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Topic 2.10

ALCOHOLS

Preparation of ethanol
Ethanol as a biofuel
Elimination reactions of alcohols
Oxidation reactions of alcohols
Tests for aldehydes

























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ALCOHOLS

Alcohols are saturated molecules containing an ­OH group. The H atom in the
OH bond can hydrogen bond with other alcohol molecules and with water, which is
why alcohols have relatively high boiling points and many are soluble in water.

Ethanol, C2H5OH, is the most commercially important of the…

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This process has a number of advantages:
it is a relatively fast process
it is a continuous flow process, which means that ethene can be entered into the
vessel continuously and the reaction never has to be stopped
it produces pure ethanol
There are also a number of disadvantages associated…

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Tertiary alcohols are those in which the carbon atom attached to the OH is attached to 3
other carbon atoms. In other words, they are molecules in which the functional group is
attached to a carbon which also has a branch attached to it.

Eg 2methypropan2ol






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3. Reactions of alcohols

Alcohol molecules are saturated and polar, containing a +ve carbon. Thus alcohols tend to
undergo nucleophilic substitution reactions.

The OH can combine with an adjacent H atom to form a stable H2O molecule. Thus
alcohols can also undergo elimination reactions.

Alcohols can lose hydrogen and undergo…

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Butan2ol but2ene:








Butan2ol but1ene







NB Alcohols which have no H atoms on the C atom adjacent to the OH group cannot
undergo elimination:




Eg dimethylpropanol:




b) oxidation reactions

Oxidation in organic chemistry can be regarded as the addition of oxygen or the removal of
hydrogen. As the full equations are…

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Ethanol Ethanal

An aldehyde is a molecule containing the following group:





If a secondary alcohol is mixed with an oxidising agent, two hydrogen atoms can be
removed and a ketone will be formed:

Eg CH3CH(OH)CH3 + [O] CH3COCH3 + H2O






Propan2ol propanone

A ketone is a molecule containing the following…

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Tertiary alcohols are not readily oxidised since they do not have available H atoms to
give up.

Aldehydes and ketones are collectively known as carbonyls and can be represented by the
general formula CnH2nO





In aldehydes, one of the R groups is a H atom. In ketones, neither of the…

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Carbonyls are more volatile than alcohols and carboxylic acids, since there is no hydrogen
bonding between aldehyde molecules. Thus if a distillation apparatus is used, the volatile
aldehyde can be distilled off as it is formed. If reflux apparatus is used, the aldehyde remains
in the reaction vessel and is…

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4. Tests to distinguish between aldehydes and ketones

a) Tollen's reagent

Aldehydes and ketones can be distinguished by their reaction with ammoniacal silver nitrate
(known as Tollen's reagent). Aledehydes are reducing agents since they can be oxidised to
carboxylic acids, but ketones are not reducing agents. Ammoniacal silver nitrate, or…

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