Exp 23:: Stereochemistry of the Addition of Bromine to Trans-Cinnamic Acid

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Subject: Experiment 23: Stereochemistry of the Addition of Bromine to trans-Cinnamic Acid

The purpose of this experiment was to carry out the bromination of trans-cinnamic acid, to determine the stereochemistry of the dibromide product of 2,3-dibromo-3-phenylpropanoic acid, and find out whether the reaction proceeds by the usual bromonium ion mechanism or some other mechanism. In this experiment trans-cinnamic acid was mixed with glacial acetic acid and stirred in which then bromine/acetic acid solution was added to the mixture little by little. The dibromide becomes the precipitate of this solution during the reaction. Once this precipitate is separated by vacuum filtration the melting point helps identify the product.

Laboratory notebook reference:
Pages 9-10

Chemical Reactions:

The experiment was begun by mixing trans-cinnamic acid and glacial acetic acid with an added stir bar and placed on the magnetic stirrer the solution mixed up very well. After stirring, bromine/acetic acid was added over five increments and stirred and the solution turned a dark orange color and then began to fade to a lighter color. After vacuum filtration the substance dried and appeared much harder and less liquefied than before. Once the dried substance was obtained the melting point was found along with the melting point range.


|Mass of filter paper |0.554 g | |Filter paper + dried substance |2.03 g | |Mass of product |1.476 g | |Melting Temperature |197-198°C |

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