Hydride Reductions of Ketones

1
Hydride Reductions of Ketones

• Our Goals Today
• Learn the mechanism for the reduction of a
  carbonyl using sodium borohydride.
• Run several hydride reduction reactions.
• Learn how to use TLC to gauge reaction progress.
• Learn how to prepare a GCMS sample.

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Sodium Borohydride

• Can be thought of as a hydride source.
• Nucleophillic B-H bonds.
• Moisture sensitive.

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Ketone Reduction Mechanism

• Nucleophilic hydride attacks the carbonyl
  carbon.
• Ketone ? alcohol.

4
Stereochemistry of the Reduction

• Hydride can attack one face of the carbonyl or
  the other.
• Facial selectivity can happen depending on
  steric bulk around the carbonyl.
• Without this selectivity, both stereroisomers
  can form.

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The TLC Reactions
acetophenone
sec-phenethyl alcohol
cis
trans
cyclohexanone
cyclohexanol

• Run each reaction according to the lab manual.
• Check the reaction via TLC.

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Reaction Progress via TLC
Reaction Co-Spot Starting Material
Reaction Co-Spot Authentic Product

• Run two plates for each reaction (acetophenone
  and cyclohexanone).
• Elution solvent 41 hexane / ethyl acetate.
• Visualize first with UV then using
  p-Anisaldehyde stain.

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The GCMS Reactions
isoborneol
borneol
camphor
norcamphor

• Run each reaction according to the lab manual.
• Prepare GCMS vial with reaction mixture. Will
  be checking the reaction via GCMS.

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Gas Chromatography-Mass Spectroscopy

• Hybrid method of gas chromatography and mass
  spectroscopy.
• Can be used to compare a reaction mixture and
  identify components via comparison to standards.
• You will submit your vials for GCMS analysis
  for the reduction of camphor and norcamphor.
• Make sure to extract your samples into heptane
  and then filter your GCMS sample into your vial
  using a pipette filter.

T2
T1
Time
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Your Task

• Use sodium borohydride to reduce acetophenone and
  cyclohexanone.
• Analyze these reactions via TLC.
• Use sodium borohydride to reduce camphor and
  norcamphor
• Analyze these reactions via GCMS

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Advisory

• Do not cross contaminate.
• Use only designated pippetors with each stock
  solution.
• Sodium borohydride is moisture sensitive.
• Sodium borohydride can be a skin irritant.
• Make sure to visualize your TLC plates with UV
  before staining them.
• Make sure you filter you GCMS samples.
• Clean up after yourselves!