Aldehydes and ketones Flashcards
Can ketones be oxidised?
No.
Can aldehydes be oxidised?
Yes.
What are aldehydes oxidised into?
Carboxylic acids.
Describe how to make Tollens reagent.
- put silver nitrate solution in a test tube (colourless)
- add sodium hydroxide (brown precipitate)
- add dilute ammonia until precipitate dissolves
Describe how to test for an aldehyde using Tollens reagent.
- add substance to Tollens reagent in test tube
- put test tube in hot water bath
- if aldehyde, silver mirror will form
What happens to the Ag+ ions in Tollens reaction?
Reduced to Ag atoms.
Why is a bunsen burner not used in the tests for aldehydes and ketones?
They are flammable.
Describe how to test for aldehydes using Fehlings solution.
- add substance to Fehlings solution in test tube
- place in hot water bath
- if aldehyde, brick red precipitate formed
What happens to the Cu2+ ions in Fehlings reaction?
Reduced to CuO.
Can aldehydes be reduced?
Yes.
Can ketones be reduced?
Yes.
What are aldehydes and ketones reduced to?
Alcohols.
What reducing agent is commonly used?
NaBH4 dissolved in methanol and water.
What type of alcohols do aldehydes reduce to?
Primary.
What type of alcohols do ketones reduce to?
Secondary.
What is the nucleophile in the reduction and where does it come from?
H- ion, from reducing agent.
Draw the mechanism for the reduction of an aldehyde.
…
Where does the H+ come from in the reduction mechanism?
The acid/water added to the reducing agent at the start.
What is the name of the reduction mechanism of aldehydes and ketones?
Nucleophillic addition.
What is the product of potassium cyanide + carbonyl compound?
Hydroxynitrile.
What is the name of the mechanism of KCN + carbonyl compoud?
Nucleophillic addition.
What form is the KCN in for the reaction?
Dissolved in acidic solution.
Draw the mechanism for the reaction of KCN and an aldehyde.
…
What is the overall reaction for aldehyde + KCN?
RCHO + KCN + H+ → RCH(OH)CN + K+
What is the overall reaction for ketone + KCN?
RCOR’ + KCN + H+ → RCR’(OH)CN + K+
What is formed if an unsymmetrical aldehyde/ketone is used?
A mixture of enantiomers.
What are the risks with using KCN?
*irritant
*dangerous if ingested/inhaled
*forms toxic gas (HCN) when reacts with moisture
What are some things that should be done when working with KCN?
*wear gloves, goggles, lab coat
*use fume cupbaord
