10.3.4 REDUCTION REACTION

10.3.4 REDUCTION REACTION

• 1.
  10.3.4 REDUCTION REACTIONS Reductionof aldehydes, ketones and carboxylic acids
• 2.
  • Common reducingagents are : *lithium aluminium hydride (LiAlH4) *Sodium borohydride (NaBH4)
• 3.
  • LiAlH4 arethe 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
• 4.
  ALDEHYDES BASIC REACTION : NaBH4 Aldehydesprimary alcohol methanol R H O R H OH + [H]
• 5.
  Examples CH3 O [H]+ CH3 OH EthanalEthanol O [H]+ OH benzaldehyde benzylalcohol
• 6.
  • A balancedequation for the reaction can be written using [H] to represent hydrogen from reducing agent: CH3CHO + 2[H]  CH3CH2OH
• 7.
  Ketones BASIC REACTION : NaBH4 ketonesecondary alcohol methanol NaBH4 methanol
• 8.
  Carboxylic acids BASIC REACTION: (i) LiAlH4 in ethoxyethane Carboxylic acids primary alcohol (ii) H+/H2O (i) LiAlH4 in ethoxyethane (ii) H+/H2O
• 9.
  • This canalso 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)
• 10.
  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 HEAT Nitrobenzene + 6[H] phenylamine aniline (ii) NaOH