Title:  Separating Ferrocene and Acetylferrocene by Adsorption Column Chromatography

Objective:  Prepare an adsorption chromatography column.  Separate a two-compound mixture using column chromatography and calculate percent recovery for each compound.

Procedure:

1. We constructed an adsorbent column using a short-stem, wide bore, 9 mm Pasteur pipet.  First a very small plug of cotton was place at its tip.  We made sure the cotton plug was snug but not too tight so that the eluent coundn't flow through it.  Next we attached the pipet to a support stand using a utility clamp so that it hung vertically.  A 1-2 mm layer of fine sand was placed on top of the cotton plug (about 50 mg of sand).  Then we slowly poured about 1 g of alumina over the sand making sure to tap the side of the pipet so it would all settle evenly.  Another 1-2 mm layer of sand was added over the alumina.

2. After this we prepared a sample mixture.  We weighed .052 g of ferrocene, .050 g of acetylferrocene and 1.0559 g of alumina.  We poured these into a 3 mL vial and added 800 uL of tert-Butyl methyl ether (TBME).  The vial was swirled until ferrocene and acetylferrocene dissolved.

3. The vial containing the sample- alumina mixture was then placed in a sand bath heated to 60 degrees C by a hot plate until all liquid was evaporated.  A gentle stream of air was also placed above the vial a few inches to aid in evaporation.

4. After evaporation was complete we poured the dry sample-alumina mixture into the Pasteur pipet column.  Another 1 g of dry alumina was then poured over this to act as a barrier between the eluent and the sample mixture.

5. Next we half-filled a 50 mL flask labeled "hexane" with liquid hexane.  An empty, pre-weighed, 50 mL beaker labeled "hexane eluent" was placed under the Pasteur pipet to collect eluent.  Then using a plastic pipet 1 mL increments of hexane were added to the top of the adsorbent column.  This addition of hexane continued until the yellow ferrocene band had reached the bottom of the column.  We made sure to drip the hexane along the sides of the Pasteur pipet so as not to disturb the dry column materials.

6. After collecting all the hexane eluent, we replaced the "hexane eluent" labeled beaker with an empty, pre-weighed 50 mL beaker labeled "ferrocene". We then collected the last bit of hexane containing the yellow ferrocene in this beaker.

7. Next, we half-filled a 50 mL flask labeled "TBME" with tert-Butyl metheyl ether.  We waited until the last trace of hexane disappeared at the top of the column bed and it appeared dry.  Then we removed the beaker labeled "ferrocene" and replaced it with an empty 50 mL beaker laabeled "TBME eluent".  We began to slowly add 1 mL increments of TBME to the top of the column with fresh pipet.

8. TBME was collected below the Pasteur pipet tip until the orange acetylferrocene band reached the bottom.  Then the beaker labeled "TBME eluent" was removed and replaced with an empty 50 mL, pre-weighed beaker to collect the acetylferrocene.

9. Finally, the beakers labeled "ferrocene" and "acetylferrocene" were placed in 60 degree C sand baths with a gentle stream of air above them until the liquid had evaporated.  The two beakers were then weighed.

Data:

Mass of ferrocene in sample= .052 g
Mass of acetylferrocene in sample= .050 g
Mass of alumina in sample= 1.0559 g

Mass of beakers labeled:
acetylferrocene= 47.1784 g
ferrocene= 60.2372 g

Mass of beaker and recovered ferrocene= 47.2264 g
Mass of beaker and recovered acetylferrocene= 60.2857

Amount of ferrocene recovered = 60.2857 - 60.2372 = 0.0485 g
Amount of acetylferrocene recovered = 47.2264 - 47.1784 = 0.0480 g

Percent recovery ferrocene = .0485/.052 (100)= 93.3 %
Percent recovery acetylferrocene= .0480/.050 (100)= 96 %

Post -Lab Questions:

1. Our percent recovery for both sample compounds was high.  We recovered 93% of the ferrocene and 96% of the acetylferrocene.

2. Acetylferrocene moved very slowly if at all during the addition of hexane because the hexane was not polar enough to pull it from the adsorbent.

3. If we had use only hexane as the eluent in this expirement, only ferrocene would have been eluted from the adsorbent column.

4. If only TBME was used separation of the two sample compounds probably would not have occurred.  Since TBME is a polar eluent it would have eluted both ferrocene and acetylferrocene perhaps simultaneously.