Question

3. For the bromination of acetanilide: a. Which product did you get? Whatevidence do you have for this? b. Was your product pure? Whatevidence do you have for this? Explain your evidence. C. Draw the mechanism for the product you got. d. Calculate percent yield. Show your work.

Answer 1

For the Bromination of acetanilide :

a) The product we get is p-bromoacetanilide . Bromination occurs only at the para position, as the substitution of bromine deactivates the benzene ring - withdraws electrons from the ring and therefore stops the resonance at the para position. In addition to take the ortho position the electrophile would face steric hindrance due to the large substituent e.g. amide,thus we can confirm that p-bromoacetanilide is formed

.

N. Br2 FeBr3 Br Acetanilide Brominated-Acetanilide

b) No ,the yeild was not pure .The practical yield was63.09 %.The melting points of the product was found to be lower than stated because it was not pure.

c) Mechanism for the the formation of p-bromoacetanilide :

Н-N— Н-Ў— Н-N— CH CH3 CH3 Br-Br Вr HBr Н Br Br

i)  A molecule of bromine reacts with the FeBr3 and when this happens, one of the bromine atoms has a positive charge.

ii) The  pair of electrons located inside the benzene ring of acetanilide acts as our nucleophile (source of electrons) and attacks the electrophilic bromine intermediate.