Separating Ferrocene and Acetylferrocene by Adsorption Column Chromatography

Separating Ferrocene and Acetylferrocene by Adsorption Column Chromatography

Aim:

The purpose of this experiment was to prepare a chromatography column and successfully separate a two-compounded mixture containing Ferrocene and Acetylferrocene using column chromatography. At the end, we calculated the percent recovery of each compound.

Introduction and Theory:

Column Chromatography is a common and highly efficient method that is used to analyze and separate compounds from a mixture. In this technique, a sample mixture is introduced to a mobile phase/eluent which carries the sample through an adsorbent known as the stationary phase. The rates at which each compound in the sample mixture move through the stationary phase is highly dependent upon the polarity and attractions for the mobile and stationary phases. In this experiment, our sample mixture consists of a 1:1 mixture of ferrocene and acetylferrocene. The mobile phase used to separate ferrocene from the mixture is Hexane and the mobile phase used to separate acetylferrocene from the mixture is Ethyl acetate. Lastly, the stationary phase is silica.

In order to carry out the process of column chromatography, a column must first be created. There are two distinct methods of packing a column – dry packing and slurry packing. In dry packing a small piece of a cotton ball was used to plug the tip of the pipet. Sand is then added to provide a level base. Dry adsorbent is added on top of the sand, then the sample mixture and some sand once again. On the other hand, in slurry packing, instead of a dry adsorbent being added, a slurry of adsorbent is prepared in the eluent. The column is filled half-way with the solvent and the slurry is added while the column drains slowly. In this experiment, we will be using the dry packing method.

Table of Physical Properties and Hazards:

Compound

Physical Properties

Hazards

Acetylferrocene

[Fe(C5H4COCH3)(C5H5)]

Molar Mass: 228.07 g/mol

Melting Point: 81-83°C

Boiling Point: 161°C

Physical State: Solid

Acetylferrocene may cause eye and skin irritation. May be fatal if swallowed and is toxic if absorbed through skin. May also be harmful if inhaled.

Ferrocene

(C10H10Fe)

Molar Mass: 186.04 g/mol

Melting Point: 172.5°C

Boiling Point: 249°C

Physical State: Solid

Ferrocene may cause eye and skin irritation. If inhaled, it may cause irritation of the digestive tract. Inhalation of dust particles may cause respiratory tract irritation.

Hexane

(C6H14)

Molar Mass: 86.18 g/mol

Melting Point: −96 to −94 °C

Boiling Point: 68°C

Physical State: Liquid

Hexane is flammable and irritating. This compound should be kept away from flames and other heat source. It should be used under a fume hood.

Ethyl acetate

(C4H8O2)

Molar Mass: 88.11 g/mol

Melting Point: -83.6°C

Boiling Point: 77.1°C

Physical State: Liquid

Ethyl acetate is highly flammable and should be handled in a fume hood. It is toxic when ingested or inhaled and can also cause irritation to the skin and eyes.

Silica/ Silicon Dioxide

(SiO2)

Molar Mass: 60.08 g/mol

Melting Point: 1,710°C

Boiling Point: 2,230°C

Physical State: Solid (Powder)

Silica is a very hazardous chemical. These small crystalline particles are classified as a human carcinogen and can cause serious lung disease and lung cancer.

Procedures and Observations:

In this experiment, a dry-packed column was created using a Pasteur pipet. To prepare this column, a small piece of a cotton ball was used to plug the tip of the pipet. It was important to ensure that the cotton plug was just above the bulb of the tip and not too far down. This would ensure that the eluent flow would not be restricted. Next, 50mg of sand is added just above the cotton plug. The adsorbent, the silica gel is added. To even the layers and alleviate any air bubbles, the Pasteur pipet is tapped several times. Next, 0.074g of 1:1 mixture containing ferrocene and acetylferrocene is added. The sand is then added just above that layer so that the next layer added, the solvent (hexane/ ethyl acetate) wouldn’t disrupt the silica gel.

After the column was successfully prepared, it was clamped to a support stand in the fume hood. It was important to ensure that the column was vertical so that the layers and the inevitable bands produced would be leveled and straight. Drops of Hexane was used as the first solvent. A 50mL flask was filled with no more that 15mL of Hexane, while another empty flask was placed just under the pipet tip to collect the hexane eluent. Using a plastic pipet, hexane was slowly added, drop by drop into the opening of the Pasteur pipet. It was important to ensure that the elements within the column never went dry because air bubble would form, and the process would elongate. A yellow band began to form and slowly travel through the column. We continued to add hexane to the top of the column until the bottom of the yellow band was at the bottom of the column bed. We switched out the flask of the hexane eluent and placed a pre-weighed vial under the column to collect the yellow band. This vial was labeled ferrocene.

After all the ferrocene was eluted from the bottom of the column, the vial was removed and capped. A clean flask was then placed under the column that would now collect the ethyl acetate eluent. Again, a few drops of ethyl acetate were added to the top of the column and this time, an orange band was produced. Once the orange band reached the bottom, the ethyl acetate eluent flask was switched with a clean pre-weighed vial. This vial then collected the acetylferrocene in liquid form. Once both vials were attained, they were placed separately in the Rotoevaporator and weighed. The percent recovery of each substance was then calculated. 

Results:

Since 0.074g of the sample mixture was added, there was 0.032g of each separate compound (ferrocene and acetylferrocene). Vial F, which later contained the ferrocene, was pre-weighed to be about 9.596g. It was then weighed after the ferrocene was separated to be 9.668g. This means that the percent yield was 225%. This percent is definitely quite large and could have been due to an excess amount of the hexane eluent dropping into the vial. The attraction and polarity of the hexane eluent was stronger to the silica and so it is possible that the vial contained more than just ferrocene in it. The ferrocene in the vial was a bright yellow color. On. The other hand, Vial A, which later contained the acetylferrocene was pre-weighed to be about 9.305g. It was weighed after the acetylferrocene was separated to 9.554. The percent yield was 25%. This low percentage could have been due to the fact that the silica gel held up a lot of the acetylferrocene because of the polarity. The color of the acetylferrocene in the vial was a bright orange.

Discussion and Conclusions:

In the final analysis, column chromatography is an efficient method used to analyze, identify, and separate compounds from mixtures. This experiment was efficient, but also meticulous. The percent yield attained by the end of these experiments may not have been the most predictable, but there is justification for why it turned out so. In Vial F, the hexane eluent may have dropped into the vial which would explain the excess weight. In Vial A, since the ethyl acetate was highly attracted to the silica, the acetyl ferrocene moved more slowly throughout the stationary phase and some may have not collected within the vial.  

References:

National Center for Biotechnology Information. PubChem Compound Database;

CID=11985924, https://pubchem.ncbi.nlm.nih.gov/compound/11985924 

NOAA Office of Response. “Chemical Datasheet: Ferrocene.” NOAA,

cameochemicals.noaa.gov/chemical/20407. 

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