Reaction of Carbonyl Compounds

Reaction of Carbonyl Compounds.

1. Reduction: react with H2, catalyst Ni, 180°C.
aldehyde, RCHO –> 1° ROH
*when using LiAlH4 (lithium aluminium hydride) in dry ether at 0°C, then hot, dilute acids, very powerfull reducing agent. aldehyde, RCHO –> RCOOH.

ketone, ROR –> 2° ROH

2. Condensation:
Reaction with 2,4-dinitro phenylhydrazine in methanol & H2SO4. Brady’s reagent. Chemical test.
Observation: yellow-orange precipitate.
aldehyde: +ve,
ketone: +ve,
carboxylic acid: -ve.

3. Addition with HCN:
Reaction aldehyde/ ketone with HCN or KCN, dilute H2SO4 or NaOH. 10-20°C to form cyanohydrin. add more carbon atom to the carbon chain.

RCHO + HCN + H2SO4 –> RCHCN(OH) (cyanohydrin)+ H+ + H2O –> RCH(OH)COOH (hydroxycarboxylic acids) + NH4+.

4. Oxidation:
Reaction with KMnO4/ H+/OH-.
1. Aldehyde [O]/H+ –> carboxylic acid.
2. Aldehyde [O]/OH- –> salt of carboxylic acid RCOO- + H2O (H+) –>  carboxylic acid.
3. Ketone [O] –> No reaction. under normal conditon.
4. Ketone [O] –> CO2 (loss of carbon atom). boiled for a long time.

5. Reaction with Tollens’s Reagent (Ag(NH3)2]+/ Silver mirror test, produce Ag.

Aldehyde + OH-, heat –> RCOO- (salt carboxylic acid) + Ag (silver mirror) + NH3 + H2O.

Ketones –> no change.
Benzaldehyde –> +ve test.

6. Reaction with Fehling’s solution, NaOH, Cu2+.

RCHO + 2Cu2+ + OH- + H2O heat–> RCOO- + CuO (copper (ii) oxide, brick-red ppt) + 4H+

ketone and benzaldehyde –> negative test.

7. Reaction with Triiodomethane (iodoform). Keyword = ADJACENT (-CH3 adjacent with C=O). +ve = yellow ppt.
aldehyde (only ethanal) –> +ve
ketone –> +ve
CH3CHO + 3I2 + NaOH –> CHi3 + CHOONa + 3Nai + 3H2O.

8. Reaction with RMgBr (grignard reagent).

RCHO + RMgBr + H2O –> ROH + Mg(OH)Br.

aldehyde (methanal only) –> 1° ROH.
other than methanal –> 2° ROH.
Ketone –> 3° ROH.

=O will become -OH, carbon that contain =O, double bond O will attach with R from RMgBr.

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