Carbonyl Compounds

Question 1

Reduction

Answer 1

Reagent: NaBH4 or LiAlH4
Both ketones and aldehydes produce alcohol

Question 2

Addition of HCN

Answer 2

Reagents: HCN
Conditions: KCN (catalyst)
Type of reaction: Nucleophilic addition
Hydroxynitrile is formed

Question 3

Why do we use KCN catalyst in the addition of HCN?

Answer 3

HCN is a weak acid, hence very weakly dissociated, hence produces a very low concentration of CN-. KCN is used as catalyst as it increases the concentration of CN-

Question 4

Reaction with 2,4-DNPH

Answer 4

Reagent: 2,4-dinitrophenylhydrazine
Type of reaction: condensation
Observation: Orande-red ppt is formed when a carbonyl is present

Question 5

Oxidation

Answer 5

Reagents: K2Cr2O7/H+ or KMnO4/H+
Conditions: heat
Aldehydes are oxidised causing the respective colour changes. No change with ketones

Question 6

Reaction with Tollens reagent

Answer 6

Reagent: Tollens reagent (AgNO3, NH3)
Conditions: warm
Aldehydes produce a silver mirror. Negative with ketones

Question 7

Reaction with Fehlings solution

Answer 7

Reagent: Fehlings solution (Cu2+ complex)
Conditions: warm
Blue solution to brick red ppt (Cu2O) is produced with aldehyde. Negative with ketone

Question 8

The tri-iodomethane reaction

Answer 8

Reagent: I2(aq), NaOH
Tri-iodomethane is formed with a methylketone

Question 9

Reactions that produce carbonyl compounds

Answer 9

1) Oxidation of primary and secondary alcohols