Question

Pre-Lab Assignment

1) Draw the reaction mechanism for the reaction.

2) Determine the limiting reagent.

Procedure 1 Place approximately 1 g of stilbene dibromide prepared in last week's experiment in a 50 mL round bottom flask. Record the exact mass. Add 0.8 g of KOH and 4 mL of triethylene glycol from the syringe provided in the fume hood (rinse any crystals from the sides of the flask while adding triethylene glycol). 2 Heat the stirred reaction mixture to a temperature of 120 "C and then maintain the temperature between 120-130 °C for 10 minutes. DO NOT OVERHEAT! 3. Note 1: A small test tube containing triethylene glycol with a clamped thermometer is placed into the fitting area of the aluminum block. The reading of the thermometer is within 3 "C of the reaction mixture temperature. (Please don't remove the test tube and the thermometer from the block) Note 2: The temperatu re of the Al heating block must be at least 20 °C higher to generate the required temperature in the reaction vessel (or in the test tube). 4. Confirm by TLC (silica, cyclohexane) that no starting material is left and a new spot of the product has appeared: While the reaction is running, add 1-2 drops of your reaction mixture to a 25 mL Erlenmeyer flask that contains 2-3 mL of cyclohexane. Mix well, then spot on the TLC plate. Run a product reference and starting material on the same TLC plate for comparison. Run co-spots as well. If your reaction mixture still contains starting material, run the reaction for another 5 5. minutes and repeat step 4 6 Cool the reaction mixture to room temperature by lifting the clamp holding the reaction flask slightly above the heating block and continue stirring. Slowly add 20 mL of ice cold deionized (DI) H2O with continuos stirring. Remove the stir bar and allow the mixture to stand at room temperature for 5 minutes, followed by 10 minutes in an ice bath until crystallization of the product is completed. 7 Collect the crystalline solid by vacuum filtration (do not rinse) 8 9 Purify by recrystallization from ethanol and water: In a 50 mL beaker obtain 4 mL ethanol. Warm it up on the heating block. Transfer the solid product to the beaker with ethanol to dissolve. If it does not dissolve completely add a little more ethanol and heat to a gentle boil.

Answer 1

TIM By phant K84/42y + Br HBY - Br ph Ph-=-ph HBr on ph egy triethylene glycol = onor of The limiting reagent is stillbene dibromide because when reaction is complete it is totally comumed.