Lab Report 7 - Separating the Components of an Acetylferrocene Mixture Through Flash Chromatography PDF

Preview

Summary

Separating the Components of an Acetylferrocene Mixture Through Flash Chromatography...

Description

Natalie Loveridge CHEM 2221L 11/7/2020 Separating the Components of an Acetylferrocene Mixture Through Flash Chromatography Introduction: The purpose of this experiment is to isolate acetylferrocene from the unreacted starting material, which is a mix of acetyl ferrocene, ferrocene, and 9-fluorenone. Sometimes, recrystallization is not sufficient for the separation of certain compounds from an original, impure mixture. When this is the case, flash column chromatography is necessary for isolating these components. Flash column chromatography was used in this experiment to isolate acetylferrocene, ferrocene, and 9-fluorenone. This method also generally yields a larger amount of each separated component in comparison to recrystallization. In all forms of chromatography there is a stationary and mobile phase; in this experiment, the very polar stationary phase (the adsorbent) was the silica gel in the column and the mobile phase (the eluent) was the solutions that were poured into the column. The more nonpolar a solvent that is poured into the column is, the less chance that the polar stationary phase will travel down the column because it more attracted to the polar phase. However, in the nonpolar solvent, nonpolar solutes will move down the column. Polar solvents will move both polar and nonpolar solutes down the column. The acetylferrocene mixture was placed right above the silica gel layer in the column, below a layer of sand. The first eluent that was added to the column was 15 mL of petroleum ether, which is nonpolar, to pull out the nonpolar/ least polar aspect of the compound, ferrocene. The second solvent that was added was 25 mL of 8% tBME/ petroleum ether, a more polar solvent used to pull the more polar 9-fluoreneone out of the mixture. The third and final solvent was the most polar solvent, 5 mL of pure tBME, to pull the most polar component out of the mixture, acetylferrocene. Eight test tubes were used to collect roughly 5mL elutes from the column throughout the experiment. After all eight tubes were filled, samples from the original solution and all test tubes were taken and ran through TLC plates to determine which test tubes contained certain components based on polarity. Rf values were calculated for each collected sample. Finally, the groups with similar polarities were identified as either acetylferrocene, ferrocene, or 9-fluorenone and combined and evaporated to collect the now separated solutes, which were massed. Both acetylferrocene and ferrocene are metallocenes, which are called “sandwich compounds” because they are generally made of two cyclopentadienyl anions bound to a metal center that has an oxidation state of II. For example, ferrocene is two cyclopentadienyl anions joined by an iron (II) ion. There is a very strong bonding interaction between the two cyclopentadienyl anions and the iron (II) ion because a whole pi-system of the cyclopentadienyl anions is interacting with that iron ion. Ferrocene is in the least polar of all the components of the mixture.

Acetylferrocene, though similar to ferrocene in that it is also a metallocene, is formed through Friedel-Crafts acylation of one of the cyclopentadienyl rings of ferrocene. The iron ion is practically only a spectator here, and instead the cyclopentadienyl ring acts similarly to a benzene ring in electrophilic substitution. Acetylferrocene is the most polar of all the components in the mixture.

Procedure: This experiment was carried out as described in the given manual procedure. The only modification to the procedure that was carried out in this experiment was the collection of close to 10 mL of elute in the 8th test tube, because the silica gel was not completely white after the first 5mL of elute. Pure tBME was added until the gel was not colored. Results: The eight test tubes, each with 5mL elutes, were collected an analyzed for polarity through a TLC plate. It was found that, through the Rf values showing three clearly different groups polarity wise from the TLC plate, there are clearly three distinct components of the original acetylferrocene mixture. The most polar acetylferrocene, the less polar 9-fluorenone, and the nonpolar ferrocene all separated out into groups on the TLC plates. Test tubes 1 and 2 tad Rf values that nearly matched the 3rd Rf value in the original mixture. Test tube 3 had Rf values that matched the 2nd and 3rd Rf values of the original mixture. Test tubes 4, 5, 6, and 7 all had similar Rf values that matched the 2nd Rf value of the original sample. Test tube 8 had an Rf value that was exactly the same as the original sample’s 1st Rf value. The percent of each component recovered in relation to the original mixture was 22.43% for ferrocene, 43.93% for 9-fluoreneone, and 16.82% for acetylferrocene. The overall percent recovery of the mixture in general was 83.18%. Table 1: Results from the TLC Place and Test Tube Observations Solution Color Rf Value 1 Rf Value 2 Rf Value 3 Component of Sample (if sample (if sample Mixture has 2 spots) has 3 spots) Original Red 0.2 0.575 0.875 Original Mix Test Tube 1 Clear 0.775 Ferrocene Test Tube 2 Yellow 0.85 Ferrocene Test Tube 3 Clear 0.85 0.475 Ferrocene and 9-fluorenone Test Tube 4 Clear 0.5 9-fluorenone Test Tube 5 Clear 0.475 9-fluorenone Test Tube 6 Clear 0.5 9-fluorenone Test Tube 7 Yellow 0.55 9-fluorenone Test Tube 8 Red 0.2 Acetylferrocen

e Table 2: Observations After Combining the Test Tubes and Gathering the Dried and Isolated Components Mass (grams) Color Percent of each compound relative to the initial quantity of the unknown mixture Original Mixture 0.107 g Dark red Ferrocene 0.024 g Orange 22.43% 9-Fluorenone 0.047 g Light green 43.93% Acetylferrocene 0.018 g Red 16.82% Figure 1: Image of the TLC plate

Sample Calculation for Percent Recovery:

((0.024 + 0.047 + 0.018)/(0.107))*100 = 83.18% Discussion/ Conclusion: In this experiment, ferrocene, 9-fluorenone, and acetylferrocene were all separated out from a “waste” acetylferrocene mixture thought the use of flash chromatography and a TLC plate analysis. Ferrocene, which was the least polar component of the mixture was separated out through the adding of the nonpolar solvent petroleum ether. 9-fluorenone, which is more polar than ferrocene, was separated out through the adding of a more polar solvent, 8% tBME/ petroleum ether. Acetylferrocene, the most polar component, was separated our though the addition of the most polar solvent, pure tBME. After analyzing similarities in Rf values of the 8 samples from the 8 test tubes, conclusions were drawn. Test tubes 1 and 2 contained pure ferrocene, as the spots from these two tubes relatively matched the 3rd and farthest-traveling spot of the original mixture. Since both of these samples had high Rf values, it can be concluded that they contained the most nonpolar component, which is ferrocene. Test tube 3 contained both ferrocene and 9-fluorenone, as two spots were produced had a high Rf value and a somewhat high Rf-value that matched the 3rd and 2nd spots from the original mixture sample. The two spots showed that two components with different polarities were in the tube, and one of those components was nonpolar (ferrocene) and the other was somewhat polar (9-fluorenone). Test tubes 4, 5, 6, and 7 all contained pure 9-fluorenone because their somewhat-high Rf values indicated that the compound in the tubes was somewhat polar and were also very similar to the 2nd spot from the original sample. Test tube 8 contained pure acetylferrocene, as it matched the 1st spot in the original mixture and had a very low Rf value, indicating strong polarity. Of all the components, 9-floreneone seemed to have comprised the majority of the mixture, with ferrocene being the second most abundant, and acetylferrocene being the least abundant. This is because the percent of each compound relative to the initial quantity of the unknown mixture was 22.43% for ferrocene, 43.93% for 9-fluorenone, and 16.82% for acetylferrocene. The solvent used in the column chromatography component-isolation process is extremely important. Polar solvents will move both nonpolar and polar solvents down a column (meaning little separation occurred), while nonpolar solvents will only move nonpolar solvents down a column (meaning only the nonpolar solute gets collected). Knowing this, it is very important to carefully choose the solvents used in the experiment in order to properly conduct the separation. If only a nonpolar solvent, like petroleum ether, was used for the entirely of this experiment, only ferrocene would be collected. The polar compounds, 9-fluorenone and acetylferrocene, would not be collected and the separation would fail. On the other hand, if only the very polar tBME was used to elute the column, all of the components would be quickly dragged through the column all at once and the collected samples would have little to no separation of products at all....