Here's the breakdown:
1. Addition of the first bromine molecule:
* Acetylene's triple bond is electron-rich and susceptible to electrophilic attack.
* Bromine (Br₂) is a weak electrophile, but its polarization in the presence of the triple bond allows one bromine atom to act as an electrophile.
* This bromine atom attacks the acetylene, forming a bromonium ion intermediate.
* The other bromine atom, now negatively charged, attacks the bromonium ion, opening the ring and forming a trans-dibromoethylene molecule.
2. Addition of the second bromine molecule:
* The resulting trans-dibromoethylene still has a double bond.
* The reaction can continue, with another bromine molecule adding to the double bond in the same manner as above.
* This results in the formation of tetrabromoethane (C₂H₂Br₄).
Overall reaction:
C₂H₂ + 2Br₂ → C₂H₂Br₄
Summary:
* The reaction proceeds in two steps, with the addition of one bromine molecule at a time.
* The initial product is trans-dibromoethylene, which is further brominated to form tetrabromoethane.
* The reaction is stereospecific, meaning the bromine atoms add to the same side of the molecule, forming the trans isomer.
Important Note: The reaction conditions play a role in determining the final product. At low temperatures, the reaction will stop after the first addition step, producing trans-dibromoethylene. At higher temperatures, the second addition step will occur, leading to the formation of tetrabromoethane.
