Chapter 11 Reactions of Alcohols

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Chapter 11Reactions of Alcohols
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Types of Alcohol Reactions
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1º, 2º, 3º Carbons
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Oxidation of 1 Alcohols

• 1 alcohol to aldehyde to carboxylic acid
• Difficult to stop at aldehyde
• Use pyridinium chlorochromate (PCC) to limit the
  oxidation.
• PCC can also be used to oxidize 2 alcohols to
  ketones.

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Oxidation of 2 Alcohols

• 2 alcohol becomes a ketone
• Reagent is chromic acid Na2Cr2O7/H2SO4
• 3? alcohols do not oxidize

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Other Oxidation Reagents

• Cr2O3 in pyridine
• KMnO4 in H2O (strong oxidizer)
• CuO, 300C (industrial dehydrogenation)
• Biological Oxidation- Catalyzed by ADH, alcohol
  dehydrogenase
• Ethanol oxidizes to acetaldehyde, then acetic
  acid, a normal metabolite.

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Alcohol as a Nucleophile

• ROH is weak nucleophile
• RO- is strong nucleophile
• New O-C bond forms, O-H bond breaks.
  
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Alcohol as an Electrophile

• -OH group is not a good leaving group unless it
  is protonated.
• Many nucleophiles not stable in acid solutions
• Convert to tosylate (good leaving group) to react
  with strong nucleophile (base)
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C-Nuc bond forms, C-O bond breaks
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Formation of Tosylate Ester
p-toluenesulfonyl chloride TsCl, tosyl chloride
ROTs, a tosylate ester
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Summary of Tosylate Reactions
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Reduction of Alcohols

• Dehydrate with conc. H2SO4, then add H2
• Tosylate, then reduce with LiAlH4

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Reaction with HBr

• -OH of alcohol is protonated
• -OH2 is good leaving group
• 3 and 2 alcohols react with Br- via SN1
• 1 alcohols react via SN2

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Dehydration Reactions

• Conc. H2SO4 produces alkene
• Carbocation intermediate
• Saytzeff product
• Bimolecular dehydration produces ether
• Low temp, 140C and below, favors ether
• High temp, 180C and above, favors alkene
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Dehydration Mechanisms
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Energy Diagram, E1
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Esterification

• Acid Alcohol yields Ester Water
• acid is catalyst.
• Each step is reversible.

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Tosylate Esters

• Alcohol p-Toluenesulfonic acid, TsOH
• Acid chloride is actually used, TsCl

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Nitrate Esters
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Phosphate Esters
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Phosphate Esters in DNA
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Double Helix of DNA

• Two complementary polynucleotide chains are
  coiled into a helix.
• Described by Watson and Crick, 1953.

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Williamson Ether Synthesis