Aldehydes & Ketones Flashcards
How are aldehydes and ketones formed?
Aldehydes - oxidation of primary alcohols
Ketones - oxidation of secondary alcohols
What are hydroxynitriles?
Product when aldehydes and ketones are reacted with HCN, process called is called nucleophilic addition across the C=O bond
Why is KCN used more than HCN?
KCN is less toxic and using this ionic compound makes the process faster
What is Fehling’s solution?
- A mild oxidising agent used to treat aldehydes and ketones
- It is blue because it contains copper(II) complex ions in alkaline solution
What happens when Fehling’s solution is warmed with an aldehyde?
The aldehyde is oxidised to a carboxylic acid and blue copper(II) ions are reduced to a brick red precipitate of copper(I) oxide
What happens when Fehling’s solution is added to a ketone?
No colour change
What is Tollens’ reagent?
- A mild oxidising agent made by adding dilute ammonia to silver (I) nitrate solution
- it contains the silver(I) complex ion diamminesilver(I)
What happens when Tollens reagent is warmed with an aldehyde?
The colourless diamminesilver(I) ions are reduced to metallic Ag(0). This causes a ‘silver mirror’ to coat the inside of the reaction vessel
What happens when Tollens reagent is added to a ketone?
No reaction and no silver mirror
Name two strong reducing agents that are used to reduce carboxylic acids and aldehydes to primary alcohols and ketones to secondary alcohols?
- Lithium tetrahydridoaluminate (LiAlH4) in a non-aqueous solvent
- Sodium tetrahydridoborate (NaBH4) in alcohol or water solution
What oxidising agent can oxidise primary alcohols, secondary alcohols and aldehydes?
Acidified potassium dichromate(VI)
What oxidising agents can oxidise an aldehyde?
- Acidified potassium dichromate(VI)
- Fehling’s solution
- Tollens’ reagent
