Title: Lesson 5 Alcohols
Learning Objectives:
– Explain the relative ease of combustion of the alcohols
– Describe the oxidation reactions of the alcohols
– Investigate the oxidation reactions of the alcohols
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
Which products can be potentially
obtained from crude oil and are
economically important?
I.
II.
III.
A.
B.
C.
D.
Plastics
Margarine
Motor fuel
I and II only
I and III only
II and III only
I, II and III
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Reviewing Your Notes
You should spend 60
seconds reviewing your
notes from last lesson
before attempting this.
Alcohols


General structure CnH2n+1OH
-OH Functional group

The –OH group is polar  increased solubility in water
compared to alkanes of comparable molar mass
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Alcohols are used as fuels:

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As a fuel for cars – either pure or blended with petrol
Methanol as fuel for competitive motorsports including dragsters
and monster trucks
TOK: A large amount of ethanol is fermented from
crops…crops that could otherwise be eaten, forcing up food
prices. Is this ok?
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Alcohols as Fuels

Alcohols combust more readily than equivalent alkanes but release less energy
since they are already partially oxidised
Alcohol + oxygen  carbon dioxide + water (+ lots of energy!)

Amount of energy released per mole increases as we go up the homologous
series, due to increasing numbers of carbon dioxide molecules produced

As with hydrocarbons, in limited supply of oxygen, alcohols will produce carbon
monoxide instead of carbon dioxide
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Oxidation of alcohols

It is possible for them to react with oxidising agents, which
selectively oxidise the carbon atom attached to the –OH group,
keeping the carbon skeleton intact

A range of compounds will oxidise them so the oxidiser is often
represented as [O]

One oxidising agent you need to know is potassium dichromate,
K2Cr2O7.

When using this, orange Cr (VI) is reduced to green Cr (III)


Reread the chapter 9 redox for a reminder of how this works
The oxidation reactions of the different alcohols are as follows:
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Primary alcohols

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Oxidised in a two step reaction
First forming the aldehyde
Oxidised further to the carboxylic acid
If you leave a bottle of wine exposed to
air, bacteria slowly oxidise the ethanol
to ethanoic acid… Giving that smell of
vinegar!
Primary = Carbon attached to
one functional group and at
least two hydrogens!
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It is possible to stop the reaction after the first step using distillation to remove
the aldehyde (which has a lower boiling point than ethanol or ethanoic acid)
before it oxidises further.
Lower boiling point is because it has no hydrogen bonding.
You can also ensure you get ethanoic acid by using reflux to prolong the contact
of the aldehyde with the oxidising agent.
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Distillation v. Reflux heating

Distillation:

Reflux:
Introduction to Reflux Video
Secondary alcohols
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Oxidised to ketones by a similar process:
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Secondary = Carbon
attached to one functional
group, one hydrogens and
two alkyl groups!
Tertiary alcohols
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Not readily oxidised under comparable conditions
This would break the carbon skeleton
This would require significantly more energy
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Tertiary = Carbon
attached to one functional
group and three alkyl
groups!
Summary of oxidation of alcohols
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Summary of Oxidation reaction scheme
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Esterification of alcohols
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Alcohols react with carboxylic acids to form esters in a condensation reaction

Water is also produced

E.g. reaction between ethanoic acid and ethanol:
 The ester has the lowest
boiling point so can be
separated by distillation
 Ester have no free –OH
groups so cannot form
hydrogen bonds and are
mostly insoluble in water
Other examples:
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Oxidising alcohols

Complete the following investigation into the oxidation of alcohols

Instructions here
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Key Points

Alcohols are highly combustible

Primary alcohols oxidise to form aldehydes, which oxidise to form carboxylic
acids

Secondary alcohols oxidise to form ketones

Tertiary do not oxidise due to the 3 strong C-C bonds surrounding the –OH
carbon
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