Download - 10.3.4 REDUCTION REACTION
10.3.4 REDUCTION REACTIONS
Reduction of aldehydes, ketones and carboxylic acids
• Common reducing agents are :*lithium aluminium hydride (LiAlH4) *Sodium borohydride (NaBH4)
• LiAlH4 are the stronger reducing agent • Can be used to reduce carboxylic acids,
aldehydes and ketones• NaBH4 only strong enough to reduce
aldehydes and ketones • NaBH4 is much easier to use than LiAlH4 and
usually preferred for the reduction of aldehydes and ketones
ALDEHYDES BASIC REACTION :
NaBH4 Aldehydes primary alcohol
methanol
RH
OR
H
OH+ [H]
Examples
CH3 O [H]+CH3
OHEthanal Ethanol
O
[H]+
OH
benzaldehyde benzylalcohol
• A balanced equation for the reaction can be written using [H] to represent hydrogen from reducing agent:
CH3CHO + 2[H] CH3CH2OH
Ketones BASIC REACTION :
NaBH4 ketone secondary alcohol
methanol
NaBH4
methanol
Carboxylic acidsBASIC REACTION :
(i) LiAlH4 in ethoxyethaneCarboxylic acids primary alcohol
(ii) H+/H2O
(i) LiAlH4 in ethoxyethane
(ii) H+/H2O
• This can also be written as a balanced equation using [H] to represent hydrogen from the reducing agent:
• CH3COOH +4[H] CH3CH2OH + H2O
If you need to make an aldehyde from a carboxylic acids, the carboxylic acids must be reduced to a primary alcohol using LiAlH4 and then the primary alcohol must be oxidised back to an aldehyde . (partial oxidation with distillation)
Reduction of nitrobenzene
• First step could be written as :C6H5NO2 + 6[H] + H+ C6H5NH3
+ + 2H2O• And the second as :C6H5NH3
+ + OH- C6H5NH2 + H2O
BASIC REACTION :
(i) Sn/ conc. HCl HEATNitrobenzene + 6[H] phenylamine aniline
(ii) NaOH