Acetylation+of+Ferrocene

=Introduction=

The purpose of this lab is to perform the acetylation of ferrocene. This is an electrophilic aromatic substitution reaction which involves the formation of a carbon to carbon bond. Ferrocene consists of a metal atom, in this case iron (Fe), bound between two cyclopentadienyl rings, shown below. The iron gives the products of the reaction a visible color. This lab will use acetic anhydride, in place of commonly used acyl chloride, to acylate the ferrocene, and phosphoric acid will be used in place of a hazardous, strong Lewis acid; therefore, this lab procedure is a greener approach to the reaction.



A Thin Layer Chromatography (TLC) analysis will be performed to compare the starting, crude and recrystallized products. Thin Layer Chromatography is a process used to separate mixtures based on their polarity. The effectiveness of the this separation depends largely on the stationary and mobile phases used. For the purposes of this lab, a silican (silicon) dioxide (polar) stationary phase will be used in concert with 30:1 toluene/ethanol (non-polar) mobile phase. As a result, the polar molecules will be more "attracted" to the stationary phase than the non-polar molecules and travel a shorter distance. For this reason, TLC can also be used to monitor a reaction's progress and identify which compounds are present in a mixture as well as aiding in determination of a product's purity. good job. nice intro. =Procedure=

The procedure for the experiment can be found here (Doxsee, 2004).

The procedure was followed with the following exceptions. In step 3, no calcium chloride drying tube was connected to the reflux condenser. In step 7, the hexanes were brought to a boil, removed from heat and stirred for two and a half minutes. This process was repeated twice. In step 8, the product was decanted into another flask in place of hot filtration.

Relevant Compounds
(Recovered via NIST)


 * Name:** 1,1'-Diacetylferrocene
 * Cas #** 1273-94-5
 * Molecular Formula:** C 14 H 14 FeO 2


 * Name:** [3M] Aqueous sodium hydroxide
 * Cas #:** 1310-73-2
 * Molecular Formula:** NaOH


 * Name:** 85% Phosphoric acid
 * Cas #:** 7664-38-2
 * Molecular Formula:** H 3 O 4 P


 * Name:** Acetic acid
 * Cas #:** 64-19-7
 * Molecular Formula:** C 2 H 4 O 2


 * Name:** Acetic anhydride
 * Cas #:** 108-24-7
 * Molecular Formula:** C 4 H 6 O


 * Name:** Acetylferrocene
 * Cas #:** 1271-55-2
 * Molecular Formula:** C 12 H 12 FeO


 * Name:** Ferrocene
 * Cas #:** 102-54-5
 * Molecular Formula:** C 10 H 10 Fe


 * Name:** Hexanes
 * Cas #:** Varies
 * Molecular Formula:** Varies


 * Name:** Sodium bicarbonate
 * Cas #:** 144-55-8
 * Molecular Formula:** NaHCO 3

=Data=

Reaction
1.514 g of ferrocene, red in color, was placed in to a 20 mL round bottom flask with a magnetic stir bar. 5.0 mL of acetic anhydride and 1.0 mL of 85% phosphoric acid was then added to the flask containing the ferrocene. The flask was lightly swirled around in order to help in the dissolution of the ferrocene. At this point, the misture's color began to darken (figure 2) and there was a noticeable amount of heat coming from the flask.



Once all of the ferrocene had dissolved, a reflux condenser was attached and heat was applied via a water bath brought to just below a boil (figure 3). The mixture was heated with active stirring via magnetic stir bar for 10 minutes. During this time, the color continued to darken. This effect was most likely ampliphied by the formation of a dark gummy solid forming on the sides of the reaction flask.



Workup and Purification 25 g of ice was placed into a 250 mL beaker. record the mass precisely! The resulting reaction mixture was then poured over the ice and the reaction flask was rinsed with 2 5 mL portions of ice water. The mixture was not as dark as it had appeared in the reaction flask, however, it was still darker than in the earlier reaction steps. There were also pieces of the darker substance that had formed on the sides of the reaction flask present in the mixture at this time. The mixture was stirred with a glass rod for approximately 5 minutes at which time all of the ice had melted (Figure 4).



37.5 mL of [3M] aqueous sodium hydroxide was added to the mixture. 1.454 g + / - .002 g of sodium bicarbonate (Figure 10) was slowly added to the mixture with magnetic stirring until a pH of 7 was obtained. The resulting mixture was still red, but it was lighter in color (Figure 5).



The mixture was allowed to stand for twenty minutes and then the crude product was collected via vacuum filtration. The resulting crude product was a brownish red (Figure 6). The filtrate was lighter than expected and had a very vibrant rosy red color (Figure 7). A small amount of the crude product was set aside for a TLC analysis.





The crude product was transferred into a small Erlenmeyer flask and mixed with 20 mL of hexanes. The resulting mixture was heated to boiling while being stirred. Once boiling, the flask was transferred to a cool hot plate and continued to be stirred for two and a half minutes. The flask was then put back on heat and brought back up to a boil. Again, once a boil was achieved, the flask was moved to the cool hot plate and stirred for an additional two and a half minutes.

The liquid was then decanted into a new flask leaving behind a dark grimy solid. A small amount of norit was added to the hot solution and swirled lightly by hand for approximately two minutes. Again, the liquid was decanted away from the norit into a new flask and set aside to cool to room temperature. Reddish brown needle crystals began to form after a few minutes.Once the liquid was cooled to room temperature, the flask was put into an ice bath to aid in the formation of crystals. After approximately ten minutes in the ice bath, the flask was removed (Figure 8). The resulting crystals were collected via vacuum filtration and washed with a small amount of cold hexanes. The final product was redish brown in color and composed of thick needle-like crystals (Figure 9).





Characterization what beautiful crystals! .773g of acetylferrocene was recovered resulting in a yield of 41.7% (Figure 11). A melting point of the sample was obtained via a MelTemp and LabQuest and recorded at 84.5℃-85.3℃.

A small amount of pure ferrocene, the crude product, and the recrystallized acetylferrocene was dissolved in a few drops of 30:1 toluene/ethanol for a TLC analysis. A silica gel plate was prepared by making a horizontal line across the plate approximatetly a quarter inch from the bottom of the plate. Three spots were marked equal distances apart from one another on this line. A small sample of each substance was transferred to a silica gel plate via a spotting capillary tubes with each being placed onto its own previously marked spot. The plate was then developed with 30:1 toluene/ethanol (Figure 10). As expected, the non-polar ferrocene shown on left had the highest R f value of .643. This was followed by an unknown substance speculated to be a acetic acid left over from the initial reaction (purple in crude and final) with an R f Value of .476. Next, was the target molecule acetylferrocene (large red blob in crude and final) with an R f Value of .19. Lastly, is a molecule speculated to be 1,1'-Diacetylferrocene with an R f Value of 4.8 x 10 -2 (Figure 13).



=Analysis=

Workup and Purification


Characterization
 * % Yield**



**Purity**




 * TLC Analysis**



=Conclusion=

In this lab, the acetylation of ferrocene was performed, resulting in acetylferrocene as a final product. The crude product was brownish red in color. The recrystalized product was a dark brownish red in color. The melting point range for the final product was 84.5° C - 85.3° C (Figure 12). This was consistent with the literature melting point ranges for acetylferrocene of 81° C - 83° C and 84° C -85° C (Doxsee 2004). This finding is strengthened by the accompanying TLC. It shows that a more polar product was formed via the reaction. The two possible products in the reaction both show up in the TLC. As expected, the more favored and least polar product (acetylferrocene) traveled further and left a much larger spot than the least favored and most polar product (1,1'-Diacetylferrocene). There was a small impurity that showed up in both the crude product and the final product represented by the small purple dot at the top of the acetylferrocene spot. By it's position, it can be determined to be less polar than either acetylferrocene or 1,1'-Diacetylferrocene but more polar than the original ferrocene. It is speculated that this impurity is acetic acid left over from the initial reaction that could not be washed during the purification process. The final mass of acetylferrocene was 0.773g, which results in a percent yield of 41.7%. The low percent yield could be due to limitations that occurred during the lab.

One possible error that may have occurred during this lab was the use of too much carbon during step 8 of the procedure. The procedure called for the addition of a spatula-full of decolorizing carbon to the hot solution. However, it was unclear what was meant by a "spatula-full". The use of too much carbon would result in a lower percent yield. As with any synthesis, each time a mixture is moved from one container to another, there is a loss of product. This experiment had 7 transfers in total. This error could also contribute to the low % yield. VERY nice. A pleasure to read!!

Resources
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 228-230.

Koster, S. K. (Artist). (2000). //Acetylation of ferrocene//. [Print Graphic]. Retrieved from http://www.uwlax.edu/faculty/koster/acetylferrocene.htm

P.J. Linstrom and W.G. Mallard, Eds., NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg MD, 20899, [|http://webbook.nist.gov], (retrieved February 29, 2012)