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experiment 7...

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Maria Blanco

Name of partners: Cailee Chaney and Lauryn Bates.

TA’s name: Yu Yan

Experiment 7: Friedel-Crafts Acylation of Ferrocene.

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Introduction

Ferrocene is considered an organometallic compound. It is a product of a reaction between cyclopentadienyl magnesium bromide with anhydrous iron (III) in benzene and ether (science direct). Ferrocene is considered to be aromatic because it contains six delocalized pi electrons, the compound is cyclic, fully conjugated, and planar (chem libre texts). Friedel-crafts acylation reactions is usually the method used for the preparation of acetylferrocene (science direct). Acetylferrocene are prepared by the reaction between ferrocene and acetic anhydride with phosphoric acid (science direct). The Friedel-crafts acylation of benzene needs aluminum chloride as the catalyst (Weldegirma, 2020). In contrast, ferrocene, has a high pi electron density, which means that it can be acylated under milder conditions with the presence of phosphoric acid as the catalyst (Weldegirma, 2020). By using this acid, the acylium cation is produced as the electrophile, as a result of the protonation of acetic anhydride and the loss of acetic acid (Weldegirma, 2020). The easiest way to separate acetylferrocene and ferrocene is by column chromatography since both compounds are very colored (Weldegirma, 2020). Figure 1 shows a detailed plausible mechanism of the reaction in this experiment with arrow pushing and figure 2 shows the possible side reaction.

Figure 1: Detailed plausible mechanism of the reaction in this experiment with arrow pushing.

Figure 2: Potential undesired reaction. 

Experimental section

1. 2. 3. 4. 5. 6.

Test tube Obtained a clean and dry test tube. Added 93 mg of ferrocene and 0.35 mL of acetic anhydride. Added 0.1mL 85% H3PO4. TLC (toluene: etOH,30:1). Warmed steam bath and heated the mixture for 10 minutes. TLC, if not fully converted continue reaction for 5-10 minutes.

Reaction workup 7. We then cooled the test tube in ice. 8. Added 0.5 mL of ice water dropwise. 9. Added 3M NaOH dropwise and monitored it by litmus paper until it’s neutral. 10. Collected the product by Hirsch funnel and washed the product with cold water and dried it. 11. Weighted the product. 12. Measured TLC and melting point.

Column chromatography 13. Added wool to the bottom and 1g of alumina. 14. Added layer of sand.

15. Filled with n-hexane 16. Transferred crude sample using hexane. 17. Carefully bulb the column to assist with separation. 18. Avoid column running dry. 19. Used 100% n-hexane. 20. Used a 10 mL Erlenmeyer flask for collection. 21. Obtained an orange-yellow band (fraction one), unreacted ferrocene. 22. Switched the solvent system 50:50, hexane: diethyl ether. 23. Collected in a Erlenmeyer flask orange-red band (fraction two), acetyl ferrocene.

Column conclusion 24. Run the TLC on both fractions. 25. Calculated Rf values. 26. Evaporated the solvent for each fraction separately using vacuum. 27. Obtained the mass. 28. Measured the melting point. 29. Obtained HNMR of acetyl ferrocene.

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Table of chemicals Chemicals used Ferrocene (C10H10Fe)

Acetic anhydride (C4H6O3)

Physical properties mm: 186.04 g/mol. Mp: 172.5 ℃ . Bp: 249 ℃ . IUPAC name: ferrocene.

mm: 102.09 g/mol. Mp: -73.1 ℃ . Bp:139.8 ℃ . IUPAC name: acetic anhydride.

Toxicity/hazards Flammable solid, target organ effect, harmful by ingestion. Harmful if swallowed. May cause respiratory tract irritation. Harmful if absorbed through skin. Flammable liquid and vapor. Harmful if swallowed. Causes severe skin burns and eye

damage. Toxic if inhaled. Wash skin thoroughly after handling. Phosphoric acid (H3PO4)

mm: 97.99 g/mol. Mp: 42.4 ℃ . Bp: 407 ℃ . IUPAC name: phosphoric acid.

May be corrosive to metals. Causes severe burns and eye damage. Wear protective gloves/ protective clothing/ eye/ face protection.

Acetyl ferrocene Fe(C5H4COCH3) (C5H5)

mm: 228.07 g/mol. Mp: 81-83 ℃ . Bp: 161-163 ℃ . IUPAC name: acetyl ferrocene.

Fatal if swallowed. Toxic if in contact with skin. Wash face, hands, and any exposed skin after handling.

Sodium hydroxide (NaOH)

mm: 39.99 g/mol. Mp: 323 ℃ . Bp: 1, 388 ℃ . IUPAC name: sodium hydroxide.

May be corrosive to metals. Causes severe skin burns and eye damage. Read label before use.

Diethyl ether (C4H10O)

mm: 74.12 g/mol. Mp: -116.3 ℃ . Bp: 34.6 ℃ . IUPAC name: ethoxyethane.

Flammable liquid. Acute toxicity. Eye irritation. Harmful if swallowed. Aspiration hazard. May cause drowsiness or dizziness.

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Results Melting point

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Ferrocene: 77.480.3 ℃ . Acetylferrocene:82. 0-82.8 ℃ . Crude acetylferrocene: 173.9-177.2 ℃ .

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Rf values

Percentage yield

Ferrocene: 0.8 cm. Acetylferrocen e: 0.125 cm. Crude acetylferrocene : 0.92 cm.

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acetylferrocen e: 9.2%

0.09 g C10H10Fe x

1 mol C 10 H 10 Fe 1 mol C 12 H 12 FeO x =0.00048 mol C 12 H 12 FeO g 1 mol C 10 H 10 Fe 186.04 C 10 H 10 Fe mol Limiting reagent: g C 12 H 12 FeO mol =0.109 C 12 H 12 O 1 mol C 12 H 12 FeO

228.07 0.00048 mol C12H12FeO x

Percent yield=

0.01 g Experimental x 100= =9. 2 % Theoretical 0.109 g

Percent of ferrocene unreacted: (Mass of pure product/Mass of crude product) X100= (0.01g/0.08g) X 100= 12.5 % Rf=

Distance travel by the compound Distancetravel by the solvent

Rf of Ferrocene: 0.8 cm. Rf of Acetylferrocene: 0.125 cm. Rf of Crude acetylferrocene: 0.92 cm.

Percent unreacted of ferrocene ? 12.5 %

Figure 3: 1H NMR spectrum of the product.

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Discussion

After following the steps for this experiment carefully, we were able to obtain the melting point of acetylferrocene. The literature value for the melting point of acetylferrocene is between 85-86 ℃ . In this experiment, our experimental melting point was 82.0-82.8

℃ , which is

not exactly the same as the literature value, but it is close enough to considered to be the desired product. One reason for the melting point deviation is that the final product was impure due to human errors. For instance, we dropped some of the product before measuring the melting point. We also measured the Rf values for each part of the experiment. The Rf of Ferrocene was 0.8 cm, Rf of acetylferrocene was 0.125 cm, and finally the Rf of the crude acetylferrocene was 0.92 cm. The Rf of the crude acetylferrocene and ferrocene was higher than the pure acetylferrocene. I expected to see this result because ferrocene is considered to be less polar than acetylferrocene. Meaning that in the TLC plate the ferrocene will move much faster than acetylferrocene which would result in a larger Rf value for ferrocene. Moreover, after performing the experiment we obtained a really small percentage yield when compare it to 100%. Our percentage yield was

12.5 %, as mentioned before, humans’ errors is one of the principal reasons for this low percentage yield. In addition, a side reaction could have taken place if precautions were not considered. For instance, the avoidance of acetic anhydride and phosphoric acid in excess. Finally, at the end of the experiment we obtained the 1H NMR of the product. The key peaks of an 1HNMR spectrum would be four, one peak at 2.5ppm, one peak at 4 ppm and the other two peaks between 4.4 and 4.5 ppm. In our 1H NMR spectra there are three peaks between 1.5-3 ppm and other 3 peaks between 4 and 5 ppm. This HNMR spectrum confirms that the final products contained some impurities in it since the peaks are not perfectly accurate with the literature values. Maybe a side reaction took place, or the mixture had some unreacted ferrocene. #1 This 1H NMR in the lab manual have four signals that shows four unique protons. The peak that is around 2.0-2.5 ppm shows some protons on the methyl group. The other peak around four ppm indicates the protons in the cyclopentyl group, which are unsubstituted. And finally, the last two peaks that are around 4.4 and 4.5 ppm correspond to the protons of the cyclopental group, which are in contrast, substituted. One of the peaks around 4.4 ppm shows the protons that are closest to the acetyl group and the peak around 4.5 ppm shows the protons that are furthest from the acetyl group. #2 From the melting point and 1H NMR from the experiment we can conclude that the results the student obtained were very similar to the literature value. However, it is evident that the product had some impurities. Some reason for these impurities could be that the product was contaminated, or the reaction had some unreacted ferrocene. When we analyze the 1H NMR we can see that it has some unreacted ferrocene in the final product. For instance, the peak that’s

around 4 ppm have 15 hydrogens instead of having five. The other 10 hydrogens are evidence of the unreacted ferrocene. 

Conclusion

The objective of this experiment was to use ferrocene and react it with acetic anhydride in an acid catalyzed Friedel-crafts reaction. And, to perform a column chromatography to obtain a pure acetylferrocene as the product. The information from the data revealed that the product obtained in this experiment contained some impurities in it, which was confirmed by the percentage yield and 1H NMR. The lab accomplished what it set out to do, we followed every step carefully in order to obtain the best product as possible. In this experiment, I learned the importance of not contaminating the mixture in order to obtain a pure product. In real life, ferrocene compounds are used in research for medicinal applications. For instance, some reports have shown that derivatives from this compound are very important against many diseases, such as cancer (Publishing).

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References

1. “Ferrocene.” Ferrocene - an Overview | ScienceDirect Topics, www.sciencedirect.com/topics/chemistry/ferrocene.

2. Libretexts. “15.4: Aromaticity and the Hückel 4n + 2 Rule.” Chemistry LibreTexts, Libretexts, 17 June 2019, chem.libretexts.org/Bookshelves/Organic_Chemistry/Map %3A_Organic_Chemistry_(McMurry)/15%3A_Benzene_and_Aromaticity/15.04%3 A_Aromaticity_and_the_H%C3%BCckel_4n___2_Rule.

3. Ornelas, Cátia. “Application of Ferrocene and Its Derivatives in Cancer Research.” New Journal of Chemistry, The Royal Society of Chemistry, 16 June 2011, pubs.rsc.org/en/content/articlelanding/2011/nj/c1nj20172g#!divAbstract. 4. Weldegirma, S. Experimental Organic Chemistry: Laboratory Manual for CHM 2210L and CHM 2211L; Pro-Copy: Tampa, FL, 2020....