ALDEHYDES AND KETONES Flashcards
What functional group do both aldehydes and ketones have
Carbonyl, C=O
What is the difference between an aldehyde and a ketone
The positioning of the carbonyl group
Where is the carbonyl group on an aldehyde
At an end carbon
Where is the carbonyl group on a ketone
On an inner carbon
What do aldehydes end in
-al
What do ketones end in
-one
How are aldehydes oxidized
Readily
How are ketones oxidized
They cannot be oxidized
Show the oxidation of both an aldehyde and a ketone
…
What test can distinguish between aldehydes and ketones
Tollen’s silver mirror test
How is Tollen’s reagent made
Silver nitrate is added to a test tube. A few drops of sodium hydroxide is added, forming a pale brown precipitate. Add a few drops of dilute ammonia until the precipitate dissolves.
How do you use Tollen’s to test for aldehydes
Add sample to a test tube of Tollen’s reagent, then place in a hot water bath. Observe the formation of a silver mirror on the test tube to confirm the presence of an aldehyde
What is the formula of Tollen’s reagent
[Ag(NH3)2]+
Why do we not use a Bunsen flame when doing the silver mirror test
Aldehydes and ketones are flammable
What is Tollen’s reagent
An oxidizing agent
What other than Tollen’s can be used to test for aldehydes
Fehling’s solution
What color is fehlings solution and why
Blue as it contains cu2+ ions
How do you test for aldehydes using fehlings solution
Warm it up in the presence of a sample. If aldehydes are present, the solution will go from blue to forming brick red precipitate. If ketones are present, there will be no reaction.
What does fehlings solution consist of
Cu2+ ions dissolved in sodium hydroxide
What reducing agents can be used to reduce aldehydes and ketones
Sodium borohydride (NaBH4) or sodium tetrahydridoborate(iii) dissolved in methanol and water
What are aldehydes reduced to, and show the reduction formula
Primary alcohols
What are ketones reduced to, and show the reduction formula
Secondary alcohols
What does a reducing agent produce to reduce aldehydes and ketones to alcohols
Hydride ions
Show the mechanism for the reduction of an aldehyde and ketone into an alcohol
What type of mechanism is the reduction of an aldehyde or ketone
Nucleophilic addition
Where does the H+ ion come from in the reduction of an aldehyde or ketone to an alcohol
The water or acid that was added to the reducing agent at the start
What is formed when potassium cyanide reacts with carbonyl compounds such as aldehydes or ketones, and what type of reaction is this
Hydroxynitriles are produced, nucleophilic addition
How is potassium cyanide used to produce CN- ions
When dissolved in acidic solution, it dissociates to form K+ and CN- ions. KCN -> K+ + CN-
What can be used as a substitute for potassium cyanide when trying to produce a hyrdoxynitrile from aldehydes or ketones, and how is the preparation of this reaction different
Hydrogen cyanide, no acid is required
Show the mechanism for the reaction of an aldehyde with potassium cyanide
What is produced if we used unsymmetrical ketones or aldehydes in the reaction with potassium cyanide
A mixture of enantiomers is produced
How is hydrogen cyanide produced
When potassium cyanide combines with moisture
Why is potassium cyanide dangerous
It is an irritant and very dangerous if ingested or inhaled
What precautions must be taken when using potassium cyanide
Wear gloves whilst handling
Use a fume cupboard
Wear a lab coat
What is the overall generic equation for the reaction of an aldehyde with potassium cyanide
RCHO (aq) + KCN (aq) + H+ (aq) -> RCH(OH)CN(aq) + K+ (aq)
What is the overall generic equation for the reaction of a ketone with potassium cyanide
RCOR(aq) + KCN(aq) + H+ (aq) -> RCR(OH)CN(aq) + K+(aq)
What are aldehydes oxidized into
Carboxylic acids
Why can enantiomers be formed by nucelophilic addition
The carbonyl group is planar, so the nucleophile can attack from above or below the plane of this carbonyl group leading to 2 isomers
