Lab 5_ Chromatography of an Acetylferrocene Mixture

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Vanderbilt University *

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MISC

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Chemistry

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Feb 20, 2024

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10.27.2023 Chromatography of an Acetylferrocene Mixture Introduction: The purpose of this experiment was to isolate the acetylferrocene from the unreacted starting material ferrocene and 9-fluorenone and determine the composition of the “waste” acetylferrocene mixture. In this experiment we used chromatography columns (packed with cotton, sand, silica gel, the targeted mixture, and solutions to aid in eluting the targeted mixture) to separate the mixtures and then used TLC chromatography to determine the success of separation and identify the end products. The sand and cotton specifically, acted as buffers so that the silica gel was not disturbed in the process of the experiment. The materials packed into the column chromatography, was the most significant aspect of separating the “waste” acetylferrocene mixture. The polar silica gel was used to separate the mixture based on polarity alongside the different eluents used. Both of these techniques looked at separating the compounds based on their polarity: the nonpolar solvent is always attracted to the nonpolar compound and will typically elute first. We also used tBME (a polar solvent) to modulate the polarity of the mobile phase and pull acetylferrocene off the column; this is also an important solvent used outside of the lab to fabricate polymer lithium ion batteries. Lastly, obtaining the percent yield and Rf values of the results were determined and compared. The importance of this experiment was to test our knowledge of the different separation techniques and analyze the polarity of acetylferrocene, ferrocene and 9-fluorenone. The main theme of each separatory technique is the use of a stationary (polar silica gel) and mobile phase. The acetylferrocene mixture was placed on top of the silica gel and then a nonpolar eluent (petroleum ether) was placed on top of that, making the most nonpolar molecule (ferrocene) of the acetylferrocene mixture separate first and eluted out of the column chromatography. This was done until each compound was separated from the mixture with different polarities of eluent. Acetylferrocene being the most polar compound, then 9-fluorenone, and lastly, ferrocene the most nonpolar compound. Procedure:

During the experiment, the procedure was followed as demonstrated in the given guidelines received prior to the experiment. One thing to note is that I weighed out 0.104 g of the mixture instead of weighing out exactly 0.100 g. Results: Acetylferrocene “Waste” Mixture: 0.104 g Compounds Weight After Evaporation (g) Percent Recovery Rf Values Ferrocene (Flask #2) 1.18 11.34% 0.88 9-Fluorenone (Flask #5+6) 0.70 6.73% 0.47 Acetylferrocene (Flask #8) 1.58 15.19% 0.24 Discussion The intent of the laboratory experiment was to successfully separate acetylferrocene (most polar), 9-fluorenone (polar) and ferrocene (non-polar) from a “waste” mixture of acetylferrocene, then using TLC to analyze the results of the polarity. In the column chromatography, the ferrocene was eluted first with the help of the polar petroleum ether, then 9-fluorenone was eluted with adding 8% tBME solvent on top of the petroleum ether, and finally the acetylferrocene was the last to be eluted with the pure tBME solvent (very polar). This was done in increments of 5 ml of solution in 8 test tubes. After analyzing the percent recovery and Rf values, the first and second tubes contained pure ferrocene (highest Rf value) and the spots on the TLC were the furthest from the bottom of the TLC plate. The 5th and 6th tubes contained pure 9-fluorenone and were demonstrated on the TLC plate as halfway traveling up the plate and approximately half of the Rf value that ferrocene had. Lastly, the 8th tube carried pure acetylferrocene and did not travel far on the TLC plate with an Rf value of 0.24 (lowest integer). The analysis of the Rf values shows the success of the experiment because it demonstrates the ratio of the solute’s distance traveled to the solvent’s distance traveled. Conclusion The purpose of this experiment was to isolate the acetylferrocene from the unreacted starting material ferrocene as well as compound 9-fluorene. One thing to note, during this experiment, was the weight ratio of acetylferrocene “waste” mixture and the weight of each component after evaporation. The weight of ferrocene and acetylferrocene were greater than the

mixture at the beginning of the experiment. This could have been a human error and an unclear conclusion to these results, and can be visualized based on the low percent recovery. I predict that some other liquid made its way into the test tubes after the column chromatography took place. I also used two different weighing stations and in the future will stay consistent with the same station used throughout the experiment. Overall, the experiment was a success; ferrocene having the highest Rf values (least polar compound) and acetylferrocene having the lowest Rf values (most polar compound). 1. Explain what you would expect to happen if you tried to elute your column with only petroleum ether. a. Petroleum ether is a very nonpolar solvent. If I attempted to elute my column solely using petroleum ether then only ferrocene would be eluted from the “waste” mixture, as it is a nonpolar molecule. 2. Explain what you would expect to observe if you tried to elute your column with only tBME a. tBME is a very polar solvent. If I tried to elute my column with only tBME, then I would expect to observe little to no separation between the three compounds due to its polarity. 3. Based on your results, what was the percent composition of the three components in the “waste” acetylferrocene a. The percent composition demonstrates by mass what percent of each constituent is present in the compound. The percent composition of the three components in the “waste” acetylferrocene were as follows: i. Ferrocene: 12.27% ii. 9-Fluorenone: 7.28% iii. Acetylferrocene: 16.43%

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Extra Credit References: https://fscimage.fishersci.com/msds/69220.htm https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/column-chromatograp hy https://academic.oup.com/chromsci/article-abstract/10/4/200/290201