Separating Ferrocene and Acetylferrocene by Adsorption Chromatography Dry Pack Method Leah Monroe February 27, 2003 Organic Chemistry Lab II Experiment performed on February 18 and 20, 2003 Abstract: Adsorption column chromatography is one way to separate compounds out of a mixture. In this technique, a solid stationary phase called the adsorbent is packed in a glass column and an eluent, which is the mobile phase, moves slowly through the packed column. In this experiment, an adsorption chromatography column was constructed using silica gel as the adsorbent.
A 50:50 mixture of ferrocene and acetylferrocene was then separated using the eluents hexane and tert-butyl methyl ether (TBME). The less polar ferrocene was attracted to the less polar hexane, so as the hexane passed through the stationary phase, the ferrocene moved with it and the acetylferrocene was left behind. When TBME was passed through the stationary phase, the acetylferrocene moved with it because the more polar acetylferrocene was attracted to the more polar TBME. The percent recovery of ferrocene was 72. 41% and the percent recovery of acetylferrocene was 82. 6%. 1 Separating Ferrocene and Acetylferrocene by Adsorption Chromatography Introduction: In this experiment, a 50:50 mixture of ferrocene and acetylferrocene will be separated using adsorption column chromatography. A microscale chromatography column will be constructed using the dry pack method. The eluents hexane and tert-butyl methyl ether will be used to separate ferrocene and acetylferrocene, and percent recoveries will be calculated. Materials Used: 2 beakers, 50-mL 3-mL conical vial cotton or Kim wipe 4 Erlenmeyer flasks, 0-mL fine sand labels marking pen microspatula 2 Pasteur pipets, with latex bulbs 9-mm Pasteur pipet water bath @ 60°C #1 stopper support stand utility clamp 20-cm wire Reagents and Properties: Substances Formula Weight Quantity Moles Used g/mol Melting Point °C Boiling Point °C Density g/mL N/A N/A 0. 7405 N/A 0. 659 acetylferrocene Silica gel Tert-butyl methyl ether ferrocene hexane 228 102 88 186 86 29 mg 3. 3 g 20 mL 29 mg 20 mL O C 1. 27 x 10-4 0. 0324 0. 1683 1. 56 x 10-4 0. 1533 81 – 83 2054 N/A 174 – 176 N/A N/A N/A 55 – 56 N/A 69 CH3 Fe ++ Fe ++ Ferrocene Acetylferrocene Procedure:
Part 1 – Labeling and Weighing Collection Containers Label four 50-mL Erlenmeyer flasks “hexane”, “hexane eluent”, “TBME”, and “TBME eluent”, respectively. Label two 50-mL beakers “ferrocene” and “acetylferrocene”, respectively. Weigh each beaker and record the masses. 2 Separating Ferrocene and Acetylferrocene by Adsorption Chromatography Part 2 – Preparing Dry Pack Column Prepare a column in a short stem, wide-bore, 9-mm Pasteur pipet by placing a small plug of cotton or Kim wipe at its tip. Use a wire to push the cotton into place. Be careful not to make the plug too tight or eluent flow will be restricted.
Using a utility clamp, attach the column to a support stand. Make sure the column is vertical. If the clamp is too large to firmly hold the column, use paper towels or a split stopper to hold the column in the clamp tightly. Then, pour approximately 50 mg of sand on top of the cotton or Kim wipe plug. Slowly pour 3 g silica gel on top of the sand. Tap the side of the pipet in order to pack the column as you add the silica gel. Part 3 – Preparing a Sample Weigh 55 – 60 mg of a 50:50 mixture of ferrocene and acetylferrocene. Place the mixture into a 3-mL vial and add 0. 5 mL TBME to the vial. Swirl the vial to dissolve the mixture. Add 100 mg of silica gel to the solution and mix. Note that the silica gel does not dissolve. Then, evaporate the mixture to dryness by placing the vial briefly in a 60°C water bath in a fume hood and then using a gentle stream of air or nitrogen to speed the evaporation. Part 4 – Applying the Sample to the Column Add the dry silica gel-sample mixture to the top of the column. Then add an additional 200 mg of silica gel on top of the sample to protect the sample layer from disruptions when adding eluent.
Part 5 – Eluating Ferrocene Half fill the 50-mL flask labeled “hexane” with hexane. Use this as your working stock of eluent and refill it if necessary. Place the flask labeled “hexane eluent” under the column. Using a Pasteur pipet, slowly add hexane in 1-mL increments to the top of the column. Allow the liquid to flow down the side of the column, being careful not to disturb the silica gel bed. Collect the hexane as it eluates from the column. Continue to add hexane to the top of the column until the bottom of the yellow ferrocene band is at the bottom of the column bed.
Then remove the hexane eluent flask from under the column and replace it with the pre-weighed 50-mL beaker labeled “ferrocene”. Collect the hexane containing the ferrocene using this labeled beaker. After all the ferrocene has eluted from the bottom of the column, remove the beaker from under the column. Place the hexane eluent flask under the column and proceed immediately to Part 6. Part 6 – Eluating Acetylferrocene Half fill the 50-mL flask labeled “TBME” with tert-butyl methyl ether. Use this TBME as your working stock eluent and refill it if necessary.
Allow hexane above the column bed to flow into the bed. When the top of the bed just begins to appear dry, use a Pasteur pipet to carefully add 1 mL TBME to the top of the column. Remove the “hexane eluent” flask from beneath the column and replace it with the flask labeled “TBME eluent”. Collect the eluent in this flask. Continue adding TBME in 1-mL increments until the bottom of the orange acetylferrocene band is at the bottom of the column bed. Then, remove the “TBME eluent flask” and replace it with the pre-weighed 50-mL “acetylferrocene” beaker.
Collect the TBME containing acetylferrocene using this beaker. If crystals of acetylferrocene form at the tip of the column, fill a Pasteur pipet with TBME and use it to rinse acetylferrocene into the labeled beaker. After all the acetylferrocene has eluted from the column, remove the “acetylferrocene” beaker from beneath the column. Collect any additional eluent in the “TBME eluent” flask. Part 7 – Drying and Weighing Compounds Evaporate the eluents from the ferrocene and acetylferrocene beakers by placing them in a 60°C water bath under a fume hood. Use a gentle tream of air or nitrogen to speed the evaporation. You may also allow the beakers to sit out for several hours in a fume hood and the eluents will evaporate on their own. When the eluents have evaporated, allow the beakers to cool. Then weigh each beaker and record the masses. Subtract the masses of the respective empty beakers and calculate percent recoveries. Part 8 – Clean-Up Place all materials in their appropriate waste containers. 3 Separating Ferrocene and Acetylferrocene by Adsorption Chromatography Data: Mass of 50:50 acetylferrocene and ferrocene mixture: 0. 058 g (0. 029 g ferrocene and 0. 29 g acetylferrocene) Mass of ferrocene: Mass of acetylferrocene: Percent Recovery ferrocene: Percent Recovery acetylferrocene: 0. 021 g 0. 024 g 72. 41% 82. 76% Calculations: Percent Recovery of ferrocene (recovered mass of ferrocene) (original mass of ferrocene) Percent Recovery of acetylferrocene (recovered mass of acetylferrocene) = (original mass of acetylferrocene) = (0. 021 g) (0. 029 g) (0. 024 g) (0. 029 g) x 100 = 72. 41% x 100 = 82. 76% Results and Conclusions: Separation of the 50:50 mixture of ferrocene and acetylferrocene was achieved by adsorption chromatography.
Ferrocene, which is a nonpolar compound, moved with hexane, a nonpolar eluent. As the nonpolar hexane moved through the silica gel adsorbent, the nonpolar ferrocene moved with it and could be seen as a yellow band moving down the column. The acetylferrocene was left behind. Acetylferrocene, which is a polar compound, moved with the polar tert-butyl-methyl ether eluent. As the polar TBME moved through the silica gel adsorbent, the polar acetylferrocene moved with it and could be seen as an orange band moving down the column. Polarity was the most important factor in separating the compounds.
Since nonpolar hexane was used first, the nonpolar compound ferrocene was eluted first as a yellow band and the more polar acetylferrocene was left behind. Then, the more polar TBME eluent was used, and thus the more polar acetylferrocene was eluted second in the TBME as an orange band. A mass of 0. 021 g ferrocene was recovered and the percent recovery of ferrocene was 72. 41%. A mass of 0. 024 g acetylferrocene was recovered and the percent recovery of acetylferrocene was 82. 76%. These percent recoveries are relatively good, but could have been higher.
One reason for this is that some product was lost when the stream of air was used to evaporate the eluent in Part 3. One way to correct this would be to simply allow the TBME to evaporate off the mixture on its own. Also, some ferrocene and acetylferrocene may have been lost during its transfer from the vial to the column. Overall, this experiment worked as desired and the percent recoveries were good. References Chemistry Lab Experiments CHEM 224 TECH 708 pgs. 1 – 11 By Wigal/Manion/LeFevre/Wade, Jr. /Rapp/Lee/Wikholm Weast, Robert C. , ed. CRC Handbook of Chemistry and Physics. 0th ed. Boca Raton, FL: CRC Press, Inc. , 1990. Post-Lab Questions 4 Separating Ferrocene and Acetylferrocene by Adsorption Chromatography 1. The percent recovery of ferrocene was 74. 12%. The percent recovery of acetylferrocene was 82. 76%. Please see the calculations section for calculations of the percent recovery. 2. During the addition of hexane to the column, acetylferrocene barely moved at all. Hexane is a nonpolar eluent and thus, the nonpolar ferrocene moved with hexane through the stationary phase while the more polar acetylferrocene was left behind.
The polar acetylferrocene did not move with the nonpolar hexane, but was left behind until it moved with the polar TBME. 3. Separation occurs when an eluent of low to moderate polarity is passed through the column. Hexane is a nonpolar eluent, so if we had only used hexane as the eluent in this experiment, separation would have occurred, but it wouldn’t have been as quick or as successful as it was when we used both hexane and TBME. The only way separation can occur when using only one eluent is if the differences in attraction between the mixture compounds are great enough.
In this experiment, the differences may have been great enough for separation to occur, but a lot more hexane would have to be used and the experiment would take more time to perform. 4. If we had only used the more polar TBME as the eluent in this experiment, separation of the ferrocene and acetylferrocene wouldn’t have occurred. As mentioned in question 3 above, separation occurs when an eluent of low to moderate polarity is used. Since TBME is polar, no separation would have occurred. 5
