from seeds. It can be used in any diesel engine, either neat or mixed with petroleum diesel. vegetable oil glycerol biodiesel
It is a green fuel, does not contribute to the carbon dioxide (CO
2
) burden and produces drastically reduced engine emissions. It is non-toxic and biodegradable.

Advantages
BIOFUELS
• renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel

BIOFUELS
Advantages • renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel
Disadvantages • poor availability - very few outlets & manufacturers
• more expensive to produce
• poorly made biodiesel can cause engine problems

BIOFUELS
Advantages • renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel
Disadvantages • poor availability - very few outlets & manufacturers
• more expensive to produce
• poorly made biodiesel can cause engine problems
Future problems • there isn’t enough food waste to produce large amounts
• crops grown for biodiesel use land for food crops
• a suitable climate is needed to grow most crops
• some countries have limited water resources