Experiment 7: Wittig reaction. synthesis of stilbene. of Purpose: To synthesize

Question

Experiment 7: Wittig reaction. synthesis of stilbene. of Purpose: To synthesize stulbene, purty it by tnturation, and analyze NMR spectrum purified product. Preparation: (5). Extraction NMR spectrometry), 42 G9). C. Separation Operations 18 (a. H Nuclear Magnetic Resonance Spectrometry Satety Caution: concentrated NaOH solution is caustic/comosrve (wear glovest). CH2CI2 can be an imitant to skun (wear gloves!). Procedure: You will need to check out a small strrmng bar (same size as tor experiment 7) in a 50 mL round-bottom flask CA 1. Place 0.78 g of tlask over a magnetic stimer. which contams a small stiming bar. Clamp the 2. LS mL dichloromethane to the flask to give a suspension the phosphonium salt Add of in the solvent. 3. Add 9.2 mL ot benzaldehyde (density 1.045 g/mL) to the suspension. 4. 12.5 mL of concentrated NaOH u0MD solution in one portion to the suspension in the flask. A yellow coloration sbould be observed atter addition ot the NaOH solution (tum up stirrer to maximum setting to see color most readily). 5. Allow reaction to stir for 30 minutes at room temperature. ot Note: It salt sticks to the wall ot tlask, munumal portions (up to 2 ml water may be added to wash t 6. Transfer reaction mixture to a separatory funnel. Wash flask with minimal amounts of duchloromethane (up to 4 mL) and devonzed water (up to 2 mL) and transter to r separatory tunnel. yo/ Add an de ionized water to the separatory funnel and shake additional 5mL of settle. patient! It may take 10-15 minutes vigorously then allowing the layers to Be for the layers to tully resolve. minutes standing, add aqueous allow Note: If layers do not resolve properly after 10-15 again, and saturated NaCI (2 mL) and additional 3-4 mL of deionized water, shake layer cloudy. W layers to separate. 1he bottom should be crystal clear and the top 8. Separate the layers. Transfer the bottom (organic) layer to a flask and put it aside. Note: Make sure that the bottom layer is indeed the organic layer by adding a few drops ot dichloromethane and observing that it does not torm a separate layer.

Explanation / Answer

PREPARTION OF STILLBENE USING WITTING RECTION :

Synthesis of symmetrical (and unsymmetrical) stilbene derivatives is achieved by a combination of one-pot steps of Kornblum type oxidation of benzyl halide, its simultaneous in situ formation of phosphonium salt, and subsequently their Wittig reaction. In other variant it is oxidized to aldehyde, treated with ylide generated from phosphonium salt (CH3PPh3X) to give styrene, and subjected to Pd catalyzed Heck reaction with arylhalide to give stilbenes as the three-step one-pot sequence.

  

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