Week+7-+Friedel-Crafts+Reaction

=Week 7- Acetylation of Ferrocene= = = =Introduction:=

Friedel-Crafts reactions, developed by Charles Friedel and James Crafts, are a set of reactions widely used to add substituents to an aromatic ring. Acetylation is a reaction that introduces an acetyl functional group into a chemical compound. Acetic anhydride is used in the acetylation shown in Picture 1 and is a very common agent in this process. Ferrocene is an organometallic compound with the formula Fe(C5H5)2. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds. The purpose of this lab is to acetylize ferrocene using acetic anhydride. After the experiment has completed, the percent yield will be determined and the purity of the end product will be compared to the intermediate crude product (from step 3 below) and the ferrocene that the experiment was started with. The percent yield will be determined by mass and the relative purity will be determined by Thin layer chromatography (TLC). This is a sheet of plastic coated with a thin layer of adsorbent silica gel. A substance is doted on the bottom of the sheet, far enough up not to touch the solvent mixture it will be placed in. The substance is then drawn up the plate via capillary action (wiki). The TLC result for ferrocene should be yellow/orange in color and farther up the developer paper and the result from the acetylferrocene should be a darker red/orange color and lower on the developer paper. This makes sense, because the more polar a substance, the slower it travels up the developer paper.

Source of picture: [] =Procedure:=

Source for procedure: [] = = =Data/Analysis:=
 * Reaction: **
 * 1) In a 25 mL round-bottom flask containing a magnetic stir bar, add 1.5 g of ferrocene. Then prepare a hot water bath, heating the water till it is nearly boiling.
 * 2) Inside the fume hood, add 1.0 mL of 85% phosphoric acid and 5.0 mL of acetic anhydride to the flask. The reaction should darken in color and heat up. Swirl the flask until all the ferrocene is dissolved.
 * 3) Attach a reflux condenser, while stirring the reaction heat in the hot water bath prepared earlier. Continue to heat and stir for ten minutes, during which time the color may change to a dark, purple/brown color.
 * Workup and purification: **
 * 1) In a 200 mL beaker place 25 g of ice. Pour the reaction mixture over the ice and rinse the flask with two 5 mL portions of ice water. (A black residue may remain in the flask.) Stir the mixture, which should be orange-brown, for a few minutes with a glass rod. If insoluble black material is present, the following steps will remove it.
 * 2) Add 37.5 mL of 3M aqueous NaOh solution. To neutralize the remaining acid, carefully add solid sodium bicarbonate is small portions. (Great care should be taken to avoid excessive foaming from the addition of sodium bicarbonate. This maybe done with the magnetic stirrer.) The suspension should be dark-brown. Crush any lumps and stir well.
 * 3) Let mixture stand for 20 minutes. Collect the crude product through vacuum filtration. Finish the drying process by placing the crude product between two sheets of filter paper. Save a little bit of crude product for TLC analysis.
 * 4) Place dried product in a small Erlenmeyer flask and add 20 mL of hexanes. Do this in the hood. Heat and stir for five minutes, being careful not to boil off the hexanes. Decant the solution, which should be dark-orange, into another Erlenmeyer flask leaving behind the black gummy substance.
 * 5) Add a spatula-full of decolorizing carbon (Norit) to the hot solution. (Do not use too much to prevent loss in yield.) Stir for a few minutes, then decant the solution into a small beaker leaving behind the Norit.
 * 6) Allow the beaker to cool slowly at room temperature. Red-brown needles of acetylferrocene should form. Once it has cooled to room temperature, cool it in an ice bath. In a vacuum filtration collect the crystalline product, pulling air through it for a few minutes.
 * Characterization: **
 * 1) Using a Mel-temp apparatus, record the melting point of the final product as well as the yield. (melting point should be either 82-83 or 84-85 ºC.)
 * 2) By TLC, analyze the initial ferrocene, the crude product, and the final acetylferrocene. To do this dissolve small amounts of each with a few drops of toluene. On the silica gel plate spot each solution and develop with 30:1 toluene/absolute ethanol. Each compound will be brightly colored making visualization simple.

added to 1.506 g Ferrocene || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">The color went from a dark-orange to a dark-brown. The reaction caused the substance to heat immediately. Then heated in a hot water bath from 9:15-9:25 am. While heating the substance turned purplish. ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Reaction: **
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Reactants || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Observation ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">5.0 mL of acetic anhydride and 1.0 mL of 85% phosphoric acid

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Two 5 mL portions of ice water || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">The reaction mixture is taken off the heat and poured over the ice in a 200 mL beaker. Ice water was used to clean the round bottom flask. The mixture turns chunky yellow brown. Mixture is stirred for a few minutes. || You had an odd melting point thing happen, there, didn't you? Not an easy one to interpret, although the wide range would indicate impurity.
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Workup: **
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Reactants/Product || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Observations ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">25.018 g of ice
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">37.5 mL of 3M aqueous NaOH solution || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">The mixture turned orange brown. No sodium bicarbonate was added. The mixture was already neutral. The mixture then sat for 20 minutes (from 9:35-9:55). ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">2.268 g of crude product collected || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">To collect the crude product vacuum filtration is used. The product was orange and the precipitate that came out was brown. A little portion of crude product is saved for the TLC analysis. ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">20 mL of hexanes || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">The hexanes is added and the mixture is brought to almost boiling and stirred for 5 minutes. Norit (decolorizing carbon) is added to the mixture and stirred for a few minutes. There is no color change. ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">0.563 g of final product || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">To remove the norit the product is decanted out into another flask and allowed to cool slowly at room temperature. Red-brown needles of acetylferrocene did not form immediately. A glass stirring rod was used to scrape the bottom of the flask to initiate crystallization. It is then cooled in an ice bath to further crystallize. The crystals were minimal and only on the bottom of the flask. Vacuum filtration is used to gather the crystals. In the collection flask, coral looking crystals formed. ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Characterization: **
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Melting point || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Observations ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">73.5 ºC || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Started to sweat then stopped (or went slowly). ||
 * <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">114.8-135.6 ºC || <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Began to sweat again and slowly melted. ||

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Mass summary: <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Starting ferrocene – 1.506 g <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Crude product – 2.268 g <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Final product – 0.563 g

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Percent Recovered Through Each Recrystallization:

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">2.268 g of crude product / 1.506 g of starting product * 100 = 150.4 % recovered <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">This high recovery is due to the additions made to the mixture. I imagine it still had solvent in it, that contributed to the high mass. <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">0.563 g of final product / 2.268 g of crude product * 100 = 24.8 % recovered <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">0.563 g of final product / 1.506 g of starting product * 100 = 37.4 % recovered through whole experiment <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Each time the substance was recrystallized substance was lost.

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Percent Yield Calculations: <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">1.506 g C10H10Fe * (1 mol/186.03g) = 0.008095 mol <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">8.095 * 10^-3 mol C10H10Fe * (1 mol C12H12FeO/ 1 mol C10H10Fe) = 8.095 * 10^-3 mol C12H12FeO <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">8.095 * 10^-3 mol C12H12FeO * (228.07g/ 1 mol C12H12FeO) = 1.846g Theoretical Yield <span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Actual Yield is 0.563 C12H12FeO

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">(0.563 g C12H12FeO/ 1.846g C12H12FeO) * 100 = 30.6% Yield

TLC :
From left to right: 1. Original sample of ferrocene 2. Intermediate step crude product 3. Final product.

=**Conclusion:**= The overall conclusion is that after all was said and done, there was a mixture of ferrocene and acetylferrocene in the final product. The purity was definitely not ideal. This conclusion is supported both by the melting point data and the TLC result. Well said. According to Wikipedia the melting point of pure ferrocene is 172.5<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">ºC and for acetylferrocene the melting point is 81-83ºC. The melting point of a mixture of two compounds will have a lower melting point than the lowest compounds pure melting point and the range will be wider. The final product began to sweat at 73.5 ºC, but stopped (or went slowly) until it began to melt completely from the range of 114.8-135.6ºC. The acetylferrocene TLC result should have been only the darker red/orange spot and the ferrocene should have been only the yellow/orange spot. The ferrocene alone acted as expected, but the acetylferrocene was not pure at all, as one can see from the presence of the ferrocene marker where there should not be one. There were several potential areas for error. The inital heating of the substance in a hot water bath may have not been hot enough. In both the first and second vacuum filtrations, there was a noticeable amount of solid making it through the filter to the waste flask. During the recrystallization, some very large (and quite pretty) crystals formed in the waste flask (pictured below). This was disappointing because the desired crystals did not form well (also pictured below). Also, the amount of norit could have been too much or too little, reducing yield. And, finally, the lack of desirable crystallization could have been due to improper cooling time, like cooling too quickly, allowing more than a few unformed crystals to make it through the filter paper and heating the hexanes mixture too much or not enough. You have responded well to your less-than ideal results. Explain, analyze, and suggest ways to do differently next time. I am sure you still felt some disappointment, but you've made a good report out of a difficult day in the lab.



[[image:perfectochemgems/2012-02-24_11.13.09.jpg width="362" height="278" caption="Picture 4: Unwanteed, yet quite pretty crystals that formed in waste flask during second vacuum filtration"]]
=Works Cited:=

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 13px;">"Acetylferrocene." //Wikipedia//. Wikimedia Foundation, 26 Feb. 2012. Web. 02 Mar. 2012. [].

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 13px;">"Ferrocene." //Wikipedia//. Wikimedia Foundation, 28 Feb. 2012. Web. 02 Mar. 2012. [].

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 13px;">"Friedel-Crafts." //Wikipedia//. Wikimedia Foundation, 26 Dec. 2011. Web. 02 Mar. 2012. [].

<span style="font-family: 'Arial','sans-serif'; font-size: 13px;">Higginbotham, Carol. Ph.D. “Acetylation of Ferrocene.” CH-335: Organic Chemistry Course. COCC/UO: Blackboard, Winter 2012. Web. 23 Feb 2012.

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 13px;">"Overview, The Friedel-Crafts Reaction: Acetylation of Ferrocene." //GEMs Home//. Web. 02 Mar. 2012. [|http://greenchem.uoregon.edu/Pages/Overview.php?CategoryIDString=].

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 13px;">"Thin Layer Chromatography." //Wikipedia//. Wikimedia Foundation, 29 Feb. 2012. Web. 02 Mar. 2012. [].