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Expt #5. Two Addition Reactions of 3-Hexene Relevant textbook readings – Karty Chap 13.3, 13.4; Nichols Chap 2.4b References (1) Porter, D. J.;
Stewart, A. T.; Wigal, C. T. J. Chem. Educ.
1995, 72, 1039-1040. Overview In this lab you will carry out an assigned addition reaction of 3-hexene; either bromohydrin formation or epoxidation. You will also be assigned either trans-3-hexene or cis-3-hexene as your starting material and determine the stereochemistry of the obtained products using NMR. Data sharing with other groups in the lab will allow the determination of the stereospecificity of each reaction.Reaction 1 - Bromohydrin formation1 In a 5.0-mL conical vial equipped with a magnetic spin vane place N-bromosuccinimide (NBS) (350 mg), water (1.0 mL), and tetrahydrofuran (0.75 mL). Add 0.25 mL 3-hexene and stir at room temperature until no solid NBS remains and solution is colorless (about 10-15 min). Dilute the reaction solution with 2.0 mL water and stir for an additional 2 min. There should be two layers in the vial. Transfer the bottom organic layer to a small Erlenmeyer flask and dry with anhydrous sodium sulfate. Prepare a chromatography column by placing 500 mg of silica gel in a Pasteur pipet that is plugged loosely with a glass-wool plug. Clamp up the column vertically above a tared 10-mL rbf and transfer the dry, crude bromohydrin to the top of the column using a Pasteur pipet. Rinse the vial containing the drying agent with 4 drops of dichloromethane and add the rinse to the column. Allow the liquid to drain until the top of the silica gel is free of liquid and then elute the column with 5.0 mL of dichloromethane. Force all of the liquid through the column with the aid of a pipet bulb and remove the solvent on the rotary evaporator.
Reaction 2 - Epoxidation2 Prepare a mixture of 0.25 mL 3-hexene in 5 mL dichloromethane in a 50 mL rbf equipped with a magnetic stirbar. Add 10 mL 10% sodium carbonate (aq) and cool on an ice bath. Prepare a solution of MCPBA (0.59 g) in dichloromethane (10 mL) and use a Pasteur pipet to add it dropwise to the stirring cold hexene solution . After the addition is complete continue stirring for an additional 20 min at 0°C. Transfer to a separatory funnel and separate the layers. Wash the organic layer with sodium carbonate (aq) (5 × 15 mL). Dry over sodium sulfate and then remove the solvent on the rotary evaporator. Characterization of Products Determine the yield and obtain the proton and C-13 NMR of your product. We may also obtain IR and GC?MS if time permits. Post
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