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Unformatted text preview: Synthesis of trans-2-Bromostyrene Purpose: To synthesize and isolate trans-2-Bromostyrene in good yield and purity Main reactions: O CH 2 (CO 2 H) 2 , pyr, heat O OH Br 2 acetic acid O OH Br Br mix of stereoisomers? Br K 2 CO 3 water or acetone Procedures: Formation of trans-cinnamic acid : In a 10-25 mL roundbottom flask, place a magnetic stirbar, 1.5 g of malonic acid and 120 mg of -alanine. Add 3 mL of pyridine in the hood (caution: stench!) Add 0.580 mL of benzaldehyde and then add a water-jacketed reflux condenser to the flask. Heat the mixture in a sandbath at 130 o C for 1.5 hours. Allow the reaction mixture to cool to room temperature. Use a Pasteur pipet to transfer the reaction mixture to a 50 mL Erlenmeyer flask containing about 12 mL of cold water. Wash the roundbottom with about 3 mL of cold water and transfer to the Erlenmeyer flask. Add 6 M HCl in small portions until a white precipitate forms and the solution is weakly acidic. (It should take about 8 mL of 6 M HCl.) Collect the solid product by vacuum filtration. Wash the collected solid with three 2 ml portions of cold water, then pull air through the filter for about 15 minutes to dry the product as well as possible. Leave the solid in an open beaker to dry until the next lab period. Obtain a melting point and 1 H NMR. Before conducting the next procedure, be sure that you have 0.500 g of product with a melting point within about 3 o of the accepted value. If you do not have this amount or high enough purity, see your AI to receive some authentic trans-cinnamic acid . (You will receive a minor point deduction if you take authentic sample, but it is better to do so than to not get the rest of the lab done.) Formation of 2,3-dibromo-3-phenylpropanoic acid . Place 0.500 grams of trans-cinnamic acid in a 25 mL roundbottom flask with a stirbar. a 25 mL roundbottom flask with a stirbar....
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