Question

Green Bromination rx

1) a student observed a persistent yellow color during the reaction. After refluxing for 40 mins, the student observed mixture had faded to a cloudy white, but the mixture still had a faint yellow color, what does this indicate? (Think of colors of reagents and what would cause this)

2) why is the peak due to c=c stretching of trans stilbene not prominent in IR? (Is this because of symmetry???)

3) why do you add NaHCO4 during the workup of rx?

Answer 1

1. The faint yellow colour is because of the excess HBr. Change of colour also shows the electrophilic addition reaction in situ formation of bromine through the oxidation of hydrobromic acid with hydrogen peroxide.

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