Aldehydes and Ketones Flashcards
What is the functional group in aldehydes and ketones?
Carbonyl group, C=O
Where is the functional group on a ketone?
Not on the end
Where is the carbonyl on an aldyhyde?
On the end
How are aldehydes made? Are they readily oxidised?
The oxidation of primary alcohols. They are readily oxidised.
How are ketones made?
The oxidation of secondary alcohols. Ketones are not readily oxidised
How can you distinguish between aldyhydes and ketones? ( . )( . )
1) Aldehydes are readily oxidised by oxidizing agents such as acidified potassium dichromate (Kr2Cr207) to form carboxylic acids. Ketones are not.
During this reaction there is a colour change from orange to green as the dichromate (VI) ions are reduced to chromium (III) ions.
2) Tollens’ reagent: When added to an aldehyde then gently warmed in a water bath at around 60 degrees, the aldehyde forms a carboxylic acid and the silver ions are reduced to silver atoms, forming a silver mirrior. If a ketone is heated with tollens reagent
Tollens reagent
Contains ammonical silver nitrate (AgNO3). When it is added to an aldehyde then heated around 60 degrees the aldehyde is oxidized to a carboxylic acid and the silver ions are reduced to silver atoms forming a silver mirror.
Reduction of aldehydes
Aldehydes can be reduced to primary alcohols by a reducing agent such as sodium borohydride (NaBH4). The reducing agent is added and then heated under reflux. Water or ethanol can be used as solvents
Reduction of ketons
Ketones can be reduced by reducing agents such as sodium borohydrate. They are reduced to secondrary alcohols
Oxiation can be described as:
1) loss of electrons
2) gain of oxygen atoms
3) loss of hydrogen atoms
Reduction can be described as:
1) gain of electrons
2) loss of oxygen atoms
3) gain of hydrogen atoms
What kind of reactions does the carbonyl group undergo?
It is polar and undergoes nucleophilic addition reactions
2,4-DNP
It is used to test for the presence of a carbonyl group.
Aldehydes and ketones both react with 2,4-DNP.
Brady’s reagent
Brady’s reagent is a solution of 2,4-DNP in methanol and sulfuric acid.
When it is added to an organic compounds that contains a carbonyl group an organge or yellow ppt. is formed
How can Brady’s reagent be used to identify an aldehyde or ketone?
The yellow or orange precipitate formed must be purified by recrystalization
The melting point of the ppt is detemined
The melting point is compared to other 2,4-DNP derivatives to positively identify the aldehyde or ketone.
BMT.
