26.4    Reactions of  Phenols

Reaction with sodium metal, Na

• Reagent     : Sodium metal, Na
  Condition  :  Room temperature
  Product    : Alkoxides and hydrogen gas
• Like alcohols, phenol will react with a reactive metal such as sodium to give sodium phenoxide and hydrogen gas
  2C6H5OH + 2Na → 2C6H5O⁻Na⁺ + H2

• The observation is that the sodium sinks and bubbles of hydrogen gas is produced. This reaction is more vigorous than the one with alcohol because phenol is more acidic

 

Reaction with sodium hydroxide, NaOH

• Reagent     :  Sodium  hydroxide, NaOH solution
  Condition  :  Room temperature
  Product      : Alkoxides and water
• Phenol is a strong enough acid to react with sodium hydroxide solution to give sodium phenoxide and water
  C6H5OH + NaOH → C6H5O⁻Na⁺ + H2O

• Since alcohols will not react with sodium hydroxide, this can be used as a test to distinguish alcohols from phenols

 

• However, phenol will not react with sodium carbonate and sodium hydrogencarbonate because it’s not acidic enough to react with these

 

Halogenation

• Reagent     :  Chlorine gas/bromine water
  Condition  :  Room temperature
  Product      :   2,4,6-trihalophenol

• Phenol will react with halogens even without the presence of halogen carriers. This proves that phenol is more reactive than benzene itself

 

• Take bromine as an example, 2,4,6-tribromophenol is produced

• The observations are:
  1. The reddish-brown of bromine decolourises
  2. A white precipitate is formed, this is 2,4,6-tribromophenol.
  3. Steamy fumes of hydrogen bromide is observed

 

Nitration

• Reagent     : Nitric acid, HNO3
  Condition : Room temperature
  Product              : Nitrophenols
•  Unlike benzenes, concentrated sulfuric acid is not needed for nitration to This proves that phenol is more reactive than benzene itself.
• 1. With dilute nitric acid, mono-substituion occurs. 2-nitrophenol and 4-nitrophenol is produced
  2. With concentrated nitric acid, tri-substituion occurs. 2,4,6-trinitrophenol is produced.

 

Tri-iodomethane(iodoform)  test  for alcohols

• This is a test used to identify the presence of CH3CH(OH)- group in an alcohol. The R can be a hydrogen or an alkyl group
• 1. Iodine solution is added to a small amount of an alcohol, followed by just enough sodium hydroxide solution to remove the colour of the iodine
  2. If the alcohol contains the CH3CH(OH)- group, then a pale yellow precipitate of tri-iodomethane, CHI3 is produced.
• 1. Ethanol is the only primary alcohol to give the tri-iodomethane (iodoform) reaction
  2. If R is a hydrocarbon group, then you have a secondary alcohol. Lots of secondary alcohols give this reaction, but those that do all have a methyl group attached to the carbon with the -OH group
  3. No tertiary alcohols can contain this group because no tertiary alcohols can have a hydrogen atom attached to the carbon with the -OH No tertiary alcohols give the triiodomethane (iodoform) reaction.

• The flow scheme is as such:

• The overall equation is:

 

Tri-iodomethane(iodoform) test for carbonyl   compounds

• This is a test used to identify the presence of CH3CO- group in carbonyl compounds. The R can be a hydrogen or an alkyl group
• 1. Iodine solution is added to a small amount of an alcohol, followed by just enough sodium hydroxide solution to remove the colour of the iodine
  2. If the alcohol contains the CH3CH(OH)- group, then a pale yellow precipitate of tri-iodomethane, CHI3 is produced.
• 1. Ethanal is the only aldehyde to give the triiodomethane(iodoform) reaction.
  2. If R is a hydrocarbon group, then you have a ketone. Lots of ketones give this reaction, but those that do all have a methyl group on one side of the C=O bond.

• The overall equation is: