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To: Kristen Dickerson From: Radhi Daya Date: 12 November 2016 Experiment 23: Stereochemistry of Bromine Addition to trans-Cinnamic Acid Partners: Harini Patel, Nho Dao, and Heidi Franz

Introduction: The purpose of this experiment was to carry out the addition of bromine to transcinnamic acid and identify the product from its melting point, isolate and purify the product, and determine the product’s stereochemistry. The product was actually a mixture of enantiomers of erytho- and threo- nomenclature. This nomenclature is used to describe the configurations between the compounds that have two chiral centers but no plane of symmetry. This naming system is also based on eythrose and threose, which are simple sugars. A bromine addition to trans-cinnamic acid was performed in this experiment to determine the stereochemistry of the product. The reaction was completed by adding bromine solution in acetic acid to a trans-cinnamic acid solution.

Oberservations: Several observations were made during the experiment. After a fifth of bromine had been added to the trans-cinnamic acid and acetic acid, the color changed from a clear

liquid to a dark orange. As the reaction proceeded under the hood, the color faded to a light orange, which indicated more bromine was needed. After the final addition of bromine, the mixture was dark orange and had to be under a reflux for 15 minutes, and within that time the mixture turned to a light yellow with the helps of additions of cyclohexene to achieve this color. Theoretical yield Percent yield Mass of Product Melting Point Range

3.08 g 94.16% 2.90 g 202 C – 204 C

Results and Discussion: Theo. yield = 10mmol x (1mol/1000mmol) x (308 g/1mol) = 3.08 g 2,3-dibromo3-phenyl propanoic acid Percent yield = actual/theoretical x 100 = 2.09g/3.08g x 100

mass of product = 2.09 g melting point range = 202C to 204 C

= 94.16% Through the results, the product was found to be erythro-2,3-dibromo-3-phenyl propanoic acid. This was evident because of this product’s melting point resembling that of the Erythro. The addition of bromine to the C=C in the final product showed an antiaddition Sources of error include improper drying of the product, loss of product when transferring to filter, and not allowing the product to fully recrystallize. The product had a high percent yield and was difficult to dry. Some of the product was filtered out during vacuum filtration. The product was hard to dry because of the reformatin of the crystals making it much difficult to dry.

First, one of the bromines attaches to the double bond to form a bromonium intermediate. Next, the other bromine attacks from the other side, which allows it to be open the bromonium ion and attaches itself to the other side. Now, both bromines are now attached to the acid and rearranged to form the final product of erythro-2,3-dibromo-3-phenyl propanoic acid. Experimental: Under the hood in a 50 mL round bottom flask, 10 mmol of trans-cinnamic acid was mixed with 6 mL of glacial acetic acid and add a stir bar inside. While under a reflux, 10 mL of 1.0 M solution of bromine/acetic acid was added and stoppered after adding. Next, 5 portions of bromine/ acetic acid was added once the color had faded to a light orange. The reaction mixture was heated to 50 C after the last addition for 15 minutes. After 15 minutes, the mixture was cooled in an ice water bath for another 15 minutes to begin crystallization. The product was then collected by vacuum filtration and washed with more acetic acid to ride the smell of odor. The product was purified by recrystallization in adding 50% aqueous ethanol and washing on a filter with 50% ethanol. The 2,3-dibromo-3-phenylpropanoic acid was dried and its melting point was

measured to determine whether the erythro or threo isomer was formed or if it had a mixture of both.

References: -Reference for Lab Manual: Lehman, J. W. Operational Organic Chemistry; A ProblemSolving Approach to the Laboratory Course, 4th Ed.; Pearson Prentice Hall, 2009; pp 181-190. -Reference for Lab Notebook: Radhi Daya. Organic Laboratory Notebook, [23]....