EAS: Bromination of Aromatic Compounds

Experiment

• The final product was synthesized by adding one of the starting materials provided, glacial acetic acid, and Pyridinium tribromide as the electrophile to a flask and mixing them together.
• It was CRITICAL to crush the Pyridinium tribromide thoroughly before adding it into solution
• Water + Sodium bisulfate was added next to get rid of unreacted bromine.
• Appearance = the solution slowly turned a cream color
• The solution was then recrystallized using ethanol or water as the solvent
• Mixture was heated then left to cool for proper recrystallization.

Results

Mechanism

Predicted Reactivity

Aniline > Phenol > Anisole > Acetanilide

• Aniline: nitrogen = electron donating group. It can easily donate electrons to make stable resonance structures for each carbocation intermediate.

• Phenol: oxygen = electron acceptor, so the benzene ring attracts electron density.

• Anisole: methyl group attached to the oxygen = can donate electron density towards the oxygen.

• Acetanilide: Carbonyl group takes electron density away from nitrogen making it less electronegative.

Objective

Discussion and Error Analysis

EAS: Bromination of Aromatic Compounds

Errors that may have occured:

- Improper recrystallization resulting in more impurities and a lower melting point

• To brominate an activated benzene group (phenol, anisole, acetanilide, or aniline
• To determine relative activating effect of the brominated products based on the substituted bromine group
• Identity and purity of product will be evaluated using recrystallization and melting point

- Not gathering all product after recrystallization resulting in lower percent recovery

- not allowing enough time for the electrophilic aromatic substitution to occur

Theory

Benzene Rings

• Undergo electrophilic substitution reactions
• Aromaticity: very electron rich
• Reactivity: the more stable the carbocation, the lower the energy state of it is and the faster the reaction
• EDG stabilize the carbocation and activate a benzene ring towards electrophilic attack
• EWG destabilize the carbocation and deactivate a benzene ring towards electrophilic attack

Analysis of Group Data

Resonance Effect

• Electron donating groups: electrons are pushed towards the benzene ring
• Allows benzene ring to be more electrophilic and stable
• Electron withdrawing groups: electrons are pushed away from the benzene ring

Future Experiments

• Half of the Aniline was trisubstituted and the other half was monosubstituted in the para position.
• All phenol was trisubstituted
• 3 out of the 4 acetanilides were monosubstituted. One was disubstituted.
• For the most part, the experiment held true to the reactivity and substitution order

Inductive Effect

• Electronegative atoms = electron withdrawing

For future experiments, H NMR could be used to identify the substitution order, if the reaction was stopped and recrystallized periodically. This is to observe the order of bromiation that occurs.

NORA SAKIZ

KATIE SHAM

JAYDON SIAO

TINA SINGH

TLC may also be used to observe the stages of substittuion when conducted mid-experiement