Chemistry - Reactions of Alcohols & Dehydration

Chemistry - Reactions of Alcohols & Dehydration

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The Reactions of Alcohols
Alcohols burn if there is enough oxygen available, like hydrocarbons, producing carbon dioxide and
Combustion is usually complete oxidation. Alcohols can also be oxidised gently and in stages.
Primary alcohols are oxidised to aldehydes., RCHO. Aldehydes can be further oxidised to carboxylic
acids, RCOOH. For example:
Secondary alcohols are oxidised to ketones, R2CO. Ketones are not oxidised further.
Tertiary alcohols are not easily oxidised. This is because oxidation would require a C-C bond to break
rather than a C-H bond (like what happens when an aldehyde is oxidised). Ketones do not oxidise
further for the same reason.
Many aldehydes and ketones have pleasant smells.
A solution of acidified potassium dichromate is often used to oxidise alcohols to aldehydes and
ketones. In the reaction, the orange dichromate (VI) ions are reduced to green chromium (III) ions.

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The Reactions of Alcohols
Aldehydes and Ketones
Aldehydes and ketones both have the C=O group (carbonyl group)
In aldehydes it is at the end of the hydrocarbon chain:
(RCHO) Suffix = al
In ketones it is in the body of the hydrocarbon chain
(RCHOR') Suffix = one
So CH3CHO is ethanal and CH3COCH3 is propanone.
Tests for aldehydes and ketones
Aldehydes and ketones have similar physical properties but there are two tests that can tell them
apart. Both tests involve gentle oxidation.…read more

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The Reactions of Alcohols
Elimination Reactions
Elimination reactions are ones in which a small molecules leaves the parent molecule. In the case of
alcohols, it is water. The water is made from the -OH group and a hydrogen from the carbon next to
the -OH group. The elimination reactions of alcohols are always dehydrations
+ H2O
Alcohols can be dehydrated with excess hot concentrated sulfuric acid or by passing their vapours
over heated aluminium oxide. An alkene is formed.…read more


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