Chem 2204 – 12 Due 2-03-15
Experiment 28: Halogenation: Synthesis of 4-Bromoacetanilide by Electrophilic Aromatic Substitution, Part 1
I Objective The objective of this lab was to learn about conditions needed for Electrophillic Aromatic Substitution. This reaction will be a halogenation reaction where acetanilide will react with bromine to yield 4-Bromoacetanillide collected by Hirsch funnel filtration. This product can have different forms, but only the para form will appear due to steric hindrance
The procedure was followed as described in Mayo, pages 369-370 with modifications listed in the blackboard document. Additional modifications to the procedure included the following
Add a stir bar
III Reaction Scheme
IV Data and Results Table
Amt mmole concentration
MP acetanillide C8H9NO
Bromine acetic acid solution
Acetanilide looks like crushed salt crystals
Glacial acetic acid has very strong smell – like vinegar since vinegar contains acetic acid
Bromo-acetic acid looks like blood with an orange tinge to it
All three combined look like liquid candy corn – some orange, some yellow, and some white in the mix
As it sits the orange starts turning more and more yellow
After 5 minutes stirring looks like bright orange pixie sticks
After 5 minutes of sitting still it looks like 5 different cheese layers. Some white layers and some yellow layers
Once water added looks like milky lemonade
Sodium bisulfate was clear, after 20 drops added plus some shaking, all the yellow was gone from the solution
After drying it looks like white, wet flour with a slight yellow tinge
1. Write a mechanism for the bromination of acetanilide with bromine in acetic acid. Be as complete as possible and include all relevant resonance structures. Show electron flow for ALL steps.
2. The acetamido group (–NHCOCH3) is an ortho-para directing group in electrophilic aromatic substitution reactions.
a) Explain why only one product is formed in this bromination reaction.
Only one product is formed in this bromination reaction due to steric hindrance. Only para position is observed because the acetamido group block addition of the bromine on the ortho position. b) Why is the acetamido group a weaker directing group than an amino group (–NH2)? Including chemical structures may help to explain your answer.
The role of the acetanilide in this reaction is to act as a nucleophile. The acetamido group on the acetanilide possess’ a carbonyl group with has electrophilic nature. The electrophilic nature of the carbonyl group reduces the nucleophilic nature of the acetanilide. NH2 does not have a carbonyl group and thus does not have this problem.
3. Draw the structure of the major monobrominated product formed when the following