Synthesis of Erythro9,10Dihydroxystearic Acid

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Synthesis of Erythro-9,10-Dihydroxystearic Acid
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Purpose

• To learn what is syn dihyroxylation.
• To do a syn dihyroxylation reaction a compound
  containing carbon carbon double bond.

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Introduction

• Hydroxylation reaction means introduction of OH
  group.

4
Introduction

• Two types of hydroxylation is known for the
  compound which has carbon carbon double bond.
• 1. SYN HYDROXYLATION
• (both OH groups are in same side)
• 2. ANTI HYDROXYLATION
• (both OH groups are in opposite side)

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Introduction

• There are many reagents to available to do the
  hydroxylation on double bonds.
• 1. MCPBA followed by hydrolysis.
• 2. KMnO4 / H2O
• 3. OsO4 / H2O

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Mechanism for MCPBA

• Epoxide is the intermediate.
• MCPBA always leads anti- dihydroxylation.

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Mechanism for OsO4

• Osmium complex is the intermediate.
• OsO4 always leads syn- dihydroxylation because
  osmium cannot form complex in other direction.

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Mechanism for KMnO4

• Manganese complex is the intermediate here.
• KMnO4 always leads syn- dihydroxylation because
  manganese cannot form complex in other direction
  like osmium.

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Todays Task

• We will be using Oleic acid as starting material.
• Alkaline potassium permanganate will be used as a
  reagent for hydroxylation.

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Why Alkaline KMnO4???

• We know that neutral KMnO4 is good oxidizing
  agent to convert carbon carbon double bond into
  hydroxyl derivative.
• 1. It is not stereospecific like alkaline
  KMnO4.
• 2. Yield is good in alkaline KMnO4.

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Procedure

• Take 0.5 g of oleic acid, 50 mL of water and 0.5
  g of sodium hydroxide in a 500 mL Erlenmeyer
  flask.
• Still well for some time and keep in an ice bath
  (5? C).

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Procedure

• Add 400 mL of cold water and 50 g of ice to it
  and maintain 5? C.
• Quickly add a solution containing 0.4 g of KMnO4
  in 40 mL of water with vigorous stirring.
• Continue stirring for 5 more minutes.

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Procedure

• Carefully add 15 mL of concentrated HCl with slow
  stirring.
• Add 3 H2O2 in drop wise with constant stirring
  till the decolorization occur.
• Why???
• To remove unreacted KMnO4

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Procedure

• Cool the mixture for 1 hour.
• Filter the precipitate and dry it using the
  suction pump itself.
• Weigh the crude product and find its of yield.

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Recrystallization

• Do the Recrystallization using ethanol (5 10
  mL).
• Find the of yield after Recrystallization.
• Find its melting point in next week.

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Notes

• You may get stains on your hand or your clothes
  when you use KMnO4.
• Just wash the stain with dilute aqueous hydrogen
  peroxide, acidified vinegar.

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DEPT NMR
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DEPT NMR

• 1H NMR informs about how many different kind of
  proton in a compound.
• From the intensity of 1H NMR spectrum, you can
  find how many protons in a compound.

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DEPT NMR

• 13C NMR tells you about how many different kind
  of carbon atom in your compound.
• You cannot interpret which signal belongs to CH3,
  CH2 and CH carbon atoms.

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DEPT NMR

• Distorsionless Enhancement by Polarization
  Transfer is called DEPT NMR.
• It is one of the most important techniques
  available for interpreting 1D 13C NMR spectra.

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DEPT NMR

• It is very useful technique to know which signals
  belong to
• 1. CH3 Carbon
• 2. CH2 Carbon
• 3. CH Carbon
• 4. Quaternary Carbon

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DEPT NMR

• Usually only one RF pulse will be used to record
  1H NMR.
• The novel feature in the DEPT sequence is a
  variable proton pulse that is set at 45?, 90?, or
  135? in three separate experiments.

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DEPT NMR

• A separate sub spectrum is recorded for each of
  the CH3, CH2 and CH groups.
• A broadband decoupled 13C NMR spectrum also
  acquired.

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DEPT NMR

• The CH3 and CH group peaks shows up.
• CH2 and quaternary carbons group peaks shows down.

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DEPT NMR
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DEPT NMR
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Lab Note Book

• We will be collecting the lab note book from 12 /
  5 / 2005 to 12 / 9 / 2005.