The Friedel-Crafts Reaction: Acylation of Ferrocene



Introduction
The goal of this lab is to produce acetylferrocene via electrophilic aromatic substitution in a greener and less hazardous reaction process in the laboratory. Ferrocene was acylated in the more favorable set of detailed methods of phosphoric acid and acetic anhydride. No organic solvents were used and the overall end product was greener due to the change in the lab compared to the more hazardous strong Lewis acid. The normal us of strong acids and hazardous organic solvents used in this lab generate large quantities of acids as well as aluminum waste. This is a second generation greener chemistry procedure and reduces potential hazards in the lab and produces a cleaner product. This lab was conducted via a hot water bath, reflux condenser, vacuum filtration, decanting, hot water filtration, an ice bath, recrystallization, melting point, and a thin layer chromatography (TLC) test. The reaction synthesis and the complete mechanism are shown below:
mechanism_edited-1.gif
Source: http://www.mesacc.edu/~minger/Organic%20Lab/236LL/Acetylation%20of%20Ferrocene.pdf



scan0014.jpg
Complete Mechanism of ferrocene to acetylferrocene





Procedure
SAFETY PRECAUTIONS: Phosphoric acid and acetic anhydride are corrosive, and acetic anhydride is also a lachrymator; avoid contact or undue exposure to vapors.

Reaction:
1. Place 1.5 g of ferrocene in a 20 mL round-bottom flask containing a magnetic stir bar. Prepare a hot water bath, heating the water to nearly the boiling point while preparing the following reaction mixture.
2. In a fume hood, add 5.0 mL of acetic anhydride and 1.0 mL of 85% phosphoric acid to the flask. The reaction mixture should heat up and darken in color. Swirl the flask, heating occasionally in a hot water bath, if necessary, until all the ferrocene dissolves.
3. Attach a reflux condenser, then heat the reaction mixture, with stirring, on a hot water bath prepared in step 1. Heat for 10 minutes, during which time a purple color may develop.

Workup and purification:
4. Pour the reaction mixture onto 25 g (ca. 60 mL) of ice in a 200 mL beaker, rinsing the flask with two 5 mL portions of ice water. (A black residue may remain in the flask.) Stir the orange-brown mixture with a glass rod for a few minutes. Any insoluble black material present will be removed in the 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 great care to avoid excessive foaming during this bicarbonate addition. This step can be done with magnetic stirring, but make sure to use a stirring plate that is not hot.) Stir well and crush any lumps, affording a dark-brown suspension.
6. Allow the mixture to stand for 20 minutes with the hot stir plate off, then collect the crude product by 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 or paper towels. Weigh the product and save about 1/3-1/2 of the crude product for TLC analysis.
7. Transfer the solid and a stir bar to a small Erlenmeyer flask and add 20 mL of hexanes. Heat gently, don't boil, for about 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. (Use of too much carbon will reduce your yield.) Heat with swirling, then perform a hot filtration to remove the decolorizing carbon.
9. Set the flask aside to cool slowly. Red-brown needles of acetylferrocene should begin to form. Once the flask has reached room temperature, cool it in ice. Collect the crystalline product by vacuum filtration, washing with a small quantity of cold hexanes, and dry it by continuing to pull air through it for a few minutes.

Characterization:
10. Record the yield and melting point range of your recrystallized acetylferrocene. (The melting point has been reported as either 82-83 or 84-85 °C.)
11. Analyze your crude and recrystallized products by TLC. Separately dissolve very small amounts of pure ferrocene, the crude product, and the recrystallized acetylferrocene in a few drops of toluene. Spot the solutions on silica gel plates and develop with 30:1 toluene/absolute ethanol. Visualization is simple---each of the compounds is brightly colored.

Source: Green Organic Chemistry-Strategies, Tools, and Laboratory Experiments by K.M. Doxsee and J.E. Hutchison, Thompson Brooks/Cole, 2004; pp. 228-230.


Data

Table 1: Solids Used for the Experiment
Solid
Mass (grams)
Observations
Molecular Formula
Structure
Ferrocene
1.522 g
220px-Photo_of_Ferrocene_(powdered).JPG
orange powder
C10H10Fe
external image 80px-Ferrocene.svg.png http://en.wikipedia.org/wiki/Ferrocene
Ice
25.10 g
index.jpg
clear cubes
H2O
[Ice Crystal]
[Ice Crystal]
http://www.benbest.com/cryonics/lessons.html
Sodium Biocarbonate
7.510 g
244px-Sodium_bicarbonate.jpg
white powder
NaHCO 3
Molecular Structure of Sodium Bicarbonate
Molecular Structure of Sodium Bicarbonate
http://www.ehow.com/about_5444991_molecular-structure-sodium-bicarbonate.html
Crude
1.813 g
after-crystals.jpg
red-orange and light orange powder


Crude Saved for TLC test
2.120 g
after-crystals.jpg red-orange powder and light orange powder


Decolorizing Carbon
spatula full
index2.jpg
black pellets
C

Acetylferrocene
0.083g
dark red-orange powder
C12H12Fe
O
Acetylferrocene, (Acetylcyclopentadienyl)cyclopentadienyliron, CAS #: 1271-55-2
Acetylferrocene, (Acetylcyclopentadienyl)cyclopentadienyliron, CAS #: 1271-55-2
http://www.chemblink.com/products/1271-55-2.htm

Table 2: Liquids Used for the Experiment
Liquid
Volume (mL)
Observations
Molecular Formula
Structure
85% Phosphoric Acid
1.0
clear aqueous
H3PO4
external image 160px-Phosphoric-acid-2D-dimensions.pnghttp://en.wikipedia.org/wiki/Phosphoric_acid
Acetic Anhydride
5.0
clear
C4H6O3
http://en.wikipedia.org/wiki/Acetic_anhydride
http://en.wikipedia.org/wiki/Acetic_anhydride

3M aqueous NaOH solution
37.5
clear
NaOH
chy113s98fe8b2sol.gif
http://www.usm.maine.edu/~tracy/chy113s04folder/textfileschy113s04/chy113s98fefolder/chy113s98fesol.htm
Cold hexanes
20
clear
C6H14
200px-Hexane-2D-flat-B.png
http://en.wikipedia.org/wiki/Hexane

Step 3: started heating at 13:15 so done at 13:25

P2170007.JPG
Step 4: Stirring orange-brown mixture with a glass rod.
P2170014.JPG
Step 8: Hot filtration to remove the decolorizing carbon.



Table 3: Melting Point of Acetylferrocene
Melting Point Range
Temperature (°C)
Start
67.8°C
End
71.4°C


Analysis
TLC_copy.jpg
Step 11: TLC of pure ferrocene, crude product, and recrystallized acetylferrocene of toulene

A-pure ferrocene
B-crude product
C-recrystallized acetylferrocene

Your TLC didn't run properly, as indicated by the swoop of the solvent front. The solvent front should be a straight line parallel to the floor. Also, it is traditional to wait for the solvent to dry before documenting the result of the TLC. Some spots may show up better after the solvent has evaporated away.

Pure ferrocene producesa yellow smear.
The pattern produce by the crude product is slightly higher than the pattern produced by the recrystallized acetylferrocene, but both of them produced an orange smear.

The lack of a faint yellow smudge above the crude product and the recrystallized product demonstrates that there is not unreacted ferrocene left in the product. Lane C shows that the recrystallization of the crude product was effective in removing nonreactive or contaminating ferrocene from the product. This TLC shows that all of the ferrocene was acylated. Ferrocene is the limiting reagent in this reaction based on the grams to moles calculations below.

(0.083 g acetylferrocene) x (1 mole acetylferrocene/ 228.07 g acetylferrocene)=0.0003639=0.00036 mole acetylferrocene

Limiting reagent: (1.522 g ferrocene) x (1 mole ferrocene/186.04 g ferrocene) = 0.008181036=0.008181 moles ferrocene

Theoretical Yield: (0.008181 mol ferrocene) x (228.07 g acetylferrocene/1 mol)=1.86584=1.867 g acetyleferrocene

Percent Yield: ( 0.083g acetylferrocene)/(1.867 g acetylferrocene)=0.044456 x 100%=4.4456=4.4 % yield
OK on your calculation, but did you do the workup on the entire sample? If not, what is the % yield for your crude product?





Conclusion
The acylation reaction to form acetylferrocene from ferrocene and acetic anhydride was a success in this laboratory experiment with a yield of 4.4%. Yield is never really a measure of "success" in the strict sense, but I think calling a 4.4% yield a success is a stretch. Best to just leave the word "success" out of it. The melting point of the product acetylferrocene made during the reaction was a range from 67.8 degrees Celsius to 71.4 degrees Celsius and the given range from the procedure was 82 to 83 degrees Celsius or 84 to 85 degrees Celsius. The difference in range of the actual melting point and the given melting point in lab does not mean the product is not acetylferrocene, but it does mean there are a significant amount of impurities that were left in the end product of the reaction. YES. The thin layer chromatography analysis described above shows that the reaction produced a pure form of acetylferrocene. Which contradicts what the melting temps indicate, right? How can you explain this apparent discrepancy? This second generation greener lab produces a cleaner product and reduces laboratory hazardous that could have occurred with the non-green procedure.


Error

Throughout the experiment some of the product was lost via the black sludge that remained in the bottom of the round-bottom flask. Another loss of the product occurred during the hot filtration on the filter paper, because crystals formed on the top edges of the filter papers while filtration to removed the carbon pellets. Some loss of the product was left on the filter paper and the container when doing vacuum filtration. Later, when doing the hot filtration, some loss of the product was also left on the rubber spatula used and on the beaker when scraping off the product from the sodium bicarbonate. yep, good.

This report earned the following scores for: format (2/2) style (1/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1.5/2) error (1/1) post-lab Q (2/2) for a total of 12/14.

Post-lab Question
Q. Draw two synthesis examples of a Friedel-Crafts Acylation Reactions.

A.
scan0013.jpg
http://library.tedankara.k12.tr/carey/ch12-6.html