Question

Lab was done on bromination of acetanilide, aniline, anisole.

One of three compound was dissolved in glacial acetic acid. Bromine/hydrobromic acid mixture was added and continue to stir for 20minutes (for anisole heat the reaciton at 80C for 40minutes)

afther 20 minutes, trasnfer the mixture to a flask containing water and satuarted sodium bisulife solution. Place it in ice bath and let it crystalize. Do recrystalizaiton.

1. If the yield was low, explain the reason for the low yield (NOT including human error)

2. When identification of the product based on melting point and NMR differs, why they might differ and which technique you have more confidence in.

Answer 1

1. All the reactions carried out under mild conditions low concentration of bromination will give good yield.

If the yield was low, the reason is bromination reactions will undergo radical substitute reactions. Hence bromine radical is less reactive than chlorine radical.

Some time bromination reactions will undergo nucleophilic substitution reactions, in this case bromine anion is more selective to react and prefers to react weak R-H bonds

Bromination of acetanilide is electrophilic substitution reaction.

In case of bromination of anisole, for good yield must be add glacial acetic acid and FeBr3

Bromination of aniline is electrophilic aromatic substitutions reaction. In this reaction steric effects in amide will leads to low yield of ortho product with para products

2) the identification of the product will give good results with NMR than melting point. Because in NMR spectroscopy will give complete information about structure