Slide 1

  • Cannizzaro reaction
    • A disproportionation reaction of aldehydes
    • In the presence of strong alkali, aldehydes can undergo self-oxidation and self-reduction simultaneously
  • Examples
    • Formaldehyde
    • Benzaldehyde

Slide 2

  • Reaction mechanism
    • The reaction proceeds via two steps: the nucleophilic attack and the hydride transfer
  • Step 1: Nucleophilic attack
    • The carbonyl carbon of the aldehyde is attacked by the hydroxide ion, resulting in the formation of a carboxylic acid anion and an alcohol
  • Step 2: Hydride transfer
    • A hydride ion is transferred from the aldehyde to the carboxylic acid anion
    • This results in the formation of a carboxylic acid and an alcohol

Slide 3

  • Reaction conditions
    • The Cannizzaro reaction occurs in the presence of strong alkali
    • Strong alkali provides the necessary hydroxide ions for the nucleophilic attack
  • Examples
    • Sodium hydroxide (NaOH)
    • Potassium hydroxide (KOH)

Slide 4

  • Limitations of Cannizzaro reaction
    • Only aldehydes without α-hydrogens can undergo the Cannizzaro reaction
    • Aldehydes with α-hydrogens cannot undergo the Cannizzaro reaction because they can undergo aldol condensation instead
  • Examples
    • Benzaldehyde can undergo the Cannizzaro reaction
    • Formaldehyde can undergo the Cannizzaro reaction as it does not have α-hydrogens

Slide 5

  • Use of Cannizzaro reaction
    • Cannizzaro reaction can be used for the preparation of carboxylic acids and alcohols
  • Examples
    • Benzoic acid can be prepared from benzaldehyde through the Cannizzaro reaction
    • Methanol can be obtained from formaldehyde through the Cannizzaro reaction

Slide 6

  • Application in industry
    • The Cannizzaro reaction is commonly used in the production of soap and detergents
    • The reaction is employed to convert fatty acids into soap and alcohol
  • Example equation
    • Stearic acid + Sodium hydroxide -> Sodium stearate (soap) + Ethanol

Slide 7

  • Stereoselectivity
    • The Cannizzaro reaction can exhibit stereoselectivity depending on the structure of the aldehyde
    • In aldehydes with chiral centers, one enantiomer is usually favored over the other
  • Example
    • Chiral aldehyde with two different substituents on the carbonyl carbon can undergo stereoselective Cannizzaro reaction

Slide 8

  • Factors influencing reaction rate
    • Concentration of the aldehyde
    • Concentration of the alkali
    • Temperature
  • Higher concentrations and higher temperature generally result in faster reaction rates

Slide 9

  • Comparison with other reactions
    • Cannizzaro vs. Aldol condensation
      • Cannizzaro: Aldehydes without α-hydrogens
      • Aldol condensation: Aldehydes with α-hydrogens
    • Cannizzaro vs. Reduction
      • Cannizzaro: Self-oxidation and self-reduction of aldehydes
      • Reduction: Conversion of aldehydes to alcohols using reducing agents like LiAlH4
    • Cannizzaro vs. Nucleophilic addition
      • Cannizzaro: Aldehydes reacting with strong alkali
      • Nucleophilic addition: Aldehydes reacting with other nucleophiles like ammonia or primary amines

Slide 10

  • Summary
    • The Cannizzaro reaction is a disproportionation reaction of aldehydes in the presence of strong alkali
    • It involves nucleophilic attack and hydride transfer steps
    • Only aldehydes without α-hydrogens can undergo the Cannizzaro reaction
    • The reaction is used for the preparation of carboxylic acids and alcohols
    • It has applications in the soap and detergent industry

Slide 11

  • Application in synthesis of pharmaceuticals
    • The Cannizzaro reaction is utilized in the synthesis of various pharmaceutical compounds
    • It can be employed to introduce functional groups or modify the structure of specific molecules
  • Use in the production of fragrances
    • Certain fragrances can be synthesized using the Cannizzaro reaction
    • This reaction allows for the transformation of aldehydes into alcohols or carboxylic acids, which are important components in fragrance synthesis
  • Conversion of aldehydes in the food industry
    • In food processing, the Cannizzaro reaction can be employed to convert aldehydes into more desirable compounds
    • This can help improve the taste, aroma, or stability of food products
  • Scope and limitations in various industries
    • While the Cannizzaro reaction finds applications in several industries, its use may be limited by factors such as reaction conditions and the specific requirements of the desired product
  • Importance in understanding reaction mechanisms
    • Studying the Cannizzaro reaction provides valuable insights into reaction mechanisms, particularly those involving carbonyl compounds
    • Understanding these mechanisms can aid in the prediction and analysis of other chemical reactions

Slide 12

  • Brief review of key concepts
    • Nucleophilic attack: Electrophilic carbon of the aldehyde is attacked by the nucleophile
    • Hydride transfer: A hydride ion is transferred from the aldehyde to the carboxylic acid anion
    • Disproportionation: Simultaneous oxidation and reduction of the same species
  • Factors influencing reaction rate
    • Concentration of reactants: Higher concentrations generally result in faster reaction rates
    • Temperature: Higher temperatures provide more energy for the reaction, increasing the rate
    • Catalysts: Certain catalysts can enhance the rate of the Cannizzaro reaction
  • Stereochemistry of the Cannizzaro reaction
    • Chiral aldehydes can undergo the Cannizzaro reaction with varying stereoselectivity
    • The resulting products may exhibit stereoisomerism
  • Comparison with other reactions
    • Cannizzaro vs. Aldol condensation
      • Cannizzaro: Aldehydes without α-hydrogens; produces carboxylic acids and alcohols
      • Aldol condensation: Aldehydes with α-hydrogens; leads to the formation of β-hydroxy aldehydes or ketones
  • Comparison with other reducing agents
    • Cannizzaro vs. Reduction using LiAlH4
      • Cannizzaro: Self-oxidation and self-reduction simultaneous; converts aldehydes to carboxylic acids and alcohols
      • LiAlH4 reduction: Uses reducing agents to convert aldehydes to alcohols

Slide 21

  • Sample problem 1: Predict the products of the following Cannizzaro reaction
    1. Benzaldehyde + Sodium hydroxide

Slide 22

  • Sample problem 1: Solution
    • Benzaldehyde undergoes disproportionation in the presence of sodium hydroxide.
    • The reaction products are:
      1. Benzoic acid
      2. Benzyl alcohol

Slide 23

  • Sample problem 2: Predict the products of the following Cannizzaro reaction
    1. Butanal + Potassium hydroxide

Slide 24

  • Sample problem 2: Solution
    • Butanal undergoes disproportionation in the presence of potassium hydroxide.
    • The reaction products are:
      1. Butanoic acid
      2. Butanol

Slide 25

  • Sample problem 3: Predict the products of the following Cannizzaro reaction
    1. Hexanal + Sodium hydroxide

Slide 26

  • Sample problem 3: Solution
    • Hexanal undergoes disproportionation in the presence of sodium hydroxide.
    • The reaction products are:
      1. Hexanoic acid
      2. Hexanol

Slide 27

  • Sample problem 4: Predict the products of the following Cannizzaro reaction
    1. Propanal + Sodium hydroxide

Slide 28

  • Sample problem 4: Solution
    • Propanal undergoes disproportionation in the presence of sodium hydroxide.
    • The reaction products are:
      1. Propanoic acid
      2. Propanol

Slide 29

  • Sample problem 5: Predict the products of the following Cannizzaro reaction
    1. 2-Methylpropanal + Sodium hydroxide

Slide 30

  • Sample problem 5: Solution
    • 2-Methylpropanal undergoes disproportionation in the presence of sodium hydroxide.
    • The reaction products are:
      1. 2-Methylpropanoic acid
      2. 2-Methylpropanol