6.1.2 - Carbonyl Compounds
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What do aldehydes and ketones contain which makes them carbonyl compounds?
C=O
What do primary alcohols oxidise to?
Aldehydes and then carboxylic acids.
What do you use as the oxidising agent?
Acidified potassium dichromate.
What is also produced in oxidation of alcohols?
Water.
What is produced when alcohols are distilled?
Aldehyde.
What does refluxing primary alcohols produce?
Carboxylic acids.
What is used as a reducing agent [H] to produce alcohols?
NaBH4
What is the equation for the reduction of an aldehyde to primary alcohol?
Aldehyde + 2[H] -> primary alcohol.
What is the reduction of aldehydes/ketones an example of?
Nucleophilic addition reactions.
Describe the mechanism of the reduction of an aldehyde / ketone.
The reducing agent supplies hydride ions, H-. The H- has a lone pair of electrons, so its a nucleophile and can attack the delta + carbon on the carbonyl group of an aldehyde or ketone.
What can also reaction with nucleophilic addition and what does it produce?
Hydrogen cyanide produces hydroxynitriles.
Describe the mechanism of HCN with an aldehyde / ketone.
HCN is a weak acid and so partially dissociates. The CN- ion attacks the slightly positive carbon atom and donates a pair of electrons to it. Both electron from the double bond transfer to the oxygen. H+ from hydrogen cyanide bonds to the oxygen to form the hydroxyl group.
How can you test that a substance is either an aldehyde or ketone?
Add Brady’s reagent. If a bright orange precipitate is produced then a carbonyl group is present.
Using the crystals from Brady’s reagent how can you tell what the substance is?
Each different carbonyl compound produces a crystalline derivative with a different melting point. so if you measure the boiling point of the crystals and compare that to the known melting points, you can identify the carbonyl compound.
How can you distinguish between an aldehyde or ketone?
Tollens’ reagent. A silver mirror is produced when an aldehyde is present.
What is Tollens’ reagent?
Silver nitrate dissolved in aqueous ammonia.
How does Tollens’ reagent work?
When heated together in a tube with an aldehyde. The aldehyde is oxidised and the silver ions in the Tollens’ regent are reduced to silver causing a silver mirror.
Why do ketones not react with Tollens reagent?
They are resistant to oxidation as they don’t have a hydrogen attached to the carbon with =O.