The main job for you this week will be to purify your crude epoxide by column chromatography.

Setup:

a. Dry method

Obtain a 25 mL burette, and clamp it securely in the hood. Place a small cotton ball on the bottom. Then add 0.5 cm of sand on top of it. Level the sand and then add ~20 cm of silica gel. Level the powder and then add another 0.5 cm of sand on top. Obtain ~250 mL of the eluent mixture that you plan to use. Carefully fill the column with the eluent to approximately 1’’ from the top. Open the stopcock at the bottom of the column and place a big beaker underneath. Then place a thermometer adapter with a glass tube of appropriate diameter on the top and open the regulator for the air supply slowly. Hold on to the tubing. This will generate a pressure that pushes down the solvent faster. When the solvent front is 1 cm away from the sand at the head of the column, take the tubing out and add more solvent. Repeat this procedure until the entire column is wetted. After this happened, allow the solvent level to go down to the sand level.

b. Wet method (slurry)

Obtain a 25 mL burette, and clamp it securely in the hood. Place a small cotton ball on the bottom. Then add 0.5 cm of sand on top of it. Then pour ~10 mL of the eluent into the column, before you add a slurry of the stationary phase (silica gel) slowly using a powder funnel. Allow the solid to settle down. Make sure that there are no gas bubbles in the column. If this is not the case, add ~0.5 cm of sand on the top. After this happened, allow the solvent level to go down to the sand level.

c. Why two methods? Although the first method is usually faster, many researchers prefer the second method since it limits the formation of gas pockets and cracks. Some more polar solvents can react with the stationary phase and virtually start to boil inside the column. This will lead to the formation of gas bubbles, which will deteriorate your separation quality and the elution speed. In either way, the final product should look like the picture on the left.

Running the column:

Dissolve your product in 2-3 mL of your eluent and add this mixture carefully to the top of the column. Push the mixture into the column using an adapter (consisting of a thermometer adapter with a glass tube with a tight seal). Rinse the container that you used to prepare the solution with 2-3 mL of eluent and load it onto the column as well. Then carefully fill the column with eluent and use the air to force it through at a rate of ~10 mL per minute. If the drip rate appears to slow, consult your TA or instructor for help. Collect ~10 mL fractions in clean test tubes.

After you are done with the column chromatography, use TLC to identify the fractions that contain your product. Starting with fraction 5, run a TLC for every other fraction. You can place your fractions 5, 7 and 9 on one plate. If you found the fractions, also test the next before and after the identified fraction. Combine fraction containing your product and remove the solvent carefully.


Analysis

Prepare a NMR sample of your compound. If you have enough material, dissolve ~0.1 mL in 0.5 mL of deuterated chloroform and place the solution in an NMR tube. Make sure that you label your NMR properly. You will have to recover your sample later on since we will use it for the GC/MS as well. Do not attempt to run an IR spectrum for the compound.


Make sure that you have all the data that you need to write your formal report as well.