Reactions of Alcohols

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Reactions of Alcohols

• Alcohols can be converted into many other
  functional groups, including
• alkanes
• by reduction
• alkenes
• dehydration
• alkyl halides
• substitution
• aldehydes or ketones
• carboxylic acids
• esters
• ethers

by oxidation
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Reactions of Alcohols

• Oxidation
• loss of electrons
• increase of oxidation number
• addition of O or O2
• loss of H2
• addition of X2 (halogens)
• Oxidation reactions
• increase the number of oxygens bonded to a carbon
• increase the number of bonds between carbon and
  oxygen

Most important definitions for organic compounds
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Reactions of Alcohols

• Reduction
• gain of electrons
• decrease in oxidation number
• addition of H2 (or H-)
• loss of O or O2
• loss of X2
• Reduction reactions
• decrease the number of oxygens bonded to a carbon
• decrease the number of bonds between carbon and
  oxygen

Most important definitions for organic compounds.
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Reactions of Alcohols

• Example Classify the following reactions as an
  oxidation or reduction.

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Reactions of Alcohols

• Primary and secondary alcohols are easily
  oxidized by a variety of oxidizing agents.
• Substances that cause another to be oxidized
• Some of the common oxidizing agents for organic
  compounds include
• chromium reagents
• PCC (pyridinium chlorochromate)
• KMnO4
• HNO3
• NaOCl

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Reactions of Alcohols

• Oxidation of 1o Alcohols
• Depending on the oxidizing agent used, primary
  alcohols can be oxidized to either aldehydes or
  carboxylic acids
• The aldehyde that forms initially is easily
  oxidized to the carboxylic acid by many reagents

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Reactions of Alcohols

• Oxidation of 1o Alcohols to Aldehydes
• The following reagents convert a primary alcohol
  to the aldehyde without further oxidation.
• Pyridinium chlorochromate (PCC)
• Swerns oxidation
• DMP

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Reactions of Alcohols

• Pyridinium chlorochromate (PCC) is used to
  oxidize a 1o alcohol to the aldehyde
• Also oxidizes 2o alcohol to ketone (discussed
  later)

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Reactions of Alcohols

• Swern Oxidation is used to convert 1o ROHs to
  aldehydes (or 2o ROH to ketones)
• Conditions
• Dimethyl sulfoxide
• Oxalyl chloride
• Et3N
• CH2Cl2 (solvent)
• -60oC

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Reactions of Alcohols

• Dess-Martin Periodinane (DMP) can be used to
  oxidize a 1o ROH to an aldehyde (or 2o ROH to
  ketone)

DMP
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Reactions of Alcohols

• Examples

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Reactions of Alcohols

• Oxidation of 1o Alcohols to Carboxylic Acids
• Common Reagents
• Chromic acid reagent
• Na2Cr2O7/H2SO4 or K2Cr2O7/H2SO4
• CrO3
• NaOCl (aq)

or
or
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Reactions of Alcohols

• Examples

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Reactions of Alcohols

• Oxidation of 2o Alcohols
• 2o alcohols are converted to ketones
• The oxidizing agents that are used to oxidize
  primary alcohols can also be used to oxidize a
  secondary alcohol to a ketone
• Chromic acid reagent
• CrO3
• PCC
• Swern oxidation
• DMP

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Reactions of Alcohols

• Examples

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Reactions of Alcohols

• Examples Predict the major product.

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Reactions of Alcohols

• Other oxidizing agents can also be used to
  oxidize alcohols
• KMnO4 (aq), OH-
• cold HNO3
• Tertiary alcohols cannot be oxidized easily.
• No hydrogen present on carbinol carbon
• Oxidation would require breaking C-C bond
• severe conditions required

Must be carefully controlled because they can
also cleave C-C bonds.
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Reactions of Alcohols

• Dehydration of Alcohols
• removal of water, forming an alkenes
• equilibrium process
• drive reaction to completion by removing alkene
  as formed (LeChateliers Principle)

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Reactions of Alcohols

• Typical reaction conditions
• acid catalyst
• conc. H2SO4
• conc. H3PO4
• heat
• Saytzeffs product
• Rearrangements occur if a more stable carbonium
  ion can be formed.

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Reactions of Alcohols

• Mechanism of Dehydration (E1)
• Step 1 Protonation of the hydroxyl group (fast)
• Step 2 Ionization (RDS)

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Reactions of Alcohols

• Step 3 Deprotonation to form alkene

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Reactions of Alcohols

• Example Predict the major product formed in the
  following reactions.

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Reactions of Alcohols

• Williamson Ether Synthesis
• SN2 reaction between an alkoxide ion and an alkyl
  halide to form an ether.
• CH3CH2O- Na CH3I CH3CH2OCH3
• Alkyl halide must be primary or methyl.

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Reactions of Alcohols

• Williamson Ether Synthesis Mechanism

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Reactions of Alcohols

• Example Give the major product for the
  following reactions.