Column Chromatography: Chromatography of a Mixture of Ferrocene and Acetylferrocene

Purpose: Column Chromatography is a method used to purify individual compounds from mixtures of compounds. This procedure was used to separate a 50/50 Ferrocene-Acetyleferrocne mix into two pure substances. Separation was based on solubility of each substance with hexane (the solvent and mobile phase) and alumina (adsorbent and stationary phase).

Procedure: A microscale chromatographic column is prepared with 4.5 grams of alumina used as adsorbent and approximately 10 ml of hexane as solvent (slurry packing method). About .5 mm of sand is placed on top of the adsorbent:

Column is not allowed to run dry as air bubbles could form and this would ruin the experiment. Next, .090 grams of a 50/50 mix of Ferrocene-Acetyleferrocine is mixed with about 2.5 ml of hexane and carefully placed into the column through the funnel at the top. Spout at bottom is opened and hexane is allowed to flow freely down column and into collecting containers. The mixture separates into two distinct layers that flow down the column with the hexane:

Yellow liquid is collected in one flask while red liquid is collected right after in another. Hexane is constantly added to keep proper flow until mixture has been separated fully and sand is not colored anymore with Ferrocene or Acetyleferrocene.

Results: After mixture has been separated, one can see that there is a flask with yellow hexane and a flask with red/orange hexane. The mixture has successfully been separated, but is still in the solvent, hexane. This is called elution.

Discussion & Conclusion:The purpose was to separate the two components of the mixture using an adsorbent (stationary phase) and a mobile phase like the solvent, hexane. Based on each molecules affinity to the alumina and the hexane they went down the tube at different rates, thus allowing us to separate them, while the mobile phase carried it down the tube to be collected in flasks. After separation of the mixture happened one can see a distinct yellow band and a distinct red/orange band. The yellow portion was lower on the tube first and this indicates that it was carrying ferrocene, which makes sense because it is the less polar substance of the two. The acetylferrocene followed as a red band after and this makes sense because it is the more polar substance of the two due to the existence of a hydrophilic group attached to it. Since like dissolves like the ferrocene was separated out first and then the acetylferrocene. Qualitative measurements can be taken by evaporating the hexane out of the samples and then testing the remaining residues, but that was not done.

Post Lab Questions:

4. Once the chromatographic column has been prepared, why is it important allow the level of the liquid in the column to drop to the level of the alumina before applying the solution of the compound to be separated?- So the sample added to the column is in the most concentrated solution possible.

5. A chemist started to carry out column chromatography on a Friday afternoon, reached the point at which the two compounds being separated were about 3/4ths of the way down the column, and then returned on Monday to find that the compounds came off the column as a mixture. Speculate the reason for this. The column had not run dry over the weekend.- The two compounds could be of very similar affinity to the adsorbent or the mobile. Also the adsorbent could have been damaged by improper mixing causing effects similar to air bubbles forming due to column running dry.