14.2 Reactions of alcohols
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What do alcohols burn completely to produce in a plentiful supply of oxygen
Carbon dioxide and water Reaction is exothermic, releasing large quantity of energy in form of heat
How does the quantity of heat released per mole change as the number of atoms in the alcohol chain increases
The quantity of heat released per mole also increases
How can primary and secondary alcohols be oxidised
By an oxidising agent
What is the usual oxidising mixture of primary and secondary alcohols
Solution of potassium divhromate, acidified with dilute sulfuric acid If alcohol is oxidised, orange solution containing dichromate ions reduced to green solution containing chromium
What can primary alcohols be oxidised to
Either aldehydes or carboxylic acids
What is formed when primary alcohols and acidified potassium dichromate are gently heated
An aldehyde is formed
How can we ensure that an aldehyde is formed rather than a carboxylic acid
The aldehyde is distilled out of the reaction mixture as it forms Prevents any further reaction with oxidising agent Dichromate ions colour changes from orange to green
What is formed if a primary alcohol is heated strongly under reflux with an excess of acidified potassium dichromate
A carboxylic acid is formed Use of excess of acidified potassium dichromate ensures that all of alcohol is oxidised Heating under reflux ensures any aldehyde formed undergoes oxidation
When preparing the aldehyde, use ______ to remove the aldehyde from the reaction mixture. When preparing the carboxylic acid, ______ the alcohol under ______.
Distillation Heat Reflux
What are secondary alcohols oxidised to
Ketones Not possible to further oxidise ketones using acidified dichromate (VI) ions Ensure reaction to completion, heated under reflux with oxidising mixture
Oxidation reactions of tertiary alcohols
NONONO THEY DO NOT UNDERGO The acidified dichromate (VI) remains orange
On oxidation:
Primary alcohol - aldehyde, carboxylic acid Secondary alcohol - ketone Tertiary alcohol - no reaction
What symbol is used to show that an oxidising agent is being used in an equation
[O]
What is dehydration
In any reaction, this is where a water molecule is removed from the starting material
What is the dehydration of an alcohol an example of
An elimination reaction
What do alcohols react with hydrogen halides to form
Haloalkanes Alcohol is heated under reflux with sulfuric acid and sodium halide, hydrogen bromide formed in situ (in place)
What is the product of the reaction of an acid under reflux in the presence of an acid catalyst such as sulfuric acid (while heated)
An alkene