Hydration of Alkynes Quiz

Hydration of Alkynes

• Alkynes undergo acid-catalyzed hydration, adding water across the triple bond.
• Mercuric ion acts as a catalyst, often using mercuric sulfate in aqueous sulfuric acid.
• Hydration resembles that of alkenes and follows Markovnikov's rule, where the more substituted carbon gets the higher electron density.
• Enol formation occurs through tautomerization, leading to the corresponding aldehyde or ketone.
• For terminal alkynes like acetylene, the product is an aldehyde.
• Higher alkynes yield a ketone after hydration.
• Example reactions:
  • $H-C\equiv C-H$ (ethyne) + $H-OH$ → Vinyl alcohol ($CH_{2}=CH-OH$).
  • $H-C\equiv C-CH_{3}$ (propyne) + $H-OH$ → Propen-1-ol ($CH_{2}=C(OH)-CH_{3}$).

Halogenation (Bromination) of Alkynes

• Bromine reacts with alkynes in a two-step process, first forming dibromoalkene (primarily in trans configuration), followed by formation of tetrabromides.
• Reaction occurs in carbon tetrachloride ($CCl_{4}$):
  • $H-C\equiv C-H$ + $Br-Br$ → 1,2-dibromoethene.
  • $HC\equiv CH$ + $Br-Br$ → 1,2-dibromoethene.
• Chlorination follows a similar mechanism to bromination.

Ozonolysis of Alkynes

• Alkynes react with ozone, resulting in the formation of ozonides.
• Ozonides can be subsequently treated with water to generate 1,2-dicarbonyl compounds.
• The reaction produces hydrogen peroxide as a byproduct.