Bromination of Trans- Stilbene to Form 1,2- Dibromo- 1,2-Diphenylethane

1069 Words May 10th, 2012 5 Pages
Bromination of trans- Stilbene to form 1,2- Dibromo- 1,2-diphenylethane


1,2-dibromo-1,2-diphenylethane was produced by the bromination of trans-stilbene through the addition of hydrobromic acid (HBr) and hydrogen peroxide (H2O2). This experiment was a greener bromination of stilbene because bromine was generated in situ and ethanol was used as the solvent. The melting point (243.30°C), mass (.427g), and percent yield (45.54) of the crystals were recorded. The FTIR was used to confirm that the product was produced. The peaks on the HNMR revealed the presence of aliphatic and aromatic hydrogens and were used to verify the identity of the product. In addition, the melting point of the crystals was also used
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Typically, elemental bromide is also used but it is corrosive and can cause chemical burns. This experiment is a green bromination of trans-stilbene because it reduces the need to use hazardous chemicals. It utilizes ethanol as a solvent and bromide is generated in situ from the reaction of hydrobromic acid and hydrogen peroxide.

Materials and Methods

First, a water bath was prepared and heated to 90-100oC on a hot plate. A 100mL round-bottom flask was equipped with a magnetic stir bar. A Mettler PJ360 DeltaRange balance was used to measure out 0.500g of 96% trans-stilbene (Sigma-Aldrich Batch# 00807JD), which was added to the 100mL flask. Next, 15mL of the 95% (general lab reagent) ethanol were also added to the flask. A reflux condenser was set up and the solution of ethanol and 96% trans- stilbene was allowed to dissolve.

After the stilbene dissolved, 0.8mL of 48% hydrobromic acid (A.C.S. reagent Batch# 06722CC, HBr content 47.0-49.0%) was added in drops while the solution was heated and stirred. The mixture appeared clear and colorless. Then, 0.8mL of 30% hydrogen peroxide (Sigma Aldrich), was also added drop-wise to the refluxing reaction while it was being heated and stirred. The color of the mixture became dark yellow. The solution was then heated and stirred of approximately 20 minutes until the solution turned cloudy white. The mixture was rinsed with 95% ethanol (GLR)

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