Organic chemistry:
Reactions of alcohols
Syllabus Statements
Understandings
» Alcohols undergo
nucleophilic substitution
reactions with acids (also
called esterification or
condensation) and some
undergo oxidation
reactions.
Applications
» Writing equations for the complete
combustion of alcohols.
» Writing equations for the oxidation
reactions of primary and secondary
alcohols (using acidified potassium
dichromate(VI) or potassium
manganate(VII) as oxidizing
agents).
» Explanation of distillation and reflux
in the isolation of the aldehyde and
carboxylic acid products.
» Writing the equation for the
condensation reaction of an
alcohol with a carboxylic acid, in
the presence of a catalyst (eg
concentrated sulfuric acid) to form
an ester.
Combustion of alcohols
https://www.youtube.com/watch?v=Ku7TdLeEGsQ
Combustion of alcohols
» Complete combustion produces
CO2 and water
CH3CH2OH (g) + 3 O2
CO2 (g) + 3 H2O (g)
(g)

2
» As for alkanes and alkenes, the
longer the carbon
chain, the larger the enthalpy
of reaction (more
Oxidation of alcohols
The combustion of alcohols will
completely oxidise the alcohol
molecule producing heat, CO2
and H2O.
It is also possible to
selectively oxidise
alcohols using
acidified reagents
such as KMnO4 or
K2Cr2O7.
Oxidation of alcohols
In chapter 9, Redox reactions, you studied this
oxidation reaction from an inorganic chemistry
perspective
• Oxidation is loss of electrons
+6
-2
-2 +1 -2 +1 -2 +1
+1
2Cr2O72−(aq)+3CH3CH2OH(l)+16H+(aq)
-2  0 () Oxidation
+6  +3 ()
Reduction
+3
0 +1
0 -2 -2 +1
+1
-2
 4Cr3+(aq)+3CH3COOH(aq)+11H2O(l)
Oxidation of alcohols
In chapter 10, you will look at the same reactions
from an organic chemistry perspective
• Oxidation is gain of oxygen
CH3CH2OH
+[O], heat
(l)

CH3COOH
(l)
1,2  and 3  alcohols
» Primary (1), secondary(2) and tertiary(3) alcohols
has the placement of the hydroxyl group (OH) on a
carbon that is bonded to one, two or three other
carbons
H
Primary Alcohol (1)
CH3 C OH
H
The carbon that holds the
hydroxyl group has one
other carbon attached to it.
1,2  and 3  alcohols
» Primary (1), secondary(2) and tertiary(3) alcohols
has the placement of the hydroxyl group (OH) on a
carbon that is bonded to one, two or three other
carbons
H 3
CH
Secondary
Alcohol
Primary Alcohol
(1)(2)
CH3 C OH
H
The carbon that holds the
hydroxyl group now
has one
has two
other carbons
carbon attached
attachedto
toit.
it.
1,2  and 3  alcohols
» Primary (1), secondary(2) and tertiary(3) alcohols
has the placement of the hydroxyl group (OH) on a
carbon that is bonded to one, two or three other
carbons
CH3
Tertiary
Alcohol
(3)(2)
Secondary
Alcohol
CH3 C OH
H
CH3
The carbon that holds the
two
hydroxyl group now has three
other carbons attached to it.
1,2  and 3  alcohols
» Although Methanol does not have an additional
carbon attached to the main carbon, it is
considered a Primary (1) as it reacts in the same
way.
Primary alcohols
» Primary, secondary and tertiary alcohols have
different reaction outcomes
» Primary alcohols can be oxidised twice:
H
CH3 C OH
H
Primary alcohols
» Primary, secondary and tertiary alcohols have
different reaction outcomes.
» Primary alcohols can be oxidised twice:
H
CH3 C O
H
First to an aldehyde
Where a double bonded
oxygen is formed.
Primary alcohols
» Primary, secondary and tertiary alcohols have
different reaction outcomes.
» Primary alcohols can be oxidised twice:
H
CH3 C O
OH
Then to an carboxylic acid
Where a hydroxyl group
is added.
Primary alcohols
» This “Gain of oxygen” results in:
H
CH3 C OH CH3 C O
H
H
Alcohol – one
bond from
carbon to oxygen.
Aldehyde – two
bonds from carbon
to oxygen.
CH3 C O
OH
Carboxylic acid –
three bonds from
carbon to oxygen
» A carbon-hydrogen bond is broken in each step
• Carbon-carbon bonds are not broken during oxidation
(contrast this with combustion)
.
Primary alcohols
Oxidised first to aldehydes, then to
carboxylic acids
O
OH
O
[O], heat
H3C
C
H
[O], heat
H3C
C
H
H3C
C
(reflux)
H
H+/Cr(VI)
Can we isolate the aldehyde? How?
Cr(III)
OH
Isolating the Aldehyde
Stopper (or thermometer attachment)
Still head
Condenser
» When the aldehyde is
produced, distillation can
be used to collect the
aldehydes as they have
lower boiling points than
alcohols (and carboxylic
acids.)
Round-bottom flask
Why do aldehydes have a
lower boiling point than
alcohols and carboxylic
acids?
Isolating the Aldehyde
Stopper (or thermometer attachment)
Still head
Condenser
Round-bottom flask
» When the aldehyde is
produced, distillation can
be used to collect the
aldehydes as they have
lower boiling points than
alcohols (and carboxylic
acids.)
Producing the Acid
Condensor
» If the process of oxidation is
allowed to continue, the
aldehyde will continue to
oxidise to a carboxylic acid.
» Refluxing will help speed this
process up.
Round-bottom flask
Aldehyde vs Acid
» If the process of oxidation is
allowed to continue, the
aldehyde will continue to
oxidise to a carboxylic acid.
Condensor
» Refluxing will help speed this
process up.
Round-bottom flask
Reagent Selectivity
Depending on the extent of oxidation required will determine
the selection of oxidising agent.
» Strong oxidising agent:
dichromate ion H+/Cr2O72O
O Mn O‒
O
» or the permanaganate ion
−
+
H /MnO4
» Weak oxidising agent:
PCC: pyradinium chlorochromate
(does not need to be acidified)
Secondary alcohols
» Secondary alcohols oxidise to ketones.
CH3
H
C CH3
[O], heat
CH3
OH
» Can use either H+/Cr2O72- or PCC
H
C CH3
O
Tertiary alcohols
» Tertiary alcohols do not oxidise.
CH3
CH3 C OH
+[O], heat
No reaction
CH3
Too much energy to break the carbon
skeleton.
Summary of Oxidation of Alcohols
Alcohol
Oxidation
Product
Colour Change
with acidified
K2Cr2O7 (aq)
Colour Change
with acidified
KMnO4 (aq)
Primary
aldehyde 
carboxylic acid
orange  green
purple 
red-brown
Secondary
ketone
orange  green
purple 
red-brown
Tertiary
cannot be
oxidised
(no C-H bonds)
no colour
change
no colour
change
Colour of Oxidised alcohols
H+/Cr2O72-
H+/MnO4-
Esterification
Esterification
» Alcohols react with carboxylic acids to form an
ESTER - ROOR’
» Condensation reaction: removal of water
» Equilibrium reaction
» Catalysed by concentrated H2SO4
Esterification
carboxylic acid + alcohol
RCOOH
+
conc. H2SO4
conc. H2SO4
R’OH
ester + water
RCOOR’
+
( & H+ )
H
H
O
H
C C
H
O H
H
O
H O
C H
H
Ethanoic acid
Methanol
Water
HOH
Esterification
carboxylic acid + alcohol
RCOOH
+
R’OH
conc. H2SO4
conc. H2SO4
ester + water
RCOOR’
+
HOH
( & H+ )
H
H
O
H
C C
H
O
C H
H
Ethanoicmethyl
acid ethanoate
Methanol
H
O
H
Water
Esterification