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Multistep Synthesis of Tetraphenylcyclopentadienone Essay

Abstract:

The aim of this experiment was to perform a multistep synthesis to form tetraphenylcyclopentadienone. The first step of the reactions was to synthesize benzoin from the condensation of benzaldehyde. A yield of 28.91% benzoin was obtained. The MP of benzoin was 127O-130O C and the IR spectra displayed a carbonyl peak at 3415 cm-1 ,,which represents and OH functional group. The second step of the reaction was to oxidize benzoin to form benzil; this reaction yielded 27.04% benzil. The MP of the benzil was 91O-93O C and the IR spectra revealed no OH functional groups. The last step of the synthesis was a double aldol condensation reaction to form tetraphenylcyclopentadienone; this reaction had a yield of 76.56% and a melting point of 222O-225O C. The IR spectra revealed a ketone carbonyl peak at 1700 cm-1.

Introduction:

In this experiment a multistep reaction will be performed in order to synthesize tetraphenycyclopentadienone. The product will be synthesized in three steps, but in the industrial world companies often produce compounds that involve up to twenty steps. Tetraphenycyclopentadienone is produced by synthesizing benzoin through the condensation of benzaldehyde and thiamine being used as a catalyst. In the second step of the reaction, benzoin is oxidized to benzil; nitric acid is used as the oxidizing agent in this step. In the last step of the reaction, a mixture of benzil and 1,3-diphenylacetone undergo a double aldol condensation reaction then a dehydration reaction in order to form tetraphenycyclopentadienone.

Experimental:
Materials
* Thermometer
* Round bottom flask (RBF)
* Reflux condenser
* Hot plate
* Hirsh Funnel
* Melttemp 2, to measure melting point
* Microlet IR 100, to measure IR

Benzoin Condensation of Benzaldehyde

First 1.20 grams of benzaldehyde was weighed out and put into a RBF containing a magnetic stir bar. Next 225 mg of thiamine was dissolved in 0.67 mL of water and 2.0 mL of 95% ethanol. This mixture was added to the RBF and 3 M NaOH was added drop wise until the solution turned a bright yellow color. If too much 3 M NaOH is added then the solution will turn a dark amber color; in this situation an additional 200 mg of thiamine should be added. The yellow solution was stored in a vial until the next weeks lab, so the mixture would have a suffienct amount of time to react.

At the start of the next lab the vial was cooled in an ice bath to achieve complete crystallization. Next, a Hirsch funnel was used to filter the crystals; the crystals were washed three times using a 50:50 mixture of cold ethanol/water and left to dry. Once dry, the product was recrystallized using 95% ethanol. The benzoin obtained (0.370 g) had a percent yield of 28.91% and melting point of 127O-130O C. The IR spectrum displayed a strong carbonyl peak at 2912 cm-1, a small OH peak at3415.24 cm-1 and an alkene group at 1472 cm-1 which represented the conjugated phenyl rings.

Oxidation of Benzoin to Benzil

This reaction was begun by placing all the benzoin that was synthesized in the previous lab into a RBF along with a magnetic stirrer. 1 mL of concentrated nitric acid was added to the RBF; the RBF was then attached to a reflux condenser and submerged into a hot water bath at 100oC for thirty minutes or until no more fumes are observed. A vacuum with a funnel attached to the end was placed on top of the reflux condenser in order to collect any nitrogen oxide fumes that formed. Once the reaction stopped producing fumes, the reaction mixture was left to cool; when the mixture reached room temperature the contents in the RBF where transferred using a Pasteur pipet into a beaker containing 3 mL of water.

Additional water was used to rinse out the RBF and it was poured into the beaker in order to insure maxim yield of benzil. Next mixture was stirred inside the beaker using a glass stir rod. At this time the benzil should begin to form a yellow solid; the solid was crushed using the end of the glass rod and filtered using a Hirsch Funnel. The benzil crystals were washed with cold water in order to remove any nitric acid that was present on the crystals. After washing the crystals three times with cold water, the crystals were dried and weighed out.

The crude benzil was then recrystallized using a 95% ethanol solution. The recrystallized product was cooled in an ice bath and filtered with 95% ethanol. The crystals were dried and weighed again. The percent recovery of the benzil synthesized had a percent yield of 26.29%. The melting point of the benzil was 910-930. Lastly, the IR spectra displayed peaks at 2917.35 cm-1, 1681.56 cm-1 and 1595 cm-1.

Synthesis of Tetraphenylcyclopentadienone

In the last part of the work up, tetraphenylcyclopentadienone was synthesized through a double aldol condensation reaction. A water bath was first prepared and heated to 100o C. Next the benzil produced in the previous step was place inside of a RBF. An equimolar amount of 1,3-diphenylacetone (0.092 g) and 1 mL of 95% ethanol was also added to the RBF. Once all three compounds were added the RBF a magnetic stir bar was added to the RBF then it was connected to the reflux condenser. Once all of the solids in the mixture were dissolved, 0.15 mL of 30% KOH solution was added using a Pasteur pipet; the addition of KOH turned the mixture a dark brown color.

The mixture was left to react for twenty minutes and it was then cooled to room temperature. Once the mixture reached room temperature the RBF was placed in an ice bath for approximately ten minutes. The crystals formed were then filtered using a Hirsch funnel and washed three times with 0.5 mL of cold ethanol. 0.113 grams of pure Tetraphenylcyclopentadienone was obtained, the yield was 76.56%, and the MP was 222O-225O. The IR spectrum of the final product displayed peaks at 1700 cm-1, which correlates to ketone carbonyl functional groups.

Results:

Benzoin Condensation:

Benzoin: 0.370 grams
Theoretical Yield: 1.28 grams
Percent Yield: 28.91%

Experimental Melting Point (Co)| Literature Melting Point (Co)| 127-130| 135-137|

Infrared Spectroscopy

Experimental Peak (cm-1)| Functional Group| Literature Peak ( cm-1)| 3415.24| OH| 2500-3600|
2912.12| Aromatic C-H| 3030|
1472.81| Phenyl Alkene| 1500-1600|
* The product formed was yellow crystal.

Oxidation of Benzoin to Benzil

Benzil: 0.092 grams
Theoretical yield:0. 350 grams
Percent Yield: 26.29%

Experimental Melting Point (Co)| Literature Melting Point (Co)| 91-93| 95|

Infrared Spectroscopy

Experimental Peak (cm-1)| Functional Group| Literature Peak (cm-1)| 2917.35| Aromatic C-H| 3030|
1681.56| C=O| 16900-1715|
1595.87| Phenyl alkene| 1500-1600|
* The missing OH peak is crucial. The product formed was a white crystal.

Synthesis of Tetraphenylcyclopentadienone

Tetraphenylcyclopentadienone: 0.113 grams
Theoretical yield: 0.1476 grams
Percent Yield: 76.56%

Experimental Melting Point Co| Literature Melting Point Co| 222-225| 218-220|

Infrared Spectroscopy

Experimental Peak (cm-1)| Functional Group| Literature Peak (cm-1)| 1700| C=O| 1690-1715|

* Final product formed was a deep purple colored crystal.

Discussion:

In this lab the condensation of benzaldehyde with thiamine acting as a nucleophile formed benzoin. Thiamine was used because its hydrochloride is stable and acts as a nucleophilic catalyst. Thiamine also attaches itself to the carbonyl of the benzaldehyde creating an intermediate that has a negatively charged carbon atom and is able to attack the second benzaldehyde molecule. When the reaction is complete, the thiamine catalyst disassembles from the benzoin. Cold water and ethanol are used in this reaction so that the in this reaction the reactants will become more soluble creating a homogenous mixture. The benzoin obtained had a percent yield of 28.91%, a melting point of 127O-130O C and distinct IR peak at 3415.14 cm-1 ,representing an OH group. The MP and IR spectra confirmed that this compound was indeed benzoin.

The next step in the synthesis was the oxidation of benzoin in order to form benzil. In this step, the OH group present in benzoin is deprotonated and the nitric acid is attached. Once the nitric acid attaches, the carbon and oxygen are able to form a double bond, which creates benzil. Adding water to the mixture makes the nitric acid become a better leaving group by deprotonating the reaction intermediate. The benzil obtained had a percent yield of 26.91%; a melting point of 91O-93O C and the IR spectra displayed a benzil ketone carbonyl group peak at 1681 cm -1. In addition there was no OH peak on the IR spectrum. The absence of the OH peaks indicated that there was no unreacted benzoin in the final product.

In the last step of the synthesis a double aldol condensation was used to form tetraphenylcyclopentadienone. An equimolar amount of 1,3-diphenylacetone was added to the benzil and then deprotonated by the addition of KOH. The benzil yielded negatively charged carbons of the carbonyl groups because of the lose of the alpha hydrogen to KOH. The bonding of the carbonyl groups caused a hydride shift because the oxygen become negatively charged and attracts the adjacent hydrogen.

Lastly, a double bond between two carbons and an alcohol group is formed; the alcohol groups is dehydrated causing the second aldol condensation to occur with the other oxygen present on benzil. The percent yield tetraphenylcyclopentadienone was 76.56%, the MP 222O-225O C, and the IR spectrum displayed a strong peak at 1700 cm-1. The double aldol condensation appeared to work well because of the high yield obtained and the IR spectra and MP supported the final product being tetraphenylcyclopentadienone.


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