3.3.8 Aldehydes and Ketones

• The reduction of pentan-2-one produces pentan-2-ol, the product has no optical activity so it won't rotate plane polarised light. This is because

  > The C=O bond is planar

  > So the hydride nucleophile attacks the C+ equally from above and below

  > This produces equal amounts of the enantiomers

  > Which produces a racemic mixture
• Aldehydes and Ketones are reduced by the reducing agents [H] to produce alcohols:

  > LiAlH4 in ether

  > NaBH4 aqueous
• A nucleophile is a species which donates a lone pair of electrons
• Nucleophilic Addition:

  Hydrogen Cyanide is a very toxic gas and it can lead to death

  Instead a solution of potassium cyanide and dilute sulphuric acid is used to produce HCN
• The hydride ion from NaBH4 is nucleophile which is attracted to regions of positive charge like the C=O in 2-methyl butanal. Hover 2-methylbut-1-ene the C=C is electron rich so the hydride ion is repelled from C=C in 2-methyl but-1-ene
• Fractional Distillation

  A) Heat

  B) Anti-bumping granules

  C) thermometer

  D) Water out

  E) Water in

  
• Reflux

  A) Water out

  B) Water in

  C) Condenser

  D) anti-bumping granules

  E) ice water

  
• Anti-bumping granules prevent explosive boiling, as they provide a large surface area for bubbles to form on.
• Nucleophilic Addition - Aldehyde/ Ketone

  Condition: aqueous

  Reagent: NaBH4 (Source of :H-)

  Forms: Aldehyde -> 1° alcohol , Ketone-> 2° alcohol

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  Condition: Alcoholic

  Reagent: KCN followed by dilute acid

  Forms: 2-hydroxynitrile
• Advantage of using KCN or NaCN is that there will be a higher concentration of the CN- ion as these compounds will completely ionise. HCN is a weak acid an will only partially ionise.

  You can use HCN for this reaction but it is a toxic gas that is difficult to contain. KCN/NaCN are still, however, toxic, because of the cyanide ion.