14.2 Reactions Of Alcohols
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What happens when alcohols burn in Oxygen?
They burn completely, forming Carbon Dioxide and Water
What type of reaction is combustion of alcohols?
Exothermic reaction
As the Carbon chain length increases, what happens to the amount of heat released per mole?
It increases
What types of alcohols can be oxidised?
Primary alcohols Secondary alcohols
Typical oxidising agent
Potassium Dichromate, acidified with dilute Sulfuric Acid K2Cr2O7 with H2SO4
Colour change of oxidising agent
Orange to green
What happens to the oxidising agent when alcohol is oxidised?
Dichromate (VI) ions are reduced to form Chromium (III) ions
What can primary alcohols be oxidised to form?
Aldehydes Carboxylic acids
How to produce aldehydes from primary alcohols
Heat the alcohol gently Aldehyde is distilled out of the reaction mixture as it forms - prevents reaction with oxidising agent to form carboxylic acid
In an equation what symbol is used to show the oxidising agent?
[O]
How to form carboxylic acids from primary alcohols
Heat alcohol strongly under reflux with excess of oxidising agent
Why is an excess of oxidising agent used when heating primary alcohols to form carboxylic acids?
Ensures all of the alcohol is oxidised
Why is the primary alcohol heated under reflux to form carboxylic acid?
Ensures that any aldehyde formed initially will be oxidised to form carboxylic acid
What are secondary alcohols oxidised to form?
Ketones
How are secondary alcohols oxidised?
They are heated under reflux with the oxidising agent to ensure the reaction goes to completion
What is a dehydration reaction?
A reaction where a water molecule is removed from the starting material
Dehydration of alcohols
Heated under reflux with an acid catalyst, forming an alkene
Acid catalyst
Concentrated Sulfuric acid H2SO4 Concentrated Phosphoric acid H3PO4
What type of reaction is dehydration?
An elimination reaction
What are substitution reactions of alcohols?
Alcohols react with hydrogen halides to form haloalkanes
Steps to substitution reactions with alcohols
Sodium halide reacts with sulfuric acid to form the hydrogen halide The hydrogen halide formed reacts with the alcohol to form the haloalkane