3.3.8 Aldehydes and ketones Flashcards
What is the functional group for an aldehyde ?
-CHO containing a carbonyl group (C=O)
How are aldehydes usually produced?
From the initial distillation and oxidation of primary alcohols
How can you test for aldehydes and ketones ?
Tollens solution or fehlings reagent
What would indicate a positive and negative results using Tollens reagent ?
-Silver mirror indicates an aldehyde and carboxylic acid formed
-No reaction when warmed with a ketone
What would indicate a positive and negative result using fehlings reagent ?
- Aldehyde turns blue solution brick red as copper ions have been oxidised and carboxylic acid formed
- No visible change occurs with a ketone and solution stays blue
When acidified potassium dichromate is added to an aldehyde and a ketone what can be observed ?
Aldehyde- Solution turns from orange to green and a carboxylic acid is formed
Ketone- No visible change so solution stays orange
What is the functional group of ketone ?
C=Oin middle of chain
How are ketones produced ?
They are produced from the oxidation of secondary alcohols with acidified potassium dichromate
Can ketones be further oxidised ?
There is no further oxidation of ketones as there is no visible change when added to both fehlings and tollens reagent
Explain why ketones cannot be easily oxidised.
As the only way to oxidise a ketone is to break the C-C bond which requires a lot of energy.
Identify a reducing agent that can be used to reduce an aldehyde to a primary alcohol
NaBH4
What is a hydroxynitrile ?
Molecules that contain a hydroxy (OH) group and a nitrile group (CN)
Where is the lone pair located on a CN ion ?
On the C
Why is there an equal chance of the electrophile attacking from below or above ?
As the C=O bond is planar
What are the hazards associated with KCN and what are 2 precautions you can take ?
It is toxic, dangerous and potentially fatal if ingested or inhaled. Should be used in a fume cupboard with gloves and goggles on
