Stereochemistry of Bromine Addition

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Chris Holet
7 – 20-12

Steriochemistry of Bromine Addition to trans-Cinnamic Acid

Purpose: To carry out the addition of bromine to trans-cinnamic acid and to identify the product from its melting point.

Molecular Structures and Chemical Reaction(s):

Results and Calculations:

Table of reagents
NameDensity (g/ml)Amount usedAmount # moles
Bromine(excess)
Trans-cinnamic Acid1.246 g/cm30.148g – do conversion
Dichloromethane1,3266 g/cm3-

Table of Results
NameAmount obtainedMolar Mass (g/mol)Amount used (moles)Melting point (Celsius)Color/observations 2,3-dibromo-3-phenylpropanoic acid0.285g307.97200.4 – 205.1White powder

Limiting reagent: Trans-cinnamic acid (148.16g/mol)
2.5g/148.16g/mol=0.01687mol
Stoichiometry ratio: 1:1 ratio
Theoretical yield:
Since 0.01687 moles of trans-cinnamic acid therefore following the 1:1 ratio one concludes that 2,3-dibromo-3-phenylpropanoic acid will be of 0.01687 moles Molar mass = 307.97 g/mol
Mass=(307.97g/mol)(0.01687mol)=5.20g
Actual yield:
Percent yield=actual yield (g) / theoretical yield (g) x 100 % yield = 3.28g/5.20g x100 = 63.08%

Discussion
This experiment involved the addition of trans-cinnamic acid to bromine for the production of 2,3-dibromo-3-phenylpropanoic acid. This process depicted an electrophilic addition of a halogen to an asymmetrically substituted alkene. A result of this process was the presence of a stereospecific bromonium ion formed by the mechanism of the reaction. The mixing of 2.5g of trans-cinnamic acid with 14.6 ml of 10% bromine in dichloromethane over a low heat enable to increase the speed of the reaction. The mixture was later cooled to room temperature and then placed on an ice bath. As the solution was cooled, small crystals formed at the bottom of the round bottom flask where impurities were present. After cooling, this mixture was separated using vacuum filtration, which allowed to separate the...
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