Background Organic Chemistry 205 Laboratory Experiment - A. Ahmed Bromination of Alkenes The halogenation of alkene is an important reaction in the chemical industry. For example, over 8 million tons of 1,2-dichloroehane per year are produced by the addition of chlorine (C12) to ethylene. This product is used both as a solvent and in the preparation of polyvinyl chloride, PVC, a common organic polymer used in household plumbing. Typically, alkenes undergo reactions through electrophilic addition, a process in which the alkene pi (π) bond is replaced with two sigma (o) bonds. The general mechanism of electrophilic addition involves two steps as mentioned in the lecture. For example stilbene (reaction A) reacts with bromine to give dibromostilbine. In reaction B and C, cis- and trans- dicarboxy ethylene. trans-Stilbenes 1 P Br Br2 Br 2 For comparison experiments, you can use cis-stilbenes; maleic acid; cinnamic acid, and fumaric acid. What is your expectation about the relative rates of reactivities between the four compounds? [HOMEWORK question] HO. Maleic Acid: Fumaric acid: OH cis- HOOCC=CCOOH → назов HOOCC(Br)C(Br) COOH trans- HOOCC=CCOOH → HOOCC(Br)C(Br)COOH Cinnamic acid: Procedure: ов OH 1. In 25 ml round bottom flask, add 6.0 mL acetic acid, 0.58 gm trans-stilbenes. {{in case of cis-stilbenes, [0.3 ml]}}. 2. Heat gently to dissolve the alkene. And place a magnetic bar, or shack occasionally. 3. Add pyridine tribromide 1.1 gm. 4. Heat gently under reflux for 20 min, until a precipitate appears. 5. Cool 5 min then add 8 ml water continue to cool the reaction mixture on ice for 15 min. 28 Background Organic Chemistry 205 Laboratory Experiment - A. Ahmed Bromination of Alkenes The halogenation of alkene is an important reaction in the chemical industry. For example, over 8 million tons of 1,2-dichloroehane per year are produced by the addition of chlorine (C12) to ethylene. This product is used both as a solvent and in the preparation of polyvinyl chloride, PVC, a common organic polymer used in household plumbing. Typically, alkenes undergo reactions through electrophilic addition, a process in which the alkene pi (π) bond is replaced with two sigma (o) bonds. The general mechanism of electrophilic addition involves two steps as mentioned in the lecture. For example stilbene (reaction A) reacts with bromine to give dibromostilbine. In reaction B and C, cis- and trans- dicarboxy ethylene. trans-Stilbenes 1 P Br Br2 Br 2 For comparison experiments, you can use cis-stilbenes; maleic acid; cinnamic acid, and fumaric acid. What is your expectation about the relative rates of reactivities between the four compounds? [HOMEWORK question] HO. Maleic Acid: Fumaric acid: OH cis- HOOCC=CCOOH → назов HOOCC(Br)C(Br) COOH trans- HOOCC=CCOOH → HOOCC(Br)C(Br)COOH Cinnamic acid: Procedure: ов OH 1. In 25 ml round bottom flask, add 6.0 mL acetic acid, 0.58 gm trans-stilbenes. {{in case of cis-stilbenes, [0.3 ml]}}. 2. Heat gently to dissolve the alkene. And place a magnetic bar, or shack occasionally. 3. Add pyridine tribromide 1.1 gm. 4. Heat gently under reflux for 20 min, until a precipitate appears. 5. Cool 5 min then add 8 ml water continue to cool the reaction mixture on ice for 15 min. 28