Chromatography of a Mixture of Ferrocene and Acetylferrocene PDF

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Organic Chemistry Lab Chantal Levy Marian McEachin May 5, 2020 Column Chromatography: Chromatography of a Mixture of Ferrocene and Acetylferrocene Abstract In this experiment, a two-component mixture comprised of ferrocene and acetylferrocene were separated by chromatography on alumina. The first compound to separate as a yellow band from the mixture was ferrocene. After increasing the solvent polarity, acetylferrocene eluted out of the solution as an orange band. Both compounds were collected in separate flasks, solvents were evaporated, products were recrystallized and weighted. The experiment produced .031 g of ferrocene and .030 g of acetylferrocene, indicating an unsuccessful recovery and a loss of product during the procedure. Introduction Column chromatography is one of the most useful methods for the separation and purification of both solids and liquids when carrying out microscale experiments. Chromatography takes advantage of the differences in polarity and binding strength that the components of a mixture have for column absorbents. Adsorbents are high surface area stationary phase materials that bind solute molecules. A mobile phase solvent, or eluent, is used to desorb solute molecules, carrying them along the column. As the solvent polarity is increased, polar molecules bound more strongly to the column begin to solubilize and are carried down the column in the mobile phase. Equilibrium is established between binding to the stationary phase and solubility in the mobile phase. As the solvent polarity increases, more tightly bound polar molecules, firmly held by the adsorbent, establish equilibrium with the eluting solvent and flow along the column [CITATION The14 \l 1033 ]. Three mutual interactions must be considered in column chromatography: the activity of the stationary absorbent phase, the polarity of the eluting mobile solvent phase, and the polarity of the compounds in the mixture being chromatographed. The most common adsorbents for column chromatography-silica gel (SiO2) and alumina (Al2O3) -are the same stationary phases as used in thin‐ layer chromatography (TLC), both are polar. Adsorption is the process of molecules ‘adhering’ to one another, without the making of chemical bonds [ CITATION Hel \l 1033 ]. The eluent is the mobile phase or the solvent that is passed through the column. Normally, a separation will begin with a nonpolar or low-polarity solvent, allowing the compounds to adsorb to the stationary phase; then the polarity of the solvent is slowly increased to desorb the compounds and allow them to move with the mobile phase. The polarity of the solvent should be changed gradually. A sudden change in solvent polarity will cause heat evolution as the alumina or silica gel adsorbs the new solvent. This will vaporize the solvent, causing channels to form in the column that severely reduce its separating power [CITATION Wil176 \p 187 \l 1033 ]. Molecules with nonpolar functional groups are least adsorbed and elute first, while more polar or hydrogen-bonding molecules are more strongly adsorbed and elute later [CITATION Wil176 \p 188 \l 1033 ]. Ferrocene is an organometallic compound with the formula Fe(C5H5)2. The

molecule consists of two cyclopentadienyl rings bound on opposite sides of a central iron atom. Fe r r o c e n ee x h i bi t st h ep r o p e r t i e so fat y p i c a la r o ma t i cmo l e c u l e .Th ec o mp o un di sr e ma r k a b l e f ori t ss t a b i l i t y ;i tc a nb eh e a t e dt o4 0 0° Cwi t ho u td e c o mp o s i t i o n .I td oe sno tr e a c tr e a d i l ywi t h a c i d so rb a s e s ;h o we v e r ,i ti ss e n s i t i v et oo xi d i z i n ga g e n t s .Acetylferrocene is an organoiron compound with the formula Fe(C5H4COCH3)(C5H5), it consists of ferrocene substituted by an acetyl group on one of the cyclopentadienyl rings [ CITATION Wik \l 1033 ]. The acetyl group makes acetylferrocene more polar than ferrocene, because acetylferrocene has a higher affinity for the stationary phase, it will move slower down the column. Procedure adapted from Pre-Lab Received instruction from the lab instructor to calculate the percent recovery of the crude and recrystallized products based on the 45 mg quantity of each in the original mixture. Choose a percentage recovery between 30-70%, and two errors of any type. Discussion Table 1 Chromatography Results of Ferrocene and Acetylferrocene Order of Elution Rf value Melting point Identity of from Column Compound First .82 172-174°C Ferrocene Second .22 85-86°C Acetylferrocene

Weight of Residue .031 g .030 g

Calculations: Actual yield of ferrocene = .031 g .031 g Percent yield = x 100% = 68.9% 0.045 g Actual yield of acetylferrocene = .030 g .030 g x 100% = 66.7 % Percent yield = 0.045 g Based on the percent yield of ferrocene (68.9%) and acetylferrocene (66.7%), it can be concluded that the separation of the two-component mixture based on their relative polarities through column chromatography was somewhat successfully performed. Separating the components out of the mixture was carried out with very little error. Ferrocene eluted first, it moved through the column faster than acetylferrocene because it is less polar and preferred to travel with the less polar solvent (hexanes). On the TLC plate, ferrocene had less affinity for the stationary phase (silica) and moved further up the plate. During the collection and evaporation process errors were made, one source of error was the proper stopping of the valve before all of the ferrocene was collected. After the flow was stopped, some of the compound remained in the column and the remaining residue at the tip of the valve was not recovered, failure to completely collect all of the ferrocene resulted in a loss of product. Instead of heating the flask containing the acetylferrocene by hand, the flask was placed on a sand bath. Acetylferrocene has a melting point between 85-86 °C, the sand bath temperature

was higher than 80°C causing the acetylferrocene to melt rather than dry which resulted in a loss of product. Conclusion The purpose of this experiment was to separate ferrocene and acetylferrocene using column chromatography. Similar to thin‐ layer chromatography (TLC), column chromatography separates mixtures based on polarity. An alumina adsorbent was used as the stationary phase, hexanes and a 50:50 mixture of hexanes and ether were used as the mobile phases. Overall, the experiment was performed with some success, the two compounds did separate out of the mixture, the less polar ferrocene eluted first followed by the more polar acetylferrocene. However due errors, only 68.9% of ferrocene and 66.7% of acetylferrocene were recovered. References Helmenstine, Anne Marie, Ph.D. "What Adsorption Means in Chemistry." ThoughtCo, Feb. 11, 2020, thoughtco.com/definition-of-adsorption-605820. “Microscale Flash Column Chromatography of a Mixture of Ferrocene and Acetylferrocene.” ThermoFisher Scientific. Retrieved from www.thermofisher.com › industrial › nmr-lesson-plans. Wikipedia contributors. "Ferrocene." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 29 Apr. 2020. Web. 4 May. 2020. Wikipedia contributors. "Acetylferrocene." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 21 Oct. 2019. Web. 4 May. 2020. Williamson, K. L., & Masters, K. M. (2017). Macroscale and microscale organic experiments. Boston, MA: Cengage Learning. pp 186-205....