7.4.2 Production of Phenol

• Phenols are organic compounds characterised by the presence of an -OH group which is attached to a benzene ring
• Phenols can be produced by the reaction of phenylamine with nitrous acid (HNO₂)

Production of phenol

• Phenols can be prepared from phenylamines under the following reaction conditions:
  • NaNO₂ with dilute acid (to form HNO₂)
  • Ice to keep the temperature below 10 ^oC (step 1)
  • Heat (step 3)

• This reaction involves three steps:
  • Step 1 - The HNO₂ is so unstable that it needs to be prepared in a test-tube by reacting sodium nitrite (NaNO₂) and dilute hydrochloric acid (HCl) while keeping the temperature below 10 ^oC using ice

Nitrous acid can be prepared in a test-tube by reacting sodium nitrate with dilute hydrochloric acid

• • Step 2 - Phenyl amine is then reacted with the HNO₂ to form an unstable diazonium salt

Formation of an unstable diazonium salt

• • Step 3 - The diazonium salt is so unstable that it will thermally decompose when heated to form a phenol

A phenol is formed upon the thermal decomposition of the diazonium salt