McMaster University - Chem2O06 Lab Manual 1997/98

Experiment 7. Part A: Oxidation of Borneol to Camphor.

In a 5-mL conical vial containing a spin vane, place ()-borneol (0.180 g), acetone (0.5 mL), and glacial acetic acid (0.15 mL). Attach an air condenser and place the conical vial in a water bath, set at 45 oC and mounted on a hot plate/magnetic stirrer. Stir the mixture until the borneol is dissolved.

While the reaction mixture is stirring, add 2.0 mL of a 5% aqueous sodium hypochlorite solution through the top of the air condenser over a period of about 30 minutes. When the addition is complete, stop the stirrer and remove a drop or two of the bottom aqueous layer with a Pasteur pipet. Transfer this liquid onto a wet piece of starch-iodide indicator paper to determine if a sufficient amount of bleach has been added. The purple colour of the starch-iodine complex indicates that an excess of hypochlorite is present. If there is no colour change, add an additional 0.2 mL of bleach to the reaction mixture, stir for 10 minutes, and repeat the starch-iodide test. Continue this process until the paper turns blue. Stir the mixture for 10 minutes after the last addition of bleach and repeat the starch-iodide test. If it is negative, add an addition 0.2 mL of bleach. Whether additional bleach was added or not, allow the reaction to continue for 10 minutes more.

When the reaction time is complete, allow the mixture to cool to room temperature. Place ~3.5 mL of dichloromethane in a clean 3 mL conical vial, cap it, and bring it to your bench for use in the next few steps. Use 1.0 mL of dichloromethane to rinse, into the reaction apparatus, the pipette you used to monitor the reaction above and the air condenser. Remove the air condenser from the reaction apparatus, and then remove the spin vane with forceps and rinse it and the forceps with a few drops of dichloromethane. Cap the vial, and shake it well with venting. Using a filter tip pipet, transfer the lower (dichloromethane) layer into another 5-mL conical vial. Extract the aqueous layer twice more with 1-mL portions of dichloromethane, and combine them with the first dichloromethane extract. Wash the combined organic extracts with 1.0 mL of 10% aqueous sodium bicarbonate solution. Stir the liquid with a spatula until bubbling due to the formation of CO2 ceases. Cap the vial and shake with frequent venting to release any pressure produced. Transfer the lower methylene chloride layer to another container and remove the aqueous layer. Return the dichloromethane layer to the vial and wash the solution successively with 1.0 mL of saturated sodium bisulfite and 1.0 mL of water. Using a dry filter-tip pipet, transfer the dichloromethane layer to a dry test tube or conical vial. Add three to four microspatulafuls of anhydrous sodium sulfate and let sit for 4-5 minutes with occasional shaking. After taring a 10 mL Erlenmeyer flask, transfer the dichloromethane solution to it. Evaporate the solvent in the hood with a gentle stream of dry air while heating the flask in a water bath (in the hood!) at 40-50 oC.

When all the liquid has evaporated and a solid has appeared, remove the flask from the heat source immediately to avoid sublimation and loss of the volatile solid. Weigh the flask to determine the crude yield of your product. Determine the melting point in a sealed capillary tube (see your TA for help making a sealed capillary tube) to prevent sublimation. Save a small amount for determination of the infrared spectrum. Store the camphor with the flask tightly sealed until the next lab period.

Arrange a five-minute time slot to determine the infrared spectrum. Dissolve the sample in a small amount of carbon tetrachloride, and place the solution between NaCl IR plates. Mount the plates in a holder and determine the spectrum.

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Part B: Sodium Borohydride Reduction of Camphor
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