Acetylation+of+Ferrocene

**Introduction:**
Acetylation is a reaction that attaches an acetyl functional group to a compound. This is an important reaction because it makes a new carbon to carbon bond, which is the foundation of chemical synthesis. In this experiment, ferrocene will undergo acetylation using acetic anhydride. Ferrocene is a organometallic compound with special properties that allows it to give up electrons to many kinds of electrophiles. To test the purity of the acetyl ferrocene, the melting point could be measured, but also a thin layer chromatography (TLC) can be effective. TLC compares the starting material, crude product, and final product by showing how much starting material and final product is in each sample.

To begin place 1.55g of ferrocene in a 20ml round bottom flask along with a magnetic stir bar. Under a fume hood add 5.0ml of acetic anhydride and 1ml of 85% phosphoric acid. Swirl the mixture and/or heat with a stir with a hot water bath until the ferrocene has dissolved. Once dissolved attach a reflux condenser and heat and stir with a hot water bath for 10min. The color should change from a dark red to a dark purple color. Now to begin the purification process pour the mixture into a flask with a few ice cubes (about 25g of ice). A black tar like substance should remain stuck inside the round bottom flask. Stir the cloudy orange slush for a few min and let the ice melt. Next add 37.5ml of 3M NaOH to the mixture and add a small increments of sodium bicarbonate until the acid has been neutralized (pH of around 7). Let the mixture sit for 20min and then collect the crude product using vacuum filtration. Make sure the crude product is fully dry by pressing it between two filter sheets (this may take a few attempts). Once dry set aside a very small amount of the crude product for Thin Line (Layer) Chromatography analysis. In the meantime add the rest of the crude product and a stir bar to an Erlenmeyer flask and add 20ml of hexanes. Using a fume hood again heat the mixture until the hexanes begin to boil then take off the heat and mix for a few minutes then repeat until most of the red crude product is dissolved. Decant the mixture on top into a new flask leaving behind gooey black impurities. Next set the flask aside to cool to room temperature. Once at room temperature put the flask into an ice bath to further recrystallize the product. Red sea urchin like crystals should form near the bottom of the flask. Collect the crystals using vacuum filtration and make sure they are fully dried using the filter paper technique used before. Measure the melting point and weight of the final product and calculated the percent yield.
 * Procedure:**

I would like you to cite the Doxsee and Hutchison book, which is the source of this procedure. Where'd you get Feiser and Williamson?


 * Data:**

Please put this reaction in the introduction section. Oops--also, there is a mistake in your curved arrows. The cyclopentadienyl ring (in the ferrocene) attacks the carbonyl carbon, not the carbon in the position next to it.
 * Experimental Reaction:**


 * Observations:**
 * Flask was warm after the acetic anhydride and 85% phosphoric acid.
 * 26.2 grams of ice was used to begin purifying the reaction mixture
 * The acetic anhydride and phosphoric acid turned a dark purple after heated.
 * When neutralizing, very little sodium bicarbonate was needed.
 * After the 3M aqueous NaOH solution was added, the mixture separated into two distinct layers.
 * After a double decant, the product recrystallized into dark red crystals


 * Final Product:**

**Results:**

 * Final Product Properties:**
 * **Sweat Point** || **Melting Point** ||
 * 73.4 Degrees Celsius || 74.1 Degrees Celsius ||
 * Literature Melting Point of Acetylferrocene:** 81-86 degrees Celsius


 * Mass of Pure Product**: 0.46 grams You appear to have dropped a digit from this measurement. That's a sig figs No-No.


 * Thin-Layer Chromatography:**
 * Pure,** **Crude,** **Ferrocene.**
 * Theoretical Yield of Ferrocene:**

1.5 g Ferrocene X 1 mol/186 g Ferrocene = .008 mol sig figs!! yikes!

.008 mol Ferrocene X 228 g Acetylferrocene/1mol = **1.82 grams T.Y.**
 * Actual Percentage Yield:**

0.461 g Pure (actual)/ 1.82 g T.Y. X 100% = **25.3%** You've got a really nice TLC. Calculations appear OK, except for sig figs issues.

**Discussion/Conclusion:**
The purpose of this lab was to show a substitution reaction where and acetyl group is substituted for a hydrogen in ferrocene. Many impurities are added to ferrocene in order for this to happen, including phosphoric acid, NaOH, and hexanes. This leads to two flirtations (filtrations) needed in order to filter out the impurities. The weight of our final "pure" product (I use quotations because we found are product was not so pure after all) is 0.46 g. The theoretical yield calculated for this experiment is 1.82 g. Therefore, our percent yield is 25.3%. This would be considered quite low for this experiment, however, not all of the crude product was used for the second half of the lab. Had we used all of the crude product, our percent would probably been a bit higher. Our final product is easy to see it is not pure by looking at the Thin-Layer Chromatography. The yellow represents the ferrocene we started with (as shown in the third column with contained just ferrocene.). The orange represents the presence of acetylferrocene. The crude product (the one in the middle) shows a presence of both ferrocene and acetylferrocene. The first column, which is supposed to be our pure product, shows mostly acetylferrocene, but ait also shows there is still some ferrocene that did not get filtered out. Our melting point range is another good example that shows our product isn't pure. Our melting point range was 73.4 - 74.1 degrees Celsius, while the literature range is 81.0 - 86.0 degrees Celsius. Almost 10 degrees lower than it should be, our low melting point suggests impurities in our final product. You've done a nice job analyzing your data.

**Errors:**
It is possible we did not wait long enough to let our mixture sit before the first filtration. We also did not wait long enough to decant the mixture after our red crude product had been dissolved. It would have been a good idea to let it sit a settle before going straight to decanting. This could be a cause for ferracene remaining in our final product.

**Citations:**
L.F. Fieser and K.L. Williamson, "Organic Experiments," 8th Edition; Houghton Migglin Co: New York, 1998