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Organic
Chemistry
Lesson 6
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
We Are Here
Lesson 6: Alcohols

Objectives:

Explain the relative ease of combustion of the alcohols

Describe the oxidation reactions of the alcohols

Investigate the oxidation reactions of the alcohols
Alcohols

General formula is CnH2n+1OH

The –OH (hydroxyl) functional group is polar

Alcohols are more soluble in water than alkanes of
comparable molar mass
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

Alcohols are used as fuels:

As a fuel for cars – either pure or blended with petrol


Methanol as fuel for competitive motorsports including dragsters and
monster trucks



Adding a small amount of gasoline improves the engine starting in cold weather
Since the 1960s methanol has been the required fuel for the Indianapolis 500 and other
types of racing. The reason for this is that methanol is made of a single chemical.
Gasoline, on the other hand, contains many different chemicals, and can vary greatly
from one batch to another.
Methanol is safer in case of accidental fire than gasoline, because it burns cooler.
Ethanol used as fuel is fermented from crops (corn, sugar
cane)…crops that could otherwise be eaten, forcing up food prices. Is
this okay?
Oxidation of alcohols

The most important reactions of the alcohols are their
oxidations

A range of compounds will oxidise them so the oxidiser is
often represented as [O]

One common laboratory oxidising agent you need to
know is acidified potassium dichromate, K2Cr2O7.

When using this, orange Cr (VI) is reduced to green Cr (III)
Oxidation reaction scheme
Oxidation of alcohols summary
1⁰
2⁰
3⁰
Reduction

We can reverse these oxidations using a suitable
reducing agent e.g. sodium borohydride in aqueous
or alcoholic solution (mild) OR lithium aluminium
hydride in dry ether followed by aqueous acid
(sledgehammer) e.g.
Esterification reaction


Alcohols react with carboxylic acids to form esters in a
condensation reaction in which water is also produced.
This is an equilibrium reaction that must be catalysed by
concentrated sulfuric acid.
Alcohol + carboxylic acid
ester + water
Oxidising alcohols

Complete the following investigation into the
oxidation of alcohols

Instructions here
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 alcohols do not oxidise due to the 3 strong C-C bonds
surrounding the –OH carbon

These oxidations can be reversed by reduction.

Esters can be made by reacting alcohols with carboxylic acids in
condensation reactions (water is also produced).