8/10/2019 Synthesis of Ferrocenylenones via Claisen Condensation Under Ultrasonication

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Synthesis of Ferrocenylenones via Claisen Condensation

Under Ultrasonication

Daniel Scarbrough, Sarah Alexander

University of Nevada Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV89154, USA

Objective:

This experiment aims to successfully synthesize Ferrocenylenone from ferrocenevia ultasonication.

Reaction Mechanisms:

Reaction for Ferrocene to Acetyl Ferrocene

+Fe

O

O O

Fe

O

+H3PO4 OH

O

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Mechanism for Ferrocene to Acetyl Ferrocene:

Fe +

O

O O

O

O

+Fe

OH

P

O

OHO

OHH

OH

O

Fe

OH

P

O

OHO

OHFe

O

+ + P

O

OHHO

OH

Mechanism for Acetyl Ferrocene to Ferrocenylenone:

Fe

O

H

HH

OHK

Fe

O

HH

K O

8/10/2019 Synthesis of Ferrocenylenones via Claisen Condensation Under Ultrasonication

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O

Fe

O

HH O

H

+

O

Fe

O

HH

O

H

O

Fe

O

HH

H

O

+

HOFe

O

+ + K OH

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Experimental Procedure:

In a round bottomed flask, combine 1.28g of ferrocene, 4ml of acetic acid anhydride and20 drops of . The flask should be attached to a water cooled condenser, and placed in ahot water bath at 90 C. Heat and stir the mixture for 20 minutes.

Once heating is completed, pour the orange mixture into a beaker containing crushed ice.Some tar-like substance is expected to be left on the inside of the flask. Once the ice has melted,slowly add until the mixture is at a pH between 5 and 6. This can be tested with litmus

paper. Addition of the will cause foaming if the mixture is still very acidic.

Use a Hirsch Funnel to vacuum filter and dry the substance. Wash the precipitate withcold water. Perform thin layer chromatography on this product and cospot with a sample ofunreacted ferrocene. The product will use 10% acetate and 90% hexanes (by volume) as asolvent and the ferrocene will use pure hexanes as solvent.

Prepare a gravity chromatography column using about 12g of silica gel. Use 10% ethylacetate and 90% hexanes as the liquid phase.

Use thin layer chromatography to confirm with chromatographic layer is the acetylferrocene.

Evaporate the correct collected fractions solvent.

To check the purity of the sample obtained, find the melting point, perform thin layerchromatography, HNMR, CNMR and IR chromatography on the sample.

Add the remaining acetyl ferrocene to an Erlenmeyer flask along with benzaldehyde(mixed at a 1:1 ratio with the acetyl ferrocene), 25ml of anhydrous ethanol and 0.179g of

powdered KOH. Suspend the mixture in an ultrasonic bath. This can be achieved with a ringstand and a clamp to hold the flask in the water, without allowing the flask to touch the sides ofthe ultrasonicator.

Monitor the reactions progress via thin layer chromatography, using ferrocene to cospot. The reaction should be checked every 20-30 minutes to monitor progress.

After two hours, remove the mixture from the ultrasonic bath and evaporate enough

solvent using a rotary evaporator (under vacuum) to barely allow crystals to form. After thesecrystals begin to appear and the solution begins to become viscous, remove the vessel from theevaporator and add about 20ml of cold water. A small amount of ice chips works as well.

Neutralize this mixture using 10% HCL. The neutralization progress can be shown byusing pH litmus paper.

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Use a Hirsch Funnel to vacuum filter the retrieved crystal, which should be a dark purple,flaky substance and have an orange liquid pulled out. Wash with cold water. Recrystalize the

product using ethanol as the solvent to obtain a more pure final product.

Characterize the final product by finding the melting point and performing HNMR,

CNMR and IR chromatography.

Results:

Yeild after gravity column:

Expected Melting Point Observed Melting Point81 - 83 C 85 - 87.5 C

IR

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HNMR

CNMR

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Expected Yield Crude Yield (beforefiltering)

Actual Yield Percent Yield

1.55g 1.271g 0.23g 14.3%

*NOTE: the original yield was too low to perform the remainder of the experiment. Another twoidentical experiments were being performed at the same time and also had extremely low yields.These three products were combined for the rest of the experiment.

Group 1 Yield Group 2 Yield Group 3 Yield Amount used forCharacterization

Total Yield forRemainder ofExperiment

0.228g 0.423g 0.163g 0.1g 0.727g

Yield after ultrasonication and recrystallization:

Expected Melting Point Observed Melting Point139 - 140 137 - 141 C

IR

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HNMR

CNMR

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Expected Yield Crude Yield (beforefiltering)

Actual Yield Percent Yield

1.009g 1.482g 0.417g 41.3%

Discussion:

The first portion of this lab had an extremely low yield. The error is still unidentified.There is probably a simple solution to the problem that was encountered. Multiple groups

performed the same error, but others had a much higher yield. One possible source of error could be the heating applied. There was an excess of tar residue on the inside of the round bottomflask, and that may be where the majority of the product for the reaction took place.

Based on melting point, NMR and IR spectroscopy, the reaction did make acetyl

ferrocene. There were some slight impurities in the product obtained at this step (this can beshown by the slightly high observed melting point). This product was deemed acceptable on thegrounds that there would be further purification steps following this section of the experiment.

As previously stated, the problem where a low percent yield was widespread and multiplegroups had to be combined to allow for the remainder of the experiment to progress.

Characterization after the ultrasonication reaction showed a relatively pureferrocenylenone, with a melting point close to reported literature. The IR and NMR spectra alsoshow concise peaks, indicating that ferrocenylenone was produced.

Conclusion:

Overall, the synthesis of ferrocenylenone by ultrasonication could be considered asuccess. Both acetyl ferrocene and ferrocenylenone were synthesized with percent yields of14.3% and 41.3% respectively. Even with the low yield, the IR and NMR spectra, paired withmelting points of 85 - 87.5 C and 137 - 141 C observed, compared to 81 - 83 C and 139 -140 from the literature, shows a fairly pure product was obtained after purification steps.

References:

Ji, S. J., Shen, Z. L., & Wang, S. Y. (2003). Aldol Condensation of Acetylferrocene underUltrasound. Chinese Chemical Letters, 14(7), 663-666.