Individual Bromination Lab Report

Bromination

Solo Experiment 3 – Individual Lab Report
(Save as pdf and submit, due by 12:00 NOON one week after experiment)

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Synthesis of Stilbene Dibromide: mix correct amounts of E-stilbene and Ethanol in an Erlenmeyer and heat gently while stirring. After Add 0.4 g pyridinum tribromide and use ethanol to rinse sides. Heat for five more minutes; cool down to room temperature, then ice bath. Collect product by vacuum filtration. Weight dry product and take melting point.

Synthesis of Bromoactanile: add correct amounts of acetanilide, sodium bromide, ethanol and acetic acid in an Erlenmeyer. Add a stir bar and plug the top with cotton. Place the flask in ice bath to cool. Add 7ml bleach and continue to stir for a while. Remove flask from ice bath and warm to room temperature. Add 0.8ml sodium thiosulphate and 0.5ml NaOH. Collect product by vacuum filtration. Weight dry crude and take melting point. Use 50/50 ethanol/water solution to purify and recrystallize bromoacetanilide. Collect product by vacuum filtration. Weight dry product and take melting point.

Results: (3
Comment on the stereoselectivity of the bromination of E-stilbene (assign stereochemistry of dibromo product, why selective?, is this molecule chiral?)

Bromine was added to Estilbene to form an anti product. This happened because no true carbocation was formed in reaction. Instead, there was an intermediate where one of the bromine atoms was partially bonded to both carbon atoms of the double bond. This prevented bond rotation around the carbon-carbon bond. The steric hindrance prevented the bromine from being added to the same side as the first bromine atom. Thus, the process of bromination was stereoselective and the product formed was chiral.

ii. Comment on the regioselectivity of the bromination of acetanilide (assign regiochemistry of bromo product - ortho/meta/para, why selective?)

The regiochemistry of the product was para. The substituent presented on the benzene ring had nitrogen right next to the carbon of the benzene. The lone pair of nitrogen could delocalize over the benzene ring and activate it. An activating group was ortho or para directing because the carbocation formed by this arrangement gave the most stabilized resonance structures. The majority was the para product because there was steric hindrance in the ortho position as the substituent was a large