sample2-Carbocations+Oxidation+Procedure

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The procedure for all lab pairs is very similar, with some differences in reagents and calculations.

Alcohol (reactant): benzhydrol Catalyst: CrO3 in Amberlite Solvent: CH2Cl2 Expected Product: benzophenone
 * Group 1 Calculations: Taylor and Demitri **

Quantity benzhydrol=1.5 g mm benzyhdrol=184.24 g/mol

184.24 g/1 mol = 1.5 g/ x mol x=0.00814 mol benzyhdrol

Quantity CrO3: twice the amount of benzyhdrol in moles 0.00814 x 2 = 0.0163 mol CrO3 mm CrO3 = 100 g/mol

100 g/1 mol = x g/0.0163 mol x=1.63 g CrO3

Source: []
 * Procedure (for CrO3 in Amberlite) **
 * 1) Add catalyst to a 100-mL round-bottom flask (for CrO3 in Amberlite, use 1 g Amberlite). Put a magnetic stir bar in the flask.
 * 2) In another flask, dissolve the alcohol in dichloromethane. The volume of dichloromethane will depend on the volume of the round-bottom flask. Make sure there is no more than 1/2 the volume of the flask (e.g. if the round-bottom flask is 50 mL, use no more than 25 mL dichloromethane).
 * 3) Prepare two stock solutions of the pure reactant and pure product (e.g. benzyhdrol and benzophenone) using a volatile solvent. Dilute to 1000 ppm. Example: add 0.010 g alcohol to 10 mL solvent. Repeat for the product stock solution.
 * 4) In-lab: the stock solutions of benzyhdrol and benzophenone were made for us from last semester.
 * 1) Set up a reflux. See figure below for a basic picture of what the apparatus will look like. The reflux apparatus we will use will have an extra arm that will allow for product testing as the reaction proceeds.

5. Combine the alcohol/dichloromethane with the catalyst in the round-bottom flask and reflux the reaction at near 40 degrees C (close to the bp of dichloromethane). 6. As the reaction is being refluxed, set up a TLC developing chamber using a mixture of a nonpolar and polar solvent. See "Results" for actual ratios of eluents used in the TLC developing chambers. 7. After 20 minutes, test the reaction progress using TLC. Use the two stock solutions of pure reactant and pure product as controls on the TLC plate. 8. Depending on the TLC results, either continue refluxing/testing with TLC or allow the solution to cool. 9. Use gravity filtration to filter out any impurities in the product solution. 10. Filter the product solution through a silica gel column. 11. Evaporate any remaining CH2Cl2 and save the product(s) for IR/NMR.
 * In lab: We tested our products after 40 minutes, then after 60 minutes of refluxing.


 * Procedure (for Collins reagent) **

1. Add 25 mL dichloromethane to a 100 mL flask with a magnetic stir bar. 2. Add 1.3 g pyridine to the flask and turn on the magnetic stir bar to the medium setting. 3. Add 1.6 g CrO3 to the the flask. 4. Add 0.85 g benzyl alcohol to the flask. 5. Stir solution at room temperature for about 30 mins. 6. Test for the product (benzyl aldehyde) with TLC, compare a stock solution of 1000 ppm benzyl aldehyde in acetone with a sample of the product from the reaction flask. Use 40% acetone and 60% hexane as the TLC eluent. Maintain stirring in reaction flask. 7. Continue to test product /w TLC until desired purity is obtained. 8. Turn off the stir bar. 9. If the reaction flask contains a precipitate, filter the product with gravity filtration. 10. Separate the product from the solution with a silica gel column. 11. Evaporate remaining dichloromethane and store product for IR/NMR.


 * Procedure (for PDC) **

1. Add 2.18 g PDC to a 50 mL round bottom flask. 2. Add magnetic stir bar to flask. 3. Dissolve approximately 1.0 g benzyl alcohol in 20 mL dichloromethane. 4. Set up a reflux (shown in the figure above). 5. Add benzyl alcohol solution to flask with PDC. 6. Reflux the mixture for 30 minutes. 7. Prepare chambers for thin layer chromatography using a mixture of hexane and acetone as the eluent. 8. Prepare two different solutions with different amounts of acetone to determine which eluent gives better separation on the TLC plate. 9. Prepare stock solutions of benzaldehyde and benzyl alcohol by diluting them with hexane to 1000 ppm. 10. Spot the TLC plate to test for products. 11. After the product solution cools down, filter it using a column of silica gel. 12. Evaporate the dichloromethane from the solution. 13. Set aside product for IR and NMR.