Friedel-Crafts+Reaction

By Heather Browning & Merissa Honey

=Friedel-Crafts Acylation=

__**Introduction:**__
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. The reaction is a widely used method of carbon-carbon bond synthesis that proceeds by the mechanism of electrophilic aromatic substitution. In this green approach, ferrocene is acylated using phosphoric acid and acetic anhydride in place of the usual, more vigorous acylation reagent generated from aluminum chloride and acetyl chloride. In addition to being a greener process, this method also leads to a cleaner product, since under these milder acylation conditions the amount of diacetylferrocene is reduced relative to conventional methods. Ferrocene is an organometallic compound with the molecular formula Fe(C5H5)2, the conformation is two cyclopentadienyl rings that are on opposite sides of a central Iron atom. The anionic nature of the five carbon ring makes it a good nucleophile and more likely to undergo electrophile additions than other benzene compounds. The Friedel-Crafts reaction allows for the acetylation of ferrocene via an acetic anhydride using phosphoric acid as a catalyst. Thanks to the carbonyl group, the subsequent ketone is always less reactive than the original molecule so multiple acetylations do not happen, this also lends to the non-formation of carbocation rearrangements.

The mechanism of reaction is seen below.



What is not illustrated in the reaction mechanism above is that when ferrocene reacts with the acetic anhydride, the double carbonyl groups are split. This results in a carbocation formed on the ferrocene molecule and a negative charge on the acetic anhydride. This results in two unstable molecules that react further to result in acylated ferrocene or acetylferrocene. I don't think I would call this a mechanism, since it doesn't show "how" the changes occur...though it does show the intermediate.

__Procedure:__
//Reaction// 1. Place 1.5 grams of ferrocene in a 20 mL round-bottom flask containing a magnetic stir bar. Use hot water or steam bath to near boiling while preparing the following reaction mixture. 2. In a fume hood, add 5.0 mL of actic anhydride and 1.0 mL of 85% phosphoric acid to the round-bottom flask. Swirl the flask, heating occasionally in the hot water bath until ferrocene dissolves. 3. Attach a reflux condenser to flask, heat mixture in hot water bath with stirring. Heat for 10 minutes in which time a purple color develops. //Workup and purification// 4. Pour the reaction mixture onto 25 grams of ice in a 200 mL beaker, rinse the flask with two 5 mL portions of water. (A black residue may remain in flask.) Stir the orange-brown mixture with a glass rod for a few minutes. Any insoluble black material present will be removed in following steps. 5. Add 37.5 mL of 3M aqueous NaOH solution, then carefully add solid sodium bicarbonate in small portions until the remaining acid has been neutralized (about 7-8 grams.) (Use cation to avoid over foaming during this addition). Stir well and crush any lumps resulting in a dark-brown suspension. 6. Allow the mixture to stand for 20 minutes, then collect the crude product y vacuum filtration and continue to pull air through the product for a few minutes to dry it. Finish the drying process by pressing the solid product between two sheets of filter paper. Save some of the crude product for TLC analysis. 7. Transfer 1/2 to 1/3 of the solid and stir bar to a small Erlenmeyer flask and add 20 mL of hexanes. Heat gently for 5 minutes with stirring, then decant the dark-orange solution into another Erlenmeyer flask, leaving behind a black gummy substance. 8. To the hot solution, add a spatula-full of decolorizing carbon. Heat with swirling, then perform a hot filtration to remove the decolorizing carbon. 9. Se the flask aside to cool slowly. Red-brown needles of acetylferrocene should begin to form. Once the flask had reached room temperture, cool it in ice. collect the crystalline product by vacuum filtration, washing with a small amount of cold hexanes and dry it by continuing to pull air through it for a few minutes. //Characterization// 10. Record yeild and melting point range of crystallized acetylferrocene. The reported melting point is either 82-83 **°** C or 84-85 **°** C. 11. Analyze crude product, crystallized product by TLC. Separately dissolve very small amounts of pure ferrocene, crude product and recrystallized acetylferrocene in a few drops of toluene. Spot the solutions on silica gel plates and develop with 30:1 toluene/absolute ethanol.

//**Source:**// Hanna Jr., James. "The Friedel-Crafts Reaction: Acetylation of Ferrocene." //Greener Education Materials for Chemists//. Department of Chemistry, Physics, and Geology at Winthrop University, Jul 2005. Web. 21 Feb 2011. .

__Data__


1.502 grams Ferrocene used in step 1 of procedure.

25.184 grams ice used, step 4 of procedure.

0.187 grams sodium bicarbonate used to achieve neutrality indicated by litmus paper, step 5 of procedure.

3.402 grams crude product resulted from step 6.

1.562 grams of crude product used in step 7 to create acetylferrocene.

0.523 grams crystals, acetylferrocene, recovered.

melting point of recovered crystals (acetylferrocene) : 76.7 - 78.7 ° C. **//Literature melting point//: 81-86° C.**


 * //Theoretical Yield://**
 * 1.502g ferrocene X __1 mole ferrocene__ X __1 mole acetylferrocene__ X __228.07 g__ = 0.6411 g acetylferrocene**
 * .................................186.034 g ferrocene.........1 mole ferrocene............1 mole acetylferrocene**

I am struggling to interpret this: 0.6411 g acetylferrocene is your theoretical yield, but then below you say 1.841 g. Can you explain this inconsistency? I think there may be a problem with the calculation above.


 * //Actual Yield:// g acetylferrocene**


 * //Percent Yield://**
 * __0.523 g acetylferrocene__ X 100% = 28.41 %**
 * 1.841 g acetylferrocene**

A small amount of crude product, recrystallized acetylferrocene and ferrocene where applied to a silica gel TLC plate. The acetylferrocene was visibly dark and moved higher than the ferrocene's dark position. This demonstrated that the ferrocene had indeed undergone acetylation in the Friedel–Crafts reaction otherwise it would be expected to move into a position matching ferrocenes position. The crude product was visible when initially applied to the TLC plate but after several minutes of processing in the solvent, was no longer visible.
 * TLC DATA**

Please be specific and candid. Why is there no image available?
 * Unfortunately no image of the TLC was available to add to this lab. The generic image below will help to demonstrate the data explanation above.



On this labs TLC plate, acetylferrocene resembled the dark spot on the far right. Ferrocene resembled the spot on the far left. The crude product was not visible on the TLC.

//**Source**//**:** "Safety data for acetylferrocene." //The Physical and Theoretical Chemistry Laboratory, Oxford University, England//. Safety Officer in Physical Chemistry at Oxford University, August 21, 2005. Web. 24 Feb 2011. .

The mechanism of Friedel-Crafts in this laboratory added a ketone to the aromatic ring that comprised the ferrocene. The percent yield for the reaction was not a high yield, but the product was pure as evinced by the Rf readings. A point of error in the lab occurred during the hot filtration, step 8 of the procedure. During the filtration crystals began to form on and in the stem of the filter funnel. This slowed and briefly stopping the filtration process. A new funnel was used and the temperature of the water used in the hot filtration was increased. A vacuum was also added to the hot filter flask to encourage filtration. With this new filter funnel and hotter water, filtration was achieved. Some crystal products may have been lost due to difficultly in collecting them from the inside and around the stem of the first filter funnel. This may have been avoided with hotter water used initially in the the hot filtration funnel.
 * __ Conclusion __**

Hot filtration is not an easy task as the water that circulates around the collection funnel must be kept warm enough to separate the components from the solution. If the water is not warmed enough, the separation of the different elements will not effectively occur. The equipment that was utilized for the hot filtration is very small equipment in the sense that the funnel is not necessarily wide enough for the solution to be passed through. The minute hole makes it difficult to pour the solution into, as some of the solution can potentially be lost in the area where the water is circulated.

The Friedel-Crafts acetylation has been used in the synthesis of triarylmethane and xanthene. These are dyes that are used in the coloration of clothing. Xanthene comes in fluorescent colors; namely yellow, blue, pink and red. (This information is courtesy of Wikipedia: "Xanthene" and "Triarylmentane") This paragraph might be appropriate in the Introduction, but it doesn't belong in your Conclusion. Keep the focus on your experiment.

Thin layer chromatography was used determine the purity between ferrocene, crude product (step 6) and the end product-acytylferrocene. All three products were initially visible on the TLC plate but after left for several minutes in solvent, the crude product was no longer visible. Why the product was no longer visible may be an indication that it was impure or that the reaction mechanism was incomplete at the point of its development and did not register with the TLC method. The higher position of acetylferrocene compared to ferrocene indicated a difference between the two substances indicating further, that acetylation of ferrocene had in fact been accomplished in the reaction. This actually surprises me a little, because acetylferrocene is more polar than ferrocene and should therefore travel up the TLC sheet more slowly than ferrocene. The melting point also indicated that acetylferrocene had been produced as the melting point of this labs end product is similar to the literature melting point of acetylferrocene. What does the melting point range indicate about purity?

This report earned the following scores for: format (1.5/2) style (2/2) data (2/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1/2) error (0.5/1) post-lab Q (2/2) for a total of 10.5/14.

Two additional Friedel-Crafts Acylation Reactions On the image below, the first reaction involves acyl chloride which is commonly used in this type of reaction. The second reaction is acylation of 1,4-naphthoquinone with various aldehydes at room temperature. The developed procedure allowed for a replacement of hazardous solvents such as benzene and acetonitrile which are commonly used for this transformation.
 * __ Post Lab __**