Download The Wittig Reaction with Chemiluminescence - Lab 9 | CHEM 333 and more Lab Reports Organic Chemistry in PDF only on Docsity! CHEM333 Lab Experiment 9 The WITTIG REACTION With CHEMILUMINESCENCE! In the Wittig reaction, an aldehyde or ketone is treated with a phosphorous ylide (also called a phosphorane) to give an olefin. Phosphorus ylides are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from the phosphine and an alkyl halide. HO PPh3 50% NaOH DMF Cl The key step of the mechanism is the formation of the oxaphosphetane, the cyclic intermediate. Wittig reactions give primarily Z olefins but often some ofthe E , and others give a mixture. Mechanism: PPh3 OHH PPh3PPh3 HOPPh3 O PPh3 PPh3 O O PPh3- PART I. Synthesis of trans-9-(2-Phenylethenyl)anthracene In a 25-mL Erlenmeyer flask place a small stir bar, 0.50g (0.00242 moles) of 9- anthraldehyde, 0.87g (0.00223 moles) of benzyltriphenylphosphonium chloride. Dissolve the mixture in 6 mL of DMF. Vigorously stir the mixture for at least 5 minutes. Carefully added 0.200 uL (10 drops) of 50% sodium hydroxide (50% NaOH w/w) solution to the rapidly stirred reaction mixture. Use the DMF in the flask to wash any solid off the walls of the Erlenmeyer flask. Note: The reaction changes color during this period, starting out dark yellowish and ending reddish-orange after 30 minutes. After stirring vigorously for 30 minutes, added 4 mL of a 1:1 of 1- propanol/distilled water to precipitate the product (yellow solid). Collect the crude product by vacuum filtration. Recrystallize the crude product with as little 1-propanol as possible (ca. 4 mL). After recrystallization, a yellowish crystalline solid is obtained 73.5% (0.50g). TLC conditions: (eluent: hexanes/ethyl acetate 5:1); Rf product = 0.75, blue spot and Rf anthraldehyde = 0.50, yellow spot. DCM = Dichloromethane DMF = N,N’-Dimethylformamide NaOH = Sodium Hydroxide Note: Use a Pasteur pipette with bulb to measure out the 0.200 uL (10 drops) of 50% NaOH. The pipette must be held exactly vertically straight for the desired amount. Part II. Procedure for Chemiluminescence In a 13-100mm test tube, placed 2 mL of 10% oxalyl chloride/dichloromethane solution, 2 mL of DCM, 1 mg of the fluororescer, and 2 mL of 30% hydrogen peroxide. Take the test tube to a darken area with a Pasteur pipette and bulb mix the solution thoroughly. Record observations. Color: Light-blue color lasts for 10 seconds and turns purple color for an additional 15 to 30 seconds. SAFETY NOTE: Caution should be use when handling the following reagents due to their corrosive properties: dichloromethane, sodium hydroxide, oxalyl chloride, and hydrogen peroxide. Wear gloves at all times.
