2211L-10 - Retro and Forward Diels-Alder Reaction PDF

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Retro and Forward Diels-Alder Reaction...

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Experiment 10: Retro and Forward Diels-Alder Reaction This week in lab we will be using the Diels-Alder reaction which is characterized by [4+2] cycloaddition. The pi systems combine to form a six-member ring. This reaction takes place in a one-step concerted step meaning that there are no reactive intermediates formed. Retro means reverse so the retro Diels-alder is the reverse of the Diels-alder reaction. Heat is required for the reaction to start with moderate temperatures. This will be achieved by using a microwave. Moderate temperatures are needed for the cycloaddition and high temperatures are needed for the retro reaction. We will be given four possible dienophiles to react with cyclopentadiene. IR and HNMR will help us determine the identity of dienophile

Balanced Equation:

Table of Reagents:

Reaction Mechanism:

Safety Information: Be cautious around glassware, chemicals, and toxic, caustic liquids. Make sure you avoid contact or inhalation. Wear appropriate protective gear at all times (laboratory coat, safety goggles, and face protection). Unused reagents need to be disposed in the marked container in the fume hood, never pour back into bottles.

Put the lid back on the reagent bottle immediately after each use. Do not breathe fumes of any kind. Fumes can cause respiratory distress. Place broken glass in the marked broken glass container. Do not pour waste down the drain unless explicitly told to do so. Before starting the experiment, make sure you know the locations of all emergency procedures. In this week’s lab, we will be working with very hot liquids and glassware. Be sure to add a boiling chip to any liquids being boiled, and never boil a sealed container. Keep the snorkel positioned over any apparatus that could release fumes or gases. Avoid sparks, flames, ad hot surfaces, as there are several highly flammable substances in this week’s experiment. Experimental Procedure: Retro Diels-Alder Reaction 1. Add 300 mL dicyclopentadiene to 500 mL microwave round bottom flask 2. Add 2 microwave absorbing chips and stir bag to flask 3. Attach fiber optic thermodetector to side arm 4. Construct distillation apparatus through microwave 5. Set up program for temperature profile 6. Start program and collect fresh “cracked” cyclopentadiene in round bottom flask in ice bath 7. Ramp for 10 minutes until temperature reaches 168°C 8. Keep this temperature for 30 minutes Forward Diels-Alder Reaction 9. Add 1.5 mL of dienophile and spin vane to 10 mL round bottom flask on aluminum block 10.Attach clamp to secure 11. Add 2.0 mL cold cyclopentadiene dropwise into flask while stirring within 30 seconds 12. Put lid on loosely 13. Allow to stir for 20 minutes at room temperature 14. Take off lid 15. Turn heat to 140°C and boil off excess, do not go over 150°C 16. Obtain IR and HNMR of final product...