14.2 : Reactions of Alcohols Flashcards
What are the reactions alcohols can undergo ?
Combustion
Oxidation
Dehydration
Substitution
Describe combustion of alcohols
They burn completely in plentiful supply of oxygen to produce carbon dioxide and water.
This is an exothermic reaction, releasing a large quantity of energy in the form of heat. As the number of carbon atoms in the alcohol chain increases the quantity of heat released per mole also increase.
How can alcohols be distilled ? Include catalyst, result, method and any colour changes.
If the alcohol is primary.
Dilute sulfuric acid catalyst.
Result = aldehyde
Method :
Gently heat alcohol with acidified potassium dichromate.
Distill aldehyde out of the reaction mixture as it forms ( prevents any further reaction with oxidising agent .
Dichromate ions change colour from orange to green.
How can primary alcohols be refluxed ? Include catalyst, result and method
Catalyst = dilute sulfuric acid
Result : carboxylic acid
Method :
Strongly heat alcohol under reflux, with excess acidic potassium dichromate. Heating under reflux ensures that any aldehyde formed in the reaction undergoes oxidation to the carboxylic acid.
How can secondary alcohols be distilled ? Include catalyst, result, method and any colour changes
Result : ketones
Catalyst : dilute sulfuric acid
Method :
Strongly heat alcohol under reflux, with oxidising mixture.
Dichromate ions : orange to green
Describe oxidation of tertiary alcohols
They do not undergo oxidation reactions.
Acidified dichromate remains orange when added to alcohol.
Define ‘dehydration reaction’
Any reaction in which a water molecule is removed from the starting material.
It is a type of elimination reaction.
Describe dehydration of alcohols
Product : alkene and water
Catalyst = concentrated sulfuric acid or concentrated phosphoric acid
Method :
Alcohol is heated under reflux in the presence of an acid catalyst.
Describe substitution of alcohols
Product : haoalkane
Method :
When the alcohol is heated under reflux with sulfuric acid and a sodium halide, the hydrogen bromide is formed.
This HBr then reacts with the alcohol to produce the haloalkane.