Topic: Bromine ti on of Stilbene 1. Suppose you are performing this reaction and
ID: 917069 • Letter: T
Question
Topic: Bromine ti on of Stilbene
1. Suppose you are performing this reaction and discover that someone left the cap off the glacial acetic acid for a long period of time. Draw the structure of any side products that might dorm. What technique would you use to determine whether this side product did indeed form? (Hint: glacial acetic acid is very hygroscopic.)
2. Based on literature values, what value would you expect to obtain for each sample if the optical rotation could be measured?
3. Why use bromine for the experiment instead of pyridoxine tribromide?
Explanation / Answer
1. Glacial acetic acid in presence of moisture would hydrolyze to acetic acid. If the reaction is run in the presence of acetic acid, the product obtained would have an acetate linkage to the carbon atom. The product thus formed would be having a higher melting point as compared to the dibromo product. Also a simple tlc would have formation of two products, the dibromo will move faster and be non-polar whereas, the bromoacetate compound would be more polar and stay slightly behind the other product.
2. Optical rotation of the diacetate would be higher than the meso dibromo compound formed. The meso-dibromo-stilbene has an optical rotation of zero, whereas, the bromoacetate would have a +ve or -ve otical rotation depending on which isomer is formed.
3. Br2 is much cheaper and more atom efficient as compared to pyridoxine tribromide compound. Both the compounds are corrosive in nature. So it is preferred to use Br2 instead of pyridoxine tribromide for this reaction.